# Effect of chemical post-processing on the compressive strength of MSLA 3D printed orthodontic models: an in vitro comparative study

## TL;DR

This study compares how different chemical treatments affect the strength of 3D-printed dental models used in orthodontics.

## Contribution

The study empirically evaluates the impact of acetone, propylene glycol, and isopropyl alcohol on the compressive strength of MSLA-printed orthodontic models.

## Key findings

- Propylene glycol increased compressive strength compared to the untreated control, but with high variability.
- Acetone significantly reduced compressive strength compared to the untreated control.
- Isopropyl alcohol had compressive strength similar to the untreated control.

## Abstract

Three-dimensional (3D) printing, particularly Masked Stereolithography (MSLA), has emerged as a transformative technology in orthodontics for the fabrication of precise dental models. However, the mechanical integrity of these models, especially compressive strength, is critical during procedures such as thermoforming of clear aligners. This study aimed to evaluate the effect of different chemical post-processing methods on the compressive strength of MSLA-printed dental models.

A total of 40 cylindrical resin samples (10 mm in height and 5 mm in diameter) were fabricated using an MSLA printer and divided into four groups (n = 10). Group 1: untreated group (acted as the control group), while Groups 2, 3, and 4 were treated with acetone, propylene glycol, and isopropyl alcohol, respectively. All treated samples were immersed in their respective chemicals for 5 min at room temperature. The compressive strength of each sample was measured utilising a Universal Testing Machine (UTM), and results were statistically analysed using Analysis of Variance (ANOVA) followed by Tukey’s post hoc test.

The compressive strength varied with statistical significance among the groups (p = 0.001). Compared to the untreated control group (107 ± 35 MPa), post-processing in propylene glycol (139 ± 48 MPa) or isopropyl alcohol (106 ± 10 MPa) resulted in statistically similar compressive strength, whereas post-processing in acetone (86 ± 19 MPa) led to significantly lower compressive strength. Furthermore, post-processing in propylene glycol resulted in significantly higher compressive strength than did post-processing in isopropyl alcohol or acetone. Propylene glycol showed greater variability, which makes its beneficial properties questionable.

In conclusion, chemical post-processing significantly influences the compressive strength of MSLA-printed models. Acetone had a deleterious impact on compressive strength. Isopropyl alcohol proved to be an acceptable solvent. Propylene glycol showed large variability in results, warranting further investigation.