Trueness and Precision of Intraoral versus Extraoral Scanning Techniques

Objectives: The objective of this in vitro study was to measure the trueness and precision of a newly-developed intraoral scanner and compare its‘ results to a common plaster cast digitizer.

Methods: An acrylic model of a lower left first molar was prepared to receive a ceramic partial crown and was duplicated by a digital-impressioning-system (cara TRIOS, Heraeus Kulzer GmbH, Hanau, Germany - TRI) and conventional one-step dual-viscosity impressions (Identium, Kettenbach GmbH, Eschenburg, Germany - IDE) as well. TRI-data were exported directly to a common quality-inspection-software, while in case of IDE, plaster models were cast and laser-scanned (7 Series, Dental Wings, Montreal, Canada), before datasets were subjectable to further computer-aided analyses. The model tooth was digitized by a structure-light-scanner to serve as a reference for trueness measurements (tooth vs impression), while overall precision was determined by superimposing one and another of the impressions. Mean quadratic deviations (RMS) were computed to estimate the congruency of two superimposed records and results were analyzed statistically by Student's t-test (n=5, α=0.05).

Results: Table 1 shows mean RMS-values for trueness and precision measurements. Differences in precision were not statistically significant (p=0.264). However, the trueness of intraorally-captured data was significantly higher when compared to digitized plaster casts (p<0.001). Qualitatively, TRI showed oversized dimensions at areas with strong curvature (e.g. preparation-finish-line, buccal cusps), while inner approximal groves were undersized. IDE featured partially undersized areas of the central occlusal and approximal boxes as well. Again, buccal and oral cusps were enlarged (Figure 1 upper row).

Conclusions: Intra- and extraoral scanning technologies showed highly reproducible results. Although differences to the reference scan were significantly lower with intraoral data capturing, both approaches showed very accurate results far within clinically acceptable standards.