In Vitro Evaluation of Experimental Self-Adhesive Orthodontic Composites Used to Bond Ceramic Brackets

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.

Influence of Pre-Etched Area and Functional Monomers on the Enamel Bond Strength of Orthodontic Adhesive Pastes

“…Various types of functional monomer have been employed in different types of adhesive systems, such as phosphoric acid ester, carboxylic acid and alcohol functional monomers [16]. The functional monomers 10-methacryloyloxydecyl dihydrogen phosphate (MDP) and 4-methacryloxyethyl trimellitate anhydride (4-META) have often been employed in orthodontic adhesive systems [17,18]. In this study, UB contained MDP as a functional monomer, but there were no significant differences in SBS between UB and the functional monomer-free orthodontic adhesive paste TB, regardless of the pre-etched area.…”