Marwah Ismael Abdulazeez
University of Baghdad, Iraq
Title: Fracture strength of Monolithic Zirconia Crowns with Modified Vertical Preparation (A Comparative in vitro Study)
Biography
Biography: Marwah Ismael Abdulazeez
Abstract
The aim of this study was to investigate the influence of different preparation designs (deep chamfer, vertical, and modified vertical with reverse shoulder) on the fracture strength and failure modes of monolithic zirconia crowns. Thirty sound human maxillary first premolar teeth with comparable size were used in this study. The teeth were divided randomly into three groups according to the preparation design (n = 10): (1) group A: teeth prepared with a chamfer finish line; (2) group B: teeth prepared with vertical preparation; and (3) group C: teeth prepared with modified vertical preparation, where a reverse shoulder of 1 mm was placed on the buccal surface at the junction of middle and occlusal thirds. All samples were scanned by using an intraoral scanner (CEREC Omnicam, Sirona, Germany), and then the crowns were designed by using Sirona InLab 20.0 software and milled with a 5-axis machine. Each crown was then cemented on its respective tooth with self-adhesive resin cement by using a custom-made cementation device. A single load to failure test was used to assess the fracture load of each crown by using a computerized universal testing machine that automatically recorded the fracture load of each sample in Newton (N). The data were analyzed statistically by using one-way analysis of variance test and Bonferroni test at a level of significance of 0.05.
The results showed that the highest mean of fracture load was recorded by chamfer (2,969.8 N), which followed by modified vertical (2,899.3 N) and the lowest mean of fracture load was recorded by vertical (2,717.9 N). One-way ANOVA test revealed a significant difference among the three groups. Bonferroni test showed a significant difference between chamfer and vertical groups while a nonsignificant difference was revealed between modified vertical with chamfer and vertical groups.
Over the years, the horizontal preparation using the chamfer and shoulder finish lines has been accepted as the gold standard for all-ceramic restoration. However, these types of margins are invasive in terms of sound tooth structure removal that is critical for biological and esthetic concepts. The introduction of high-strength polycrystalline materials allowing the use of vertical