# Health and environmental hazards of shape memory polymer used in orthodontic aligners – a scoping review

## TL;DR

This review explores the health and environmental risks of shape memory polymers used in orthodontic aligners, finding limited evidence on their safety and sustainability.

## Contribution

The study provides a comprehensive scoping review of health and environmental risks of SMPs in orthodontic aligners, highlighting gaps in current research.

## Key findings

- Certain SMP formulations release residual monomers and degradation products with potential cytotoxic effects.
- Environmental concerns include low degradability and lack of recycling strategies for SMP waste.
- Long-term clinical data and environmental life-cycle analyses for SMPs are insufficient.

## Abstract

Shape memory polymers (SMPs) are gaining traction in orthodontics, particularly in clear aligners, due to their stimulus-responsive behavior and potential to improve treatment outcomes. However, their use in biomedical devices raises questions about biocompatibility and environmental sustainability.

This scoping review aims to map current evidence on the health and environmental risks of SMPs used in orthodontic aligners, identify knowledge gaps, and guide future research.

A systematic search of PubMed, Scopus, Web of Science, Embase, ProQuest, and Cochrane databases was conducted, focusing on studies from the past decade. Search terms included SMPs, orthodontic aligners, toxicity, biodegradability, and environmental impact.

Eligible studies involved original in vitro, in vivo, clinical, or environmental research related to SMPs in orthodontic applications.

Key information from each study was extracted using a standardized Excel spreadsheet by one reviewer (SA) and validated by another (MKN). Extracted data included study design, polymer type, health and environmental risks, and conclusions. Due to heterogeneity, results were synthesized narratively.

Sixteen studies met the inclusion criteria. Evidence on SMP biocompatibility is emerging but limited. Certain SMP formulations released residual monomers and degradation products with potential cytotoxic or systemic effects. Environmental concerns included low degradability, accumulation of polymer waste, and lack of recycling strategies. Notably, there was a lack of long-term clinical data and environmental life-cycle analyses.

While SMPs offer promise in orthodontics, their safety and environmental impacts are insufficiently studied. Future research should focus on standardized toxicological testing, long-term evaluations, and sustainable material development.

This scoping review was prospectively registered in PROSPERO (ID: CRD42022308725). The authors report no conflicts of interest.