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Advisory Committee Chair

John Burgess

Advisory Committee Members

Nathaniel Lawson

Keith Kinderknecht

Amjad Javed

Perng-Ru Liu

Document Type

Thesis

Date of Award

2017

Degree Name by School

Master of Science in Dentistry (MScD) School of Dentistry

Abstract

Resin-bonded fixed partial dentures (RBFPDs) have evolved from metal frameworks to esthetic all ceramic tooth colored restorations. However these restorations frequently fail due to a loss of retention of the retainers. As the frameworks for these restorations have changed to more esthetic ceramic materials, the search for the ideal conservative preparation design providing maximum retention is critical to improve the life span of these restorations. Purpose: This in vitro evaluation measured and compared the resistance and retention created with different abutment preparation designs with a zirconia framework. Method: 21 extracted human maxillary central incisors were divided into three groups of 7 specimens. The specimens in each group were prepared in three different designs including, Group 1 lingual wing design, Group 2 lingual wing with pit design, and Group 3 lingual wing with two proximal grooves design. Prepared teeth were scanned using True Definition Scanner. Restorations were designed and milled in zirconia with two lateral extensions. During the bonding procedure, teeth in each group were etched with 37% phosphoric acid followed by application of Scotchbond Universal. The intaglio surface of zirconia restorations was sandblasted with aluminum oxide, Scotchbond Universal was applied and bonded with RelyX Ultimate resin cement. All specimens were stored for 24 hours in an incubator, load cycled under compression for 100,000 cycles with a load of 20 N at rate 40 cycles/minute, and thermocycled between water temperature of 5-55°C. Specimens were further stored at oral temperature (37°C) for 6 months in water. Restoration retention was then measured by applying a tensile load to failure in the Universal Testing Machine to the specimens at a crosshead speed of 0.05 in/min. After failure, the mode of failure was analyzed with Keyence digital microscope. The tensile failure load data were analyzed with One-Way ANOVA and Tukey HSD post-hoc test with significant set at p=0.05. Results: The mean ± SD tensile failure load values were 817.32 ± 277.16 N for lingual wing design and 607.35 ± 160.56 N for lingual wing with pit design and 958.88 ±243.69 N for lingual wing with two proximal grooves design. There was no statistical significant difference in the failure loads between groups with p=0.094. However, dominant failure mechanism observed in lingual wing with two proximal grooves design was cohesive enamel failure, while mixed failure is seen in the other two designs. Conclusion: Lingual wing with two proximal grooves design showed a tendency to have better retentive resistance.

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