Cure width potential for MOD resin composite molar restorations

Abstract

Objectives To investigate the capability of modern light-curing units exhibiting differences in emission spectra and light source exit window dimensions, for “one-shot” full-width curing of extensive (molar MOD) resin composite restorations. Method Specimens of Tetric (TT), Tetric Ceram HB (TC), Tetric Evoceram (TE) and Tetric Ceram Bleach (TB) resin composites containing varying ratios of Lucirin (TPO) and/or camphorquinone (CQ) photoinitiators were packed into a bar-shaped mould (12 mm length × 2 mm width × 2 mm thickness). Each product was irradiated using a halogen (Optilux 401; QTH), a conventional LED (LEDemetron; LED) and two so-called “third generation” oval-footprint LED light-curing units (LCUs) of the same model. The latter featured bimodal emission spectra (blue and ultraviolet diodes) with either high (unmodified output) and approximately 50% (modified output) blue light intensity (UltraLume-5; ULs, ULm, respectively). Vickers hardness number was obtained across the lateral extent of the bar at 1 mm increments from the centre point on both upper and lower surfaces of the specimens. Results Significant linear relationships ( R 2 = 0.71–0.98) for each distance from the central position of all LCUs were identified between measured light intensity and corresponding upper and lower surface hardness values for each product ( P < 0.05). No significant differences ( P > 0.05) were recorded in total upper surface hardness of TC or TE cured with LED (68.7 ± 3.2 and 70.5 ± 2.5) or ULm (56.8 ± 2.0 and 57.7 ± 2.0). However, upper surface hardness of TT (CQ only) cured with ULm was significantly decreased ( P < 0.05) compared with other LCUs. When the ratio of hardness at the edge to central positions of the bar-shaped specimens for either surface was calculated, no significant difference ( P > 0.05) was identified for TB (containing TPO and decreased CQ) cured with either ULs or ULm ( P > 0.05) and was significantly increased (P < 0.05) when cured with ULs compared with LED and QTH. Significance Variability in light intensity across the curing-tip face, spectral output of dental light-curing units and differences in product photoinitiator chemistry all influence curing efficiency significantly across the width of extensive resin composite geometries.