# A comparative in vitro study on monomer release from flash-free or conventional bonding systems

## TL;DR

This study compares the release of harmful monomers from different orthodontic bracket adhesives, finding that a new flash-free system releases more.

## Contribution

This is the first study to evaluate residual monomer release from adhesive-precoated flash-free brackets.

## Key findings

- The flash-free system released more total monomers than traditional systems, except for hydroxyethyl methacrylate.
- The chemical cure group showed the highest hydroxyethyl methacrylate monomer release.
- The APC flashless system's higher monomer release suggests potential cytotoxic effects need further evaluation.

## Abstract

To examine the amount of residual monomer released from adhesive-precoated flash-free brackets and compare it to traditional light cure and chemical cure adhesives.

Sixty stainless steel brackets were bonded on upper premolar teeth using three groups of adhesive systems: Adhesive-precoated flash-free system, Transbond XT light cure, Sia chemical cure. The extracts of 0.5 ml of liquid samples were taken on the first, 7th, 21st, and 35th days. To determine the amount of residual monomer release, extracted samples were analyzed using a liquid chromatography device.

Urethane-dimethacrylate, triethylene glycol dimethacrylate, hydroxyethyl methacrylate and Bisphenol A-glycidyl methacrylate monomers were released from all study groups. The amount of total monomer release except hydroxyethyl methacrylate was detected as greater in adhesive-precoated flash-free system. Among the study groups, the chemical cure group showed the highest hydroxyethyl methacrylate monomer release.

This in vitro study indicate that the APC flashless system exhibited the greatest release of residual monomers, suggesting that its possible cytotoxic effects need to be evaluated prior to clinical application.

This is the first study that evaluates the residual monomer release from adhesive-precoated flash-free brackets. The novel bracket system has a different mesh structure at the bracket base compared to traditional systems with different chemical components which might alter the amount of residual monomer release. To investigate the harmful effects of adhesives used in orthodontic applications is very important for the health of the patient and the orthodontist.

The online version contains supplementary material available at 10.1007/s00784-025-06250-3.