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Tissue reaction to root canal cements in the rat molar
Endodontics American
Association
of Endodontists
I. B. Bender, Editor
Tissue reaction to root canal cementsin the rat molar Jorge Erausquin, D.D.S.,” Buenos Aires, Argentina UNIVERSIDAD
DE BUENOS
and Margarita
AIRES,
FACULTAD
Muruzhbal,
D.D.S.,
DE ODONTOLOGiA
A
pproximately three years ago, a research program was started with the purpose of studying the reaction of the periapieal tissues of the rat molar to different root canal filling materials used in endodontics. During the course of this investigation, successive modifications of the original technique and the observation of longer postoperative periods considerably increased the amount of material to be examined. For this reason, we decided to divide the work into three parts : one dealing with root canal cements, another dealing with resorbable pastes, and the third dealing with plastic root canal fillings. The present article will report a study devoted to root canal cements-zinc oxide-eugenol cement, Kerr cement, Grossman sealer, and N,. Zinc oxide-eugenol cement, described previously,l was selected because its well-defined physicochemical properties make it an adequate basis for comparison of other cements. Kerr cement and Grossman sealer were chosen because of their widespread use in the United States, and N, was chosen because of its popularity in Europe and Latin America. MATERIAL
AND
METHODS
A total of 710 white rats of either sex, from 60 to 90 days old, were used. The number of root canal fillings made with each cement, as well as the different postoperative periods studied, are shown in Table I. Operative
technique
The standard technique used has been described in detail in a previous article7; however, several modifications were subsequently introduced in order to obtain either an overfilling, a short filling, or necrosis of the cementum. This study waz supported by a grant (DE Research, United States Public Health Service. *Professor of Histology.
360
02290)
from
the National
Institute
of Dental
Tissue reaction to root canal fillings
Volume 26 Number 3
Table
361
I Postoperative
Zoe Kerr Grossman N, P ?iT,T
0 day 7 1 -
1 day 29 :i
Total per period
s
67
11 -
d days 25 23 15 15 4 E
4 da?lS 27 20 19 13 3 sz
period
7 days 64 37 30 31 5
15 &YS 16 ii
167
54
8 3
SO &YS 32 16 19 21 3
60 &YS 29 10 14 11 2
90 &YS 31 19 19 21 3
iii-
ss
93
Total per cement 253 159 144 131 23 710
Fig.
QO-day postoperative period. Fissures Fig. 1. Filling with zinc oxide-eugenol; histologic technique. Remains of zinc oxide-eugenol cement adhering to dentine at (arrows), but detached from canal wall, producing a crack (C) in its upper portion. tion of necrotic cementum and underlying dentine. (Magnification, x55; reduced I$.) Fig. 8. Filling with NZ Temporary; 2-day postoperative period. In spite produced by histologic technique, most of dentine shows adhering N, Temporary (Magnification, x80; reduced 1/s,)
caused by apical zone R, Resorpof
fissures (arrows).
Overfillings were obtained in young animals (50 to 60 days old) by overinstrumentation and enlargement of the apical foramen, filling of the canal with a spiral lentulo, and pressing a small heated baseplate gutta-percha sphere into the orifice of the canal. In animals from 80 to 100 days old fillings short of the apex were achieved with a fine short Hedstriim file. In order to study the necrotizing action of the root canal sealer on the cementum, the canal was considerably enlarged so as to reduce the thickness of the dentinal layer, or even to remove it entirely. Histologic
procedure
In all cases, specimens were (1) subjected to simultaneous fixation decalcification in formol-EDTA, (2) embedded in butyl alcohol-paraffin,
and (3)
2
O.H., 0.31. B 0.1’. September, 1968
362 Erausquifk and Mumz6bal oriented buccolingually, following and (4) stained with hematoxylin BEHAVlOR Plasticity
OF THE CEMENTS
the axis of the mesial root, of the first, molar, and co&u.
WITHIN
THE ROOT CANAL
This property was evaluated by the degree of adaptation of the cement to the canal walls. All four of the cements tested showed very good plasticity, as evidenced by microscopic observation (Figs. 1 and 2). Dimensional
changes
Shrinkage or distortion of root canal cements, either during or after the setting period, was difficult to evaluate by microscopic observation. Since histologic processing caused marked tissue retraction, the fissures almost constantly appearing in the lumen of the canal may be the result of dimensional changes of the cement or shrinkage due to the histologic technique. However, since fissures became infiltrated with polymorphonuclear leukocytes, it is reasonable to assume that the empty fissures are technical artifacts. Thus, microscopic observation showed that none of the four cements underwent appreciable dimensional changes after being placed in the canal, Adhesion
to the canal
walls
Fissures caused by tissue shrinkage during histologic processing permitted a rough evaluation of the degree of adhesion of the filling material to the canal walls. When fissures appeared between the cement and the canal wall, it was assumed that the strength of adhesion of the root canal cement was not as great as its resistance to fracture; conversely, cracks located within the cement were taken to indicate that strength of adhesion to the canal wall was greater than resistance of the cement to fracture (Fig. 1). Considered from this standpoint, none of the four cements can be described as adhering firmly to the canal walls. N, Temporary showed the greatest tendency to adhere to the dentinal wall, probably because of its lower resistance to fracture. On the other hand, zinc oxide-eugenol also showed a tendency to adhere to the dentine, although to a lesser degree. The other cements-Kerr, Grossman, and N, Permanent-lined the canal walls but did not adhere to them. These observations are in agreement with those obtained by Tschame?, 0 in laboratory tests, using N, Permanent. A rough estimate of the degree of adhesion of N, Temporary and zinc oxideeugenol, evaluated by establishing the ratio between the area of dentine with adhered root canal cement and the total canal surface, showed that more than 80 per cent of this surface presented adhering cement when N, Temporary was used, as compared with 20 to 30 per cent when zinc oxide-eugenol was used. Tendency
to overfilling
Root canal overfilling depends, to a certain degree, on the pressure applied to the material in the canal, the size of the foramen, and the fluidity of the material. Disregarding the first two factors, the fluidity of the cements depends
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Tissue reaction to root canal fillings
363
both on the proportion of powder to liquid in the mixture and on the degree of spatulation. Taking only these variables into account it was rather difficult to make an accurate comparative evaluation; however, when a standard technique was used, Kerr cement mo’st frequently extruded through the apical foramen (Fig. 3) and, in some cases, even scattered in the adjacent bone-marrow lacunae. REACTION OF THE APICAL PERIODONTAL LIGAMENT Necrosis Overfilling of the mesial root of the lower first molar of the rat, frequently causes infarction of the adjacent periodontal ligament due to destruction, compression, or thrombosis of the vessels of the alveolar fundus.lO This necrotizing action was observed with all four root canal cements used in the present study. In order to evaluate the degree of tissue injury, cases of overfilling were studied two days postoperatively. Zinc oxide-eugenol cement provoked the largest zones of necrosis in relation to the extent of the overfilled mass (Fig. 4). The other three root canal cements provoked only a few small areas of necrosis, even in cases of gross overfilling. Four days postoperatively, the area of periodontal ligament necrosis had been replaced by newly formed tissue in practically all cases. Occasionally, in specimens in which zinc oxide-eugenol had been used, remnants of necrotic periodontal tissue could still be seen adjoining the apical foramen.
