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A Method for Bonding to Dentin and Enamel
ARTICLES
The conservation of retenti on-form dentin in this method could increase patient comfort, reduce treatment and lessen fatigue for dentists.
time,
A method for bonding to dentin and enamel Rafael L. Bowen, DDS
Everett N. Cobb, DDS
s
ince the acid-etch technique was in troduced for the bonding of resins to enamel for the prevention of pit and fis sure caries,U2 this technique has been found useful in the practice of orthodon tics,3 pedodontics,4 endodontics,s re storative dentistry,6 periodontics,7-8 and other areas.9 Unfortunately, the acid-etch technique does not give adequate bond strengths to dentin surfaces (Table). Further, the use of hypertonic solutions of phosphoric or citric acid on vital dentin is usually contraindicated because they can have h arm fu l effects on the dental p u lp .10,11 BIS-GMA1213 and other dimethacrylate resins currently used in composites, sealants, and bonding agents are not inherently adhesive to enamel or dentin. For more than a quarter of a century, many investigators have sought to obtain strong adhesive bonding of resins and c o m p o s ite s to b o th d e n tin a n d enamel.1416 Recently, a procedure was discovered that apparently accomplishes bonding, at least in vitro.1718
Materials and methods Figure 1 shows the three active ingredients that were used in the new method. The me chanically prepared tooth surface was treated with a 5.3% aqueous solution of ferric oxalate [Fe2(C204)3] for 60 seconds, washed with 734 ■ JADA, Vol. 107, November 1983
Fig 1 ■ Presumptive formulas of adhesion-promoting compounds. Each must be applied in sequence. One of two isomers of PMDM is shown; both isomers are effective. None has yet (November 1983) been used in den tistry.
A R T IC L E S
water for ten seconds, and blown with air for ten seconds (Fig 2). A 10% acetone solution of NTG-GMA [the adduct of N(p-tolyl)glycine and glycidyl methacrylate]18 was then applied and allowed to stand for 60 seconds, during which time most of the solvent evaporated. A drop of clean acetone was placed on this sur face and removed after ten seconds to elimi nate unbound NTG-GMA (Fig 3). The surface was then blown with air for ten seconds. Next, a 5% acetone solution of PMDM (the addition reaction product of pyromellitic dianhydride and 2- hydroxyethylm ethacrylate)18 was applied for 60 seconds, after which the surface was blown for ten seconds with an air jet (Fig 4). A highly filled composite was mixed and pressed against the prepared surface and al lowed to harden. The bonded specimens were then soaked in water at room temperature for several days. Bond strengths were determined by the tensile adhesion testing apparatus de scribed previously.18,19 This procedure was compared with an acidetch technique using 30% phosphoric acid for 60 seconds, followed by a ten-second rinse with distilled water and drying with an air jet.
Results and discussion The new p ro c e du re y ie ld e d b ond strengths to enamel comparable to those obtained with the acid-etch technique (Table). With the acid-etch technique, the bond strengths to enamel were increased significantly by the use of the “bonding agent” (unfilled BIS-GMA resin). For the purpose of comparison (Table, control), when composite resins were applied to dentin after it was “treated” with water and acetone without the use of the active ingredients previously de scribed, the bond strengths were nearly zero after immersion in water for one or more days. The bond strengths to dentin obtained by the use of this new combina tion of materials were about one ton (2,000 lb) per square inch (Table). This is
Fig 2 ■ Scanning electron m icrograph of crosssectional view of dentin surface altered by ferric oxa late solution. Treated surface (top) was rinsed and blown dry before specimen was fractured to show ef fects in depth. Smeared dentin layer was converted into rigid surface layer structurally contiguous with underlying unaltered dentin (width of field is about
Table ■ Average tensile strengths of adhesive bonds between a composite* and treated surfaces of extracted teeth. Treatment New procedure (described in text) Acid-etch without bonding agent Acid-etch with bonding agent Control (water, acetone)
Enamel (psi)t
Dentin (psi)
2,400 (890; 12)* 1,580 (520; 6) 2,750 (480; 8) 420 (410; 6)
2,020 (430; 23) 260 (190; 5)§ 590 (120; 4)§ 8 (13; 5)
*Adaptic. +To convert pounds of force per square inch, psi, to megapascals, MPa, m ultiply by 0.006895; to convert psi to kilograms of force per square centimeter, kg/cm2, divided by 14.22. t in parentheses: (standard deviation, V ^ x P - n x '^ /n - l; and num ber of mea surements). §The acid-etch technique on vital dentin is not recommended.
