Available online 23 April 2024

Author links open overlay panel, , , AbstractStatement of problem

Digital scanning is gradually replacing conventional impression making, but consensus on how tooth preparation influences the accuracy of intraoral scanning is lacking.

Purpose

The purpose of this in vitro study was to evaluate the effect of substrate material and abutment geometry on the accuracy of digital casts obtained by intraoral scanning.

Material and methods

The height and total occlusal convergence (TOC) angle were measured in 5 different groups that contained 5 specimens of different materials: natural tooth, cobalt chromium alloy, titanium, zirconium dioxide ceramic, and resin. The specimens were scanned with an industrial scanner to obtain reference data. Each specimen was placed in a maxillary standard dentition model that was assembled in a head simulator. Each dentition model was scanned 10 times with an intraoral scanner (IOS) under operatory lighting conditions to acquire intraoral scanning files for each specimen. All data were imported into a metrology software program and processed. A total of 10 trueness deviations, the mean superimposition results between IOS scanning data and reference data, and precision deviations, the mean superimposition results between IOS scanning data in pairs, were recorded. Two-way analysis of variance (ANOVA) and Tukey multiple comparison test were used to analyze the accuracy of intraoral scanning in relation to the height or TOC angle of the abutment (α=.05). The total means of each substrate material were compared with the Kruskal-Wallis test and Dunn test for multiple comparisons.

Results

The accuracy of scanning images was related to material and abutment geometry (P<.05). Bias was larger as abutment height increased with most substrates. Larger TOC angles increased the accuracy of the digital scans. The trueness deviation of translucent materials and the precision deviation of reflective materials were generally larger.

Conclusions

Substrate material and abutment geometry influence the accuracy of intraoral scanning. The accuracy of IOS generally tended to improve with decreasing height and increasing TOC angle and was affected by different substrates.

Section snippetsMATERIAL AND METHODS

The TOC angle and the height from the buccal cusp to the preparation margin were evaluated in this study. Two maxillary first premolar human teeth were prepared with the guidance of a milling device (af350; Amann Girrbach AG) and by conforming to the requirements of complete crown preparations.27, 28 The TOC angle of a preparation has been defined as the converging angle of 2 opposite axial walls in a given plane (Fig. 1).29 One tooth was prepared with an 8-mm height, 2-degree angle, 1-mm

RESULTS

Two-way ANOVA showed that the accuracy of intraoral scanning was related to substrate material and abutment geometry (P<.05) (Table 1, Table 2). Table 3, Table 4, Table 5, Table 6 show comparisons of different abutment heights and TOC angles for each substrate material. Both abutment height and TOC angle had a statistically significant interaction with the substrate materials.

The Tukey multiple comparison test indicated that more errors occurred in trueness when scanning higher specimens with

DISCUSSION

The aim of this in vitro study was to evaluate the trueness and precision of an IOS when scanning abutment teeth with different substrate materials and geometries. A head simulator was used to simulate the intraoral environment as far as possible. Based on the results of the study, the null hypothesis that no differences would be found in the accuracy of intraoral scanning when comparing different substrate material surfaces or when comparing abutment teeth with different geometries was

CONCLUSIONS

Based on the findings of this in vitro study, the following conclusions were drawn:

The material influenced the accuracy of intraoral scanning, with translucent substrates having larger trueness deviation and reflective materials having larger precision deviation.

The abutment height affected the accuracy of intraoral scanning. The accuracy of digital scans was worse with increasing height when most substrate materials were scanned.

The accuracy of digital scans was influenced by the TOC angle of

CRediT authorship contribution statement

Ziwei Zhang: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Writing - original draft. Xianqing Ming: Investigation, Data Curation. Yichen Luo: Writing - review and editing, Visualization. Wei Zhang: Conceptualization, Resources, Supervision, Project administration.

Acknowledgments

The authors thank Nanjing Jingyi Denture Company for assistance in fabricating models. The authors also thank the Affiliated Stomatological Hospital of Nanjing Medical University for their intraoral scanner technical support.

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