The effect of different modes of light irradiation to cure the orthodontic adhesive on the shear band strength and enamel damage

Abstract

Background: Light cure composite resins have become the most popular orthodontic adhesives. This gives the orthodontist a reduced risk of contamination, easier removal of excess adhesive, and more time to accurately place brackets. Light-emitting diode (LED) technology is currently the most common means of light curing in connecting brackets to teeth. LED devices are said to be more effective at polymerizing composite resins than halogen curing systems. They emit less heat, have a longer life, and have the least efficiency reduction over time. The polymerization capacity of the light curing device is directly related to the power of the light as well as the irradiation time. If the resin material is sufficiently polymerized, a higher bond strength is predicted compared to a material with a lower conversion rate. Optimal Sari The physical and mechanical properties of the composite resin depend on achieving a sufficient degree of curing, and the degree of curing of the light-activated resin is directly related to the light intensity and irradiation time.

Materials and Methods: The laboratory study will be performed on 45 human premolars with healthy and defective crowns that have been extracted for orthodontic reasons from 12 to 25 years old. As long as the acrylic is mounted and the teeth are used, they are kept in distilled water at room temperature to prevent dehydration and bacterial growth. The teeth are then placed inside the self-polymerizing acrylic generator so that the roots are completely inside the acrylic to CEJ and the labial surface of the crown is perpendicular to the underside of the mold. After mounting, the teeth are coded by the researcher and They are randomly divided into 5 groups based on curing conditions: Group 1: Using LED light curing device with output power (1600 (mW / cm2) for 5 seconds for orthodontic adhesive curing Group 2: Using LED light curing device with output power (1600 (mW / cm2) for 10 seconds for orthodontic adhesive curing Group 3: Using LED light curing device with 70% output power (1100 (mW / cm2) for 20 seconds for orthodontic adhesive curing Group 4: Use of LED light curing device starting with 10% output power (160 (mW / cm2) and reaching maximum power within 10 seconds and continuing for another 10 seconds Group 5: Using a pulsed LED light cure device, every 0.15 seconds for 20 seconds with output power (1600 (mW / cm2) Prior to attachment, the buccal surfaces of the teeth are cleaned with a fine-grained brush in the micromotor at a slow speed for 10 seconds to remove any scale deposits and crust stains with fine pumice powder without fluoride in water. The teeth are then thoroughly rinsed and dried with water for 10 seconds. After polishing the tooth surfaces, the buccal surface of each tooth is gel etched with 37% phosphoric acid for 30 seconds. Each tooth is then rinsed with distilled water spray for 5 seconds and dried with oil-free air until the etched tooth appears gypsum white. After applying the adhesive primer on the enamel, the adhesive light cure is applied on the base of the bracket and placed in the center of the buccal surface in the long axis of the crown. Curing will then be done based on the study group. Using a universal tester, the force required to separate the brackets is measured in Newtons and the shear bond strength (MPa) is determined by dividing the force by the base area of the bracket. After removing the brackets, the ARI (adhesive remaning index) scores are evaluated with a stereomicroscope. In the next step, the remaining adhesive is removed. And a skilled and trained person observes the number and length of cracks under a 40-magnification stereomicroscope connected to a digital camera capable of linear measurement. The technician performing the tests to determine which group the test specimen belongs to; He is blind. Data are analyzed by one-way ANOVA and, if necessary, appropriate post hoc test (p˂0.05). Results: Examination of shear bond strength in the 5 groups showed that there is a significant difference between the groups. A pairwise comparison of the groups by Tukey test showed that group one showed the lowest shear strength among the 5 groups. Group five also had lower shear strength than group four. There was no significant difference in shear strength in other groups. In group two, 10% of the samples were cracked, in groups one, three and five, 20% and in group four, 30% were cracked. However, Chi-square test did not show a significant difference in the frequency of cracks caused by debonding between the 5 groups. Examination of crack length in 5 groups showed that the difference in crack length before and after bracket deposition in 5 groups shows a significant difference. Comparison of the two groups by Tukey test showed that in group four, the longest crack length (due to debonding brackets) was among the 5 groups. In other groups, no significant difference was observed during crack (due to debonding of brackets). The results show that there is no significant difference in the frequency of ARI between the 5 groups. It is also observed that ARI = 0 is not present in any of the studied groups. In other words, different amounts of adhesive remain in all groups.

Conclusion: Curing time of 5 seconds with power (1600 (mW / cm2) significantly reduced shear bond strength. In addition, pulsed radiation resulted in lower shear bond strength. Debonding processes of orthodontic metal brackets may increase the length of enamel microtracks for teeth. Are harmful. The crack length also had the highest increase with 10% output power (160 (mW / cm2 and reaching maximum power in 10 seconds and continuing for another 10 seconds). According to the ARI score of this group (scale = 2) The highest rate among the groups is justifiable.