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Pulp response in the rhesus monkey to “composite” dental restorative materials in unlined cavities
Pulp response in the rhesus monkey to “composite” dental restorative materials in unlined cavities Sat&h R. Rae, B.D.S., SCHOOL UNIVERSITY
OF DENTAL
M.S.,’
MEDICINE,
Pittsbwgh, DEPARTMENT
Pa. OF PEDODONTICS,
OF PITTSBURGH
An investigation was carried out to compare the effects of new composite restorative materials with those of zinc oxide and eugenol and unlined silicates. The results indicate that composite materials can be considered biologically acceptable but that they are attended by a mild and persistent inflammatory response when used in deep, unlined cavities. It is recommended that the composite resins be used clinically with a protective base or liner.
I
n the last few years increasing efforts have been made to produce improved restorative materials, particularly those with adhesive qualities. Though adhesion has not yet been achieved, two new restorative materials--Addent-%t and Dakort-have shown superior physical and chemical properties and merit bio-assays to evaluate their biologic compatibility. They have the advantage of possessing lower shrinkage and coefficient of thermal expansion, greater hardness and resistance to abrasion, higher compressive strength, and better translucence values than the conventional acrylic resins.l-* In contrast to silicates, they have virtually no solubility in oral fluids. At the time this work was initiated there were no published pulp studies involving these materials. A recent publication by St,anley and his co-workers2 reported that a Dakor prototype produced milder pulp reactions than Addentin terms of resolution of response over similar postoperative intervals. Though Based on a thesis submitted to the University of Rochester School of Medicine Dentistry in partial fulfillment of the requirements for the M.S. degree. *Assistant Professor of Pedodontics. t3M Company, St. Paul, Minn. $L.D. Caulk Company, Milford, Del.
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the base resins in both Adder&35 and Dakor appear to be chemically similar, they have different fillers. Whereas Addenthas glass beads as the major filler, along with some glass fibers, Dakor has synthetic calcium hydroxyapatite as the major ingredient. The present investigation was undertaken to provide information on the effect of these restorative materials in deep, unlined cavities, comparing their response under similar conditions to a mild control material, such as zinc oxide and eugenol, at one end of the scale and unlined silicates, which are known to have substantial irritating qualities, at the other end of the scale. An experimental formulation using the same ingredients as in Dakor, but with hydrophobed glass beads substituted for the calcium hydroxyapatite, was also tested to assessthe role of the latter filler on pulp response. A finding that the new composite materials are relatively nonirritating to the pulp would lend encouragement to the present direction of research and could result in new materials that can be employed without protective bases or liners, a procedure which at present not only takes valuable time, but also prevents adhesion between the restorative material and the tooth structure. One approach to the improvement of acrylic filling materials, according to Phillips1 and Buonocore,4 is to add inert fillers which, by reducing the amount of polymerizable material, substantially reduce setting shrinkage and also improve certain other physical properties. Early in 1966 the 3M Company produced a restorative material called Addentcontaining 70 per cent inorganic fillers, with an organic binder probably similar to the one synthesized by Bowen. Langeland and his coworker@ evaluated Addentclinically and histologically and concluded that the pulp response was similar to but not as severe as those caused by cold-curing plastic materials. In 1967 Stanley, Swerdlow, and Buonocore2 reported that a Dakor prototype produced better long-term pulp reactions than Addent-35. They also came to the conclusion that the recommended liner was not adequate to protect the pulp tissues from the irritating properties of Addent-35. On the other hand, Cotton and Leonard’ evaluated pulp response to Addentwithout a liner in rat molars and concluded that, with a few exceptions, the reactions were minimal. More recently, in 1968, Baume and Fiore-Donno studied histologically the effects of Addentin carious as well as intact human teeth and concluded that, unlike the group of teeth in which cavity liners were used, a calcium hydroxide base provided lasting protection against pulp injury up to 290 days. MATERIALS AND METHODS
Class V cavities were prepared in the cervical portion of the facial surfacee, of 230 intact teeth in rhesus monkeys which were immobilized by intramuscular injection of phenylcyclohexyl piperidine hydrochloride.*9 Following local ane&,he*Sernylan,
Parke Davis & Co., Detroit,
Mich.
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sia, a No. 35 inverted-cone carbide bur was used at approximately 12,000 r.p.m., with air and water stream as coolants. Forty-six teeth were restored with each of the following materials: (1) zinc oxide and eugenol, (2) silicate cement, (3) Dakor, (4) Addent-35, and (5) an experimental formulation which was a variant of Dakor in that the hydroxyapatite filler was replaced by silane-treated glass beads. The zinc oxide and eugenol material was prepared by combining zinc oxide, U.S.P. with eugenol U.S.P. at a ratio of 85 per cent by 15 per cent by weight, with 0.5 per cent zinc acetate added. Excess eugenol was squeezed out with an absorbent cloth, the resulting mix being similar to that used clinically for a temporary restoration. The silicate cement,” Dakor, and Addentwere used without a cavity liner or base, but the manufacturer’s instructions regarding manipulation of the materials were followed in other respects. With the exception of the experimental formulation, all the other materials are commercially available and hence their composition needs no further elaboration. Experimental
formulation
This formulation consisted of a paste and two liquids and contained the following ingredients by percentage weight: Organic binder, ae in Dakor, 33; methyl methacrylate monomer, 3; hydrophobed glass beads, 64; and a few tenths of a per cent of a thickening agent. Essentially, the mixture is the same as Dakor except that the synthetic calcium hydroxyapatite was replaced by hydrophobed glass beads. The purpose of using this material was to evaluate the contribution of the synthetic calcium hydroxyapatite. Postoperative intervals of 1, 4, and 12 weeks were used so that the early response, its development, and the rate of resolution of the lesion could be studied. At the end of each postoperative interval the teeth were carefully extracted, processed,l” and stained with hematoxylin and eosin. The intensity of the histopathologic response was evaluated by surveying the remaining dentine thickness in alternate serial sections of each specimen at x40 magnification with a calibrated grid in the ocular to determine which section or sections of each specimen presented the thinnest remaining dentine thickness between the floor of the cavity and the odontoblastic layer. Sections showing preparation artifacts were not included. The criteria utilized to interpret the histopathologic response are similar to those suggested by Stanley,ll> l2 with slight modifications. These consisted of measuring remaining dentine thickness as well as dentinal tubular length and the incidence as well as the amount of reparative dentine formed. A 0 to 3 degree scale was used to denote the amount of reparative dentine formed, where a grade 0 indicated no reparative dentine. The histopathologic characteristicsll> I2 were observed and recorded for each specimen of each category at the various postoperative intervals. Sections “New FilZing
Porcelain,
5. S. White,
1 Federal
St., Pittsburgh,
Pa.
