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A Study of Zinc Oxide-Rosin Cements I. Some Variables Which Affect the Hardening Time
A STUDY OF ZINC OXIDE-ROSIN CEMENTS I. SOME VARIABLES WHICH AFFECT THE HARDENING TIME By E. J. M o ln a r ,* M.D., D .D .S ., and E. W. S k in n e r ,! P h .D ., C h icago, 111.
IN C oxide-eugenol cements have been used by dentists for the past sixty years. Most users of these cements have been enthusiastic concern ing their value. However, some object to them because their hardening times are variable, oftentimes in a manner beyond the operator’s control. The odor and taste of eugenol are also objection able factors.
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T H E LIT E R A T U R E AND GENERAL CO N SIDERATION S
These cements mark a natural evolu tion from the zinc-oxychloride cement first announced by Sorel1 in 1855. It was discovered that the latter could not be Used for pulp capping because of the toxicity of the liquid employed, and a search was begun immediately for a less active liquid. Creosote was the first substitute used, by King,2 according to his statements, but probably a similar ma terial was employed independently by some of his contemporaries.3 Later, the creosote was mixed with oil of cloves4 and, in time, oil of cloves was used en tirely.5’ 6’ 7 The first proprietary eugenol cement (pulpol) was introduced in 1894 by Wessler,8 in Sweden. Studies have been carried on by Hentze9 and by Ross10 and others.11’ 12 Read before the Dental Materials Group of the International Association for Dental Research, St. Louis, Mo., March 15, 1941. *Research associate, Northwestern Univer sity Dental School. (Supported in part by George M. Hollenback.) fAssociate professor of physics, Northwest ern University Dental School. Jour. A .D .A ., V o l. 29, M a y 1942
Forster13 attempted to prove that the hardening of the zinc oxide-eugenol ce ment is a physicomechanical process in which the structure of the zinc oxide re mains unchanged. Howe14 demonstrated the efficacy of silver nitrate as an ac celerator for these cements, but it was not until the excellent paper by Wallace and Hansen15 was written that this mat ter of the influence of constituent in gredients of the cement on hardening time was given systematic and scientific attention. This work was later extended by Paffenbarger and Caul16 to include the influence of these ingredients on crushing strength, disintegration and sol ubility. The work of Wallace and Hansen was limited to the investigation of two pow der formulas and one liquid. The pur pose of the present investigation is to study the effect of other ingredients on the hardening time and, to a limited ex tent, on the odor of the liquid. There is little to be found in the litera ture regarding the nature and effect of accelerators of these cements. According to Wallace and Hansen, “Laboratory studies on proprietary and non-proprie tary products . . . indicate that the set ting time of the zinc oxide-rosin-eugenol mixture may be decreased by the ad dition of various metallic salts, such as zinc acetate and such substances as benzoic acid.” The importance of the accelerator aside from control of hardening time is suggested by the data in Table 1. It may be noted that the less the amount of
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accelerator (zinc acetate) used, the less the solubility and the greater the crush ing strength. The reason for this may be that any zinc acetate in the hardened cement dissolves in the water, some acetic acid being produced by ionization. The acetic acid then possibly dissolves the zinc oxide, and the cement disintegrates readily. Such a condition suggests the search for an effective accelerator which is less soluble in the mouth fluids. m a t e r ia l s
The raw materials used for processing the cement were as follows: i. Zinc oxide, C.P.* 2. Hydrogenated rosin. (Pine T a b le
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investigation, a pebble mill was found adequate, although very slow, for the control of particle size and homogeneity. In order to produce numerous samples under as nearly uniform conditions as possible, the following method was used: 1. The rosin was ground in a porcelain mortar and pestle and sieved through a standard 6o-mesh wire screen. 2. The sieved rosin was then mixed with a proportionate amount of zinc oxide in a mortar and pestle for ten minutes. 3. The mixture was placed in a half gallon pebble mill jar with one-half inch porcelain balls the weight of which was
S o l u b i l i t y a n d C o m p r e s s iv e S t r e n g t h o f Z i n c O x i d e - R o s i n - E u g e n o l C e m e n t *
Formula No.
Percentage Zinc Acetate by Weight
II III
0 .7 0.35
Solubility in Seven Days Per Cent 0.1 0.02
Compressive Strength After Seven Days (Lb. / Sq. In.) 2,000 5,500
*From Paffenbarger and Caul’s Table 4 . T a b le
2 .—
H a r d e n i n g T im e W i t h o u t A c c e l e r a t o r s
Powder A B C
Eugenol 2-3 days 2-3 days 5 hours
Hardening Time with Liquid Oil of Bay Guaiacol > 1 day 2-3 days > 1 day > 1 day 3 hours 4 hours
Powder:Liquid Ratio 1 gm./0.15 ml. * 1 gm./0.15 ml. * 1 gm./0.15 ml. *
Approximately 0.15 cc. wood rosin treated with hydrogen under pressure in the presence of a catalyzer. The resin so produced is more stable chemically than rosin, particularly to oxidation and the effect of ultraviolet light.) 3. Accelerator, either reagent or C.P. materials. 4. Eugenol, U.S.P. X I. 5. O il of bay, N.F. V I. 6. Guaiacol, U.S.P. X I . m e t h o d s o f c o m p o u n d in g a n d t e s t in g z in c o x id e
-e u g e n o l c e m e n t s
The difficulty of mixing powders con taining a sticky substance such as rosin is well known in industry. In the present
*Staybelite, Hercules Powder Co.
