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Cutting Procedures with Minimized Trauma
ORIGINAL ARTICLES
Cutting procedures with minimized trauma
le ss w e ll fo u n d e d .3 W h en ev a lu a tin g th e b io lo g ic effe c ts o f n ew te c h n ica l aid s ad ap ted fo r d en ta l cu ttin g p r o c e dures,; so m e in v estig a to rs4»5 c o n clu d e d th a t th e re a c tio n s c a u se d b y an u ltra so n ic p rep aration and b y co n v e n tio n a l cu ttin g w ere id en tica l, so m e 6 th at an u ltra so n ic p rep a ra tio n c a u se d a m ild re a ctio n , an d so m e 7 th a t an u ltra so n ic p rep a ra tio n c a u se d a sig n ifica n tly stronger reaction . In e v a lu
T o d eterm in e w h eth er w e t o r dry ca v ity p re p ara tio n sh o u ld b e u sed , th e sp e e d o f ro ta tin g e n g in e s w as c o n sid ered . W h e n th e ro ta tio n a l sp e e d o f th ese e n g in e s w a s r a ised fro m a b o u t 3 ,0 0 0 to 1 0 ,0 0 0 rpm , a m eth o d o f c o o lin g w a s g en era lly co n sid e r ed n ecessa ry , b u t th ere w a s d isa g reem en t in regard to w h ich c o o lin g sy stem w a s b est. S o m e in v estig a to rs12’13 p referred air, a n d o th e r s14’16 a je t o f w ater o r an a ir-w ater spray. O n e a u th o r17 c o n clu d e d th a t w ater w a s b est, air n e x t b est, and an air-w ater spray th e le a s t e ffe c tiv e . T h e g en era l v ie w ex p r e sse d in G erm a n litera tu re w a s th a t n o w ater sh o u ld b e u se d d u rin g d rillin g , b u t that w ater sh o u ld b e u se d d u rin g g rin d in g . L ater, it w a s m a in ta in e d 18 th at w a ter sh o u ld a lso b e u sed d u rin g d rillin g. In early stu d ies th a t m ea su red tem p eratu re ch a n g es in th e d en tin , th e bur, an d th e p u lp d ur ing ca v ity p rep aration , a sig n ific a n t in c re a se in th e tem p eratu re o f th e d en tin co n ta c tin g th e b u r14,19 a n d in th e bur h e a d it s e lf w a s s e e n .16 In th e in v iv o ex p erim en ts, th is tem p era tu re in crea se w as n o t e a sily tran sferred to th e p u lp .12 A lso , w h en u sin g h is to lo g y as a to o l fo r th e ev a lu a tio n , research ers h a d d iffe r en t resu lts, a l th o u g h th ey in v e stig a ted th e sa m e p ro b lem , b e c a u se n o n e o f th em h a d r eco rd ed th e im m e d ia te rea ctio n s to ca v ity p r ep a ra tio n p er se a n d b ec a u se so m e o f th e criteria u se d in th e h is to lo g ic ev a lu a tio n w ere n o t v a lid . W h e n th e first air tu rb in e for d en ta l u se w as e v a lu a te d ,11’20 o n e im m e d ia te r e a c tio n to dry ca v ity p r ep a ra tio n w a s th e m ig ra tio n
atin g th e air a b rasiv e te ch n ic an d co n v e n tio n a l d rillin g , so m e in v estig a to rs8;10 h e ld th at th e se te c h n ics c a u se d id en tica l rea ctio n s, w h erea s o th e r s11 th o u g h t th at th e a b ra siv e te ch n ic c a u se d a d e sic c a tio n o f th e den tin .
o f o d o n to b la st n u c le i in to th e c u t d en tin a l tu b u les, w h ich in d ica ted th a t th e o d o n to b la sts d isin te grated . T h is rea ctio n w a s p rev en ted i f th e d en tin w a s k ep t m o is t.11’20 In th e first ev a lu a tio n o f th e B o rd en air-rotor, e r y th ro cy tes an d o d o n to b la st
Kaare Langeland, DDS, PhD Leena K. Langeland, DDS, Williamsville, NY
Operative procedures must cause as little destruc tion as possible; therefore, as this study indicates, cavity and crown preparation should be made un der wet conditions. By use of a wet preparation, the least possible trauma is caused, and the life span of the restorative procedure is lengthened. Dry preparation would add to the destructive pro cesses in the pulp.
T h e resu lts o f in v estig a tio n s o n p u lp r ea c tio n s to c a v ity an d cro w n p rep aration w ith co n v e n tio n a l b e lt-d r iv e n e n g in e s rev o lv in g at sp eed s u p to 3 ,0 0 0 rpm in d ic a te th a t th e d en tist sh o u ld b e ca r e fu l to a v o id p u lp d a m a g e.1»2 O th er c o n c lu sio n s se e m e d
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nuclei were found in the cut dentinal tubules. T his phenomenon indicated another immediate reaction, a hemorrhage.21’22 An increased affinity o f the dentin in the cavity bottom and walls to basophilic stains in hematoxylin-eosin (appear ing bright red in Masson trichrome stain) indi cated a third immediate reaction, a burn.23 The criteria for reactions occurring from 1 to 30 days and those occurring after 30 days were out lined.24'25 Regardless o f their different interpretations o f specific details found in the histologic sections— details that some authors26’27 regarded as patho logic changes and others11 as artifacts— all au thors11’ 23_25, 28-30 who based their conclusions mainly on histologic investigations and who used an adequate histologic technic agreed that it was important to keep the dentin moist during high speed preparation to prevent tissue damage. Other investigators, who mainly based their conclusions on the lack o f a temperature increase in the pulp when air was used as a coolant, recommended air blowing to prevent pulp injury,31 ignoring the fact that the lack o f a temperature increase in the pulp proves that dentin is an excellent thermal in sulator.12-14 In addition, they ignored the fact that a significant temperature increase would occur at the spot o f contact of the dentin and the drill,14 that the air blast alone caused the disintegration o f the odontoblasts and an inflammation o f the pulp,11’20-21’23-25’30 and that a 150 C material32 applied in a cavity caused severe pulp damage.33 In two studies that he claimed were clinical, an investigator34’ 35 discussed histologic technic and criteria on the basis o f nine teeth and concluded that the use o f air was preferable to any other cooling method. In a later study, the number o f teeth was increased to 86, but the same histologic technic was used.36 The purpose o f the present study was to record and interpret the reactions that occurred in the teeth as a result o f wet and dry cavity and crown preparation.
Materials and methods The material in this study consisted o f 1,664 ex periments o f which 6 7424 and 13811 experiments have been previously discussed. In this investiga tion, the previous experiments and the new ones were used to demonstrate the effect o f different kinds o f spray, anti-inflammatory agents, and variations in temperature o f the involved tissue. 992 ■ JADA, Vol. 76, May 1968
The engines and spray systems that were tested in these experiments were as follows: ■ A Kavo handpiece with reduction gear 10:1, running at 1 5 0 to 3 0 0 rpm. ■ A Ritter belt-driven engine running at 5 to 6.000 rpm. ■ A belt-driven engine working at .speeds up to 10.000 rpm and having an air-water spray attached to the handpiece. ■ A Ritter belt-driven engine with a Kavo or, Micro-Mega speed increasing wrist joint, at about 4 0 .0 0 0 rpm, and a Kavo or Ritter automatic spray directing an air-water spray on the bur and the field o f operation. ■ A M icro-Mega geared contra-angle handpiece (belt or air-driven) revolving at 8 0 ,0 0 0 rpm. ■ A Dentalair, an air turbine engine revolving at 5 0 .0 0 0 rpm. ■ A Dentalair air turbine engine with a MicroMega geared handpiece revolving at 1 2 0 ,0 0 0 rpm. ■ An experimental air-driven handpiece revolv ing at 9 4 ,0 0 0 to 1 0 4 ,0 0 0 rpm. ■ LD X , an experimental vane motor revolving at 1 2 8 ,0 0 0 to 1 3 5 ,0 0 0 rpm. ■ Original and modified Borden air rotors.* ■ A modified Borden air rotor with a Kavo exper imental handpiece having three outlets for the spray. ■ A Starflite with an adjustable spray coming from one side o f the bur. ■ A Midwest air turbine with one outlet for the spray near the shaft o f the bur. ■ An Aero Turbex air turbine with two outlets for the spray at some distance from the shaft of the bur. ■ A Bien Air air turbine having one outlet for spray far away from the shaft o f the bur. ■ A Bien Air air turbine having three outlets for spray near to the shaft o f the bur. ■ An experimental air turbine accommodating burs with a central hole through the shaft and the head, allowing water to penetrate through openings in the head. ■ A new M idwest air turbine with spray as al ready described. ■ A new Starflite air turbine. ■ A new M idwest handpiece in combination with cryo-anesthesia. The teeth used for these experiments were mainly premolar teeth from children 10 to 16 years old, although a considerable number of teeth from individuals up to 7 3 years old were used; a third group consisted o f miniature pig and monkey teeth. Cavities were prepared in the buc-
cal, the lingual, and under specific requirements, in the occlusal surfaces; in crown preparation, full crowns were made. Some teeth were extracted from 3 to 20 minutes after the cavity preparation was started; in other teeth, zinc oxide-eugenol or amalgam was introduced in the cavity for observa tion periods o f from 1 to 620 days. To evaluate whether anti-inflammatory agents eliminated reactions that were initially caused by dry preparation, corticosteroids were tested in M osteller’s37 solution and in Ledermix. Since no corticosteroid was effective when used according to the manufacturer’s directions, in another series H 3 prednisolone and the vehicle were applied separately to freshly cut dentin to determine if the prednisolone reached the site o f possible in flammation. To evaluate whether the temperature o f the teeth and jaws influenced cutting procedures, preparations were made while th e patient was un der local cryo-anesthesia. Although all the steps o f the procedure were not known, some teeth that had been extracted, after a full crown had been seated for more than ten years, were also examined. The control material consisted o f clinically in tact human, pig, and monkey teeth exposed only to extraction and the histologic preparation; more specifically, the control was sought in each tooth, ie, the region in which the cavity or crown prep aration had been made and the region in which the implied dentinal tubules ended in the pulp were compared with the surrounding regions, and the differences were recorded according to the criteria that are described. The histologic method described in previous publications11’ 23-24 was used with modifications. Fixation in part o f the material took place in cyanuric chloride. Optimal penetration o f the fixa tive was insured since the teeth were precut down to 3 to 4 mm parallel specimens. Demineraliza tion took place in nitric acid (two days), acetic acid (four to five days), and ethylenediaminetetraacetic acid (19 to 30 days). The end point o f de mineralization was examined and determined in an X-ray fluoroscope. The sections were 4 n to 5 ii thick. In addition to hematoxylin-eosin, iron hematoxylin, Mallory azan, and M asson’s tri chrome stain were used. For evaluation o f mast cells, Alcian blue at pH 2.2 was applied to tissue which had not been exposed to mineralization. For demonstration o f penetration and location o f H3 labeled prednisolone, a nuclear tracer solu tion was applied directly on the cut paraffin slides.
Fig 1 ■ A: Cavity flo o r and wall in dentin; narrow, dark, su p e rficia l area indicates burn caused by c u ttin g w ith engine w ith o u t spray or w ith in s u ffic ie n t spray. B: Dentin and pulp under ca vity c u t as in A; elongated, black bodies are odonto blast nuclei th a t have m igrated into involved dentinal tu bules; adjacent odontoblast layer irre g u la rly reduced. Note th a t odontoblasts s till rem ain in involved area. Presence of odontoblasts is no evidence of new fo rm a tio n o f these cells. C: A ir blow ing a fte r cavity preparation. O dontoblast nuclei in dentinal tubules; ruptured c a p illa rie s in odontoblast layer; fewer rem aining odontoblasts than in B. D, E: Cavity c u t w ith engine having in s u ffic ie n t spray. Elongated bodies in dentinal tu b ules are erythrocytes th a t have m igrated into cu t dentinal tubules. Presence o f e rythrocytes in tu b u le s is evidence th a t there m ust be a pressure gra d ie n t between cavity and pulp re su ltin g in suction and th a t c u ttin g pro cedure has caused hemorrhage subjacent to involved den tin a l tubules.
