The Influence of Indirect Bonding Technique on Adhesion of Orthodontic Brackets and Post-Debonding Enamel Integrity-An In Vitro Study

Abstract

The increasing demand for orthodontic treatments due to the high prevalence of malocclusion has inspired clinicians and material scientists to investigate innovative, more effective, and precise bonding methods with reduced chairside time. This study aimed at comparing the shear bond strength (SBS) of metal and ceramic brackets bonded to enamel using the indirect bonding technique (IDB). Victory Series metal brackets (Metal-OPC, Metal-APC) and Clarity™ Advanced ceramic brackets (Ceramic-OPC) (3M Unitek, Monrovia, CA, USA) were bonded indirectly to extracted human premolars through the etch-and-rinse technique. A qualitative assessment of the enamel surface using microscopic methods was performed, and the amount of residual adhesive was reported as per the adhesive remnant index (ARI). Moreover, the bracket surface was evaluated with SEM-EDS. The highest SBS mean values were observed in the Ceramic-OPC group (16.33 ± 2.01 MPa), while the lowest ones were obtained with the Metal-OPC group (11.51 ± 1.40 MPa). The differences between the Metal-AOPC vs. Metal-APC groups (p = 0.0002) and the Metal-OPC vs. Ceramic-OPC groups (p = 0.0000) were statistically significant. Although the Ceramic-OPC brackets bonded indirectly to the enamel surface achieved the highest SBS, the enamel damage was significantly higher compared to that of the other groups. Thus, considering the relatively high bond SBS and favourable debonding pattern, Metal-APC brackets bonded indirectly may represent the best choice.

Keywords: APC brackets; ARI; SBS; adhesion; ceramic brackets; etch-and-rinse technique; indirect bonding; shear bond strength.

Figure 1

Main stages of IDB: (20×). (a) Bracket positioned on the cast. (b) Bracket immersed in the transparent polyvinylsiloxane transfer tray. (c) Bracket bonded to enamel surface.

Figure 2

Bracket–enamel connection in SEM (65×): (a) Metal-OPC, (b) Ceramic-OPC.

Figure 3

SEM image of the bracket–enamel interface in ER protocol (500×): (a) Metal-OPC (b) Ceramic-OPC. B—bracket base; A—orthodontic adhesive; E—etched enamel surface covered with adhesive resin.

Figure 4

SEM image of the bracket–enamel interface in ER protocol (1000×): (a) Metal-OPC (b) Ceramic-OPC. Arrows represent the connection area.

Figure 5

Mean SBS in tested groups (n = 10). SD: Metal-OPC = 1.4; Metal-APC = 1.64; Ceramic-OPC = 2.01, ×—mean value.

Figure 6

ARI score in tested groups.

Figure 7

BARI score in tested groups.

Figure 8

SEM image of bracket before bonding (not covered with adhesive); (a) Metal bracket; (b) Ceramic bracket (20,000×). Not applicable for APC brackets.

Figure 9

EDS analysis. Spectra obtained from s bracket before bonding (not covered with adhesive); (a) Metal bracket; (b) Ceramic bracket (20,000×). Not applicable for APC brackets.

Figure 10

SEM images of tooth specimens with ARI scores of 3 (65×): (a) Metal-OPC, (b) Metal-APC, (c) Ceramic-OPC.

Figure 11

SEM observation of brackets with BARI scores of 5. (a) Metal-OPC, (b) Metal-APC, (c) Ceramic-OPC. Mag. 50,000×.

Figure 12

EDS observation of brackets with BARI scores of 5. (a) Metal-OPC, (b) Metal-APC, (c) Ceramic-OPC.