CURING EFFECTIVENESS OF NANOFILLED RESIN COMPOSITE USING DIFFERENT LED CURING INTENSITIES AT DIFFERENT IRRADIATION TIME

Aim: evaluated the effectiveness of different LED curing light intensities at different irradiation time on the microhardness and depth of cure (hardness ratio) of nanofilled resin composite material.
Materials and methods: Nanofilled resin composite material (Filtex Z350XT, 3M, ESPE) and LED curing unit (Dr’s light AT, Good doctors co.ltd. korea) with two different light intensities were used in this study. Two Circular Teflon moulds with two different thickness were used to prepare 25Resin composite discs specimen that were divided into five groups (5 discs each). For group 1, 2mm thick resin composite disc specimens where polymerized using standard light curing intensity (800 mW/cm2) for 30 sec. while for group 2, 4mm thick resin composite disc specimens where polymerized using standard light curing intensity (800 mW/cm2) for 30 sec. group 3, 2mm thick resin composite disc specimens where polymerized using high intensity light curing mode (1400 mW/cm2) for 10 sec. group 4, 4mm thick resin composite disc specimens where polymerized using high intensity light curing mode (1400 mW/cm2) for 10 sec. Group 5, 4mm thick resin composite disc specimens where polymerized using high intensity light curing mode (1400 mW/cm2) for 20 sec. Microhardness testing was performed and the mean microhardness values and hardness ratio % of the specimens were calculated, tabulated and statistically analyzed using independent (unpaired) t test for 2 groups comparisons while one way analysis of variance (ANOVA) and Tukey post hoc tests were used to study the significance between more than 2 groups. The significance level was set at p ≤ 0.05. Statistical analysis was performed with SPSS 19.0
Results: The highest mean value was recorded in group 5: 4mm thick disc specimens cured with high intensity for 20 sec (91.16%), whereas the lowest mean was recorded in group 4: 4mm disc specimens cured with high intensity for 10 sec (73.34%). A significant difference was found between both groups (p=0.032). However, no significant difference was detected between group 3: High 10 (2mm) that recorded 85.56% , group 5: High 20 (4mm) recording 91.16% and group 1 and 2: standard ( 2mm and 4mm respectively) recording 86.96% and 81.08% respectively.
Conclusions: 1. Depth of cure and microhardness values were greatly affected by the interaction between curing light intensities and irradiation time and material thickness as well. 2. Nanofilled resin composites irradiated with LED high light intensity (1400 mW/cm2) for 20 sec. demonstrated a higher microhardness. 3. Composites might be cured in increments higher than 2 mm and up to 4mm when using LED high intensity light curing system with special caution to the irradiation time applied.