# In Vitro Evaluation of Surface and Mechanical Behavior of 3D-Printed PMMA After Accelerated and Chemical Aging Under Simulated Oral Conditions

## TL;DR

This study evaluates how 3D-printed PMMA materials used in dental restorations change after being exposed to simulated oral conditions, finding that thermal aging causes more significant degradation than chemical aging.

## Contribution

The study introduces a comparative analysis of two 3D-printed PMMA resins under simulated oral aging conditions, revealing distinct degradation patterns.

## Key findings

- Thermal aging in artificial saliva caused a 35-46% reduction in elastic modulus compared to the reference.
- Chemical aging in mouthwash led to a time-dependent decrease in mechanical properties, with eventual stabilization.
- Surface free energy increased with prolonged thermal aging but remained stable after chemical aging.

## Abstract

Studying surface energy and permeability offers insights into the relationship between temporary polymers and the oral environment. Variations in contact angle and surface free energy may signify modifications in surface polarity and tendency for plaque buildup, staining, or microcrack formation. Objectives: The present study aims to evaluate the influence of simulated salivary and chemical aging conditions on the surface and mechanical properties of 3D-printed PMMA provisional materials. Methods: Two 3D-printed polymethyl methacrylate (PMMA) resins were investigated, namely Anycubic White (Anycubic, Shenzhen, China) and NextDent Creo (NextDent, 3D Systems, Soesterberg, The Netherlands), using two aging protocols. Protocol A consisted of chemical aging in an alcohol-based mouthwash, while Protocol B involved thermal aging in artificial saliva. After aging, surface properties (wettability and SFE) and compressive behaviour were analyzed. Statistical analysis was conducted to assess the influence of temperature, immersion duration, and aging medium, with significance established at p < 0.05. Results: In Protocol A, mechanical properties showed a time-dependent decrease, with material-specific stabilization trends. In Protocol B, thermal aging resulted in elastic modulus reductions ranging from 35% to 46% relative to the reference. The yield strength exhibited similar tendencies. In Protocol A, X samples exhibited a consistent decline, while C samples stabilized after 14 days. For Protocol B, the fitted model produced residuals under 2%, confirming temperature as the primary variable. Conclusions: Chemical and thermal aging influence the physical and mechanical properties of the analyzed 3D-printed PMMA. Among the two protocols, thermal aging in artificial saliva resulted in more pronounced material degradation. After chemical aging in mouthwash, the surface free energy remained almost constant. After thermal aging, all samples demonstrated a gradual rise in SFE with prolonged immersion duration. The current study offers valuable insights into the environmental stability of printed PMMA; however, it is an in vitro evaluation. The findings indicate that temperature exposure and prolonged contact with oral hygiene products may affect the mechanical reliability of 3D-printed provisional restorations, which must be considered during material selection for longer temporary usage. Additionally, spectroscopic and microscopic analyses might better clarify the molecular-level chemical alterations linked to aging.