All ETDs from UAB

Advisory Committee Chair

Nathaniel C Lawson

Advisory Committee Members

Nathaniel C Lawson

Daniel A Givan

Amjad Javed

Keith E Kinderknecht

Perng-Ru Liu

Document Type

Thesis

Date of Award

2020

Degree Name by School

Master of Science in Dentistry (MScD) School of Dentistry

Abstract

Purpose: To measure retention of zirconia crowns bonded with resin and RMGI cements and the effect of salivary contamination following 10,000 cycles of thermocycling. Materials and Methods: 64 extracted human mandibular premolars were divided into eight groups (n = 8/group). The specimens in each group were prepared for Katana HT zirconia (eight groups) and one of four luting cements (one for each group): 3M ESPE RelyX Luting Plus RMGI, 3M ESPE Rely X Unicem 2 self-adhesive, Kuraray Panavia SA Universal self-adhesive, and 3M ESPE RelyX Ultimate dual cure resin cement with Scotchbond Universal. The roots of the selected teeth were notched with a disc, and the occlusal surfaces were ground flat on a model trimmer. Teeth were centered in Teflon cylinders and embedded in auto-polymerizing acrylic resin. After complete curing of the acrylic, samples were fixed into a lathe for precise uniform reduction with diamond burs (20° total taper and 2 mm height). Bonding surface areas of the prepared surfaces were calculated under 20X magnification using a Keyence digital microscope. Prepared teeth were scanned using a 3M True Definition Scanner. Restorations were designed in 3Shape TRIOS Design Studio with a 10 micron cement gap and milled in Katana HT zirconia. The crowns were designed with a handle to attach to a wire loop for debonding. All crowns were abraded with 50 micron alumina at 2 bar pressure for 10 seconds. For four of the zirconia groups, 0.5 mL of fresh whole saliva was applied to the preparation for 10 seconds prior to cementation. Each cement was applied to the crowns according to manufacturer’s IFU. Excess cement was carefully removed with a microbrush in an uncured stage with the crown held fixed. Cemented crowns were immediately placed under a 2.5 kg load. All crowns were self-cured only for the amount of time reported in their IFU. All crowns were stored for 24 hours at 37°C and thermocycled for 10,000 cycles from 5-55°C with dwell time of 30 seconds. Crown retention was measured by placing the specimens in the INSTRON. The handles on the crown were grasped by a wire loop. Specimens were loaded in tension at a crosshead speed of 1 mm/min until debonding; the debonding force (N) was recorded. Retention force was calculated in MPa by dividing the debonding force (N) by the total bonding surface area of the preparation (mm2). Crown retention strength and force were analyzed with two-way ANOVA. Failure mode was examined under 100X on the Keyence digital microscope and classified in one of five categories: cement mainly on prepared tooth (over 75%), cement on both crown and tooth (between 25 and 75%), cement mainly on crown (over 75%), fracture of tooth without crown separation, or fracture of crown. Results: A two-way ANOVA comparing crown retention strength for cement type (RelyX Luting Plus, RelyX Unicem 2, Panavia SA Universal, RelyX Ultimate) and contamination (clean and saliva contamination) showed no significant interaction (p = 0.34 > 0.05) between the two factors; however, the factor “contamination” was significant (p = 0.01). A two-way ANOVA comparing crown retention force for factors cement type and contamination showed no significant interaction (p = 0.38 > 0.05) between the two factors; however, the factor “contamination” was significant (p = 0.02). Conclusion: Salivary contamination significantly reduced crown retention strength and crown retention force regardless of cement type. KEYWORDS: Crown retention strength, crown retention force, zirconia, lithium disilicate, cements.

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