resin: A historic
Takao Fusayama, D.D.S., Ph.D. Tokyo Medical and Dental University, Tokyo, Japan Since development of the BIS-GMA composite resin, there have been many innovations to improve the physical properties for posterior use. Subsequent development of a caries detector and chemically adhesive composite resin has further revolutionally raised the value of composite resin restoration, replacing the traditional restorative system of mechanical approach by the new system of biological approach. In this system only the infected irreversibly detriorated insensitive tissue, stainable with the caries detector, is removed painlessly. The cavity is immediately filled with the composite resin with no further tissue reduction for retention or resistance form or extension for prevention. Both enamel and dentin walls are etched by a single etchant without lining. The chemical adhesion to the cavity margin and wall minimizes the marginal failure in size and prevalence and prevents secondary caries penetration along the wall. The chemically adhesive composite resin is thus a useful restorative material much kinder to teeththan amalgam.(J PROSTHETDENT~BB~;~~:~~~-S.)
he development of the BIS-GMA composite resin by Bowenl initiated an active subject for research. Originally, resin was introduced to replace silicate cement as an esthetic restorative material. Since its inception, there have been many innovations in chemistry, fillers, manipulation, and finishing, plus the development of adjunct materials. The purpose was to improve the physical properties. Improved physical properties gave rise to the concept that this material might serve to restore posterior teeth. Several clinical projects tested the early composite resins *ProfessorEmeritus. 10/l/22124
for 2 or 3 year periods in conventional and retentive class I and II preparations. 2Y7The results were mixed.
According to recent studies of dentinal caries, the affected dentin consists of two layers. The outer layer is bacterially contaminated, incapable of being remineralized and unable to transmit sensation. The inner layer is uninfected, remineralizable, and sensitive.8-11 The Caries Detector (Kuraray Co., Osaka, Japan) instrument was developed to stain only the outer layer.12*l3 This made it possible to excavate the outer layer of carious dentin and conserve the inner layer. Thus, the removal of carious dentin was not only positive but also painless.14
Fig. 1. Both molars were originally restored with amalgam. First molar restoration fractured at 1 year. It was replaced with Clearfil Posterior resin. Note marginal integrity of composite resin after 2 years and marginal fracture of amalgam at 3 years.
2. Index of marginal fracture of amalgam and composite resin restorations at 5 years. (Courtesy M. Fukushima)
Adhesive restorative dentistry started with enamel etching.15 Resin-bonded micromechanically by tags penetrating irregularities of etched enamel, did not bond to dentin. In 1976, a chemically adhesive bonding agent, Clearfil Bond (Kuraray Co.), was developed.16 With this material, etching increased the bond strength to both enamel and dentin by combined micro-mechanical and chemical bonding. The result made the retention form inutile. A new restorative system was thus established by the combination of the Caries Detector instrument and the chemically adhesive composite resins.14 Scotchbond (3M Co., St. Paul, Minn.) and Pyrofil-D21 (Sankin Co., Tokyo, Japan) materials were later developed and proved similarly adhesive.i7 When the regularion of mercury content in the waste water of hospitals became strict in Japan, Clearfil Posterior (Kuraray Co.) resin was developed to improve physical properties so that it could replace amalgam in posterior teeth. P-10 (3M Co.) resin that had been reinforced for posterior use was also combined with Scotchbond’ resin to simplify cavity restoration by chemical adhesion.
To establish acceptance of the Clearfil system, several aspects of the therapy required biologic investigation. Compatibility of the various materials with the pulp has been thoroughly researched. There was no pulpal response to the application of the Caries Detector instrument for THE
differentiating the outer and inner layers of carious dentin.18 The application of the Clearfil etchant, which contains 40% phosphoric acid, for 30 to 60 seconds slightly increased the initial pulp response but considerably decreased the subsequent response by sealing the dentinal tubule apertures.lg When enamel and dentin were etched (total etching), the application of Clearfil bond and composite resin was nonirritating to the pul~.~~,21The similar use of Scotchbond and P-10 resins was equally nonirritating.22 A composite resin insulates the pulp from thermal and electrical injury. The cavity preparation in this system does not irritate the pulp and is actually painless because it requires excavation of only the insensitive necrotic outer layer of carious dentin.14,23 In contrast, the conventional preparation requires that the retention form be prepared in the sensitive vital dentin.
