Effect of high irradiance and short exposure times on the shear bond strength of metal and ceramic brackets

Abstract

Orthodontic brackets are bonded to the tooth surface using adhesive systems, and the quality of this bonding plays a critical role in the success of orthodontic treatment. Light-cured composite resins are widely used for this purpose, and their effectiveness depends on several factors, including light intensity, wavelength, and exposure time. High-intensity LED curing units have been reported to provide adequate polymerization even with short exposure times. This study aimed to compare the shear bond strength (SBS) values of metal and ceramic brackets bonded using three different LED curing units (Q6 Corded, Valo X, and Dentac Vega) at various exposure times (3, 5, and 10 s). One hundred twelve intact premolars extracted for orthodontic reasons were randomly divided into 16 groups ( n = 7). Groups were formed based on bracket type, LED unit, and exposure time. Brackets were polymerized with the respective devices for the specified times, and light intensities were controlled with a radiometer. All samples were subjected to SBS testing after all samples were stored in water for 24 h and thermocycled 500 times between 5 and 55 °C. Data were analyzed using ANOVA. Light-curing time had a significant effect on SBS ( p < 0.001), whereas bracket type did not ( p = 0.765). The Vega and Q6 Corded 3-second groups exhibited the lowest strength, and no statistically significant difference was found between the other groups ( p = 0.272). Five-second curing with high-intensity LED units significantly shortens clinical time while maintaining bond security. Regardless of bracket type, no significant difference was found in SBS among the Q6 Corded, Valo X, and Dentac Vega devices.