Comparison of the Degree of Conversion of Orthodontic Adhesive when Cured with Different Curing Lights

Abstract

Abstract Introduction: The final physical and mechanical properties of composites are determined by the degree of conversion (DC%) of monomer in the composite, which in turn determines the quality of bonding. Incomplete conversion of monomer might lead to the leach of various chemical compounds from the uncured resin. Aims and Objectives: This study assessed the DC% of Transbond XT composite resin when cured with three different light-curing units using Fourier transform infrared (FTIR) spectroscopy. Materials and Methods: A total of 60 metallic brackets were used. The bonding system was Transbond XT Primer, followed by Transbond XT composite resin that cured for 10 s, 3 s with Elipar DeepCure-L 3M and Woodpecker iLED, respectively, as recommended by the manufacturers and 20 s by BeeCool light-emitting diode-corded (taken as control) on extracted natural teeth which were mounted on the plaster of Paris base. One millimetre was used to standardise the distance between the light source and each specimen. Immediately after polymerisation, the debonded cured composites were tested using FTIR spectroscopy to assess DC%. Non-cured resin specimens were also subjected to FTIR spectroscopy, to serve as non-cured references. Results: With 3M, Woodpecker and BeeCool, the DC% of monomer was 58.83%, 58.53% and 21.55%, respectively. No statistically significant difference was found between 3M and Woodpecker lights. BeeCool showed significantly lower DC%. Conclusion: It is essential for clinicians to have prior knowledge of light-curing units before committing to purchase one as the reduction in exposure time is beneficial for both the patient and the orthodontist.