Effect of Preparation Design on the Trueness and Precision of Intraoral Scanners: A Comparative Analysis Across Two IOS Systems.

Objective

The accuracy of intraoral scanners is commonly described by trueness and precision; however, the extent to which single-tooth crown preparation geometry influences these outcomes across different scanner systems remains unclear. This in vitro study aimed to evaluate trueness and to descriptively assess precision across different preparation designs and scanner systems.

Methods

A maxillary phantom model with nine single-tooth crown preparation designs and one unprepared control was scanned with Trios 5 and Primescan. For trueness, each preparation-scanner combination was scanned five times and compared with a high-accuracy industrial reference scan (ATOS Q) using RMS deviation after best-fit alignment. Trueness was analyzed with two-way ANOVA. Precision was evaluated descriptively using the interquartile range (IQR) of repeated scan RMS values.

Results

Trueness RMS values ranged from 0.0247 to 0.0623 mm. The lowest value was observed for occlusal veneer (VE3; partial occlusal) scanned with Trios 5, and the highest value was observed for anterior veneer (VE2; buccal + palatal) scanned with Primescan. Preparation design significantly affected trueness (F(9, 80) = 9.26, p < 0.001), while scanner type showed no statistically significant difference (p = 0.056); the preparation design × scanner interaction was significant (F(9, 80) = 4.84, p < 0.001). Precision varied across preparation designs and scanner types, as reflected by differences in IQR values.

Conclusions

Cavity preparation geometry significantly affected IOS trueness, and this effect was scanner-dependent. Simpler and more optically accessible geometries generally showed lower RMS deviations, although this pattern varied according to specific preparation features. Precision, assessed descriptively using IQR values, varied across preparation designs and scanner systems and should be interpreted cautiously.