All ETDs from UAB

Advisory Committee Chair

Nathaniel C Lawson

Advisory Committee Members

John O Burgess

Jack E Lemons

Perng-Ru Liu

Amjad Javed

Document Type

Thesis

Date of Award

2020

Degree Name by School

Master of Science in Dentistry (MScD) School of Dentistry

Abstract

Background: Ceramic crowns (lithium disilicate and zirconia) have become the most prescribed material for the restoration of anterior and posterior teeth due to the esthetic concerns of patients and the high cost of noble alloys. Different types of cements are used for luting crowns such as zinc phosphate, glass ionomer, resin modified glass ionomer (RMGI), resin cements and bioactive cements. Selection of different cements and bonding protocols for zirconia or lithium disilicate crowns to increase their bonding strength remains a clinical challenge for dentists. Objectives: To measure the retention strength of lithium disilicate and zirconia crowns cemented with different cements. Methods: Extracted human premolars were mounted in acrylic and prepared to uniform dimensions with a flat-end tapered diamond bur in a lathe. The surface area of the prepared surface was calculated with digital microscopy. The teeth were scanned with a True Definition Scanner (3M). Lithium disilicate crowns or zirconia crowns were milled and crystallized or sintered following manufacturers recommendations. For lithium disilicate crowns, the intaglio surfaces were etched with 5% hydrofluoric acid for 20 seconds. All zirconia crowns were airborne particle abraded with 50 microns alumina at 2 bar pressure for 10 seconds. The adhesive and cement were applied to the teeth and crowns according to manufacturer’s instructions. Crowns were allowed to self-cure under a 2.5 kg weight, stored in a moist bag for 24 hours at 37°C and then thermocycled for 10,000 cycles from 5-500C with a 30 second dwell time. The specimens were placed in a custom fixture in a universal testing machine and loaded in tension at a crosshead speed of 5mm/min until debonding. The tensile strength (MPa) at debonding was calculated using the maximum recorded tensile force and surface area of the preparation. Data were compared with a 1-way ANOVA and Tukey analysis (alpha=0.05). Results: Part 1 - The self-adhesive resin cement demonstrated greater retention compared to the bioactive, GI and RMGI cements. The bioactive cements had similar retention strength as RMGI cements. Part 2 - Significant differences between the experimental and five different resin cements were noted with 1-way ANOVA (p<.01). The Tukey post-analysis determined that the experimental resin cement showed no difference in retention strength compared to Link Force, Calibra Ceram, or Variolink Esthetic but higher retention strength than Nexus 3 and Panavia V5. Panavia V5 was also significantly less retentive than Nexus 3. A large number of tooth fractures (60%) were noted during crown retention testing when stronger resin cements were used. Part 3 - For cementing zirconia crowns, the RMGI cement had no significant difference in retention strength compared to the self-adhesive resin cements or the resin cement used with an adhesive. For cementing lithium disilicate crowns, the RMGI cement had significantly lower retention strength compared to the self-adhesive resin cements and the resin cement used with an adhesive. A novel self-adhesive resin cement (Panavia SA Universal) used on lithium disilicate crowns without silane application achieved statistically similar retention strength as another self-adhesive resin cement with silane application, albeit the retention strength was numerically lower. Conclusions: Within the limitations of the present study, different cements could provide different retention strength. In general, resin cement provided higher retention than RMGI cement when used with lithium disilicate crowns. With the use of zirconia crowns, the difference in retention between RMGI and resin cements was less pronounced. Clinicians should choose different cements based on crown retention requirements, type of ceramics and also consider other factors such as shade, translucency, strength of crowns, isolation, microleakages, resistant forms and so on. Keywords: Crown retention strength, bioactive, zirconia, lithium disilicate, dental cements.

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