Fi,q. 3
Fhg. 4
Fig. 3. Filling with Kerr sealer; go-day postoperative period, Overfilled material appears scattered in apical periodontal ligament (thin arrows). Ingrowing tissue in canal started resorption of canal wall (R). Thick arrow: Kerr sealer in canal. (Magnification, x80; reduced Y3.) Fig. 4. Filling with zinc oxide-eugenol cement; 2-day postoperative period. Overfilling with zinc oxide-eugenol (ZOE) causing periodontal ligament necrosis (PLN), alveolar bone necrosis (ABN) and cementurn necrosis (CN). (Magnification, x70; reduced IA.)
344 E~azcsquin and Mumzciba~l Inflammatory
O.S., ON. & O.P. September, 1968
reactions
Periapical inflammatory reactions provoked by the root canirl ccmcnt s varied considerably. Since all specimens studied were normal teeth of tho name age, and since the same root was studied in each case, variations in inflammatory I’+ sponse may be conseqnent,ial to both the specific propertics of each cement and the differences in t,he operative techniques employed. The close interaction of
F ig. 5
E;'i.4.
2-day postoperative period. Surrounding overfilled Fig. 5. Filling with Nz Permanent; material appears a pseudocapsule (P(J) due to compression of periodontal ligament. Scarce polymorphonuclear leukocyte infiltrate (PI). (Magnification, x110; reduced J$) Fig. 6. Filling with Kerr cement; 4-day postoperative period. Debris (0) due to instrumentation, pushed through foramen by Kerr cement (Ii;), appears densely infiltrated with polymorphonuclear leukocytes. (Magnification, x120 ; reduced I,$) period. CementoPig. 7. Filling with zinc oxide-eugenol cement; 60-day postoperative dentinal wall resorbed and replaced by intiltrated tissue (IT). Debris (arrows) mixed with zinc oxide-eugenol cement. BS, Bone sclerosis. (Magnification, x60; reduced I$$.)
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Tissue reaction
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365
these two factors makes it difficult t,o evaluate the inflammatory reaction of the tissue to a given cement, unless the technique is carefully described in detail. When the filling was made flush to the apex or slightly beyond it and the cement was well condensed, showing a smooth surface, only a mild inflammatory reaction was seen. During the first few days, zinc oxide-eugenol and Grossman sealers provoked a generally mild and brief polymorphonuclear leukocyte infiltration In cases of overfilling, the periodontal ligament reaction depended mainly on the degree to which the material mixed with tissue fluid and debris. Zinc oxideeugenol and Grossman cements induced a polymorphonuclear leukocyte infiltration. This reaction beca,me more severe when the amount of tissue remnants increased, and the overfilled mass was less compact. N, showed a similar though less intense response (Fig. 5). This is in agreement with observations made by Sargenti and Richterll in human material and by Snyder, Seltzer, and Moodnik6 in dogs ; Overdiek12 also reported a favorable reaction to N, in guinea pig implants. On the other hand, Kuroiwa13 described several cases of severe tissue reaction to overfillings with N, in dogs. Rappaport, Lilly, and Kapsimalis’4 observed a severe inflammatory reaction to N, implants in the subcutaneous connective tissue of the rat. While Kerr cement has a tendency to extrude through the foramen and spread in the periodontal space, it did not mix with tissue remnants. The ensuing inflammatory reaction was mild, which confirmed the observations made by Stewart,15 Guttuso,16 and Rappaport and associates.14 A polymorphonuclear infiltrate was found only in those cases in which Kerr cement pushed the tissue remnants beyond the apical foramen (Fig. 6). The aforementioned correspond to short postoperative periods, in which infiltration of the periodontal ligament is the response to direct action of the overfilled material. However, 15 days postoperatively and thereafter, irritation provoked by the overfilled material mixed with debris due to instrumentation may involve bone and cementum, causing secondary infiltrative and granulomatous reactions in the periodontal ligament. This granulomatous response is often associated with resorption of cementum and resorption and/or sclerosis of the alveolar fundus (Fig. 7). Variable occurrence of short fillings was found after 15 days postoperatively. For instance, when a small segment of the remaining pulp with little injury was left in the apical canal, the inflammatory reaction was generally mild and the periapical tissues showed optimal tolerance (Fig. 8). This favorable response was found to the four cements studied. On the other hand, if the apical pulp stump remained in contact with pulp remnants adhering to the canal wall, dense infiltration frequently occurred and caused necrosis of the adjacent cementum followed by a periapical abscess surrounded by a granuloma of variable dimensions (Fig. 9). Zinc oxide-eugenol, Grossman, Kerr, and N, Permanent cements showed this unfavorable periapical reaction in cases of poor ddbridement and filling of the canal; only N, Temporary showed less tendency to provoke infiltration of pulp remnants and inflammatory reaction of the periapical tissues.
Fig. 8
Fig.
9
Fig. 8. Filling short of apex with Kerr cement; 60.da.y postoperative period. Favorable reaction of residual pulp and apical periodontal ligament.. Arrow indicates junction between filling and pulp. NB, New bone at alveolar fundus. (Magnification, x55; reduced ‘/3.) Pig. 9. Filling with Kerr cement; ‘i-day postoperative period. Apical abscess (A) surrounded by small granuloma (G). Resorption (E) of alveolar fundus and bone sclerosis (BS) of underlying bone marrow. Cement mixed with debris (arrows) in root canal. (Magnification, x60; reduced 14.)
The favorable response mentioned by some authors for N2 Permanentl*s 17-ls was observed only when trauma of the apical pulp stump was minimal. Under these circumstances, all the cements showed a similar favorable response. The poor results obtained when any of the cements became mixed with debris are in agreement with those which demonstrate the hazards of a deficient filling of the canaL6r 2o Resorption
of the overfilled
material
The fate of the overfilled cement depended largely on the proportion to which it became mixed with tissue fluids and the debris of instrumentation when extruding beyond the foramen. Tightly packed root canal cements without debris were resorbed very slowly. A small number of foreign-body giant cells (Figs. 10 to 14)) whose function was somehow related to root canal cement resorption, appeared on the surface of the overfilled material. The remaining area was surrounded by normal connective tissue, made up mainly of collagen fibers. N, Temporary showed a peculiar tendency to fragmentation with release of opaque granules (titanium dioxide) that were rapidly phagocytized by the macrophages (Fig. If,). During this process, polymorphonuelear leukocytes were scarce or entirely in 2-day implants absent. Guttuso,l” who observed this lack of acute infiltration in rats, postulated that “regular inflammatory cells could not migrate readily
Tissue reaction to root canal fillirl,gs
Fig.
367
lt?
Fig. 10. Filling with zinc oxide-eugenol (ZOEJ cement; 60-day postoperative period. Giant cells (arrows) on surface of overfilled material, surrounded by fibrous capsule (FC) with minimal infiltration. (Magnification, xl 70 ; reduced l/s,) Fig. 21. Filling with Kerr cement; go-day postoperative period. Giant cells (arrows) on fragment of Kerr cement (EC) isolated in periodontal tissue. (Magnification, x400; reduced ?-ix.) Fig. 18. Filling with zinc oxide-eugenol cement; do-day postoperative period. Giant cells (arrows) on fragment of zinc oxide-eugenol cement (ZOE) isolated in periodontal tissue and surrounded by fibrous capsule (PC). (Magnification, x200; reduced I$.) Fig. IS. Filling with Kerr cement; go-day postoperative period. Giant cells showing large silver particles. (Magnification, x800; reduced l/‘J.)
into the area” because “the tissue cells seemingly were killed or ‘fixed’ on the eipot,” and added that “a critical analysis proved that actually a severe injury had occurred.” Our histologic specimens showed, however, that no polymorphonuclear leukocytes could be found in the neighborhood of the filling material either 15 or 90 days after treatment. When the cement became mixed with tissue debris due to instrumentation and/or with the interstitial fluids of the apical periodontal ligament, the reaction of the adjoining tissue was much more severe. Polymorphonuclear and ma.crophage infiltration generally occurred, progressively disintegrating the cement. It was not possible to establish the fate of the cement granules, but it may be assumed that they were phagocytized by the macrophages.
