Correlation between 2D and 3D measurements of cement space in CAD-CAM crowns.

Statement Of Problem: Although the 2D analysis of prosthesis cementation space has been popular, its correlation with volumetric comparison (3D data) of cement space is unclear.

Purpose: The purpose of this in vitro study was to evaluate the cement space in computer-aided design and computer-aided manufacturing (CAD-CAM) crowns of different materials and correlate 2D measurements of cement space with their corresponding 3D values (volume of cement space) by using microcomputed tomography (μCT) analysis of regions of interest.

Material And Methods: Ten molar crowns were milled in lithium disilicate (LD), resin nanoceramic (RN), and zirconia (Z) ceramics. Silicone replicas were produced and used as the analog cement layer and scanned with a desktop X-ray microfocus CT scanner. Twenty-eight slices were evaluated in 3 regions: marginal, axial, and occlusal (n=84 measurement points/specimen). After 3D reconstruction of the cement space, the volume was calculated. Data were statistically evaluated through 2-way ANOVA and Bonferroni test (α=.05). The Pearson correlation test was used to investigate the correlation between the 2D and 3D data.

Results: The volumes of the occlusal (LD 10 ±1 mm; RN 9 ±1 mm) and axial regions (LD 9 ±2 mm; RN 8 ±1 mm) were significantly higher than the volume of the marginal region for LD and RN specimens (LD 6 ±2 mm; RN 4 ±1 mm) (both P<.001). For the Z group, the axial region had the highest volume (19 ±2 mm), followed by the volumes of the occlusal (15 ±1 mm) and marginal regions (12 ±1 mm). The Pearson correlation test determined a moderate positive correlation of the marginal area (r=0.606, P<.001) and of the axial region (r=0.588, P<.001). However, a moderate negative correlation was found between volume and thickness of the occlusal area (r=-0.437, P=.016).

Conclusions: Z showed more volume of cement space, as well as thicker cement space than LD and RN. The μCT analysis is an efficient method of analyzing cement thickness and volume in ceramic crowns at the selected regions of interest. A moderate positive correlation was found between the 2D and 3D analyses for the axial and marginal regions of ceramic crowns.