Accuracy of two best-fit alignment strategies with different reference areas for wear measurement with an intraoral scanner: an in vitro study.

Aim: The aim of the present in vitro study was to assess and compare the accuracy of two best-fit alignment strategies with different reference areas for wear measurement with an intraoral scanner (IOS).

Materials and methods: Eight anatomic contour zirconia crowns were fabricated and scanned twice with an IOS. One of the scan datasets (Data Trueness) was duplicated and wear facets were simulated (Data Wear). The other scan dataset (Data Baseline) was aligned to Data Wear by two best-fit alignment strategies with different reference areas (the occlusal surface with no signs of wear [Group Occlusal], and the axial surface [Group Axial]), and 3D deviation analysis was performed to detect wear loss. The 3D deviation between Data Trueness and Data Wear was calculated as the truth-value for accuracy evaluation (Group Trueness).

Results: The color-difference map showed Group Occlusal had a similar wear-facet distribution to Group Trueness while Group Axial showed an obvious tilting position, and the obtained height loss values were larger and with large standard deviations. Both Group Occlusal and Group Axial showed significant differences compared with Group Trueness in maximum height loss and mean height loss (P < 0.05) while showed no significant difference in mean distance (P > 0.05). The paired t test showed significant differences between Group Occlusal and Group Axial in maximum height loss and mean height loss (P < 0.05) while showed no significant difference in mean distance (P > 0.05).

Conclusions: Best-fit alignment with the occlusal reference area produced a better alignment result than that with the axial reference area. Measuring wear with an IOS has potential, but the method is prone to overestimating the height loss.