Journal of Oral Rehabilitation, 1976, Volume 3, pages 315-322
Marginal leakage with diflFerent composite restorative materials in vitro Effect of cavity design
HARALD M. ERIKSEN fl«^ MICHAEL G. BUONOCORE Fastman Dental Center, Rochester, New York
Summary
In this preliminary study the degree of marginal leakage was assessed for different cavity designs using both ultra violet-curing and self-curing composite restorative materials and sealants. Butt joint restorations placed in etched and sealant primed cavities failed to prevent leakage. Both saucer-shaped and funnel-shaped cavities and cavities with rounded margins were able to prevent leakage when the restorations were bonded to etched and sealant primed peripheral enamel. Further, less than 1 mm of gingival enamel available for bonding seemed to be suflicient in most instances to prevent leakage. Introduction
Marginal leakage is an inherent shortcoming of all restorative materials and techniques traditionally used in operative dentistry (Going, 1972). The acid etch technique has been demonstrated to give long-lasting and impermeable bonding between resins and acid treated enamel surfaces (Buonocore, 1955; Buonocore, Matsui & Gwinnett, 1968; Laswell, Welk & Regenos, 1971; Silverstone, 1974). Prevention of marginal leakage (Buonocore, Sheykholeslam & Glena, 1973), caries prevention by fissure sealing (Buonocore, 1971; Rock, 1974) and anterior fracture restorations without gross removal of tooth structures (Buonocore & Davila, 1973; Nelson, Till & Hinding, 1974) are some ofthe promising clinical applications of this technique. The development of composite resins with superior physical properties compared to the unfilled self-curing resins has broadened the advantages of the acid etch technique. Consistent prevention of marginal leakage appears to be attainable with a sealant primer featheredge technique. This consists of placing a thin layer of sealant over the etched enamel peripheral to the cavity margins finally covered with a featheredge of the restorative material (Buonocore et al, 1973; Eriksen & Buonocore, 1976). The purpose of the investigation reported here was to test new alternatives in cavity design and restoration techniques utilizing the acid etch principle for eliminating marginal leakage with different restorative materials. Correspondence: Dr Harald M. Eriksen, Department of Operative Dentistry, Dental Faculty, University of Oslo, Geitmyrsvegen, 71 Oslo 4, Norway. 315
316
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Materials and methods The following restorative materials and sealants were used in this study: Nuva-Fil/ Nuva-Seal,* Adaptic/Nuva-Seal Adaptic/Adaptic bonding agent,t Concise/Enamel Bond,J Restodent/§ (no sealant recommended), and an experimental self-curing composite/sealant from L. D. Caulk Co. Restodent was used with 2 drops of monomer to 1 scoop of polymer instead ofthe 1 : 1 ratio recommended by the manufacturer. This experimental low viscosity mix was used because the proportions recommended by the manufacturer provided a very dry mix that was diflicult to featheredge. All the other materials were handled according to the manufacturer's instructions.
(a)
(d)
(c)
(e
Fig. 1. (a) Longitudinal cross-section ofa conventional composite resin butt joint restoration placed in an etched and sealant primed cavity. The sealant is shown in black in all figures. (b) Composite resin restoration featheredged over etched and sealant primed peripheral enamel. The average amount of gingival enamel available for bonding is equal to or less than 1 mm. . (c) Composite resin restoration placed in a saucer-shaped etched and sealant primed cavity including a featheredge over 1 mm peripheral enamel. (d) Composite resin restoration placed in a funnel-shaped cavity and bonded to etched and sealant primed bevelled enamel margins. (e) Composite resin restoration featheredged over 1-5 mm peripheral etched and sealant primed enamel. The cavity margins are rounded.
Intact buccal surfaces of human molars selected from a large pool of extracted teeth were used in the investigation (Eriksen & Buonocore, 1976). The cavity designs and restorative procedures used in the study are described below and illustrated in Figs la-e. After preparation of the cavity designs, the teeth were randomly allocated to five different test groups of six teeth each for restoration with the various test materials. * Nuva-Fil/Nuva-Seal, L. D. Caulk Co., Miiford, Delaware. t Adaptic/Adaptic bonding agent, Johnson & Johnson, East Windsor, N.J. X Concise/Enamel Bond, 3M Company, St. Paul, Minnesota. § Restodent, Lee Pharmaceuticals, South El Monte, California.
