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Abstract
Objective
The purpose of this study was to evaluate the shear bond strength of rebonded ceramic brackets according to each condition and find an appropriate method to rebond ceramic brackets with proper shear bond strength in clinical practice.
Methods
The study consisted of 12 experimental groups, according to the types of brackets, debonding methods, and treatment methods of the bracket base. Shear bond strength was measured, and adhesive residues left on the tooth surface were assessed. The base of the bracket was examined under scanning electron microscopy.
Results
The shear bond strength of the monocrystalline ceramic bracket group was significantly higher than thatof the polycrystalline bracket group with only sandblasting (p < 0.05). There was no significant difference in shear bond strength between groups that used rebonded brackets which were debonded with shear force and debonded with laser (p > 0.05). The shear bond strength of the sandblasted/silane group was significantly higher than that of the selectively grinded group with a low-speed round bur and the sandblasted only group (p < 0.001). The retentive structure was more presented in groups where laser was applied than in groups where shear force was applied to debond brackets prior to rebonding. The bracket bases which were treated before rebonding presented smoother surfaces than new brackets.
Conclusions
Shear bond strength could be increased by applying a silane coupling agent after sandblasting before rebonding. Also, the bond strength of the selectively grinded group with a low-speed round bur and the sandblasted group showed acceptable bond strength for clinical orthodontic treatment.
Figures and Tables
Fig 1
A, Experimental set-up for shear bond strength measurement; B, lasing positions (▴). Notice that the lasing direction is vertical to the slot.
Fig 2
SEM images of the new ceramic bracket base. A, B, MISO™ (Original magnification: 25, 250 times, respectively; scale bar: 1 mm, 100 µm, respectively); C, D, Transcend™ series 6000 (Original magnification: 25, 250, respectively; scale bar: 1 mm, 100 µm, respectively).
Fig 3
Comparison of SEM images of the ceramic bracket base debonded by shear force using universal testing machine (A-D) and by laser (E-H). Lasing positions (arrow). A, B, E, F, MISO™ (Original magnification: 25, 250 times, respectively; scale bar: 1 mm, 100 µm, respectively); C, D, G, H, Transcend™ series 6000 (Original magnification: 25, 250 times, respectively; scale bar: 1 mm, 100 µm, respectively).
Fig 4
Comparison of SEM images of the ceramic bracket base grinded selectively with low-speed round bur after being debonded by shear force using universal testing machine (A-D) and by laser (E-H). A, B, E, F, MISO™ (Original magnification: 25, 250 times, respectively; scale bar: 1 mm, 100 µm, respectively); C, D, G, H, Transcend™ series 6000 (Original magnification: 25, 250 times, respectively; scale bar: 1 mm, 100 µm, respectively).
Fig 5
Comparison of SEM images of the ceramic bracket base sandblasted after being debonded by shear force using universal testing machine (A-D) and by laser (E-H). Lasing positions. A, B, E, F, MISO™ (Original magnification: 25, 250 times, respectively; scale bar: 1 mm, 100 µm, respectively); C, D, G, H, Transcend™ series 6000 (Original magnification: 25, 250 times, respectively; scale bar: 1 mm, 100 µm, respectively).
Fig 6
Comparison of SEM images of the ceramic bracket base sandblasted and coated with silane after being debonded by shear force using universal testing machine (A-D) and by laser (E-H). Lasing positions. A, B, E, F, MISO™ (Original magnification: 25, 250 times, respectively; scale bar: 1 mm, 100 µm, respectively); C, D, G, H, Transcend™ series 6000 (Original magnification: 25, 250 times, respectively; scale bar: 1 mm, 100 µm, respectively).
Table 2
Comparison of shear bond strength values (MPa) according to bracket types
The same abbreviation as Table 1. SD, Standard deviation; *p < 0.05; †p < 0.001.
Table 3
Comparison of shear bond strength values (MPa) according to debonding methods
The same abbreviation as Table 1. SD, Standard deviation.
Table 4
Comparison of shear bond strength values (MPa) according to treatment methods of bracket base
The same abbreviation as Table 1. SD, Standard deviation; *p < 0.001. The same letters were not significantly different at the level of p < 0.001 (a < b < c < d).
Table 5
Residual adhesive ratings of rebonded brackets according to the adhesive remnant index (ARI)
The same abbreviation as Table 1. *ARI scores: 1, all of the composite remained on the tooth; 2, more than 90% of the composite remained on the tooth; 3, more than 10% but less than 90% of the composite remained on the tooth; 4, less than 10% of composite remained on the tooth; 5, no composite remained on the tooth.
Table 6
Comparison of adhesive remnant index scores of rebonded brackets according to bracket types, debonding methods, and treatment methods of bracket base
The same abbreviation as Table 1. *p < 0.05; †p < 0.01; ‡p < 0.001. The same letters were not significantly different at the level of p < 0.001 (a < b < c < d).
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