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Published on: January 28, 2020
Comparison of two virtual bracket removal workflows for orthodontic retainer fabrication: surface replacement versus
Chaoran Xue1, Yuxi Zhao1, Shuhan Tang1
1State Key Laboratory of Oral Diseases & National Clinical Research Center for Oral Diseases & Department of Orthodontics, West China Hospital of Stomatology, Sichuan University, No. 14, 3rd Section of Renmin Nan Road, Chengdu, 610041, China.
Objective:
To compare the accuracy of two virtual bracket removal (VBR) workflows for orthodontic retainer fabrication: a novel surface replacement (RP) workflow and a well-established surface reconstruction (RC) workflow. Accuracy was evaluated on digital models, three-dimensionally (3D)-printed models, and vacuum-formed retainers (VFRs), with a focus on tooth-type-specific performance.
Materials And Methods:
14 sets of paired pre-treatment and post-treatment dental models were included. Post-treatment models were bonded with brackets/tubes in vitro and scanned to simulate pre-debonding data. Each scan was processed with both RP and RC workflows to create modified bracket-free digital models (RP-CAD and RC-CAD), which were 3D‑printed into working models (RP‑P and RC‑P). VFRs were thermoformed on the printed models and scanned into digital files (RP-VFR and RC-VFR). Surface deviations at each stage were measured as root mean square (RMS) values relative to the original post-treatment model and compared between RC and RP workflows across different tooth types.
Results:
Both RP and RC workflows demonstrated clinically acceptable accuracy. RC-P showed significantly lower overall deviation on printed models than RP-P (median RMS 0.058 vs. 0.069 mm; P < 0.001), especially for upper incisors, upper premolars, and lower premolars. At the digital model stage, RP‑CAD showed lower deviations than RC-CAD in posterior teeth (e.g., upper and lower molars; P < 0.01), whereas RC‑CAD performed better in anterior teeth (upper incisors; P < 0.001, lower incisors and canines; P < 0.05). Retainers made on RC-P models had significantly more accurate internal fit than those made on RP-P models (median 0.15 vs. 0.21 mm; P < 0.001).
Conclusions:
Both VBR workflows yielded clinically acceptable accuracy, but RC proved more consistent overall. RP showed an initial accuracy advantage for posterior teeth at the digital stage, but this benefit was diminished after 3D printing, indicating that RC better preserves accuracy through the full workflow.
Clinical Relevance:
Both RC and RP VBR workflows are viable for retainer fabrication. RC is preferable for routine use due to its simplicity and efficiency, whereas RP may be selectively advantageous, especially for complex posterior regions, particularly if future improvements in 3D printing and software automation streamline the RP procedure.