twice as high as the best values previ ously measured by this test method dur ing a long study of adhesive b on d ing.14-19-20 Although storage in water for four to five weeks before testing gave the lower average value of 1,740 psi (410 SD; n, 6), strengths of this magnitude are ex pected to correlate with clinical signifi cance.21-22 In preliminary studies with extracted teeth, composites bonded w ith this method to cervical regions (without re tention form) have been retained both during thermocycling (5 to 55 C, 2.7 m in/ cycle) for one week (3,700 cycles) and subsequent sectioning; there was m ini mal microleakage as evidenced by a stain ing technique (50% aqueous silver nitrate for two hours, bright light and photo graphic developer for three hours), after thermocycling.23-24 There have been no previous incidents of cohesive failure of dentin during ten
sile adhesion tests of this kind. However, the new treatments have resulted in more than ten dentin fractures (Fig 5,6). A l though literature values for the average tensile strength of dentin25 (about 7,500 psi) are considerably higher than those for enamel25 (about 1,500 psi), and the av erage bond strength in these adhesion tests was slightly higher for enamel than for dentin (2,400 vs 2,020 psi), there have been these numerous incidences of cohe sive failure of dentin, but no apparent cohesive failure in enamel during the breaking of bonds. These adhesion test results suggest that the tensile strength of enamel in the direction of the enamel rods (more or less perpendicular to the plane of the surface in these adhesive bonds) might be higher than the tensile strength of dentin. During most of the tests, the materials did not produce any visible discoloration of the dentin, enamel, or composite.
Fig 3 ■ Excess NTG-GMA in form of crystals on dentin surface. These are removed by brief application of solvent (SEM; w idth of field about 130 /u.m).
Fig 4 H Thin film of PMDM remaining on dentin surface after solvent is blown away. Polymerization of layer is apparently initiated at tooth surface. Res ins did not penetrate dentinal tubules enough to form tags (SEM; w idth of field about 90 /xm).
20 fxm ).
Bowen-Cobb : METHOD FOR BONDING TO DENTIN AND ENAMEL ■ 735
A R T IC L E S
Fig 5 ■ SEM view of tooth’s dentin surface showing defect where piece of dentin (Fig 6) had been pulled out when joint broke at loading of 2,100 psi (148 kgI cm2). Grooves from prelim inary resurfacing with abrasive cloth can still be seen where bond had frac tured near interface. Other areas show composite material clinging to dentin where fracture was cohe sive in composite material. Dentin surface had been treated with ferric oxalate, NTG-GMA, and PMDM (width of field about 6 mm).
Fig 6 ■ Corresponding composite surface retaining piece of dentin was pulled from tooth’s surface when bond broke. Composite had also fractured cohesively as seen in upper right portion of picture. Cracks in dentin are artifacts from SEM study (width of field about 6 mm).
The bond strengths to dentin obtained by the use of this new combination of materials were about 1 ton per square inch. However, there have been a few instances (about 5%) of a black staining of the den tin surface during immersion in water at room temperature. Attempts to determine its cause are continuing; it might be as sociated with the repeated use of the same teeth, corrosion of the stainless steel as semblies, or disintegration of the gypsum (calcium sulfate) used to hold the teeth (or all three). Pulp response and other as pects of biocompatibility must precede clinical trials. Also, color stability of this system must be ascertained before clini cal use in anterior teeth is initiated. The apparent sealing of dentinal tubules without penetration of resin into the lumens, in vitro, suggests potential uses for hypersensitive dentin, cervical erosions, root caries, and other clinical conditions in which oral fluids and bac teria have access to open dentinal tubules.