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from each tooth showing the greatest intensity of response were used to obtain an average score for the group of teeth, for each histopathologie characteristic, and for each material. By average total response was meant the mean of the sum of the values for cellular displacement, superficial response, and deep response. The percentage of specimens with 2 or more degrees of average total response was computed and recorded for all three postoperative intervals. These values are considered to be indicative of trends toward resolution of the lesion. For each material the response was considered favorable if, after a postoperative interval of 12 weeks, there was a significant increase in the percentage of specimens with 1 degree or less of average total response and a significant decrease in the percentage of specimens with 2 degrees or more of average total response. Although composite materials are considered better than conventional resins and silicates in certain physical properties and esthetic qualities, their biologic qualities have not been fully assessed.Since there is a general agreement on the mild nature of zinc oxide and eugenol and the damaging effects of unlined silicates on the dental pulp, it was thought that if pulp response to the new and experimental restorative materials were intermediate to the two control materials, they could be considered biologically acceptable. RESULTS
The results are presented in Table I. The values for the ranges of remaining dentine thickness as well as the dentinal tubular length indicate a comparable spectrum of remaining dentine thicknesses for all categories at each postoperative interval, thereby eliminating the possibility of unintentional biasing of the results by the occurrence of a large number of specimens with remaining dentine thickness values that were either too small or too large. Zinc
oxide
and
eugenol
Teeth restored with zinc oxide and eugenol showed a minimal response. The average degree of intensity values for cellular displacement, superficial response, and deep response was less than all the other categories for each postoperative interval. In almost all cases the response was localized and confined to the area in the pulp corresponding to cut dentinal tubules at the floor of the cavity. Specimens showed a reduction of average intensity values from 1 degree to 0 degree by the end of the 1Zweek postoperative interval. Whereas the average amount of reparative dentine found was 1 degree for the 4-week period aa well as for the 12-week period, there was no evidence of abscessformation or foci of necrosis in this category. The predominating i&ammatory cells in the specimen representing a l-week postoperative interval were polymorphonuclear leukocytes, whereas those in the 4-week specimen were lymphocytes and a few scattered monoeytes and histiocytes.
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Table I. Summary of results of 184 specimens 1 Number
of specimens
Number
of animals
Zinc otide 11
and ezlgenol
10
)
Silicate
14
13
13
12
4
4
4
4
4
4
1
4
12
1
4
12
0.51 0.030.85
0.70 o.zo1.30
0.88 0.451.20
0.52 O.lO0.90
0.71 Q.201.50
0.66 0.151.00
0.55 0.030.90
0.73 0.201.30
0.94 0.541.20
0.57 O.lO1.00
0.74 0.201.50
0.73 0.151.10
1
0.5
0
2
1.5
0.5
Average degree of superficial response (0 to 4)
1
0.5
0
2
2.5
1.5
Average degree of deep response (0 to 4)
1
0.5
0
2
2.5
1.5
Postoperative
interval
(weeks)
Average R.D. thickness and ranges
(mm.)
Average dentinal tubular (mm.) and ranges
Iength
Average degree of cellular ment (0 to 4)
displace-
Percentage of specimens with reparative dentine (incidence/ amount, 0 to 3) Percentage vascular
of specimens with changes
0
50 1
14.2 1
0
53.8 1
41.6 1
54.5
40
28.5
46.1
61.5
58.3
Percentage of specimens with foci of necrosis
0
0
30.1
30.7
16.6
Percentage of specimens with abscesses
0
0
7.6
15.3
8.3
Percentage of specimens with 2” or more of average total response
18
0
92.3
69.2
8.3
Percentage of specimens with 1” or less of average total response
81.8
0
0
90
100
50
The percentage of specimens with 2 or more degrees of average total response was the lowest among all the categories while the percentage of specimens with 1 degree or less of average total response was the highest. The values are considered to indicat;e that the zinc oxide and eugenol category provided the most favorable response of the materials evaluated. A representative lesion is shown in Fig. 1. Silicate
The initial average intensity values were higher than all the other categories, in addition to which the lesions were not as well localized as in the zinc oxide and eugenol category but tended to be rather diffused. The average value for the amount of reparative dentine formed was 1 degree at the end of both the 4-week postoperative interval and the 1Zweek postoperative interval. The irregular and sparsely tubular nature of the reparative dentine with evidence of entrapped odontoblasts was considered indicative of disorganized odontoblastic activity due to continued irritation.
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Dakor
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Add.ent-35
materids
Experimental
12
9
4
4
4
4
4
4
12
1
4
12
0.70 0.351.00
0.55 0.201.10
0.57 0.041.00
0.72 0.201.10
0.65 Q.lO1.10
0.77 0.401.10
0.60 0.201.20
0.63 0.041.00
0.79 0.201.30
1.5
1
0
1.5
1
0
1
2
1.5
1
1.5
1.5
1.5
2
1
2
2
1
2
2
1.5
72.7 2
61.5 3
0
--69.2 2
76 3
0
66.6 1
60 --i-
75
22.2
46.6
11.1
20
11
4 1 0.56 o.zo1.00
0.61 Q.151.00
0.60 0.201.00
13
11
13
4
4
4
4
12
1
0.60 0.250.90
0.55 0.15. 0.90
0.62 O.lO1.10
0.64 0.151.10
0.64 0.251.00
0.60 0.15. 1.00
1
1
0
1.5
2
1.5
35.7
100
38.4
27.2
38
14.2
0
15.3
27.2
15.3
53.8 7.6
8.3
681
formulation
13
14
0
dental restorative
15
0
9.0
0
0
7.6
0
0
0
0
21.4
69.2
0
45.4
30.7
0
33.3
33.3
0
42.8
9
69
9
38.4
61
16.6
22.2
26
This category had the highest percentage of specimens showing evidence of foci of necrosis, except in the 12-week postoperative interval. The predominating inflammatory cells in the l-week postoperative interval were polymorphonuclear leukocytes, whereas lymphocytes, monocytes, and histiocytes predominated in the 4-week and the 1Zweek postoperative intervals. The percentage of specimens with 2 degrees or more of average total response was the highest among all the categories-indicative of the severity of the response. However, the percentage of specimens with 1 degree or less of average total response suggests that, unlike the other materials, the trend toward a decrease in the intensity of the response began in the period between 4 and 12 weeks. By the end of 12 weeks, 50 per cent of the specimens showed signs of resolution of the lesion. A representative lesion is shown in Fig. 2. Dakor
Teeth restored with Dakor had lower intensity values for initial response than all the other categories except zinc oxide and eugenol. Over a 4-week interval,
682
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Fig. 1. Specimen showing typical response to zinc oxide and eugenol (control) 4 weeks postoperatively. This shows 0.5 degree of superficial and deep inflammatory response. Note the reparative dentine formation (1 degree). Remaining dentine thickness 0.57 mm. (Hematoxylin and eosin stain. Magnification, x120.)