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A. Sealant lined butt joint restorations in etched cavities ^ ^• Conventional butt joint Class V cavities were prepared with a carbide fissure bur using an air rotor with water spray at 300,000 rev/min. Mechanical retention at the cavity base was accentuated with an inverted cone carbide bur and the cavity margins finished with a flame-shaped finishing burr, at conventional speed with water coolant. The cavity walls and floor were then etched according to a recommended procedure with the acid conditioning solutions accompanying the respective restorative material used, thoroughly washed with tap water and dried with clean air. The difi"erent sealants were applied as cavity varnishes before final butt joint restorations were made (Eig. la). Nuva-Seal and the Caulk experimental sealant were allowed to cure before applying the restoration while the application of Adaptic bonding agent and Concise Enamel Bond were immediately followed by application of the composite restorative materials as recommended by the manufacturers. In all test groups the Nuva-Seal surface was wiped free of unpolymerized material before Adaptic was applied and cured onto the sealed surface. B. Featheredged restorations over sealant primed etched enamel: gingival enamel equal to or less than 1 mm Class V cavities were prepared as described under group A. However, the gingival margins of the cavities were equal to or less than 1 mm short of the cemento-enamel junction to test the critical amount of gingival enamel necessary to prevent leakage. The sealant-primed featheredge restorative procedure described by Buonocore et al. (1973), was used (Eig. lb). C. Featheredged non-retentive saucer-shaped restorations over sealant primed etched enamel To test the retentive capacity of the acid etch technique in a non-retentive cavity, saucer-shaped preparations were made with a diamond wheel in an air rotor with water spray. The preparations reached the dentine in the deepest areas. After the recommended etching procedures were fulfilled including both the cavity and peripheral enamel, the cavities and surrounding enamel equal to or less than 1 mm were covered by the different sealants. The composite restorations were then applied and finished to a featheredge (Eig. lc). D. Funnel-shaped restorations over sealant primed etched bevelled enamel margins Conventional Class V preparations were prepared as described under group A, but the margins were bevelled to a funnel-shaped opening with a flame-shaped diamond burr. Only the bevelled part of the preparations were acid etched followed by a sealantcomposite resin restorative procedure (Eig. Id). E. Featheredged restorations over sealant primed etched enamel, rounded cavity margins Conventional Class V cavities were prepared as described under group A, except that the enamel margins were slightly rounded before featheredge restorations were placed over acid etched and sealant primed peripheral enamel (Eig. le). Eor group A, marginal leakage was assessed both immediately after finishing of the restorations and after a 0-60 °C hot/cold cycling procedure at 1 min intervals for 1 h. Eor all the other test groups (B-E) the leakage was only assessed after the teeth had been exposed to the hot/cold cycling procedure. The marginal leakage was visualized
318
H. M. Eriksen and M. G. Buonocore .
by an 0-25 % aqueous solution of basic fuchsin dye. All the teeth were covered with utility wax except for the restoration and a 1-2 mm peripheral area before exposure to the dye solution for 24 h. After removal from the dye, the teeth were dewaxed, thoroughly washed and sectioned longitudinally with a Gillings-Hamco sectioning machine, obtaining an average of five sections from each tooth (Eriksen & Buonocore, 1976). All sections were examined through a dissection microscope and the leakage evaluated according to the following index system: 0, no marginal penetration; 1, penetration limited to the dento-enamel border; 2, penetration limited to the walls of the cavity; 3, penetration including both walls and floor of the cavity; and 4, penetration partly or completely through the dentine to the pulp (Buonocore et al., 1973). Kruskal-Wallis one-way analysis of variance (Siegel, 1956) was used to test the differences among leakage scores obtained from the different materials and cavity designs tested. The final evaluation of the leakage was performed by one person and the intra-examiner error was shown to be negligible. Results A. Sealant-lined butt joint restorations in etched cavities (Eig. la) Statistically significant differences were found in this series of experiments suggesting that the different sealant-restorative material combinations varied in their bonding capacity to etched cavity walls (Table 1). Adaptic bonding agent and the experimental Caulk composite-sealant appeared to produce the best sealing qualities. The overall degree of leakage in this experimental series was however high and increased after the hot/cold cycling procedure (Eig. 2a) (Table 1). B. Featheredged restorations over sealant primed etched enamel: gingival enamel equal to or less than 1 mm (Eig. lb) The leakage scores for the materials tested in this series were not significantly different. The majority of the restorations showed a complete prevention of leakage in spite of the limited amount of gingival enamel available for bonding and being stressed through the hot/cold cycling procedure for 1 h (Eig. 2b). A few restorations however, showed heavy leakage, particularly among the Adaptic/Nuva-Seal group (Table 1). The amount of gingival enamel left for bonding in these series was comparable among all the groups investigated (Table 1). C. Featheredged non-retentive saucer-shaped restorations over sealant primed etched enamel (Eig. lc) No statistically significant differences were found between the materials used to restore these non-retentive cavities. Absence of leakage was most frequently detected for all the materials tested (Eig. 2c), although a slight penetration of the dye limited to small areas of the outer part of the restorations (score 1 or 2) was present in some of the teeth (Table 1). D. Funnel-shaped restorations over sealant primed etched bevelled enamel margins (Eig. Id) Except for Restodent, httle or no leakage was the most frequent finding among the different groups (Eig. 2d). The Nuva-Seal/Nuva-Eil restorations showed the least leakage although the difference in leakage scores among the groups in this experimental series was not statistically significant (Table 1).