O.S., O.M. & 0.1’. September, 1968
Fig. 14
E
E’ig. 24. Filling with Grossman cement; 30.da? postoperative period. Giant cells (arrows) on fragment of Gross,man cement (GC) isolated m periodontal tissue. (Magnification, x250; reduced $4.) Pig. 15. Filling with N, Temporit~y ; 1S-day postopw:ttivr pvriotl. Disintegrated N, Temporary (NKC) with titanium dioxide granules being phagocytized by macrophages (arrows). Minimal polymorphonuclear leukocyte infiltrate. (Magnification, x350; reduced $4.)
long-term
tissue
tolerance
to ovetfllied
cements
The most frequent reaction found after 60- to 90-day postoperative periods in cases of overfilled cements was encapsulation. When the overfilling was dense, the capsule was found to be thin, lying in direct contact with the cement (Fig. 16) ; conversely, when the overfilling contained debris, the fibrous capsule was thicker (Fig. 17) and a zone of loose connective tissue, polymorphonuclear leukocytes, macrophages, and, in some cases, giant cells was found between it and the cement. In two cases of overfillings made with Grossman cement (Fig. 18) and in one case of overfilling zinc oxide-eugenol (Fig. 19), bone tissue was found deposited directly on the overfilled cement. RESPONSE OF THE CEMENTUM
As discussed in a previous article, *I differences in thickness and structure between the cementum of the rat molar and that of the human molar induced us to assume that cementum in the rat is biologically less resistant than its counterpart in man. Therefore, although the basic tissue response to trauma provoked by root canal treatment is similar in both species, it appeared to be more severe in the rat. Cementum
necrosis
Cementum necrosis caused by the irritating action of root canal cements has been a common finding in the course of our work. Each of the cements caused a similar degree of necrosis when it came in contact with the cementum, either at the apical end of the root, normally devoid of dentine, or where dentine had been removed by mechanical instrumentation.
15
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369
16
Fig.
Fig . 18
Fig.
Fig.
Fig. 26. Filling with zinc oxide-eugenol cement; 30.day postoperative period. Overfilled zinc oxide-eugenol cement (ZOE) appears surrounded by thin fibrous capsule, without infiltrate. (Magnification, x80 ; reduced l/g.) Fig. 17. Filling with zinc oxide-eugenol cement; 30-day postoperative period. Overfilled zinc oxide-eugenol cement (ZOE), mixed with some debris, shows thicker capsule than in Fig. 16, with mild infiltration. (Magnification, x100; reduced :,$.) Fig. 28. Filling with Grossman cement; 30.day postoperative period. Bone lamella (BLJ deposited directly on fragment of Grossman root canal cement (GC). (Magnification, x350; reduced $5.) Fig. 29. Filling with zinc oxide-eugenol cement; go-day postoperative period. Fragment of zinc oxide-eugenol cement (ZOE) totally surrounded by newly formed bone. Bone lamella (BLJ deposited directly on cement. (Magnification, x100; reduced I$.)
Likewise, all the cements caused partial necrosis of the cementum, starting at the inner surface, in specimens with a thin dentinal layer. Conversely, good cementum tolerance was found where dentine width exceeded 80 to 100 microns and the root canal fillings were tightly packed and without debris. Cementum
resorption
Resorption of the cementum was frequently found to be preceded, accompanied, or followed by resorption of the adjoining dentine and apparently did not depend directly on the type of filling material. Notwithstanding this fact, the filling material may indirectly influence resorption of the calcified tissues,
19
Fig. $0. Filling with Kerr cement; 30-day postoperative period. tissue (IPT), and dentinal cementum resorption (R). (Magnification,
Ingrowth of periodontal x180; reduced I,.)
as was seen in cases of cementum necrosis or ingrowth of periodontal tissue into the root canal. Necrotic cementum showed a definite tendency to be resorbed. This process started at the periodontal surface of the cementum and reached variable depths, even to the point of entirely removing the wall of the apical portion of the canal. However, no special features were noted in the resorption process that could be ascribed to the type of cement used. The ingrowing apical periodontal tissue, found in short fillings with blood clots in the apical canal, also induced severe resorptions, this time starting at the inner surface of the dentine. This type of response could occasionally be observed with all four cements, when the postoperative period was longer than 15 days. To exemplify the behavior of a specific cement, when Kerr sealer was used, cementum resorption started earlier and was more severe than when the other cements were used (Figs. 3 and 20), proba,bly because of the mild infiltration caused by this material, which allowed quicker ingrowth of the periapical tissue. REACTION OF THE ALVEOLAR BONE The alveolar fundus showed two types of reaction to t,he cement: (1) direct, due to the contact between the overfilled material and the alveolar bone, and (2) indirect, provoked by inflammatory changes of the periodontal ligament, caused by poor filling of the canal. Direct reaction Any of the cements, when overfilled and coming in direct contact with the alveolar fundus, caused necrosis of the superficial bone lamellae. In some cases,
Tissue reaction
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371
this necrosis was followed within 7 days by osteosclerosis of the underlying bone marrow. No specific reaction to the different cements was found, with the exception of Kerr sealer, which showed a greater tendency to scatter throughout the periodontal ligament rather than to adhere to the alveolar surface. Indirect
reaction
of the alveolar
fundus
When fillings remained short of the apex, the apical portion of the root canal was seen to be occupied by the pulp stump, tissue remnants, or blood clot. In some cases, these structures underwent polymorphonuclear leukocyte and macrophage infiltration or were invaded by ingrowing apical connective tissue. A periapical abscess, surrounded by granulomatous tissue, frequently developed after infiltration of the canal, inducing resorption of the alveolar surface and osteosclerosis of the underlying bone marrow. When marked ingrowth of the periodontal tissue took place, severe resorption of the dentine and cementum was frequently seen. Despite marked destruction of the apical end of the root, however, necrosis, resorption, or sclerosis of the alveolar bone was rarely observed, apposition of new bone lamellae being the most common finding. INFLUENCE
OF THE OPERATIVE
TECHNIQUE
The biologic material used in these experiments has been basically uniform, namely, the normal mesial root of the first lower molar. Therefore, the difference in responses was probably due to the type of cement and the technique used. Findings reported here show a wide range of responses, and experimental evidence appears to indicate that this diversity depends more on the technical approach than on the choice of filling material. Histologic studies showed, for instance, that different periapical tissue reactions can be obtained, even when the same cement is used, according to the type of filling made (short of the apex, flush to the apex, or overfilling). On the other hand, results were very similar with the four cements if debridement was thorough and the fillings were tightly packed and flush to the apex. This would indicate that none of the cements, per se was able to compensate for poor technique. Influence
of technique
on density
of the filling
Thorough d6bridement of the canal and tight packing of the cement were basic requirements for obtaining hermetic fillings. The presence of blood clot and of tissue remnants, which was a common finding because of the oval or fusiform shape of the canal, seriously hindered the accomplishment of hermetic fillings. In order to overcome this difficulty, a small amount of cement was introduced into the canal with a Hedstrijm file in a counterclockwise motion, in order to impregnate the canal walls and mix the cement with the debris. This later was removed by clockwise rotation of the file, after which the permanent filling was ma,de.