■ Criteria fo r evaluation o f pulp reactions to cav ity and crown preparation: (1) Immediate reac tions were discoloration o f the cavity floor or the prepared crown surface, which indicated a burn (Fig 1A); odontoblast nuclei in the pulpal ends o f the cut dentinal tubules with a reduced number o f odontoblasts-in the adjacent odontoblast layer, Langeland—Langeland: CUTTING WITH M IN IM U M TRAUMA ■ 993
Fig 2 ■ A: Dentin and pulp subjacent to cavity prepared under s u ffic ie n t w ater spray but afterw ard desiccated by two m in ute s o f a ir blowing. Alm ost a ll odontoblasts have m igrated into involved dentinal tubules; c a p illa rie s in sub ja ce n t odontoblast layer fille d , and num ber o f n e u tro p h ilic leukocytes in vessel in layer o f Weil sig n ific a n tly increased. B: Typical pulp co n d itio n caused by any m ethod o f cavity preparation causing odontoblasts to m igrate in itia lly from about three hours to several days a fte r preparation. O donto blast nuclei in involved dentinal tubules, layer o f odonto blasts reduced, and n e u tro p h ilic leukocytes in pulpal region of c u t dentinal tubules. C: S ig n ifica n t increase o f neutro p h ilic leukocytes in a fferent vessels.
which indicated that the odontoblasts were de stroyed (Fig IB, C); erythrocytes in the pulpal ends o f the cut dentinal tubules, which indicated a hemorrhage (Fig ID , E); and capillaries filled with blood confined to the region in which the cut dentinal tubules end in the pulp, which indi cated an immediate hyperemia (Fig 2A). These reactions indicated a harmful effect; their absence indicated that the method was inert. Additional experiments must be carried out to de termine the aftereffect o f the method. (2) Reactions after 3 hours to 30 days were dis coloration o f the cavity floor or the prepared crown surface, which indicated a burn; odonto blast nuclei in the pulpal ends o f the cut dentinal tubules with a reduced number o f odontoblasts in the adjacent odontoblast layer, which indicated that the odontoblasts were destroyed; erythro cytes in the pulpal ends o f cut dentinal tubules, which indicated a hemorrhage; capillaries filled with blood confined to the region in which the cut dentinal tubules end in the pulp, which indi cated hyperemia and circulatory disturbances; leukocytes, mostly neutrophilic and occasionally
Fig 3 ■ A: Typical irre g u la r irrita tio n d e ntin in area subja cent to cavity c u t w ith any procedure causing in itia l de s tru ctio n o f odontoblasts. T his accounts fo r few er tubules and in clusion o f pulp tissu e in poor condition, since reduced num ber o f odontoblasts cannot adequately cover area. Note th a t odontoblasts which o rig in a lly disappeared have not been replaced. Irrita tio n d entin is scar tissue. B, C: Severe circ u la to ry disturbances and hemorrhages a fte r long obser vation periods show up as brown pigm ent (C) th a t is b iré frin g e n t in polarized lig h t (B). D: Severe, acute involvem ents and extensive pulp tissue d estruction a fte r long observa tio n periods are seen by presence o f ch ro n ic in fla m m a to ry cells. E: If c u ttin g procedure was carried o u t under s u ffi c ie n t water spray, not causing odontoblast nuclei to m igrate in itia lly into involved tubules, and if cavity flo o r and w alls were ca re fu lly, nondesiccatively dried, no changes can be seen a fte r long observation periods if n o n irrita n t m aterial has been used to occlude cavity.
Fig 4 ■ A: Reduction handpiece ro ta tin g at 150 to 300 rpm. B, C: Belt-driven engines at 40,000 rpm; higher pressure o f spray in B covers rota tin g in stru m e n t better than th a t in C. D: A ir-ro to r at 50.000 rpm w ith spray h ittin g shaft and head o f bur. E: Same engine as in D; spray regulated to je t o f w ater h ittin g base of diam ond and leaving e n tire working area dry. Air-w ater spray as in D covers better although there is less water. F, G: Experim ental handpieces at 50j000 rpm showing th a t same brand of handpieces may vary. In F, spray misses entirely; in G, one spray je t h its bur. H: Hand piece rotating at 80,000 rpm; o u tle t o f spray near shaft o f bur. Spray washes e n tire bur on same side as o u tle t but leaves o ther side dry. I to L: Experim ental handpieces run n in g at 95,000 to 100.000 rpm, I and K w ith water jets, J and L w ith air-w ater spray. All sprays were s u ffic ie n t to prevent dentin and pulp reactions; J and L preferable because they had less water and better v is ib ility . M to P: Experim ental handpiece rota tin g from 95,000 to 100,000 rpm; three je ts o f water h ittin g 2.5-mm shaft o f bur. A lthough d e ntin and pulp reactions were m inim ized, no regu lation of spray adequately covered instrum ent; v is ib ility was obscured.
eosinophilic, in the odontoblast layer adjacent to the dentinal tubules in which the odontoblast nuclei or erythrocytes or both appeared, which in dicated chemotaxis caused by the disintegration o f the odontoblasts or erythrocytes or both (Fig 2B); increase o f leukocytes inside the circulatory vessels o f the subjacent pulp region, which indi cated chemotaxis caused by cells deteriorating in the area (Fig 2C); decreasing visibility o f the cell remnants in the involved dentinal tubules as the observation period was increased, which indi cated that the migrated cells disintegrated; an in creasing degree o f irregularity o f the involved dentin and no regeneration o f the odontoblast layer as the observation period was increased(Fig 3A); and the presence o f brown pigment with the extravasated erythrocytes in the involved area, which indicated a hemorrhage (Fig 3B, C). These reactions indicated a harmful effect; their absence indicated that the method was in ert (Fig 3E). If the method caused an acute reac tion, experiments with longer observation peri ods were carried out to determine the long-term effect. (3) Criteria after 30 days was discoloration o f the cavity floor and margin, which indicated a burn; no more cells or cell remnants in the cut dentinal tubules (Fig 3A); irregularly formed ir ritation dentin adjacent to the pulpal end o f the cut dentinal tubules and bordered by a reduced layer o f odontoblasts, which indicated that the migrated cells disintegrated and that new odonto blasts did not form (Fig 3A); neutrophilic or eosinophilic leukocytes or both in the adjacent odontoblast layer, which indicated that the in fluence o f irritation products from the cut den tinal tubules persisted (this reaction may or may not be present regardless o f the marginal leakage); lymphocytes, plasma cells, macrophages, and rflitosis in the inflammatory cells, in the subjacent pulp tissue, and if these cell types appear in the subjacent tissue with leukocytes in the adjacent odontoblast layer, the reaction is considered to be more severe than if these cells appear alone (Fig 3D).
Observations ■ Clinical observations: Burnt dentin was oc casionally smelled when a cavity was prepared carefully without water or when air-rotors with automatic sprays were used. When the automatic spray o f various engines rotated from about 10,000 rpm to 200,000 to 300,000 rpm at free-running speed, the water could reach the bur or be con stantly or intermittently deflected from the revolv ing bur (Fig 4, 5). Deflection occurred more often at higher speeds, and there was a correlation be tween the rotational speed and the force o f the spray (Fig 5E to L, O, P). The direction o f the outlet also determined whether a spray reached the bur effectively (Fig 4B to D), since the spray might hit only part o f a diamond (Fig 4E ) or not hit it at all (Fig 4F), which would result in dry cutting regardless o f the amount o f water emitting from the outlet. Other variations were the placement o f the spray at one side o f the bur (Fig 4H), the use o f air-water spray (Fig 4B to D, H, J, L, 5A to D, O, P) or jets o f water (Fig 4F, G, I, K, M to P, 5E to M, Q to T), the shape o f the rotating instru ment (Fig 5K, L), the lack in centricity o f the in strument (Fig 5M, N), and the position and dis tance o f the spray from the shaft o f the bur. The position and distance o f the shaft helped deter mine whether the spray would enter the cavity during actual working conditions (Fig 5Q to T). A clinical condition was demonstrated in which an air-rotor had two jets o f water. Although there was a considerable amount o f water, the direction o f the jets resulted in dry drilling (Fig 6). Some patients felt pain during the drilling re gardless o f the engine used, but the patients re acted far more favorably to wet than to dry prep arations. In laboratory tests, sparks sometimes d e veloped when the enamel o f extracted teeth was drilled with air-rotors under dry conditions, and the head o f a steel bur, under extreme conditions that were not used clinically, changed in color to blue.
Fig 5 ■ A, B: Experim ental handpiece rotating at 135,000 rpm, having th re e o u tle ts to be regu lated fo r water je t or air-w ater spray. With water jets, coverage less than w ith air-w ater spray in B. C, D: Free-running speed about 300,000 rpm; since a ir pressure increased in D, coverage better in D than in C. E to G: Two w ater jets; fu ll pressure in E and F; reduced pressure in G. Jet nearest bur h its shaft o f any "bur, decreasing v is ib ility w ith o u t increasing effectiveness; decreased pressure and am ount results in to ta l defle ction and dry d rillin g . H to L, 0 , P: Effectiveness of spray-depends on pressure of spray and shape o f instrum ent; no autom atic spray can cover working surface o f in strum ent in K, L, M, N; Inaccurate chuck (M) and noncentered in stru m e n t (N) cause excessive v i brations and d e fle c t spray. Q, R; Spray o u tle t fa r away from bur is in e ffe ctive because cusp or cavity wall w ill prevent spray from reaching area o f cu ttin g . S, T: Same engine as in Q, R after head reconstructed; th re e spray o u tle ts near shaft of bur under m ost circum stances are effective.
Fig 6 ■ A ir-ro to r w ith tw o water je ts operating under c lin ical conditions. A lthough there is large am ount o f water, none reaches area o f cu ttin g.
Fig 7 ■ Cavity preparation under a ir blow ing in carious area o f tooth o f 57-year-old person. A: Cavity shown at top le ft; irrita tio n d e n tin caused by caries under rig h t part of cavity; prim ary d e n tin under le ft part. B: Odontoblast nu cle i in dentinal tu b u le s in prim ary d entin is evidence th a t narrowness o f den tina l tu b ules does not prevent irrita tio n from periphery. C: High m ag n ifica tio n o f irrita tio n dentin; few irregular canals and three m igrated odontoblast nu clei are evidence th a t dentinal tu b ules in irrita tio n dentin rem ain open and pervious.
998 ■ JADA, Vol. 7 6 , May 1 9 6 8
■ Histologic observations: To simplify the inter pretation o f the reactions that were observed in detail, the engines were grouped according to the number o f revolutions per minute, and an esti mated average o f the reactions, based on the cri teria, was recorded. When dentin was cut at ex tremely low speeds o f up to 300 rpm, with sharp burs and in an excavating movement with low pressure, very minor or no reactions would oc cur. The strongest reaction that was observed, in one instance only, was the migration o f odonto blast nuclei into the dentinal tubules that were opened by the cavity preparation. When zinc oxide-eugenol was used in these low-speed prep arations, only a slight to moderate reaction ap-
Fig 8 ■ Non-Dolor engine; constant blowing of a ir o f 1 C in cavity d u ring cavity preparation; cavity fille d w ith zinc oxide-eugenol fo r 16 days. A: Ruptured c a p illa rie s in odon to b la st layer subjacent to ca vity and in fla m m a to ry cells in adjacent region o f a ffe re n t vessels. B: O dontoblast layer w ith m u ltip le hemorrhages. C: Erythrocytes in den tina l tu bules are evidence o f hemorrhage.
Fig 9 ■ Cavity prepared w ith engine having s u fficie n t water spray; steel in stru m e n t heated over alcohol flam e was pressed against d e ntin of cavity floor; ca vity fille d w ith zinc oxide-eugenol fo r 38 days. A: S uperficial dentin contacted by h o t in s tru m e n t appears dark in hem atoxylineosin; red in Masson. B: Rest o f odontoblast nuclei in den tin a l tu b ules bordered by reduced odontoblast layer. C: High m ag n ifica tio n o f odontoblast layer showing few re m aining odontoblasts th a t w ill form irregular irrita tio n den tin . D: In fla m m a tory ce lls gathered in e n tire pulp subjacent to ca vity in B are shown to be macrophages.
peared initially, and a repair occurred that left no sign o f the initial reaction other than a narrow layer of irritation dentin. In the speed range of 3.000 to 6,000 rpm, reactions occurred more often than in the low-speed group when the en gines were used without water spray. The reac tions decreased to nil when water was used and increased again considerably if air was blown into the cavity. These reactions were the same in in stances in which a desiccation o f the dentin o f the cavity took place after a wet preparation, which indicated that the desiccation o f the content of the dentinal tubules was as important as the sur face burn (Fig 1A, 2A). This reaction occurred regardless o f the age o f the tooth or if irritation dentin was present, indicating that neither nar rowness nor irregularity o f the dentinal tubules will prevent the desiccative reaction. The reac tion also showed that the irritation dentin was permeable (Fig 7). In this respect, the tempera ture o f the air made no difference. In the NonDolor preparations in which air o f 1 C was con stantly blown into the cavity while it was prepared, odontoblast nuclei and erythrocytes appeared in the cut dentinal tubules as an immediate reaction, and an inflammatory reaction was seen in the sub jacent pulp (Fig 8). When the speed o f the engine was increased to 50.000 rpm, there was no evident change in the pattern o f reactions, and immediate as well as in-
Fig 10 ■ Crown preparation under s u ffic ie n t air-water spray; im pression taken w ith n o n irrita n t m aterial. Tempo rary crown was made o f co ld-curing p lastic m aterial, Sevriton, placed d ire c tly on abutm ent and le ft on tooth fo r in itia l setting, and removed and cem ented w ith zinc oxideeugenol fo r two days, a fte r w hich tooth was extracted. Shortest distance to pulp was 1.8 mm. A: Odontoblast nuclei in c u t dentinal tu b u le s and accum ulation o f ce lls in entire pulp horn. B: One area o f involved odontoblast layer, ty p i cal o f e n tire involved area, showing few rem aining odonto blasts and n e u tro p h ilic leukocytes in odontoblast layer. C: Entire pulp horn heavily in filtra te d w ith n e u tro p h ilic leukocytes.