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Fig. 2. (a) Longitudinal cross-section of a composite resin butt joint restoration placed in an etched and sealant primed cavity (Fig. la). Marginal leakage of basic fuchsin dye penetrating into underlying dentine is present. (For all figures, magnification x 3.) (b) Composite resin restoration featheredged over 0-8 mm gingival etching and sealant primed enamel. No penetration of basic fuchsin dye. (c) Composite resin restoration placed in a saucer.-shaped etched and sealant primed cavity including 1 mm peripheral enamel (Fig. Ic). No leakage after exposure to basic fuchsin dye. (d) Composite resin restoration placed in a funnel-shaped cavity and bonded to etched and sealant primed bevelled cavity margins. No penetration of basic fuchsin dye.
E. Featheredged restorations over sealant primed etched enamel, rounded cavity margins (Fig. le) The differences found among the various materials tested with this restorative technique were statistically not significant and leakage was minimal or absent in most instances. The Adaptic/Adaptic bonding agent group tended to show greater leakage than the others (Table 1). Discussion Acid etching of the whole cavity and application of the sealant as a cavity liner before placing the restorations has been mentioned as a possibility for preventing marginal leakage (Ibsen & Neville, 1975). Although this is a simple and easily applied technique, it consistently failed to prevent marginal leakage with all the materials tested in the present study. This is in agreement with previous findings by Buonocore et al. (1973)
Marginal leakage with composite restorative materials
321
and Baharlov & Moore (1974). The somewhat better adaptation achieved by Adaptic/ Adaptic bonding agent and Caulk experimental composite/sealant may be related to compositional characteristics of these materials. The overall tendency to increase in leakage after hot/cold cycling indicates a low stress-resistance of this bonding technique. The overall poor leakage results may be explained on the basis that bonding to surfaces of longitudinally cut enamel prisms is not as strong as to cross-cut enamel prisms (Gwinnett & Matsui, 1967; Buonocore et al, 1968). Cavities frequently have to be placed close to the cemento-enamel junction. Since a dentine/adhesive interface is not able to prevent leakage with, any of the restorative procedures and materials available today (Friedman & Retief, 1973), the availability of cervical enamel to provide a bonding surface is of great clinical importance. The present investigation shows that an amount of cervical enamel equal to or less than 1-0 mm available for bonding seems to be sufficient in most instances for preventing marginal leakage and even a few restorations with as little as 0-4-0-5 mm of gingival enamel prevented marginal leakage. The cervical enamel has in general a more irregular prism structure than the bulk of enamel and the surface layer may be devoid of the characteristic prism markings (Gwinnett, 1967). This might result in poorer bonding qualities and may account in part for leakage observed with some of the restorations. The acid etch procedure was able to establish a high degree of prevention against gross marginal leakage for all the different combinations of resins tested in the saucershaped non-retentive cavitities through a hot/cold cycling procedure. These results suggest the probability of more conservative means of treating early smooth surface caries lesions. The sealing of white spot lesions using a covering of a fissure sealant has been studied by Davila (1972). The saucer-shaped cavity may be used in connection with such sealing procedures when carious cavitations are present in parts of the white spot lesion. Although some of the restorations with bevelled enamel margins showed a slight degree of leakage after hot/cold cycling, the overall results indicate that this technique has potential for preventing marginal leakage. This cavity design may be beneficial because the margins of the restoration may be more easily defined than with the featheredge technique. This procedure may be applicable in interproximal areas where a featheredge design may not be feasible because of space limitation. Additional preliminary investigations in our laboratory have shown that when dentine is exposed at the gingival margin or if only minute amounts of enamel are left, the bevelling procedure does not prevent leakage. The cavity design with rounded