This technique yielded good results when zinc oxide-eugcnol and 3, were used ; conversely, Kerr and Grossman cements were more difficult to mix with the debris and were less adherent to the moist canal wall. The spatulation technique is likewise important in obtaining hermetic fillings of the canal; best results were achieved when thick cement was usc~l and spatulation was carefully accomplished. Influence resorption
of operutive technique of cementum
in the
necrosis
and
Excessive enlargement of the root canal during mechanical instrumentation caused reduction of the dentine layer. Under these circumstances, all the cements provoked necrosis of the cementum, which started at the cementodentinal junction and then spread toward the periodontal surface. As the dentine layer became thinner, it was found that the necrotic layer of cementum increased. Finally, when the entire cementum was necrotized, resorption induced by the periodontal ligament was frequently observed. Moreover, in specimens with thorough debridement of the canal, filled short of the apex, the remaining empty space was frequently occupied by a blood clot, which was rapidly invaded by ingrowing tissue coming from the periodontal ligament. This newly formed tissue showed a marked tendency to resorb dentine and cementum, starting from the canal wall. SUMMARY
AND
CONCLUSIONS
The response of periapical tissue to root canal fillings with zinc oxide-eugenol cement, Rickert sealer, Grossman sealer, and Nz was studied in 710 white rats between 60 and 90 days old. Root canal treatments were performed in the mesial root of the lower left first molar. Postoperative periods ranged from 1 to 90 days. The following conclusions were based on histologic studies: 1. Tested root canal cements showed good plasticity; no dimensional cha.nges could be detected after the filling was placed. 2. Grossman, Kerr, and N, Permanent cements did not adhere to the canal wall; zinc oxide-eugenol was only slightly adherent; N, Temporary showed the greatest adherence. 3. Zinc oxide-eugenol, Grossman, and N, Permanent cements, when mixed with debris, mostly provoked severe inflammatory infiltration; N, Temporary caused a mild reaction; Rickert sealer frequently induced moderate infiltration, ingrowth of periapical tissue, and resorption of the canal wall. 4. The most favorable tissue reaction was found in specimens with fillings short of the apex and with minimal injury of the remaining pulp stump. 5. All root canal cements tested, in cases of overfillings, showed a tendency to be resorbed. Resorption of compact overfilled masses, without debris, proceeded slowly. No polymorphonuclear leukocytes were observed, although giant cells were nearly always found. When the extruded root canal cement became mixed with tissue remnants, a severe inflammatory reaction was frequently seen. 6. When the cements directly contacted the alveolar surface, necrosis and resorption of the superficial bone lamellae frequently occurred. However, the
Tissue reaction
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canal
fillings
373
most severe resorptions were constantly associated with osteosclerosis of the underlying bone marrow. This response was indirectly induced by inflammation of the apical periodontal ligament, caused by poor d6bridement and filling of the canal. REFERENCES
1. Erausquin, J., and Muruzkbal, M.: Root Canal Fillings 2. 3. 4.
5. 6. 7. 8. 9.
10. 11. 12. 13. 14. 15. 16. 17.
18.
With Zinc Oxide-Eugenol Cement in the RatMolar,ORA~ SURG., ORAL MED.& ORALPATH. 24: 547.558,1967. Dixon. C. M.. and Rickert. U. G.: Histologic Verification of Results of Root-Canal Therapy_. in Ex&imental A.nimals.‘J. Am. Dent. A. 25: 1’781-1803. 1938. Gross&n, L. I.: Endodontic Practice, ed. 6, Philadelphia, 1965, Lea & Febiger, p. 354. American Dental Association: Council on Dental Therapeutics: Hazards of Formaldehyde Preparations for Single Treatment Procedures in Endodontics, N, and the R Method, J. Am. Dent. A. 64: 689-700, 1962. Sargenti. A., and Council on Dental Therapeutics: Notes and Comments, D. Abst. 10: 139240, ‘1965. Endodontic Snyder, D. E., Seltzer, S. and Moodnik, R.: Effects of N, in Experimental Therapy, ORAL SURG., ORAL MED. & ORAL PATH. 21: 635-656,1966. Erausquin, J., and Muruzabal, M.: A Method for Root Canal Treatment in the Molar of the Rat, ORAL SURG., ORAL MED. &ORAL PATH. 24: 540~546,1967. Tschamer, H. : Priifung einiger Wurzelfiillmaterialien auf ihre Eigenschaften, insbesondere der Abschlussdichte, Stoma 13: 172-192, 1960. Tschamer, H. : Vorlaufige klinisch-rontgenologisehe Kontrollergebnisse nach Wurzelkanalfiillungen mit den Wurzelfiillmitteln AH 26 (De Trey), Renium (Cardex), N2 (Sargenti) und der Kunstharzkombinierten Wurzelfiillmasse nach Riebler, Deutsche Zahnarztl. 18: 394-406, 1963. Erausquin, J., Muruzabal, M., Devoto, F. C. H., and Rikles, A.: Necrosis of the Periodontal Ligament in Root Canal Overfillings, J. D. Res. 45: 1084-1092, 1966. Sargenti, A., and Richter, S. L.: Rationalized Root Canal Treatment, New York, 1959, AGSA, Scientific Publications. Overdiek. H. F.: Zur Gewebsreaktion auf imolantierte Wurzelfiillmaterialien im Vernleieh a zum N2,‘Zahnarztl. Rdsch. 69: 402-406, 1960: Kuroiwa, K.: Experimental Study on Root Canal Filling Using New Filling Material, N2 and AN2, Tokyo D. Coll. Bull. Oral Path. 4: 45-74, 1960. Rappaport, H. M., Lilly, G. E., and Kapsimalis, P.: Toxicity of Endodontic filling Materials, ORAL SURG., ORAL MED. & ORAL PATH. 18: 785802, 1964. Stewart, G. G.: A Comparative Study of Three Root Canal Sealing Agents, ORAL SURG., ORAL MED. & ORAL PATH. 11: 1029-1041, 1174-1178, 1958. Guttuso, J. : Histopathologic Study of Rat Connective Tissue Responses to Endodontic Materials, ORAL SURG., ORAL MED. & ORAL PATH. 16: 713-727, 1963. Zerosi! C., Baratieri, A., and Amici, G.: Osservazioni istologiche sul comportamento dei tessuti periapicali dopo otturazione canalare con cement0 N2, Rass. Trim. di Odont. 40: 555584, 1959. Sargenti, A. : Zur Diskussion iiber die NB-Wurzelbehandlung, Schweiz. Monatsschr. Zahnh.
73: 127-132, 1963. 19. Rowe, A. H.: Treatment 20. Nicholls, E.: &sorbable
with N2 Root Canal Sealer, Brit. D. J. 117: 27-30, 1964. Canal Fillings, Including N2, in Grossman, L. I.: Transactions of the Third International Conference on Endodontics, Philadelphia, 1963, University of Pennsylvania Press, pp. 144-157. 21. Erausquin, J., and Muruzabal, M.: Necrosis of Cementum Induced by Root Canal Treatments in the Molar Teeth of Rats, Arch. Oral. Biol. 12: 1123-1132, 1967. Charms
2146.
