- Email: [email protected]
Necessity of bevels for box only Class II composite restorations
Necessity of bevels for box only Class II composite restorations Niek J. M. Opdam, DMD, PhD,a Joost J. M. Roeters, DMD, PhD,b Ruud Kuijs, DMD,c and Rob C. W. Burgersdijk, DMD, PhDd University of Nijmegen, Nijmegen, The Netherlands Statement of problem. The tooth preparation of a bevel is recommended to improve marginal quality of a composite restoration. However, in small Class II restorations, it is unclear if a bevel also contributed to a better marginal fit. Purpose. This study investigated the influence of tooth preparation design on microleakage of minimal posterior Class II composite restorations. Material and methods. Box-shaped Class II tooth preparations for posterior composite restorations in maxillary premolars were restored with a total etch technique. The tooth preparations were beveled or nonbeveled and the box prepared at a right angle cervically or additionally excavated. The facial and lingual box margins were also either beveled or unbeveled. The teeth were thermocycled and immersed in a dye solution. After sectioning specimens, dye penetration at the facial and palatal margins was recorded. Results. A bevel-reduced microleakage both at the cervical and ascending walls. Enamel cracks were observed along certain unbeveled margins as recorded in this study. The additional excavation did not contribute to reduction of microleakage. Conclusions. Tooth preparation of a bevel is recommended for an optimal marginal seal in small box-type Class II composite restorations. (J Prosthet Dent 1998;80:274-9.)
CLINICAL IMPLICATIONS It is recommended to place a bevel at the margins of small box-type Class II composite restorations to control marginal leakage.
W
hen a tooth is restored for the first time, an adhesive restoration can preserve sound tooth tissue compared with conventional silver amalgam.1 This is particularly true when a tooth is initially restored. Therefore small carious lesions for the proximal surfaces of premolars and molars should conserve sound tooth tissue. Tunnel restorations or box-type (saucer-shaped) restorations are viable alternatives. However, the tunnel restoration has been difficult to control because of a limited access to the cavity and poor clinical performance.2,3 Although clinical studies have been limited, current investigations have demonstrated a suitable clinical performance for box-type restorations.4,5 Considerable effort has been made to reduce the microleakage of restorations. The inability of restorative materials to seal the interface with tooth structure encouraged microleakage of intraoral irritants. 6 Bergenholtz et al.7 stated positively that microleakage This investigation was financially supported by the Dutch Dental Association (NMT)-Nieuwegein, The Netherlands. aAssistant Professor, Department of Cariology and Endodontology. bAssistant Professor, Department of Cariology and Endodontology. cAssistant Professor, Department of Cariology and Endodontology. dProfessor, Department of Cariology and Endodontology. 274 THE JOURNAL OF PROSTHETIC DENTISTRY
of restorative materials has great clinical significance. Sensitivity, bacterial infiltration, and secondary caries may develop from microleakage. An adhesive restoration technique can reduce microleakage particularly when advanced adhesive systems are selected.8,9 The dentist has the opportunity to modify the tooth preparation design of the carious surface with minimal removal of sound tooth tissue, especially with previously unrestored teeth. During removal of dental caries of a Class II defect, the dentist has the opportunity to either extend the cervical outline of the tooth preparation to the carious-free dentinoenamel junction or restrict the tooth preparation to sound enamel. The dental caries is later removed at the dentinoenamel junction with a round bur. Tooth preparation of a bevel is recommended to improve the bonding surface and reduce microleakage. However, tooth preparation of a bevel is arduous in small cavity preparations when the approximal margins are in contact with the adjacent tooth. In extensive loss of tooth structure, tooth preparation of a bevel at a cervical margin may result in removal of remaining enamel. Another effect of beveling is an enlargement of the tooth preparation, unless unsupported enamel is preserved. VOLUME 80 NUMBER 3
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Fig. 1. Unbeveled tooth preparation (group 1).
Fig. 2. Beveled tooth preparation (group 2).
The purpose of this study was to investigate the influence of a bevel on microleakage of minimal Class II composite restorations.
tooth long axis. The cervical margin ended 2 mm superior to the enamel-cement junction. Teeth were divided into 4 groups of cavity designs, according to tooth preparations: Group 1: Tooth preparation remained as described, which resulted in a butt-joint outline at the cervical margin and a concave-shaped margin at facial and lingual walls of the box because of the shape of the diamond stone (Fig. 1). Group 2: Tooth preparation was beveled at the facial, lingual, and cervical margins. The 45-degree bevel, 1 mm in width, was made with a fine diamond stone (Horico FG 539 F 007) (Fig. 2). Group 3: Same procedures as group 1, except at the
MATERIAL AND METHODS Box-shaped Class II tooth preparations were completed for 20 extracted sound maxillary premolars, which were stored in a 1% chloramine solution after extraction. Each tooth received 2 box tooth preparations at the mesial and distal surfaces, which were performed with a diamond stone (Meisinger 836012). The width of the box was 3 mm buccolingual and the axial depth was 1.5 mm at the cervical margin. The axial wall was prepared in a parallel direction with the SEPTEMBER 1998
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OPDAM ET AL
Fig. 3. Unbeveled tooth preparation combined with excavation (group 3).
