Clinical Relevance Use of the centripetal open-sandwich technique may allow for placement of a Class II resin composite restoration with better marginal adaptation, fewer voids and reduced microleakage than the closed sandwich technique. SUMMARY Purpose: This study evaluated whether a Class II restoration in a flowable resin composite has to be placed prior to (open-sandwich technique) or after (closed-sandwich technique) construction of the interproximal wall in the centripetal build-up technique in order to reduce microleakage. Methods and Materials: Thirty non-carious molars were selected and randomly divided into two groups (n=15). A standardized Class II preparation was made with the cervical margin 1 mm below the cementum-enamel junction. In Group 1, flowable resin composite was applied as a 1 mm base, remaining exposed at the cervical margin. In Group 2, the hybrid resin composite was applied to the interproximal wall, followed by a layer of flowable composite on the pulpal floor, away from the margins. The restorations were then subjected to 500 thermal cycles, each with a dwell time of 20 seconds at 5°C and 55°C. Adaptation at the cervical margin was evaluated by dye penetration and SEM analysis using the replica technique. The data were statistically analyzed using the Mann-Whitney U-test ( p <0.05). Results: The centripetal open-sandwich technique led to significantly lower dye penetration than the centripetal closed-sandwich technique ( p <0.001). Conclusion: Flowable resin composite placed under hybrid resin composites in Group 1 provided better marginal adaptation and fewer voids. However, neither Group 1 nor Group 2 was able to completely prevent microleakage.
Clinical Relevance Disposable sheaths are now recommended as a method of cross infection control when light curing resin composite. However, these sheaths may affect the depth of cure of the resin composite, resulting in a compromise of the mechanical properties of the restorative material. SUMMARY Objective: This study investigated the influence of a disposable light cure sheath on both the surface hardness and hardness at varying thicknesses of resin composite. Methods: A series of resin composite discs (Spectrum) were fabricated with varying depths up to 6 mm. The light curing units used were a standard halogen unit (Elipar Trilight) and an LED unit (Elipar Freelight 2). Recommended curing times from the manufacturer were followed. The disposable light-curing sheath (Cure Sleeve) was used with both light-curing units. Two additional groups without the sheath were employed as controls. Each specimen (n=4) was subjected to hardness testing to evaluate hardness from 0 mm to 5 mm thick. A 200g load was applied for 10 seconds using a Vickers diamond indenter and six indentations were obtained from each specimen. Statistical analysis was performed using two-way ANOVA. Results: The LED without a sheath achieved the highest surface hardness value (47.2 VHN ± 5.5). There was no significant difference between the groups regarding surface hardness ( p >0.05). As the thicknesses of the resin composite increased, the hardness values decreased in all groups. The LED light curing unit, in combination with a sheath, demonstrated the lowest hardness values at a 5 mm thickness of resin composite ( p <0.05). Conclusion: All four different methods of light curing resulted in a significant reduction in hardness values with increasing resin composite thickness, which could compromise the mechanical properties of the resin composite. However, the use of the light cure sheaths still provided an acceptable depth of cure when used following the 2 mm increment rule. It was not until 3 mm that the use of the light cure sheaths compromised the hardness results. It is recommended that the curing depth should not exceed 2 mm, regardless of light curing method.