ABSTRACT
Purpose: This study aimed to assess the effect of preparation design on fracture resistance (FR) of endodontically treated maxillary premolars restored with lithium disilicate (LDS) endocrowns fabricated by the computer-aided design/computer-aided manufacturing (CAD/CAM) technology. Materials and Methods: In this in vitro, experimental study, 30 sound maxillary premolars were randomly assigned to three groups (n = 10) of control (no preparation), endocrown preparation with butt-joint design without ferrule, and endocrown preparation with ferrule (shoulder design with 1 mm height). After restoration fabrication and cementation, the teeth underwent thermocycling, were mounted with 45° angle, and subjected to compressive load in a universal testing machine to measure their FR. The mode of failure was also determined under a stereomicroscope. Data were analyzed using one-way ANOVA and Tukey's test (α =0.05). Results: The shoulder group showed the highest FR (1768.98 ± 386.1 N). The difference in FR was statistically significant among the three groups (P < 0.05). Pairwise comparisons revealed that the shoulder group had significantly higher FR than the butt-joint (P = 0.001) and control (P = 0.009) groups. However, the difference in FR between the butt-joint and control groups was not significant (P = 0.75). The mode of failure was not significantly different among the three groups (P > 0.05). Conclusions: Preparation design had a significant effect on FR of endodontically treated maxillary premolars restored with LDS CAD/CAM Endocrowns, such that addition of a short axial wall in shoulder group significantly increased the FR of endocrowns.
ABSTRACT
BACKGROUND: Despite of the rapid development in the field of dental adhesives, the issue of reduction in dentin bond durability has still not been resolved. The activity of dentinal endogenous enzymes such as MMPs is one of the most important causes of failure in resin composite restorations. The aim of this study was to investigate the influence of Chlorhexidine on micro-tensile bond strength of two types of commercially available self-etch adhesives. MATERIAL AND METHODS: Twenty four sound and freshly extracted molars were selected. Four standardized flat mid-coronal dentinal disks were prepared from each tooth. The specimens were randomly assigned to 6 groups (n=16). Groups A(control group) and B were treated with Clearfill SE Bond based on the manufacturer's instructions. Groups C and D were treated with 2% Chlorhexidine 60 seconds before applying Clearfill SE Bond. Groups E and F were treated with Peak Universal Bond according to the manufacturer's instructions. All groups were stored in distilled water in room temperature. Microtensile bond strength in groups A, C, and E were tested 24 hours after preparation, while microtensile bond strength in groups B, D, and F were tested after 3 months storage and 3000 thermal cycles(5-55 °C). Statistical analysis was performed with SPSS 20 and µTBS test results were analyzed using the Two-way ANOVA test. RESULTS: µTBS was not significantly different between groups A, C, and E after 24 hours (P>0.5). There was no significant difference between groups B (Clearfill SE Bond + Aging) and D (Clearfill SE Bond + 2% CHX + Aging). The Peak Universal µTBS significantly decreased after the aging procedure (P<0.001). CONCLUSIONS: Based on the findings of this study, pretreatment with 2% CHX had no negative effect on the Clearfill SE Bond µTBS. However the µTBS of 0.2% CHX contained Peak Universal adhesive decreased significantly after aging. Key words:Self-etch adhesives, Micro-tensile bond strength, chlorhexidine, bond durability.