Pig. 8. Specimen showing representative response to silicate (control) 4 weeks postoperatively. Note disorganization of the odontoblastic zone, 2.5 degrees of superficial and deep tiammatory response, and vascular changes. Remaining dentine thickness, 0.50 mm. (ffematoxylin and eosin stain. Magnification, x120.)
although the average intensity values for cellular displacement remained the same, the average values for superficial and deep response increased from 1.5 degrees to 2 degrees. Over a B-week period, however, the values for cellular displacement dropped to 1 degree, indicating a decided trend toward resolution of the response. The percentage of specimens showing evidence of reparative dentine
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Fig. J. Specimen showing typical response to Dakor 4 weeks postoperatively. Note slight evidence of cellular displacement and 2 degrees of superficial and deep inflammatory response. Note also tubular quality and amount (2 degrees) of reparative dentine formation. Remaining dentine thickness, 0.46 mm. (Hematoxylin and eosin stain. Magnification, x120.)
formation (72.7 per cent) at the end of the 4-week postoperative interval was the highest among all the categories. At the end of 12 weeks 61.5 per cent of the specimens showed reparative dentine formation. The reparative dentine formed, in all cases, showed regularity and good tubular character. The percentage of specimens with vascular change shows an increase from 35.7 per cent at 1 week to 100 per cent at 4 weeks and a subsequent reduction to 38.4 per cent at 12 weeks. An increase in vascular supply prior to repair and resolution of tissue injury is an accepted biologic concept,13 and these results are indicative of the trend toward repair. The over-all response of the Dakor category can be considered intermediate to that of zinc oxide and eugenol and silicate. A representative lesion is shown in Fig. 3. Addent-
Teeth restored with Addenthad higher initial average intensity values than those restored with Dakor and were similar to those in which silicates were used. The average intensity values for cellular displacement and superficial response decreased in severity with time, suggesting a trend similar to that exhibited by the Dakor category. Values for the incidence, amount, and nature of the reparative dentine formation were similar to those of the Dakor category at the end of both the 4-week and 1Zweek postoperative intervals. A particularly significant factor here is that although the long-term values for Dakor and Addentare similar, the remaining dentine thickness in Dakor specimens was 100 microns smaller than in the Addentspecimens. The over-all response of the Addentcategory can also be considered intermediate to that of zinc oxide and eugenol and silicate. A representative lesion is shown in Fig. 4.
604 Rno
Fig. 4. Specimen showing typical response to Addent4 weeks postoperatively. Note 2 degrees of superficial and 2.5 degrees of deep inflammatory response, Note also irregular nature of reparative dentine and entrapped odontoblasts. Remaining dentine thickness, 0.61 mm. (Hematoxylin and eosin stain. Magnification, x115.)
Experimental
formulation
Teeth restored with this material showed initial and 4-week average intensity values comparable to those of Addent-35. However, at the end of 12 weeks, though the average intensity values for cellular displacement dropped to 0, resembling those of Addentand Dakor, the average intensity values for both superficial and deep response remained at 1.5 degrees, resembling those of the silicate group. The percentage of specimens showing, reparative dentine formation decreased from 66.6 per cent at the end of 4 weeks to 60 per cent at the end of 12 weeks, but the amount remained t.he same. This material did not show any evidence of eliciting abscess formation at any of the three postoperative intervals. However, the percentage of specimens with foci of necrosis at the end of 12 weeks was the highest among all the categories. The over-all response of this material was considered biologically unfavorable. A representative lesion is shown in Fig. 5. DISCUWON
During the course of describing the nature of type.2 Besides providing these composite resins, study.
this study several reports appeared in the literature the pulp response to Addent-356-s and a Dakor protoinformation regarding the biologie acceptability of their genera1 findings are similar to those of this
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Fig. 5. Specimenshowing typical responseto experimental material 4 weekspostoperatively. Note 2 degreesof superficial and deep in&mmatory response.Note also beginning of reparative dentine formation. Remaining dentine thickness, 0.48. (Hematoxylin and eosin stain. Magnification, x100.) For the type of cavity location employed in this study, the findings support those of Stanley and others 6l 2l ~2314-17 for human teeth and those of other investigatorsl*l 17-21for the teeth of various animals, in that the remaining dentine thickness would appear to be the most important single factor determining pulp response. While dentinal tubular length measurements were found to be greater than the direct remaining dentine thickness measurements, the conclusions to be drawn would be the same as with the latter, which are considerably easier to obtain and more precise. Both Dakor and Addentshowed a decrease in the intensity of the response over the experimental period. The rise in the intensity of average total response of 2 degrees or more between the l- and 4-week postoperative intervals with Dakor could be attributed to the leaching of irritating products from the resin mix, with their gradual penetration through dentine to reach the pulp. With Addent-35, the passage of the irritating products could have occurred earlier than with Dakor, thus giving a more intense response initially. The important fact here, however, is the more definite trend toward resolution shown by both of these materials, which would suggest a greater biologic acceptability than silicate, which had a higher proportion of responses with 2 degress or more of average total response and a smaller proportion of responses with 1 degree or less of average total response at the end of the 12-week postoperative interval. The experimental formulation was not considered as desirable as Addentand Dakor, since it had the lowest percentage increase in specimens with minimal or no response of any of the materials at the end of 12 weeks. The more favorable response of Dakor, compared to the experimental formulation, could be attributed to the presence of the synthetic calcium hydroxyapatite
686
Rao
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1971