Summary and conclusions In vitro tensile bond strengths of about 1 ton per square inch between composites and dentin and enamel were obtained by applying a 5.3% solution of ferric oxalate to the tooth surface, followed by water and air cleaning; by applying a 10% solu tion of NTG-GMA, followed by cleansing with solvent and air; by applying a 5% so lution of PMDM, followed by air to re-
736 ■ JADA, Vol. 107, November 1983
move the solvent; and by placing the freshly mixed composite against the treated surface. If this breakthrough in the laboratory leads to sufficiently durable adhesion in clinical practice, the conservation of retention-form dentin could increase pa tient comfort, reduce treatment time and cost, and lessen fatigue for dentists.
__________________________ j m A This investigation was supported, in part, by re search grant 2 ROI DE05129-05A l to the American Dental Association Health Foundation from the Na tional Institutes of Health-National Institute of Dental Research and is part of the dental research program conducted by the National Bureau of Standards in cooperation with the American Dental Association Health Foundation. Certain commercial materials are identified in this paper to specify the experimental procedure. In no in stance does such identification imply recommenda tion or endorsement by the National Bureau of Stan dards or that the materials identified are necessarily the best available for the purpose. Dr. Bowen is director, American Dental Associa tion Health Foundation Research Unit, National Bureau of Standards, Washington, DC 20234. Dr. Cobb is associate professor, Georgetown University School of Dentistry, Washington, DC. Address re quests for reprints to Dr. Bowen. 1. Buonocore, M.G. Simple method of increasing the adhesion of acrylic filling materials to enamel sur faces. J Dent Res 34:849-853,1955. 2. Buonocore, M.G.; Wileman, W.; and Brudevold, F. Report on a resin composition capable of bonding
to human dentin surfaces. J Dent Res 35:846-851, 1956. 3. Newman, G.V. Bonding plastic orthodontic at tachments to tooth enamel. J NJ Dent Soc 35:346-358, 1965. 4. Doyle, W.A. Pedodontic operative procedures. In McDonald, R., ed. Current therapy in dentistry, vol 3. St. Louis, C. V. Mosby Co, 1968, chap 38. 5. Heiman, G.R., and others. Temporary splinting using an adhesive system. Oral Surg 31:819-822, 1971. 6. Laswell, H.R.; Welk, D.A.; and Regenos, J.W. At tachment of resin restorations to acid pretreated enamel. JADA 82(3):558-563, 1971. 7. Rochette, A.L. Attachment of a splint to enamel of lower anterior teeth. J Prosthet Dent 30:418-423, 1973. 8. Poison, A.M., and Billen, J.R. Temporary splint ing of teeth using ultraviolet-light-polymerized bonding materials. JADA 89(5):1137-1141, 1974. 9. Livaditis, G.J., and Thompson, V.P. Etched cast ings: an improved retentive mechanism for resinbonded retainers. J Prosthet Dent 47(l):52-58, 1982. 10. Stanley, H.R.; Going, R.E.; and Chauncey, H.H. Human pulp response to acid pretreatment of dentin and to composite restoration. JADA 91(4):817-825, 1975. 11. Eriksen, H.M. Pulpal response of monkeys to a composite resin cement. J Dent Res 53:565-570,1974. 12. Bowen, R.L. Properties of a silica-reinforced polymer for dental restorations. JADA 66(l):57-64, 1963. 13. Bowen, R.L. Dental filling material comprising vinyl silane treated fused silica and binder consisting of the reaction product of bis phenol and glycidyl ac rylate, US patent no. 3,066,122, 1962. 14. Bowen, R.L. Investigation of the surfaces of hard tooth tissues by a surface activity test. In Phil lips, R.W., and Ryge, G., eds. Proceedings of the workshop on adhesive restorative dental materials, Indiana University, Sept 28, 29, 1961. Spencer, Ind, Owen Litho Service, pp 177-191. 