Fig 11 ■ Upper rig h t firs t prem olar o f 55-year-old person th a t had repeated caries, fillin g s, and crown placed; re moval o f tooth about ten years a fte r crown procedures be cause p a tie nt fe lt pain. A, B: Serial sections somewhat apart; A shows p u lp tissue in root canal, B in coronal part. C: Despite p a tie n t’s pain, vital p u lp tissue in root canal co n ta in in g vessels, nerves, d iffu se ca lcifica tio n s, and in fla m m a to ry cells.
flammatory reactions were still prevented in the wet preparations. In an experimental series in which the cavity floor was intentionally heated after a wet prepara tion, a more severe reaction occurred. A burn was seen on the cavity floor, and in the subjacent pulp tissue, a severe inflammatory reaction oc curred (Fig 9). As seen in Figures 8 and 9, cold or heat caused the odontoblast nuclei to migrate into the dentinal tubules following destruction o f these odontoblasts. In the 100,000 to 135,000 rpm group o f en gines, the number o f reactions increased with a wet preparation and increased considerably more with a dry preparation. This trend was even more significant in the 160,000 to 200 ,0 0 0 rpm group o f engines. Reactions were obvious in the wet as well as in the dry preparations, and for some o f the engines, it did not seem to make any differ ence whether wet or dry preparations were used. N o inflammatory reactions occurred, however, when the spray o f an engine was corrected or when the chairside assistant gave extra spray. 1000 ■ JADA, Vol. 76, May 1968
In crown preparation, it was possible to carry out the entire procedure, including cementation, without pathologic reactions, although severe re actions would occur in the pulp if each step o f the procedure, including the crown preparation per se, was not carefully done (Fig 10). Because o f the shape o f the instruments used in this pro cedure, extra spray was needed more often (Fig 4E, 5K, L). Particularly in instances o f crown procedures that had observation periods o f several years, the cumulative effect o f all the necessary proce dures was seen. In teeth extracted more than ten years after the crown procedure was done, the pulp chamber was almost filled with irritation dentin. Many o f the serial sections indicated that the pulp chamber was completely destroyed, but other sections showed finger-like extensions o f pulp tissue far into an extremely irregular irrita tion dentin. Although all the constituents o f an inflamed pulp tissue were found, ie, vessels, nerves, fibroblasts, ground substance, and inflam matory cells, the patient might not have felt specific pain until the tooth had to be extracted (Fig 11). The application o f prednisolone to freshly cut dentin caused no changes that were different than those caused in similar preparations in which the drug had not been applied. A s a result o f the dry preparation, odontoblasts and occasionally ery throcytes immediately appeared in the cut den tinal tubules, and after a day, neutrophilic leuko cytes gathered in the adjacent odontoblast layer. After longer observation periods o f up to a half year, a layer o f variable thickness o f irritation dentin occurred in all preparations in which odon toblast nuclei had initially migrated into the cut dentinal tubules. The irritation dentin was lined with a reduced layer o f odontoblasts, the odonto blasts that did not migrate initially into the cut tubules. The preparations in which H3 predniso lone had been applied to the freshly cut dentin showed that the labeled particles penetrated the dentinal tubules in the primary dentin and in the irregular irritation dentin (Fig 12A to C). In ad dition, the labeled particles also appeared in mac rophages subjacent to the experimental cavity (Fig 12D to F). Dentinogenesis was evidenced by the presence o f irritation dentin (Fig 12A, C). When cutting took place after the temperature o f the involved quadrant was decreased by means o f cryo-anesthesia, the reaction pattern was un changed. N o reactions occurred with a wet prep aration, whereas with a dry preparation, all the
reactions that occurred when mouth tempera tures were normal also occurred when the temper atures decreased.
Discussion If investigators have different results when they study histologically the same clinical phenomenon, the histologic method should be investigated. In one clinical study, an investigator 3 4 - 3 6 drew con clusions on the basis o f histologic experiments in which the method o f demineralization, the choice o f stain, the section thickness, the observations, and the interpretations were questionable. ■ M eth o d o f dem ineralization: Regardless of the chemical and method used, it is well known that prolonged demineralization o f a tissue af fects the stainability o f the sections. Therefore, it is extremely important to determine the end point o f demineralization in order to remove the specimen from the reagent at the earliest possible time . 11 This was not done in these investigations 3 4 - 3 6 because the investigator kept his specimens in H N O 3 for three weeks instead o f the necessary two days. Three weeks in H N O 3 destroys the normal stainability o f the sections, rendering the nuclear structures invisible. The loss o f stainabil ity is one reason why the photomicrographs do not show the nuclear structures in the involved dentinal tubules that were shown in other investi11,20 —25,28
30 , 38,39
■ Choice o f stain: N o stain other than hematoxylin-eosin seems to have been applied, which indicates that the specific stains needed to identify the changes that an investigator should look for have been left out. For example, the Masson tri chrome stain would reveal burns o f the dentin.23’24 The specificity o f this stain and others would prob ably be jeopardized in the overdemineralized sec tions. ■ Section thicknesses: Eight to 12 p . sections were used although the dentinal tubule to be ex amined has a diameter o f about 4 to 5 p. When examining sections thicker than 5 /u one will ob serve a number o f dentinal tubules on top o f each other, as in ground sections, and be unable to de scribe the content o f the dentinal tubule. There are no visible changes in the dentinal tubules be
Fig 12 ■ Cavity prepared in m onkey tooth under a ir blow ing; H3 prednisolone, amalgam le ft in tooth fo r 98 days. A: Cavity and subjacent dentin; num erous layers o f irrita tio n d e ntin below cavity. B: C avity flo o r and subjacent den tin a l tu b ules in coated section showing th a t labeled ma te ria l penetrated tubules. C; Coated sections showing pene tra tio n o f tubules in irrita tio n dentin. D to F: Separate cells from coated sections showing labeled m aterial in m acro phages. Labeled prednisolone penetrates d entinal tu b ules and enters pulp but does not prevent in fla m m a tio n or dentinogenesis.
cause o f the large section thickness, as seen in the unclear photomicrographs.34-36 ■ Observations: In spite o f the unclear photo micrographs, it can be seen that the odontoblasts have disappeared from the odontoblast layer in the experimental cavity, but the thickness and poor stainability o f the sections do not show where the odontoblasts disappeared, although in Figure 9, the erythrocytes seem to appear in the dentinal tubules.34 In addition, irregular irritation dentin, which is caused when the odontoblasts are destroyed, is shown in some photomicrographs o f dentinal tubules from experiments o f longer periods. The changes that are shown in other histologic studies L a n g e la n d — L a n g e la n d : CUTTING WITH M IN IM U M TRAUMA ■ 1001
must have occurred here, although they are not visible in the photomicrographs.34-36 ■ Interpretations: The photomicrographs in these investigations34-36 showed that the odonto blasts had disappeared, as is generally agreed in histologic publications. However, although this technic fails to show where the odontoblasts moved, there is no reason to doubt the'evidence found in other investigations in which a suitable technic was used. Although this evidence was missed, the investigators should have found addi tional evidence that the odontoblasts were de stroyed in the fact that irritation dentin was pres ent after longer observation periods and that this dentin was bordered by a reduced layer o f odonto blasts in their Figures 4 and 5 .36 Perhaps the most serious misconception was expressed in the paper35 which implied that in flammatory cells appear after one and a half hours and in the paper36 that said: “Evidence o f inflammatory response is indicated by slight round cell infiltration. This specimen was extracted 20 minutes after completion o f the grinding proce dure (Fig 1).” General knowledge o f histopathology and special knowledge o f pulp histopathology would prevent this misunderstanding. It is not possible in a connective tissue reaction that chronic inflammatory cells would accumulate within a 20-minute time interval. In addition, the fact that chronic inflammatory cells may be pres ent in the pulp tissue o f clinically intact teeth, even in impacted teeth, should have been con sidered.38-39 The following conclusions may be drawn: the sections o f the papers34-36 mentioned previously show a reduction in the number o f odontoblasts in short observation-period experiments; the sec tions are too thick to show single tubules and their content; the prolonged retention o f the specimens in nitric acid will destroy nuclear structures and prevent their staining; adequate histologic meth ods and valid criteria are available to evaluate pulp conditions. Other investigators,40 who conducted an experi ment with a seven-day observation period and a similarly inadequate histologic method and cri teria, also found no significant differences be tween wet and dry preparations, although the photomicrographs showed an inflammation in one and no reactions in the other. To determine whether a wet or dry cavity prep aration should be used, both clinical and histologic factors must be considered. I f the practical re 1002 ■ JADA, Vol. 76, May 1968
quirements for preventing dentin and pulp changes were such that the accuracy o f the clinical proce dures was jeopardized, a consideration o f which procedure would constitute a greater overall risk would be necessary. Therefore, it is important to compare these two risks to arrive at a practical solution. In these experimental series, the cavity prepa rations were made as they would have been made by any careful operator. Except for the Dentalair, Injector, and L D X series, in which the number o f revolutions per minute were recorded and the pressure estimated by frequent comparison on a scale, there is no exact information regarding these factors. However, all air-rotors were used with a brushing technic without the use o f pressure, which clearly reduced the rotational speed. The reactions in the pulp depend on the amount o f friction and desiccation. Whether friction is created by low speed and high pressure or by high speed and low pressure is unimportant. In addi tion, air blowing— cold, temperate, or hot— causes the desiccation o f the dentinal tubules re gardless o f the temperature in the pulp. Thus, the conclusions from the early temperature measure ment are unchanged. If the bur has not been suf ficiently cooled, there will be a considerable temperature increase in the dentin and bur localIyi4-i6 that is reflected in the burned lesions in the histologic sections. Burns were successfully prevented by use o f water spray or air-water spray in engines with rotational speeds o f up to 50,000 rpm, in which instances there was a sig nificant difference between the wet and dry prep arations (Table). This difference was considerably smaller when an overall count was made in en gines with 160,000 rpm. In some engines, no dif ference was seen since the spray was deflected from the bur. This means that the preparations re corded as wet, but still showing reactions, were in fact dry, which is why the clinical difference may not be obvious when such engines are used in wet or dry preparations. An evaluation o f the effectiveness o f the spray by measuring cubic centimeters per minute must be inaccurate. The water at the site o f contact be tween bur and tooth structure and not the amount of water emitting from the outlet is decisive for the result. Because large amounts o f water de crease the visibility into the cavity, an air-water spray is preferable. N ot all air-water sprays are equally effective because o f the distance o f the outlets from the shank o f the bur and because o f the direction o f the spray. In addition, an air-
Table ■ The engines and spray systems th a t were tested in th e experim ents.
