Available online 24 November 2022

Author links open overlay panelAbstractStatement of problem

Scan path length and the presence of edentulous alveolar ridge sections have a negative influence on scanning accuracy. How different artificial landmarks combined with an adapted scanning method affect accuracy is unclear.

Purpose

The purpose of this in vitro study was to determine the influence of 2 different artificial landmarks combined with an adapted scanning method on the scanning accuracy of a partially edentulous maxillary model.

Material and methods

The model simulated a maxilla with 6 prepared teeth to accommodate a complete arch fixed partial denture. Five ceramic precision balls (ball center P1–P5), distributed buccally to the dental arch, were used to detect the dimensional and angular changes between the reference model and the intraoral scans. One intraoral scanner (Primescan) was used to make 30 scans each with either the scanning strategy recommended by the manufacturer (M) or with an adapted scanning strategy and the use of a bar (B) or 4 plates (P) as artificial landmarks in the dorsal palate. Data were statistically analyzed using a generalized least squares regression model (α=.05).

Results

Scanning with artificial landmarks reduced the maximum absolute distance deviations (M: 249 μm, B: 190 μm, P: 238 μm) and the maximum angle deviations (M: 0.31 degrees, B: 0.28 degrees, P: 0.26 degrees). Vertical distance deviations were improved by 10 to 50% with the use of artificial landmarks. Absolute mean distance deviations were significantly lower for group M (P<.001). In contrast, with artificial landmarks, mean angle (P<.001) and mean vertical distance deviations (P<.014) improved significantly.

Conclusions

Scanning with artificial landmarks in the dorsal palate combined with an adapted scanning method improved the scanning accuracy and reliability of vertical distance deviations.

Section snippetsMaterial and Methods

A test model designed according to the International Organization for Standardization (ISO) standard 20 89624 was produced simulating a patient treated with a complete arch FPD, with the central incisors, canines, and first molars prepared for complete crowns (Fig. 1A). The teeth were fabricated in 2 layers and consisted of a cobalt–chromium alloy core (Colado CAD CoCr4; Ivoclar AG) to which a polymethyl methacrylate crown (SR Vivodent CAD Multi; Ivoclar AG) was adhesively attached. The teeth

Results

The signed total distance deviations are displayed in Figure 5. For all 3 scanning methods (groups M, B, and P), nearly all reference distances were either over- or underestimated, with a clear tendency toward overestimating scan distances (positive distance deviations).

For all 3 scanning methods, the largest absolute distance deviation occurred over the cross-arch span (249 μm in group M, 190 μm in group B, and 238 μm in group P) (Fig. 6 and Table 2). Comparisons of the 3 scanning methods

Discussion

The null hypothesis that no significant difference in scanning accuracy of the complete dental arch would be found among the scanning methods was partially rejected. Total distance deviations and angle deviations did not differ significantly between the groups (P>.05). However, a significant difference was found between the groups for vertical distance deviations (P<.05).

This study used a model of a partially edentulous maxilla with teeth prepared to accommodate a cross-arch FPD. Most studies

Conclusions

Based on the findings of this in vitro study, the following conclusion was drawn:

1.

The use of an artificial landmark in the dorsal palate in combination with an adapted scanning method can significantly improve the scanning accuracy and reliability of vertical distance deviations.

Acknowledgments

The authors thank Claire Bacon for English language editing of the manuscript.

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© 2022 by the Editorial Council for the Journal of Prosthetic Dentistry.