tiller in Dakor. The basic hydroxyapatite probably serves to neutralize the toxic methacrylic acid. The failure to produce more severe generalized pulp reactions and the relative absence of pulp necrosis and abscessesin the rather deep cavities used in this study indicate the absence of ingredients strongly toxic to the pulp in any of the materials. While the present study indicates that the new composite resins, Addentand Dakor, are biologically acceptable, being milder than unlined silicates but more irritating than zinc oxide and eugenol, their use is attended with somewhat prolonged pulp reactions, although these are admittedly of a mild nature. It would be most desirable if resolution could be achieved at shorter postoperative intervals than demonstrated here. However, considering the great depths of cavities employed in this study, a restorative material would have to be essentially neutral to avoid a reaction. The fact that reactions were relatively mild, even in very deep cavities, indicates that these materials will probably present little hazard when employed with a protective base, as shown by Baume and Fiore-Donno.8 Since the problem of marginal leakage has been reduced but not eliminated,22l 23 the observed prolonged reactions noted with these materials may be attributable in part to this factor. It is apparent that the values for average cellular displacement and average degrees of superficial and deep response are closely related. Displacement of odontoblasts can be due to a variety of factors, among which is cavity preparation.24 Since cavity preparation was standardized and cavity depth comparable in this experiment, differences in superficial and deep response, which were important criteria for evaluation of the materials, may be attributed to differences in their irritational qualities. SUMMARY
Class V cavities with remaining dentine thicknesses of 0.7 mm. were used to compare the pulp response without liners of Addent-35, Dakor, zinc oxide and eugenol, silicate cements, and a variant of Dakor, in which the hydroxyapatite filler was replaced by hydrophobe-d glass beads to evaluate the contribution of the former. Postoperative intervals of 1, 4, and 12 weeks were used, with from nine to fifteen teeth per interval per material. Comparisons were made by noting the incidence and average intensities of cellular displacement into dentinal tubules, the inflammatory response in the superficial tissues (odontoblastic layer, zone of Weil, and cell-rich zone), and the deeper tissues of the pulp. Recorded also were incidence and amount of reparative dentine formation, vascular changes, foci of necrosis, and abscesses.Intensity of response was based on a 0 to 4 degree scale, with a response of less than 1 degree usually representing a few inflammatory cells. The zinc oxide and eugenol evoked a minimal response. The silicate cement and the experimental variant of Dakor produced the greatest inflammatory
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response, with the latter showing the lowest percentage of specimens with an average total response of 1 degree or less. Addentand Dakor produced comparable intermediate responses. With all materials, the response decreased in severity with time. Teeth filled with the composite materials showed the greatest amount of reparative dentine, suggesting that these materials provide a strong and continued stimulus for reparative dentine formation. The results indicate that, while composite materials can be considered biologically acceptable, they are attended by a mild and persistent inflammatory reaction which is evident even after 12 weeks when used in deep, unlined cavities. It is recommended that the composite resins should be used clinically with a protective base or liner. Grateful acknowledgment is extended to Dr. Basil G. Bibby for giving me the opportunity to participate in the graduate program at the Eastman Dental Center and to Dr. Michael G. Buonocore for providing the necessary guidance. I wish to thank Dr. Harold R. Stanley for his technical advice and continued encouragement. Acknowledgment is also extended to Mrs. Audrey Postava for typing this manuscript meticulously.
REFERENCES
6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
Phillips, Ralph: Recent Improvements in Dental Materials, J. Amer. Dent. Ass. 73: 82, 1966. Stanley, H. R., Swerdlow, J., and Buonocore, M. G.: Pulp Reactions to Anterior Restorative Materials, J. Amer. Dent. Ass. 75: 132-141, 1967. Buonocore, M. G., Matsui, A., and Yamaki, M.: Abrasion of Restorative Materials, New York Dent. J. 32: 395-406, 1966. Buonocore, M. G.: New Antenor Restorative Materials, Int. Dent. J. 18: 406-420, 1968. Bowen, R. L.: Dental Filling Material Comprising of Vinyl Silane Treated Fused Silica and a Binder Consisting of the Reaction Produet of Bisphenol and Glyeidyl Acrylate, U.S. patent 3, 066, 112, Nov. 27, 1962. Langeland, L. K., Guttuso, J., Jerome, D. R., and Langeland, K.: Histological and Clinical Comparison of Addent With Silicate Cements and Cold Curing Materials, J. Amer. Dent. Ass. 72: 373-385, 1966. Cotton, W. R., and Leonard, E. P.: Pulpal Response in Rat Molars to a New Restorative Material Without a Liner, J. Prosth. Dent. 18: 482, 1967. Baume. L. J.. and Fiore-Donno. G.: Resuonse of the Human Pulr,A to a New Restorative Material, J. Amer. Dent. Ass. $6: 1016-1522, 1968. Chen, G. M., and Weston, J. K.: The Analgesic and Anesthetic Effect of l-(1 Phenylcyclohexvl‘l Pineridine-HCl on the Monkey, Anesth. AnalE. 39: 132-137. 1962. Stanley, H. *R.., and Weaver, K.: A Technique for the “Preparation of Human Pulpal Tissues. In Finn, 8. B. (editor) : Biology of the Dental Pulp Organ: A Symposium, Birmingham, Ala., 1968, University of Alabama Press. Stanley, H. R.: Design for Human Pulp Study. Part I, OKAL Suno. 24: 633-647, 1968. Stanley, H. R.: Design for Human Pulp Study. Part II, ORAL BURG. 25: 756-764, 1968. Robbins, S. L.: Textbook of Pathology,-_ ed. 2, Philadelphia, _ , 1962, W. B. Saunders Company, chap. IV. Shroff, F. R.: Effects of Filling Materials on the Dental Pulp: An Histological Experimental Study With Special Reference to Synthetic Porcelain, New Zeal. Dent. J. 42: 145, 1946; 43: 35,1947; 42: 99,1946. Kramer. I.. and McLean. J.: Resuonse of the Human PulpA to Self-uolvmerizing a I ” Acrvlic ” Restorations, Brit. Dent.‘J. 92: 255, 281, 1952. Stanley, H. R.: Changing Concepts of the Dental Pulp Based on Recent Investigations, J. DC Dent. Sot. 37: 6-9, 1962. Langeland, K.: Tissue Changes in the Dental Pulp, Odont. T. 65: 239-385, 1957. Fish, E. W.: Reaction of the Dental Pulp to Peripheral Injury to Dentin, Proc. Roy. Sot. [Biol.] 108: 196, 1931. Mitchell, D. F., Buonocore, M. G., and Shazer, S.: Pulp Reaction to Silicate Cement and Other Materials in Relation to Cavity Depth, J. Dent. Res. 41: 591, 1962. ------I
~
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20. Seltzer, S., and Bender, I. B.: The Dental Pulp. Philadelphia, 1965, J. B. Lippincott Company, p. 158. Dentinal and Pulpal Changes Following Cavity 21. James, V., and Schour, I.: Early Preparation and Filling Materials in Dogs, ORAL SURG. 8: 1305, 1955. 22. Tsni, Y., and Buonocore, M. G.: Marginal Leakage and Penetration of Basio Fuchsin Dye in Anterior Restorative Materials, J. Amer. Dent. Ass. 78: 542-548, 1969. 23. Lee, H. L., Jr., and Swartz, M. L.: Scanning Electron Microscope Study of Composite Restorative Materials, J. Dent. Res. 49: 149-158, 1970. 24. Tiecke, R. W. (editor): Oral Pathology, New York, 1965, McGraw-Hill Book Company, Inc., pp. 95-125. Reprilzt requests to : Dr. Satish R. Rao Department of Pedodontics School of Dental Medicine University of Pittsburgh Pittsburgh, Pa. 15213
OF DENTAL
M.S.,’
MEDICINE,
Pittsbwgh, DEPARTMENT
Pa. OF PEDODONTICS,
OF PITTSBURGH
An investigation was carried out to compare the effects of new composite restorative materials with those of zinc oxide and eugenol and unlined silicates. The results indicate that composite materials can be considered biologically acceptable but that they are attended by a mild and persistent inflammatory response when used in deep, unlined cavities. It is recommended that the composite resins be used clinically with a protective base or liner.