margins not only reduces stress concentrations at the restoration margins but also serves to minimize over-contouring when restoring the tooth by the featheredge technique (Buonocore, 1975). The excellent leakage results from this restorative technique are comparable to the featheredge procedure tested previously where cavity margins were not rounded (Eriksen & Buonocore, 1976). There did not seem to be any major differences detectable in this preliminary study between self-curing and ultra violet-curing materials in preventing marginal leakage when used according to recommended principles. However, the ultra violet polymerized materials permitted unlimited working time to insert and properly contour the restorations and to minimize excess. These advantages could be important in clinical use. Restoration margins terminating against etched dentine or against longitudinally cut etched enamel walls prepared as recommended in conventional restorative procedures seems to provide little protection against marginal leakage with the materials 22
322
H. M. Eriksen and M. G. Buonocore
tested in the present experimental series. The results from this study indicate that the acid etch technique together with the combination of free-flowing sealants and composite resins offer new possibilities for cavity design in operative dentistry for eliminating marginal leakage. A crucial factor for prevention of marginal leakage by the acid etch technique seems to be the utilization of enamel surface peripheral to the cavity margins for bonding a featheredge extention of the restoration. Acknowledgments This investigation was supported in part by the American Association for Dental Research grant no. DE 00197-06 DTL. The authors thank Ms Harta D. Allison for her technical assistance. ; References & MOORE, D . L . (1974) Effect of acid etching on marginal penetration of composite resin restorations. Journal of Prosthetic Dentistry, 32, 152. BUONOCORE, M . G . (1975) Personal communication. BUONOCORE, M.G. (1971) Adhesive seah'ng of pit and fissures for caries prevention with use of ultra violet light. Journal of the American Dental Association, 82, 1090. BUONOCORE, M.G. (1955) A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. Journal of Dental Research, 34, 849. BUONOCORE, M.G. & DAVILA, J . M . (1973) Restoration of fractured anterior teeth with ultra violet light-polymerized bonding materials: A new technique. Journal of the American Dental Association, 86, 1349. BUONOCORE, M.G., MATSUI, A. & GV^/INNETT, A . J . (1968) Penetration of resin dental materials into enamel surfaces with reference to bonding. Archives of Oral Biology, 13, 61. BUONOCORE, M.G., SHEYKHOLESLAM, Z . & GLENA, R . (1973) Evaluation of an enamel adhesive to prevent marginal leakage: An in vitro study. Journal of Dentistry for Children, 40, 119. DAVILA, J.M. (1972) The protective effect of adhesive penetration into early carious lesions. Masters Degree "thesis. University of Rochester. ERIKSEN, H . M . & BUONOCORE, M.G. (1976) Marginal leakage with diflferent composite restorative materials: Effect of restorative technique. Journal of American Dental Association (in press). FRIEDMAN, M . & RETIEF, D . H . (1973) A clinical and laboratory evaluation of a new composite restorative material. Journal of the Dental Association of South Africa, 28, 460. GOING, R . E . (1972) Microleakage around dental restorations: a summarizing review. Journal of the American Dental Association, 84, 1349. GwiNNETT, A.J. (1967) The ultrastructure of the 'prismless' enamel of permanent human teeth. Archives of Oral Biology, 12, 381. GwiNNETT, A.J. & MATSUI, A. (1967) A study of enamel adhesives. The physical relationship between enamel and adhesive. Archives of Oral Biology, 12, 1615. IBSEN, R . L . & NEVILLE, K . (1975) Adhesive restorative dentistry, p. 54. W.B. Saunders, Philadelphia LASWELL, H.R., WELK, D . A . & REGENOS, J . W . (1971) Attachment of resin restorations to acid pretreated enamel Journal of the American Dental Association, 82, 558. NELSON, S.R., TILL, M . J . & HINDING, J . H . (1974) Comparison of materials and methods used in acid etch restorative procedures. Journal of the American Dental Association, 89, 1123. ROCK, W . P . (1974) Fissure sealants: further results of clinical trials. British Dental Journal, 136, 377. SiLVERSTONE, L. (1974) Fissure sealsants. Laboratory studies. Caries Research, 8, 2. SIEGEL, S. (1956) Non-parametric statistics, p. 184. McGraw-Hill, New York. BAHARLOV, D .
