Effect of photoactivation intensity in the reinforcement of experimentally weakened roots restored with composite resin and fiber posts

Abstract

The objective of this study is to evaluate in vitro different photoactivation intensities on the dentin/adhesive/resin/cement/intracanal post interface after the reinforcement of weakened roots with composite resin (CR) and quartz fiber posts. With this purpose, it will be verified: 1) shear bond strength and the failure type occurred after push out test; 2) the resulting dentine/adhesive/resin/cement/post interface by means of scanning electron microscopy (SEM). The crowns of 60 human maxillary incisive will be removed and roots standardized at 17 mm. After instrumentation and obturation, root canals will be prepared at 12 mm and assigned to 4 groups (n=15): 1 control, in which roots will not be weakened (CG); and 3 that will be weakened with diamond tips (Vortex, #4137 and KG 717), creating a 1-mm space between post and dentin. In the reinforced groups, after the application of All Bond 2 adhesive system, the CR (Light Core) will be photoactivated using three light-curing units and light-intensities (500, 800 and 1000 mW/cm2): Group 1, Curing Light 2500 (3M ESPE, St. Paul, MN); Group 2, UltraLume LED V (Ultradent, USA) and Group 3, Jet Lite Plus 4000 (J Morita, USA). After 24h of post cementation, the specimens will be sectioned transversally in six slices (F1 to F6) with 1-mm (± 0.1) thickness. In 3 slices (F2, F4 and F6), the bond strength will be analyzed by push out test (0.5 mm/min, Instron 4444) and failure types observed in stereoscopic lens (10x). The other 3 slices of each third with be processed for SEM analysis to observe bonding interface, quality of the hybrid layer, tags formation and the presence of lateral ramifications in a quali-quantitative way, using the scores method (0 to 3). Obtained data will be submitted to statistical analysis. (AU)