Preparation of conventional cavities for adhesive composite resin is contraindicated. The box or mortise form, prepared in sensitive vital dentin, irritates the pulp and weakens the structure. Only the stainable carious enamel and necrotic dentin identified with the caries detector should be removed, resulting in a conical cavity corresponding to the morphology of the necrotic outer layer of carious dentin. The adhesive composite resin system does not require extension for prevention on smooth surfaces.23 Under535
Chemically adhesive composite
3. Diagrammatic comparison of marginal defects affecting posterior amalgam and composite resin restorations.
TRADITIONAL TECHNIQUE endodontic treatment and cast restoration Impossible with amalgam
Fig. 4. Diagrammatic comparison of traditional and adhesive composite resin therapies for extensive caries. Extensive carious lesion that was to be restored with cast crown after endodontic therapy and foundation can be immediately restored with adhesive composite resin.
mined enamel may be retained when etched and supported by the adhesive system. The enamel wall should be prepared in the most efficacious direction. Beveled margins have been recommended to create the best marginal seal in a laboratory experiment.24 However, the chemically adhesive composite resin can adhere to the unbeveled enamel. Thinner composite resin margins on the bevel are most apt to fracture as a result of mastication.25 The obtuse cavosurface angle of a beveled margin is apt to result in a composite resin featheredge which is subject to peeling and possible recurrent caries. On the other hand, an enamel wall parallel to the rods is likely to cause separations of the rods by contraction of the composite resin. The enamel wall should,
therefore, incline 60 to 80 degrees to have optimum marginal seal and a definite cavosurface angle.
Since amalgam has been an almost universal restorative material for posterior restorations, it became the control for clinical research of posterior composite resin restorations (Fig. 1). Early reports, mostly on class II composite resin restorations, found marginal integrity and absence of recurrent caries the outstanding features of posterior composite resins.2p4 The loss of marginal integrity of amalgam restorations was a serious disadvantage. The difference was even more remarkable when the chemically adhesive composite resins were clinically tested.
The initial product of Clearfil bonding agent was studied longitudinally by inserting it in cavities under the guide of the Caries Detector instrument and total etching.26 After 5 to 6 years, the marginal discrepancies were unexpectedly rare. When the prevalence of marginal fracture was compared between amalgam restorations and three types of composite resin in a clinical test for 5 years, marginal fracture was markedly less with the composite resins, particularly with the chemically adhesive composite resin, Clearfil Posterior27 (Fig. 2). In another clinical test of 4 years, Clearfil Posterior and Scotchbond-PlO resins were compared by placing them in extensive posterior cavities by the same technique. The results were similarly gratifying. They indicated that the chemically adhesive posterior composite resins placed in the nonmortise, nonretentive cavities with total etching surpassed the conventional amalgam restoration (Fig. 3). Deep-seated carious lesions are less likely to result in mechanical exposure of pulp with the simplified cavity preparation and adhesive composite resin. With detection and removal of only the outer infected necrotic layer of dentin, the undermined enamel in extensive carious lesions may be supported by the adhesive composite resin (Fig. 4). There is no need to design outline, retention, and resistance forms. Restoration of extensive carious lesions is thus quite simple, with the adhesive composite resin conserving the structure and vitality. Similar conservation is impossible with amalgam and cast restorations. The most fundamental advantage of the chemically adhesive composite resin is that it can restore a decayed tooth without sacrificing uninfected, remineralizable sensitive living dentin (Fig. 5). This is, therefore, painless without anesthesia and impossible with amalgam or gold foil. This conservative cavity preparation minimizes the chance of pulp extirpation and tooth extraction. The longevity of teeth is thus maximized. Initially, the low wear-resistance was a major shortcoming of composite resins. 2r4 The more recent developments have, however, established that excessive wear is no longer a meaningful problem because the resistance to wear has been considerably improved.22, 26*2s-30In addition, if the occlusal surface is slightly worn, it may be readily repaired without furthr sacrifice of dental tissue. A slight reduction of the abraded surface permits repair by the addition of the same composite resin that bonds to the reduced restoration with the strength of 15 MPa.31
For minimizing the chance of failure, the technique must be simple. For securing the best adhesion, the technique must be quick, minimizing the intervals between preparation, pretreatment, and application of the bonding agent and composite resin. Etching both the enamel and the dentin at once simplifies the technique. Separate treatment of enamel and dentin accurately distinguishing them is
Chemically adhesive composite restoration
Non-adhesive amalgam restorajion
Fig. 5. Chemically adhesive composite resin restoration sacrifices only infected irreversibly deteriorated dental tissue whereas amalgam restoration sacrifices a great deal of important uninfected living tissue.
