Experimental in vitro study of the adhesive strength of universal adhesives for orthodontic bracket fixation

Background: An optimal adhesive system must ensure quick and easy application while also demonstrating adequate adhesive strength that does not change over time. The development of adhesive systems continues, and each currently available adhesive system has advantages and disadvantages. During orthodontic treatment, practitioners must not only address malocclusion and minimize damage to intact tooth tissues, but also prevent dental caries. Despite ongoing advancements in adhesive systems, there are no studies that confirm the long-term durability of 8^th generation systems containing the 3D-SR monomer.

Aim: To assess the adhesive strength of metal braces when using the Tokuyama Universal Bond II adhesive system (Tokuyama Dental, Japan) in a laboratory setting before and after thermal cycling with and without the SHIELD FORCE PLUS sealant (Tokuyama Dental, Japan).

Methods: The study included 60 intact extracted teeth without signs of dental caries and extensive restorations. There were four groups of samples. Group 1 included 15 samples with metal braces placed without a sealant and thermal cycling; Group 2 included 15 samples with metal braces placed without a sealant, with thermal cycling; Group 3 included 15 samples with metal braces placed with a sealant, without thermal cycling; and Group 4 included 15 samples with metal braces placed with a sealant and thermal cycling.

Results: Thermal cycling decreased shear adhesive strength: in samples with brackets placed without the SHIELD FORCE PLUS sealant, the adhesive strength before thermal cycling was higher (4.10±0.96 MPa) than after thermal cycling (3.44±1.03 MPa). The SHIELD FORCE PLUS sealant significantly increased shear adhesive strength: in samples with brackets placed with the sealant, the adhesive strength in the group without thermal cycling was higher than in the group after thermal cycling (3.71±0.61 MPa and 2.58±0.76 MPa, respectively; p=0.0005).

Conclusion: The statistical analysis revealed no significant differences (p >0.05) in the adhesive strength of braces placed with and without the sealant. Thermal cycling significantly (p ≤0.05) reduces the adhesive strength of braces placed with and without the sealant. The sealant does not reduce the adhesive strength of braces; thus, they can be used to prevent dental caries, decrease tooth sensitivity, and improve the mineral composition of tooth tissues.