Nondestructive three-dimensional analysis of conventional and CAD/CAM restorations

Objective:

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. 

Method:

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.

Result:

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.

Conclusion:

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.