Engine M icro -M e g a , Kavo reduction Electric BelNDriven Ritter, S.S. W h ite , Kavo
N o n -D o lo r Ritter, Kavo
RPM during preparation 1-300 3,0006,000
10,000 40,00050,000
M icro-M e ga Dentolair
Heating o f cavity flo o r LDX, M icro -M e g a , Kavo Injector
O rig in al Borden, Kavo Borden 7/3 Spray, S.S. W hite V i Spray M idw est, Bien A ir I/3 Spray, S ta rfliie adjustable, A e ro Turbex C enter hole S farflife (new chuck) monkey teeth Midwest (new chuck) monkey teeth A nti-inflam m atory a g e ntsf Preparation under decreased te m p e ra tu re f Total
50,000 1 0 0 ,0 0 0 135,000
16 0 ,0 0 0 200,000
N o. of cases 69 11 14 19 29 30 33 27 25 36 35 165 47 27 29 13 10 33 • 25 16 119 229 74 125 25 21
Type o f spray N o ne
W et
A ir
0 5-91 0 1-620 0 1-65 0 1-77 0 1-395 0
+ + + + + + + + + +
86
M od era te
4
2 1 Ì2 10 2 2 28 25 25 36 31
5 7 5 2
7 1 22 24
7 1 2 9 7 2 5 2
Severe
Repair
4
6 5 8
6 15
+
0 0-301 0-301
6 37 15
20 8 43
10 14
0-301 0-301
10
+
23 8
7 32
10
■+ + + + +
+
20 20
Slight
+ + +
+ + +
40 45
60* 5
151 39
+ +
+ +
N o . o f cases showing reaction N one
0 1-294 0 1-304 0 7-79 0 2-105 0 1-460 0 2-180 0-321 0 74
+ +
32 50 62
O bservation p eriod (days)
25 12 3 34 29 10
7 7 2 73 49 30 12
4 1 6 11 12 151 26 95 25 15
10 13 6
6
75 27 25 21
5 min189 days
63
1,664
*The figures which in dicate reactions in the experim ental groups, in which the teeth have n ot been extracted im mediately, may add up to more than the to ta l number o f instances because re p a ir and no reaction and re p air and reactions may be recorded simultaneously. fP relim in a ry results are re p orte d in the paper.
water spray may be deflected. This deflection is easily corrected when the outlets are brought nearer the bur shaft and the air pressure o f the spray increased. In crown preparation where longer or wider instruments often have to be used, reactions may not be prevented by the automatic spray; in this instance, an adjustable spray is useful.38 N ot all operations can be covered, and the operator is responsible for administering extra spray. Another important point in regard to an ade quate water spray is that o f keeping the rotating instrument— a bur or a diamond— wet in order to keep the cutting edges free o f debris. Besides being biologically acceptable, the spray will lengthen the life o f the instrument. An instrument that is smeared with debris will cut poorly and generate more friction. The influence o f the overall temperature changes in the Non-Dolor and in the Cryodent series was nil. The decisive factor in all these ex
periments was desiccation, and a general decrease in temperature did not significantly alter the ef fect o f a local temperature change or desiccation. There is a definite temperature increase locally where the revolving bur contacts the dentin, but the temperature increase in the pulp is insignifi cant.14’ 19>13’32 Therefore, to look for the burned lesion in the pulp40 rather than in the surface o f the dentin where it is known to occur and to stain the dentinal tubule only in hematoxylin-eosin rather than using an adequate staining method to show burns in the tissue is incorrect.23-25 Whether the irritation dentin is beneficial will be evaluated based on the sequence o f its forma tion which is shown in the experiments. The irri tation dentin forms after the loss o f the odonto blasts. As an initial response to a peripheral in jury, the odontoblasts migrate into the cut den tinal tubules. After three to four weeks, they are no longer seen, but during that time, neutrophilic leukocytes gather at the pulpal ends o f the cut Langeland—Langeland: CUTTING WITH M INIM UM TRAUMA ■ 1003
tubules as evidence that the migrated odonto blasts disintegrate. The dentin, which then has fewer dentinal tubules and is bordered by the re maining odontoblasts, is evidence that the in volved odontoblasts have been destroyed. This destruction indicates that the formation o f irrita tion dentin is a regressive, destructive process and that the end product is scar tissue. A lso, as more tissue is involved, more scar tissue will form, as shown in the crown experiments (Fig 10, 11). The initial destruction o f the odontoblasts caused the formation o f calcified tissue that could not be con trolled arid that finally destroyed the entire pulp. This dentin was pervious and included soft tissue in poor condition. Some investigators37-42 disagree with the ob servation that, when anti-inflammatory agents are applied to freshly cut dentin, the pathologic re sponse to the cutting injury is not reduced. In re gard to the inflammation, our results agree with those o f Fiore-Donno and Baume,43 but their statement that no dentinogenesis occurred after minor amounts o f corticosteroids were applied is not corroborated in our study. We found that irri tation dentin formed at a similar rate whether or not a drug was applied. The theoretical basis for the use o f M osteller’s37 solution, that the prednisolone would pre vent the release o f heparin from the mast cells and that heparin would prevent inflammation, should be considered speculative for at least four reasons: mast cells are not prevalent in the human pulp; after peripheral injury to the pulp, neutro philic leukocytes, not mast cells, are the first to accumulate, as in the soft, connective tissue o f the human body; since neutrophilic leukocytes gather first, the theory has no possible basis; after odonto blast destruction, prednisolone in any form did not prevent the accumulation o f leukocytes. There fore, the histologic findings do not corroborate the theoretical assumption. Although a cavity preparation in most in stances will not immediately, or after short peri ods, cause definite, clinical symptoms, the shortperiod histologic reactions will indicate the future development o f reactions. We must cause as little destruction as possible by our operative proce dures; therefore, as this study indicates, cavity and crown preparation should be made under wet conditions. By use o f a wet preparation, the least possible trauma is caused, and the life-span o f the restorative procedure is lengthened. Dry preparation would add to the destructive process es in the pulp. 1004 ■ JADA, Vol. 76, May 1968
Summary and conclusions Cavity and crown preparations by means o f en gines rotating from 150 to 300,000 rpm free-run ning speed were histologically evaluated in 1,664 experiments. The effect o f various types o f cutting instruments, spray systems, temperatures, and anti-inflammatory agents were evaluated. ■ Histologic conclusions: Dry cavity preparation causes the following immediate reactions: burns in the dentin, the migration o f odontoblasts, the migration o f erythrocytes, and hyperemia. A center hole through the bur would seem to make the spray arrive at the right place and there by keep the bur or diamond clean most effective ly. Despite this theoretically desirable situation, our preliminary results with this technical solution were not entirely successful because reactions oc curred in 26 o f 32 patients. Leakage problems occurred in the experimental handpieces so that we could not be certain whether the drilling took place under optimal technical conditions. There fore, a center hole may still be the optimal solu tion if adequate instruments are manufactured. Reactions after 1 to 30 days were burns in the dentin, the migration o f odontoblasts, the migra tion o f erythrocytes, hyperemia o f circulatory disturbances, and an acute inflammatory reaction in the pulp subjacent to the cavity. Reactions after more than 30 days were bums in the dentin; irregularly formed irritation den tin; lymphocytes, plasma cells, and macrophages in the subjacent pulp tissue if desiccation had been extensive; and,no inflammatory reaction, but evi dence o f a burn in the dentin and a scar tissue in the pulp if desiccation had been less extensive. Wet cavity preparation with a properly directed and working spray caused minor or no reactions. ■ Clinical conclusions: Normal pulp has suffi cient recuperative power to withstand the reac tions caused by dry preparation in a confined re gion. The severity o f the reactions increases with the expansion o f the exposed region. The reac tions to cavity preparation add to those o f subse quent procedures and may be decisive in breaking down the resistance o f the pulp. After a desiccative preparation, the pulp is more vulnerable to harmful influences such as the effect o f active chemicals in many of the materials used to restore a tooth. These chemicals will re place the water in the desiccated, peripheral ends
o f the Cut dentinal tubules. With a wet cavity prep aration, slight or no reactions will occur if harm less materials are used. I f irritant materials are used, the severity o f the reactions is considerably less in the wet preparations than in the dry prep arations.
T his investigation was supported by th e USPHS research grant DE-02006 from the N ational In s titu te o f Dental Re search, N ational In s titu te s o f Health, Bethesda, Md. and by gra n t 50-0970 from Serco Surgical Engineering and Re search Corporation, Victoria, Texas. Kaare Langeland is professor o f oral biology and Leena Langeland is research associate, instructor, departm ent of operative dentistry, Oral H istology Laboratory, School of Dentistry, State U niversity o f New York, Buffalo, NY. *AII a ir rotors w ith the tu rb in e in the head have working speeds o f about 160,000 to 200,000 rpm, regardless of m uch higher free-running speeds. 1. Thoma, K.H. Oral pathology, ed 3. St. Louis, C. V. Mosby Co., 1958. 2. Stones, H.H. Oral and dental diseases, ed 2. B a lti more, W illiam s & W ilkin s Co., 1951. 3. Barker, J.N. Reactions of the p u lp to various fillin g m aterials and c lin ic a l procedures. Aust J Dent 46:226 Dec 1942. 4. Oman, C.R., and Applebaum, E. Ultrasonic cavity preparation. P relim inary report. New York Dent J 20:256 June-July 1954. 5. Friedman, J.; Lite, T., and Solomon, H. Pulp reac tio n s to u ltrasonic tooth preparation. New York Dent J 26: 144 March 1956. 6. Zach, L., and Brown, G.N. Pulpal e ffe ct o f ultrasonic ca vity preparation. Prelim inary report. New York Dent J 22: 9 Jan 1956. 7. Hansen, L.S., and Nielsen, A.G. Comparison of tissue response to rotary and u ltrasonic dental c u ttin g procedures. JADA 52:131 Feb 1956. 8. James, V.E.; Schour, I., and Spence, J.M. Response o f human p u lp to gutta-percha and cavity preparation. JADA 49:639 Dec 1954. 9. Van Huysen, G., and Boyd, D.A. Operative procedures and th e tooth. J Prosth Dent 3:818 Nov 1953. 10. Black, R.B. A pplication and réévaluation o f air abrasive technic. JADA 50:408 A pril 1955. 11. Langeland, K. Tissue changes in the dental pulp. An experim ental h isto lo g ic study. O d o ntT 65:239 Aug 1957. 12. Lisanti, V.F., and Zander, H.A. Thermal in ju ry to norm al dog teeth: in vivo m easurements o f pulp tem pera tu re increases and th e ir e ffe ct on the pulp tissue. J Dent Res 31:548 Aug 1952. 13. Perreault, J.G.; Massler, M., and Schour, I. Reaction o f odontoblasts to m edicam ents placed in cavity prepara tio n s o f rat incisors. JADA 52:533 May 1956. 14. Peyton, F.A. Tem perature rise and c u ttin g e fficie n cy o f rota tin g instrum ents. New York Dent J 18:439 Nov 1952. 15. Ingraham, R., and Tanner, H.M. Adaptation o f modern in stru m e n ts and increased operating speeds to restorative procedures. JADA 47:311 Sept 1953. 16. Hudson, D.C., and Sweeney, W.T. Tem peratures de veloped in ro ta tin g dental c u ttin g instrum ents. JADA 48: 127 Feb 1954. 17. Sullivan, E.J. Cem entation and esthetic problem s in crown and bridge procedures. JADA 51:34 July 1955. 18. Dausch, H. Zur Frage der Feucht-oder Trochenpreparation desvita le n Zahnes. Deutsch Zahnaerztl Z 10:75, 1955. 19. Peyton, F.A., and Vaughn, R.C. Thermal changes de
