Curing depth and degree of conversion of different nano-hybrid composites

Introduction
The increasing use of composite resin as a posterior restorative material puts it under constant masticatory stresses. Depth of cure, considered as the most important factor helps resist these stresses.

Objectives
The aim of the study was to assess the curing depth and degree of conversion of four different nano-hybrid composites (two conventional methacrylate and two pure Ormocer composites), using ISO 4049 digital caliper and micro-hardness test.

Material and methods
20 cylindrical composite samples per group were created using Admira Fusion x-tra (Admira Fusion; VOCO GmbH, Cuxhaven, Germany) and Tetric N-Ceram Bulk Fill (Ivoclar Vivadent; Schaan, Liechtenstein) composites. Curing depth was calculated using ISO 4049 digital caliper, and micro-hardness test was applied to assess degree of conversion of all composites using digital micro-Vickers hardness tester (Galileo LTF; Italy). 20 seconds of curing was performed with curing LED unit (Guilin Woodpecker Medical Instrument Co., Ltd.; China), with a light intensity of 1,000 mw/cm2. A statistical analysis was done using SPSS, version 17, and the results were compared with one-way and multiple-way analysis of variance (ANOVA). P-value < 0.05 was considered statistically significant.

Results
Average curing depth of Tetric N-Ceram was 1.60 mm (± 0.09), with mean micro-hardness of 78.17%. Tetric N-Ceram Bulk Fill mean curing depth was 2.76 mm (± 0.18), and micro-hardness of 73.97%. Admira Fusion x-tra showed 2.92 mm (± 0.15) as mean depth of cure and 80.20% of micro-hardness, while for Admira Fusion it was 1.71 mm (± 0.19), with micro-hardness of 80.605%.

Conclusions
All the tested materials showed acceptable results according to ISO 4049 test. Only Admira Fusion and Admira Fusion x-tra accomplished micro-hardness tests.