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.

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.

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