Association
of Endodontists
I. B. Bender, Editor
Tissue reaction to root canal cementsin the rat molar Jorge Erausquin, D.D.S.,” Buenos Aires, Argentina UNIVERSIDAD
DE BUENOS
and Margarita
AIRES,
FACULTAD
Muruzhbal,
D.D.S.,
DE ODONTOLOGiA
A
pproximately three years ago, a research program was started with the purpose of studying the reaction of the periapieal tissues of the rat molar to different root canal filling materials used in endodontics. During the course of this investigation, successive modifications of the original technique and the observation of longer postoperative periods considerably increased the amount of material to be examined. For this reason, we decided to divide the work into three parts : one dealing with root canal cements, another dealing with resorbable pastes, and the third dealing with plastic root canal fillings. The present article will report a study devoted to root canal cements-zinc oxide-eugenol cement, Kerr cement, Grossman sealer, and N,. Zinc oxide-eugenol cement, described previously,l was selected because its well-defined physicochemical properties make it an adequate basis for comparison of other cements. Kerr cement and Grossman sealer were chosen because of their widespread use in the United States, and N, was chosen because of its popularity in Europe and Latin America. MATERIAL
AND
METHODS
A total of 710 white rats of either sex, from 60 to 90 days old, were used. The number of root canal fillings made with each cement, as well as the different postoperative periods studied, are shown in Table I. Operative
technique
The standard technique used has been described in detail in a previous article7; however, several modifications were subsequently introduced in order to obtain either an overfilling, a short filling, or necrosis of the cementum. This study waz supported by a grant (DE Research, United States Public Health Service. *Professor of Histology.
360
02290)
from
the National
Institute
of Dental
Tissue reaction to root canal fillings
Volume 26 Number 3
Table
361
I Postoperative
Zoe Kerr Grossman N, P ?iT,T
0 day 7 1 -
1 day 29 :i
Total per period
s
67
11 -
d days 25 23 15 15 4 E
4 da?lS 27 20 19 13 3 sz
period
7 days 64 37 30 31 5
15 &YS 16 ii
167
54
8 3
SO &YS 32 16 19 21 3
60 &YS 29 10 14 11 2
90 &YS 31 19 19 21 3
iii-
ss
93
Total per cement 253 159 144 131 23 710
Fig.
QO-day postoperative period. Fissures Fig. 1. Filling with zinc oxide-eugenol; histologic technique. Remains of zinc oxide-eugenol cement adhering to dentine at (arrows), but detached from canal wall, producing a crack (C) in its upper portion. tion of necrotic cementum and underlying dentine. (Magnification, x55; reduced I$.) Fig. 8. Filling with NZ Temporary; 2-day postoperative period. In spite produced by histologic technique, most of dentine shows adhering N, Temporary (Magnification, x80; reduced 1/s,)
caused by apical zone R, Resorpof
fissures (arrows).
Overfillings were obtained in young animals (50 to 60 days old) by overinstrumentation and enlargement of the apical foramen, filling of the canal with a spiral lentulo, and pressing a small heated baseplate gutta-percha sphere into the orifice of the canal. In animals from 80 to 100 days old fillings short of the apex were achieved with a fine short Hedstriim file. In order to study the necrotizing action of the root canal sealer on the cementum, the canal was considerably enlarged so as to reduce the thickness of the dentinal layer, or even to remove it entirely. Histologic
procedure
In all cases, specimens were (1) subjected to simultaneous fixation decalcification in formol-EDTA, (2) embedded in butyl alcohol-paraffin,
and (3)
2
O.H., 0.31. B 0.1’. September, 1968
362 Erausquifk and Mumz6bal oriented buccolingually, following and (4) stained with hematoxylin BEHAVlOR Plasticity
OF THE CEMENTS
the axis of the mesial root, of the first, molar, and co&u.
WITHIN
THE ROOT CANAL
This property was evaluated by the degree of adaptation of the cement to the canal walls. All four of the cements tested showed very good plasticity, as evidenced by microscopic observation (Figs. 1 and 2). Dimensional
changes
Shrinkage or distortion of root canal cements, either during or after the setting period, was difficult to evaluate by microscopic observation. Since histologic processing caused marked tissue retraction, the fissures almost constantly appearing in the lumen of the canal may be the result of dimensional changes of the cement or shrinkage due to the histologic technique. However, since fissures became infiltrated with polymorphonuclear leukocytes, it is reasonable to assume that the empty fissures are technical artifacts. Thus, microscopic observation showed that none of the four cements underwent appreciable dimensional changes after being placed in the canal, Adhesion
to the canal
walls
Fissures caused by tissue shrinkage during histologic processing permitted a rough evaluation of the degree of adhesion of the filling material to the canal walls. When fissures appeared between the cement and the canal wall, it was assumed that the strength of adhesion of the root canal cement was not as great as its resistance to fracture; conversely, cracks located within the cement were taken to indicate that strength of adhesion to the canal wall was greater than resistance of the cement to fracture (Fig. 1). Considered from this standpoint, none of the four cements can be described as adhering firmly to the canal walls. N, Temporary showed the greatest tendency to adhere to the dentinal wall, probably because of its lower resistance to fracture. On the other hand, zinc oxide-eugenol also showed a tendency to adhere to the dentine, although to a lesser degree. The other cements-Kerr, Grossman, and N, Permanent-lined the canal walls but did not adhere to them. These observations are in agreement with those obtained by Tschame?, 0 in laboratory tests, using N, Permanent. A rough estimate of the degree of adhesion of N, Temporary and zinc oxideeugenol, evaluated by establishing the ratio between the area of dentine with adhered root canal cement and the total canal surface, showed that more than 80 per cent of this surface presented adhering cement when N, Temporary was used, as compared with 20 to 30 per cent when zinc oxide-eugenol was used. Tendency
to overfilling
Root canal overfilling depends, to a certain degree, on the pressure applied to the material in the canal, the size of the foramen, and the fluidity of the material. Disregarding the first two factors, the fluidity of the cements depends
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Tissue reaction to root canal fillings
363
both on the proportion of powder to liquid in the mixture and on the degree of spatulation. Taking only these variables into account it was rather difficult to make an accurate comparative evaluation; however, when a standard technique was used, Kerr cement mo’st frequently extruded through the apical foramen (Fig. 3) and, in some cases, even scattered in the adjacent bone-marrow lacunae. REACTION OF THE APICAL PERIODONTAL LIGAMENT Necrosis Overfilling of the mesial root of the lower first molar of the rat, frequently causes infarction of the adjacent periodontal ligament due to destruction, compression, or thrombosis of the vessels of the alveolar fundus.lO This necrotizing action was observed with all four root canal cements used in the present study. In order to evaluate the degree of tissue injury, cases of overfilling were studied two days postoperatively. Zinc oxide-eugenol cement provoked the largest zones of necrosis in relation to the extent of the overfilled mass (Fig. 4). The other three root canal cements provoked only a few small areas of necrosis, even in cases of gross overfilling. Four days postoperatively, the area of periodontal ligament necrosis had been replaced by newly formed tissue in practically all cases. Occasionally, in specimens in which zinc oxide-eugenol had been used, remnants of necrotic periodontal tissue could still be seen adjoining the apical foramen.