I
n the last few years increasing efforts have been made to produce improved restorative materials, particularly those with adhesive qualities. Though adhesion has not yet been achieved, two new restorative materials--Addent-%t and Dakort-have shown superior physical and chemical properties and merit bio-assays to evaluate their biologic compatibility. They have the advantage of possessing lower shrinkage and coefficient of thermal expansion, greater hardness and resistance to abrasion, higher compressive strength, and better translucence values than the conventional acrylic resins.l-* In contrast to silicates, they have virtually no solubility in oral fluids. At the time this work was initiated there were no published pulp studies involving these materials. A recent publication by St,anley and his co-workers2 reported that a Dakor prototype produced milder pulp reactions than Addentin terms of resolution of response over similar postoperative intervals. Though Based on a thesis submitted to the University of Rochester School of Medicine Dentistry in partial fulfillment of the requirements for the M.S. degree. *Assistant Professor of Pedodontics. t3M Company, St. Paul, Minn. $L.D. Caulk Company, Milford, Del.
676
and
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the base resins in both Adder&35 and Dakor appear to be chemically similar, they have different fillers. Whereas Addenthas glass beads as the major filler, along with some glass fibers, Dakor has synthetic calcium hydroxyapatite as the major ingredient. The present investigation was undertaken to provide information on the effect of these restorative materials in deep, unlined cavities, comparing their response under similar conditions to a mild control material, such as zinc oxide and eugenol, at one end of the scale and unlined silicates, which are known to have substantial irritating qualities, at the other end of the scale. An experimental formulation using the same ingredients as in Dakor, but with hydrophobed glass beads substituted for the calcium hydroxyapatite, was also tested to assessthe role of the latter filler on pulp response. A finding that the new composite materials are relatively nonirritating to the pulp would lend encouragement to the present direction of research and could result in new materials that can be employed without protective bases or liners, a procedure which at present not only takes valuable time, but also prevents adhesion between the restorative material and the tooth structure. One approach to the improvement of acrylic filling materials, according to Phillips1 and Buonocore,4 is to add inert fillers which, by reducing the amount of polymerizable material, substantially reduce setting shrinkage and also improve certain other physical properties. Early in 1966 the 3M Company produced a restorative material called Addentcontaining 70 per cent inorganic fillers, with an organic binder probably similar to the one synthesized by Bowen. Langeland and his coworker@ evaluated Addentclinically and histologically and concluded that the pulp response was similar to but not as severe as those caused by cold-curing plastic materials. In 1967 Stanley, Swerdlow, and Buonocore2 reported that a Dakor prototype produced better long-term pulp reactions than Addent-35. They also came to the conclusion that the recommended liner was not adequate to protect the pulp tissues from the irritating properties of Addent-35. On the other hand, Cotton and Leonard’ evaluated pulp response to Addentwithout a liner in rat molars and concluded that, with a few exceptions, the reactions were minimal. More recently, in 1968, Baume and Fiore-Donno studied histologically the effects of Addentin carious as well as intact human teeth and concluded that, unlike the group of teeth in which cavity liners were used, a calcium hydroxide base provided lasting protection against pulp injury up to 290 days. MATERIALS AND METHODS
Class V cavities were prepared in the cervical portion of the facial surfacee, of 230 intact teeth in rhesus monkeys which were immobilized by intramuscular injection of phenylcyclohexyl piperidine hydrochloride.*9 Following local ane&,he*Sernylan,
Parke Davis & Co., Detroit,
Mich.
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sia, a No. 35 inverted-cone carbide bur was used at approximately 12,000 r.p.m., with air and water stream as coolants. Forty-six teeth were restored with each of the following materials: (1) zinc oxide and eugenol, (2) silicate cement, (3) Dakor, (4) Addent-35, and (5) an experimental formulation which was a variant of Dakor in that the hydroxyapatite filler was replaced by silane-treated glass beads. The zinc oxide and eugenol material was prepared by combining zinc oxide, U.S.P. with eugenol U.S.P. at a ratio of 85 per cent by 15 per cent by weight, with 0.5 per cent zinc acetate added. Excess eugenol was squeezed out with an absorbent cloth, the resulting mix being similar to that used clinically for a temporary restoration. The silicate cement,” Dakor, and Addentwere used without a cavity liner or base, but the manufacturer’s instructions regarding manipulation of the materials were followed in other respects. With the exception of the experimental formulation, all the other materials are commercially available and hence their composition needs no further elaboration. Experimental
formulation
This formulation consisted of a paste and two liquids and contained the following ingredients by percentage weight: Organic binder, ae in Dakor, 33; methyl methacrylate monomer, 3; hydrophobed glass beads, 64; and a few tenths of a per cent of a thickening agent. Essentially, the mixture is the same as Dakor except that the synthetic calcium hydroxyapatite was replaced by hydrophobed glass beads. The purpose of using this material was to evaluate the contribution of the synthetic calcium hydroxyapatite. Postoperative intervals of 1, 4, and 12 weeks were used so that the early response, its development, and the rate of resolution of the lesion could be studied. At the end of each postoperative interval the teeth were carefully extracted, processed,l” and stained with hematoxylin and eosin. The intensity of the histopathologic response was evaluated by surveying the remaining dentine thickness in alternate serial sections of each specimen at x40 magnification with a calibrated grid in the ocular to determine which section or sections of each specimen presented the thinnest remaining dentine thickness between the floor of the cavity and the odontoblastic layer. Sections showing preparation artifacts were not included. The criteria utilized to interpret the histopathologic response are similar to those suggested by Stanley,ll> l2 with slight modifications. These consisted of measuring remaining dentine thickness as well as dentinal tubular length and the incidence as well as the amount of reparative dentine formed. A 0 to 3 degree scale was used to denote the amount of reparative dentine formed, where a grade 0 indicated no reparative dentine. The histopathologic characteristicsll> I2 were observed and recorded for each specimen of each category at the various postoperative intervals. Sections “New FilZing
Porcelain,
5. S. White,
1 Federal
St., Pittsburgh,
Pa.