Fig. 4. Beveled tooth preparation combined with excavation (group 4).
cervical wall of the tooth preparation, excavation was simulated with a round bur (Meisinger HM 1012) (Fig. 3). Group 4: Same procedures as group 3; however, the tooth preparation was beveled at the facial, lingual, and cervical margins according to the procedure in group 2 (Fig. 4). The teeth were mounted in an artificial jaw and were in contact with adjacent teeth to simulate clinical conditions. A Lucifix transparent matrix with light-reflecting Luciwedges material (Hawe Neos, Bioggio, Switzerland) was placed around each tooth. Tooth preparations were etched with 35% phosphoric acid (DMG, Hamburg, Germany) for 15 seconds, rinsed
with water spray for 20 seconds, then gently dried with a stream of air. Clearfil Photo Bond material (Kuraray, Osaka, Japan) was mixed and applied to the cavity, thinned with a gentle stream of air, and cured during 10 seconds of light polymerization (Translux, Kulzer, Wehrheim, Germany) at an intensity of 600 mW/cm2. Composite (Clearfil Ray Posterior, Kuraray, Osaka, Japan) was injected in the cavity with a Centrix tip (Hawe Neos, Bioggio, Switzerland), in a composite delivery gun (Caulk - DeTrey Dentsply, Konstanz, Germany). Composite was applied in 2 layers. The first layer was inserted on the floor of the cavity and carefully shaped against the palatal wall of the cavity. This layer was
276
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Table I. Results for dye penetration 0
Cervical dye penetration Group 2–bevel Group 4–bevel with excavation Group 3–no bevel with excavation Group 1–no bevel Approximal dye penetration Group 1/3–no bevel Group 2/4–bevel
1
2
10 5
4
1
2
3
2
1
1
6
6 19
12 1
2
3
4
* 1
2 2
*Results within same level of significance are marked.
cured for 30 seconds through the light-reflecting wedge and palatal cusp. Subsequently, a second layer was injected in the cavity to complete the restoration. This layer was cured for 30 seconds from the buccal side through the cusp. Finally, the restoration was cured for an additional 30 seconds from the occlusal surface (Fig. 5). The restorations were removed from the artificial jaw and finished occlusally with a fine grit diamond stone (830 C 016, Meisinger, Düsseldorf, Germany) and approximally with Soflex disks (3M, St. Paul, Minn.). After 24 hours storage in tap water, the teeth were thermocycled (500 cycles at 5° to 55°C) and coated with 2 layers of nail varnish with the surfaces of restorations remaining free. The teeth were then immersed in a dye solution (basic fuchsin) for 24 hours. After embedding the teeth in an acrylic resin (Fastacryl), the teeth were sectioned with a 0.5-mm thick diamond saw (Bronwill, Rochester, N.Y.). Teeth were sectioned horizontally so the cervical half of the restorations remained intact. The section was inspected from the occlusal surface with a microscope. Dye penetration at the facial and palatal margins was scored on a 5-point ordinal rating scale: 0, no leakage; 1, leakage restricted to enamel; 2, leakage in dentin not reaching axial cavity wall; 3, leakage to axial cavity wall; 4, leakage beyond axial cavity wall into the pulp. Each tooth was subsequently sectioned mesiodistally along the fissure system, and cervical dye penetration was also scored according to the identical ordinal rating scale. Dye penetration at the palatal and facial margins was statistically compared by using a Mann-Whitney U-test at P<.05. The data for cervical dye penetration were statistically compared by using a Kruskal-Wallis analysis of variance (ANOVA) at P<.05. Statistically significant differences in microleakage between separate groups were computed with the Mann-Whitney U-test at P<.05, corrected to .01 for multiple group testing. SEPTEMBER 1998
Fig. 5. Restorative procedure. A, Application and polymerization of first layer. B, Application and polymerization of second layer.