Manuscript accepted 11 July 1975
Marginal leakage with diflFerent composite restorative materials in vitro Effect of cavity design
HARALD M. ERIKSEN fl«^ MICHAEL G. BUONOCORE Fastman Dental Center, Rochester, New York
Summary
In this preliminary study the degree of marginal leakage was assessed for different cavity designs using both ultra violet-curing and self-curing composite restorative materials and sealants. Butt joint restorations placed in etched and sealant primed cavities failed to prevent leakage. Both saucer-shaped and funnel-shaped cavities and cavities with rounded margins were able to prevent leakage when the restorations were bonded to etched and sealant primed peripheral enamel. Further, less than 1 mm of gingival enamel available for bonding seemed to be suflicient in most instances to prevent leakage. Introduction
Marginal leakage is an inherent shortcoming of all restorative materials and techniques traditionally used in operative dentistry (Going, 1972). The acid etch technique has been demonstrated to give long-lasting and impermeable bonding between resins and acid treated enamel surfaces (Buonocore, 1955; Buonocore, Matsui & Gwinnett, 1968; Laswell, Welk & Regenos, 1971; Silverstone, 1974). Prevention of marginal leakage (Buonocore, Sheykholeslam & Glena, 1973), caries prevention by fissure sealing (Buonocore, 1971; Rock, 1974) and anterior fracture restorations without gross removal of tooth structures (Buonocore & Davila, 1973; Nelson, Till & Hinding, 1974) are some ofthe promising clinical applications of this technique. The development of composite resins with superior physical properties compared to the unfilled self-curing resins has broadened the advantages of the acid etch technique. Consistent prevention of marginal leakage appears to be attainable with a sealant primer featheredge technique. This consists of placing a thin layer of sealant over the etched enamel peripheral to the cavity margins finally covered with a featheredge of the restorative material (Buonocore et al, 1973; Eriksen & Buonocore, 1976). The purpose of the investigation reported here was to test new alternatives in cavity design and restoration techniques utilizing the acid etch principle for eliminating marginal leakage with different restorative materials. Correspondence: Dr Harald M. Eriksen, Department of Operative Dentistry, Dental Faculty, University of Oslo, Geitmyrsvegen, 71 Oslo 4, Norway. 315
316
H. M. Eriksen and M. G. Buonocore
Materials and methods The following restorative materials and sealants were used in this study: Nuva-Fil/ Nuva-Seal,* Adaptic/Nuva-Seal Adaptic/Adaptic bonding agent,t Concise/Enamel Bond,J Restodent/§ (no sealant recommended), and an experimental self-curing composite/sealant from L. D. Caulk Co. Restodent was used with 2 drops of monomer to 1 scoop of polymer instead ofthe 1 : 1 ratio recommended by the manufacturer. This experimental low viscosity mix was used because the proportions recommended by the manufacturer provided a very dry mix that was diflicult to featheredge. All the other materials were handled according to the manufacturer's instructions.
(a)
(d)
(c)
(e
Fig. 1. (a) Longitudinal cross-section ofa conventional composite resin butt joint restoration placed in an etched and sealant primed cavity. The sealant is shown in black in all figures. (b) Composite resin restoration featheredged over etched and sealant primed peripheral enamel. The average amount of gingival enamel available for bonding is equal to or less than 1 mm. . (c) Composite resin restoration placed in a saucer-shaped etched and sealant primed cavity including a featheredge over 1 mm peripheral enamel. (d) Composite resin restoration placed in a funnel-shaped cavity and bonded to etched and sealant primed bevelled enamel margins. (e) Composite resin restoration featheredged over 1-5 mm peripheral etched and sealant primed enamel. The cavity margins are rounded.
Intact buccal surfaces of human molars selected from a large pool of extracted teeth were used in the investigation (Eriksen & Buonocore, 1976). The cavity designs and restorative procedures used in the study are described below and illustrated in Figs la-e. After preparation of the cavity designs, the teeth were randomly allocated to five different test groups of six teeth each for restoration with the various test materials. * Nuva-Fil/Nuva-Seal, L. D. Caulk Co., Miiford, Delaware. t Adaptic/Adaptic bonding agent, Johnson & Johnson, East Windsor, N.J. X Concise/Enamel Bond, 3M Company, St. Paul, Minnesota. § Restodent, Lee Pharmaceuticals, South El Monte, California.