twice that of the zinc oxide-rosin com pound. The mixture was then ball-milled for thirty minutes at 60 revolutions per minute. 4. The material was scraped from the jar and sieved through an 80-mesh standard sieve. 5. Step 3 was repeated. 6. The mixture was sieved through a 1oo-mesh standard sieve. 7. Step 3 was repeated. 8. The material was sieved through a 200-mesh standard sieve. The liquid generally employed for this type of cement was eugenol, but, in addition, oil of bay and guaiacol were
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used. The oil of bay, containing 50-60 per cent phenol, was found to be effec tive after many experiments with various essential oils. Guaiacol was selected for use on the basis that it is a derivative of creosote. Neither of these liquids exhibit as generally objectionable a taste and odor as do eugenol and creosote. For the actual mixing of the powder with the liquid, the usual cement mixing slab and a stainless steel spatula were employed. The slab temperature was kept nearly constant at the arbitrary temperature of 7 8 °F. (25.5°C .). The powder : liquid ratio used was 1 gm./
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needle impressed for five seconds. Gen erally, if the hardening time was longer than one hour the results were con sidered negative. Xylene and toluene were used to dissolve the cement from the slab and the spatula. SE A R C H FO R AN A C CE LER ATO R
Zinc oxide-rosin-eugenol mixture alone requires two or three days to harden. Substances known as accelerators are added in order to shorten the hardening period. Inasmuch as the present problem seemingly exhibited certain analogies to
T a b l e 3 .— E f f e c t o f D i f f e r e n t A c e t a t e A c c e l e r a t o r s
Accelerator Ag C2H3O2 Na C'2IIgO2 Zn C2H3O2 UO2 C2H3O2 Pb (neutral) C2H3O2 Pb (basic) C2H3O2 Co C2HSO2 Mn C2H3O2 Ferrous C2H3O2 Cu C2H3O2 Ferric (basic) C2H3O2 Mg C2H3O2 Ca C2H3O2 Al (basic) C2H3O2 Ba C2H3O2
Hardening Time Eugenol Oil of Bay 4 minutes 6-7 minutes 5-6 minutes
6 minutes 9 minutes 17-18 minutes 2.5 hours 3.5 hours 3 hours 3 hours 5.5 hours
6 hours 12 hours 12 hours 15 hours
minutes minutes 6-8 minutes 12 minutes 11-12 minutes 13-14 minutes 2 hours 2 hours 2.5 hours 2.5 hours 3.5 hours 4 hours 10 hours 10 hours 14 hours
3 4
Solubility of Accelerator Gm./lOO Ml. 0 . 72- 1.0 2 7 6 .2 3 1 .1 7 .6 9 45.61 V .S .*
s. s. v.s. 7 .2
insol. 3 6 .2 3 7 .4
s. 7 6 .4
*v.s. very soluble; s., soluble. 0.15 ml. unless otherwise stated. The mix was spatulated for one minute, one quarter of the powder being introduced into the liquid every fifteen seconds. An additional five seconds was allowed for gathering the cement together into a mass when a ring was not used. One third of the slab surface was used for mixing. The instrument used for obtaining the hardening time was a standard 1-pound Gillmore needle. The material was con sidered hardened if no impression ob servable with a magnifying glass could be made by the weight of the Gillmore
the drying of paints, some suggestions from this industry as to paint dryers17 were adapted to these cements, but with out success, as shown in Table 2. Powder A was zinc oxide, 70 per cent, and rosin (hydrogenated), 30 per cent by weight. Powder B was a zinc oxide-zinc resinate (70-30 per cent) mixture, and powder G was zinc oxide-manganese resinate, 70-30 per cent. As may be noted, pow der C was a distinct improvement over powder A, but the need of an adequate accelerator for all the combinations is evident. However, manganese dioxide was
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found to be without accelerating effect, as was silver oxide. Boric acid anhyd ride was also without effect. Inasmuch as acetic and benzoic acids were known accelerators, the following related organic acids were tested for ac celerating action, but with negative re sults: tannic, gallic, isobutyric, oxalic, maleic, tartaric, citric and uric acids. Inasmuch as zinc acetate was known to be an excellent accelerator, other ace tates were tried. The salts were selected from each group of the periodic table as far as was practicable, with particular T a b le
Accelerator Zinc chloride Calcium chloride Lithium chloride Stannous chloride Stannic chloride Ferrous chloride Ferric chloride Cupric chloride Cobalt chloride Cuprous chloride Manganese chloride Aluminum chloride Magnesium chloride Nickel chloride Sodium chloride c.p. Sodium chloride (table) Silver chloride Lead chloride Barium chloride
4 .— E
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lead acetates (Group V ) were good. Cobalt acetate (Group V II I) was a poor accelerator, although its salts are su perior to those of lead when used in “drying oils” for the same purpose. Uranyl acetate in the radioactive Group V I was found to be a good accelerator. The salts with cations from Group V I I were unsatisfactory. O f all of the acetate salts tried, silver acetate appears to be the best as far as present knowledge is concerned. In the light of the previously postulated theory, it should decrease the solubility of the
f f e c t o f V a r io u s C h lo r id e A c c e le r a t o r s
Hardening Time Minutes Oil of Bay
Guaiacol
Solubility of Accelerator Gm./1 0 0 Ml.
>1 >1 >1 1
>1 >1 >1 2
>1 >1 >1 1
4 3 4
5 4 4
3
s.
2
6
8 6
6
6 4 .4 7 4 .4 4 3 .5 1 9 0 .7 1 .5 2 6 2 .2 6 9 .9 3 5 .3 2 5 4 .0 3 5 .7
7 13 7 13 28 30 53 80
10 hours 16 hours 11 hours
5 7 60 5 13 26 26 28 36
16
12 11 15 28 44 41
hours 12 hours 9 hours
5.5
attention to low solubility. Table 3 shows the results, arranged in increasing hardening time. In all cases, a zinc oxide-rosin powder (70-30) was used with an accelerator, 0.05 per cent by weight, incorporated in the powder. As may be noted, other elements than zinc in Group II of the periodic table (magnesium, calcium, barium) were not effective as accelerators when used as acetates. Sodium and silver acetates (Group I) are both good accelerators, but copper acetate is poor. In Group III, aluminum acetate was poor, but the
8 hours hours 8 hours
13
4 3 2 .0 5 9 .5 4 5 .4 8 3 .9
0.0 000 89 0 .6 7 3 3 1 .0
hardened cement markedly. This pos sibility, together with a possible germi cidal effect, is being studied at the pres ent time. CH LO R ID E AND N ITRATE A C C E L E R A T O R S
It was thought best to study salts with anions other than acetate, such as the chlorides and nitrates. The data for the metallic chlorides are shown in Table 4. Table salt, even in small concentra tion, is an accelerator. Saturation of a metallic compound decreases its acceler
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ating properties, because the increased valence value of metals renders them less reactive; i.e., ferrous chloride (FeCl2, ferric chloride (FeCl3), stannous chlor ide (SnCl2.2H2o), stannic chloride (SnCl4). The tin chlorides were found more effective than iron chlorides. Both are reducing agents. With cuprous chloride, which has a low solubility, the T a b le
A ccelerator
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The nitrates (Table 5) selected were found to be, as a class, the most effective accelerators. However, before advocat ing their use, the other properties of the hardened cement must be investigated thoroughly. These salts are very soluble and even chemically unstable. With the exception of silver nitrate, they are also either deliquescent or hygroscopic.
