Margin and Internal Fit Evaluation of the CAD-CAM Zirconia Bridge

Objectives: Evaluate and compare the marginal gap and internal fit of a three unit bridge fabricated by 2 different computer-aid design/manufacturing (CAD-CAM) systems.
Methods: A total of 50 specimens were used. A standardized specimen following the ISO 12836 for crown and bridge die preparation were used and duplicated. The specimens were divided into 2 groups and were marked with a code for identification (n=25 per group). First group was scanned using the laboratory scanner 3-Shape; a 3 unit bridge was digital designed and milled using a 5-axis milling machine (VHF-CAM5-S1). Vericore Zr HT zirconia discs 25mm was used. The second group was scanned using the CEREC chairside system with the Omnicam intraoral scanner. The 3 unit bridge was design using the software 4.4, and milled with the CEREC milling machine MC-XL with the blocks CEREC Zirconia blocks– inCoris TZI. All zirconia bridges were cemented with a Rely X dual cure self-adhesive resin cement (Unicem, 3M ESPE). Each restoration was seated on the abutments with firm finger pressure. Excess cement was removed and margins were light-cure. The specimens were stored in distilled water at 37C for 24 hours and then thermocycled for 5000 cycles. All specimens were sectioned mesio-distal using the saw machine (Isomet 5000; Buehler). The marginal fit and internal adaptation of each retainer of the bridge was examined under stereomicroscope (LEICA M125, Leica Microsystems) with 20 x Magnification. Marginal discrepancy and internal adaptation was measured on eight points in each sectioned abutment.
Results: The Data was analyzed using Student’s t-test at a significance level of p<0.05. No significant differences were recorded concerning the abutment position and convergence angle. All discrepancy values were within the clinically acceptable range.
Conclusions: All zirconia bridges showed clinically acceptable marginal adaptation values.