Fracture Resistance of Endodontically Treated Premolars Reconstructed by Traditional Casting and CAD-CAM Milling Post and Cores.

Purpose: Restoration of endodontically treated premolars has always been considered as a challenging procedure. This study compared the fracture strength and mode of failure of root canal treated premolars reconstructed with various post and core systems. Materials and Methods: Twenty healthy extracted premolars were selected and underwent root canal treatment and then randomly assigned into 4 groups (n = 5). The teeth in group 1 restored with amalgam, whereas others reconstructed with post and cores made by cobalt-chromium (Co-Cr) casting (group 2), nonprecious gold (NPG) casting (group 3), or computer-aided design (CAD) and computer-aided manufacturing (CAM) milling (group 4). The force at fracture was measured in a universal testing machine, and the failure mode was recorded as repairable or nonrepairable. Results: ANOVA revealed a significant difference in fracture resistance between groups (P=0.001). The control group displayed significantly lower strength than that of the CAD-CAM or CO-Cr groups (P < 0.05). The CAD-CAM posts were also more resistant to fracture than the NPG group (P < 0.05). The frequencies of repairable fracture in the control, Co-Cr, NPG, and CAD-CAM groups were 40%, 20%, 20%, and 60%, respectively. The chi-square test revealed no significant difference in the distribution of failure modes between groups (P=0.415). Conclusion: The teeth reconstructed with post and cores were more resistant to fracture than those restored with amalgam alone. CAD-CAM milling could be considered as the best system for reconstruction of endodontically treated teeth, as it provided the highest fracture strength with less risk of nonrepairable tooth fracture.

Effect of Silane Heat Treatment by Laser on the Bond Strength of a Repair Composite to Feldspathic Porcelain.

PURPOSE: Ceramic restoration fracture may occur in the oral cavity. Intraoral repair of fractured porcelain could be advantageous to both patient and dentist. The aim of this study was to evaluate the effect of heat treatment of the silane coupling agent by Er:YAG and CO2 lasers on the microshear bond strength of a repair composite to feldspathic porcelain. MATERIALS AND METHODS: Sixty ceramic blocks were prepared and randomly divided into six groups (n = 10): (i) HF + silane (HS); (ii) silane + CO2 laser (SC); (iii) CO2 laser + silane (CS); (iv) silane + Er:YAG laser (SE); (v) Er:YAG laser + silane (ES); (vi) bur + HF + silane (BuHS). An adhesive resin was applied to the prepared ceramic surfaces and light-cured. Two transparent plastic tubes were placed perpendicularly to each ceramic block. The composite resin was then placed on the treated ceramic surface and light-cured for 40 seconds. The bonded blocks were stored in distilled water at 37°C for 24 hours and subjected to 3000 thermocycles. Microshear bond strength (µSBS) tests were performed using a wire and loop method. Data were analyzed using one-way ANOVA and Duncan's multiple range tests (p ≤ 0.05). RESULTS: The comparison of the mean µSBS values showed no significant differences between the ES and HS groups (p = 0.914). On the other hand, the specimens in these groups exhibited significantly higher bond strengths than those in the other groups (p < 0.01). The mean µSBS of the BuHS group was statistically similar to that of CS and SE groups (p > 0.05). The µSBS for the SC group was significantly lower than that of the other groups (p < 0.01), with the exception of the CS group (p = 0.674). CONCLUSIONS: Treatment with Er:YAG laser prior to silane application can be as effective as HF etching. Heat treatment of silane by CO2 or Er:YAG lasers does not improve the bond strength between feldspathic porcelain and composite resin.

Three-dimensional accuracy of different impression techniques for dental implants.

BACKGROUND: Accurate impression making is an essential prerequisite for achieving a passive fit between the implant and the superstructure. The aim of this in vitro study was to compare the three-dimensional accuracy of open-tray and three closed-tray impression techniques. MATERIALS AND METHODS: Three acrylic resin mandibular master models with four parallel implants were used: Biohorizons (BIO), Straumann tissue-level (STL), and Straumann bone-level (SBL). Forty-two putty/wash polyvinyl siloxane impressions of the models were made using open-tray and closed-tray techniques. Closed-tray impressions were made using snap-on (STL model), transfer coping (TC) (BIO model) and TC plus plastic cap (TC-Cap) (SBL model). The impressions were poured with type IV stone, and the positional accuracy of the implant analog heads in each dimension (x, y and z axes), and the linear displacement (ΔR) were evaluated using a coordinate measuring machine. Data were analyzed using ANOVA and post-hoc Tukey tests (α = 0.05). RESULTS: The ΔR values of the snap-on technique were significantly lower than those of TC and TC-Cap techniques (P < 0.001). No significant differences were found between closed and open impression techniques for STL in Δx, Δy, Δz and ΔR values (P = 0.444, P = 0.181, P = 0.835 and P = 0.911, respectively). CONCLUSION: Considering the limitations of this study, the snap-on implant-level impression technique resulted in more three-dimensional accuracy than TC and TC-Cap, but it was similar to the open-tray technique.