Adhesive shear strength of a universal adhesive with a different way of preparing the enamel before fixing the braces

Relevance. The success of orthodontic correction on fixed devices largely depends on the stability of each element on the enamel surface during the entire course of treatment. Braces should not interfere with oral hygiene of patients undergoing orthodontic treatment, and should withstand occlusive loads, chewing, and traction forces generated by the arch. In addition, the braces should be removed after treatment without damaging the enamel. Variables such as the type of polymerization, the adhesives used, and the methods of preparing the enamel before fixation affect the adhesive strength of the bracket. Modern scientific research is being conducted in the direction of improving the adhesion properties of bonds and is an urgent task. Treatment with sodium hypochlorite helps to remove demineralized collagen from the tooth surface. In turn, the role of phosphoric acid is to enhance the shear strength when fixing braces. This article evaluates the shear strength of an adhesive system with pretreatment with sodium hypochlorite and orthophosphoric acid in laboratory conditions.

Aims: to study the shear strength of a universal adhesive system in the laboratory when fixing braces with various methods of enamel surface preparation.

Materials and methods. The samples of teeth removed according to orthodontic indications n=60 (100%), without carious lesions and large fillings, were prepared for the study. Each tooth was placed in a block with self-hardening plastic or plaster. The samples were divided into three groups of n=20 samples. Before applying the adhesive system, the surfaces of n=20 (33.3%) samples were treated with 37% phosphoric acid, n=20 (33.3%) other samples were treated with 3.25% sodium hypochlorite, n=20 (33.3%) samples were without pretreatment. Then metal braces were fixed on the prepared samples. Each of the groups was divided into 2 subgroups – n=10 samples with thermal cycling and n=10 samples without thermal cycling. Two-component self-curing adhesive system Universal Bond II (Tokuyama Dental); adhesive fixing cement ESTECEM II PLUS (Tokuyama Dental), 37% orthophosphoric acid and 3.25% sodium hypochlorite were used to fix the braces.

Results: there was a statistically significant difference between the groups with 37% phosphoric acid and 3.25% sodium hypochlorite pretreatment and the group without pretreatment, both before and after thermal cycling. The highest shear strength values before thermal cycling were obtained in the group with phosphoric acid pretreatment (10.12±1.27 MPa). The weakest shear strength (4.10±0.96 MPa) was found in samples without pretreatment of the enamel. After thermal cycling, the results of adhesive strength significantly decreased.

Conclusions. The use of 37% orthophosphoric acid and 3.25% sodium hypochlorite can increase the adhesion strength of braces to enamel by more than two times. Thermal cycling reduces shear strength in all groups. However, the available studies are insufficient to assess the role of 37% phosphoric acid and 3.25% sodium hypochlorite in shear strength, and therefore further research is needed in this area.

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