15. Bowen, R.L. Development of an adhesive re storative material. University of Virginia Workshop, Adhesive restorative dental materials II. Public Health Service Pub no. 1494, Washington, DC, US Government Printing Office, 1966, pp 225-231. 16. Bowen, R.L. Adhesive bonding of various ma terials to hard tooth tissues. Metal salts as mordants for coupling agents. In Moskowitz, H.D.; Ward, G.T.; and Woolridge, E.D., eds. Dental adhesive materials. Proceedings from sym posium Nov 8, 9, 1973, Hunter-Bellevue School of Nursing. New York City, Prestige Graphic Services, 1974, pp 205-221. 17. Bowen, R.L., and Cobb, E.N. Method for obtain ing strong adhesive bonding of composites to dentin. J Dent Res 61:230, abstract no. 463,1982. 18. Bowen, R.L.; Cobb, E.N.; and Rapson, J.E. Adhesive bonding of various materials to hard tooth tissues. Improvement in bond strength to dentin. J Dent Res 61(9):1070-1076, 1982. 19. Bowen, R.L. Adhesive bonding of various ma terials to hard tooth tissues. Method of determining bond strength. J Dent Res 44:690-695, 1965. 20. Bowen, R.L. Use of epoxy resins in restorative materials. J Dent Res 35:360-369,1956. 21. Bowen, R.L.; Nemoto, K.; Rapson, J.E. Adhe sive bonding of various materials to hard tooth tis sues: forces developing in composite materials dur ing hardening. JADA 106(4):475-477, 1983. 22. Causton, B.E., and Johnson, N.W. The influ ence of mineralizing solutions on the bonding of composite restorations to dentin. Cyanoacrylate pretreatment. J Dent Res 60(7):1315-1320, 1981. 23. Wu, W., and Cobb, E.N. A silver staining tech nique for investigating wear of restorative dental composites. J Biom Mats Res 15:343-348, 1981. 24. Wu, W., and others. Detecting margin leakage of dental composite restorations. J Biomed Mater Res, to be published. 25. Bowen, R.L., and Rodriguez, M.S. Tensile strength and modulus of elasticity of tooth structure and several restorative materials. JADA 64(3):378387,1962.
The conservation of retenti on-form dentin in this method could increase patient comfort, reduce treatment and lessen fatigue for dentists.
time,
A method for bonding to dentin and enamel Rafael L. Bowen, DDS
Everett N. Cobb, DDS
s
ince the acid-etch technique was in troduced for the bonding of resins to enamel for the prevention of pit and fis sure caries,U2 this technique has been found useful in the practice of orthodon tics,3 pedodontics,4 endodontics,s re storative dentistry,6 periodontics,7-8 and other areas.9 Unfortunately, the acid-etch technique does not give adequate bond strengths to dentin surfaces (Table). Further, the use of hypertonic solutions of phosphoric or citric acid on vital dentin is usually contraindicated because they can have h arm fu l effects on the dental p u lp .10,11 BIS-GMA1213 and other dimethacrylate resins currently used in composites, sealants, and bonding agents are not inherently adhesive to enamel or dentin. For more than a quarter of a century, many investigators have sought to obtain strong adhesive bonding of resins and c o m p o s ite s to b o th d e n tin a n d enamel.1416 Recently, a procedure was discovered that apparently accomplishes bonding, at least in vitro.1718
Materials and methods Figure 1 shows the three active ingredients that were used in the new method. The me chanically prepared tooth surface was treated with a 5.3% aqueous solution of ferric oxalate [Fe2(C204)3] for 60 seconds, washed with 734 ■ JADA, Vol. 107, November 1983
Fig 1 ■ Presumptive formulas of adhesion-promoting compounds. Each must be applied in sequence. One of two isomers of PMDM is shown; both isomers are effective. None has yet (November 1983) been used in den tistry.
