| Abstract|| |
Aim: To evaluate the effect of direct and indirect technique, bevel placement, and aging on the fracture resistance of composite restorations bonded to sectioned incisal edges.
Materials and Methods: Incisal thirds of 80 human maxillary incisors were sectioned. Four treatment groups of 20 teeth each were formed as follows: Direct composite with bevel and without bevel (Adper single bond 2/Filtek Z350); indirect composite with bevel and without bevel (prepolymerized Filtek Z350 cemented with Adper single bond 2/Relay × ARC). Ten teeth from each group were stored in distilled water for 24 h. The remaining ten teeth were stored in distilled water for 180 days with two thermocycling treatments. The specimens were subjected to shear testing using universal testing machine. Fractured specimens were examined with a stereomicroscope at ×10 magnification to evaluate the failure patterns. The obtained data were statistically analyzed by using ANOVA, Bonferroni test, and Student's t-test.
Results: Beveled restorations exhibited higher fracture resistance values than nonbeveled restorations. Long-term water storage decreased the fracture resistance.
Conclusion: The use of bevels resulted in improved fracture resistance of composite restorations and reduced the impact of aging.
Keywords: Adhesive system, composite resins, polymerization shrinkage, shear bond strength
|How to cite this article:|
Poojary PK, Bhandary S, Srinivasan R, Nasreen F, Pramod J, Mahesh M C. Influence of restorative technique, Bevelling and aging on composite bonding to sectioned incisal edges: A comparative in vitro study. J Conserv Dent 2013;16:28-31
|How to cite this URL:|
Poojary PK, Bhandary S, Srinivasan R, Nasreen F, Pramod J, Mahesh M C. Influence of restorative technique, Bevelling and aging on composite bonding to sectioned incisal edges: A comparative in vitro study. J Conserv Dent [serial online] 2013 [cited 2019 Aug 19];16:28-31. Available from: http://www.jcd.org.in/text.asp?2013/16/1/28/105294
| Introduction|| |
Composite resins allow functional and esthetic restoration of anterior teeth fractured due to dental trauma. Use of cavosurface bevels traditionally has been recommended to enhance the retention of anterior composite restorations.  However, recent studies have suggested that due to improvements in materials and techniques it is possible to overcome problems related to retention without placing a bevel. , Long-term success of anterior composite restoration depends upon durable bond between dentin and composite resin. Marginal leakage, hydrolysis, and polymerization shrinkage are the important factors that can contribute to dentin adhesion breakdown especially with aging. , The aim of the study was to evaluate the effect of restorative technique, bevel placement, and aging on the fracture resistance of direct and indirect composite restorations bonded to sectioned incisal edges.
| Materials and Methods|| |
Eighty human maxillary incisors were used in this study. Teeth without dental caries, nonattrited teeth and teeth extracted for periodontal reasons were included in this study. Teeth with caries, fracture, and attrition were excluded.
The surfaces of teeth were cleaned with scalers to remove calculus and remnants of periodontal ligament. Teeth were assigned to four different treatment groups with 20 teeth per group.
Four different groups are as follows:
Group 1: Direct composite without bevel
Group 2: Direct composite with bevel
Group 3: Indirect composite without bevel
Group 4: Indirect composite with bevel
Approximately 2.5 mm of the incisal third of the teeth were sectioned using a diamond disk. A cavosurface bevel 1 mm wide was prepared circumferentially with a flame-shaped diamond bur for 40 teeth. Roots of all prepared teeth were embedded in auto polymerizing acrylic resin up to the cementoenamel junction. Of the 40 beveled specimens, 20 were restored with direct composite restoration, and 20 with an indirect composite restoration. Similar procedure was carried out on 40 nonbeveled specimens.
Direct restoration procedure
Enamel and dentin were etched with etchant (3M ESPE) for 15 s. The adhesive (Adper single bond 2, 3M ESPE) was applied according to the manufacturer's instructions and cured. The incisal edge was restored with increments of composite resin (Filtek Z350, 3M ESPE). Each increment was light cured for 40 s.
