The null hypothesis to be done tested was that microhardness and compressive strength of restorative materials is influenced by curing time and curing method. MATERIALS AND METHODS A light-cured hybrid composite (Tetric Ceram, Ivoclar Vivadent AG, Bendererstrasse, Liechtenstein), a compomer (Compoglass, Ivoclar Vivadent) and a RMGIC (Fuji II LC, GC Corporation, Tokyo, Japan) were evaluated. Materials used in this study are listed in Table 1. Table 1 The tested materials with their compositions, specifications and manufacturers. A halogen light (Optilux 501, OP, Kerr Corp, Orange, CA, USA) and a LED unit (LED Bluephase C5, Ivoclar, Vivadent AG) were used. Technical details of the halogen and LED light-curing units are shown in Table 2. Table 2 Technical details of the light-curing units used in this study.

For each material, 60 disc-shaped specimens (5 mm diameter and 2 mm thickness) in A4 shade were prepared using plastic molds for microhardness measurement. The specimens were then divided randomly into nine subgroups according to light curing method and exposure time (n=180) The restorative materials were handled according to the manufacturers�� instructions. The molds were placed on flat glass plates on top of acetate strips and then filled with resin based material. The material was covered with an acetate strip and gently pressed with another glass plate against the mold to extrude excess material. The distance between the light source and sample was standardized by using a 1 cm glass plate. The light tip was in close contact with the restoration surface during polymerization.

All specimens were prepared in a temperature controlled room at 23��1��C. Immediately after light-curing, the cover glasses were removed from the mold and the lower surfaces were marked with a pen and stored in the dark container in distilled water at 37��C for 7 days to maximize post polymerization prior to microhardness and compressive strength testing. Vickers hardness (VHN) Microhardness measurements of top surfaces of the specimens were determined by Vickers Hardness Testing Machine (Buehler, Lake Bluff, ILL, USA). The Vicker��s surface microhardness test method consisted of indenting the test material with a diamond tip, in the form of a right pyramid with a square base and Vickers microhardness readings were undertaken using a load of 50g for 20 seconds.

Three indentations were made at random on each specimen and a mean value was calculated. Compressive strength The compressive strength measurements were recorded on teflon cylindirical specimens with a diameter of 4 mm and a thickness of 2 mm. Five specimens for each above mentioned 9 subgroups were prepared as described previously (n=45). The compression tests were implemented with Cilengitide a constant cross-head speed of 0.5 mm min?1 on a mechanical test machine (Material Test System-MTS 810, MTS System Corp., Eden Prairie, Minn., USA).