veloped d u ring the c u ttin g o f tooth tissue. Fortn Rev Chicago Dent Soc 20:9 Dec 15, 1950. 20. Langeland, K. En sam m enligning av pulpareaksjoner pa low og high speed preparering, og om pulpareaksjoner pa fyllin g sm ate ria le t Cavinyl. Norske Tannlaegeforen Tid 66: 528, 1956. 21. Langeland, K. Pulp reactions to high speed in stru m entation. Norske Tannlaegeforen Tid 68:137 March 1958. 22. Ostby, B.N. C linical and experim ental experience w ith th e Borden Airotor. Dent A bstr 3:671 Nov 1958. 23. Langeland, K. Pulp reactions to ca vity preparation and to burns in th e dentin. A p re lim in a ry report. Odont T 68(no. 5):463, 1960. 24. Langeland, K. Tissue changes in cid e n t to cavity prep aration. An evaluation o f some dental engines. Acta Odont Scand 19:397 Dec 1961. '25. Langeland, K. Reactions pulpaires aux travaux ex écutés avec les in stru m e n ts a grande vitesse (turbines). Ef fic a c ité des nouveaux types de “ spray.” Rev Franc Odontosto m a t9 :5 3 3 April 1962. 26. Bernier, J.L., and Knapp, M.J. New pulpal response to high-speed dental instrum ents. Oral Surg 11:167 Feb 1958. 27. Weder, M. Ueber die Veränderungen der Pulpa des m enschlichen Zahnes nach Beschliefen m it hohen Geschwin digkeiten. Deutsch Zahnaerztl Z 15:104 Jan 1960. 28. Swerdlow, H., and Stanley, H.R. Reaction of th e hu man dental pulp to cavity preparation. I. E ffect o f water spray at 20,000 rpm. JADA 56:317 March 1958. 29. Stanley, H.R., and Swerdlow, H. Biological effects o f various c u ttin g m ethods in cavity preparation: the part pressure plays in pulpal response. JADA 61:450 Oct 1960. 30. Brannstrom , M. Dentinal and pulpal response. III. A pplication o f an a ir stream to exposed dentin. Long observa tio n periods. An experim ental study. Acta O dont Scand 18: 234 Nov 1960. 31. Aplin, A.W.; Cantwell, K.R., and Manny, V.R. Effect o f coolants on tem perature rise resulting from ca vity prep aration. J Dent Res 38:761 July-Aug 1959. 32. Jarby, S. On tem perature m easurem ents in teeth in v itro and in vivo. O dont T 66:421 Dec 1958. 33. Langeland, K. Pulpareaksjoner ved bruk av Cavinyl. O d o n tT 65:12 A pril 1957. 34. Schuchard, A. Pulpal response at 160,000 rpm, using air coolant. J C alif Dent Assn 38:26 Feb 1962. 35. Schuchard, A., and W atkins, CÆ. Pulpal response at conventional and ultra-high speeds, using a ir coolant. South C alif Dent Assn 31:391 Dec 1963. 36. Schuchard, A., and W atkins, C.E. Thermal and histo logic response to high-speed and ultrahigh-speed c u ttin g in tooth structure. JADA 71:1451 Dec 1965. 37. Mosteller, J.H. A b ility o f prednisolone solution to e lim in a te pulpal inflam m ation. J Prosth Dent 13:754 JulyAug 1963. 38. Langeland, K., and Langeland, L.K. H istologic study o f 155 im pacted teeth. O d o ntT 73:527 Oct 1965. 39. Langeland, K., and Langeland, L.K. Pulp reactions to crown preparation, impression, tem porary crow n fixation, and perm anent cem entation. J Prosth Dent 15:129 Jan-Feb 1965. 40. Dachi, F.S., and Stigers, R.W. Pulpal e ffe cts o f water and a ir coolants used in high-speed cavity preparation. JADA 76:95 Jan 1968. 41. Stanley, H.R., and Swerdlow, H. M in im izin g pulpal reactions w ith prednisolone therapy. The e ffe cts o f a delayed steroid application to cu t dentin. J Oral Ther 3:1 July 1966. 42. Schroeder, A., and Triadan, H. “ K linische und histo logische Untersuchungen Uber die W irkung von K ortikoster oiden bei der Pulpabehandlung.” Deutsch Zahnaerztl Z 20: 248 A pril 1966. 43. Fiore-Donno, G., and Baume, L J . Contrôles histopathologiques du coiffage pulpaire aux corticostéroides. Schweiz M schr Zahnheilk 73:413 May 1963. Langeland—Langeland: CUTTING WITH M INIM UM TRAUMA ■ 1005
Cutting procedures with minimized trauma
le ss w e ll fo u n d e d .3 W h en ev a lu a tin g th e b io lo g ic effe c ts o f n ew te c h n ica l aid s ad ap ted fo r d en ta l cu ttin g p r o c e dures,; so m e in v estig a to rs4»5 c o n clu d e d th a t th e re a c tio n s c a u se d b y an u ltra so n ic p rep aration and b y co n v e n tio n a l cu ttin g w ere id en tica l, so m e 6 th at an u ltra so n ic p rep a ra tio n c a u se d a m ild re a ctio n , an d so m e 7 th a t an u ltra so n ic p rep a ra tio n c a u se d a sig n ifica n tly stronger reaction . In e v a lu
T o d eterm in e w h eth er w e t o r dry ca v ity p re p ara tio n sh o u ld b e u sed , th e sp e e d o f ro ta tin g e n g in e s w as c o n sid ered . W h e n th e ro ta tio n a l sp e e d o f th ese e n g in e s w a s r a ised fro m a b o u t 3 ,0 0 0 to 1 0 ,0 0 0 rpm , a m eth o d o f c o o lin g w a s g en era lly co n sid e r ed n ecessa ry , b u t th ere w a s d isa g reem en t in regard to w h ich c o o lin g sy stem w a s b est. S o m e in v estig a to rs12’13 p referred air, a n d o th e r s14’16 a je t o f w ater o r an a ir-w ater spray. O n e a u th o r17 c o n clu d e d th a t w ater w a s b est, air n e x t b est, and an air-w ater spray th e le a s t e ffe c tiv e . T h e g en era l v ie w ex p r e sse d in G erm a n litera tu re w a s th a t n o w ater sh o u ld b e u se d d u rin g d rillin g , b u t that w ater sh o u ld b e u se d d u rin g g rin d in g . L ater, it w a s m a in ta in e d 18 th at w a ter sh o u ld a lso b e u sed d u rin g d rillin g. In early stu d ies th a t m ea su red tem p eratu re ch a n g es in th e d en tin , th e bur, an d th e p u lp d ur ing ca v ity p rep aration , a sig n ific a n t in c re a se in th e tem p eratu re o f th e d en tin co n ta c tin g th e b u r14,19 a n d in th e bur h e a d it s e lf w a s s e e n .16 In th e in v iv o ex p erim en ts, th is tem p era tu re in crea se w as n o t e a sily tran sferred to th e p u lp .12 A lso , w h en u sin g h is to lo g y as a to o l fo r th e ev a lu a tio n , research ers h a d d iffe r en t resu lts, a l th o u g h th ey in v e stig a ted th e sa m e p ro b lem , b e c a u se n o n e o f th em h a d r eco rd ed th e im m e d ia te rea ctio n s to ca v ity p r ep a ra tio n p er se a n d b ec a u se so m e o f th e criteria u se d in th e h is to lo g ic ev a lu a tio n w ere n o t v a lid . W h e n th e first air tu rb in e for d en ta l u se w as e v a lu a te d ,11’20 o n e im m e d ia te r e a c tio n to dry ca v ity p r ep a ra tio n w a s th e m ig ra tio n
atin g th e air a b rasiv e te ch n ic an d co n v e n tio n a l d rillin g , so m e in v estig a to rs8;10 h e ld th at th e se te c h n ics c a u se d id en tica l rea ctio n s, w h erea s o th e r s11 th o u g h t th at th e a b ra siv e te ch n ic c a u se d a d e sic c a tio n o f th e den tin .
o f o d o n to b la st n u c le i in to th e c u t d en tin a l tu b u les, w h ich in d ica ted th a t th e o d o n to b la sts d isin te grated . T h is rea ctio n w a s p rev en ted i f th e d en tin w a s k ep t m o is t.11’20 In th e first ev a lu a tio n o f th e B o rd en air-rotor, e r y th ro cy tes an d o d o n to b la st
Kaare Langeland, DDS, PhD Leena K. Langeland, DDS, Williamsville, NY
Operative procedures must cause as little destruc tion as possible; therefore, as this study indicates, cavity and crown preparation should be made un der wet conditions. By use of a wet preparation, the least possible trauma is caused, and the life span of the restorative procedure is lengthened. Dry preparation would add to the destructive pro cesses in the pulp.
T h e resu lts o f in v estig a tio n s o n p u lp r ea c tio n s to c a v ity an d cro w n p rep aration w ith co n v e n tio n a l b e lt-d r iv e n e n g in e s rev o lv in g at sp eed s u p to 3 ,0 0 0 rpm in d ic a te th a t th e d en tist sh o u ld b e ca r e fu l to a v o id p u lp d a m a g e.1»2 O th er c o n c lu sio n s se e m e d
991
nuclei were found in the cut dentinal tubules. T his phenomenon indicated another immediate reaction, a hemorrhage.21’22 An increased affinity o f the dentin in the cavity bottom and walls to basophilic stains in hematoxylin-eosin (appear ing bright red in Masson trichrome stain) indi cated a third immediate reaction, a burn.23 The criteria for reactions occurring from 1 to 30 days and those occurring after 30 days were out lined.24'25 Regardless o f their different interpretations o f specific details found in the histologic sections— details that some authors26’27 regarded as patho logic changes and others11 as artifacts— all au thors11’ 23_25, 28-30 who based their conclusions mainly on histologic investigations and who used an adequate histologic technic agreed that it was important to keep the dentin moist during high speed preparation to prevent tissue damage. Other investigators, who mainly based their conclusions on the lack o f a temperature increase in the pulp when air was used as a coolant, recommended air blowing to prevent pulp injury,31 ignoring the fact that the lack o f a temperature increase in the pulp proves that dentin is an excellent thermal in sulator.12-14 In addition, they ignored the fact that a significant temperature increase would occur at the spot o f contact of the dentin and the drill,14 that the air blast alone caused the disintegration o f the odontoblasts and an inflammation o f the pulp,11’20-21’23-25’30 and that a 150 C material32 applied in a cavity caused severe pulp damage.33 In two studies that he claimed were clinical, an investigator34’ 35 discussed histologic technic and criteria on the basis o f nine teeth and concluded that the use o f air was preferable to any other cooling method. In a later study, the number o f teeth was increased to 86, but the same histologic technic was used.36 The purpose o f the present study was to record and interpret the reactions that occurred in the teeth as a result o f wet and dry cavity and crown preparation.
Materials and methods The material in this study consisted o f 1,664 ex periments o f which 6 7424 and 13811 experiments have been previously discussed. In this investiga tion, the previous experiments and the new ones were used to demonstrate the effect o f different kinds o f spray, anti-inflammatory agents, and variations in temperature o f the involved tissue. 992 ■ JADA, Vol. 76, May 1968
The engines and spray systems that were tested in these experiments were as follows: ■ A Kavo handpiece with reduction gear 10:1, running at 1 5 0 to 3 0 0 rpm. ■ A Ritter belt-driven engine running at 5 to 6.000 rpm. ■ A belt-driven engine working at .speeds up to 10.000 rpm and having an air-water spray attached to the handpiece. ■ A Ritter belt-driven engine with a Kavo or, Micro-Mega speed increasing wrist joint, at about 4 0 .0 0 0 rpm, and a Kavo or Ritter automatic spray directing an air-water spray on the bur and the field o f operation. ■ A M icro-Mega geared contra-angle handpiece (belt or air-driven) revolving at 8 0 ,0 0 0 rpm. ■ A Dentalair, an air turbine engine revolving at 5 0 .0 0 0 rpm. ■ A Dentalair air turbine engine with a MicroMega geared handpiece revolving at 1 2 0 ,0 0 0 rpm. ■ An experimental air-driven handpiece revolv ing at 9 4 ,0 0 0 to 1 0 4 ,0 0 0 rpm. ■ LD X , an experimental vane motor revolving at 1 2 8 ,0 0 0 to 1 3 5 ,0 0 0 rpm. ■ Original and modified Borden air rotors.* ■ A modified Borden air rotor with a Kavo exper imental handpiece having three outlets for the spray. ■ A Starflite with an adjustable spray coming from one side o f the bur. ■ A Midwest air turbine with one outlet for the spray near the shaft o f the bur. ■ An Aero Turbex air turbine with two outlets for the spray at some distance from the shaft of the bur. ■ A Bien Air air turbine having one outlet for spray far away from the shaft o f the bur. ■ A Bien Air air turbine having three outlets for spray near to the shaft o f the bur. ■ An experimental air turbine accommodating burs with a central hole through the shaft and the head, allowing water to penetrate through openings in the head. ■ A new M idwest air turbine with spray as al ready described. ■ A new Starflite air turbine. ■ A new M idwest handpiece in combination with cryo-anesthesia. The teeth used for these experiments were mainly premolar teeth from children 10 to 16 years old, although a considerable number of teeth from individuals up to 7 3 years old were used; a third group consisted o f miniature pig and monkey teeth. Cavities were prepared in the buc-
cal, the lingual, and under specific requirements, in the occlusal surfaces; in crown preparation, full crowns were made. Some teeth were extracted from 3 to 20 minutes after the cavity preparation was started; in other teeth, zinc oxide-eugenol or amalgam was introduced in the cavity for observa tion periods o f from 1 to 620 days. To evaluate whether anti-inflammatory agents eliminated reactions that were initially caused by dry preparation, corticosteroids were tested in M osteller’s37 solution and in Ledermix. Since no corticosteroid was effective when used according to the manufacturer’s directions, in another series H 3 prednisolone and the vehicle were applied separately to freshly cut dentin to determine if the prednisolone reached the site o f possible in flammation. To evaluate whether the temperature o f the teeth and jaws influenced cutting procedures, preparations were made while th e patient was un der local cryo-anesthesia. Although all the steps o f the procedure were not known, some teeth that had been extracted, after a full crown had been seated for more than ten years, were also examined. The control material consisted o f clinically in tact human, pig, and monkey teeth exposed only to extraction and the histologic preparation; more specifically, the control was sought in each tooth, ie, the region in which the cavity or crown prep aration had been made and the region in which the implied dentinal tubules ended in the pulp were compared with the surrounding regions, and the differences were recorded according to the criteria that are described. The histologic method described in previous publications11’ 23-24 was used with modifications. Fixation in part o f the material took place in cyanuric chloride. Optimal penetration o f the fixa tive was insured since the teeth were precut down to 3 to 4 mm parallel specimens. Demineraliza tion took place in nitric acid (two days), acetic acid (four to five days), and ethylenediaminetetraacetic acid (19 to 30 days). The end point o f de mineralization was examined and determined in an X-ray fluoroscope. The sections were 4 n to 5 ii thick. In addition to hematoxylin-eosin, iron hematoxylin, Mallory azan, and M asson’s tri chrome stain were used. For evaluation o f mast cells, Alcian blue at pH 2.2 was applied to tissue which had not been exposed to mineralization. For demonstration o f penetration and location o f H3 labeled prednisolone, a nuclear tracer solu tion was applied directly on the cut paraffin slides.