A R T IC L E S
water for ten seconds, and blown with air for ten seconds (Fig 2). A 10% acetone solution of NTG-GMA [the adduct of N(p-tolyl)glycine and glycidyl methacrylate]18 was then applied and allowed to stand for 60 seconds, during which time most of the solvent evaporated. A drop of clean acetone was placed on this sur face and removed after ten seconds to elimi nate unbound NTG-GMA (Fig 3). The surface was then blown with air for ten seconds. Next, a 5% acetone solution of PMDM (the addition reaction product of pyromellitic dianhydride and 2- hydroxyethylm ethacrylate)18 was applied for 60 seconds, after which the surface was blown for ten seconds with an air jet (Fig 4). A highly filled composite was mixed and pressed against the prepared surface and al lowed to harden. The bonded specimens were then soaked in water at room temperature for several days. Bond strengths were determined by the tensile adhesion testing apparatus de scribed previously.18,19 This procedure was compared with an acidetch technique using 30% phosphoric acid for 60 seconds, followed by a ten-second rinse with distilled water and drying with an air jet.
Results and discussion The new p ro c e du re y ie ld e d b ond strengths to enamel comparable to those obtained with the acid-etch technique (Table). With the acid-etch technique, the bond strengths to enamel were increased significantly by the use of the “bonding agent” (unfilled BIS-GMA resin). For the purpose of comparison (Table, control), when composite resins were applied to dentin after it was “treated” with water and acetone without the use of the active ingredients previously de scribed, the bond strengths were nearly zero after immersion in water for one or more days. The bond strengths to dentin obtained by the use of this new combina tion of materials were about one ton (2,000 lb) per square inch (Table). This is
Fig 2 ■ Scanning electron m icrograph of crosssectional view of dentin surface altered by ferric oxa late solution. Treated surface (top) was rinsed and blown dry before specimen was fractured to show ef fects in depth. Smeared dentin layer was converted into rigid surface layer structurally contiguous with underlying unaltered dentin (width of field is about
Table ■ Average tensile strengths of adhesive bonds between a composite* and treated surfaces of extracted teeth. Treatment New procedure (described in text) Acid-etch without bonding agent Acid-etch with bonding agent Control (water, acetone)
Enamel (psi)t
Dentin (psi)
2,400 (890; 12)* 1,580 (520; 6) 2,750 (480; 8) 420 (410; 6)
2,020 (430; 23) 260 (190; 5)§ 590 (120; 4)§ 8 (13; 5)
*Adaptic. +To convert pounds of force per square inch, psi, to megapascals, MPa, m ultiply by 0.006895; to convert psi to kilograms of force per square centimeter, kg/cm2, divided by 14.22. t in parentheses: (standard deviation, V ^ x P - n x '^ /n - l; and num ber of mea surements). §The acid-etch technique on vital dentin is not recommended.
twice as high as the best values previ ously measured by this test method dur ing a long study of adhesive b on d ing.14-19-20 Although storage in water for four to five weeks before testing gave the lower average value of 1,740 psi (410 SD; n, 6), strengths of this magnitude are ex pected to correlate with clinical signifi cance.21-22 In preliminary studies with extracted teeth, composites bonded w ith this method to cervical regions (without re tention form) have been retained both during thermocycling (5 to 55 C, 2.7 m in/ cycle) for one week (3,700 cycles) and subsequent sectioning; there was m ini mal microleakage as evidenced by a stain ing technique (50% aqueous silver nitrate for two hours, bright light and photo graphic developer for three hours), after thermocycling.23-24 There have been no previous incidents of cohesive failure of dentin during ten
sile adhesion tests of this kind. However, the new treatments have resulted in more than ten dentin fractures (Fig 5,6). A l though literature values for the average tensile strength of dentin25 (about 7,500 psi) are considerably higher than those for enamel25 (about 1,500 psi), and the av erage bond strength in these adhesion tests was slightly higher for enamel than for dentin (2,400 vs 2,020 psi), there have been these numerous incidences of cohe sive failure of dentin, but no apparent cohesive failure in enamel during the breaking of bonds. These adhesion test results suggest that the tensile strength of enamel in the direction of the enamel rods (more or less perpendicular to the plane of the surface in these adhesive bonds) might be higher than the tensile strength of dentin. During most of the tests, the materials did not produce any visible discoloration of the dentin, enamel, or composite.
