College of Dental Medicine Student Theses, Dissertations and Capstones

Document Type

Thesis - NSU Access Only

Degree Name

Master of Science (M.S.) in Dentistry

Copyright Statement

All rights reserved. This publication is intended for use solely by faculty, students, and staff of Nova Southeastern University. No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, now known or later developed, including but not limited to photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the author or the publisher.

Department

College of Dental Medicine

Publication Date / Copyright Date

2013

Abstract

A thesis submitted to the College of Dental Medicine of Nova Southeastern University of the degree of Master of Science in Dentistry.

Purpose: This study will evaluate the influence of different convergence angles and tooth preparation heights on the marginal adaptation and retention of allceramic CAD/CAM crowns. Materials & Methods: Seventy two typodont teeth (Ivorine teeth; Columbia Dentoform Corp, Long Island City, NY) were prepared using milling burs (Brasseler, USA) and a parallometer (PFG 100, Cendres and Metaux, Switzerland) with 1.0 mm rounded shoulder finish lines. Specimens were divided into 3 groups (n=24) according to 3, 4.5 and 6mm occluso-gingival (O-G) heights. The teeth within each group were then subdivided into 3 subgroups (8 in each sub-group) according to total occlusal convergence (TOC) of 8,16 and 22 degrees. Using the intra-oral camera wand of the Cerec AC machine (Sirona, Germany), optical impressions were made of each tooth. This data was then transferred to the Cerec MC XL milling unit for fabrication of all-ceramic crowns using IPS Empress II (Ivoclar Vivadent, US). The crowns were cemented on typodont teeth with glass ionomer cement. The marginal discrepancy was measured at 6 points with optical microscopy. Retention was evaluated by measuring the tensile force required to dislodge or break the crown from the corresponding tooth preparation in a universal testing machine. Data were analysed using Shapiro-Wilke tests for normality and Leven's tests for equal variances. To look for differences between groups, analysis of variance (ANOVA) with Tukey's HSD test was performed. Results: Mean marginal gap was 35.9 ± 18.4ìm to 81.4 ± 61.3ìm. 2- way ANOVA shows no significant difference in marginal gap among the groups (P< 0.05). The height mean retentive force 183.84 ± 27.0 N, was measured for 6mm height and 8° group and lowest force 86.01±10.75 N, was measured for 3 mm and 22° group. 2- way ANOVA with turkey's HSD test shows significant difference among the groups (P > 0.05). Conclusion: Marginal adaptation of the CAD/CAM all-ceramic crowns is comparable to conventional cast crowns. The preparation recommendation for conventional porcelain fused to metal crowns can be applied to CAD/CAM crown restorations. Retention of cemented CAD/CAM crowns is comparable to conventional cast crowns

Disciplines

Dentistry

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