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from each tooth showing the greatest intensity of response were used to obtain an average score for the group of teeth, for each histopathologie characteristic, and for each material. By average total response was meant the mean of the sum of the values for cellular displacement, superficial response, and deep response. The percentage of specimens with 2 or more degrees of average total response was computed and recorded for all three postoperative intervals. These values are considered to be indicative of trends toward resolution of the lesion. For each material the response was considered favorable if, after a postoperative interval of 12 weeks, there was a significant increase in the percentage of specimens with 1 degree or less of average total response and a significant decrease in the percentage of specimens with 2 degrees or more of average total response. Although composite materials are considered better than conventional resins and silicates in certain physical properties and esthetic qualities, their biologic qualities have not been fully assessed.Since there is a general agreement on the mild nature of zinc oxide and eugenol and the damaging effects of unlined silicates on the dental pulp, it was thought that if pulp response to the new and experimental restorative materials were intermediate to the two control materials, they could be considered biologically acceptable. RESULTS
The results are presented in Table I. The values for the ranges of remaining dentine thickness as well as the dentinal tubular length indicate a comparable spectrum of remaining dentine thicknesses for all categories at each postoperative interval, thereby eliminating the possibility of unintentional biasing of the results by the occurrence of a large number of specimens with remaining dentine thickness values that were either too small or too large. Zinc
oxide
and
eugenol
Teeth restored with zinc oxide and eugenol showed a minimal response. The average degree of intensity values for cellular displacement, superficial response, and deep response was less than all the other categories for each postoperative interval. In almost all cases the response was localized and confined to the area in the pulp corresponding to cut dentinal tubules at the floor of the cavity. Specimens showed a reduction of average intensity values from 1 degree to 0 degree by the end of the 1Zweek postoperative interval. Whereas the average amount of reparative dentine found was 1 degree for the 4-week period aa well as for the 12-week period, there was no evidence of abscessformation or foci of necrosis in this category. The predominating i&ammatory cells in the specimen representing a l-week postoperative interval were polymorphonuclear leukocytes, whereas those in the 4-week specimen were lymphocytes and a few scattered monoeytes and histiocytes.
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Table I. Summary of results of 184 specimens 1 Number
of specimens
Number
of animals
Zinc otide 11
and ezlgenol
10
)
Silicate
14
13
13
12
4
4
4
4
4
4
1
4
12
1
4
12
0.51 0.030.85
0.70 o.zo1.30
0.88 0.451.20
0.52 O.lO0.90
0.71 Q.201.50
0.66 0.151.00
0.55 0.030.90
0.73 0.201.30
0.94 0.541.20
0.57 O.lO1.00
0.74 0.201.50
0.73 0.151.10
1
0.5
0
2
1.5
0.5
Average degree of superficial response (0 to 4)
1
0.5
0
2
2.5
1.5
Average degree of deep response (0 to 4)
1
0.5
0
2
2.5
1.5
Postoperative
interval
(weeks)
Average R.D. thickness and ranges
(mm.)
Average dentinal tubular (mm.) and ranges
Iength
Average degree of cellular ment (0 to 4)
displace-
Percentage of specimens with reparative dentine (incidence/ amount, 0 to 3) Percentage vascular
of specimens with changes
0
50 1
14.2 1
0
53.8 1
41.6 1
54.5
40
28.5
46.1
61.5
58.3
Percentage of specimens with foci of necrosis
0
0
30.1
30.7
16.6
Percentage of specimens with abscesses
0
0
7.6
15.3
8.3
Percentage of specimens with 2” or more of average total response
18
0
92.3
69.2
8.3
Percentage of specimens with 1” or less of average total response
81.8
0
0
90
100
50
The percentage of specimens with 2 or more degrees of average total response was the lowest among all the categories while the percentage of specimens with 1 degree or less of average total response was the highest. The values are considered to indicat;e that the zinc oxide and eugenol category provided the most favorable response of the materials evaluated. A representative lesion is shown in Fig. 1. Silicate
The initial average intensity values were higher than all the other categories, in addition to which the lesions were not as well localized as in the zinc oxide and eugenol category but tended to be rather diffused. The average value for the amount of reparative dentine formed was 1 degree at the end of both the 4-week postoperative interval and the 1Zweek postoperative interval. The irregular and sparsely tubular nature of the reparative dentine with evidence of entrapped odontoblasts was considered indicative of disorganized odontoblastic activity due to continued irritation.
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Dakor
1
Add.ent-35
materids
Experimental
12
9
4
4
4
4
4
4
12
1
4
12
0.70 0.351.00
0.55 0.201.10
0.57 0.041.00
0.72 0.201.10
0.65 Q.lO1.10
0.77 0.401.10
0.60 0.201.20
0.63 0.041.00
0.79 0.201.30
1.5
1
0
1.5
1
0
1
2
1.5
1
1.5
1.5
1.5
2
1
2
2
1
2
2
1.5
72.7 2
61.5 3
0
--69.2 2
76 3
0
66.6 1
60 --i-
75
22.2
46.6
11.1
20
11
4 1 0.56 o.zo1.00
0.61 Q.151.00
0.60 0.201.00
13
11
13
4
4
4
4
12
1
0.60 0.250.90
0.55 0.15. 0.90
0.62 O.lO1.10
0.64 0.151.10
0.64 0.251.00
0.60 0.15. 1.00
1
1
0
1.5
2
1.5
35.7
100
38.4
27.2
38
14.2
0
15.3
27.2
15.3
53.8 7.6
8.3
681
formulation
13
14
0
dental restorative
15
0
9.0
0
0
7.6
0
0
0
0
21.4
69.2
0
45.4
30.7
0
33.3
33.3
0
42.8
9
69
9
38.4
61
16.6
22.2
26
This category had the highest percentage of specimens showing evidence of foci of necrosis, except in the 12-week postoperative interval. The predominating inflammatory cells in the l-week postoperative interval were polymorphonuclear leukocytes, whereas lymphocytes, monocytes, and histiocytes predominated in the 4-week and the 1Zweek postoperative intervals. The percentage of specimens with 2 degrees or more of average total response was the highest among all the categories-indicative of the severity of the response. However, the percentage of specimens with 1 degree or less of average total response suggests that, unlike the other materials, the trend toward a decrease in the intensity of the response began in the period between 4 and 12 weeks. By the end of 12 weeks, 50 per cent of the specimens showed signs of resolution of the lesion. A representative lesion is shown in Fig. 2. Dakor
Teeth restored with Dakor had lower intensity values for initial response than all the other categories except zinc oxide and eugenol. Over a 4-week interval,
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Fig. 1. Specimen showing typical response to zinc oxide and eugenol (control) 4 weeks postoperatively. This shows 0.5 degree of superficial and deep inflammatory response. Note the reparative dentine formation (1 degree). Remaining dentine thickness 0.57 mm. (Hematoxylin and eosin stain. Magnification, x120.)
