Quality of curing in relation to hardness, degree of cure and polymerization depth measured on a nano-hybrid composite

Abstract

Purpose: To analyze the curing behavior and the curing quality of a nano-hybrid composite material (Tetric EvoCeram) in relation to degree of cure, variation of hardness with depth and polymerization depth.

Methods: The composite was evaluated after polymerizing the material with 13 different curing regimens of two LED devices and one halogen curing unit by assessing in real time the degree of cure at depths of 2 and 6 mm, the variation of hardness with depth and the polymerization depth. The sample preparation simulated the clinical incremental technique as well as a bulk fill procedure.

Results: No correlation was found for the tested curing regimens between polymerization depth and surface hardness respectively between surface hardness and radiant exposure, whereas the polymerization depth was strongly dependent on polymerization time and radiant exposure. It can be therefore concluded that the surface hardness is not a reliable indicator of the quality of curing. The degree of cure was strongly influenced by depth and curing time, whereas the influence of the curing regimen and of the interaction products between these three factors was low. The higher effect on the variation of the Vickers hardness, measured 24 hours after polymerization, was exercised also by the depth, followed by curing regimen and curing time.