# The Evaluation of Degree of Monomer Conversion, Biaxial Flexural Strength, and Surface Mineral Precipitation of Orthodontic Adhesive Containing Sr-Bioactive Glass Nanoparticles, Calcium Phosphate, and Andrographolide

## TL;DR

This study evaluates new orthodontic adhesives with added bioactive ingredients to assess their performance compared to commercial products.

## Contribution

The study introduces experimental orthodontic adhesives with Sr-bioactive glass, calcium phosphate, and andrographolide, assessing their conversion and mechanical properties.

## Key findings

- Transbond XT showed higher monomer conversion and biaxial flexural strength than experimental adhesives.
- Experimental adhesives with low additive concentrations had comparable flexural modulus to Transbond XT.
- All experimental materials met ISO standards despite lower performance than commercial products.

## Abstract

This study examined the degree of monomer conversion (DC) and mechanical properties of experimental orthodontic adhesives containing monocalcium phosphate monohydrate (MCPM), Sr-bioactive glass (Sr-BAG) nanoparticles, and andrographolide. Experimental adhesives were prepared with a 4:1 powder-to-liquid ratio, containing methacrylate monomers with varying formulations of glass fillers and additives. DC was measured using ATR-FTIR (n = 5) with and without bracket placement under two curing protocols: conventional LED (1200 mW/cm2, 20 s) and high-intensity LED (3200 mW/cm2, 3 s). The biaxial flexural strength and modulus were tested after 4-week water immersion (n = 8). Transbond XT was used as the commercial comparison. Transbond XT exhibited higher DC (33–38%) than the experimental materials. Conventional LED curing produced higher DC than high-intensity LED, while bracket placement reduced DC by approximately 10% in the experimental materials but minimally affected Transbond XT. Transbond XT demonstrated a superior biaxial flexural strength (188 MPa) compared to the experimental adhesives (106–166 MPa, p < 0.05). However, the experimental formulations with low additive concentrations showed a comparable biaxial flexural modulus (5.0–5.5 GPa) to Transbond XT (5.6 GPa) (p > 0.05). Although the experimental adhesives exhibited lower DC and strength than the commercial product, their values still met the ISO standards, suggesting their potential clinical viability despite their modified compositions.