Fig 3 ■ Excess NTG-GMA in form of crystals on dentin surface. These are removed by brief application of solvent (SEM; w idth of field about 130 /u.m).
Fig 4 H Thin film of PMDM remaining on dentin surface after solvent is blown away. Polymerization of layer is apparently initiated at tooth surface. Res ins did not penetrate dentinal tubules enough to form tags (SEM; w idth of field about 90 /xm).
20 fxm ).
Bowen-Cobb : METHOD FOR BONDING TO DENTIN AND ENAMEL ■ 735
A R T IC L E S
Fig 5 ■ SEM view of tooth’s dentin surface showing defect where piece of dentin (Fig 6) had been pulled out when joint broke at loading of 2,100 psi (148 kgI cm2). Grooves from prelim inary resurfacing with abrasive cloth can still be seen where bond had frac tured near interface. Other areas show composite material clinging to dentin where fracture was cohe sive in composite material. Dentin surface had been treated with ferric oxalate, NTG-GMA, and PMDM (width of field about 6 mm).
Fig 6 ■ Corresponding composite surface retaining piece of dentin was pulled from tooth’s surface when bond broke. Composite had also fractured cohesively as seen in upper right portion of picture. Cracks in dentin are artifacts from SEM study (width of field about 6 mm).
The bond strengths to dentin obtained by the use of this new combination of materials were about 1 ton per square inch. However, there have been a few instances (about 5%) of a black staining of the den tin surface during immersion in water at room temperature. Attempts to determine its cause are continuing; it might be as sociated with the repeated use of the same teeth, corrosion of the stainless steel as semblies, or disintegration of the gypsum (calcium sulfate) used to hold the teeth (or all three). Pulp response and other as pects of biocompatibility must precede clinical trials. Also, color stability of this system must be ascertained before clini cal use in anterior teeth is initiated. The apparent sealing of dentinal tubules without penetration of resin into the lumens, in vitro, suggests potential uses for hypersensitive dentin, cervical erosions, root caries, and other clinical conditions in which oral fluids and bac teria have access to open dentinal tubules.
Summary and conclusions In vitro tensile bond strengths of about 1 ton per square inch between composites and dentin and enamel were obtained by applying a 5.3% solution of ferric oxalate to the tooth surface, followed by water and air cleaning; by applying a 10% solu tion of NTG-GMA, followed by cleansing with solvent and air; by applying a 5% so lution of PMDM, followed by air to re-
736 ■ JADA, Vol. 107, November 1983
move the solvent; and by placing the freshly mixed composite against the treated surface. If this breakthrough in the laboratory leads to sufficiently durable adhesion in clinical practice, the conservation of retention-form dentin could increase pa tient comfort, reduce treatment time and cost, and lessen fatigue for dentists.
__________________________ j m A This investigation was supported, in part, by re search grant 2 ROI DE05129-05A l to the American Dental Association Health Foundation from the Na tional Institutes of Health-National Institute of Dental Research and is part of the dental research program conducted by the National Bureau of Standards in cooperation with the American Dental Association Health Foundation. Certain commercial materials are identified in this paper to specify the experimental procedure. In no in stance does such identification imply recommenda tion or endorsement by the National Bureau of Stan dards or that the materials identified are necessarily the best available for the purpose. Dr. Bowen is director, American Dental Associa tion Health Foundation Research Unit, National Bureau of Standards, Washington, DC 20234. Dr. Cobb is associate professor, Georgetown University School of Dentistry, Washington, DC. Address re quests for reprints to Dr. Bowen. 