0099-2399/92/1810-0473/$03.00/0 JOURNAL OF ENDODONTICS Copyright © 1992 by The American Association of Endodontists
Printed in U.S.A. VOL. 18, NO. 10, OCTOBER1992
SCIENTIFIC ARTICLES MicroleakagemFull Crowns and the Dental Pulp Melvin Goldman, DDS, Pinit Laosonthorn, DDS, and Robed R. White, DMD
directly into the pulp chamber. Tjan and Chiu (7) reported a similar study in which crowns were cemented on natural teeth as well as the four cores mentioned above. The results were the same, and their concern for the pulp was discussed. Thus, the "unimpeded lethal highways" seem to be open and available. The purpose of this study was to try to determine whether or not any of three crown margin preparation techniques could have an effect on microleakage since various cements and protective agents seem to be unable to 9revent microleakage.
Recent studies have described microleakage under full crowns cemented with several different cements. This study tested three different types of crown margin preparationsma chamfer, a shoulder, and a shoulder plus a bevel to determine whether or not the margin preparation could affect microleakage. All crowns were cemented with zinc phosphate cement. The crowns were tested for leakage in thermocycled dye. All crowns demonstrated significant leakage following the path of the dentinal tubules into the pulp. This could possibly be one of the causes of pulpal inflammation and even pulpal death under full crowns.
MATERIALS AND M E T H O D S Thirty freshly extracted molar teeth either noncarious or with small restorations were stored in deionized water. The teeth were mounted in acrylic resin blocks and divided into three groups. Group 1 was prepared with a full shoulder. Group 2 was prepared with a chamfer. Group 3 was prepared with a shoulder and a bevel. The teeth were prepared with diamond stones in a highspeed handpiece and copious water spray. The occlusal surface of each tooth was prepared to form a flat plane buccolingually and mesiodistally. The height of the preparation was standardized at 4.5 m m measured from the gingival shoulder to the occlusal plane. The axial walls were tapered 5 to 10 degrees toward the occlusal (Fig. 1).
In 1973 Naidorf(1), in discussing the relationship of infection and inflammation of the pulp and full crowns, asked "How many of us remember to point out that these beautifully cut tubules are unimpeded lethal highways leading to pulp necrosis following final cementation...?" Certainly, these words must give us pause. Recent literature indicates that there are those who are studying this aspect of pulpal inflammation. Mondelli et al. (2) observed the penetration of radioisotopes around the margins of full crowns cemented with zinc phosphate cement and various protective agents and found that they all leaked. Larson and Jensen (3) found that all crowns leaked after thermocycling and that there was no difference due to aging. Tjan et al. (4) found that all crowns cemented using zinc phosphate or polycarboxylate cements leaked both at the cement metal and cement tooth interface, with or without thermocycling. Kawamura et al. (5) used glass iohomer cement in addition to the zinc phosphate and polycarboxylate and found that "none of the current luting agents routinely prevent marginal leakage of cast restorations." Laosonthorn (6) reported leakage after thermocycling crowns cemented with zinc phosphate, glass ionomer, and a resin cement on natural teeth as well as teeth with cores of composite, gold, amalgam, and glass ionomer. During the evaluation of the specimens in that study, it was noted, especially in the case of the natural tooth, that, in addition to leakage that extended to varying degrees coronally, there was a leakage pattern that extended apically following the dentinal tubules
Cast Crown Construction
After tooth preparation, an impression was made using a polyether impression material (Impregum; ESPE Premier, Norristown, PA). Casts were made using type III dental stone (Die-Keen; Columbus Dental Stone, St. Louis, MO). Two layers of die spacer (Blue Die Spacer; Belle De St. Clairs, Chatsworth, CA) were applied, yielding an additional thickness of 20 to 25 #m to each die. A light coat of separating medium (Lubritex; Whip Mix Corp., Louisville, KY) was added after the die spacer dried. A dip wax technique (Belle De St. Clairs) was used to fabricate the wax pattern. The pattern was cylindrical in shape with a flat occlusal surface and an average thickness of 0.4 mm. The patterns were invested with phosphate-bonded investment (Hi-Temp;
Goldman et al.