RESULTS Table I presents the microleakage values for various tooth preparation designs. The Kruskal-Wallis ANOVA revealed a significant influence of tooth preparation design on cervical microleakage. The differences in microleakage between groups were statistically significant (Mann-Whitney U-test; P<.05) (Table I). A bevel at the facial and palatal margins resulted in 95% of restorations without microleakage. The absence of a bevel resulted in 30% restorations without leakage and these differences were statistically significant (Mann-Whitney U-test, P<.05). Microleakage at the ascending wall extended into the dentin in 10% of the restorations. For microleakage at the cervical margin, the cervical bevel used in groups 2 and 4 resulted in 75% of the restorations without microleakage at the cervical margins. Group 2 without microleakage produced the best results. However, an unbeveled cervical outline resulted in only 15% of restorations without leakage and 70% of the restorations exhibited microleakage in dentin. 277
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The differences of the groups with additional excavation (3 and 4) with comparable groups without excavation (1 and 2) were not statistically significant. The pattern of microleakage recorded for groups with excavation was commonly dye penetration through a horizontal fracture between enamel prisms adjacent to the cervical margin of the restoration. Enamel cracks inducing microleakage were also observed in restorations of group 1.
DISCUSSION Research has focused on alternatives to dental silver amalgam in the treatment of dental caries. Composites are available that have recorded satisfactory results in clinical studies. A 3-year clinical study with the same composite selected for this study demonstrated excellent responses of the restorations without signs of postoperative sensitivity.10 Insertion of a composite restoration has become less complicated because of the development of total etch adhesives that can be applied to dentin and enamel. The adhesive in our study has demonstrated adequate performance in other in vitro and in vivo studies.8-10 Therefore, in our study, excellent results were possibly restricted to small Class II cavities. The beveled restorations recorded virtually no leakage. The experimental tooth preparation designs in this study were used to investigate the influence of either a simplification of tooth preparation design (no bevel) or a design that preserved cervical enamel. Tooth preparation of a bevel appeared to reduce the microleakage both at the cervical and ascending walls. This was in agreement with other studies that also observed the phenomenon of enamel cracks along an unbeveled margin11,12; these cracks were also reported by Crim and Chapman.13 The additional excavation did not contribute to a reduction of microleakage. In similar research, a retentive groove at the cervical wall was discovered beneficial to reduce microleakage.14 This experimental tooth preparation with a cavosurface design resembling the cavity preparation of group 4 reduced microleakage.15 However, in one study, a chemical-curing composite was selected, with a different shrinkage pattern.15 Another factor may be that, in this study, more unsupported enamel remained, as fractures in the enamel close to the margin of the restoration were observed. These fractures were also verified by Oilo and Jørgensen.16 Marginal leakage in the ascending walls in this study was restricted to enamel in 95% of the cases, but a bevel did affect diminished microleakage. Evidently, microleakage was more pronounced along the cervical margin. The results may also have been influenced by the consistency of the composite selected and the mode of application. Excessive manipulation of the composite may have also resulted in a reduced adaptation to 278
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the cavity wall.17 In addition, the narrow-shaped area of the bevel may have hindered the flow of composite to the cervical outline. However, a suitable adaptation to the cavity wall was discovered in this study because the selected composite had a medium consistency and was injected in the cavity.18,19 This study indicated that a bevel is recommended when a tooth preparation is made for a minimal Class II composite restoration. However, in a 5-year clinical study, different responses were not recorded for Class II composite restorations with or without a bevel.20 An 11-year clinical study of beveled and nonbeveled Class III restorations reported no difference in survival rate.21 Therefore a clinical study that compares beveled and nonbeveled small Class II box-restorations is necessary to establish the clinical relevance of this study.