Fi,q. 3
Fhg. 4
Fig. 3. Filling with Kerr sealer; go-day postoperative period, Overfilled material appears scattered in apical periodontal ligament (thin arrows). Ingrowing tissue in canal started resorption of canal wall (R). Thick arrow: Kerr sealer in canal. (Magnification, x80; reduced Y3.) Fig. 4. Filling with zinc oxide-eugenol cement; 2-day postoperative period. Overfilling with zinc oxide-eugenol (ZOE) causing periodontal ligament necrosis (PLN), alveolar bone necrosis (ABN) and cementurn necrosis (CN). (Magnification, x70; reduced IA.)
344 E~azcsquin and Mumzciba~l Inflammatory
O.S., ON. & O.P. September, 1968
reactions
Periapical inflammatory reactions provoked by the root canirl ccmcnt s varied considerably. Since all specimens studied were normal teeth of tho name age, and since the same root was studied in each case, variations in inflammatory I’+ sponse may be conseqnent,ial to both the specific propertics of each cement and the differences in t,he operative techniques employed. The close interaction of
F ig. 5
E;'i.4.
2-day postoperative period. Surrounding overfilled Fig. 5. Filling with Nz Permanent; material appears a pseudocapsule (P(J) due to compression of periodontal ligament. Scarce polymorphonuclear leukocyte infiltrate (PI). (Magnification, x110; reduced J$) Fig. 6. Filling with Kerr cement; 4-day postoperative period. Debris (0) due to instrumentation, pushed through foramen by Kerr cement (Ii;), appears densely infiltrated with polymorphonuclear leukocytes. (Magnification, x120 ; reduced I,$) period. CementoPig. 7. Filling with zinc oxide-eugenol cement; 60-day postoperative dentinal wall resorbed and replaced by intiltrated tissue (IT). Debris (arrows) mixed with zinc oxide-eugenol cement. BS, Bone sclerosis. (Magnification, x60; reduced I$$.)
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Tissue reaction
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365
these two factors makes it difficult t,o evaluate the inflammatory reaction of the tissue to a given cement, unless the technique is carefully described in detail. When the filling was made flush to the apex or slightly beyond it and the cement was well condensed, showing a smooth surface, only a mild inflammatory reaction was seen. During the first few days, zinc oxide-eugenol and Grossman sealers provoked a generally mild and brief polymorphonuclear leukocyte infiltration In cases of overfilling, the periodontal ligament reaction depended mainly on the degree to which the material mixed with tissue fluid and debris. Zinc oxideeugenol and Grossman cements induced a polymorphonuclear leukocyte infiltration. This reaction beca,me more severe when the amount of tissue remnants increased, and the overfilled mass was less compact. N, showed a similar though less intense response (Fig. 5). This is in agreement with observations made by Sargenti and Richterll in human material and by Snyder, Seltzer, and Moodnik6 in dogs ; Overdiek12 also reported a favorable reaction to N, in guinea pig implants. On the other hand, Kuroiwa13 described several cases of severe tissue reaction to overfillings with N, in dogs. Rappaport, Lilly, and Kapsimalis’4 observed a severe inflammatory reaction to N, implants in the subcutaneous connective tissue of the rat. While Kerr cement has a tendency to extrude through the foramen and spread in the periodontal space, it did not mix with tissue remnants. The ensuing inflammatory reaction was mild, which confirmed the observations made by Stewart,15 Guttuso,16 and Rappaport and associates.14 A polymorphonuclear infiltrate was found only in those cases in which Kerr cement pushed the tissue remnants beyond the apical foramen (Fig. 6). The aforementioned correspond to short postoperative periods, in which infiltration of the periodontal ligament is the response to direct action of the overfilled material. However, 15 days postoperatively and thereafter, irritation provoked by the overfilled material mixed with debris due to instrumentation may involve bone and cementum, causing secondary infiltrative and granulomatous reactions in the periodontal ligament. This granulomatous response is often associated with resorption of cementum and resorption and/or sclerosis of the alveolar fundus (Fig. 7). Variable occurrence of short fillings was found after 15 days postoperatively. For instance, when a small segment of the remaining pulp with little injury was left in the apical canal, the inflammatory reaction was generally mild and the periapical tissues showed optimal tolerance (Fig. 8). This favorable response was found to the four cements studied. On the other hand, if the apical pulp stump remained in contact with pulp remnants adhering to the canal wall, dense infiltration frequently occurred and caused necrosis of the adjacent cementum followed by a periapical abscess surrounded by a granuloma of variable dimensions (Fig. 9). Zinc oxide-eugenol, Grossman, Kerr, and N, Permanent cements showed this unfavorable periapical reaction in cases of poor ddbridement and filling of the canal; only N, Temporary showed less tendency to provoke infiltration of pulp remnants and inflammatory reaction of the periapical tissues.
Fig. 8
Fig.
9
Fig. 8. Filling short of apex with Kerr cement; 60.da.y postoperative period. Favorable reaction of residual pulp and apical periodontal ligament.. Arrow indicates junction between filling and pulp. NB, New bone at alveolar fundus. (Magnification, x55; reduced ‘/3.) Pig. 9. Filling with Kerr cement; ‘i-day postoperative period. Apical abscess (A) surrounded by small granuloma (G). Resorption (E) of alveolar fundus and bone sclerosis (BS) of underlying bone marrow. Cement mixed with debris (arrows) in root canal. (Magnification, x60; reduced 14.)
The favorable response mentioned by some authors for N2 Permanentl*s 17-ls was observed only when trauma of the apical pulp stump was minimal. Under these circumstances, all the cements showed a similar favorable response. The poor results obtained when any of the cements became mixed with debris are in agreement with those which demonstrate the hazards of a deficient filling of the canaL6r 2o Resorption
of the overfilled
material
The fate of the overfilled cement depended largely on the proportion to which it became mixed with tissue fluids and the debris of instrumentation when extruding beyond the foramen. Tightly packed root canal cements without debris were resorbed very slowly. A small number of foreign-body giant cells (Figs. 10 to 14)) whose function was somehow related to root canal cement resorption, appeared on the surface of the overfilled material. The remaining area was surrounded by normal connective tissue, made up mainly of collagen fibers. N, Temporary showed a peculiar tendency to fragmentation with release of opaque granules (titanium dioxide) that were rapidly phagocytized by the macrophages (Fig. If,). During this process, polymorphonuelear leukocytes were scarce or entirely in 2-day implants absent. Guttuso,l” who observed this lack of acute infiltration in rats, postulated that “regular inflammatory cells could not migrate readily
Tissue reaction to root canal fillirl,gs
Fig.
367
lt?
Fig. 10. Filling with zinc oxide-eugenol (ZOEJ cement; 60-day postoperative period. Giant cells (arrows) on surface of overfilled material, surrounded by fibrous capsule (FC) with minimal infiltration. (Magnification, xl 70 ; reduced l/s,) Fig. 21. Filling with Kerr cement; go-day postoperative period. Giant cells (arrows) on fragment of Kerr cement (EC) isolated in periodontal tissue. (Magnification, x400; reduced ?-ix.) Fig. 18. Filling with zinc oxide-eugenol cement; do-day postoperative period. Giant cells (arrows) on fragment of zinc oxide-eugenol cement (ZOE) isolated in periodontal tissue and surrounded by fibrous capsule (PC). (Magnification, x200; reduced I$.) Fig. IS. Filling with Kerr cement; go-day postoperative period. Giant cells showing large silver particles. (Magnification, x800; reduced l/‘J.)
into the area” because “the tissue cells seemingly were killed or ‘fixed’ on the eipot,” and added that “a critical analysis proved that actually a severe injury had occurred.” Our histologic specimens showed, however, that no polymorphonuclear leukocytes could be found in the neighborhood of the filling material either 15 or 90 days after treatment. When the cement became mixed with tissue debris due to instrumentation and/or with the interstitial fluids of the apical periodontal ligament, the reaction of the adjoining tissue was much more severe. Polymorphonuclear and ma.crophage infiltration generally occurred, progressively disintegrating the cement. It was not possible to establish the fate of the cement granules, but it may be assumed that they were phagocytized by the macrophages.
