Degree of Conversion of Nano-ceramic and Micro-hybrid Composites Activated by Different Polymerization Modes at Different Intervals: An In Vitro Comparative Study

INTRODUCTION: This is an in vitro study to evaluate the degree of conversion (DC) of nanoceramic and microhybrid composites activated by different polymerization modes at different intervals. AIM: To determine the DC of two resin composites at different time intervals and modes of polymerization on DC. MATERIALS AND METHODS: Two commercially available composite resins-nanoceramic (Ceram X, Dentsply) and microhybrid (Spectrum TPH, Dentsply)-were used in this study. A total of 80 cylindrical samples (n = 40 each) were made by packing the composites in one increment into (5 × 2 mm) Teflon molds and cured using a light-emitting diode (LED) at an irradiance of 1,200 mW/cm2. Each group was further divided into two groups (n = 20) based on the curing modes (20 seconds, 40 seconds). These 20 samples were further subdivided (n = 10) based on the time interval (2 days, 7 days). Degree of conversion was assessed by Fourier-transform infrared spectrophotometer (FTIR) using a direct technique (attenuated total reflectance) on the top surface of the samples. Degree of conversion was measured for samples cured for 20 seconds (n = 10) and 40 seconds (n = 10) after 2 days and 7 days during which the samples were stored in an incubator at 37°C, 90% ± 10% relative humidity. The results obtained were statistically analyzed using two-way and three-way analysis of variance (ANOVA) test and p value set at (<0.005) significance level. RESULTS: Degree of conversion for the tested composites varied between 44% and 55% for Ceram X and 42% and 45% for Spectrum TPH. A significant difference was observed in DC for Ceram X samples for different polymerization modes (20 seconds and 40 seconds) as well as at 2-7 days measurement, whereas Spectrum TPH did not show any significant difference for polymerization modes. CONCLUSION: Ceram X demonstrated high DC values compared with that of Spectrum TPH with regard to two different polymerization modes. CLINICAL SIGNIFICANCE: Lesser the time required for conversion and less the residual monomer left, better is the prognosis of the restoration, and better is the patient satisfaction.