Fig 1 ■ A: Cavity flo o r and wall in dentin; narrow, dark, su p e rficia l area indicates burn caused by c u ttin g w ith engine w ith o u t spray or w ith in s u ffic ie n t spray. B: Dentin and pulp under ca vity c u t as in A; elongated, black bodies are odonto blast nuclei th a t have m igrated into involved dentinal tu bules; adjacent odontoblast layer irre g u la rly reduced. Note th a t odontoblasts s till rem ain in involved area. Presence of odontoblasts is no evidence of new fo rm a tio n o f these cells. C: A ir blow ing a fte r cavity preparation. O dontoblast nuclei in dentinal tubules; ruptured c a p illa rie s in odontoblast layer; fewer rem aining odontoblasts than in B. D, E: Cavity c u t w ith engine having in s u ffic ie n t spray. Elongated bodies in dentinal tu b ules are erythrocytes th a t have m igrated into cu t dentinal tubules. Presence o f e rythrocytes in tu b u le s is evidence th a t there m ust be a pressure gra d ie n t between cavity and pulp re su ltin g in suction and th a t c u ttin g pro cedure has caused hemorrhage subjacent to involved den tin a l tubules.
■ Criteria fo r evaluation o f pulp reactions to cav ity and crown preparation: (1) Immediate reac tions were discoloration o f the cavity floor or the prepared crown surface, which indicated a burn (Fig 1A); odontoblast nuclei in the pulpal ends o f the cut dentinal tubules with a reduced number o f odontoblasts-in the adjacent odontoblast layer, Langeland—Langeland: CUTTING WITH M IN IM U M TRAUMA ■ 993
Fig 2 ■ A: Dentin and pulp subjacent to cavity prepared under s u ffic ie n t w ater spray but afterw ard desiccated by two m in ute s o f a ir blowing. Alm ost a ll odontoblasts have m igrated into involved dentinal tubules; c a p illa rie s in sub ja ce n t odontoblast layer fille d , and num ber o f n e u tro p h ilic leukocytes in vessel in layer o f Weil sig n ific a n tly increased. B: Typical pulp co n d itio n caused by any m ethod o f cavity preparation causing odontoblasts to m igrate in itia lly from about three hours to several days a fte r preparation. O donto blast nuclei in involved dentinal tubules, layer o f odonto blasts reduced, and n e u tro p h ilic leukocytes in pulpal region of c u t dentinal tubules. C: S ig n ifica n t increase o f neutro p h ilic leukocytes in a fferent vessels.
which indicated that the odontoblasts were de stroyed (Fig IB, C); erythrocytes in the pulpal ends o f the cut dentinal tubules, which indicated a hemorrhage (Fig ID , E); and capillaries filled with blood confined to the region in which the cut dentinal tubules end in the pulp, which indi cated an immediate hyperemia (Fig 2A). These reactions indicated a harmful effect; their absence indicated that the method was inert. Additional experiments must be carried out to de termine the aftereffect o f the method. (2) Reactions after 3 hours to 30 days were dis coloration o f the cavity floor or the prepared crown surface, which indicated a burn; odonto blast nuclei in the pulpal ends o f the cut dentinal tubules with a reduced number o f odontoblasts in the adjacent odontoblast layer, which indicated that the odontoblasts were destroyed; erythro cytes in the pulpal ends o f cut dentinal tubules, which indicated a hemorrhage; capillaries filled with blood confined to the region in which the cut dentinal tubules end in the pulp, which indi cated hyperemia and circulatory disturbances; leukocytes, mostly neutrophilic and occasionally
Fig 3 ■ A: Typical irre g u la r irrita tio n d e ntin in area subja cent to cavity c u t w ith any procedure causing in itia l de s tru ctio n o f odontoblasts. T his accounts fo r few er tubules and in clusion o f pulp tissu e in poor condition, since reduced num ber o f odontoblasts cannot adequately cover area. Note th a t odontoblasts which o rig in a lly disappeared have not been replaced. Irrita tio n d entin is scar tissue. B, C: Severe circ u la to ry disturbances and hemorrhages a fte r long obser vation periods show up as brown pigm ent (C) th a t is b iré frin g e n t in polarized lig h t (B). D: Severe, acute involvem ents and extensive pulp tissue d estruction a fte r long observa tio n periods are seen by presence o f ch ro n ic in fla m m a to ry cells. E: If c u ttin g procedure was carried o u t under s u ffi c ie n t water spray, not causing odontoblast nuclei to m igrate in itia lly into involved tubules, and if cavity flo o r and w alls were ca re fu lly, nondesiccatively dried, no changes can be seen a fte r long observation periods if n o n irrita n t m aterial has been used to occlude cavity.
Fig 4 ■ A: Reduction handpiece ro ta tin g at 150 to 300 rpm. B, C: Belt-driven engines at 40,000 rpm; higher pressure o f spray in B covers rota tin g in stru m e n t better than th a t in C. D: A ir-ro to r at 50.000 rpm w ith spray h ittin g shaft and head o f bur. E: Same engine as in D; spray regulated to je t o f w ater h ittin g base of diam ond and leaving e n tire working area dry. Air-w ater spray as in D covers better although there is less water. F, G: Experim ental handpieces at 50j000 rpm showing th a t same brand of handpieces may vary. In F, spray misses entirely; in G, one spray je t h its bur. H: Hand piece rotating at 80,000 rpm; o u tle t o f spray near shaft o f bur. Spray washes e n tire bur on same side as o u tle t but leaves o ther side dry. I to L: Experim ental handpieces run n in g at 95,000 to 100.000 rpm, I and K w ith water jets, J and L w ith air-w ater spray. All sprays were s u ffic ie n t to prevent dentin and pulp reactions; J and L preferable because they had less water and better v is ib ility . M to P: Experim ental handpiece rota tin g from 95,000 to 100,000 rpm; three je ts o f water h ittin g 2.5-mm shaft o f bur. A lthough d e ntin and pulp reactions were m inim ized, no regu lation of spray adequately covered instrum ent; v is ib ility was obscured.
eosinophilic, in the odontoblast layer adjacent to the dentinal tubules in which the odontoblast nuclei or erythrocytes or both appeared, which in dicated chemotaxis caused by the disintegration o f the odontoblasts or erythrocytes or both (Fig 2B); increase o f leukocytes inside the circulatory vessels o f the subjacent pulp region, which indi cated chemotaxis caused by cells deteriorating in the area (Fig 2C); decreasing visibility o f the cell remnants in the involved dentinal tubules as the observation period was increased, which indi cated that the migrated cells disintegrated; an in creasing degree o f irregularity o f the involved dentin and no regeneration o f the odontoblast layer as the observation period was increased(Fig 3A); and the presence o f brown pigment with the extravasated erythrocytes in the involved area, which indicated a hemorrhage (Fig 3B, C). These reactions indicated a harmful effect; their absence indicated that the method was in ert (Fig 3E). If the method caused an acute reac tion, experiments with longer observation peri ods were carried out to determine the long-term effect. (3) Criteria after 30 days was discoloration o f the cavity floor and margin, which indicated a burn; no more cells or cell remnants in the cut dentinal tubules (Fig 3A); irregularly formed ir ritation dentin adjacent to the pulpal end o f the cut dentinal tubules and bordered by a reduced layer o f odontoblasts, which indicated that the migrated cells disintegrated and that new odonto blasts did not form (Fig 3A); neutrophilic or eosinophilic leukocytes or both in the adjacent odontoblast layer, which indicated that the in fluence o f irritation products from the cut den tinal tubules persisted (this reaction may or may not be present regardless o f the marginal leakage); lymphocytes, plasma cells, macrophages, and rflitosis in the inflammatory cells, in the subjacent pulp tissue, and if these cell types appear in the subjacent tissue with leukocytes in the adjacent odontoblast layer, the reaction is considered to be more severe than if these cells appear alone (Fig 3D).
Observations ■ Clinical observations: Burnt dentin was oc casionally smelled when a cavity was prepared carefully without water or when air-rotors with automatic sprays were used. When the automatic spray o f various engines rotated from about 10,000 rpm to 200,000 to 300,000 rpm at free-running speed, the water could reach the bur or be con stantly or intermittently deflected from the revolv ing bur (Fig 4, 5). Deflection occurred more often at higher speeds, and there was a correlation be tween the rotational speed and the force o f the spray (Fig 5E to L, O, P). The direction o f the outlet also determined whether a spray reached the bur effectively (Fig 4B to D), since the spray might hit only part o f a diamond (Fig 4E ) or not hit it at all (Fig 4F), which would result in dry cutting regardless o f the amount o f water emitting from the outlet. Other variations were the placement o f the spray at one side o f the bur (Fig 4H), the use o f air-water spray (Fig 4B to D, H, J, L, 5A to D, O, P) or jets o f water (Fig 4F, G, I, K, M to P, 5E to M, Q to T), the shape o f the rotating instru ment (Fig 5K, L), the lack in centricity o f the in strument (Fig 5M, N), and the position and dis tance o f the spray from the shaft o f the bur. The position and distance o f the shaft helped deter mine whether the spray would enter the cavity during actual working conditions (Fig 5Q to T). A clinical condition was demonstrated in which an air-rotor had two jets o f water. Although there was a considerable amount o f water, the direction o f the jets resulted in dry drilling (Fig 6). Some patients felt pain during the drilling re gardless o f the engine used, but the patients re acted far more favorably to wet than to dry prep arations. In laboratory tests, sparks sometimes d e veloped when the enamel o f extracted teeth was drilled with air-rotors under dry conditions, and the head o f a steel bur, under extreme conditions that were not used clinically, changed in color to blue.
Fig 5 ■ A, B: Experim ental handpiece rotating at 135,000 rpm, having th re e o u tle ts to be regu lated fo r water je t or air-w ater spray. With water jets, coverage less than w ith air-w ater spray in B. C, D: Free-running speed about 300,000 rpm; since a ir pressure increased in D, coverage better in D than in C. E to G: Two w ater jets; fu ll pressure in E and F; reduced pressure in G. Jet nearest bur h its shaft o f any "bur, decreasing v is ib ility w ith o u t increasing effectiveness; decreased pressure and am ount results in to ta l defle ction and dry d rillin g . H to L, 0 , P: Effectiveness of spray-depends on pressure of spray and shape o f instrum ent; no autom atic spray can cover working surface o f in strum ent in K, L, M, N; Inaccurate chuck (M) and noncentered in stru m e n t (N) cause excessive v i brations and d e fle c t spray. Q, R; Spray o u tle t fa r away from bur is in e ffe ctive because cusp or cavity wall w ill prevent spray from reaching area o f cu ttin g . S, T: Same engine as in Q, R after head reconstructed; th re e spray o u tle ts near shaft of bur under m ost circum stances are effective.
Fig 6 ■ A ir-ro to r w ith tw o water je ts operating under c lin ical conditions. A lthough there is large am ount o f water, none reaches area o f cu ttin g.
Fig 7 ■ Cavity preparation under a ir blow ing in carious area o f tooth o f 57-year-old person. A: Cavity shown at top le ft; irrita tio n d e n tin caused by caries under rig h t part of cavity; prim ary d e n tin under le ft part. B: Odontoblast nu cle i in dentinal tu b u le s in prim ary d entin is evidence th a t narrowness o f den tina l tu b ules does not prevent irrita tio n from periphery. C: High m ag n ifica tio n o f irrita tio n dentin; few irregular canals and three m igrated odontoblast nu clei are evidence th a t dentinal tu b ules in irrita tio n dentin rem ain open and pervious.
998 ■ JADA, Vol. 7 6 , May 1 9 6 8
■ Histologic observations: To simplify the inter pretation o f the reactions that were observed in detail, the engines were grouped according to the number o f revolutions per minute, and an esti mated average o f the reactions, based on the cri teria, was recorded. When dentin was cut at ex tremely low speeds o f up to 300 rpm, with sharp burs and in an excavating movement with low pressure, very minor or no reactions would oc cur. The strongest reaction that was observed, in one instance only, was the migration o f odonto blast nuclei into the dentinal tubules that were opened by the cavity preparation. When zinc oxide-eugenol was used in these low-speed prep arations, only a slight to moderate reaction ap-
Fig 8 ■ Non-Dolor engine; constant blowing of a ir o f 1 C in cavity d u ring cavity preparation; cavity fille d w ith zinc oxide-eugenol fo r 16 days. A: Ruptured c a p illa rie s in odon to b la st layer subjacent to ca vity and in fla m m a to ry cells in adjacent region o f a ffe re n t vessels. B: O dontoblast layer w ith m u ltip le hemorrhages. C: Erythrocytes in den tina l tu bules are evidence o f hemorrhage.