Pig. 8. Specimen showing representative response to silicate (control) 4 weeks postoperatively. Note disorganization of the odontoblastic zone, 2.5 degrees of superficial and deep tiammatory response, and vascular changes. Remaining dentine thickness, 0.50 mm. (ffematoxylin and eosin stain. Magnification, x120.)
although the average intensity values for cellular displacement remained the same, the average values for superficial and deep response increased from 1.5 degrees to 2 degrees. Over a B-week period, however, the values for cellular displacement dropped to 1 degree, indicating a decided trend toward resolution of the response. The percentage of specimens showing evidence of reparative dentine
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Fig. J. Specimen showing typical response to Dakor 4 weeks postoperatively. Note slight evidence of cellular displacement and 2 degrees of superficial and deep inflammatory response. Note also tubular quality and amount (2 degrees) of reparative dentine formation. Remaining dentine thickness, 0.46 mm. (Hematoxylin and eosin stain. Magnification, x120.)
formation (72.7 per cent) at the end of the 4-week postoperative interval was the highest among all the categories. At the end of 12 weeks 61.5 per cent of the specimens showed reparative dentine formation. The reparative dentine formed, in all cases, showed regularity and good tubular character. The percentage of specimens with vascular change shows an increase from 35.7 per cent at 1 week to 100 per cent at 4 weeks and a subsequent reduction to 38.4 per cent at 12 weeks. An increase in vascular supply prior to repair and resolution of tissue injury is an accepted biologic concept,13 and these results are indicative of the trend toward repair. The over-all response of the Dakor category can be considered intermediate to that of zinc oxide and eugenol and silicate. A representative lesion is shown in Fig. 3. Addent-
Teeth restored with Addenthad higher initial average intensity values than those restored with Dakor and were similar to those in which silicates were used. The average intensity values for cellular displacement and superficial response decreased in severity with time, suggesting a trend similar to that exhibited by the Dakor category. Values for the incidence, amount, and nature of the reparative dentine formation were similar to those of the Dakor category at the end of both the 4-week and 1Zweek postoperative intervals. A particularly significant factor here is that although the long-term values for Dakor and Addentare similar, the remaining dentine thickness in Dakor specimens was 100 microns smaller than in the Addentspecimens. The over-all response of the Addentcategory can also be considered intermediate to that of zinc oxide and eugenol and silicate. A representative lesion is shown in Fig. 4.
604 Rno
Fig. 4. Specimen showing typical response to Addent4 weeks postoperatively. Note 2 degrees of superficial and 2.5 degrees of deep inflammatory response, Note also irregular nature of reparative dentine and entrapped odontoblasts. Remaining dentine thickness, 0.61 mm. (Hematoxylin and eosin stain. Magnification, x115.)
Experimental
formulation
Teeth restored with this material showed initial and 4-week average intensity values comparable to those of Addent-35. However, at the end of 12 weeks, though the average intensity values for cellular displacement dropped to 0, resembling those of Addentand Dakor, the average intensity values for both superficial and deep response remained at 1.5 degrees, resembling those of the silicate group. The percentage of specimens showing, reparative dentine formation decreased from 66.6 per cent at the end of 4 weeks to 60 per cent at the end of 12 weeks, but the amount remained t.he same. This material did not show any evidence of eliciting abscess formation at any of the three postoperative intervals. However, the percentage of specimens with foci of necrosis at the end of 12 weeks was the highest among all the categories. The over-all response of this material was considered biologically unfavorable. A representative lesion is shown in Fig. 5. DISCUWON
During the course of describing the nature of type.2 Besides providing these composite resins, study.
this study several reports appeared in the literature the pulp response to Addent-356-s and a Dakor protoinformation regarding the biologie acceptability of their genera1 findings are similar to those of this
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Fig. 5. Specimenshowing typical responseto experimental material 4 weekspostoperatively. Note 2 degreesof superficial and deep in&mmatory response.Note also beginning of reparative dentine formation. Remaining dentine thickness, 0.48. (Hematoxylin and eosin stain. Magnification, x100.) For the type of cavity location employed in this study, the findings support those of Stanley and others 6l 2l ~2314-17 for human teeth and those of other investigatorsl*l 17-21for the teeth of various animals, in that the remaining dentine thickness would appear to be the most important single factor determining pulp response. While dentinal tubular length measurements were found to be greater than the direct remaining dentine thickness measurements, the conclusions to be drawn would be the same as with the latter, which are considerably easier to obtain and more precise. Both Dakor and Addentshowed a decrease in the intensity of the response over the experimental period. The rise in the intensity of average total response of 2 degrees or more between the l- and 4-week postoperative intervals with Dakor could be attributed to the leaching of irritating products from the resin mix, with their gradual penetration through dentine to reach the pulp. With Addent-35, the passage of the irritating products could have occurred earlier than with Dakor, thus giving a more intense response initially. The important fact here, however, is the more definite trend toward resolution shown by both of these materials, which would suggest a greater biologic acceptability than silicate, which had a higher proportion of responses with 2 degress or more of average total response and a smaller proportion of responses with 1 degree or less of average total response at the end of the 12-week postoperative interval. The experimental formulation was not considered as desirable as Addentand Dakor, since it had the lowest percentage increase in specimens with minimal or no response of any of the materials at the end of 12 weeks. The more favorable response of Dakor, compared to the experimental formulation, could be attributed to the presence of the synthetic calcium hydroxyapatite
