Abstract
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(triethoxysily1) 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 la. 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.