Evaluation of an experimental silane primer system in promoting adhesion between orthodontic bracket and ceramic

The aim of the study was to evaluate in vitro the effect of an experimental silane primer system on the adhesion strength of metallic orthodontic brackets bonded to a ceramic surface. For this purpose, a total of 180 glazed ceramic porcelain fused to metal (PFM) veneer were randomly assigned into 2 groups of 90 specimens, according to the primer used. Each group was further divided into 3 subgroups according to the surface treatment to be received, thus there were 6 study groups; three with 3-acryloxypropyltrimethoxysilane (ACPS) silane primer, namely 1a (pretreatment with hydrofluoric acid, HF), 1b (pretreatment with grit-blasting) and 1c (pretreatment with tribochemical silica-coating) and 3 with a novel silane system (ACPS+bis-1,2(triethoxysilyl) ethane (BTSE)) assigned as 2a (HF), 2b (grit-blast), and 2c (tribochemical silica coating). The samples were evaluated for surface roughness (Ra) before and after surface conditioning. Next, 15 samples from each subgroups were subjected to thermo-cycling and remaining 15 samples served as the baseline (n = 15). Adhesion strength (the shear bond strength, SBS) was recorded using a universal testing machine. Debonding failure types were classified according to the adhesive remnant index (ARI). Contact angles of the primers were measured. Data were analyzed by ANOVA and Tukey’s multiple comparison post hoc analysis. The highest SBS at baseline (26 8+1 7 MPa) and after thermocycling (24 6+1 7 MPa) was observed in group 2c, and the lowest (9 6+1 5 MPa and 4 5+1 1 MPa) was found in group 1a. Specimens pretreated with tribochemical silica-coating exhibited the highest Ra and the lowest Ra was observed in HF treated specimens. The application of experimental silane primer system on specimens pretreated with tribochemical silica-coating demonstrated increased adhesion of orthodontic brackets making it an excellent choice in orthodontic bonding for a relatively long term use