Influence of photoactivation protocol and light guide distance on conversion and microleakage of composite restorations

• Published in: Operative dentistry Vol. 34; no. 4; p. 408
• Main Authors: Fróes-Salgado, N R G, Pfeifer, C S C, Francci, C E, Kawano, Y
• Format: Journal Article
• Language: English
• Published: United States 01.07.2009
• Subjects: Acrylic Resins - chemistry; Animals; Cattle; Composite Resins - chemistry; Dental Leakage; Dental Restoration, Permanent; In Vitro Techniques; Incisor; Light-Curing of Dental Adhesives; Polyurethanes - chemistry
• ISSN: 0361-7734; 1559-2863
• DOI: 10.2341/08-104

To evaluate the effect of light guide distance and the different photoactivation methods on the degree of conversion (DC) and microleakage of a composite. Three photoactivation protocols (600 mW/cm2 x 40 seconds; 400 mW/cm2 x 60 seconds or 200 mW/cm2 x 20 seconds, followed by 500 mW/cm2 x 40 seconds) and three distances from the light source (0, 3 or 7 mm) were tested. Cylindrical specimens (5 mm diameter; 2 mm tall; n=3) were prepared for the DC test (FT-Raman). Class V cavities were made in 90 bovine incisors to conduct the microleakage test. The specimens were conditioned for 15 seconds with phosphoric acid (37%), followed by application of the adhesive system Prime & Bond NT (Dentsply/Caulk). The preparations were restored in bulk. The specimens were stored for 24 hours in distilled water (37 degrees C) before being submitted to the silver-nitrate microleakage protocol. The restorations were sectioned and analyzed under 25x magnification. Statistical analyses (two-way ANOVAs and Tukey test, alpha=0.05) found significance only for the factor distance (p=0.015) at the top of the composite for the DC test. Conversion was statistically lower for the 7 mm groups compared to the 0 and 3 mm groups, which were equivalent to each other. At the bottom of the specimens, none of the factors or interactions was significant (p<0.05). The Kruskal-Wallis test showed that, in general, the soft-start method led to lower microleakage scores when compared to the continuous modes, mainly when associated with a distancing of 7 mm (p<0.01). With the exception of specimens irradiated with 400 mW/cm2 that did not demonstrate variations on scores for the distances tested, higher microleakage was observed for shorter distances from the light source. Soft-start methods may reduce microleakage when the light guide distancing provides a low level of irradiance, which also causes a discrete reduction in the DC.