Three-dimensional comparison of 2 digital models obtained from cone-beam computed tomographic scans of polyvinyl siloxane impressions and plaster models

Abstract

Purpose: This study was performed to evaluate the dimensional accuracy of digital dental models constructed from cone-beam computed tomographic (CBCT) scans of polyvinyl siloxane (PVS) impressions and cast scan models.

Materials and methods: A pair of PVS impressions was obtained from 20 subjects and scanned using CBCT (resolution, 0.1 mm). A cast scan model was constructed by scanning the gypsum model using a model scanner. After reconstruction of the digital models, the mesio-distal width of each tooth, inter-canine width, and inter-molar width were measured, and the Bolton ratios were calculated and compared. The 2 models were superimposed and the difference between the models was measured using 3-dimensional analysis.

Results: The range of mean error between the cast scan model and the CBCT scan model was -0.15 mm to 0.13 mm in the mesio-distal width of the teeth and 0.03 mm to 0.42 mm in the width analysis. The differences in the Bolton ratios between the cast scan models and CBCT scan models were 0.87 (anterior ratio) and 0.72 (overall ratio), with no significant difference (P>0.05). The mean maxillary and mandibular difference when the cast scan model and the CBCT scan model were superimposed was 53 µm.

Conclusion: There was no statistically significant difference in most of the measurements. The maximum tooth size difference was 0.15 mm, and the average difference in model overlap was 53 µm. Digital models produced by scanning impressions at a high resolution using CBCT can be used in clinical practice.

Keywords: Cone-Beam Computed Tomography; Dental Models; Orthodontics.

Fig. 1. The cone-beam computed tomography (CBCT) equipment and model scanner used in this study. A. CBCT equipment (Rayscan α+; Ray Co., Ltd., Seongnam, Korea). B. CBCT scanning of a polyvinyl siloxane impression. C. Fabrication of a digital model from a model scanner (Identica Hybrid; Medit Co, Seoul, Korea).

Fig. 2. Three-dimensional digital models of the plaster casts were obtained using a model scanner (A and B) and cone-beam computed tomography (C and D), respectively.

Fig. 3. Linear measurements of tooth width (A, B, and C), and arch width (D) were made on the digital models.

Fig. 4. Three-dimensional analysis of a cast scan model and a cone-beam computed tomography scan model based on the best-fit algorithm. A and B. Deviations between the 2 models. The difference color map is set from −0.5 mm to 0.5 mm.

Fig. 5. Box-plot of dimensional discrepancies between the cast scan models and cone-beam computed tomography scan models.

^*Maximum outliers.