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tiller in Dakor. The basic hydroxyapatite probably serves to neutralize the toxic methacrylic acid. The failure to produce more severe generalized pulp reactions and the relative absence of pulp necrosis and abscessesin the rather deep cavities used in this study indicate the absence of ingredients strongly toxic to the pulp in any of the materials. While the present study indicates that the new composite resins, Addentand Dakor, are biologically acceptable, being milder than unlined silicates but more irritating than zinc oxide and eugenol, their use is attended with somewhat prolonged pulp reactions, although these are admittedly of a mild nature. It would be most desirable if resolution could be achieved at shorter postoperative intervals than demonstrated here. However, considering the great depths of cavities employed in this study, a restorative material would have to be essentially neutral to avoid a reaction. The fact that reactions were relatively mild, even in very deep cavities, indicates that these materials will probably present little hazard when employed with a protective base, as shown by Baume and Fiore-Donno.8 Since the problem of marginal leakage has been reduced but not eliminated,22l 23 the observed prolonged reactions noted with these materials may be attributable in part to this factor. It is apparent that the values for average cellular displacement and average degrees of superficial and deep response are closely related. Displacement of odontoblasts can be due to a variety of factors, among which is cavity preparation.24 Since cavity preparation was standardized and cavity depth comparable in this experiment, differences in superficial and deep response, which were important criteria for evaluation of the materials, may be attributed to differences in their irritational qualities. SUMMARY
Class V cavities with remaining dentine thicknesses of 0.7 mm. were used to compare the pulp response without liners of Addent-35, Dakor, zinc oxide and eugenol, silicate cements, and a variant of Dakor, in which the hydroxyapatite filler was replaced by hydrophobe-d glass beads to evaluate the contribution of the former. Postoperative intervals of 1, 4, and 12 weeks were used, with from nine to fifteen teeth per interval per material. Comparisons were made by noting the incidence and average intensities of cellular displacement into dentinal tubules, the inflammatory response in the superficial tissues (odontoblastic layer, zone of Weil, and cell-rich zone), and the deeper tissues of the pulp. Recorded also were incidence and amount of reparative dentine formation, vascular changes, foci of necrosis, and abscesses.Intensity of response was based on a 0 to 4 degree scale, with a response of less than 1 degree usually representing a few inflammatory cells. The zinc oxide and eugenol evoked a minimal response. The silicate cement and the experimental variant of Dakor produced the greatest inflammatory
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Effects of “compositef’
31 5
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response, with the latter showing the lowest percentage of specimens with an average total response of 1 degree or less. Addentand Dakor produced comparable intermediate responses. With all materials, the response decreased in severity with time. Teeth filled with the composite materials showed the greatest amount of reparative dentine, suggesting that these materials provide a strong and continued stimulus for reparative dentine formation. The results indicate that, while composite materials can be considered biologically acceptable, they are attended by a mild and persistent inflammatory reaction which is evident even after 12 weeks when used in deep, unlined cavities. It is recommended that the composite resins should be used clinically with a protective base or liner. Grateful acknowledgment is extended to Dr. Basil G. Bibby for giving me the opportunity to participate in the graduate program at the Eastman Dental Center and to Dr. Michael G. Buonocore for providing the necessary guidance. I wish to thank Dr. Harold R. Stanley for his technical advice and continued encouragement. Acknowledgment is also extended to Mrs. Audrey Postava for typing this manuscript meticulously.
REFERENCES
6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
Phillips, Ralph: Recent Improvements in Dental Materials, J. Amer. Dent. Ass. 73: 82, 1966. Stanley, H. R., Swerdlow, J., and Buonocore, M. G.: Pulp Reactions to Anterior Restorative Materials, J. Amer. Dent. Ass. 75: 132-141, 1967. Buonocore, M. G., Matsui, A., and Yamaki, M.: Abrasion of Restorative Materials, New York Dent. J. 32: 395-406, 1966. Buonocore, M. G.: New Antenor Restorative Materials, Int. Dent. J. 18: 406-420, 1968. Bowen, R. L.: Dental Filling Material Comprising of Vinyl Silane Treated Fused Silica and a Binder Consisting of the Reaction Produet of Bisphenol and Glyeidyl Acrylate, U.S. patent 3, 066, 112, Nov. 27, 1962. Langeland, L. K., Guttuso, J., Jerome, D. R., and Langeland, K.: Histological and Clinical Comparison of Addent With Silicate Cements and Cold Curing Materials, J. Amer. Dent. Ass. 72: 373-385, 1966. Cotton, W. R., and Leonard, E. P.: Pulpal Response in Rat Molars to a New Restorative Material Without a Liner, J. Prosth. Dent. 18: 482, 1967. Baume. L. J.. and Fiore-Donno. G.: Resuonse of the Human Pulr,A to a New Restorative Material, J. Amer. Dent. Ass. $6: 1016-1522, 1968. Chen, G. M., and Weston, J. K.: The Analgesic and Anesthetic Effect of l-(1 Phenylcyclohexvl‘l Pineridine-HCl on the Monkey, Anesth. AnalE. 39: 132-137. 1962. Stanley, H. *R.., and Weaver, K.: A Technique for the “Preparation of Human Pulpal Tissues. In Finn, 8. B. (editor) : Biology of the Dental Pulp Organ: A Symposium, Birmingham, Ala., 1968, University of Alabama Press. Stanley, H. R.: Design for Human Pulp Study. Part I, OKAL Suno. 24: 633-647, 1968. Stanley, H. R.: Design for Human Pulp Study. Part II, ORAL BURG. 25: 756-764, 1968. Robbins, S. L.: Textbook of Pathology,-_ ed. 2, Philadelphia, _ , 1962, W. B. Saunders Company, chap. IV. Shroff, F. R.: Effects of Filling Materials on the Dental Pulp: An Histological Experimental Study With Special Reference to Synthetic Porcelain, New Zeal. Dent. J. 42: 145, 1946; 43: 35,1947; 42: 99,1946. Kramer. I.. and McLean. J.: Resuonse of the Human PulpA to Self-uolvmerizing a I ” Acrvlic ” Restorations, Brit. Dent.‘J. 92: 255, 281, 1952. Stanley, H. R.: Changing Concepts of the Dental Pulp Based on Recent Investigations, J. DC Dent. Sot. 37: 6-9, 1962. Langeland, K.: Tissue Changes in the Dental Pulp, Odont. T. 65: 239-385, 1957. Fish, E. W.: Reaction of the Dental Pulp to Peripheral Injury to Dentin, Proc. Roy. Sot. [Biol.] 108: 196, 1931. Mitchell, D. F., Buonocore, M. G., and Shazer, S.: Pulp Reaction to Silicate Cement and Other Materials in Relation to Cavity Depth, J. Dent. Res. 41: 591, 1962. ------I
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20. Seltzer, S., and Bender, I. B.: The Dental Pulp. Philadelphia, 1965, J. B. Lippincott Company, p. 158. Dentinal and Pulpal Changes Following Cavity 21. James, V., and Schour, I.: Early Preparation and Filling Materials in Dogs, ORAL SURG. 8: 1305, 1955. 22. Tsni, Y., and Buonocore, M. G.: Marginal Leakage and Penetration of Basio Fuchsin Dye in Anterior Restorative Materials, J. Amer. Dent. Ass. 78: 542-548, 1969. 23. Lee, H. L., Jr., and Swartz, M. L.: Scanning Electron Microscope Study of Composite Restorative Materials, J. Dent. Res. 49: 149-158, 1970. 24. Tiecke, R. W. (editor): Oral Pathology, New York, 1965, McGraw-Hill Book Company, Inc., pp. 95-125. Reprilzt requests to : Dr. Satish R. Rao Department of Pedodontics School of Dental Medicine University of Pittsburgh Pittsburgh, Pa. 15213