Effect of three-dimensional target and reference data alignment method in an open digital dental communication application on the external surface trueness of CAD-CAM provisional crowns

Statement of problem. There are still no consistent standards for evaluating 3D deviation in computer-aided design and computer-aided manufacturing (CAD/CAM) restorations, causing results to differ. Typically, information about the effect of alignment methods in the measurement software on the trueness of restorations is lacking.
Material and methods. An upper first molar typodont tooth was prepared for a ceramic crown, a full contour CAD design was completed, 30 provisional crowns were processed using Ceramill CAD-CAM system (Ceramill map scanner, Ceramill mind software, and Ceramill motion 2 milling machine; Amann Girrbach). All the crowns were milled from the same CAD design (reference data). The milled crowns were then scanned by a dental laboratory scanner to get STL files (Target data). To measure the trueness of the milled crowns the target and reference data were aligned using Medit Link Application. According to the method of data alignment in the application, there were three groups, automatic alignment (AA), manual alignment (MA), and alignment with selected area (ASA). The root mean square (RMS) values as a measure of trueness were then statistically analyzed.
Results. The Kruskal-Wallis’ test results indicated that there were non-significant differences in the trueness of provisional crowns when different data alignment methods were used(P>.05). The trueness of provisional crowns was (RMS=78.35 µm) for AA method, (87.6 µm) for MA, and (91.15 µm) for ASA.
Conclusions. According to the results of this study, there was no significant differences among the three alignment methods used to evaluate the external surface trueness of CAD-CAM restorations.