Comparison of biogenerically reconstructed and waxed-up complete occlusal surfaces with respect to the original tooth morphology

Recently, it has become possible to reconstruct complete occlusal surfaces using the biogeneric tooth model. This study aimed to mathematically assess and compare the morphologic agreement between original morphology and CAD-reconstructed, waxed-up and CAM partial crowns. Thirty-nine intact first permanent molars (39 participants) were included. Impressions, bite registrations and three gypsum replicas were made. Preparations for CAD/CAM partial crowns were performed and scanned. The restorations were biogenerically reconstructed (CERECA (R) v3.80) and milled. Wax-ups of these preparations were scanned as well as the milled restorations and original teeth. Discrepancies were evaluated by matching the scans with the original morphologies (Match3D, output: volume/area, z difference) and by contact patterns. The discrepancies were compared between CAD-reconstructions and either wax-ups or milled restorations (paired t test, alpha = 0.025 for two multiple tests). The mean differences between natural tooth morphology (triangular stabilisation 71.8 %) and biogeneric reconstructions, wax-ups and milled restorations (triangular stabilisation 87.2 %) were: 184 +/- 36 mu m (volume/area), 187 +/- 41 mu m (z difference); 263 +/- 40 mu m (volume/area), 269 +/- 45 mu m (z difference) and 182 +/- 40 mu m (volume/area), 184 +/- 41 mu m (z difference). Differences associated with biogeneric reconstructions were significantly less than those of wax-ups (volume/area and z difference, p < 0.0001), but not significantly different than those of milled restorations (p = 0.423 (volume/area), p = 0.110 (z difference)). CAD software enables a closer reconstruction of teeth than do wax-ups, even when no cusps remain. The milling device is precise enough to transfer CAD into the final restoration. This study shows that state of the art CAD/CAM can effectively produce natural tooth morphology and may be ideal for fixed partial dentures.