STATEMENT OF PROBLEM

The accuracy of digital scanning for complete dental arch and implant-supported complete-arch restorations has been reported. However, research addressing the accuracy of digital scanning methods for complete-arch tooth preparation is lacking.

PURPOSE

The purpose of this in vitro study was to compare the accuracy of intraoral scanning, impression scanning, and cast scanning for complete-arch preparation.

MATERIAL AND METHODS

Maxillary and mandibular jaw typodonts with 28 teeth prepared for complete crowns were used as reference casts and digitized as reference data sets with a desktop scanner. Three digital scanning methods were applied. First, the reference casts were each scanned 10 times with an intraoral scanner to generate the intraoral scanning group data sets. Second, the reference casts were each captured 10 times by using polyvinyl siloxane impression material, and the impressions were scanned with a desktop scanner to generate the impression scanning group data sets. Third, the impressions obtained in the impression scanning group were used to make gypsum casts which were then digitized with a desktop scanner to generate the cast scanning group data sets. Accuracy was determined by trueness and precision. Three-dimensional deviations of the prepared arches and anterior and posterior segments were measured from root mean square values and depicted on color-difference maps. Differences among test groups were analyzed by using a 1-way ANOVA and the post hoc Bonferroni test for normally distributed data or the Kruskal-Wallis test with Bonferroni correction for non-normally distributed data (α=.05).

RESULTS

The trueness of the maxillary arch was significantly higher in the impression scanning group than in the cast scanning and intraoral scanning groups (P<.05), but no significant differences were found among the 3 groups of the mandibular arch (P>.05). The precision of both arches was significantly higher in the impression scanning and intraoral scanning groups than in the cast scanning group (P<.05). Color maps showed horizontal symmetrical displacement in the intraoral scanning group relative to the reference data sets and within-group unilateral distal-end distortion. Irregular arch deformations were noted in the impression scanning group, and buccal and occlusal expansion occurred in the anterior-posterior direction in the cast scanning group. Pooled data for anterior teeth indicated that the trueness was lowest in the intraoral scanning group; however, that for the maxillary anterior teeth did not differ, while that for the mandibular anterior teeth differed significantly among groups (P<.05). For the posterior teeth, deviation was the lowest in the impression scanning group, and significant differences were noted in both arches among the 3 groups (P<.05).

CONCLUSIONS

Of the methods tested, impression scanning was the most accurate for the creation of a digital cast of a complete prepared arch.