Indirect restoration procedure
K Y Jelly (Johnson and Johnson) was applied on the sectioned incisal edge that acts as a separating medium. The composite resin (Filtek Z350, 3M ESPE) was applied in increments and cured. Then the restorations were removed and washed. The internal surface of the composite restoration were sand blasted using 50 μm Al 2 O 3 to improve retention. Enamel and dentin were etched with etchant (3M ESPE) for 15 s. The adhesive (Adper single bond 2, 3M ESPE) was applied according to manufacturer's instructions and cured. Resin cement (Rely X ARC, 3M ESPE) was mixed and applied on to the sectioned incisal edge according to manufacturer's instructions. The restoration was positioned and held in place with digital pressure and light cured for 40 s at all margins. All restorations were polished with Sof-lex discs (3M ESPE).
Ten teeth from each group were stored in distilled water for 24 h and tested for fracture resistance. The remaining teeth were stored in distilled water for 180 days with two thermocycling treatments. Fracture resistance of the specimens was tested in a Universal testing machine using a shear device with a cross head speed of 0.5 mm/min. Fractured specimens were examined with a stereomicroscope at ×10 magnification to evaluate the failure patterns.
The obtained data were statistically analyzed by using ANOVA, Bonferroni test, and Student's t-test.
| Results|| |
Results for the bond strength are tabulated in [Table 1] and shown in [Figure 1]. Tests showed that after 24 h of water storage direct beveled composite restorations (Group 2) recorded highest shear bond strength, which was 348.50 N. Lowest mean shear bond strength was recorded for indirect nonbeveled composite restorations (Group 3), which was 141.67 N. ANOVA showed that direct and indirect beveled composite restorations exhibited significantly higher fracture resistance compared to nonbeveled restorations [Figure 1].
After 180 days of water storage direct beveled composite restorations (Group 2) recorded highest shear bond strength, which was 252.60 N. Lowest mean shear bond strength was recorded for indirect nonbeveled composite restorations (Group 3), which was 101.28 N. Comparison of mean shear bond strengths showed that direct and indirect beveled composite restorations exhibited significantly higher fracture resistance than nonbeveled restorations [Figure 1].
An intergroup comparison between direct and indirect composite restorations at both evaluation periods showed similar results. After 6 months of water storage shear bond strengths were significantly decreased for all the groups [Figure 1].
Tests showed that after 24 h of water storage more mixed failures were occurred in direct and indirect beveled composite restorations compared to nonbeveled composite restorations [Table 2]. After 180 days of water storage more mixed failures occurred in direct and indirect beveled composite restorations. More adhesive failures occurred in direct and indirect nonbeveled composite restorations [Table 2]. After 180 days of water storage, there was 40% increase in adhesive failures in direct nonbeveled specimens and 30% increase in adhesive failures in indirect nonbeveled specimens.
| Discussion|| |
Anterior tooth restorations are more challenging in the practice of esthetic dentistry. The search for an ideal esthetic material for restoring anterior teeth has resulted in significant improvements in esthetic materials and techniques. Composite resins and acid etch techniques represent two major advances in contemporary restorative dentistry. They have changed the traditional concepts of restorative dentistry and made several new treatment options possible. Such restorations are accomplished with minimal loss of tooth structure, relatively short operating time, and modest expense to patients compared to esthetic porcelain crowns and veneers.
Researchers have varied the preparation designs to attain optimally durable retention for anterior composite restorations. ,, Currently, most clinicians prefer to either only remove unsupported enamel or to prepare a bevel in the enamel. 
