A comparative in vitro study of the load at fracture of all-ceramic crowns with various thicknesses of In-Ceram core.

AIM: The aim of this study was to investigate the influence of three different thicknesses of In-Ceram core on the load at fracture of all-ceramic crowns. METHODS AND MATERIALS: Thirty standardized crown-shaped nickel-chromium alloy dies were fabricated using a milling machine. Twenty dies were prepared with a 1 mm shoulder for Groups A and B. The only difference in the ten dies used for Group C was a smaller 0.5 mm lingual shoulder. The thicknesses of In-Ceram were 0.5 mm, 1.5 mm, and 0.75 mm for Groups A, B, and C. All all-ceramic crowns were fabricated in accordance with the manufacturer's instructions. After cementation of the crowns, their fracture resistance was tested with a universal testing machine. The load was directed to a point located 3 mm from the lingual aspect of the incisal edge at 30 degrees to the long axis of each specimen until catastrophic failure occurred. RESULTS: The mean loads at fracture for Groups A, B, and C were 1117+/-388 N, 2083+/-385 N, and 1439+/-368 N, respectively. No statistically significant difference in load at fracture between Groups A and C was found (p>0.05). However, the differences were statistically significant between Groups A and B (p<0.001) and Groups B and C (p<0.001). CONCLUSION: Under the guidelines of this study, increasing the thickness of the In-Ceram core increased the fracture resistance of the all-ceramic crowns. CLINICAL SIGNIFICANCE: The sufficient thickness of the In-Ceram core of all-ceramic crowns is an important factor in fracture resistance. Therefore, dental practitioners should be careful in patient selection; if the horizontal overlap of a tooth to be restored is too limited, then all-ceramic crowns may not be a feasible option.

A short-term clinical trial on selected outcomes for immediately loaded implant-supported mandibular overdentures.

PURPOSE: This clinical trial aimed to evaluate the outcomes of implant-supported mandibular overdentures (ISMOs) using 2 different loading protocols. MATERIALS AND METHODS: Two groups of 10 edentulous patients each were selected for the study. Each patient received 2 implants placed in the mandibular canine sites. After 1 week, ISMOs were delivered to the 10 patients in the test group, while conventional mandibular dentures were delivered to the 10 patients in the control group. The conventional prostheses were converted to ISMOs after 3 months. Treatment outcomes for the ISMOs were evaluated 1 year after implant surgery. RESULTS: The number of appointments and time needed for fabrication of ISMOs revealed statistically significant differences between the patient groups. The requirements for prosthodontic maintenance of ISMOs in the test group were higher than those in the control group; however, these differences were not statistically significant. The mean marginal bone resorption for each group was 0.3 mm after 1 year. CONCLUSION: The results of this clinical trial suggest that early loading of a specific length of implants used to support mandibular overdentures does not jeopardize treatment outcomes during the first year of service.