Abstract
A newly introduced high-powered light-emitting diode (LED) light-polymerization unit with various polymerization modes is purported to polymerize dental resins more quickly than standard units. However, there is insufficient information about the effects of this type of light source and its polymerization modes on resin luting agents (RLAs). This in vitro study evaluated the effects of different modes of a high-powered LED polymerization unit on the shear bond strength of a light-polymerized RLA to ceramic and dentin. Sixty ceramic cylinders (3 x 3 mm) were fabricated from a heat-pressed ceramic (IPS Empress 2). Specimen surfaces were abraded using 600-grit silicon carbide paper and airborne-particle abraded with 50-mum desiccant alumina particles, cleaned ultrasonically, etched using hydrofluoric acid, and treated with a silane coupling agent (Ceramic primer). Sixty noncarious, freshly extracted, permanent human molar teeth were embedded in autopolymerizing acrylic resin, and their dentin surfaces were wet-ground using a grinding and polishing machine fitted with 180-grit abrasive disks. The ground dentin surfaces were then etched with 37% phosphoric acid gel, and an adhesive agent (Single Bond) was applied. Ceramic specimens (n = 15) were bonded to dentin surfaces with a dual-initiated RLA (Rely-X ARC) and individually polymerized by 1 of 4 different modes, as follows: Halogen standard mode (Control) (600 mW/cm2 for 40 seconds); high-powered LED fast mode (1100 mW/cm2 for 10 seconds); high-powered LED pulse mode (1100 mW/cm2 for 10 seconds); and high-powered LED exponential mode (1100 mW/cm2 for 20 seconds). Cemented specimens were subjected to shear loading until fracture using a universal testing machine. A stereomicroscope (x25) was used to identify the mode of fracture. Bond strength (MPa) data were analyzed using 1-way analysis of variance and the Tukey HSD test (alpha = .05). Specimens polymerized using halogen standard mode (23.9 +/- 1.3 MPa) and LED exponential mode (23.0 +/- 1.1 MPa) had significantly higher ( P < .001) mean shear bond strengths compared with both LED fast (15.1 +/- 1.3 MPa) and pulse (14.6 +/- 1.3 MPa) modes. The Tukey HSD tests showed no significant differences in shear bond strength between specimens polymerized using high-powered LED exponential mode and halogen standard mode. Most failures were adhesive failures at the dentin-RLA interface or the RLA-ceramic interface in specimens polymerized using high-powered LED fast or pulse modes. Within the limitations of this study, the shear bond strength of an RLA to ceramic and dentin was found to be similar when polymerized using halogen light in standard mode and high-powered LED light in exponential mode, whereas shear bond strength was significantly lower when polymerized using LED in fast or pulse mode.
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