ABSTRACT
PURPOSE: To compare marginal and internal gaps of zirconia substructure of single crowns with those of three-unit fixed dental prostheses. MATERIALS AND METHODS: Standardized Co-Cr alloy simulated second premolar and second molar abutments were fabricated and subsequently duplicated into type-III dental stone for working casts. After that, all zirconia substructures were made using Lava(TM) system. Marginal and internal gaps were measured in 2 planes (mesial-distal plane and buccal-palatal plane) at 5 locations: marginal opening (MO), chamfer area (CA), axial wall (AW), cusp tip (CT) and mid-occlusal (OA) using Replica technique. RESULTS: There were significant differences between gaps at all locations. The mean +/- SD of marginal gap in premolar was 43.6 +/- 0.4 microm and 46.5 +/- 0.5 microm for single crown and 3-unit bridge substructure respectively. For molar substructure the mean +/- SD of marginal gap was 48.5 +/- 0.4 microm and 52.6 +/- 0.4 microm for single crown and 3-unit bridge respectively. The largest gaps were found at the occlusal area, which was 150.5 +/- 0.5 microm and 154.5 +/- 0.4 microm for single and 3-unit bridge premolar substructures respectively and 146.5 +/- 0.4 microm and 211.5 +/- 0.4 microm for single and 3-unit bridge molar substructure respectively. CONCLUSION: Independent-samples t-test showed significant differences of gap in zirconia substructure between single crowns and three-unit bridge (P<.001). Therefore, the span length has the effect on the fit of zirconia substructure that is fabricated using CAD/CAM technique especially at the occlusal area.