E f f e c t o f D iffe r e n t N it r a t e A c c e le r a to r s
Hardening Tim e M inutes Oil o f B ay
Eugenol
Zinc nitrate Lithium nitrate Aluminum nitrate Bism uth nitrate Silver nitrate Cobaltous nitrate Ferric nitrate Nickelous nitrate M agnesium nitrate Sodium nitrate Barium nitrate Lead nitrate
D
> 1 > 1 > 1 3 3 3 7 70 75 3 hours 3 hours 4 | hours
Guaiacol
> 1 >1 >1 3 5 4 5 50 70
>1 > 1 > 1 2 2 .5 3 3 34 90
2 § hours 1 $ hours 2 hours
I f hours 2 hours 2 hours
Solubility o f Accelerator G m . / 1 0 0 M l.
3 2 7 .3 5 2 .2 6 3 .7 d.*
12 2 .0 13 3 .8 s.
2 3 8 .5 7 3 .Ô 8 .7 3 7 .6 5
*d., decompose T a b le
6 .— H a rd e n in g Tim e w it h P u r e Z in c O x id e P o w d e r a s A f f e c t e d bv
S e v e r a l A ccelerators
Accelerator* Zinc oxide (alone) Silver nitrate Zinc acetate Silver acetate U ranyl acetate Cuprous chloride
Eugenol
3 13 16 20 28 90
days minutes minutes minutes minutes minutes
Liquid Oil o f B ay
24 30 35 60 40 150
hours minutes minutes minutes minutes minutes
Guaiacol
24 8 16 22 28 120
hours minutes minutes minutes minutes minutes
*Used in 0 . 5 per cent concentrations with pure zinc oxide powder; arranged in order o f decreasing accelerating action. m ix t u r e h a r d e n s w i t h e u g e n o l i n th ir t e e n
E F F E C T O F ROSIN
minutes; with guaiacol, in one hour in 0.5 per cent concentration. In 1 per cent concentration, the cement hardens with eugenol in seven minutes and turns green. With guaiacol, fifty minutes is required and the cement remains white. Repeated tests yielded the same results. The hard ening time, using the three liquids, varies only slightly in the presence of satis factory accelerators other than cuprous chloride.
Inasmuch as zinc oxide-eugenol ce ments are occasionally used without rosin,18 the action of a few of the ac celerators was tested in the absence of rosin (Table 6). It was found necessary to reduce the powder ¡liquid ratio to 0.75 gm./o.i5 ml. (cc.) in order to main tain approximately the same consistency as before. It is evident that acceleration is ob tained, but in the concentrations used,
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the accelerators are not so effective as before. Apparently rosin is an active in gredient of some nature in the powder. It further appears to improve the work ing properties and to reduce the fri ability of the hardened cement. It m ay be noted that the zinc oxideoil of bay cement hardened more rapidly than did the zinc oxide-eugenol cement, but the zinc oxide-rosin-oil of bay ce ment hardened even more rapidly (Table 2). T h e data suggest that rosin is essen tial to a rapid hardening rate as well as the accelerator.
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heating to 2 75 °F . ( i 3 5 ° C .) , and no hardening occurred after the mixture was heated to 400°F. (2 0 4 .4 °C .). N a tural resins with low acid numbers such as clear amber, gum kauri, a special resin* and synthetic resins such as “ flexoresin” (no acid number) and poly methyl methacrylate were substituted for the original resin in the zinc oxide pow der, but without success. E F F E C T OF LIQ UID CO M PO SITIO N
As might be expected, the composition of the liquid affccts the hardening time
T a b l e 7 .— E f f e c t s o n H a r d e n i n g T i m e o f S u b s t i t u t i o n s i n t h e L i q u i d P o r t i o n o f Z in c O x id e -R o s in C e m e n ts
Accelerator* F e(N 0 3)s F e C l, CuCls M n C l2 F e C l, AICI3 A g(C 2H 30 2) C0CI2 M gC l2 Z n (C 2H 30 2)ä U 0 2(C 2H 3 0 2)2 Cu2C12 N iC l2 N aC l N i(N 0 3)2
Eugenol
EugenolPhenol
Liquid EugenolFurfural Guaiacol
2 2
1
3
2
1.5
6 6
4 5
4
>1 1
7
5
8
15
13 19 30 60 90
8 12 11
20 120
2 '
GuaiacolFurfural
H
3 3 3
3
2 2 2
5
6
4 7
4 3
6 6
4
5 3 45
2
11 ¡2
35 75
GuaiacolPhenol
16 35 60
60 17
10
*0 .5 p e r c e n t c o n c e n t r a t io n in a z i n c o x id e -r o s in ( 7 0 -3 0 p e r c e n t ) m i x t u r e .
Bare19 states that a direct proportional relationship exists between the acid num ber of the rosin and its solubility. Fur thermore, it is a well-.known fact that the higher the acid number of the rosin, the greater its chemical reactivity. A s suming that such relationships might obtain under the conditions of these ex periments, the acid number of the rosin was reduced by heating the cement pow der to 2750 F. ( i3 5 ° C .) , which is just below the fusing point of the rosin, and 400° F. (20 4.4°C .). Both procedures definitely increased the hardening time from four minutes for the rosin mixture before heating to eleven minutes after
of the cement (Tables i-6 ). T w o pos sible causes for this have been investi gated : the effect of ( i ) the phenol con tent, and (2) the solubility of the rosin in the liquid. O ne gram o f phenol was added to the liquid to investigate the first-mentioned possibility, and 1 ml. of furfural, a rosin solvent which is not a phenol, was added to test the second idea. T en milliliters of liquid were used in all cases. T h e data are given in Table 7. A ny difference in results between those in this table and previous tables m ay probably *Staybelite Ester No. 10, Hercules Powder Co.