Fig 9 ■ Cavity prepared w ith engine having s u fficie n t water spray; steel in stru m e n t heated over alcohol flam e was pressed against d e ntin of cavity floor; ca vity fille d w ith zinc oxide-eugenol fo r 38 days. A: S uperficial dentin contacted by h o t in s tru m e n t appears dark in hem atoxylineosin; red in Masson. B: Rest o f odontoblast nuclei in den tin a l tu b ules bordered by reduced odontoblast layer. C: High m ag n ifica tio n o f odontoblast layer showing few re m aining odontoblasts th a t w ill form irregular irrita tio n den tin . D: In fla m m a tory ce lls gathered in e n tire pulp subjacent to ca vity in B are shown to be macrophages.
peared initially, and a repair occurred that left no sign o f the initial reaction other than a narrow layer of irritation dentin. In the speed range of 3.000 to 6,000 rpm, reactions occurred more often than in the low-speed group when the en gines were used without water spray. The reac tions decreased to nil when water was used and increased again considerably if air was blown into the cavity. These reactions were the same in in stances in which a desiccation o f the dentin o f the cavity took place after a wet preparation, which indicated that the desiccation o f the content of the dentinal tubules was as important as the sur face burn (Fig 1A, 2A). This reaction occurred regardless o f the age o f the tooth or if irritation dentin was present, indicating that neither nar rowness nor irregularity o f the dentinal tubules will prevent the desiccative reaction. The reac tion also showed that the irritation dentin was permeable (Fig 7). In this respect, the tempera ture o f the air made no difference. In the NonDolor preparations in which air o f 1 C was con stantly blown into the cavity while it was prepared, odontoblast nuclei and erythrocytes appeared in the cut dentinal tubules as an immediate reaction, and an inflammatory reaction was seen in the sub jacent pulp (Fig 8). When the speed o f the engine was increased to 50.000 rpm, there was no evident change in the pattern o f reactions, and immediate as well as in-
Fig 10 ■ Crown preparation under s u ffic ie n t air-water spray; im pression taken w ith n o n irrita n t m aterial. Tempo rary crown was made o f co ld-curing p lastic m aterial, Sevriton, placed d ire c tly on abutm ent and le ft on tooth fo r in itia l setting, and removed and cem ented w ith zinc oxideeugenol fo r two days, a fte r w hich tooth was extracted. Shortest distance to pulp was 1.8 mm. A: Odontoblast nuclei in c u t dentinal tu b u le s and accum ulation o f ce lls in entire pulp horn. B: One area o f involved odontoblast layer, ty p i cal o f e n tire involved area, showing few rem aining odonto blasts and n e u tro p h ilic leukocytes in odontoblast layer. C: Entire pulp horn heavily in filtra te d w ith n e u tro p h ilic leukocytes.
Fig 11 ■ Upper rig h t firs t prem olar o f 55-year-old person th a t had repeated caries, fillin g s, and crown placed; re moval o f tooth about ten years a fte r crown procedures be cause p a tie nt fe lt pain. A, B: Serial sections somewhat apart; A shows p u lp tissue in root canal, B in coronal part. C: Despite p a tie n t’s pain, vital p u lp tissue in root canal co n ta in in g vessels, nerves, d iffu se ca lcifica tio n s, and in fla m m a to ry cells.
flammatory reactions were still prevented in the wet preparations. In an experimental series in which the cavity floor was intentionally heated after a wet prepara tion, a more severe reaction occurred. A burn was seen on the cavity floor, and in the subjacent pulp tissue, a severe inflammatory reaction oc curred (Fig 9). As seen in Figures 8 and 9, cold or heat caused the odontoblast nuclei to migrate into the dentinal tubules following destruction o f these odontoblasts. In the 100,000 to 135,000 rpm group o f en gines, the number o f reactions increased with a wet preparation and increased considerably more with a dry preparation. This trend was even more significant in the 160,000 to 200 ,0 0 0 rpm group o f engines. Reactions were obvious in the wet as well as in the dry preparations, and for some o f the engines, it did not seem to make any differ ence whether wet or dry preparations were used. N o inflammatory reactions occurred, however, when the spray o f an engine was corrected or when the chairside assistant gave extra spray. 1000 ■ JADA, Vol. 76, May 1968
In crown preparation, it was possible to carry out the entire procedure, including cementation, without pathologic reactions, although severe re actions would occur in the pulp if each step o f the procedure, including the crown preparation per se, was not carefully done (Fig 10). Because o f the shape o f the instruments used in this pro cedure, extra spray was needed more often (Fig 4E, 5K, L). Particularly in instances o f crown procedures that had observation periods o f several years, the cumulative effect o f all the necessary proce dures was seen. In teeth extracted more than ten years after the crown procedure was done, the pulp chamber was almost filled with irritation dentin. Many o f the serial sections indicated that the pulp chamber was completely destroyed, but other sections showed finger-like extensions o f pulp tissue far into an extremely irregular irrita tion dentin. Although all the constituents o f an inflamed pulp tissue were found, ie, vessels, nerves, fibroblasts, ground substance, and inflam matory cells, the patient might not have felt specific pain until the tooth had to be extracted (Fig 11). The application o f prednisolone to freshly cut dentin caused no changes that were different than those caused in similar preparations in which the drug had not been applied. A s a result o f the dry preparation, odontoblasts and occasionally ery throcytes immediately appeared in the cut den tinal tubules, and after a day, neutrophilic leuko cytes gathered in the adjacent odontoblast layer. After longer observation periods o f up to a half year, a layer o f variable thickness o f irritation dentin occurred in all preparations in which odon toblast nuclei had initially migrated into the cut dentinal tubules. The irritation dentin was lined with a reduced layer o f odontoblasts, the odonto blasts that did not migrate initially into the cut tubules. The preparations in which H3 predniso lone had been applied to the freshly cut dentin showed that the labeled particles penetrated the dentinal tubules in the primary dentin and in the irregular irritation dentin (Fig 12A to C). In ad dition, the labeled particles also appeared in mac rophages subjacent to the experimental cavity (Fig 12D to F). Dentinogenesis was evidenced by the presence o f irritation dentin (Fig 12A, C). When cutting took place after the temperature o f the involved quadrant was decreased by means o f cryo-anesthesia, the reaction pattern was un changed. N o reactions occurred with a wet prep aration, whereas with a dry preparation, all the
reactions that occurred when mouth tempera tures were normal also occurred when the temper atures decreased.
Discussion If investigators have different results when they study histologically the same clinical phenomenon, the histologic method should be investigated. In one clinical study, an investigator 3 4 - 3 6 drew con clusions on the basis o f histologic experiments in which the method o f demineralization, the choice o f stain, the section thickness, the observations, and the interpretations were questionable. ■ M eth o d o f dem ineralization: Regardless of the chemical and method used, it is well known that prolonged demineralization o f a tissue af fects the stainability o f the sections. Therefore, it is extremely important to determine the end point o f demineralization in order to remove the specimen from the reagent at the earliest possible time . 11 This was not done in these investigations 3 4 - 3 6 because the investigator kept his specimens in H N O 3 for three weeks instead o f the necessary two days. Three weeks in H N O 3 destroys the normal stainability o f the sections, rendering the nuclear structures invisible. The loss o f stainabil ity is one reason why the photomicrographs do not show the nuclear structures in the involved dentinal tubules that were shown in other investi11,20 —25,28
30 , 38,39
■ Choice o f stain: N o stain other than hematoxylin-eosin seems to have been applied, which indicates that the specific stains needed to identify the changes that an investigator should look for have been left out. For example, the Masson tri chrome stain would reveal burns o f the dentin.23’24 The specificity o f this stain and others would prob ably be jeopardized in the overdemineralized sec tions. ■ Section thicknesses: Eight to 12 p . sections were used although the dentinal tubule to be ex amined has a diameter o f about 4 to 5 p. When examining sections thicker than 5 /u one will ob serve a number o f dentinal tubules on top o f each other, as in ground sections, and be unable to de scribe the content o f the dentinal tubule. There are no visible changes in the dentinal tubules be
Fig 12 ■ Cavity prepared in m onkey tooth under a ir blow ing; H3 prednisolone, amalgam le ft in tooth fo r 98 days. A: Cavity and subjacent dentin; num erous layers o f irrita tio n d e ntin below cavity. B: C avity flo o r and subjacent den tin a l tu b ules in coated section showing th a t labeled ma te ria l penetrated tubules. C; Coated sections showing pene tra tio n o f tubules in irrita tio n dentin. D to F: Separate cells from coated sections showing labeled m aterial in m acro phages. Labeled prednisolone penetrates d entinal tu b ules and enters pulp but does not prevent in fla m m a tio n or dentinogenesis.
cause o f the large section thickness, as seen in the unclear photomicrographs.34-36 ■ Observations: In spite o f the unclear photo micrographs, it can be seen that the odontoblasts have disappeared from the odontoblast layer in the experimental cavity, but the thickness and poor stainability o f the sections do not show where the odontoblasts disappeared, although in Figure 9, the erythrocytes seem to appear in the dentinal tubules.34 In addition, irregular irritation dentin, which is caused when the odontoblasts are destroyed, is shown in some photomicrographs o f dentinal tubules from experiments o f longer periods. The changes that are shown in other histologic studies L a n g e la n d — L a n g e la n d : CUTTING WITH M IN IM U M TRAUMA ■ 1001
must have occurred here, although they are not visible in the photomicrographs.34-36 ■ Interpretations: The photomicrographs in these investigations34-36 showed that the odonto blasts had disappeared, as is generally agreed in histologic publications. However, although this technic fails to show where the odontoblasts moved, there is no reason to doubt the'evidence found in other investigations in which a suitable technic was used. Although this evidence was missed, the investigators should have found addi tional evidence that the odontoblasts were de stroyed in the fact that irritation dentin was pres ent after longer observation periods and that this dentin was bordered by a reduced layer o f odonto blasts in their Figures 4 and 5 .36 Perhaps the most serious misconception was expressed in the paper35 which implied that in flammatory cells appear after one and a half hours and in the paper36 that said: “Evidence o f inflammatory response is indicated by slight round cell infiltration. This specimen was extracted 20 minutes after completion o f the grinding proce dure (Fig 1).” General knowledge o f histopathology and special knowledge o f pulp histopathology would prevent this misunderstanding. It is not possible in a connective tissue reaction that chronic inflammatory cells would accumulate within a 20-minute time interval. In addition, the fact that chronic inflammatory cells may be pres ent in the pulp tissue o f clinically intact teeth, even in impacted teeth, should have been con sidered.38-39 The following conclusions may be drawn: the sections o f the papers34-36 mentioned previously show a reduction in the number o f odontoblasts in short observation-period experiments; the sec tions are too thick to show single tubules and their content; the prolonged retention o f the specimens in nitric acid will destroy nuclear structures and prevent their staining; adequate histologic meth ods and valid criteria are available to evaluate pulp conditions. Other investigators,40 who conducted an experi ment with a seven-day observation period and a similarly inadequate histologic method and cri teria, also found no significant differences be tween wet and dry preparations, although the photomicrographs showed an inflammation in one and no reactions in the other. To determine whether a wet or dry cavity prep aration should be used, both clinical and histologic factors must be considered. I f the practical re 1002 ■ JADA, Vol. 76, May 1968
quirements for preventing dentin and pulp changes were such that the accuracy o f the clinical proce dures was jeopardized, a consideration o f which procedure would constitute a greater overall risk would be necessary. Therefore, it is important to compare these two risks to arrive at a practical solution. In these experimental series, the cavity prepa rations were made as they would have been made by any careful operator. Except for the Dentalair, Injector, and L D X series, in which the number o f revolutions per minute were recorded and the pressure estimated by frequent comparison on a scale, there is no exact information regarding these factors. However, all air-rotors were used with a brushing technic without the use o f pressure, which clearly reduced the rotational speed. The reactions in the pulp depend on the amount o f friction and desiccation. Whether friction is created by low speed and high pressure or by high speed and low pressure is unimportant. In addi tion, air blowing— cold, temperate, or hot— causes the desiccation o f the dentinal tubules re gardless o f the temperature in the pulp. Thus, the conclusions from the early temperature measure ment are unchanged. If the bur has not been suf ficiently cooled, there will be a considerable temperature increase in the dentin and bur localIyi4-i6 that is reflected in the burned lesions in the histologic sections. Burns were successfully prevented by use o f water spray or air-water spray in engines with rotational speeds o f up to 50,000 rpm, in which instances there was a sig nificant difference between the wet and dry prep arations (Table). This difference was considerably smaller when an overall count was made in en gines with 160,000 rpm. In some engines, no dif ference was seen since the spray was deflected from the bur. This means that the preparations re corded as wet, but still showing reactions, were in fact dry, which is why the clinical difference may not be obvious when such engines are used in wet or dry preparations. An evaluation o f the effectiveness o f the spray by measuring cubic centimeters per minute must be inaccurate. The water at the site o f contact be tween bur and tooth structure and not the amount of water emitting from the outlet is decisive for the result. Because large amounts o f water de crease the visibility into the cavity, an air-water spray is preferable. N ot all air-water sprays are equally effective because o f the distance o f the outlets from the shank o f the bur and because o f the direction o f the spray. In addition, an air-
Table ■ The engines and spray systems th a t were tested in th e experim ents.