CONCLUSIONS The following conclusions were drawn from this study. 1. Tooth preparation of a bevel-reduced microleakage at both the cervical and ascending walls of a small Class II box-type composite resin restoration. 2. Tooth preparation of a bevel is recommended for both cavity designs in this study. REFERENCES 1. Walls AW, Murray JJ, McCabe JF. The management of occlusal caries in permanent molars. A clinical trial comparing a minimal composite restoration with an occlusal amalgam restoration. Br Dent J 1988;164: 288-92. 2. Do Amaral Zenkner JE, Baratieri LN, Monteiro S, Caldeira De Andrada MA, Vieira LCC. Clinical and radiographic evaluation of cermet tunnel restorations on primary molars. Quintessence Int 1993;24:783-91. 3. Strand GV, Nordbø H, Tveit AB, Espelid I, Wikstrand K, Eide GE. A 3-year clinical study of tunnel restorations. Eur J Oral Sci 1996;104:384-9. 4. Nordbø H, Leirskar J, Von der Fehr FR. Saucer-shaped cavity preparation for composite resin restorations in Class II carious lesions: three-year results. J Prosthet Dent 1993;69:155-9. 5. Kreulen CM. A study on assessing quality aspects of class II restorations. [Thesis.] Amsterdam: ACTA; 1992. p. 75-81. 6. Brännström M. Infection beneath composite resin restorations: Can it be avoided? Oper Dent 1987;12:158-63. 7. Bergenholtz G, Cox CF, Loesche WJ, Syed SA. Bacterial leakage around dental restorations: its effect on the dental pulp. J Oral Pathol 1982;11: 439-50. 8. Abdalla AI, Davidson CL. Comparison of the marginal integrity of in vivo and in vitro Class II composite restorations. J Dent 1993;21:158-62. 9. Abdalla AI, Davidson CL. Comparison of the marginal axial wall integrity of in-vivo and in-vitro made adhesive class V restorations. J Oral Rehabil 1993;20:257-69. 10. Wendt SL, Leinfelder KF. Clinical evaluation of Clearfil photo posterior: 3year results. Am J Dent 1992;5:121-5. 11. Lösche GM, Neuerburg CM, Roulet JF. Die adhäsive Versorgung konservativer Klasse II Kavitäten. Deutsch Zahn Zeitschr 1993;48:26-30. 12. Hilton TJ, Schwartz RS, Ferracane JL. Microleakage of four Class II resin composite insertion techniques at intraoral temperature. Quintessence Int 1997;28:135-44. 13. Crim GA, Chapman KW. Reducing microleakage in Class II restorations: an in-vitro study. Quintessence Int 1994;25:781-5. 14. Shahani DR, Menezes JM. The effect of retention grooves on posterior composite resin restorations: an in vitro microleakage study. Oper Dent 1992;17:156-64. 15. Porte A, Lutz F, Lund MR, Swartz ML, Cochran MA. Cavity designs for composite resins. Oper Dent 1984;9:50-6.
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16. Oilo G, Jørgensen KD. Effect of beveling on the occurrence of fracture in the enamel surrounding composite resin fillings. J Oral Rehabil 1977;4: 305-8. 17. Hansen EK, Asmussen E. Efficacy of dentin-bonding agents in relation to application technique. Acta Odontol Scand 1989;47:117-20. 18. Opdam N, Roeters JJ, Peters TC, Burgersdijk RC, Teunis M. Cavity wall adaptation and voids in adhesive Class I resin restorations. Dent Mater 1996;12:230-5. 19. Opdam N, Roeters JJ, Peters TC, Burgersdijk RC, Kuyijs RH. Consistency of resin composites for posterior use. Dent Mater 1996;12:350-4. 20. Wilson NH. Performance of occlusion in butt-joint and bevel-edged preparations: five-year results. 4. Dent Mater 1991;7:92-8. 21. Qvist V, Strøm C. Eleven-year assessment of Class-III resin restorations completed with two restorative procedures. Acta Odontol Scand 1993;51:253-62.
Noteworthy Abstracts of the Current Literature
Reprint requests to: DR. N. J. M. OPDAM DEPARTMENT OF CARIOLOGY AND ENDODONTOLOGY UNIVERSITY OF NIJMEGEN PO BOX 9101 NL 6500 NIJMEGEN THE NETHERLANDS Copyright © 1998 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/98/$.500 + 0. 10/1/91495
Effect of heating delay on conversion and strength of a post-cured resin composite Loza-Herrero MA, Rueggeberg FA, Caughman WF, Schuster GS, Lefebvre CA, Gardner FM. J Dent Res 1998;77:426-31.
Purpose. This investigation examined the effect of delayed and post-cure heating (after initial light-polymerization) on the strength and monomer conversion of 1 commercially available composite. Material and Methods. A total of 160 disk-shaped specimens (10 × 1 mm thick) were fabricated from a commercially available composite material (Herculite XRV, Shade A3, Kerr/Sybron). All specimens were initially light-polymerized for 60 seconds on each side in an aluminum mold using a controlled light source. Two types of specimens were fabricated. One type was used as a “light-polymerized only” control, and the other was subjected to post-cure heat treatment for 7 minutes at 100°C. All specimens were coded and stored at room temperature in a light tight container until needed. The following time intervals between initial light-polymerization and post-cure treatment of the specimens were 5 and 30 minutes, and 6, 24, 48, 72, 96, and 120 hours. Ten test specimens and 10 control specimens were used for each time interval. After the designated time delay, the unheated and post-cured composite specimens were subjected to testing to determine biaxial flexural strength. Ten specimens per test group were then analyzed for monomer conversion using infrared spectroscopy. Analyses of variance (α = 0.05), Fischer’s Protected LSD tests, Dunnett’s t tests, and Student’s t tests were used to analyze the data. Results. Both delay time and type of treatment revealed a significant effect upon the biaxial flexure strength of the specimens, as did the interaction of these parameters. Control specimens seemed to gain strength with increasing time. This was confirmed by linear regression analysis. No such correlation existed between strength and delay time for post-cure heated specimens. The only time intervals that demonstrated greater strength values for the post-cured specimens compared with the unheated control group specimens were the 5- and 30-minute delays. Both delay time and type of treatment significantly affected the observed cure values (monomer conversion) and the interaction of these variables. Cure values of unheated specimens were observed to increase with time after initial light-polymerization. Monomer conversion of heated specimens also declined with delay in heat application. Conclusions. Post-cure heating did not significantly affect the biaxial flexural strength of the composite tested, and time delay of heat application was not a significant factor in strength. Postcure heating of the composite significantly affected the increase in monomer conversion, and the time after which heat was applied following initial light-polymerization was influential. Early application of heat, after initial light-polymerization, resulted in higher monomer conversion values. For the greatest amount of polymerization, post-cure heating should be applied within 6 hours after light-polymerization. 17 References.—DL DIXON
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279
CLINICAL IMPLICATIONS It is recommended to place a bevel at the margins of small box-type Class II composite restorations to control marginal leakage.
