Depth of cure and distance between curing light and resin

Depth of cure of a composite resin is an important property because poorly polymerized resin can lead to undesirable effects. Objective: The aim of this study was to examine the relationship between depth of cure and irradiation distance with different restorative resin and different lamps. Methods: Three different composite resins (Simile, Filtek Z 250, Filtek Supreme XT) and three different light sources were used (Elipar High Light (EHL), Elipar Visio (EV), and L.E.Demetron (LED)). Depth of cure was tested according to ISO 4049. A stainless steel mould was used for the preparation of specimens (8mm x 4mm). The mould was filled with one of the composites and irradiated for 40 sec. The distance between the exit window of the lamp and the surface of the resin was 0, 2, 4, 8, 16 and 32mm. After polymerization the specimens were removed from the mould and the inadequately cured soft material was removed from the bottom of the mould with a plastic spatula. The height of the cylinder of the cured material was measured with a micrometer (accuracy ± 0.1mm). The relationship between the irradiation distance and the depth of cure was analyzed by linear regression (p<0.05). Results: Analyses of regression coefficient ranked the lamps in order of decreasing effectiveness as follows: LED > EHL > EV. All resins had, with all three curing units, the same reduction in the depth of cure with increased irradiation distance. Conclusions: The depth of cure of light-activated composites decreases in a moderate and linear manner with the distance between the exit window and the surface of the material.