ABSTRACT
Objective: Different methods have been suggested to overcome the polymerization shrinkage of composite restorations. Changing the light curing protocol to improve polymerization by using new light curing units is among these methods. The new devices are more efficient, portable and durable and produce less heat. This study aimed to assess the marginal microleakage of class V composite restorations subjected to three different light curing protocols and mechanical cycles
Methods: This was an in-vitro experimental study. Class V cavities measuring 2x3x1.5 mm were prepared on the buccal and lingual surfaces of 90 extracted human premolar teeth 1.5 mm above and below the cement enamel junction [CEJ]. The samples were selected using convenience sampling and divided into 9 experimental groups of 10 each by using the Table of Random Numbers to control for the bias. The cavities were restored with packable composite resin along with Tetric-NBond and cured using three light curing protocols of conventional [680 mW/cm[2] for 30s], soft-start [380 mW/cm[2] for 10s followed by 680 mW/cm[2] for 20s] and pulse [680 mW/cm[2] for 30s,1s interval and 1s of lighting]. The teeth were then subjected to mechanical cycles of 0, 500,000 and 1,000,000 and immersed in 2% Fuchsin for 24h. The teeth were then sectioned in half from the middle of the restoration buccolingually and the degree of microleakage was evaluated under a stereomicroscope [Zeiss, Germany] with 40X magnification. Data were analyzed using the Kruskal Wallis and the Mann-Whitney tests
Results: Despite the structural differences between the enamel and dentin margins, no significant difference was found in the degree of microleakage between the enamel [occlusal wall, p>0.05] and dentin [gingival wall, p>0.05] margins among the understudy groups
Conclusion: The degree of marginal microleakage in soft-start [SS] polymerization was not significantly different from that in conventional and pulse polymerizations of class V composite restorations
ABSTRACT
Today, use of adhesive systems is the most common materials in restorative dental procedures. The aim of this study was to evaluate the effect of different air-drying periods on the microtensile bond strength of composite to dentin using adhesive. 15 sound molar teeth were selected. The occlusal surfaces of teeth were removed with silicon carbide disks [3M/USA] to reach the flat surface of dentin. Then according to the air drying of solvent, the teeth were divided to five groups. After 5 sec etching and rinsing for 15 sec, the teeth were air dried for 3 sec. Then Singlebond [3M] was used with different air-drying times [0s, 2s, 5s, 10s, 30s] and cured. Then after insertion and curing of Saremco [microhybrid low shrinkage/Switzerland] composite, the teeth were thermocycled for 500 cycles. Then hour glass slabs with 1 mm[2] interface was created. Specimens were then subjected to microTBS force until fracture. Data were analyzed using ANOVA and Bonferroni tests. Statistical tests showed that there were significant differences between bond strength of groups [P=0.002]. The mean of microTBS for the 2 Sec and 30 Sec evaporating time was the most and the least vawes, respectively. An optimum air-drying time for solvent evaporation was the lowest time recommended by the manufacturer. Over and under evaporation time decreased microTBS significantly.