Marginal leakage with composite restorative materials
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A. Sealant lined butt joint restorations in etched cavities ^ ^• Conventional butt joint Class V cavities were prepared with a carbide fissure bur using an air rotor with water spray at 300,000 rev/min. Mechanical retention at the cavity base was accentuated with an inverted cone carbide bur and the cavity margins finished with a flame-shaped finishing burr, at conventional speed with water coolant. The cavity walls and floor were then etched according to a recommended procedure with the acid conditioning solutions accompanying the respective restorative material used, thoroughly washed with tap water and dried with clean air. The difi"erent sealants were applied as cavity varnishes before final butt joint restorations were made (Eig. la). Nuva-Seal and the Caulk experimental sealant were allowed to cure before applying the restoration while the application of Adaptic bonding agent and Concise Enamel Bond were immediately followed by application of the composite restorative materials as recommended by the manufacturers. In all test groups the Nuva-Seal surface was wiped free of unpolymerized material before Adaptic was applied and cured onto the sealed surface. B. Featheredged restorations over sealant primed etched enamel: gingival enamel equal to or less than 1 mm Class V cavities were prepared as described under group A. However, the gingival margins of the cavities were equal to or less than 1 mm short of the cemento-enamel junction to test the critical amount of gingival enamel necessary to prevent leakage. The sealant-primed featheredge restorative procedure described by Buonocore et al. (1973), was used (Eig. lb). C. Featheredged non-retentive saucer-shaped restorations over sealant primed etched enamel To test the retentive capacity of the acid etch technique in a non-retentive cavity, saucer-shaped preparations were made with a diamond wheel in an air rotor with water spray. The preparations reached the dentine in the deepest areas. After the recommended etching procedures were fulfilled including both the cavity and peripheral enamel, the cavities and surrounding enamel equal to or less than 1 mm were covered by the different sealants. The composite restorations were then applied and finished to a featheredge (Eig. lc). D. Funnel-shaped restorations over sealant primed etched bevelled enamel margins Conventional Class V preparations were prepared as described under group A, but the margins were bevelled to a funnel-shaped opening with a flame-shaped diamond burr. Only the bevelled part of the preparations were acid etched followed by a sealantcomposite resin restorative procedure (Eig. Id). E. Featheredged restorations over sealant primed etched enamel, rounded cavity margins Conventional Class V cavities were prepared as described under group A, except that the enamel margins were slightly rounded before featheredge restorations were placed over acid etched and sealant primed peripheral enamel (Eig. le). Eor group A, marginal leakage was assessed both immediately after finishing of the restorations and after a 0-60 °C hot/cold cycling procedure at 1 min intervals for 1 h. Eor all the other test groups (B-E) the leakage was only assessed after the teeth had been exposed to the hot/cold cycling procedure. The marginal leakage was visualized
318
H. M. Eriksen and M. G. Buonocore .
by an 0-25 % aqueous solution of basic fuchsin dye. All the teeth were covered with utility wax except for the restoration and a 1-2 mm peripheral area before exposure to the dye solution for 24 h. After removal from the dye, the teeth were dewaxed, thoroughly washed and sectioned longitudinally with a Gillings-Hamco sectioning machine, obtaining an average of five sections from each tooth (Eriksen & Buonocore, 1976). All sections were examined through a dissection microscope and the leakage evaluated according to the following index system: 0, no marginal penetration; 1, penetration limited to the dento-enamel border; 2, penetration limited to the walls of the cavity; 3, penetration including both walls and floor of the cavity; and 4, penetration partly or completely through the dentine to the pulp (Buonocore et al., 1973). Kruskal-Wallis one-way analysis of variance (Siegel, 1956) was used to test the differences among leakage scores obtained from the different materials and cavity designs tested. The final evaluation of the leakage was performed by one person and the intra-examiner error was shown to be negligible. Results A. Sealant-lined butt joint restorations in etched cavities (Eig. la) Statistically significant differences were found in this series of experiments suggesting that the different sealant-restorative material combinations varied in their bonding capacity to etched cavity walls (Table 1). Adaptic bonding agent and the experimental Caulk composite-sealant appeared to produce the best sealing qualities. The overall degree of leakage in this experimental series was however high and increased after the hot/cold cycling procedure (Eig. 2a) (Table 1). B. Featheredged restorations over sealant primed etched enamel: gingival enamel equal to or less than 1 mm (Eig. lb) The leakage scores for the materials tested in this series were not significantly different. The majority of the restorations showed a complete prevention of leakage in spite of the limited amount of gingival enamel available for bonding and being stressed through the hot/cold cycling procedure for 1 h (Eig. 2b). A few restorations however, showed heavy leakage, particularly among the Adaptic/Nuva-Seal group (Table 1). The amount of gingival enamel left for bonding in these series was comparable among all the groups investigated (Table 1). C. Featheredged non-retentive saucer-shaped restorations over sealant primed etched enamel (Eig. lc) No statistically significant differences were found between the materials used to restore these non-retentive cavities. Absence of leakage was most frequently detected for all the materials tested (Eig. 2c), although a slight penetration of the dye limited to small areas of the outer part of the restorations (score 1 or 2) was present in some of the teeth (Table 1). D. Funnel-shaped restorations over sealant primed etched bevelled enamel margins (Eig. Id) Except for Restodent, httle or no leakage was the most frequent finding among the different groups (Eig. 2d). The Nuva-Seal/Nuva-Eil restorations showed the least leakage although the difference in leakage scores among the groups in this experimental series was not statistically significant (Table 1).
