Distributed Force Measurement and Mapping Using Pressure-Sensitive Film and Image Processing for Active and Passive Aligners on Orthodontic Attachments

Abstract

Orthodontic clear aligners, along with their attachments, are used for the corrective alignment of teeth during orthodontic treatment. Although the clear aligner technique has gained widespread popularity due to its aesthetic quality, studies that examine and map the measurement of forces applied to clear aligner attachments are lacking. This investigation describes the topographical visualisation of the force in clear aligner attachments. We describe a method using Prescale® pressure film and an image processing technique to obtain the topographical visualisation of a clear aligner’s distributed force on the attachment in an in-vitro study using resin models. The variation of colour density due to the distributed force is calibrated with a force gauge for validation. The image processing technique is demonstrated through the histogram-based K-means clustering method with 3D visualisation of the distributed force. This method involves pressure film calibration, followed by sample preparation and image processing analysis. The proposed topographical pressure mapping system illustrates the distributed force on the clear aligner attachment as the force applied is directly proportional to intensity. For active aligners, the mean force ranged from 6.2–6.3 N, and for passive aligners, the mean force ranged from 4.8–4.9 N. Therefore, the net force exerted on a single clear aligner attachment in a resin model for this study was 1.3–1.4 N. The preliminary findings of this work can be developed further to be a reference in future clinical orthodontic clear aligner and attachment research.