Analysis of the Internal Fit of CAD/CAM-restorations: A New Digital Approach

Objectives: Studies analyzing the internal fit of FDPs normally rely on conventional methods (replica technique). Nevertheless, with this technique, the number of measurement points is limited and the entire procedure is time-consuming. Furthermore, the copings are often made of zirconia, which requires a sintering after milling and entails high manufacturing costs. Therefore, it was the aim of this study to develop a new digital method and compare this technique with the replica technique using different coping materials.
Methods: Two models, representing a partial upper jaw with the first molar(26, FDI) prepared, were fabricated. In model A both adjected teeth(25,27) were presented, whereas in model B only the adjected premolars(24,25) were there. Digital impressions were conducted with a Trios3(3Shape) and copings were made of three different materials (CAD/CAM-composite(LuxaCamComposite), zirconia(LavaPlus), non-precious(FinoframeCoCr)). First, the replica technique(EXA'lence,GC) was carried out. Each specimen was sliced and analyzed under a microscope(Smartzoom5,Zeiss) at 16 measurement points. For digital inspection each coping were set on the dye with a high-viscosity silicone(FitTestC&B,Voco). After removal of the coping the dye with the adherent silicone layer was scanned. For digital inspection a 3D-software(GOM-Inspect) was used. Statistical analysis was performed by a Kruskall-Wallis-test.
Results: No statistical difference could be shown between the digital and conventional method (p=.997) and the two models (A,B) (p=.234). Whereas, occlusal measurement points (means±SD, 198±36µm) displayed significant higher internal discrepancy (ID) compared to axial (170±74µm) and marginal (53±24µm) measurement points (p < .00). Between the three coping materials no significant difference was observed, but CAD/CAM-composite showed the lowest ID (136±70µm), followed by zirconia (152±74µm) and non-precious alloy (157±93µm).
Conclusions: Overall, the results demonstrate that the digital methods is a valid alternative to conventional replica technique. Additional, it offers the possibility to make a full 3D-analysis. Furthermore, manufacturing costs can be reduced by using new materials such as CAD/CAM-composites.