Beveled direct and indirect composite restorations exhibited higher fracture resistance than nonbeveled restorations in this study. The difference was statistically significant at evaluation periods of 24 h and 180 days of water storage. Previous studies have shown better results with beveled restorations than with non beveled restorations. , Loguercio et al. observed that bevel placement provides the restoration a fracture resistance similar that of the intact teeth.  The bevel preparation has been commonly used for its superior esthetics and retention compared to butt joint margin. Preparation of a cavosurface bevel improves esthetics by masking the transition between tooth and composite. Some studies have reported that the use of a bevel in the preparation margin have decreased microleakage by better marginal sealing of composite restoration. 
Indirect composite resins are used commonly for restoration of teeth using the indirect technique. Indirect resins are used because of their improved physical properties such as hardness, wear resistance, compressive strength, flexural strength, and reduced water sorption. In addition the effects of polymerization shrinkage are also reduced. Despite these advantages, indirect composite resins are approximately twice as expensive as direct composite resins. Recently, Cesselli et al., in a study, demonstrated that the diametrical tensile strength of direct composite Filtek Z-250 was more than the indirect composites like Targis and Solidex.  This study suggested that direct composites like filtek Z-250 could be used in the indirect technique. In another study, the same author evaluated the fracture resistance of teeth restored with composite resins in the direct and indirect technique.  Direct composite material Filtek Z-250 was used in this study in both, direct and indirect technique. Results showed no statistical difference between the two techniques.
For indirect restorations, the technique employed in our study is a semidirect technique using direct composite resins. In our study it was observed that there was no significant difference between direct and indirect restoration for both the evaluation durations. These results are similar to those found by Coelho-De-Souza et al.,  who observed similar fracture resistance values for both restorative techniques. Our result shows that the semidirect technique can be used for restoration of anterior teeth. Hence, Filtek Z-350 can be used for semidirect restorations. Indirect techniques are usually preferred over direct techniques to minimize the adverse effect of polymerization shrinkage of composite resin also they have some additional advantages over direct techniques. Indirect technique improves the control over marginal adaptation, proximal contacts, anatomic form compared to direct composite resin restorations.
The simulated aging employed in this study using water storage and two thermocycling treatments. , Long-term water storage of 6 months and two thermocycling treatments decreased the fracture resistance values in all the groups. It is very important to recognize that the occurrence of adhesive failures have increased after long-term water storage. Results of our study support the observations of previous study by Armstrong et al. He observed that long-term water storage decreases dentin bond strength due to hydrolytic degradation of adhesive joint. Beveled direct and indirect composite restorations exhibited higher fracture resistance compared to nonbeveled specimens even after aging.
In our study more mixed failures were observed at both the evaluation times in beveled restorations. More adhesive failures occurred in nonbeveled specimens after 6 months of water storage. Occurrences of adhesive failures have increased after long term water storage. Results indicated that aging decreased dentin bond strength due to damage or degradation of adhesive bond in nonbeveled specimens.  Higher fracture resistance values and occurrence of more mixed failures showed that beveled restorations maintained good retention even after long-term water storage.
This study demonstrated that beveling contributed significantly to fracture resistance and reduced the impact of aging on restoration quality. Bevels should be recommended as the routine procedure for clinicians when replacing the incisal edge lost due to caries or trauma. However, the result obtained in the present in vitro study does not exactly simulate clinical conditions. Randomized clinical trials are needed to evaluate different materials and techniques.
| Conclusions|| |
The following conclusion can be drawn from the present study.
Use of bevels improved fracture resistance of both direct and indirect composite restorations used to replace the lost incisal edges and bevels reduced the impact of aging.
Long-term water storage decreased the fracture resistance values of both direct and indirect restorations tested.
Indirect restorations had similar results to direct restorations in both evaluation periods.
| Acknowledgment|| |
I thank all my Professors and my colleagues for thier support in this article.
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Pradeep K Poojary
A.E.C.S Maaruti College of Dental Sciences and Research Centre, # 108, Hulimavu Tank Bund Road, B.T.M. 6th Stage, Ist Phase, Off Bannerghatta Road, Kamanahalli, Bangalore - 560 076
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2]