W
hen a tooth is restored for the first time, an adhesive restoration can preserve sound tooth tissue compared with conventional silver amalgam.1 This is particularly true when a tooth is initially restored. Therefore small carious lesions for the proximal surfaces of premolars and molars should conserve sound tooth tissue. Tunnel restorations or box-type (saucer-shaped) restorations are viable alternatives. However, the tunnel restoration has been difficult to control because of a limited access to the cavity and poor clinical performance.2,3 Although clinical studies have been limited, current investigations have demonstrated a suitable clinical performance for box-type restorations.4,5 Considerable effort has been made to reduce the microleakage of restorations. The inability of restorative materials to seal the interface with tooth structure encouraged microleakage of intraoral irritants. 6 Bergenholtz et al.7 stated positively that microleakage This investigation was financially supported by the Dutch Dental Association (NMT)-Nieuwegein, The Netherlands. aAssistant Professor, Department of Cariology and Endodontology. bAssistant Professor, Department of Cariology and Endodontology. cAssistant Professor, Department of Cariology and Endodontology. dProfessor, Department of Cariology and Endodontology. 274 THE JOURNAL OF PROSTHETIC DENTISTRY
of restorative materials has great clinical significance. Sensitivity, bacterial infiltration, and secondary caries may develop from microleakage. An adhesive restoration technique can reduce microleakage particularly when advanced adhesive systems are selected.8,9 The dentist has the opportunity to modify the tooth preparation design of the carious surface with minimal removal of sound tooth tissue, especially with previously unrestored teeth. During removal of dental caries of a Class II defect, the dentist has the opportunity to either extend the cervical outline of the tooth preparation to the carious-free dentinoenamel junction or restrict the tooth preparation to sound enamel. The dental caries is later removed at the dentinoenamel junction with a round bur. Tooth preparation of a bevel is recommended to improve the bonding surface and reduce microleakage. However, tooth preparation of a bevel is arduous in small cavity preparations when the approximal margins are in contact with the adjacent tooth. In extensive loss of tooth structure, tooth preparation of a bevel at a cervical margin may result in removal of remaining enamel. Another effect of beveling is an enlargement of the tooth preparation, unless unsupported enamel is preserved. VOLUME 80 NUMBER 3
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THE JOURNAL OF PROSTHETIC DENTISTRY
Fig. 1. Unbeveled tooth preparation (group 1).
Fig. 2. Beveled tooth preparation (group 2).
The purpose of this study was to investigate the influence of a bevel on microleakage of minimal Class II composite restorations.
tooth long axis. The cervical margin ended 2 mm superior to the enamel-cement junction. Teeth were divided into 4 groups of cavity designs, according to tooth preparations: Group 1: Tooth preparation remained as described, which resulted in a butt-joint outline at the cervical margin and a concave-shaped margin at facial and lingual walls of the box because of the shape of the diamond stone (Fig. 1). Group 2: Tooth preparation was beveled at the facial, lingual, and cervical margins. The 45-degree bevel, 1 mm in width, was made with a fine diamond stone (Horico FG 539 F 007) (Fig. 2). Group 3: Same procedures as group 1, except at the
MATERIAL AND METHODS Box-shaped Class II tooth preparations were completed for 20 extracted sound maxillary premolars, which were stored in a 1% chloramine solution after extraction. Each tooth received 2 box tooth preparations at the mesial and distal surfaces, which were performed with a diamond stone (Meisinger 836012). The width of the box was 3 mm buccolingual and the axial depth was 1.5 mm at the cervical margin. The axial wall was prepared in a parallel direction with the SEPTEMBER 1998
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Fig. 3. Unbeveled tooth preparation combined with excavation (group 3).