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be attributed to slight differences in humidity and room temperature, since all other variables were held identical as far as possible except as mentioned in the previous paragraph. According to the data in Table 7, the phenol enhances the action of the ac celerator, but so does the furfural. In fact, the furfural is somewhat more effec tive than the phenol, but it is not known whether this is due to the more rapid solvent action of the furfural on the rosin, to a difference in concentration between the phenol and furfural, or to a chemical reaction which is more rapid with the unsaturated furfural. Two facts are made clear by these ex periments : (1) rosin is necessary to a short hardening time of the cement when an accelerator is used (Table 6 and 7) and (2) phenolic groups are probably only one of many organic radicals which aid in the chemical reaction during the hardening of these cements. It is not known how many organic radicals may be effective in this connection, but the foregoing experiments appear to indicate that the reaction is by no means simple. Essential oils containing phenol de rivatives (anethol, safrol, thymol, carvacrol) were tried, but without success. SU M M A R Y AND CO N CLU SIO N S
Variables which affect the hardening time of zinc oxide-rosin-eugenol cements were studied: composition of the pow der, composition of the liquid and the use of various accelerators. It was shown th at: 1. An accelerator is necessary inas much as the various liquids used failed to give a sufficiently short hardening time. 2. O il of bay and guaiacol can be suc cessfully substituted for eugenol, with a different taste and odor resulting. Other essential oils containing a phenol deriva tive were tried without success. 3. Various metallic salts were found to be effective accelerators, such as acetates,
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chlorides and nitrates. It was suggested that salts of low solubility would reduce the solubility of the set cement. The ni trates are probably contraindicated as accelerators for this reason, and also be cause many of them are chemically un stable. Probably silver acetate and cu prous chloride come the closest to being ideal accelerators. 4. Resins, natural or synthetic, with low acid numbers cannot be substituted for natural or ordinary hydrogenated resin. 5. Rosin is necessary to a short hard ening time. 6. The hardening reactions of these cements are by no means simple. B IB LIO G R A PH Y
1. S o r e l : Proce’de’ pour la formation d’un ciment tres solide par l’action d’un chlorure sur l’oxyde de zinc. Compt. Rend. Acad. Sc., 41:784-785, 1855. 2. K i n g , J. S . : Treatment of Exposed Pulps. D. Cosmos, 14:193-194, April 1872. 3. T a f t , J.: Practical Treatise of Opera tive Dentistry. Philadelphia: Lindsay & Blakiston, 1877, p. 301. 4. C h i s h o l m , E. S.: D. Register, 27:517, December 1873. 5. F l a g g , J. F . : Dental Pathology and Therapeutics. D. Cosmos, 27:465, September l8 75 6 . S m i t h , D. D.: Combination and Thera peutic Action of Some Filling Material. D. Cosmos, 20:525, October 1878. 7. T o m e s , J o h n , and T o m e s , C h a r l e s : System of Dental Surgery. Ed. 3. London: John Churchill, 1887, p. 414. 8. W e s s l e r , J.: Pulpol, ein neues medicamentoses Cement. Deutsche Monatschr. /. Zahnheilk., 12:478-484, 1894. 9. H e n t z e : Die Behandlung infizierter Zahnpulpen. Deutsche Monatschr. f. Zahnheilk., 25:415-425, 1907. 10. Ross, R. A.: Zinc Oxide Impression Pastes. J.A.D.A., 21:2029, November 1934. 11. Tijdschr. v. Tandheilk., 35:412-416, 840-842, 1928; 36:38-41, 197, 1929. 12. W e y e r h a u s e r , K a r l : Wieheit ist die Expansion des Zinkoxyd-Eugenols imstande, die Kontraktion der Albrechtschen Wurzelfullung auszugleichen. Marburg, 1922. 13. F o r s t e r , E.: II cemento prorvisorio all’ ossido di zinco ed il carattere fisicomeccanico della sua presa. Stomatologia, 27:217221, March 1929.
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orney,
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o r n ey and
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14. H o w e , P. R .: Conservation of Dental Pulp. D. Items Int., 41:933-941, December
1919-
15. W a l l a c e , D. A., and H a n s e n , H . L . : Zinc Oxide-Eugenol Cements. J.A.D.A., 2 6 : i 536- i 54° ) September 1939. 16. P a f f e n b a r g e r , G. C . , and C a u l , H . J.: Dental Cements. Proc. D. Centenary Celebra tion, March 1940, pp. 232-240.
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17. F r i t z , F . : Die Trockenstoffe und ihre Verwendung. Chem. Zeitung, 60:921-924, 1936. 18. G r a h a m , F. W., J r . : Silver Nitrate and Zinc Oxide in Treatment of Children’s Teeth. J.A.D.A., 28:124-128, January 1941. 19. B a r e , W. K .: Rosin as a Linoleum Component. Symposium on rosin, 1930. 311 East Chicago Avenue.
CREATION OF A MANDIBULAR RIDGE BY DEEPENING THE LABIAL SULCUS AND LINING IT WITH A SKIN GRAFT By H
aro ld
S. G o r n e y ,
D .M .D .; A r t h u r J. G o r n e y , M.D., and Ph.D., M.D., Boston, Mass.
Sam u el F omon,
HE dentist is frequently confronted with the problem of making a full lower denture for a patient whose alveolar process has been resorbed to such an extent that the use of this part of the mouth as a retentive and stabiliz ing factor is impractical. In these cases, the usual practice of using the mylohyoid ridge and sublingual fossa region for retention seldom proves satisfactory. At best, this part of the mouth provides in sufficient anchorage, allowing the den ture to become movable. Moreover, any small portion of the alveolar process which remains and may assist in retain ing the denture is likely to be resorbed, and this necessitates frequent trimming of the denture, reducing the already poor retentive ability of the part. The question as to what to do to in crease the comfort and efficiency of a denture under these circumstances arises. It is generally agreed that it is best to deal with the problem by recourse to a common surgical procedure, the creation of. a ridge by the formation of a prealveolar sulcus. The mandible is thus enabled to furnish the desired support. On this principle, many surgical pro cedures have been suggested. A com
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mon procedure is to incise the labial fold along the alveolar margin, deepen the cavity to the desired level and attempt to prevent union of the resultant raw surfaces by interposing a piece of rubber dam and suturing it in place. Kazanjian1 incises the mucosa parallel to and at some distance (1.5 cm.) from the alveo lar ridge, undermines the tissues medially and pushes the flap thus formed down against the periosteum of the mandible and sutures it in place. Sometimes, the radio knife is resorted to, on the grounds that its use reduces the amount of cica trization to a minimum and thus prevents to some extent a reobliteration of the newly formed sulcus when healing takes place. The final results of these and other methods have been only partially satisfactory and, in some instances, totally unsuccessful, in that little or no pro vision is made against subsequent re union of the raw surfaces by the inevi table formation of scar tissue. That this complication has been satisfactorily overcome by a method sug gested by one of us (S.F.),2 featuring the use of an inlay skin graft, was evidenced by the gratifying results of the procedure in the case here described.
