Abstract
The aim of this study was to evaluate the degree of conversion (DC), flexural strength (FS), and shear bond strength (SBS) of ceramic brackets bonded to enamel with experimental self-adhesive orthodontic composites. Functional monomers 10-methacryloyloxy-decyl-dihydrogen-phosphate (MDP) and glycerol-dimethacrylate-phosphate (GDMA-P) were used in experimental composites. They were compared to the same composite without an acidic monomer (negative control) and with enamel acid-etching prior to adhesive application (positive control). DC was evaluated by Raman micro-spectroscopy. Flexural three-point bending testing was performed in a universal testing machine. Ceramic brackets were bonded to bovine enamel and SBS was evaluated before and after 2000 thermal-cycles. Fracture patterns were surveyed with manual removal with specific pliers and analyzed by SEM. Statistics was performed using ANOVA and Tukey’s test (p < 0.05). DC of the control composite was significantly higher (p < 0.001) than that of GDMA-P and MDP. FS showed no significant difference between composites (p = 0.451). Regarding adhesion, the positive control (8.47 ± 0.88 MPa) and MDP (7.07 ± 2.69 MPa) obtained higher overall results. The predominant fracture pattern of the positive control and MDP was mixed while it was adhesive for further groups. The MDP-containing orthodontic composite attained similar adhesion to a conventional three-step orthodontic bonding system, with a similar fracture pattern and mechanical properties. Nevertheless, the presence of acidic functional monomers reduced the DC.
Highlights
The traditional gold standard etching protocol for orthodontic bracket bonding presents enamel acid etching with 37% ortho-phosphoric acid and the application of adhesive for posterior application of an orthodontic composite [1,2]
The aim of the present study was to evaluate the degree of conversion, flexural strength, and enamel shear bond strength before and after the thermocycling of experimental self-adhesive orthodontic composites associated with ceramic brackets, and the fracture pattern after the simulation of clinical bracket removal
Only the experimental composite with MDP presented immediate shear bond strength similar to that of the positive control. The addition of both acidic functional monomers significantly dropped the degree of conversion in comparison with the control composite
Summary
The traditional gold standard etching protocol for orthodontic bracket bonding presents enamel acid etching with 37% ortho-phosphoric acid and the application of adhesive for posterior application of an orthodontic composite [1,2]. The introduction of acid etching to the bonding procedure of fixed appliances has been one of the most significant changes in orthodontics [3,4]. It creates micro-retentions on the enamel surface which aid the feasible process of fixing the bracket. Ceramic brackets are an essential part of current orthodontic practice due to their aesthetic advantage [6,7] Their high brittleness may disrupt their removal as a monoblock, leading to more fractures of the enamel [8,9]. A suitable alternative to reduce this problem would be the usage of an orthodontic composite with lower bond strength in order to ease bracket detachment, attaining
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