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Fig. 2. (a) Longitudinal cross-section of a composite resin butt joint restoration placed in an etched and sealant primed cavity (Fig. la). Marginal leakage of basic fuchsin dye penetrating into underlying dentine is present. (For all figures, magnification x 3.) (b) Composite resin restoration featheredged over 0-8 mm gingival etching and sealant primed enamel. No penetration of basic fuchsin dye. (c) Composite resin restoration placed in a saucer.-shaped etched and sealant primed cavity including 1 mm peripheral enamel (Fig. Ic). No leakage after exposure to basic fuchsin dye. (d) Composite resin restoration placed in a funnel-shaped cavity and bonded to etched and sealant primed bevelled cavity margins. No penetration of basic fuchsin dye.
E. Featheredged restorations over sealant primed etched enamel, rounded cavity margins (Fig. le) The differences found among the various materials tested with this restorative technique were statistically not significant and leakage was minimal or absent in most instances. The Adaptic/Adaptic bonding agent group tended to show greater leakage than the others (Table 1). Discussion Acid etching of the whole cavity and application of the sealant as a cavity liner before placing the restorations has been mentioned as a possibility for preventing marginal leakage (Ibsen & Neville, 1975). Although this is a simple and easily applied technique, it consistently failed to prevent marginal leakage with all the materials tested in the present study. This is in agreement with previous findings by Buonocore et al. (1973)
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and Baharlov & Moore (1974). The somewhat better adaptation achieved by Adaptic/ Adaptic bonding agent and Caulk experimental composite/sealant may be related to compositional characteristics of these materials. The overall tendency to increase in leakage after hot/cold cycling indicates a low stress-resistance of this bonding technique. The overall poor leakage results may be explained on the basis that bonding to surfaces of longitudinally cut enamel prisms is not as strong as to cross-cut enamel prisms (Gwinnett & Matsui, 1967; Buonocore et al, 1968). Cavities frequently have to be placed close to the cemento-enamel junction. Since a dentine/adhesive interface is not able to prevent leakage with, any of the restorative procedures and materials available today (Friedman & Retief, 1973), the availability of cervical enamel to provide a bonding surface is of great clinical importance. The present investigation shows that an amount of cervical enamel equal to or less than 1-0 mm available for bonding seems to be sufficient in most instances for preventing marginal leakage and even a few restorations with as little as 0-4-0-5 mm of gingival enamel prevented marginal leakage. The cervical enamel has in general a more irregular prism structure than the bulk of enamel and the surface layer may be devoid of the characteristic prism markings (Gwinnett, 1967). This might result in poorer bonding qualities and may account in part for leakage observed with some of the restorations. The acid etch procedure was able to establish a high degree of prevention against gross marginal leakage for all the different combinations of resins tested in the saucershaped non-retentive cavitities through a hot/cold cycling procedure. These results suggest the probability of more conservative means of treating early smooth surface caries lesions. The sealing of white spot lesions using a covering of a fissure sealant has been studied by Davila (1972). The saucer-shaped cavity may be used in connection with such sealing procedures when carious cavitations are present in parts of the white spot lesion. Although some of the restorations with bevelled enamel margins showed a slight degree of leakage after hot/cold cycling, the overall results indicate that this technique has potential for preventing marginal leakage. This cavity design may be beneficial because the margins of the restoration may be more easily defined than with the featheredge technique. This procedure may be applicable in interproximal areas where a featheredge design may not be feasible because of space limitation. Additional preliminary investigations in our laboratory have shown that when dentine is exposed at the gingival margin or if only minute amounts of enamel are left, the bevelling procedure does not prevent leakage. The cavity design with rounded margins not only reduces