Fig. 4. Beveled tooth preparation combined with excavation (group 4).
cervical wall of the tooth preparation, excavation was simulated with a round bur (Meisinger HM 1012) (Fig. 3). Group 4: Same procedures as group 3; however, the tooth preparation was beveled at the facial, lingual, and cervical margins according to the procedure in group 2 (Fig. 4). The teeth were mounted in an artificial jaw and were in contact with adjacent teeth to simulate clinical conditions. A Lucifix transparent matrix with light-reflecting Luciwedges material (Hawe Neos, Bioggio, Switzerland) was placed around each tooth. Tooth preparations were etched with 35% phosphoric acid (DMG, Hamburg, Germany) for 15 seconds, rinsed
with water spray for 20 seconds, then gently dried with a stream of air. Clearfil Photo Bond material (Kuraray, Osaka, Japan) was mixed and applied to the cavity, thinned with a gentle stream of air, and cured during 10 seconds of light polymerization (Translux, Kulzer, Wehrheim, Germany) at an intensity of 600 mW/cm2. Composite (Clearfil Ray Posterior, Kuraray, Osaka, Japan) was injected in the cavity with a Centrix tip (Hawe Neos, Bioggio, Switzerland), in a composite delivery gun (Caulk - DeTrey Dentsply, Konstanz, Germany). Composite was applied in 2 layers. The first layer was inserted on the floor of the cavity and carefully shaped against the palatal wall of the cavity. This layer was
276
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Table I. Results for dye penetration 0
Cervical dye penetration Group 2–bevel Group 4–bevel with excavation Group 3–no bevel with excavation Group 1–no bevel Approximal dye penetration Group 1/3–no bevel Group 2/4–bevel
1
2
10 5
4
1
2
3
2
1
1
6
6 19
12 1
2
3
4
* 1
2 2
*Results within same level of significance are marked.
cured for 30 seconds through the light-reflecting wedge and palatal cusp. Subsequently, a second layer was injected in the cavity to complete the restoration. This layer was cured for 30 seconds from the buccal side through the cusp. Finally, the restoration was cured for an additional 30 seconds from the occlusal surface (Fig. 5). The restorations were removed from the artificial jaw and finished occlusally with a fine grit diamond stone (830 C 016, Meisinger, Düsseldorf, Germany) and approximally with Soflex disks (3M, St. Paul, Minn.). After 24 hours storage in tap water, the teeth were thermocycled (500 cycles at 5° to 55°C) and coated with 2 layers of nail varnish with the surfaces of restorations remaining free. The teeth were then immersed in a dye solution (basic fuchsin) for 24 hours. After embedding the teeth in an acrylic resin (Fastacryl), the teeth were sectioned with a 0.5-mm thick diamond saw (Bronwill, Rochester, N.Y.). Teeth were sectioned horizontally so the cervical half of the restorations remained intact. The section was inspected from the occlusal surface with a microscope. Dye penetration at the facial and palatal margins was scored on a 5-point ordinal rating scale: 0, no leakage; 1, leakage restricted to enamel; 2, leakage in dentin not reaching axial cavity wall; 3, leakage to axial cavity wall; 4, leakage beyond axial cavity wall into the pulp. Each tooth was subsequently sectioned mesiodistally along the fissure system, and cervical dye penetration was also scored according to the identical ordinal rating scale. Dye penetration at the palatal and facial margins was statistically compared by using a Mann-Whitney U-test at P<.05. The data for cervical dye penetration were statistically compared by using a Kruskal-Wallis analysis of variance (ANOVA) at P<.05. Statistically significant differences in microleakage between separate groups were computed with the Mann-Whitney U-test at P<.05, corrected to .01 for multiple group testing. SEPTEMBER 1998
Fig. 5. Restorative procedure. A, Application and polymerization of first layer. B, Application and polymerization of second layer.
RESULTS Table I presents the microleakage values for various tooth preparation designs. The Kruskal-Wallis ANOVA revealed a significant influence of tooth preparation design on cervical microleakage. The differences in microleakage between groups were statistically significant (Mann-Whitney U-test; P<.05) (Table I). A bevel at the facial and palatal margins resulted in 95% of restorations without microleakage. The absence of a bevel resulted in 30% restorations without leakage and these differences were statistically significant (Mann-Whitney U-test, P<.05). Microleakage at the ascending wall extended into the dentin in 10% of the restorations. For microleakage at the cervical margin, the cervical bevel used in groups 2 and 4 resulted in 75% of the restorations without microleakage at the cervical margins. Group 2 without microleakage produced the best results. However, an unbeveled cervical outline resulted in only 15% of restorations without leakage and 70% of the restorations exhibited microleakage in dentin. 277
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The differences of the groups with additional excavation (3 and 4) with comparable groups without excavation (1 and 2) were not statistically significant. The pattern of microleakage recorded for groups with excavation was commonly dye penetration through a horizontal fracture between enamel prisms adjacent to the cervical margin of the restoration. Enamel cracks inducing microleakage were also observed in restorations of group 1.
