For the analysis of internal fit, destructive and non-destructive methods are available. The downside to the destructive analysis is the loss of the restoration for clinical use. With nondestructive analysis, the internal fit can be identified by using a conventional (2D) or a computerized three-dimensional (3D) replica method. Aim of this study was to compare two methods of 3D-analysis for measuring internal fit and to assess the influence of manufacturing processes, restoration materials and tooth shape on the internal fit of conventional and CAD/CAM-made restorations.
Ten patients received a chamfer preparation in the posterior tooth region. Three duplicate dies were made from each master-model. A single crown was fabricated on each duplicate die with one of three materials and procedures: (1) slip-casting densely sintered zirconia (ce.novation GmbH, Hermsdorf, Germany), (2) laser-sintering non-precious alloy (infiniDent, Sirona Dental System Bensheim, Germany) and (3) conventionally made non-precious alloy restoration (Flemming Dental Laboratory Dental, Leipzig, Germany).
Mechanical digitization of the crown inside (Triclone 90, Renishaw, Gloucestershire, GB) and optical digitization (ODKM 97, Fraunhofer IOF, Jena, Germany) of a replication of the internal crown surface with a digitizable silicone (KwikkModel fluid, R-dental dental products, Hamburg, Germany) were compared and the differences between the mechanically (negative) and optically (positive) digitized inside of the crown were calculated.
Depending on the manufacturing in mean deviations between 0.093mm (SD: 0.007, CI: 0.079-0.107mm) and 0.143mm (SD: 0.007, CI: 0.129-0.157mm) were found. The comparison of mechanical digitizing and 3D-replica-method regarding the reproduction of the internal fit revealed no significant difference (p=0.969). Manufacturing process (p<0.000) and tooth shape (p=0.003) showed significant differences regarding internal fit.
Mechanical digitizing and the 3D-replica-method are both suitable for the 3D-analysis of internal fit. All crown frameworks were clinically suitable. Applying CAD/CAM-technology does not coercively provide an advantage in accuracy.
Keywords: CAD/CAM, Ceramics, Internal fit and Prosthodontics