1. Buonocore, M.G. Simple method of increasing the adhesion of acrylic filling materials to enamel sur faces. J Dent Res 34:849-853,1955. 2. Buonocore, M.G.; Wileman, W.; and Brudevold, F. Report on a resin composition capable of bonding
to human dentin surfaces. J Dent Res 35:846-851, 1956. 3. Newman, G.V. Bonding plastic orthodontic at tachments to tooth enamel. J NJ Dent Soc 35:346-358, 1965. 4. Doyle, W.A. Pedodontic operative procedures. In McDonald, R., ed. Current therapy in dentistry, vol 3. St. Louis, C. V. Mosby Co, 1968, chap 38. 5. Heiman, G.R., and others. Temporary splinting using an adhesive system. Oral Surg 31:819-822, 1971. 6. Laswell, H.R.; Welk, D.A.; and Regenos, J.W. At tachment of resin restorations to acid pretreated enamel. JADA 82(3):558-563, 1971. 7. Rochette, A.L. Attachment of a splint to enamel of lower anterior teeth. J Prosthet Dent 30:418-423, 1973. 8. Poison, A.M., and Billen, J.R. Temporary splint ing of teeth using ultraviolet-light-polymerized bonding materials. JADA 89(5):1137-1141, 1974. 9. Livaditis, G.J., and Thompson, V.P. Etched cast ings: an improved retentive mechanism for resinbonded retainers. J Prosthet Dent 47(l):52-58, 1982. 10. Stanley, H.R.; Going, R.E.; and Chauncey, H.H. Human pulp response to acid pretreatment of dentin and to composite restoration. JADA 91(4):817-825, 1975. 11. Eriksen, H.M. Pulpal response of monkeys to a composite resin cement. J Dent Res 53:565-570,1974. 12. Bowen, R.L. Properties of a silica-reinforced polymer for dental restorations. JADA 66(l):57-64, 1963. 13. Bowen, R.L. Dental filling material comprising vinyl silane treated fused silica and binder consisting of the reaction product of bis phenol and glycidyl ac rylate, US patent no. 3,066,122, 1962. 14. Bowen, R.L. Investigation of the surfaces of hard tooth tissues by a surface activity test. In Phil lips, R.W., and Ryge, G., eds. Proceedings of the workshop on adhesive restorative dental materials, Indiana University, Sept 28, 29, 1961. Spencer, Ind, Owen Litho Service, pp 177-191. 15. Bowen, R.L. Development of an adhesive re storative material. University of Virginia Workshop, Adhesive restorative dental materials II. Public Health Service Pub no. 1494, Washington, DC, US Government Printing Office, 1966, pp 225-231. 16. Bowen, R.L. Adhesive bonding of various ma terials to hard tooth tissues. Metal salts as mordants for coupling agents. In Moskowitz, H.D.; Ward, G.T.; and Woolridge, E.D., eds. Dental adhesive materials. Proceedings from sym posium Nov 8, 9, 1973, Hunter-Bellevue School of Nursing. New York City, Prestige Graphic Services, 1974, pp 205-221. 17. Bowen, R.L., and Cobb, E.N. Method for obtain ing strong adhesive bonding of composites to dentin. J Dent Res 61:230, abstract no. 463,1982. 18. Bowen, R.L.; Cobb, E.N.; and Rapson, J.E. Adhesive bonding of various materials to hard tooth tissues. Improvement in bond strength to dentin. J Dent Res 61(9):1070-1076, 1982. 19. Bowen, R.L. Adhesive bonding of various ma terials to hard tooth tissues. Method of determining bond strength. J Dent Res 44:690-695, 1965. 20. Bowen, R.L. Use of epoxy resins in restorative materials. J Dent Res 35:360-369,1956. 21. Bowen, R.L.; Nemoto, K.; Rapson, J.E. Adhe sive bonding of various materials to hard tooth tis sues: forces developing in composite materials dur ing hardening. JADA 106(4):475-477, 1983. 22. Causton, B.E., and Johnson, N.W. The influ ence of mineralizing solutions on the bonding of composite restorations to dentin. Cyanoacrylate pretreatment. J Dent Res 60(7):1315-1320, 1981. 23. Wu, W., and Cobb, E.N. A silver staining tech nique for investigating wear of restorative dental composites. J Biom Mats Res 15:343-348, 1981. 24. Wu, W., and others. Detecting margin leakage of dental composite restorations. J Biomed Mater Res, to be published. 25. Bowen, R.L., and Rodriguez, M.S. Tensile strength and modulus of elasticity of tooth structure and several restorative materials. JADA 64(3):378387,1962.