Advisory Committee Chair
Nathaniel C Lawson
Advisory Committee Members
Chin-Chuan Fu
Amjad Javed
Amir Hossein Nejat
Augusto Robles
Document Type
Thesis
Date of Award
2023
Degree Name by School
Master of Science (MS) School of Dentistry
Abstract
Background: Conventionally, the strength of dental materials used for fixed restorations is measured using specimens of simplified geometry (i.e bars or discs). There is value in measuring the strength of these materials in their anatomic geometry (i.e crowns) under clinically relevant loading conditions. One advantage of performing the so-called crown fracture test is that the material may benefit from its ability to be strengthened by its bond to a tooth-mimicking die. When performing a crown fracture test, the ideal die material is natural tooth structure. However, the variability in natural tooth anatomy and microstructure makes the use of a standardized, synthetic die material advantageous. Milled resin-based composites may be used to fabricate the synthetic dies as they have a similar modulus of elasticity as dentin. Newer 3D printed resins may be an alternative material choice as they are easier and less expensive to fabricate than milled resin-based composite. Additionally, Zirconia and lithium disilicate have been often utilized as materials for tooth-supported complete-coverage restorations. Different categories of cements have been recommended for the cementation of these restorations. Nevertheless, there is limited evidence regarding the influence of the type of cement and the material thickness used on the clinical outcomes of teeth restored with zirconia or lithium disilicate restorations. Objective: The aim of the present study is to evaluate the effect of using different supporting die materials with different mechanical characteristics on the fracture strength of 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP). Furthermore, we seek to investigate the fracture resistance of different thicknesses of 3Y-TZP and lithium disilicate crowns using different luting cements. Methods: A standardized premolar crown preparation was performed on a typo-dont tooth and scanned. The preparation was fabricated into resin dies (n=10) by 3D printing or milling. .8 mm thick zirconia crowns were designed and milled to fit on the dies. The crowns were bonded to the resin dies. The fracture load of the crowns was tested against a 3.5 mm diameter steel indenter in a universal testing machine. Ten extracted human premolars were prepared to a standardized crown preparation using a fixed handpiece on a rotating base. The preparations were then scanned, and duplicates of the prepared teeth were 3D printed out of a resin. 1 mm thick zirconia crowns were fabricated for each preparation. The crowns were bonded to the dies and natural teeth then loaded until fracture. Data were compared with a t-test or a 1-way ANOVA and Tukey post-hoc analysis. For the second part of the study, three experimental crown groups made from 3 mol% yttria-stabilized zirconia polycrystalline ceramic material of 0.8mm, 1.0mm, and 1.25mm uniform thickness were fabricated. Moreover, three experimental crown groups were made from lithium disilicate material of 1 mm, 1.25 mm, and 1.5 mm uniform thickness. The crowns were then luted to one of the 3D printed die materials selected from the first part of the study (NextDent C&B) with either resin cement or RMGI cement. Then all specimens will be loaded at the universal testing machine until fracture, Data were compared with a 1-way ANOVA and Tukey post-hoc analysis. Results: In part one, A one-way ANOVA revealed no significant differences be-tween the fracture force of the zirconia crowns on the three die materials. A t-test re-vealed that there was no significant difference in the crown fracture force of zirconia crowns on natural tooth dies (1313.792 N) and a 3D printed resin die (1156.293 N) (p=.618). Regarding the second part of this study, a one-way ANOVA showed that in-creasing the thickness of 3Y-TZP zirconia and lithium disilicate crowns as well as using resin cements significantly increased the fracture load of these indirect restorations (p
Recommended Citation
Sayed Ahmed, Akram Mohamed Mohamed Gad, "Effect of Different Supporting Die Materials and Crown Thicknesses on the Fracture Load of Monolithic 3Y-TZP Zirconia and Lithium Disilicate Crowns" (2023). All ETDs from UAB. 78.
https://digitalcommons.library.uab.edu/etd-collection/78