practically impossible in small cavities. Full coverage of an axial or pulpal wall with a lining agent is an ineffective and harmful additional step because it impairs the adhesion to dentin and the gingival marginal seal.32The pulp is better protected by the direct bond to etched dentin.33 A rubber dam is not necessary with the described recommended system. Seepagedoes not affect the adhesion after the bonding agent is applied to a cavity if the enamel margin is immediately spray-washed and dried.34 The time required to keep the cavity dry is usually less than 1 minute after etching. Such a short time to maintain dryness is easy because insertion of the composite resin does not require condensation as required for amalgam. A rubber-dam clamp may injure the gingiva and disturb complicated therapy in posterior regions. The efficiency of this system not only secures adequate adhesion but also eliminates the use of the rubber dam.
It is no longer true that the complexity and sensitivity of finishing technique is one of the shortcomings of composite resin restorations. Development of superfine diamond burs has simplified finishing because they trim efficiently and leave a smooth surface. It does not affect the surface if used under a water spray. The composite is then polished with silicone points under a water spray at the next appointment. The glossy surface polymerized against a matrix must be removed by polishing from the proximal surface of anterior teeth because it may discolor regardless of the smoothness.35On the other hand, the glossy surface must be conserved on the proximal surface of posterior teeth in order to prevent abrasion of adjacent teeth. Discoloration is not a problem in this region. Abrasion of opposing teeth has been considerably decreased by the development of microfilled or hybrid filled composite resins.
CONCLUSION The clinical merit of esthetic composite resin restorations has been greatly raised by development of the chem-
ically adhesive composite resin and the unique technique. The adhesive composite resin has completely replaced silicate cement and, in many instances, gold foil in anterior restorations. It is now replacing amalgam for posterior restorations as a material that is kinder to teeth and inviting to patients and dentists. REFERENCES 1. Bowen RL. Properties of a silica reinforced polymer for dental restoration. J Am Dent Assoc 1963;66:57-64. 2. Phillips RW, Avery DR, Swarm ML, McCune RJ. Observations on a composite resin for class II restorations. Three year report. J PROSTHET DENT 1973;30:891-7.
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4. Leinfelder KF, Sluder TB, Sockwell CL, Strickland WD, Wall JT. Clinical evaluation of composite resins as anterior and posterior restorative materials. J PROSTHET DENT 1975;33:407-16. 5. Jorgensen KD, Asmussen E. Occlusal abrasion of an composite restorative resin with ultra-fine filler-an initial study. Quintessence Int 1978;8:73. 6. Jorgensen KD, Horsted P, Janum 0, Krogh J, Schultz J. Abrasion of class I restorative resins. Stand Dent J 1979;82:140. 7. Wu W, Toth EE, Moffa JF, Ellison JA. Subsurface damage layer of in vivo worn dental composite restorations. J Dent Res 1984;63:675-80. 8. Kato S, Fusayama T. Recalcification of artificially decalcified dog dentin in viva. J Dent Res 1970;49:1060-7. 9. Ohgushi K, Fusayama T. Electron microscopic structure of the two layers of carious dentin. J Dent Res 1975;54:1019-26. 10. Kuboki Y, Ohgushi K, Fusayama T. Collagen biochemistry of the two layers of carious dentin. J Dent Res 1977;56:1233-7. 11. Miyauchi H, Iwaku M, Fusayama T. Physiological recalcification of carious dentin. Bull Tokyo Med Dent Univ 1978;25:169-79. 12. Fusayama T. Two layers of carious dentin, diagnosis and treatment. Oper Dent 1979;4:63-70. 13. Fusayama T, Takatsu T, Inokoshi S, Itoh K, Yamauchi J, Shibatani K. New composition of caries detector. Jpn J Conserv Dent 1979;261-4. 14. Fusayama T. New concepts in operative dentistry. Chicago: Quintessence Publishing Co, 1980;14-59,61-156. 15. Buonocore MG. A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. J Dent Res 1955;34:849-