IN C oxide-eugenol cements have been used by dentists for the past sixty years. Most users of these cements have been enthusiastic concern ing their value. However, some object to them because their hardening times are variable, oftentimes in a manner beyond the operator’s control. The odor and taste of eugenol are also objection able factors.
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T H E LIT E R A T U R E AND GENERAL CO N SIDERATION S
These cements mark a natural evolu tion from the zinc-oxychloride cement first announced by Sorel1 in 1855. It was discovered that the latter could not be Used for pulp capping because of the toxicity of the liquid employed, and a search was begun immediately for a less active liquid. Creosote was the first substitute used, by King,2 according to his statements, but probably a similar ma terial was employed independently by some of his contemporaries.3 Later, the creosote was mixed with oil of cloves4 and, in time, oil of cloves was used en tirely.5’ 6’ 7 The first proprietary eugenol cement (pulpol) was introduced in 1894 by Wessler,8 in Sweden. Studies have been carried on by Hentze9 and by Ross10 and others.11’ 12 Read before the Dental Materials Group of the International Association for Dental Research, St. Louis, Mo., March 15, 1941. *Research associate, Northwestern Univer sity Dental School. (Supported in part by George M. Hollenback.) fAssociate professor of physics, Northwest ern University Dental School. Jour. A .D .A ., V o l. 29, M a y 1942
Forster13 attempted to prove that the hardening of the zinc oxide-eugenol ce ment is a physicomechanical process in which the structure of the zinc oxide re mains unchanged. Howe14 demonstrated the efficacy of silver nitrate as an ac celerator for these cements, but it was not until the excellent paper by Wallace and Hansen15 was written that this mat ter of the influence of constituent in gredients of the cement on hardening time was given systematic and scientific attention. This work was later extended by Paffenbarger and Caul16 to include the influence of these ingredients on crushing strength, disintegration and sol ubility. The work of Wallace and Hansen was limited to the investigation of two pow der formulas and one liquid. The pur pose of the present investigation is to study the effect of other ingredients on the hardening time and, to a limited ex tent, on the odor of the liquid. There is little to be found in the litera ture regarding the nature and effect of accelerators of these cements. According to Wallace and Hansen, “Laboratory studies on proprietary and non-proprie tary products . . . indicate that the set ting time of the zinc oxide-rosin-eugenol mixture may be decreased by the ad dition of various metallic salts, such as zinc acetate and such substances as benzoic acid.” The importance of the accelerator aside from control of hardening time is suggested by the data in Table 1. It may be noted that the less the amount of
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accelerator (zinc acetate) used, the less the solubility and the greater the crush ing strength. The reason for this may be that any zinc acetate in the hardened cement dissolves in the water, some acetic acid being produced by ionization. The acetic acid then possibly dissolves the zinc oxide, and the cement disintegrates readily. Such a condition suggests the search for an effective accelerator which is less soluble in the mouth fluids. m a t e r ia l s
The raw materials used for processing the cement were as follows: i. Zinc oxide, C.P.* 2. Hydrogenated rosin. (Pine T a b le
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investigation, a pebble mill was found adequate, although very slow, for the control of particle size and homogeneity. In order to produce numerous samples under as nearly uniform conditions as possible, the following method was used: 1. The rosin was ground in a porcelain mortar and pestle and sieved through a standard 6o-mesh wire screen. 2. The sieved rosin was then mixed with a proportionate amount of zinc oxide in a mortar and pestle for ten minutes. 3. The mixture was placed in a half gallon pebble mill jar with one-half inch porcelain balls the weight of which was
S o l u b i l i t y a n d C o m p r e s s iv e S t r e n g t h o f Z i n c O x i d e - R o s i n - E u g e n o l C e m e n t *
Formula No.
Percentage Zinc Acetate by Weight
II III
0 .7 0.35
Solubility in Seven Days Per Cent 0.1 0.02
Compressive Strength After Seven Days (Lb. / Sq. In.) 2,000 5,500
*From Paffenbarger and Caul’s Table 4 . T a b le
2 .—
H a r d e n i n g T im e W i t h o u t A c c e l e r a t o r s
Powder A B C
Eugenol 2-3 days 2-3 days 5 hours
Hardening Time with Liquid Oil of Bay Guaiacol > 1 day 2-3 days > 1 day > 1 day 3 hours 4 hours
Powder:Liquid Ratio 1 gm./0.15 ml. * 1 gm./0.15 ml. * 1 gm./0.15 ml. *
Approximately 0.15 cc. wood rosin treated with hydrogen under pressure in the presence of a catalyzer. The resin so produced is more stable chemically than rosin, particularly to oxidation and the effect of ultraviolet light.) 3. Accelerator, either reagent or C.P. materials. 4. Eugenol, U.S.P. X I. 5. O il of bay, N.F. V I. 6. Guaiacol, U.S.P. X I . m e t h o d s o f c o m p o u n d in g a n d t e s t in g z in c o x id e
-e u g e n o l c e m e n t s
The difficulty of mixing powders con taining a sticky substance such as rosin is well known in industry. In the present
*Staybelite, Hercules Powder Co.