DISCUSSION Research has focused on alternatives to dental silver amalgam in the treatment of dental caries. Composites are available that have recorded satisfactory results in clinical studies. A 3-year clinical study with the same composite selected for this study demonstrated excellent responses of the restorations without signs of postoperative sensitivity.10 Insertion of a composite restoration has become less complicated because of the development of total etch adhesives that can be applied to dentin and enamel. The adhesive in our study has demonstrated adequate performance in other in vitro and in vivo studies.8-10 Therefore, in our study, excellent results were possibly restricted to small Class II cavities. The beveled restorations recorded virtually no leakage. The experimental tooth preparation designs in this study were used to investigate the influence of either a simplification of tooth preparation design (no bevel) or a design that preserved cervical enamel. Tooth preparation of a bevel appeared to reduce the microleakage both at the cervical and ascending walls. This was in agreement with other studies that also observed the phenomenon of enamel cracks along an unbeveled margin11,12; these cracks were also reported by Crim and Chapman.13 The additional excavation did not contribute to a reduction of microleakage. In similar research, a retentive groove at the cervical wall was discovered beneficial to reduce microleakage.14 This experimental tooth preparation with a cavosurface design resembling the cavity preparation of group 4 reduced microleakage.15 However, in one study, a chemical-curing composite was selected, with a different shrinkage pattern.15 Another factor may be that, in this study, more unsupported enamel remained, as fractures in the enamel close to the margin of the restoration were observed. These fractures were also verified by Oilo and Jørgensen.16 Marginal leakage in the ascending walls in this study was restricted to enamel in 95% of the cases, but a bevel did affect diminished microleakage. Evidently, microleakage was more pronounced along the cervical margin. The results may also have been influenced by the consistency of the composite selected and the mode of application. Excessive manipulation of the composite may have also resulted in a reduced adaptation to 278
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the cavity wall.17 In addition, the narrow-shaped area of the bevel may have hindered the flow of composite to the cervical outline. However, a suitable adaptation to the cavity wall was discovered in this study because the selected composite had a medium consistency and was injected in the cavity.18,19 This study indicated that a bevel is recommended when a tooth preparation is made for a minimal Class II composite restoration. However, in a 5-year clinical study, different responses were not recorded for Class II composite restorations with or without a bevel.20 An 11-year clinical study of beveled and nonbeveled Class III restorations reported no difference in survival rate.21 Therefore a clinical study that compares beveled and nonbeveled small Class II box-restorations is necessary to establish the clinical relevance of this study.
CONCLUSIONS The following conclusions were drawn from this study. 1. Tooth preparation of a bevel-reduced microleakage at both the cervical and ascending walls of a small Class II box-type composite resin restoration. 2. Tooth preparation of a bevel is recommended for both cavity designs in this study. REFERENCES 1. Walls AW, Murray JJ, McCabe JF. The management of occlusal caries in permanent molars. A clinical trial comparing a minimal composite restoration with an occlusal amalgam restoration. Br Dent J 1988;164: 288-92. 2. Do Amaral Zenkner JE, Baratieri LN, Monteiro S, Caldeira De Andrada MA, Vieira LCC. Clinical and radiographic evaluation of cermet tunnel restorations on primary molars. Quintessence Int 1993;24:783-91. 3. Strand GV, Nordbø H, Tveit AB, Espelid I, Wikstrand K, Eide GE. A 3-year clinical study of tunnel restorations. Eur J Oral Sci 1996;104:384-9. 4. Nordbø H, Leirskar J, Von der Fehr FR. Saucer-shaped cavity preparation for composite resin restorations in Class II carious lesions: three-year results. J Prosthet Dent 1993;69:155-9. 5. Kreulen CM. A study on assessing quality aspects of class II restorations. [Thesis.] Amsterdam: ACTA; 1992. p. 75-81. 6. Brännström M. Infection beneath composite resin restorations: Can it be avoided? Oper Dent 1987;12:158-63. 7. Bergenholtz G, Cox CF, Loesche WJ, Syed SA. Bacterial leakage around dental restorations: its effect on the dental pulp. J Oral Pathol 1982;11: 439-50. 8. Abdalla AI, Davidson CL. Comparison of the marginal integrity of in vivo and in vitro Class II composite restorations. J Dent 1993;21:158-62. 9. Abdalla AI, Davidson CL. Comparison of the marginal axial wall integrity of in-vivo and in-vitro made adhesive class V restorations. J Oral Rehabil 1993;20:257-69. 10. Wendt SL, Leinfelder KF. Clinical evaluation of Clearfil photo posterior: 3year results. Am J Dent 1992;5:121-5. 11. Lösche GM, Neuerburg CM, Roulet JF. Die adhäsive Versorgung konservativer Klasse II Kavitäten. Deutsch Zahn Zeitschr 1993;48:26-30. 12. Hilton TJ, Schwartz RS, Ferracane JL. Microleakage of four Class II resin composite insertion techniques at intraoral temperature. Quintessence Int 1997;28:135-44. 13. Crim GA, Chapman KW. Reducing microleakage in Class II restorations: an in-vitro study. Quintessence Int 1994;25:781-5. 14. Shahani DR, Menezes JM. The effect of retention grooves on posterior composite resin restorations: an in vitro microleakage study. Oper Dent 1992;17:156-64. 15. Porte A, Lutz F, Lund MR, Swartz ML, Cochran MA. Cavity designs for composite resins. Oper Dent 1984;9:50-6.
