Smart Flexible 3D Sensor for Monitoring Orthodontics Forces: Prototype Design and Proof of Principle Experiment

Abstract

There is a critical need for an accurate device for orthodontists to know the magnitude of forces exerted on the tooth by the orthodontic brackets. Here, we propose a new orthodontic force measurement principle to detect the deformation of the elastic semi-sphere sensor. Specifically, we aimed to detail technical issues and the feasibility of the sensor performance attached to the inner surface of the orthodontic aligner or on the tooth surface. Accurate force tracking is important for the optimal decision of aligner replacement and cost reduction. A finite element (FE) model of the semi-sphere sensor was developed, and the relationship between the force and the contact area change was investigated. The prototype was manufactured, and the force detection performance was experimentally verified. In the experiment, the semi-sphere sensor was manufactured using thermoplastic polymer, and a high-precision mold sized 3 mm in diameter. The change in the contact area in the semi-sphere sensor was captured using a portable microscope. Further development is justified, and future implementation of the proposed sensor would be an array of multiple semi-sphere sensors in different locations for directional orthodontic force detection.

The applications of flexible electronics in dental, oral, and craniofacial medicine

“…Lee et al developed a flexible hemispherical sensor that could be affixed between the tooth surface and a clear aligner (Fig. 5c) 33 . The thermoplastic hemispherical sensor fixed its semicircular bottom on the tooth surface, and its top side touched the clear aligner.…”

“…Many natural hydrogels that are edible, such as chitosan and cellulose, are adopted for device fabrication 17,19 . Another strategy is employing chemically inertial materials (e.g., PDMS, silk film (SF), parylene, and silicone) to embed electric materials 19,[31][32][33][34] . When constructing the electrodes of flexible electronics, metals like Ag, Pt, and Au, and conductive nano-materials such as CNTs and MXene, which have been proven to show little toxicity under limited dosage, are employed to ensure ample biological safety 19,21,22,31,35 .…”

Dental Restorations

“…Thanks to its ability to reduce oral mucosa pain [92] and enamel lesions due its conventional bracket system [93], to enable the treatment of severe orthodontic disorders [94] and to allow better comfort, esthetics and hygiene, orthodontic treatment using clear aligners has gained popularity. Through the growth of producer companies [95], nowadays, over 10 million patients have tried out this new orthodontic technique [96]. Nevertheless, the main side effect is that, although general treatment time has decreased compared to conventional systems, in extraction cases it has increased.…”

“…Multiple studies have followed the development of new techniques to measure orthodontic forces [99,105], but a universal device capable of precisely detecting the strength applied by orthodontic treatments has not yet been found. For this reason, Lee's study [96] shows an innovative orthodontic force-measurement method which allows the monitoring of the deformation of a pliant semi-sphere sensor, composed of a biocompatible polymer bonded to the inner aligner surface or to the tooth surface. The sensor is economic, simple and states the symmetry and homogeneity of the forces on the attachment, calculating the exerted force and the resulting orthodontic movement over the tooth's surface.…”

“…The change in the contact area in the semisphere sensor was measured by a microscope, while the changing force can be monitored by changes to the contact area between the sensor and the aligner's inner surface. Hence, the sensor could establish the force exerted on a specific sensor part: further improvements to this 3D sensor would be a group of numerous semi-sphere sensors in different positions for the directional investigation of the forces [96]. Furthermore, it could also be useful to analyze forces applied in more complex situations, such as in malformations or transversal deficits.…”