twice that of the zinc oxide-rosin com pound. The mixture was then ball-milled for thirty minutes at 60 revolutions per minute. 4. The material was scraped from the jar and sieved through an 80-mesh standard sieve. 5. Step 3 was repeated. 6. The mixture was sieved through a 1oo-mesh standard sieve. 7. Step 3 was repeated. 8. The material was sieved through a 200-mesh standard sieve. The liquid generally employed for this type of cement was eugenol, but, in addition, oil of bay and guaiacol were
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used. The oil of bay, containing 50-60 per cent phenol, was found to be effec tive after many experiments with various essential oils. Guaiacol was selected for use on the basis that it is a derivative of creosote. Neither of these liquids exhibit as generally objectionable a taste and odor as do eugenol and creosote. For the actual mixing of the powder with the liquid, the usual cement mixing slab and a stainless steel spatula were employed. The slab temperature was kept nearly constant at the arbitrary temperature of 7 8 °F. (25.5°C .). The powder : liquid ratio used was 1 gm./
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needle impressed for five seconds. Gen erally, if the hardening time was longer than one hour the results were con sidered negative. Xylene and toluene were used to dissolve the cement from the slab and the spatula. SE A R C H FO R AN A C CE LER ATO R
Zinc oxide-rosin-eugenol mixture alone requires two or three days to harden. Substances known as accelerators are added in order to shorten the hardening period. Inasmuch as the present problem seemingly exhibited certain analogies to
T a b l e 3 .— E f f e c t o f D i f f e r e n t A c e t a t e A c c e l e r a t o r s
Accelerator Ag C2H3O2 Na C'2IIgO2 Zn C2H3O2 UO2 C2H3O2 Pb (neutral) C2H3O2 Pb (basic) C2H3O2 Co C2HSO2 Mn C2H3O2 Ferrous C2H3O2 Cu C2H3O2 Ferric (basic) C2H3O2 Mg C2H3O2 Ca C2H3O2 Al (basic) C2H3O2 Ba C2H3O2
Hardening Time Eugenol Oil of Bay 4 minutes 6-7 minutes 5-6 minutes
6 minutes 9 minutes 17-18 minutes 2.5 hours 3.5 hours 3 hours 3 hours 5.5 hours
6 hours 12 hours 12 hours 15 hours
minutes minutes 6-8 minutes 12 minutes 11-12 minutes 13-14 minutes 2 hours 2 hours 2.5 hours 2.5 hours 3.5 hours 4 hours 10 hours 10 hours 14 hours
3 4
Solubility of Accelerator Gm./lOO Ml. 0 . 72- 1.0 2 7 6 .2 3 1 .1 7 .6 9 45.61 V .S .*
s. s. v.s. 7 .2
insol. 3 6 .2 3 7 .4
s. 7 6 .4
*v.s. very soluble; s., soluble. 0.15 ml. unless otherwise stated. The mix was spatulated for one minute, one quarter of the powder being introduced into the liquid every fifteen seconds. An additional five seconds was allowed for gathering the cement together into a mass when a ring was not used. One third of the slab surface was used for mixing. The instrument used for obtaining the hardening time was a standard 1-pound Gillmore needle. The material was con sidered hardened if no impression ob servable with a magnifying glass could be made by the weight of the Gillmore
the drying of paints, some suggestions from this industry as to paint dryers17 were adapted to these cements, but with out success, as shown in Table 2. Powder A was zinc oxide, 70 per cent, and rosin (hydrogenated), 30 per cent by weight. Powder B was a zinc oxide-zinc resinate (70-30 per cent) mixture, and powder G was zinc oxide-manganese resinate, 70-30 per cent. As may be noted, pow der C was a distinct improvement over powder A, but the need of an adequate accelerator for all the combinations is evident. However, manganese dioxide was
M
o ln ar and
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found to be without accelerating effect, as was silver oxide. Boric acid anhyd ride was also without effect. Inasmuch as acetic and benzoic acids were known accelerators, the following related organic acids were tested for ac celerating action, but with negative re sults: tannic, gallic, isobutyric, oxalic, maleic, tartaric, citric and uric acids. Inasmuch as zinc acetate was known to be an excellent accelerator, other ace tates were tried. The salts were selected from each group of the periodic table as far as was practicable, with particular T a b le
Accelerator Zinc chloride Calcium chloride Lithium chloride Stannous chloride Stannic chloride Ferrous chloride Ferric chloride Cupric chloride Cobalt chloride Cuprous chloride Manganese chloride Aluminum chloride Magnesium chloride Nickel chloride Sodium chloride c.p. Sodium chloride (table) Silver chloride Lead chloride Barium chloride
4 .— E
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lead acetates (Group V ) were good. Cobalt acetate (Group V II I) was a poor accelerator, although its salts are su perior to those of lead when used in “drying oils” for the same purpose. Uranyl acetate in the radioactive Group V I was found to be a good accelerator. The salts with cations from Group V I I were unsatisfactory. O f all of the acetate salts tried, silver acetate appears to be the best as far as present knowledge is concerned. In the light of the previously postulated theory, it should decrease the solubility of the
f f e c t o f V a r io u s C h lo r id e A c c e le r a t o r s
Hardening Time Minutes Oil of Bay
Guaiacol
Solubility of Accelerator Gm./1 0 0 Ml.
>1 >1 >1 1
>1 >1 >1 2
>1 >1 >1 1
4 3 4
5 4 4
3
s.
2
6
8 6
6
6 4 .4 7 4 .4 4 3 .5 1 9 0 .7 1 .5 2 6 2 .2 6 9 .9 3 5 .3 2 5 4 .0 3 5 .7
7 13 7 13 28 30 53 80
10 hours 16 hours 11 hours
5 7 60 5 13 26 26 28 36
16
12 11 15 28 44 41
hours 12 hours 9 hours
5.5
attention to low solubility. Table 3 shows the results, arranged in increasing hardening time. In all cases, a zinc oxide-rosin powder (70-30) was used with an accelerator, 0.05 per cent by weight, incorporated in the powder. As may be noted, other elements than zinc in Group II of the periodic table (magnesium, calcium, barium) were not effective as accelerators when used as acetates. Sodium and silver acetates (Group I) are both good accelerators, but copper acetate is poor. In Group III, aluminum acetate was poor, but the
8 hours hours 8 hours
13
4 3 2 .0 5 9 .5 4 5 .4 8 3 .9
0.0 000 89 0 .6 7 3 3 1 .0
hardened cement markedly. This pos sibility, together with a possible germi cidal effect, is being studied at the pres ent time. CH LO R ID E AND N ITRATE A C C E L E R A T O R S
It was thought best to study salts with anions other than acetate, such as the chlorides and nitrates. The data for the metallic chlorides are shown in Table 4. Table salt, even in small concentra tion, is an accelerator. Saturation of a metallic compound decreases its acceler
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ating properties, because the increased valence value of metals renders them less reactive; i.e., ferrous chloride (FeCl2, ferric chloride (FeCl3), stannous chlor ide (SnCl2.2H2o), stannic chloride (SnCl4). The tin chlorides were found more effective than iron chlorides. Both are reducing agents. With cuprous chloride, which has a low solubility, the T a b le
A ccelerator
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The nitrates (Table 5) selected were found to be, as a class, the most effective accelerators. However, before advocat ing their use, the other properties of the hardened cement must be investigated thoroughly. These salts are very soluble and even chemically unstable. With the exception of silver nitrate, they are also either deliquescent or hygroscopic.
