The predictability of expansion with Invisalign: A retrospective cohort study.

INTRODUCTION: Few studies have evaluated the predictability of expansion with Invisalign for the current SmartTrack material. METHODS: Pretreatment, predicted, and posttreatment digital models from Invisalign's ClinCheck software were obtained for 57 adult patients with a planned arch expansion of at least 3 mm. Arch width measurements were collected using a software measuring tool (MeshLab), Invisalign's arch width table, and the centroid of the clinical crown. Data for 30 patients were remeasured for each method to assess intrarater reliability. Predictability of expansion was calculated by comparing the amount of achieved expansion to predicted expansion. RESULTS: The predictability of expansion across centroids for the maxillary teeth was: 72.2% canines, 78.9% first premolars, 81.1% second premolars, 63.5% first molars, and 41.5% second molars. The predictability of expansion across centroids for the mandibular teeth was: 82.3% canines, 93.0% first premolars, 87.7% second premolars, 79.8% first molars, and 42.9% second molars. The average expansion was significantly different from that predicted for each type of tooth in both the maxilla and mandible. Both underexpansion and overexpansion were observed. Arch width measurement reliability for each employed method was as follows: MeshLab (average error 0.197 mm); calculated centroids (0.002 mm); ClinCheck arch width table (0.000 mm). CONCLUSIONS: On average, the amount of predicted expansion is not achieved with the Invisalign system and varies according to tooth type and arch. Discretion is required when overcorrecting to compensate for expansion inaccuracy. Both underexpansion and overexpansion were observed; further investigation into factors influencing underexpansion and overexpansion is required.

Accuracy of mandibular repositioning surgery using new technology: Computer-aided design and manufacturing customized surgical cutting guides and fixation plates.

INTRODUCTION: Recent 3-dimensional technology advancements have resulted in new techniques to improve the accuracy of intraoperative transfer. This study aimed to validate the accuracy of computer-aided design and manufacturing (CAD-CAM) customized surgical cutting guides and fixation plates on mandibular repositioning surgery performed in isolation or combined with simultaneous maxillary repositioning surgery. METHODS: Sixty patients who underwent mandibular advancement surgery by the same surgeon were retrospectively evaluated by 3-dimensional surface-based superimposition. A 3-point coordinate system (x, y, z) was used to identify the linear and angular discrepancies between the planned movements and actual outcomes. Wilcoxon rank sum test was used to compare the outcomes between the mandible-only and the bimaxillary surgery groups with significance at P <0.05. Pearson correlation coefficient compared planned mandible advancement to the outcome from advancement planned. The centroid, which represents the mandible as a single unit, was computed from 3 landmarks, and the discrepancies were evaluated by the root mean square error (RMSE) for clinical significance set at 2 mm for linear discrepancies and 4° for angular discrepancies. RESULTS: There was no statistically significant difference between the planned and actual position of the mandible in either group when considering absolute values of the differences. When considering raw directional data, a statistically significant difference was identified in the y-axis suggesting a tendency for under-advancement of the mandible in the bimaxillary group. The largest translational RMSE for the centroid was 0.77 mm in the sagittal dimension for the bimaxillary surgery group. The largest rotational RMSE for the centroid was 1.25° in the transverse dimension for the bimaxillary surgery group. Our results show that the precision and clinical feasibility of CAD-CAM customized surgical cutting guides and fixation plates on mandibular repositioning surgery is well within clinically acceptable parameters. CONCLUSION: Mandibular repositioning surgery can be performed predictably and accurately with the aid of CAD-CAM customized surgical cutting guides and fixation plates with or without maxillary surgery.