The effect of preparation designs on the marginal and internal gaps in Cerec3 partial ceramic crowns

Objectives: The purpose of this study was to evaluate the marginal and internal gaps in Cerec3 partial ceramic crowns (PCCs) of three different preparation designs in vitro using microcomputed tomography (mu CT). Methods: Cerec3 PCCs of three different preparation designs (n = 20) were fabricated according to the following: Group I-conventional. functional cusp capping/shoulder preparation, Group II-horizontal reduction of cusps and Group Ill-complete reduction of cusps/shoulder preparation. After fixation of PCCs, the mu CT scanning was performed. For obtaining the average internal gap (AIG), the mu CT sections were reconstructed 3-dimensionally, and then the total volume of the internal gap was divided by the contact surface area. The 2-dimensional (2D) mu CT views were used to investigate the gaps at predetermined key positions in seven bucco-lingual sections and three mesio-distal cross sections. The gaps were measured using the mu CT at each reference point. Statistical analysis was performed using one-way ANOVA and Tukey's test. Results: For the 3D reconstruction technique, the AIGs were as followed: Group 1 197.3 +/- 48.2 mu m, Group II 171.2 +/- 45.1 mu m, and Group III 152.7 +/- 27.1 mu m. For the 2D mu CT views, the gaps of each group were the smallest on the margins ranging from 35.4 +/- 32.2 to 128.4 +/- 69.5 mu m, and the largest on the horizontal or angle walls ranging from 184.5 +/- 41.2 to 406.5 +/- 176.1 mu m. According to the results, Group I showed larger marginal and internal gaps compared with the other groups. Conclusions: For the PCCs, the simplified designs (Groups II and III) demonstrated superior results compared to the traditional cusp capping design (Group I). The marginal gaps were smaller than the internal gaps in all groups. (C) 2009 Elsevier Ltd. All rights reserved.