Effect of different types of tooth and post space lengths on the accuracy of the digital post space with intraoral scanning.

Statement of problem: To create custom posts for endodontically treated teeth with a digital workflow, clinical guidelines governing digital scan techniques are needed. However, the evidence for the accuracy of intraoral scanners (IOSs) is limited for different tooth types and post space lengths.

Purpose: The purpose of this in vitro study was to evaluate the trueness of post space scans made with 2 different IOSs for various tooth types and post space lengths.

Material and methods: Three different tooth types (maxillary central incisor, maxillary first premolar, and maxillary first molar) with 4 different post space lengths (10, 11, 12, and 13 mm) were digitally designed and 3-dimensionally (3D) printed. For each specimen, scans of the post space were made with 2 different IOSs (TRIOS 4 and Primescan). With a computer-aided design (CAD) software program, each scanned post space was compared with the reference file used to 3D print the tooth specimens for trueness and % volume difference of the scanned areas. The 1-way Welch ANOVA and post hoc pairwise Welch t tests were used to analyze normally distributed data. The Kruskal-Wallis and post hoc Dunn tests were used to analyze nonnormally distributed data; when multiple tied values were found, a permutation test was used (α=.05).

Results: The TRIOS 4 IOS failed to capture the apical 2 mm of post space ≥10 mm. Primescan showed high trueness and volume capture of post space for maxillary central incisors and molars up to 13 mm and maxillary first premolars up to 12 mm in length. Within the same tooth type, statistically significant differences were found among the 4 different post space length groups for both trueness and volume capture (P<.05). For trueness, the median root mean square (RMS) ranged from 26 µm to 134 µm; central incisors had the highest trueness, followed by molars, then by premolars. The effect of different post-space lengths on trueness (RMS) varied by tooth type. The volume (%) of the scanned area had a mean percentage range from 76.3% to 100%; premolar teeth had the lowest volume results, followed by central incisors, then by molars.

Conclusions: The Primescan IOS can reliably scan post spaces of maxillary central incisors up to 13 mm, maxillary first premolars up to 11 mm, and maxillary first molars up to 12 mm. The TRIOS 4 IOS could not adequately scan post spaces ≥10 mm in length for all the tooth types examined.