Journal of Endodontics
FIG 1. Typical preparation measured from shoulder to occlusal surface.
F~G2. Tooth and crown are completely encased in epoxy resin and then sliced into three sections.
Whip-Mix Corp.) and cast using nickel-chrome alloy (Rexillium III; Rx Jeneric, Wallingford, CT). The castings were allowed to bench cool completely before divestment.
Cementation All crowns were tried on the prepared teeth and examined with a stereomicroscope to determine their adaptation and fit. The crowns were air-abraded with 50-#m diameter aluminous oxide powder for l0 s, to clean and standardize the texture of the internal surface. All crowns were cemented with zinc phosphate cement (S. S. White Zinc Improved; S. S. White, Holmdel, N J). The cement was mixed (a powder to liquid ratio = 1.4 g:0.6 ml) to a good homogeneous consistency considered ideal for cementation of castings, all according to the manufacturer's recommendation. The crowns were seated on the teeth with a constant static force of 15 kg (5). After 10 min, the teeth were placed in 100% humidity for 7 days.
Microleakage All of the cemented crowns were cycled 100 times between 4 and 60°C water bath containing 0.05% crystal violet dye. The teeth were placed in each bath for 30 s. Total immersion time was 100 min. All of the cemented crowns were embedded in clear autopolymerizing acrylic resin (Orthodontic Resin; L. D. Caulk Co., Milford, DE) and sectioned buccolingually into three equally thick sections with an Isomet sectioning machine (Fig. 2). RESULTS All crowns leaked gingivally regardless of the type of crown margin preparation. The leakage pattern was the same and the leakage followed the dentinal tubules directly into the pulp in every case (Figs. 3 and 4). There was no difference in the leakage pattern or the extent of the leakage in any of the three preparation methods and thus quantitative measurements were not done, since the end point of the leakage was the pulp chamber in all cases.
F~G3. Typical section examined under dissecting microscope. Note the penetration of the dye along the path of the dentinal tubules directly into the pulp. c, crown; d, dentin; p, pulp cavity; dp, dye penetration (original magnification xl0).
DISCUSSION The clinical impression of many endodontists is that many of their cases are done through full crowns. Their estimates range from 20 to 50%. This is, of course, only a clinical impression. Many teeth with full crowns may have had very large restorations or were badly broken down to begin with, thus requiring a crown. However, there are many teeth that are crowned for abutments of fixed restorations which do not have large restorations and are not badly broken down. For these teeth, the crown preparation itself may cause pulpal injury due to mechanical trauma or the heat generated by the
Vol. 18, No. 10, October 1992
Microleakage of Full Crowns
possible assumption is that this microleakage can be an important causative factor in pulp inflammation and possible pulp death. Tjan and Chiu (7) agree. They state "serious pulpal irritation is most likely the result of microleakage because of bacterial infiltration closer to the dental pulp." Dr. Goldman is a clinical professor, Department of Endodontics, Tufts University School of Dental Medicine, Boston, MA. Dr. Laosonthorn is a former graduate student, Department of Postgraduate Prosthodontics, Tufts University School of Dental Medicine. Dr. White is an associate professor, Department of Endedontics, Tufts University School of Dental Medicine. Address requests for reprints to Dr. Melvin Goldman, Department of Endodontics, Tufts University School of Dental Medicine, 1 Kneeland Street, Boston, MA 02111.
References FIG 4. Higher magnification of another specimen. Note penetration o f dye into the pulp cavity. C, crown; D, dentin; pc, pulp cavity; dp, dye penetration (original magnification x40).
