Comparison of the effect of the feldspathic sample surface preparation method on the strength of the bond with orthodontic aesthetic brackets

As the amount of orthodontically treated adults is steadily increasing, the need arose of adhesive cementation of brackets for crowns and other ceramic restorations. The surface of dentist porcelain does not undergo etching with phosphoric acid (H3PO4) and requires a different procedure protocol.

Aim
The aim of the research was to evaluate the strength of the polycrystalline bracket bonds with feldspathic ceramics processed using some selected methods.

Material and methods
Feldspathic ceramic samples fired onto a metal cylinder were divided into five groups and processed with the selected methods. The surface was subjected to scanning electron microscope (SEM) imaging and roughness profile examination. Next, after cementing the olycrystalline brackets and after conducting a thermocycling process (24h, 1450 cycles), a technical shear resistance test was performed in a strength testing machine. The resulting adhesive-cohesive fracture was evaluated as well as the ARI (Adhesive Remnant Index). The findings were subjected to statistical analysis.

Results
All the samples tested demonstrated that the orthodontic bracket bonding strength with ceramics examined using the shear resistance test amounted to more than 7 MPa, with such bonding strength being considered sufficient to conduct orthodontic treatment. The highest mean strength was obtained and the most frequent adhesive-cohesive fracture with damage to the ceramics was observed in group HF (12,85 MPa). The preparation applied in group MEP (10,03 MPa) had the lowest influence on the ceramics structure. This was observed in the roughness profile test and in the SEM test. The surface structure of the samples in the MEP group did not significantly differ from that in the K group.

Conclusions
The tests demonstrated that the alternative procedure methods applied during the feldspathic ceramics surface preparation for adhesive cementing comply with the requirements set by the contemporary orthodontics.