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Advisory Committee Chair

Nathaniel C Lawson

Advisory Committee Members

Amjad Javed

Jack E Lemons

Augusto Robles

Document Type

Thesis

Date of Award

2017

Degree Name by School

Master of Science in Dentistry (MScD) School of Dentistry

Abstract

Objective: To measure and compare the retention of zirconia crowns cemented with Ceramir (Calcium phosphate-based Bioactive Cement), RelyX Luting Plus (RMGI Cement) and RelyX Unicem (Self-adhesive resin cement) to extracted teeth following thermocycling. Methods: 30 sound extracted non-carious human molars were collected following IRB approval. The selected molars were notched at the roots and mounted into PVC molds filled with acrylic resin (Yates Motloid, USA). The occlusal surface was ground flat on a model trimmer. The axial reductions were performed with a standardized crown preparation device using a Komet 5845KR (“onlay”) diamond bur. A 10 degree ramp was used to increase the taper of the preparations. This bur produced a variable taper between 27-32 degrees. The crowns preparation was done so that all axial walls were 1.5 mm tall. All axial walls were in dentin. The surface area of the crown preparations was measured by adding the surface area of the occlusal surface, margin surface area and the area of the axial walls with a digital microscope. The teeth were scanned with a true definition scanner and all .stl files were sent to Glidewell Labs for the fabrication of the crowns. The prepared teeth were placed in a moist bag for 24 hours at 37 ̊C PBS solution. The teeth were then rinsed and dried to leave moist dentin. The zirconia crowns were also rinsed with water and air dried. The crowns were sandblasted with Al2O3 particle at 40psi for 10 sec at a 10mm distance and cleaned in an ultrasonic bath for 5 minutes. The crowns were then placed at 37 ̊C PBS solution in a water bath for 10min. No primer was placed on the zirconia surface. The crowns (n=10) were then cemented with Ceramir Crown & Bridge (Doxa), RelyX Luting Plus (3M ESPE) and RelyX Unicem (3M ESPE). Crowns were allowed to self-cure under a 2.5kg weight and the excess cement was cleaned. Following 6 minutes of seating force, the weights were removed and the crowns were placed immediately in a 37 ̊C PBS solution for 48 hours. The crowns were thermocycled for 10,000 cycles from 5°C- 55°C with a 15 second dwell time and kept in PBS solution until crown retention testing was performed. The specimens were placed in custom fixture in a universal testing machine and loaded at a crosshead speed of 0.5mm/min until debonding. The retention (MPa) at debonding was determined from the maximum recorded tensile force and surface area of the preparation. Data was compared with 1-way ANOVA and Tukey analysis (alpha=0.05). Results: The mean values of crown retention ranged from 3.69 (Ceramir) to 5.15 MPa (Unicem). The Unicem 2 cement showed the highest bond strength compared to the other two cements.

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