Effect of Endodontic Access Preparation on Fracture Load of Translucent versus Conventional Zirconia Crowns with Varying Occlusal Thicknesses.

PURPOSE: To evaluate the effect of endodontic access hole preparation on fracture resistance of translucent zirconia (5Y) and conventional zirconia crowns (3Y) with varying occlusal thicknesses. MATERIALS AND METHODS: Polymethylmethacrylate (PMMA) dies, representing a prepared tooth, were milled. Zirconia crowns with 1 mm thick axial walls and varying occlusal thicknesses were milled from 3Y (Cercon HT) or 5Y (Cercon XT) zirconia discs and sintered. 160 crowns were divided into 16 groups (n = 10 per group) based on the zirconia type (3Y, 5Y), occlusal thickness (0.5, 1.0, 1.5, 2.0 mm), and access hole preparation (with access hole, control). Crowns were cemented on the PMMA dies with resin-modified glass ionomer cement (Rely X Luting Plus) under constant weight (500 g) and thermocycled for 10,000 cycles. In half of the samples, following 5000 cycles of thermocycling, a uniform endodontic access hole was created using a diamond bur and restored immediately with resin composite (Filtek Supreme Ultra, 3M ESPE). The fracture resistance of the specimens was tested on an Instron 5566 universal testing machine with a stainless steel ball indenter (9.0 mm dia.) and the maximum load before failure was recorded as fracture load (N). Three-way ANOVA testing examined the effect of zirconia type, occlusal thickness, and access hole preparation on fracture loads of the crowns. Statistical tests were two-sided and significance level was set at 95% (α = 0.05). RESULTS: Fracture load was significantly affected by the type of zirconia, occlusal thickness, and access hole preparation (p < 0.001). Pairwise comparisons revealed that access hole preparation significantly reduced the fracture load of 3Y crowns with 0.5 or 1.0 mm of occlusal thickness and 5Y zirconia crowns with 0.5, 1.0, or 1.5 mm of occlusal thickness (p < 0.05). Increasing occlusal thickness reduced the effect of access hole preparation on fracture load. CONCLUSION: Type of zirconia, occlusal thickness, and access hole preparation had significant effects on the fracture load of zirconia crowns. The effect of endodontic access was significant on the 3Y and 5Y zirconia crowns with ≤1.0 and ≤1.5 mm occlusal thicknesses, respectively.

Titanium implant wear from a zirconia custom abutment: A clinical report.

This clinical report describes damage to a 1-piece zirconia abutment where both biological and mechanical complications developed, resulting in premature loss of the implant. Scanning electron microscopy showed significant damage to the internal connection of the implant. When using 1-piece zirconia abutments with a titanium internal connection, periodic recall and identification of wear is necessary, especially in patients with repeated screw loosening.

Student and faculty perspectives of a faculty-student mentoring programme in a dental school.

PURPOSE/OBJECTIVES: In addition to an established peer mentoring programme, the Louisiana State University Health Sciences Center, School of Dentistry introduced a faculty-student mentoring programme, the first-year dental student (D1)-Faculty Guide Program, in 2013. The intent of the D1-Guide Program was to provide faculty mentorship for D1 students. The purpose of this study was to evaluate the outcomes of the programme and identify areas for improvement. METHODS: Faculty members, D2 and D3 students were surveyed regarding their experiences and perceptions of the D1-Guide Program with a seven question and 12 question survey, respectively, via Survey Monkey® and data were analysed. RESULTS: The response rate for the students and faculty was 61% and 64%, respectively. The majority of faculty (92%) felt comfortable serving as a guide to the D1 students with 79% of those surveyed having served as a guide for 3 or 4 years. The majority of students (81%) felt that the D1-Guide Program provided mentoring that was not redundant to existing peer mentoring and valuable to their acclimation to dental school. CONCLUSIONS: Despite adding additional duties for faculty and students, the D1-Guide Program was considered valuable during the student's first year of dental school with encouragement to continue the programme. The programme helped establish a student-faculty rapport beyond the boundaries of the classroom.

Load to failure of different zirconia implant abutments with titanium components.

STATEMENT OF PROBLEM: Abutments with a zirconia superstructure and a titanium insert have recently become popular. Although they have been tested under static load, their performance under simulated mastication is not well known. PURPOSE: The purpose of this in vitro study was to compare the cyclic load to failure of 3 types of zirconia abutments with different mechanisms of retention of the zirconia to the titanium interface. MATERIAL AND METHODS: Fifteen implants (n=5 per system) and abutments (3 groups: 5 friction fit [Frft]; 5 bonded; and 5 titanium ring friction fit [Ringfrft]) were used. Abutments were thermocycled in water between 5°C and 55°C for 15000 cycles and then cyclically loaded for 20000 cycles or until failure at a frequency of 2 Hz by using a sequentially increased loading protocol up to a maximum of 720 N. The load to failure for each group was recorded, and 1-way analysis of variance was performed. RESULTS: The mean load-to-failure values for the Frft group was 526 N, for the Bond group 605 N, and for the Ringfrft group 288 N. A statistically significant difference was found among all abutments tested (P<.05). CONCLUSIONS: Abutments with the bonded connection showed the highest load-to-failure value, and the abutment with the titanium ring friction fit connection showed the lowest load-to-failure value.