Internal 3D-fit of CAD/CAM-made zirconia copings. A comparative in-vitro study

Introduction: With high strength Y-TZP zirconia, conventional seating of CAD/CAM-manufactured restorations is possible. The internal fit of conventionally seated all-ceramic FDP's should be comparable with cast restorations. For the evaluation of internal fit, 3D-methods are more reliable than conventional 2D-methods, due to a high number of measurement points and the possibility of a spatial display.

Objective: Aim of the study was the evaluation of internal fit of posterior CAD/CAM-made zirconia copings by a 3D-method.

Methods: Starting point of the study was a ceramic master die of tooth 14 and 16 with a surface that can be detected by optically non-contact digitizing and a corresponding virtual CAD surface-model, created by reverse-engineering. After impression taking and pouring gypsum dies, five optimized copings per tooth were manufactured with CAD/CAM-systems ce.novation, Cercon, Cerec and Lava. The inside of the copings and all margins remained untouched (no try-on). Evaluation of internal fit was performed with the elastomeric wash technique (replica technique). Replica (ceramic die with adherent silicone) and after removing the silicone the ceramic die itself were consecutively optically digitized in same coordinate system of the measuring device. The replica data was then aligned to the CAD surface-model. Internal fit was determined as discrepancy of replica data to the virtual CAD surface-model (Surfacer, SDRC Imageware, Neu Isenburg, Germany). For statistical analysis, a multivariate analysis of variance was done (SPSS 15.0, SPSS Inc., Chicago, USA).

Results: Average internal discrepancies ce.novation/Cercon/Cerec/Lava were 85±4/111±10/92±32/101±7µm for molar and 87±11/82±4/115±50/83±3µm for premolar copings. No statistically significant difference between systems was found (p=0.37).

Conclusion: Within the limitations of this in-vitro study, well fitting copings, corresponding to today's recommendations for conventional seating, can be manufactured. Differences among systems resulted from high occlusal discrepancies (Cercon) or interferences on internal surface (Cerec).

Blanks/copings courtesy of: ce.novation, Degudent, Vita, 3M–Espe.