A new method assessing predicted and achieved mandibular tooth movement in adults treated with clear aligners using CBCT and individual crown superimposition

The purpose of this study was to demonstrate a new method for quantifying the difference between predicted and achieved tooth movement with Invisalign using stable three-dimensional (3D) mandibular landmarks and dental superimposition. Cone-beam computed tomography (CBCT) scans before (T1) and after (T2) the first series of aligners, their corresponding digital models (ClinCheck initial of the first series as T1 and ClinCheck initial of the refinement series as T2), and the ClinCheck final model of the first series as the predicted were obtained from 5 patients treated with non-extraction Invisalign therapy. After segmentation of the mandible and its dentition, T1 and T2 CBCTs were superimposed on stable anatomic structures (Pogonion and bilateral mental foramen) along with the pre-registered ClinCheck models. The 3D prediction differences between the predicted and achieved tooth position for 70 teeth with four types (incisor, canine, premolar and molar) were measured using a combination of software. The method employed in this study was tested to be reliable and repeatable with a very high intraclass correlation coefficient (ICC) for both intra- and inter-examiner reliability. Premolar Phi (rotation), Incisor Psi (mesiodistal angulation), and Molar Y (mesiodistal translation) showed a significant prediction difference (P < 0.05), which is also clinically relevant. The method involving CBCT and individual crown superimposition to measure the 3D positional changes in the mandibular dentition is a robust and novel one. While, our finding in terms of the predictability of Invisalign treatment in the mandibular dentition mainly served as a crude, cursory examination, which warrants further and more rigorous investigations. With this novel methodology, it is possible to measure any amount of 3D tooth position difference in the mandibular dentition either between the simulated and the actual or with treatment and/or growth. Deliberate use of overcorrection of which specific type of tooth movement with clear aligner treatment and to what extent, might be possible with future studies.