Influence of light intensity and curing cycle on microleakage of Class V composite resin restorations

The aim of this study was to determine the effect of a softstart polymerization method from Quartz-Tungsten-Halogen (QTH) and Plasma Arc (PAC) curing units on microleakage of Class V composite resin restorations with dentin cavosurface margins. Seventy-five bovine incisors received standardized class V cavities in all dentin margins. Teeth were divided into 5 equal groups according to the curing cycle. The cavities were incrementally restored with a composite resin (Single Bond/Z-100, 3M). Light curing was applied as follows: Group I: PAC light continuous-cycle curing at 1600 mW/cm² for 3s; Group II: PAC light step-cycle curing (2s at 800 mW/cm² then 4s at 1600 mW/cm²); Group III: QTH light continuous-cycle curing at 400 mW/cm² for 40s; Group IV: QTH light ramp-cycle curing (from 100 to 600 mW/cm² in 15s followed by 25s at 600 mW/cm²); Group V: QTH light pulse-delay curing (200 mW/cm² for 3s followed by 3 min delay then 600 mW/cm² for 30s). Teeth were stored in distilled water at 37ºC for 30 days and then subjected to thermocycling for 500 cycles at 5 and 55ºC. Root apices were sealed and teeth coated with nail varnish before they were immersed in 0.5% fuchsine red dye solution. Teeth were then sectioned and slices were scanned with a computer scanner to determine the area of dye leakage using a computer program (Image Tools). Images of tooth slices were also visually examined under magnification and dye penetration along the tooth/restoration interface was scored. Significant differences in the degree of dye penetration and leakage were detected between groups (p<.05). Groups I and II had significantly higher values of dye penetration and leakage than groups III, IV and V. In conclusion, the use of PAC light curing in a continuous or step cycle modes resulted in increased microleakage of Class V resin composite restorations compared with medium intensity QTH light curing. Pulse, ramp and continuous-cycle curing modes with QTH light resulted in similar degrees of microleakage.