E f f e c t o f D iffe r e n t N it r a t e A c c e le r a to r s
Hardening Tim e M inutes Oil o f B ay
Eugenol
Zinc nitrate Lithium nitrate Aluminum nitrate Bism uth nitrate Silver nitrate Cobaltous nitrate Ferric nitrate Nickelous nitrate M agnesium nitrate Sodium nitrate Barium nitrate Lead nitrate
D
> 1 > 1 > 1 3 3 3 7 70 75 3 hours 3 hours 4 | hours
Guaiacol
> 1 >1 >1 3 5 4 5 50 70
>1 > 1 > 1 2 2 .5 3 3 34 90
2 § hours 1 $ hours 2 hours
I f hours 2 hours 2 hours
Solubility o f Accelerator G m . / 1 0 0 M l.
3 2 7 .3 5 2 .2 6 3 .7 d.*
12 2 .0 13 3 .8 s.
2 3 8 .5 7 3 .Ô 8 .7 3 7 .6 5
*d., decompose T a b le
6 .— H a rd e n in g Tim e w it h P u r e Z in c O x id e P o w d e r a s A f f e c t e d bv
S e v e r a l A ccelerators
Accelerator* Zinc oxide (alone) Silver nitrate Zinc acetate Silver acetate U ranyl acetate Cuprous chloride
Eugenol
3 13 16 20 28 90
days minutes minutes minutes minutes minutes
Liquid Oil o f B ay
24 30 35 60 40 150
hours minutes minutes minutes minutes minutes
Guaiacol
24 8 16 22 28 120
hours minutes minutes minutes minutes minutes
*Used in 0 . 5 per cent concentrations with pure zinc oxide powder; arranged in order o f decreasing accelerating action. m ix t u r e h a r d e n s w i t h e u g e n o l i n th ir t e e n
E F F E C T O F ROSIN
minutes; with guaiacol, in one hour in 0.5 per cent concentration. In 1 per cent concentration, the cement hardens with eugenol in seven minutes and turns green. With guaiacol, fifty minutes is required and the cement remains white. Repeated tests yielded the same results. The hard ening time, using the three liquids, varies only slightly in the presence of satis factory accelerators other than cuprous chloride.
Inasmuch as zinc oxide-eugenol ce ments are occasionally used without rosin,18 the action of a few of the ac celerators was tested in the absence of rosin (Table 6). It was found necessary to reduce the powder ¡liquid ratio to 0.75 gm./o.i5 ml. (cc.) in order to main tain approximately the same consistency as before. It is evident that acceleration is ob tained, but in the concentrations used,
M
oln ar and
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the accelerators are not so effective as before. Apparently rosin is an active in gredient of some nature in the powder. It further appears to improve the work ing properties and to reduce the fri ability of the hardened cement. It m ay be noted that the zinc oxideoil of bay cement hardened more rapidly than did the zinc oxide-eugenol cement, but the zinc oxide-rosin-oil of bay ce ment hardened even more rapidly (Table 2). T h e data suggest that rosin is essen tial to a rapid hardening rate as well as the accelerator.
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heating to 2 75 °F . ( i 3 5 ° C .) , and no hardening occurred after the mixture was heated to 400°F. (2 0 4 .4 °C .). N a tural resins with low acid numbers such as clear amber, gum kauri, a special resin* and synthetic resins such as “ flexoresin” (no acid number) and poly methyl methacrylate were substituted for the original resin in the zinc oxide pow der, but without success. E F F E C T OF LIQ UID CO M PO SITIO N
As might be expected, the composition of the liquid affccts the hardening time
T a b l e 7 .— E f f e c t s o n H a r d e n i n g T i m e o f S u b s t i t u t i o n s i n t h e L i q u i d P o r t i o n o f Z in c O x id e -R o s in C e m e n ts
Accelerator* F e(N 0 3)s F e C l, CuCls M n C l2 F e C l, AICI3 A g(C 2H 30 2) C0CI2 M gC l2 Z n (C 2H 30 2)ä U 0 2(C 2H 3 0 2)2 Cu2C12 N iC l2 N aC l N i(N 0 3)2
Eugenol
EugenolPhenol
Liquid EugenolFurfural Guaiacol
2 2
1
3
2
1.5
6 6
4 5
4
>1 1
7
5
8
15
13 19 30 60 90
8 12 11
20 120
2 '
GuaiacolFurfural
H
3 3 3
3
2 2 2
5
6
4 7
4 3
6 6
4
5 3 45
2
11 ¡2
35 75
GuaiacolPhenol
16 35 60
60 17
10
*0 .5 p e r c e n t c o n c e n t r a t io n in a z i n c o x id e -r o s in ( 7 0 -3 0 p e r c e n t ) m i x t u r e .
Bare19 states that a direct proportional relationship exists between the acid num ber of the rosin and its solubility. Fur thermore, it is a well-.known fact that the higher the acid number of the rosin, the greater its chemical reactivity. A s suming that such relationships might obtain under the conditions of these ex periments, the acid number of the rosin was reduced by heating the cement pow der to 2750 F. ( i3 5 ° C .) , which is just below the fusing point of the rosin, and 400° F. (20 4.4°C .). Both procedures definitely increased the hardening time from four minutes for the rosin mixture before heating to eleven minutes after
of the cement (Tables i-6 ). T w o pos sible causes for this have been investi gated : the effect of ( i ) the phenol con tent, and (2) the solubility of the rosin in the liquid. O ne gram o f phenol was added to the liquid to investigate the first-mentioned possibility, and 1 ml. of furfural, a rosin solvent which is not a phenol, was added to test the second idea. T en milliliters of liquid were used in all cases. T h e data are given in Table 7. A ny difference in results between those in this table and previous tables m ay probably *Staybelite Ester No. 10, Hercules Powder Co.
