الفهرس 
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Abstract
As the demand for fixed orthodontic treatment increases, esthetics becomes an important concern, making ceramic brackets a suitable option. However, a major problem arises during debonding of these ceramic brackets due to their very high shear bond strengths. Conventional debonding may result in significant enamel damage, bracket fragmentation and patient discomfort. Many different techniques have been introduced for ceramic bracket debonding including the use of specially designed pliers, ultrasonic instruments, electrothermal instruments, and also lasers of different wavelengths.
AIM OF THE STUDY: To evaluate and compare the effects diode laser-aided debonding has on the shear bond strength (SBS), surface enamel characteristics and the Adhesive Remnant Index (ARI) of monocrystalline and polycrystalline ceramic brackets.
MATERIALS AND METHODS: Forty extracted premolars were examined under a stereomicroscope and the frequency and lengths of enamel cracks present were recorded. The teeth were then randomly and equally allocated to one of the four groups (n=10): group MC and group ML had monocrystalline brackets bonded to them while group PC and group PL had polycrystalline brackets bonded to them. A diode laser was applied to the teeth in group ML and group PL. Thereafter, the brackets were debonded using a universal testing machine and the SBS of each bracket was recorded. After debonding, the ARI and the frequency and lengths of enamel cracks was examined using a stereomicroscope and recorded. Statistical analysis was performed.
RESULTS: The SBS values of group MC (33.22 ± 3.99 MPa) and group PC (39.97 ± 7.61 MPa) were significantly higher than those of group ML (19.92 ± 3.53 MPa) and group PL (18.63 ± 4.16 MPa) respectively (p < 0.001). There was no statistically significant difference between the SBS values of group ML and PL. The frequency of enamel cracks at the end of the experiment were significantly higher in group MC (4.50 ± 1.58) and group PC (7.40 ± 2.07) when compared to group ML (2.10 ± 0.74) (p = 0.007) and group PL (3.10 ± 1.97) (p = 0.001) respectively. There was no statistically significant difference between the frequency of enamel cracks in group ML and PL. While all four groups had statistically significant increases in the frequency of enamel cracks, the increase was significantly higher in Groups MC (p = 0.021) and PC (p = 0.037). The lengths of enamel cracks at the end of the experiment were significantly higher in group MC (1947.2 ± 966.7 μm) and group PC (1762.6 ± 1054.5 μm) when compared to group ML (1249.8 ± 619.7 μm) (p = 0.001) and group PL (1152.4 ± 420.6 μm) (p < 0.001) respectively. There was no statistically significant difference between the lengths of enamel cracks in group ML and PL. While all four groups had statistically significant increases in the lengths of enamel cracks, the increase was significantly higher in Groups MC (p = 0.03) and PC (p = 0.002). ARI scores did not significantly differ among the four groups.
CONCLUSIONS: The diode laser is effective in debonding both monocrystalline and polycrystalline brackets by lowering their shear bond strengths. It also results in significantly less enamel damage during debonding.