O.S., O.M. & 0.1’. September, 1968
Fig. 14
E
E’ig. 24. Filling with Grossman cement; 30.da? postoperative period. Giant cells (arrows) on fragment of Gross,man cement (GC) isolated m periodontal tissue. (Magnification, x250; reduced $4.) Pig. 15. Filling with N, Temporit~y ; 1S-day postopw:ttivr pvriotl. Disintegrated N, Temporary (NKC) with titanium dioxide granules being phagocytized by macrophages (arrows). Minimal polymorphonuclear leukocyte infiltrate. (Magnification, x350; reduced $4.)
long-term
tissue
tolerance
to ovetfllied
cements
The most frequent reaction found after 60- to 90-day postoperative periods in cases of overfilled cements was encapsulation. When the overfilling was dense, the capsule was found to be thin, lying in direct contact with the cement (Fig. 16) ; conversely, when the overfilling contained debris, the fibrous capsule was thicker (Fig. 17) and a zone of loose connective tissue, polymorphonuclear leukocytes, macrophages, and, in some cases, giant cells was found between it and the cement. In two cases of overfillings made with Grossman cement (Fig. 18) and in one case of overfilling zinc oxide-eugenol (Fig. 19), bone tissue was found deposited directly on the overfilled cement. RESPONSE OF THE CEMENTUM
As discussed in a previous article, *I differences in thickness and structure between the cementum of the rat molar and that of the human molar induced us to assume that cementum in the rat is biologically less resistant than its counterpart in man. Therefore, although the basic tissue response to trauma provoked by root canal treatment is similar in both species, it appeared to be more severe in the rat. Cementum
necrosis
Cementum necrosis caused by the irritating action of root canal cements has been a common finding in the course of our work. Each of the cements caused a similar degree of necrosis when it came in contact with the cementum, either at the apical end of the root, normally devoid of dentine, or where dentine had been removed by mechanical instrumentation.
15
Tissue reaction to root canal fillings
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369
16
Fig.
Fig . 18
Fig.
Fig.
Fig. 26. Filling with zinc oxide-eugenol cement; 30.day postoperative period. Overfilled zinc oxide-eugenol cement (ZOE) appears surrounded by thin fibrous capsule, without infiltrate. (Magnification, x80 ; reduced l/g.) Fig. 17. Filling with zinc oxide-eugenol cement; 30-day postoperative period. Overfilled zinc oxide-eugenol cement (ZOE), mixed with some debris, shows thicker capsule than in Fig. 16, with mild infiltration. (Magnification, x100; reduced :,$.) Fig. 28. Filling with Grossman cement; 30.day postoperative period. Bone lamella (BLJ deposited directly on fragment of Grossman root canal cement (GC). (Magnification, x350; reduced $5.) Fig. 29. Filling with zinc oxide-eugenol cement; go-day postoperative period. Fragment of zinc oxide-eugenol cement (ZOE) totally surrounded by newly formed bone. Bone lamella (BLJ deposited directly on cement. (Magnification, x100; reduced I$.)
Likewise, all the cements caused partial necrosis of the cementum, starting at the inner surface, in specimens with a thin dentinal layer. Conversely, good cementum tolerance was found where dentine width exceeded 80 to 100 microns and the root canal fillings were tightly packed and without debris. Cementum
resorption
Resorption of the cementum was frequently found to be preceded, accompanied, or followed by resorption of the adjoining dentine and apparently did not depend directly on the type of filling material. Notwithstanding this fact, the filling material may indirectly influence resorption of the calcified tissues,
19
Fig. $0. Filling with Kerr cement; 30-day postoperative period. tissue (IPT), and dentinal cementum resorption (R). (Magnification,
Ingrowth of periodontal x180; reduced I,.)
as was seen in cases of cementum necrosis or ingrowth of periodontal tissue into the root canal. Necrotic cementum showed a definite tendency to be resorbed. This process started at the periodontal surface of the cementum and reached variable depths, even to the point of entirely removing the wall of the apical portion of the canal. However, no special features were noted in the resorption process that could be ascribed to the type of cement used. The ingrowing apical periodontal tissue, found in short fillings with blood clots in the apical canal, also induced severe resorptions, this time starting at the inner surface of the dentine. This type of response could occasionally be observed with all four cements, when the postoperative period was longer than 15 days. To exemplify the behavior of a specific cement, when Kerr sealer was used, cementum resorption started earlier and was more severe than when the other cements were used (Figs. 3 and 20), proba,bly because of the mild infiltration caused by this material, which allowed quicker ingrowth of the periapical tissue. REACTION OF THE ALVEOLAR BONE The alveolar fundus showed two types of reaction to t,he cement: (1) direct, due to the contact between the overfilled material and the alveolar bone, and (2) indirect, provoked by inflammatory changes of the periodontal ligament, caused by poor filling of the canal. Direct reaction Any of the cements, when overfilled and coming in direct contact with the alveolar fundus, caused necrosis of the superficial bone lamellae. In some cases,
Tissue reaction
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to root canal fillings
371
this necrosis was followed within 7 days by osteosclerosis of the underlying bone marrow. No specific reaction to the different cements was found, with the exception of Kerr sealer, which showed a greater tendency to scatter throughout the periodontal ligament rather than to adhere to the alveolar surface. Indirect
reaction
of the alveolar
fundus
When fillings remained short of the apex, the apical portion of the root canal was seen to be occupied by the pulp stump, tissue remnants, or blood clot. In some cases, these structures underwent polymorphonuclear leukocyte and macrophage infiltration or were invaded by ingrowing apical connective tissue. A periapical abscess, surrounded by granulomatous tissue, frequently developed after infiltration of the canal, inducing resorption of the alveolar surface and osteosclerosis of the underlying bone marrow. When marked ingrowth of the periodontal tissue took place, severe resorption of the dentine and cementum was frequently seen. Despite marked destruction of the apical end of the root, however, necrosis, resorption, or sclerosis of the alveolar bone was rarely observed, apposition of new bone lamellae being the most common finding. INFLUENCE
OF THE OPERATIVE
TECHNIQUE
The biologic material used in these experiments has been basically uniform, namely, the normal mesial root of the first lower molar. Therefore, the difference in responses was probably due to the type of cement and the technique used. Findings reported here show a wide range of responses, and experimental evidence appears to indicate that this diversity depends more on the technical approach than on the choice of filling material. Histologic studies showed, for instance, that different periapical tissue reactions can be obtained, even when the same cement is used, according to the type of filling made (short of the apex, flush to the apex, or overfilling). On the other hand, results were very similar with the four cements if debridement was thorough and the fillings were tightly packed and flush to the apex. This would indicate that none of the cements, per se was able to compensate for poor technique. Influence
of technique
on density
of the filling
Thorough d6bridement of the canal and tight packing of the cement were basic requirements for obtaining hermetic fillings. The presence of blood clot and of tissue remnants, which was a common finding because of the oval or fusiform shape of the canal, seriously hindered the accomplishment of hermetic fillings. In order to overcome this difficulty, a small amount of cement was introduced into the canal with a Hedstrijm file in a counterclockwise motion, in order to impregnate the canal walls and mix the cement with the debris. This later was removed by clockwise rotation of the file, after which the permanent filling was ma,de.
