Effects of the conventional, soft start, and pulse delay modes produced by light-emitting diode device on metal brackets bond strength and enamel damage: An in vitro comparative study.

OBJECTIVES: This study aimed to compare the bond strength and enamel damage following debonding of metal brackets cured by different light-curing modes: conventional, soft start, and pulse delay modes. MATERIAL AND METHODS: Sixty extracted upper premolars were randomly divided into three groups according to the used light-curing mode. Metal brackets were bonded with a light-emitting diode device employing different modes. Group 1: conventional mode (10s mesial+10 s distal); group 2: soft start mode (15s mesial+15s distal); group 3: pulse delay mode (3s mesial+3s distal, followed by 3min of no photoactivation, then 9s mesial+9s distal). Radiant exposure was the same in all study groups. Shear bond strengths of the brackets were tested with a universal testing machine. A stereomicroscope was used to determine the number and length of enamel microcracks. One-Way ANOVA and Kruskal-Wallis tests were used to detect significant differences in shear bond strength and microcracks number and length among groups. RESULTS: The soft start and pulse delay modes produced significantly greater shear bond strength than the conventional mode (19.46±4.90MPa; 20.47±4.97MPa; 12.14±3.79MPa, respectively, P<0.001). However, there was no significant difference between the soft start and pulse delay groups (P=0.768). The number and length of microcracks increased significantly after debonding in all study groups. The change in microcracks length was not different among study groups. CONCLUSION: The soft start and pulse delay modes produced greater bond strength than the conventional mode without predisposing enamel to higher risk of damage. Conservative methods for debonding are still required.

Effects of the conventional, soft start, and pulse delay modes produced by light-emitting diode device on microleakage beneath metal brackets: An in vitro comparative study.

BACKGROUND: This study aimed to evaluate microleakage beneath metal brackets cured by different light curing modes. MATERIALS AND METHODS: Sixty extracted human premolars were randomly divided into three groups according to the light curing mode. Metal brackets were bonded in all groups according to the manufacturer's recommendations with a light-emitting diode device. Light curing was applied as follows: group 1: conventional mode (10 s mesial+10 s distal); group 2: soft start mode (15 s mesial+15 s distal); group 3: pulse delay mode (3 s mesial+3 s distal, followed by 3min of no photoactivation, then 9 s mesial+9 s distal). Radiant exposure was the same in all study groups. After curing, the teeth were incubated at 37 degrees for 24hours, then thermocycled 500 times. Next, they were sealed with nail varnish, immersed in methylene blue 1% for 24hours, sectioned, and examined under a stereomicroscope. Microleakage was measured at both enamel-adhesive and bracket-adhesive interfaces, and the total microleakage for each tooth was computed. Statistical analyses were performed using Kruskal-Wallis and Welch test for comparing microleakage among groups. Wilcoxon signed ranks test was used for comparing microleakage between the bracket-adhesive and enamel-adhesive interfaces. RESULTS: There was no significant difference in microleakage at the bracket-adhesive interface among study groups. At the enamel-adhesive interface and total microleakage, the pulse delay group exhibited significantly lower microleakage than the conventional group. Whereas there was no significant difference between the soft start group and other study groups. In all study groups, microleakage at the enamel-adhesive interface was greater than that at the bracket-adhesive interface. CONCLUSION: The pulse delay mode caused lesser microleakage than the conventional mode. This supports the use of this mode in orthodontic bonding.