# Dimensional stability of pet-g clear aligners with different thickness through cyclic compressive load tests: An in vitro study

## TL;DR

This study tested how well PET-G clear aligners of different thicknesses maintain their shape under pressure, both with and without saliva.

## Contribution

The study introduces new empirical data on dimensional stability of PET-G aligners under cyclic compressive loads.

## Key findings

- 0.75-mm aligners showed better stability in intercanine distance than 0.88-mm aligners.
- 0.88-mm aligners were more stable in intermolar distance compared to 0.75-mm aligners.
- Molar FA distances showed higher changes with saliva, but intercanine FA distances remained stable.

## Abstract

The purpose of this in vitro study was to evaluate the dimensional stability of PET-G clear aligners.

Two starting passive aligners of different thicknesses (0.75 mm and 0.88 mm) were subjected to cyclic compressive loading tests using the Instron 3343 testing machine in the laboratory, both with and without saliva. The intermolar and intercanine distances, measured in the occlusal direction, and the intermolar and intercanine Facial Axis (FA) distances, calculated between the most vestibular points of the crowns defined as Facial Axis points, were recorded using the dedicated software 3Shape Orthoviewer. Finally, the aligners were scanned using a laboratory scanner (3Shape TRIOS®) and then compared with the untested aligners of the control group.

The 0.75-mm-thick aligners exhibited greater dimensional stability than the 0.88-mm-thick aligners when measuring intercanine distance, both with and without saliva. In contrast, the 0.88-mm-thick aligners demonstrated greater stability than the 0.75-mm-thick aligners when measuring intermolar distance under the same conditions. In the measurement of FA distances, higher values were observed at the molar level when the tests were conducted both with and without saliva, whereas no significant changes were observed in the intercanine distance.

The 0.88-mm-thick aligners demonstrated better dimensional stability during tests with and without saliva in the intermolar distance, while the 0.75-mm-thick aligners showed better dimensional stability in the intercanine distance.

Key words:Clear Aligners, PET-G, thickness, dimensional stability, cyclic compressive load tests.