The effect of post-curing on Vickers Hardness of four light-cure resin composite materials.

The use of post-curing ovens to post-cure light-cured resin composite restorations leads to a decrease in the negative effects of polymerization shrinkage and an increase in the hardness and wear resistance of the material. The aim of this study was to compare the Vickers Hardness (VH) of four different light-cure resin composite materials. In one group, samples of the four materials, Z100, Tetric Ceram, F2000 and Heliomolar were light-cured only, and in the other group a similar set of samples were light-cured and also post-cured in a DI 500 post-curing oven. VH vests were then carried out on the samples. All samples in the post-cured group had higher VH values (p = 0.000) than the corresponding samples in the light-cured only group. Z100 and F2000 had, in both groups, significantly higher VH values (p = 0.000) than Tetric Ceram and Heliomolar.

Depth of cure of light-cured composite resin with light-curing units of different intensity.

An increase in light intensity is known to produce greater surface hardness of composite resin. The purpose of this study was to determine the depth of cure produced by two light-curing units with different light intensity outputs. Two light-curing units were selected, the one producing 600 mW/cm2 and the other 300 mW/cm2. Five metal plates with thicknesses 1, 2, 3, 4 and 6 mm were selected and 20 holes of 5 mm diameter were drilled through each plate. Each hole was slightly over filled with composite resin (Z100, 3M), covered with a polyester strip, compressed, and light-cured; 10 samples on each plate with the 300 mW/cm2 unit and 10 samples with the 600 mW/cm2 unit. The bases of all samples were subjected to Vickers Hardness testing immediately and one hour after curing. Results were analysed with the Student-t-test. There was a decrease in Vickers Hardness with every increase in depth. Significant differences were found between all the immediate and one hour groups, between the 300 and 600 mW/cm2 light intensities at 2 mm depth and the 2 mm and 3 mm groups. Increments of light-curing composite resin should not exceed 2 mm; optimal hardness only developed after one hour; at a depth of 2 mm an increase in light intensity produced a significant increase in Vickers Hardness; beyond 2 mm depth the increased light intensity did not produce a significant increase in Vickers Hardness.

Surface hardness of light-cured composite resin cured directly or through a transparent matrix using three different light guides.

The purpose of this study was to compare the Vickers Hardness (HV) of composite resin which was light-cured by 3 different light guides, either through or without a transparent polyester matrix band. The 3 light guides, standard Demetron (SG), Turbo Tip (TT) and a standard Demetron, with obvious accidental damage (DL) were tested with both Model 100 and Cure Rite radiometers. HV tests were done on all samples both immediately and one hour after light-curing. Results were analysed using the Anova and Student t-test. The light intensity readings in mW/cm2 were SG 600 and TT 850 with both radiometers and DL tested 350 and 380. Composite resin surfaces undergo significant surface hardening in the first hour after light-curing. A 350-380 mW/cm2 intensity gives significantly lower HV than 600 + mW/cm2 but 800 mW/cm2 does not produce significantly greater HV than 600 mW/cm2. Curing through a transparent polyester matrix gives marginally greater HV than curing directly. The output of light guides is a significant factor in the surface hardness of cured composite resin.

Aesthetic alternative to conventional posterior restorations.

In South Africa silver amalgam is still widely used as a filling material. Concern about the safety of the patient and dental personnel does exist, however, due to the possibilities of mercury poisoning. Demands for aesthetic dentistry are increasing in response to wider media coverage. More and more patients are asking their dentists to replace acceptable and faulty amalgam restorations with aesthetic alternatives. Such alternatives to conventional posterior restorations are discussed and their respective merits are considered.