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be attributed to slight differences in humidity and room temperature, since all other variables were held identical as far as possible except as mentioned in the previous paragraph. According to the data in Table 7, the phenol enhances the action of the ac celerator, but so does the furfural. In fact, the furfural is somewhat more effec tive than the phenol, but it is not known whether this is due to the more rapid solvent action of the furfural on the rosin, to a difference in concentration between the phenol and furfural, or to a chemical reaction which is more rapid with the unsaturated furfural. Two facts are made clear by these ex periments : (1) rosin is necessary to a short hardening time of the cement when an accelerator is used (Table 6 and 7) and (2) phenolic groups are probably only one of many organic radicals which aid in the chemical reaction during the hardening of these cements. It is not known how many organic radicals may be effective in this connection, but the foregoing experiments appear to indicate that the reaction is by no means simple. Essential oils containing phenol de rivatives (anethol, safrol, thymol, carvacrol) were tried, but without success. SU M M A R Y AND CO N CLU SIO N S
Variables which affect the hardening time of zinc oxide-rosin-eugenol cements were studied: composition of the pow der, composition of the liquid and the use of various accelerators. It was shown th at: 1. An accelerator is necessary inas much as the various liquids used failed to give a sufficiently short hardening time. 2. O il of bay and guaiacol can be suc cessfully substituted for eugenol, with a different taste and odor resulting. Other essential oils containing a phenol deriva tive were tried without success. 3. Various metallic salts were found to be effective accelerators, such as acetates,
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chlorides and nitrates. It was suggested that salts of low solubility would reduce the solubility of the set cement. The ni trates are probably contraindicated as accelerators for this reason, and also be cause many of them are chemically un stable. Probably silver acetate and cu prous chloride come the closest to being ideal accelerators. 4. Resins, natural or synthetic, with low acid numbers cannot be substituted for natural or ordinary hydrogenated resin. 5. Rosin is necessary to a short hard ening time. 6. The hardening reactions of these cements are by no means simple. B IB LIO G R A PH Y
1. S o r e l : Proce’de’ pour la formation d’un ciment tres solide par l’action d’un chlorure sur l’oxyde de zinc. Compt. Rend. Acad. Sc., 41:784-785, 1855. 2. K i n g , J. S . : Treatment of Exposed Pulps. D. Cosmos, 14:193-194, April 1872. 3. T a f t , J.: Practical Treatise of Opera tive Dentistry. Philadelphia: Lindsay & Blakiston, 1877, p. 301. 4. C h i s h o l m , E. S.: D. Register, 27:517, December 1873. 5. F l a g g , J. F . : Dental Pathology and Therapeutics. D. Cosmos, 27:465, September l8 75 6 . S m i t h , D. D.: Combination and Thera peutic Action of Some Filling Material. D. Cosmos, 20:525, October 1878. 7. T o m e s , J o h n , and T o m e s , C h a r l e s : System of Dental Surgery. Ed. 3. London: John Churchill, 1887, p. 414. 8. W e s s l e r , J.: Pulpol, ein neues medicamentoses Cement. Deutsche Monatschr. /. Zahnheilk., 12:478-484, 1894. 9. H e n t z e : Die Behandlung infizierter Zahnpulpen. Deutsche Monatschr. f. Zahnheilk., 25:415-425, 1907. 10. Ross, R. A.: Zinc Oxide Impression Pastes. J.A.D.A., 21:2029, November 1934. 11. Tijdschr. v. Tandheilk., 35:412-416, 840-842, 1928; 36:38-41, 197, 1929. 12. W e y e r h a u s e r , K a r l : Wieheit ist die Expansion des Zinkoxyd-Eugenols imstande, die Kontraktion der Albrechtschen Wurzelfullung auszugleichen. Marburg, 1922. 13. F o r s t e r , E.: II cemento prorvisorio all’ ossido di zinco ed il carattere fisicomeccanico della sua presa. Stomatologia, 27:217221, March 1929.
G
orney,
G
o r n ey and
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om on—
14. H o w e , P. R .: Conservation of Dental Pulp. D. Items Int., 41:933-941, December
1919-
15. W a l l a c e , D. A., and H a n s e n , H . L . : Zinc Oxide-Eugenol Cements. J.A.D.A., 2 6 : i 536- i 54° ) September 1939. 16. P a f f e n b a r g e r , G. C . , and C a u l , H . J.: Dental Cements. Proc. D. Centenary Celebra tion, March 1940, pp. 232-240.
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17. F r i t z , F . : Die Trockenstoffe und ihre Verwendung. Chem. Zeitung, 60:921-924, 1936. 18. G r a h a m , F. W., J r . : Silver Nitrate and Zinc Oxide in Treatment of Children’s Teeth. J.A.D.A., 28:124-128, January 1941. 19. B a r e , W. K .: Rosin as a Linoleum Component. Symposium on rosin, 1930. 311 East Chicago Avenue.
CREATION OF A MANDIBULAR RIDGE BY DEEPENING THE LABIAL SULCUS AND LINING IT WITH A SKIN GRAFT By H
aro ld
S. G o r n e y ,
D .M .D .; A r t h u r J. G o r n e y , M.D., and Ph.D., M.D., Boston, Mass.
Sam u el F omon,
HE dentist is frequently confronted with the problem of making a full lower denture for a patient whose alveolar process has been resorbed to such an extent that the use of this part of the mouth as a retentive and stabiliz ing factor is impractical. In these cases, the usual practice of using the mylohyoid ridge and sublingual fossa region for retention seldom proves satisfactory. At best, this part of the mouth provides in sufficient anchorage, allowing the den ture to become movable. Moreover, any small portion of the alveolar process which remains and may assist in retain ing the denture is likely to be resorbed, and this necessitates frequent trimming of the denture, reducing the already poor retentive ability of the part. The question as to what to do to in crease the comfort and efficiency of a denture under these circumstances arises. It is generally agreed that it is best to deal with the problem by recourse to a common surgical procedure, the creation of. a ridge by the formation of a prealveolar sulcus. The mandible is thus enabled to furnish the desired support. On this principle, many surgical pro cedures have been suggested. A com
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mon procedure is to incise the labial fold along the alveolar margin, deepen the cavity to the desired level and attempt to prevent union of the resultant raw surfaces by interposing a piece of rubber dam and suturing it in place. Kazanjian1 incises the mucosa parallel to and at some distance (1.5 cm.) from the alveo lar ridge, undermines the tissues medially and pushes the flap thus formed down against the periosteum of the mandible and sutures it in place. Sometimes, the radio knife is resorted to, on the grounds that its use reduces the amount of cica trization to a minimum and thus prevents to some extent a reobliteration of the newly formed sulcus when healing takes place. The final results of these and other methods have been only partially satisfactory and, in some instances, totally unsuccessful, in that little or no pro vision is made against subsequent re union of the raw surfaces by the inevi table formation of scar tissue. That this complication has been satisfactorily overcome by a method sug gested by one of us (S.F.),2 featuring the use of an inlay skin graft, was evidenced by the gratifying results of the procedure in the case here described.