The Effect of Multiple Heat Firing Cycles on the Surface Hardness of a  Nano-Lithium Disilicate CAD/CAM Material

Introduction

Nano-Lithium Disilicate CAD/CAM blocks are introduced with the ability to reach the desired translucency by firing at a specific temperature. Additional heat treatment cycles may be performed in order to lower the translucency of the restoration which may pose an adverse effect on the mechanical properties of the materials. The objective of this research was to evaluate the effect of multiple heat-treatment cycles on the surface hardness of lithium disilicate CAD/CAM material.

Methods

Nano-lihtium disilicate CAD/CAM blocks (Amber® Mill) (Fig. 1)  were sectioned into rectangular-shaped specimens (n=15) (Fig. 2) with dimensions of 12.0 x 14.0 mm and 1.0 mm thickness (Fig. 3) and polished up to 600-grits of silicon carbide sandpaper. Each specimen was subjected to four firing cycles according to the manufacturer’s instruction. After each firing cycle, surface indentation with a constant load of 1000-grams (9.807 N) and dwelling time of 15s was performed to measure the Vickers hardness (Fig. 4, 5). An image analyzer was used to measure the diameters of the indentation to calculate the hardness value (kgf/mm2).

Resuts