This technique yielded good results when zinc oxide-eugcnol and 3, were used ; conversely, Kerr and Grossman cements were more difficult to mix with the debris and were less adherent to the moist canal wall. The spatulation technique is likewise important in obtaining hermetic fillings of the canal; best results were achieved when thick cement was usc~l and spatulation was carefully accomplished. Influence resorption
of operutive technique of cementum
in the
necrosis
and
Excessive enlargement of the root canal during mechanical instrumentation caused reduction of the dentine layer. Under these circumstances, all the cements provoked necrosis of the cementum, which started at the cementodentinal junction and then spread toward the periodontal surface. As the dentine layer became thinner, it was found that the necrotic layer of cementum increased. Finally, when the entire cementum was necrotized, resorption induced by the periodontal ligament was frequently observed. Moreover, in specimens with thorough debridement of the canal, filled short of the apex, the remaining empty space was frequently occupied by a blood clot, which was rapidly invaded by ingrowing tissue coming from the periodontal ligament. This newly formed tissue showed a marked tendency to resorb dentine and cementum, starting from the canal wall. SUMMARY
AND
CONCLUSIONS
The response of periapical tissue to root canal fillings with zinc oxide-eugenol cement, Rickert sealer, Grossman sealer, and Nz was studied in 710 white rats between 60 and 90 days old. Root canal treatments were performed in the mesial root of the lower left first molar. Postoperative periods ranged from 1 to 90 days. The following conclusions were based on histologic studies: 1. Tested root canal cements showed good plasticity; no dimensional cha.nges could be detected after the filling was placed. 2. Grossman, Kerr, and N, Permanent cements did not adhere to the canal wall; zinc oxide-eugenol was only slightly adherent; N, Temporary showed the greatest adherence. 3. Zinc oxide-eugenol, Grossman, and N, Permanent cements, when mixed with debris, mostly provoked severe inflammatory infiltration; N, Temporary caused a mild reaction; Rickert sealer frequently induced moderate infiltration, ingrowth of periapical tissue, and resorption of the canal wall. 4. The most favorable tissue reaction was found in specimens with fillings short of the apex and with minimal injury of the remaining pulp stump. 5. All root canal cements tested, in cases of overfillings, showed a tendency to be resorbed. Resorption of compact overfilled masses, without debris, proceeded slowly. No polymorphonuclear leukocytes were observed, although giant cells were nearly always found. When the extruded root canal cement became mixed with tissue remnants, a severe inflammatory reaction was frequently seen. 6. When the cements directly contacted the alveolar surface, necrosis and resorption of the superficial bone lamellae frequently occurred. However, the
Tissue reaction
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Number 3
to root
canal
fillings
373
most severe resorptions were constantly associated with osteosclerosis of the underlying bone marrow. This response was indirectly induced by inflammation of the apical periodontal ligament, caused by poor d6bridement and filling of the canal. REFERENCES
1. Erausquin, J., and Muruzkbal, M.: Root Canal Fillings 2. 3. 4.
5. 6. 7. 8. 9.
10. 11. 12. 13. 14. 15. 16. 17.
18.
With Zinc Oxide-Eugenol Cement in the RatMolar,ORA~ SURG., ORAL MED.& ORALPATH. 24: 547.558,1967. Dixon. C. M.. and Rickert. U. G.: Histologic Verification of Results of Root-Canal Therapy_. in Ex&imental A.nimals.‘J. Am. Dent. A. 25: 1’781-1803. 1938. Gross&n, L. I.: Endodontic Practice, ed. 6, Philadelphia, 1965, Lea & Febiger, p. 354. American Dental Association: Council on Dental Therapeutics: Hazards of Formaldehyde Preparations for Single Treatment Procedures in Endodontics, N, and the R Method, J. Am. Dent. A. 64: 689-700, 1962. Sargenti. A., and Council on Dental Therapeutics: Notes and Comments, D. Abst. 10: 139240, ‘1965. Endodontic Snyder, D. E., Seltzer, S. and Moodnik, R.: Effects of N, in Experimental Therapy, ORAL SURG., ORAL MED. & ORAL PATH. 21: 635-656,1966. Erausquin, J., and Muruzabal, M.: A Method for Root Canal Treatment in the Molar of the Rat, ORAL SURG., ORAL MED. &ORAL PATH. 24: 540~546,1967. Tschamer, H. : Priifung einiger Wurzelfiillmaterialien auf ihre Eigenschaften, insbesondere der Abschlussdichte, Stoma 13: 172-192, 1960. Tschamer, H. : Vorlaufige klinisch-rontgenologisehe Kontrollergebnisse nach Wurzelkanalfiillungen mit den Wurzelfiillmitteln AH 26 (De Trey), Renium (Cardex), N2 (Sargenti) und der Kunstharzkombinierten Wurzelfiillmasse nach Riebler, Deutsche Zahnarztl. 18: 394-406, 1963. Erausquin, J., Muruzabal, M., Devoto, F. C. H., and Rikles, A.: Necrosis of the Periodontal Ligament in Root Canal Overfillings, J. D. Res. 45: 1084-1092, 1966. Sargenti, A., and Richter, S. L.: Rationalized Root Canal Treatment, New York, 1959, AGSA, Scientific Publications. Overdiek. H. F.: Zur Gewebsreaktion auf imolantierte Wurzelfiillmaterialien im Vernleieh a zum N2,‘Zahnarztl. Rdsch. 69: 402-406, 1960: Kuroiwa, K.: Experimental Study on Root Canal Filling Using New Filling Material, N2 and AN2, Tokyo D. Coll. Bull. Oral Path. 4: 45-74, 1960. Rappaport, H. M., Lilly, G. E., and Kapsimalis, P.: Toxicity of Endodontic filling Materials, ORAL SURG., ORAL MED. & ORAL PATH. 18: 785802, 1964. Stewart, G. G.: A Comparative Study of Three Root Canal Sealing Agents, ORAL SURG., ORAL MED. & ORAL PATH. 11: 1029-1041, 1174-1178, 1958. Guttuso, J. : Histopathologic Study of Rat Connective Tissue Responses to Endodontic Materials, ORAL SURG., ORAL MED. & ORAL PATH. 16: 713-727, 1963. Zerosi! C., Baratieri, A., and Amici, G.: Osservazioni istologiche sul comportamento dei tessuti periapicali dopo otturazione canalare con cement0 N2, Rass. Trim. di Odont. 40: 555584, 1959. Sargenti, A. : Zur Diskussion iiber die NB-Wurzelbehandlung, Schweiz. Monatsschr. Zahnh.
73: 127-132, 1963. 19. Rowe, A. H.: Treatment 20. Nicholls, E.: &sorbable
with N2 Root Canal Sealer, Brit. D. J. 117: 27-30, 1964. Canal Fillings, Including N2, in Grossman, L. I.: Transactions of the Third International Conference on Endodontics, Philadelphia, 1963, University of Pennsylvania Press, pp. 144-157. 21. Erausquin, J., and Muruzabal, M.: Necrosis of Cementum Induced by Root Canal Treatments in the Molar Teeth of Rats, Arch. Oral. Biol. 12: 1123-1132, 1967. Charms
2146.