Effect of Implant Angulation on the Rotational Displacement of a 3-Unit Bridge after Digital Impression

Abstract

Objectives. This study aimed to assess the effect of implant angulation on the rotational displacement of a 3-unit bridge following a digital impression. Materials and Methods. This in vitro experimental study evaluated 3 master models of the maxilla with Kennedy’s class III partial edentulism and bilateral three-unit implant-supported fixed partial dentures. Two implants were placed with 0° (first model), 15° (second model), and 30° (third model) interimplant angles. The implants were placed bilaterally at the sites of first premolars and first molars from the posterior towards the anterior region and coded A (posterior) and B (anterior) in the left, and C (posterior) and D (anterior) in the right side. Next, their position was recorded using a coordinate measuring machine to serve as a reference. The models were then scanned by both 3Shape and Sirona digital scanners (12 times by each scanner). The obtained data were compared with the reference data three-dimensionally using GOM Inspect software to determine the rotational displacement of the implants. Data were analyzed by repeated-measures ANOVA, one-way ANOVA, paired sample t-test, and independent sample t-test ( $P$  < 0.05). Results. Since repeated-measures ANOVA showed that the interaction effect was significant ( $P$  = 0.010), the data were analyzed by subgroup analysis. The 3Shape scanner showed significantly higher accuracy for C-D region in model 2 ( $P$  = 0.001), and A-B region in model 1 ( $P$  ≤ 0.01). In the use of the 3Shape scanner, model 3 showed a lower error rate in the A-B region, compared with models 1 and 2. Model 1 showed higher error rate than models 2 and 3 in the C-D region ( $P$  ≤ 0.01). In the use of the Sirona scanner, model 1 showed a higher error rate than models 2 ( $P$  = 0.031) and 3 ( $P$  = 0.004) in the C-D region. Conclusion. In digital impressions of angulated implants in 3-unit bridges by using 3Shape and Sirona scanners, the rotational error decreases as the interimplant angle increases.