Effect of light curing units on marginal adaptation and hardness of Class II composite resin restorations.

AIMS: The aim of this study was to test the influence of different curing protocols on dentin marginal adaptation and the hardness of two composites. METHODS AND MATERIALS: Three light-curing-units (LCUs): Quartz-Tungsten-Halogen (QTH: 541 mW/cm2), Argon-Ion-Laser (AL: 277 mW/cm2), and Plasma-Arc-Curing (PAC: 1818 mW/cm2) and two composites FiltekZ250 (F) and Tetric Ceram HB (TC) were tested. Sixty standardized "vertical-slot-Class II-cavities" were prepared at the mesial surface of bovine incisors and divided into six groups (n=10). Composites were placed using the Single Bond adhesive system and cured in 2 mm increments according to the manufacturers' instructions. After polishing, epoxy replicas were processed for scanning electron microscopy (SEM) marginal adaptation analysis at 500x magnification. The specimens were then sectioned transversally to the dental long axis, embedded in polyester resin, then polished and submitted to the Knoop hardness test at gingival and occlusal portions of the restoration. Data were analyzed using two-way analysis of variance (ANOVA) and Tukey's test (p=0.05). RESULTS: The gap margins ranged between 4.3 to 5.8 microm, and no statistically significant differences were revealed in marginal adaptation for LCUs or for composites (p>0.05). Location influenced hardness (p=0.01). The occlusal portion presented significantly higher KHN than the gingival portion for all composite-LCU combinations. Regardless of the LCU used, TC produced statistically significant lower hardness values (ranging between 82.8 to 110.7 KHN) than F (ranging between 105.9 to 117.3 KHN). CONCLUSIONS: Hardness and gap formation were not dependent on the LCUs tested in this study. Different resin composite was found to be a significant factor with regards to hardness but not gap formation.

Effect of photoactivation systems and resin composites on the microleakage of esthetic restorations.

AIM: The aim of this study was to evaluate the influence of four photoactivation systems [quartz tungsten halogen (QTH), light-emitting diode (LED), argon ion laser (AL), and plasma arc curing PAC)] on cementum/dentin and enamel microleakage of Class II restorations using a microhybrid [Z250-3M ESPE] and two packable composites [(SureFil-Dentsply and Tetric Ceram HB-Ivoclair/Vivadent]. METHODS AND MATERIALS: Three hundred sixty "vertical-slot Class II cavities" were prepared at the mesial surface of bovine incisors using a 245 carbide bur in a highspeed handpiece. Specimens were divided into twelve groups (composite-photoactivation systems). Half of the specimens had the gingival margin placed in enamel (n=15) and the other half in cementum/dentin (n=15). Composites were inserted and cured in 2 mm increments according to manufacturers' recommended exposure times. After polishing, the samples were immersed in 2% methylene blue solution, sectioned, and evaluated at the gingival margins. Data were submitted to statistical analysis using the Kruskal-Wallis and Mann-Whitney tests. RESULTS: No significant differences were found among the photoactivation systems and among resin composites (p>0.05). Microleakage was not significantly affected by location (enamel vs. cementum/dentin, p>0.05). These findings suggested neither the photoactivation systems nor the resin composite types might have an effect on the microleakage at gingival margins Class II cavities.