Flexural strength of small connector designs of zirconia-based partial fixed dental prostheses.

STATEMENT OF PROBLEM: Partial fixed dental prostheses with a small connector size are required for optimal esthetics and limited interarch space; however, final strength is endangered. PURPOSE: The purpose of this in vitro study was to evaluate the effect of different connector designs on the flexural strength of simulated 3-unit partial fixed dental prostheses made of yttria-stabilized tetragonal zirconia polycrystalline using computer-aided design and computer-aided manufacturing technology. MATERIAL AND METHODS: To simulate a 3-unit partial fixed dental prosthesis, 20 rectangular bar-shaped specimens were fabricated with dimensions of 4 ± 0.05 mm (H) × 4 ± 0.05 mm (W) × 30 0.5 mm (L). Each bar specimen had 2 constricted parts on both sides, representing the connector and defining a central pontic of 10 ± 0.10 mm in length. The specimens were divided into 4 groups according to the connector diameter and design, as follows: SR: 2 mm (H) × 3 mm (W) round 0.6 mm radius of curvature; SS: 2 mm (H) × 3 mm (W) sharp 0.1 mm radius of curvature; CR: 3 mm (H) × 3 mm (W) round 0.6 mm radius of curvature; and CS: 3 mm (H) × 3 mm (W) sharp 0.1 mm radius of curvature. An additional 5 specimens were fabricated with no constriction and served as the control group. The specimens were subjected to a 3-point flexural strength test in a universal testing machine with a crosshead speed of 0.5 mm/min until failure. Scanning electron microscopic and photomicrograph images were used to examine the fracture surfaces. Two-way ANOVA and the Tukey-Kramer post hoc test were used to analyze the data (α = .05). RESULTS: The mean flexural strength for SR 2 mm (H) × 3 mm (W) round 0.6 mm radius of curvature (583.6 ± 49.7 MPa) was significantly higher than that of SS, which was 2 mm (H)× 3 mm (W) sharp 0.1 mm radius of curvature (502.8 ± 23.3 MPa). Similarly, the mean flexural strength for CR was 3 mm (H) × 3 mm (W) round 0.6 mm radius of curvature (682.9 ± 36.8), which was significantly higher than that of CC, 3 mm (H) × 3 mm (W) sharp 0.1 mm radius of curvature (486.7 ± 35.6 MPa). CONCLUSIONS: The flexural strength of the yttria-stabilized tetragonal zirconia polycrystalline-based ceramics was affected by the connector dimension and design. The 2-round connector design was more able to withstand occlusal forces than the sharp design. The 3-connector design with a minimum cross section of 2 × 3 mm is recommended for anterior fixed dental prostheses, provided it has a round curvature.

Accuracy of ceramic restorations made with two CAD/CAM systems.

STATEMENT OF PROBLEM: Different types of CAD/CAM systems are currently available, but information regarding which system produces the best marginal fit is lacking. PURPOSE: The purpose of this study was to evaluate the effect of 2 different CAD/CAM systems (Cerec inLab, Kavo Everest) on the marginal fit of 2 types of zirconia-based and lithium disilicate crowns. MATERIAL AND METHODS: Forty zirconia-based and lithium disilicate crowns, 20 each, were fabricated with the Cerec inLab and Everest CAD/CAM systems on a specially designed stainless steel die to ensure the standardization of specimen shape and dimensions. The vertical marginal fit for all tested crowns was evaluated by using a digital microscope at ×100 magnification, and the data were tabulated and statistically analyzed with 2-way ANOVA, followed by the Tukey honestly significant difference (HSD) test with a confidence level of .05 to determine the mean differences. RESULTS: The results showed that the CAD/CAM technique, ceramic type, and their interaction had a statistically significant effect on the mean marginal fit of both ceramic types tested. CONCLUSIONS: Better marginal fit values were exhibited by the Everest CAD/CAM technique for both ceramic types tested.