Design, numerical simulation, and in vitro examination of a CAD/CAM-fabricated active orthodontic treatment element

Orthodontic treatments with custom-made active elements may lead to more efficient treatment with fewer side effects. The objective of the present in vitro study was to determine whether individually constructed, mathematically simulated, and 3D-printed power chains could generate adequate forces for orthodontic tooth movement.

An individual measurement device was developed using a high-precision load cell, amplifier, and microcontroller for signal processing. Elastic chains were designed and subsequently printed from two different thermoplastic polyurethane (TPU) filaments and a thermoplastic elastomer (TPE) filament. With the CAD data, a finite element analysis (FEA) was performed to calculate the reactive forces to be expected at different activation levels. The measured force development of the test objects was compared with the results from the FEA.

The results showed a high precision of the measurement device, with an intraclass correlation coefficient (ICC) of 0.999 and a Dahlberg error of 0.05 N. The measured forces ranged from 196 to 681 g. There was a significant correlation between the measured and calculated forces (R 0.91 to 0.98).

In the present study, the fully digital workflow of producing an individualized active orthodontic treatment element, which developed almost exactly the force values calculated in the FEA, was shown. Future clinical use seems promising, in combination with fully individualized and digitally planned treatment approaches. This offers the possibility to integrate these insights from exemplary applications into patient-specific digital planning in orthodontics. The combination of CBCT root reconstruction, intraoral scans with customized brackets, and wires is the perfect starting point to add mechanical and numerical simulations. This would be the next step from shape-driven planning to force-driven planning. The goal is to reduce treatment time and negative side effects, eg, root resorption.

The present in vitro study is the first to show the possible individualized construction and 3D printing of elastic chains exhibiting reproducible, predefined forces.