Engine M icro -M e g a , Kavo reduction Electric BelNDriven Ritter, S.S. W h ite , Kavo
N o n -D o lo r Ritter, Kavo
RPM during preparation 1-300 3,0006,000
10,000 40,00050,000
M icro-M e ga Dentolair
Heating o f cavity flo o r LDX, M icro -M e g a , Kavo Injector
O rig in al Borden, Kavo Borden 7/3 Spray, S.S. W hite V i Spray M idw est, Bien A ir I/3 Spray, S ta rfliie adjustable, A e ro Turbex C enter hole S farflife (new chuck) monkey teeth Midwest (new chuck) monkey teeth A nti-inflam m atory a g e ntsf Preparation under decreased te m p e ra tu re f Total
50,000 1 0 0 ,0 0 0 135,000
16 0 ,0 0 0 200,000
N o. of cases 69 11 14 19 29 30 33 27 25 36 35 165 47 27 29 13 10 33 • 25 16 119 229 74 125 25 21
Type o f spray N o ne
W et
A ir
0 5-91 0 1-620 0 1-65 0 1-77 0 1-395 0
+ + + + + + + + + +
86
M od era te
4
2 1 Ì2 10 2 2 28 25 25 36 31
5 7 5 2
7 1 22 24
7 1 2 9 7 2 5 2
Severe
Repair
4
6 5 8
6 15
+
0 0-301 0-301
6 37 15
20 8 43
10 14
0-301 0-301
10
+
23 8
7 32
10
■+ + + + +
+
20 20
Slight
+ + +
+ + +
40 45
60* 5
151 39
+ +
+ +
N o . o f cases showing reaction N one
0 1-294 0 1-304 0 7-79 0 2-105 0 1-460 0 2-180 0-321 0 74
+ +
32 50 62
O bservation p eriod (days)
25 12 3 34 29 10
7 7 2 73 49 30 12
4 1 6 11 12 151 26 95 25 15
10 13 6
6
75 27 25 21
5 min189 days
63
1,664
*The figures which in dicate reactions in the experim ental groups, in which the teeth have n ot been extracted im mediately, may add up to more than the to ta l number o f instances because re p a ir and no reaction and re p air and reactions may be recorded simultaneously. fP relim in a ry results are re p orte d in the paper.
water spray may be deflected. This deflection is easily corrected when the outlets are brought nearer the bur shaft and the air pressure o f the spray increased. In crown preparation where longer or wider instruments often have to be used, reactions may not be prevented by the automatic spray; in this instance, an adjustable spray is useful.38 N ot all operations can be covered, and the operator is responsible for administering extra spray. Another important point in regard to an ade quate water spray is that o f keeping the rotating instrument— a bur or a diamond— wet in order to keep the cutting edges free o f debris. Besides being biologically acceptable, the spray will lengthen the life o f the instrument. An instrument that is smeared with debris will cut poorly and generate more friction. The influence o f the overall temperature changes in the Non-Dolor and in the Cryodent series was nil. The decisive factor in all these ex
periments was desiccation, and a general decrease in temperature did not significantly alter the ef fect o f a local temperature change or desiccation. There is a definite temperature increase locally where the revolving bur contacts the dentin, but the temperature increase in the pulp is insignifi cant.14’ 19>13’32 Therefore, to look for the burned lesion in the pulp40 rather than in the surface o f the dentin where it is known to occur and to stain the dentinal tubule only in hematoxylin-eosin rather than using an adequate staining method to show burns in the tissue is incorrect.23-25 Whether the irritation dentin is beneficial will be evaluated based on the sequence o f its forma tion which is shown in the experiments. The irri tation dentin forms after the loss o f the odonto blasts. As an initial response to a peripheral in jury, the odontoblasts migrate into the cut den tinal tubules. After three to four weeks, they are no longer seen, but during that time, neutrophilic leukocytes gather at the pulpal ends o f the cut Langeland—Langeland: CUTTING WITH M INIM UM TRAUMA ■ 1003
tubules as evidence that the migrated odonto blasts disintegrate. The dentin, which then has fewer dentinal tubules and is bordered by the re maining odontoblasts, is evidence that the in volved odontoblasts have been destroyed. This destruction indicates that the formation o f irrita tion dentin is a regressive, destructive process and that the end product is scar tissue. A lso, as more tissue is involved, more scar tissue will form, as shown in the crown experiments (Fig 10, 11). The initial destruction o f the odontoblasts caused the formation o f calcified tissue that could not be con trolled arid that finally destroyed the entire pulp. This dentin was pervious and included soft tissue in poor condition. Some investigators37-42 disagree with the ob servation that, when anti-inflammatory agents are applied to freshly cut dentin, the pathologic re sponse to the cutting injury is not reduced. In re gard to the inflammation, our results agree with those o f Fiore-Donno and Baume,43 but their statement that no dentinogenesis occurred after minor amounts o f corticosteroids were applied is not corroborated in our study. We found that irri tation dentin formed at a similar rate whether or not a drug was applied. The theoretical basis for the use o f M osteller’s37 solution, that the prednisolone would pre vent the release o f heparin from the mast cells and that heparin would prevent inflammation, should be considered speculative for at least four reasons: mast cells are not prevalent in the human pulp; after peripheral injury to the pulp, neutro philic leukocytes, not mast cells, are the first to accumulate, as in the soft, connective tissue o f the human body; since neutrophilic leukocytes gather first, the theory has no possible basis; after odonto blast destruction, prednisolone in any form did not prevent the accumulation o f leukocytes. There fore, the histologic findings do not corroborate the theoretical assumption. Although a cavity preparation in most in stances will not immediately, or after short peri ods, cause definite, clinical symptoms, the shortperiod histologic reactions will indicate the future development o f reactions. We must cause as little destruction as possible by our operative proce dures; therefore, as this study indicates, cavity and crown preparation should be made under wet conditions. By use o f a wet preparation, the least possible trauma is caused, and the life-span o f the restorative procedure is lengthened. Dry preparation would add to the destructive process es in the pulp. 1004 ■ JADA, Vol. 76, May 1968
Summary and conclusions Cavity and crown preparations by means o f en gines rotating from 150 to 300,000 rpm free-run ning speed were histologically evaluated in 1,664 experiments. The effect o f various types o f cutting instruments, spray systems, temperatures, and anti-inflammatory agents were evaluated. ■ Histologic conclusions: Dry cavity preparation causes the following immediate reactions: burns in the dentin, the migration o f odontoblasts, the migration o f erythrocytes, and hyperemia. A center hole through the bur would seem to make the spray arrive at the right place and there by keep the bur or diamond clean most effective ly. Despite this theoretically desirable situation, our preliminary results with this technical solution were not entirely successful because reactions oc curred in 26 o f 32 patients. Leakage problems occurred in the experimental handpieces so that we could not be certain whether the drilling took place under optimal technical conditions. There fore, a center hole may still be the optimal solu tion if adequate instruments are manufactured. Reactions after 1 to 30 days were burns in the dentin, the migration o f odontoblasts, the migra tion o f erythrocytes, hyperemia o f circulatory disturbances, and an acute inflammatory reaction in the pulp subjacent to the cavity. Reactions after more than 30 days were bums in the dentin; irregularly formed irritation den tin; lymphocytes, plasma cells, and macrophages in the subjacent pulp tissue if desiccation had been extensive; and,no inflammatory reaction, but evi dence o f a burn in the dentin and a scar tissue in the pulp if desiccation had been less extensive. Wet cavity preparation with a properly directed and working spray caused minor or no reactions. ■ Clinical conclusions: Normal pulp has suffi cient recuperative power to withstand the reac tions caused by dry preparation in a confined re gion. The severity o f the reactions increases with the expansion o f the exposed region. The reac tions to cavity preparation add to those o f subse quent procedures and may be decisive in breaking down the resistance o f the pulp. After a desiccative preparation, the pulp is more vulnerable to harmful influences such as the effect o f active chemicals in many of the materials used to restore a tooth. These chemicals will re place the water in the desiccated, peripheral ends
o f the Cut dentinal tubules. With a wet cavity prep aration, slight or no reactions will occur if harm less materials are used. I f irritant materials are used, the severity o f the reactions is considerably less in the wet preparations than in the dry prep arations.
T his investigation was supported by th e USPHS research grant DE-02006 from the N ational In s titu te o f Dental Re search, N ational In s titu te s o f Health, Bethesda, Md. and by gra n t 50-0970 from Serco Surgical Engineering and Re search Corporation, Victoria, Texas. Kaare Langeland is professor o f oral biology and Leena Langeland is research associate, instructor, departm ent of operative dentistry, Oral H istology Laboratory, School of Dentistry, State U niversity o f New York, Buffalo, NY. *AII a ir rotors w ith the tu rb in e in the head have working speeds o f about 160,000 to 200,000 rpm, regardless of m uch higher free-running speeds. 1. Thoma, K.H. Oral pathology, ed 3. St. Louis, C. V. Mosby Co., 1958. 2. Stones, H.H. Oral and dental diseases, ed 2. B a lti more, W illiam s & W ilkin s Co., 1951. 3. Barker, J.N. Reactions of the p u lp to various fillin g m aterials and c lin ic a l procedures. Aust J Dent 46:226 Dec 1942. 4. Oman, C.R., and Applebaum, E. Ultrasonic cavity preparation. P relim inary report. New York Dent J 20:256 June-July 1954. 5. Friedman, J.; Lite, T., and Solomon, H. Pulp reac tio n s to u ltrasonic tooth preparation. New York Dent J 26: 144 March 1956. 6. Zach, L., and Brown, G.N. Pulpal e ffe ct o f ultrasonic ca vity preparation. Prelim inary report. New York Dent J 22: 9 Jan 1956. 7. Hansen, L.S., and Nielsen, A.G. Comparison of tissue response to rotary and u ltrasonic dental c u ttin g procedures. JADA 52:131 Feb 1956. 8. James, V.E.; Schour, I., and Spence, J.M. Response o f human p u lp to gutta-percha and cavity preparation. JADA 49:639 Dec 1954. 9. Van Huysen, G., and Boyd, D.A. Operative procedures and th e tooth. J Prosth Dent 3:818 Nov 1953. 10. Black, R.B. A pplication and réévaluation o f air abrasive technic. JADA 50:408 A pril 1955. 11. Langeland, K. Tissue changes in the dental pulp. An experim ental h isto lo g ic study. O d o ntT 65:239 Aug 1957. 12. Lisanti, V.F., and Zander, H.A. Thermal in ju ry to norm al dog teeth: in vivo m easurements o f pulp tem pera tu re increases and th e ir e ffe ct on the pulp tissue. J Dent Res 31:548 Aug 1952. 13. Perreault, J.G.; Massler, M., and Schour, I. Reaction o f odontoblasts to m edicam ents placed in cavity prepara tio n s o f rat incisors. JADA 52:533 May 1956. 14. Peyton, F.A. Tem perature rise and c u ttin g e fficie n cy o f rota tin g instrum ents. New York Dent J 18:439 Nov 1952. 15. Ingraham, R., and Tanner, H.M. Adaptation o f modern in stru m e n ts and increased operating speeds to restorative procedures. JADA 47:311 Sept 1953. 16. Hudson, D.C., and Sweeney, W.T. Tem peratures de veloped in ro ta tin g dental c u ttin g instrum ents. JADA 48: 127 Feb 1954. 17. Sullivan, E.J. Cem entation and esthetic problem s in crown and bridge procedures. JADA 51:34 July 1955. 18. Dausch, H. Zur Frage der Feucht-oder Trochenpreparation desvita le n Zahnes. Deutsch Zahnaerztl Z 10:75, 1955. 19. Peyton, F.A., and Vaughn, R.C. Thermal changes de
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