stress concentrations at the restoration margins but also serves to minimize over-contouring when restoring the tooth by the featheredge technique (Buonocore, 1975). The excellent leakage results from this restorative technique are comparable to the featheredge procedure tested previously where cavity margins were not rounded (Eriksen & Buonocore, 1976). There did not seem to be any major differences detectable in this preliminary study between self-curing and ultra violet-curing materials in preventing marginal leakage when used according to recommended principles. However, the ultra violet polymerized materials permitted unlimited working time to insert and properly contour the restorations and to minimize excess. These advantages could be important in clinical use. Restoration margins terminating against etched dentine or against longitudinally cut etched enamel walls prepared as recommended in conventional restorative procedures seems to provide little protection against marginal leakage with the materials 22
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tested in the present experimental series. The results from this study indicate that the acid etch technique together with the combination of free-flowing sealants and composite resins offer new possibilities for cavity design in operative dentistry for eliminating marginal leakage. A crucial factor for prevention of marginal leakage by the acid etch technique seems to be the utilization of enamel surface peripheral to the cavity margins for bonding a featheredge extention of the restoration. Acknowledgments This investigation was supported in part by the American Association for Dental Research grant no. DE 00197-06 DTL. The authors thank Ms Harta D. Allison for her technical assistance. ; References & MOORE, D . L . (1974) Effect of acid etching on marginal penetration of composite resin restorations. Journal of Prosthetic Dentistry, 32, 152. BUONOCORE, M . G . (1975) Personal communication. BUONOCORE, M.G. (1971) Adhesive seah'ng of pit and fissures for caries prevention with use of ultra violet light. Journal of the American Dental Association, 82, 1090. BUONOCORE, M.G. (1955) A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. Journal of Dental Research, 34, 849. BUONOCORE, M.G. & DAVILA, J . M . (1973) Restoration of fractured anterior teeth with ultra violet light-polymerized bonding materials: A new technique. Journal of the American Dental Association, 86, 1349. BUONOCORE, M.G., MATSUI, A. & GV^/INNETT, A . J . (1968) Penetration of resin dental materials into enamel surfaces with reference to bonding. Archives of Oral Biology, 13, 61. BUONOCORE, M.G., SHEYKHOLESLAM, Z . & GLENA, R . (1973) Evaluation of an enamel adhesive to prevent marginal leakage: An in vitro study. Journal of Dentistry for Children, 40, 119. DAVILA, J.M. (1972) The protective effect of adhesive penetration into early carious lesions. Masters Degree "thesis. University of Rochester. ERIKSEN, H . M . & BUONOCORE, M.G. (1976) Marginal leakage with diflferent composite restorative materials: Effect of restorative technique. Journal of American Dental Association (in press). FRIEDMAN, M . & RETIEF, D . H . (1973) A clinical and laboratory evaluation of a new composite restorative material. Journal of the Dental Association of South Africa, 28, 460. GOING, R . E . (1972) Microleakage around dental restorations: a summarizing review. Journal of the American Dental Association, 84, 1349. GwiNNETT, A.J. (1967) The ultrastructure of the 'prismless' enamel of permanent human teeth. Archives of Oral Biology, 12, 381. GwiNNETT, A.J. & MATSUI, A. (1967) A study of enamel adhesives. The physical relationship between enamel and adhesive. Archives of Oral Biology, 12, 1615. IBSEN, R . L . & NEVILLE, K . (1975) Adhesive restorative dentistry, p. 54. W.B. Saunders, Philadelphia LASWELL, H.R., WELK, D . A . & REGENOS, J . W . (1971) Attachment of resin restorations to acid pretreated enamel Journal of the American Dental Association, 82, 558. NELSON, S.R., TILL, M . J . & HINDING, J . H . (1974) Comparison of materials and methods used in acid etch restorative procedures. Journal of the American Dental Association, 89, 1123. ROCK, W . P . (1974) Fissure sealants: further results of clinical trials. British Dental Journal, 136, 377. SiLVERSTONE, L. (1974) Fissure sealsants. Laboratory studies. Caries Research, 8, 2. SIEGEL, S. (1956) Non-parametric statistics, p. 184. McGraw-Hill, New York. BAHARLOV, D .
Manuscript accepted 11 July 1975