preparation. But, we must also consider the unimpeded lethal highways of the freshly cut, open dentinal tubules. Since these are available and since this and other studies have demonstrated that there is leakage in every case of a cemented crown, no matter which cement or luting agent is used (5-7) or which kind of crown margin preparation is used, we must be aware of the possibility of subsequent microbiological damage to the pulp through the dentinal tubules. Our results showed that not only was there microleakage in every case, but that the microleakage extended to the pulp through the dentinal tubules
in every case. Bergenholtz and Warfvinge (8) reported that microbial factors from dental plaque caused pulpal inflammation when the plaque was placed in open cavities. Brannstrom and Vojinovic (9) were the first to demonstrate that pulpal inflammation can be prevented beneath several different filling materials by blocking the ingress of oral bacteria. This has been corroborated by many others since then using all of the presently available filling materials (10-19). Thus, it becomes apparent that microleakage of bacteria is the main cause of pulpal inflammation, and not the material itself. A recent study by Cox et al. (20) demonstrated that even in teeth with pulpal exposures, when the cavities were restored with various filling materials and the ingress of bacteria was blocked by surface sealing with zinc oxide and eugenol, there was no inflammation and actual healing of the exposures. They state that "healing of the dental pulp exposures is . . . dependent o n . . . the capacity of the capping material to prevent bacterial leakage" (20). Thus, with full crowns, given the fact that there is microleakage in all instances that extends to the pulp chamber, a
1. Naidorf IJ. Inflammation and infection of pulp and periapical tissues. In: Siskin M, ed. The biology of the human dental pulp. St. Louis; CV Mosby, 1973:391-402. 2. Mondelli J, Ishikiriama A, Galan J. Marginal microleakage in cemented complete crowns. J Prosthet Dent 1978;40:632-6. 3. Larson TD, Jensen JR. Microleakage of composite resin and amalgam core material under complete cast core crowns. J Prosthet Dent 1980;44: 40-4. 4. Tjan AHL, Miller GD, Whang SB, Sarkissian R. The effect of thermal stress on the marginal seat of cast gold full crowns. J Am Dent Assoc 1980; 100:48-51. 5. Kawamura RM, Swartz ML, Phillips RW, Dykema RW, Davis WH. Marginal seal of cast full crowns: an in vitro study. Gen Dent 1983;31:282-4. 6. Laosonthorn P. Microleakage of cast crowns cemented with various materials [MSD Thesis]. Boston, MA: Tufts University School of Dental Medicine, 1984. 7. ]'jan AHL, Chiu J. Microleakage of core materials for complete cast gold crowns. J Prosthet Dent 1989;61:659-64. 8. Bergenholtz G, Warfvinge J. Migration of leukocytes in dental pulp in response to plaque bacteria. Scand J Dent Res 1982;90:354-62. 9. Brannstrom M, Vojinovic O. Response of the dental pulp to invasion of bacteria around three dental filling materials. J Dent Child 1976;43:83-9. 10. Beagrie GS, Brannstrom M Pulpal response to cavity treatment with microbicidal solution and silicate restorations in monkeys. J Can Dent Assoc 1977;43:239-43. 11. Watts A. Bacterial contamination and the toxicity of silicate and zinc phosphate cements. Br Dent J 1979;146:7-13. 12. Patterson RC, Watts A. Caries, bacteria, the pulp and plastic restorations. Br Dent J 1981 ;151:54-8. 13. Tobias RS, Plant CG, Browne RM. A comparative pulpal study of the irritant effects of silicate cements. Br Dent J 1980;150:119-24. 14. Tobias RS, Plant CG, Browne RM. Reduction in pulpa[ inflammation beneath surface-sealed silicates. Int Endod J 1982;15:173-80. 15. Browne RM, Tobias RS, Crombie IK, Plant CG. Bacterial microleakage and pulpal inflammation in experimental cavities. Int Endod J 1983;16: 147-55. 16. Watts A, Paterson RC. Bacterial contamination and the "toxicity" of materials to the exposed pulp. Oral Surg 1983;56:542-8. 17. Bergenholtz G, Cox CF, Leesche W J, Syed SA. Bacterial leakage around dental restorations: its effect on the dental pulp. J Oral Pathol 1982; 11:439-50. 18. Bergenholtz G. Inflammatory response of the dental pulp to bacterial irritation. J Endodon 1981 ;7:100-4. 19. Paterson RC, Watts A. Further studies on the exposed germ-free dental pulp. Int Ended J 1987;20:112-21. 20. Cox CF, Keall CL, Keall HJ, Ostro E, Bergenholtz G. Biocompatibility of surface-sealed dental materials against exposed pulps. J Prosthet Dent 1987 ;57:1-8.