Effect of Mesh Homogeneity and Choice of Target Surface on Statistical Evaluation of Mesh Differences

Abstract

In dentistry, clinical wear is typically measured by superimposition of plaster replica scans of the patient's actual and baseline situation. Intraoral scanning could save time and circumvent replica fabrication and associated errors. However, intraoral scanners are made for commercial use without the possibility to implement comprehensive user-specific settings. Analysis of exported stl-data is, in general, executed with commercial quality control software.

This study investigated the effect of mesh inhomogeneities on distance measurements based on target surfaces generated by different scanners and parameter settings. To quantify errors, an analytical solution for mean value and standard deviation of evenly distributed distance measurements for a spherical cap situation (resembling either a worn cusp or a wear track in a once flat surface) was derived. In vitro experiments with scans of precise spherical moulds gradually reduced in height complemented the investigation.

Due to non-weighted statistics in the quality control software, errors increased with increasing mesh inhomogeneity. Worst results were given for intraoral scans with mean relative errors of up to 13.2% and 20.5% for mean value and standard deviation of the distributed distance measurements. Homogeneous remeshing of the intraoral scan surfaces could almost eliminate these unwished effects.