Optimizing implant workflows: The role of fixation screws and tripod configurations in enhancing mandibular registration accuracy.

STATEMENT OF PROBLEM: Different reference landmarks can be used to guide the scan registration of an implant scanning workflow, including fixation screws. However, the effect of arch distribution on registration accuracy remains unknown.

PURPOSE: The purpose of this in vitro study was to evaluate the effect of the number and spatial distribution of fixation screws on the accuracy (trueness and precision) of the registration between tooth and tissue scans in a mandibular implant scanning workflow.

MATERIAL AND METHODS: A mandibular typodont was obtained. Six reference markers (2 on the buccal and 4 on the lingual) were placed to facilitate posterior measurements. Three fixation screws were placed: 1 in the anterior symphysis and 1 on each of the retromolar pads. A laboratory scan was recorded (control file). Thirty scans with the typodont teeth were obtained, including the 6 markers and 3 fixation screws, by using an intraoral scanner (IOS) (Aoralscan Elite). The typodont teeth were then removed, and a layer of putty polyvinyl siloxane was applied only over the edentulous areas. Then, 30 tissue scans (without the teeth) were obtained with the 6 markers and 3 fixation screws using the same IOS. Three groups were created based on the fixation screws used to register the tooth and tissue scans: 1 anterior (ANT group), 2 posterior (POST group), and 3 with tripod distribution (TRIPOD group). In the ANT group, each experimental tooth scan was modified by trimming the 2 posterior fixation screws. Then, each tooth and tissue pair of scans was aligned with the best fit algorithm using the anterior fixation screw as the common information. In the POST group, each experimental tooth scan was modified by trimming the anterior fixation screw. Then, each tooth and tissue pair of scans was aligned using the posterior fixation screws as the common information. In the TRIPOD group, each pair of tooth and tissue scans was aligned using the 3 fixation screws as the common information. In the control and each pair of aligned experimental scans, linear measurements were calculated between the buccal markers of the tooth scan and the anterior and posterior lingual markers of the tissue scan. The measurements obtained in the control scan were used to calculate registration discrepancies with each specimen. One-way ANOVA and Tukey tests were used to analyze trueness. The Levene test was used to analyze precision (α=.05).

RESULTS: Significant anterior (P<.001) and posterior (P<.001) trueness discrepancies were found. The TRIPOD group obtained significantly better anterior trueness than the ANT and POST groups. The POST and TRIPOD groups obtained better posterior trueness than the ANT group. The Levene test revealed significant posterior precision discrepancies (P<.001). The posterior precision in the ANT group was significantly worse than in the POST and TRIPOD groups.

CONCLUSIONS: Three fixation screws with a tripod spatial distribution obtained better accuracy than 1 fixation screw in the anterior or 2 fixation screws in the posterior areas of the arch.