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16. Oilo G, Jørgensen KD. Effect of beveling on the occurrence of fracture in the enamel surrounding composite resin fillings. J Oral Rehabil 1977;4: 305-8. 17. Hansen EK, Asmussen E. Efficacy of dentin-bonding agents in relation to application technique. Acta Odontol Scand 1989;47:117-20. 18. Opdam N, Roeters JJ, Peters TC, Burgersdijk RC, Teunis M. Cavity wall adaptation and voids in adhesive Class I resin restorations. Dent Mater 1996;12:230-5. 19. Opdam N, Roeters JJ, Peters TC, Burgersdijk RC, Kuyijs RH. Consistency of resin composites for posterior use. Dent Mater 1996;12:350-4. 20. Wilson NH. Performance of occlusion in butt-joint and bevel-edged preparations: five-year results. 4. Dent Mater 1991;7:92-8. 21. Qvist V, Strøm C. Eleven-year assessment of Class-III resin restorations completed with two restorative procedures. Acta Odontol Scand 1993;51:253-62.
Noteworthy Abstracts of the Current Literature
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Effect of heating delay on conversion and strength of a post-cured resin composite Loza-Herrero MA, Rueggeberg FA, Caughman WF, Schuster GS, Lefebvre CA, Gardner FM. J Dent Res 1998;77:426-31.
Purpose. This investigation examined the effect of delayed and post-cure heating (after initial light-polymerization) on the strength and monomer conversion of 1 commercially available composite. Material and Methods. A total of 160 disk-shaped specimens (10 × 1 mm thick) were fabricated from a commercially available composite material (Herculite XRV, Shade A3, Kerr/Sybron). All specimens were initially light-polymerized for 60 seconds on each side in an aluminum mold using a controlled light source. Two types of specimens were fabricated. One type was used as a “light-polymerized only” control, and the other was subjected to post-cure heat treatment for 7 minutes at 100°C. All specimens were coded and stored at room temperature in a light tight container until needed. The following time intervals between initial light-polymerization and post-cure treatment of the specimens were 5 and 30 minutes, and 6, 24, 48, 72, 96, and 120 hours. Ten test specimens and 10 control specimens were used for each time interval. After the designated time delay, the unheated and post-cured composite specimens were subjected to testing to determine biaxial flexural strength. Ten specimens per test group were then analyzed for monomer conversion using infrared spectroscopy. Analyses of variance (α = 0.05), Fischer’s Protected LSD tests, Dunnett’s t tests, and Student’s t tests were used to analyze the data. Results. Both delay time and type of treatment revealed a significant effect upon the biaxial flexure strength of the specimens, as did the interaction of these parameters. Control specimens seemed to gain strength with increasing time. This was confirmed by linear regression analysis. No such correlation existed between strength and delay time for post-cure heated specimens. The only time intervals that demonstrated greater strength values for the post-cured specimens compared with the unheated control group specimens were the 5- and 30-minute delays. Both delay time and type of treatment significantly affected the observed cure values (monomer conversion) and the interaction of these variables. Cure values of unheated specimens were observed to increase with time after initial light-polymerization. Monomer conversion of heated specimens also declined with delay in heat application. Conclusions. Post-cure heating did not significantly affect the biaxial flexural strength of the composite tested, and time delay of heat application was not a significant factor in strength. Postcure heating of the composite significantly affected the increase in monomer conversion, and the time after which heat was applied following initial light-polymerization was influential. Early application of heat, after initial light-polymerization, resulted in higher monomer conversion values. For the greatest amount of polymerization, post-cure heating should be applied within 6 hours after light-polymerization. 17 References.—DL DIXON
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