Abstract
Purpose: The objective of this study was to assess the quality of posterior teeth prepared for monolithic zirconia crowns. Materials and Methods: A total of 392 STL-files of posterior preparations for monolithic zirconia crowns were evaluated in this study. Three-dimensional (3D) images were evaluated using a software (3D Viewer; 3Shape A/S, Copenhagen, Denmark) for finish line design, finish line width, occluso-cervical dimension, total occlusal convergence (TOC), intercuspal angulation, finish line quality, line angle form, and presence or absence of undercut at the axial wall and unsupported lip of enamel. The assessment was performed by two calibrated evaluators. Then, data were descriptively analyzed. Data for occluso-cervical dimension and TOC were descriptively analyzed according to their location. Results: Thirty-nine percent of premolars, 77% of first molars, and 91% of second molars had an average occluso-cervical dimension of less than 3 mm (premolars) and 4 mm (molars), with most of the preparations having a TOC of more than 20 degrees. More than 50% of preparations had undercut, unsupported enamel and/or unacceptable finish line quality. Conclusions: The quality of tooth preparation including finish line quality, absence of unsupported enamel and undercut at the axial wall should be evaluated when preparing monolithic zirconia crowns.
Highlights
Published: 27 September 2021Historically, dental practitioners have employed a wide variety of materials when fabricating complete coverage crowns
This study suggested that feather edge and 0.4 mm chamfer finish line designs have a significantly higher fracture load compared to 0.8 mm chamfer finish line designs [30]
The finish line width ranged between 0.0 and 2.3 mm with a mean of 0.62 mm (±0.2); a comparison of different finish line designs showed that chamfer design accounted for 82%
Summary
Published: 27 September 2021Historically, dental practitioners have employed a wide variety of materials when fabricating complete coverage crowns. While 65% of the single-unit fixed restorations were fabricated from metal-ceramic in 2007, only 20% of the restorations manufactured by one of the largest dental laboratories in the United States were metal-ceramic in 2012 [2]. Because of their high strength, wear compatibility with natural dentition, esthetic appeal, and low cost, multiple sources report a large increase in the use of all-ceramic restorations during the past decade [3,4]. 32% of dental practitioners select monolithic zirconia as the material of choice for use in complete coverage restoration of posterior teeth [5]. At one of the largest laboratories in the United States, 75% of complete coverage crowns are fabricated from monolithic zirconia [6]
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