18. Shimizu C, Itoh K, Yamada T, Hachiya Y, Iwaku M, Ohba J. Pulp reaction to fuchsin solution for caries disgnosis. J Jpn Conserv Dent 1977;20:140-3. 19. Fujitani M, Inokoshi S, Hosoda H. Effects of acid etching on dental pulp in adhesive composite restoration [Abstract]. J Dent Res 198665764. 20. Inokoshi S, Iwaku M, Hosoda H, Fusayama T. Pulpal response to a new adhesive restorative resin. J Dent Res 1982;61:1014-9. 21. Inokoshi S. Pulp response to a new adhesive restorative resin. Jpn J Conserv Dent 1980;47:410-26. 22. Shintani H, Satou J, Satou N. Clinical evaluation of two adhesive composites for posterior restorations. J PROSTHET DENT 1989;62:627-32. 23. Fusayema T. Cavity preparation for a new adhesive restorative resin. Quintessence Int 1983;14:397-409. 24. Porte A, Lutz F, Lund MR, Swartz M, Cochran MA. Cavity designs for composite resins. Oper Dent 1984;9:50-6. 25. Kubo S. Study on the mechanism of marginal fracture of the posterior composite resin. Part I. Relation between cavity wall adhesion of resins and marginal fracture. Jpn J Conserv Dent 1987;30:13-27. 26. Iwaku M, Inokoshi S, Hosoda H, Fusayama T. Conservative dentistry with a caries detector and a chemically adhesive composite. A longitudinal study of a new system. Br Dent J 1983;155:19-22. 27. Fukushima M, Nobumata T, Hirata N, et al. Five year clinical results of posterior composite restoration [Abstract]. Jpn J Conserv Dent 1987;Autumn:B-19. 28. Horie K. Studies on the occlusal wear of posterior composite resin restorations. Part 2. Clinical evaluation. J Jpn Stom Sot 1984;51:45-65. 29. Hendriks FHJ. Posterior composite restorations. Holland:Grafisch Bedrijf Outhuis BV. 1985;76. 30. Leinfelder KF. Composite. Proceeding of International State of the Arts Conference on Restorative Dent Mater of NIH. Bethesda, Md: 1986;393. 31. Chiba K, Hosoda H. Fusayama T. Additional placement of adhesive composite: bond strength and clinical technique. J PROSTHET DENT 1988;61:669-75.
32. Fusayama A, Kono A. Marginal closure of class V composite restorations with the gingival wall in cementum/dentin. J PROSTHET DENT 1989;61:293-6..
33. Fusayama T. Factors and prevention of pulp irritation by adhesive composite resin restoration. Quintessence Int 1987;18:633-41. 34. Endo A, Fujitani M, Hosoda H. A study on the adaptation to wall of various adhesive resin restorations [Abstract]. Jpn J Conserv Dent 1987;Autumn:B-34. 35. Hachiya Y, Hosoda H, Fusayama T. Relation of finish to discoloration of composite resins. J PROSTHET DENT 1984;52:811-4.
53. 16. Fusayama T, Nakamura M, Kurosaki N, Iwaku M. Nonpressure adhesion of a new adhesive restorative resin. J Dent Res 1979;58:1364-70. 17. Dogon IL, Stambler S. Study to determine the effectiveness of dentin bonding agents [Abstract]. J Dent Res 1981;60:
DR. T. FUSAYAMA 16-23 KAMIIGUSA 4-CHOME SUGINAMI-KU, TOKYO 167 JAPAN
The Guide to Preparing Articles for the JOURNAL OFPROSTHETIC DENTISTRY, revised by Professor Paul Barton, Editorial Consultant to the JOURNAL, and the editors, is available to prospective authors. The guide provides the format for developing different types of scientific manuscripts, a checklist for effective writing, and detailed instructions for preparing manuscripts in the style acceptable by the JOURNAL. Also available are the Guidelines for Reporting Statistical Results and an Author’s Guide to Controlling the Photograph. Guides can be obtained from the oflice of the Editor (Dr. Judson C. Hickey, The Journal of Prosthetic Dentistry, Medical College of Georgia, School of Dentistry, Augusta, GA 30912).