Abstract
BackgroundAlthough using light-cured composites for bonding orthodontic brackets has become increasingly popular, curing light cannot penetrate the metallic bulk of brackets and polymerization of composites is limited to the edges. Limited access and poor direct sight may be a problem in the posterior teeth. Meanwhile, effectiveness of the trans-illumination technique is questionable due to increased bucco-lingual thickness of the posterior teeth. Light-emitting diode (LED) light-curing units cause less temperature rise and lower risk to the pulpal tissue. The purpose of this study was to evaluate the clinical effectiveness of trans-illumination technique in bonding metallic brackets to premolars, using different light intensities and curing times of an LED light-curing unit.MethodsSixty premolars were randomly divided into six groups. Bonding of brackets was done with 40- and 80-s light curing from the buccal or lingual aspect with different intensities. Shear bond strengths of brackets were measured using a universal testing machine. Data were analyzed by one-way analysis of variance test and Duncan's post hoc test.ResultsThe highest shear bond belonged to group 2 (high intensity, 40 s, buccal) and the lowest belonged to group 3 (low intensity, 40 s, lingual). Bond strength means in control groups were significantly higher than those in experimental groups.ConclusionsIn all experimental groups except group 6 (80 s, high intensity, lingual), shear bond strength was below the clinically accepted values. In clinical limitations where light curing from the same side of the bracket is not possible, doubling the curing time and increasing the light intensity during trans-illumination are recommended for achieving acceptable bond strengths.
Highlights
Using light-cured composites for bonding orthodontic brackets has become increasingly popular, curing light cannot penetrate the metallic bulk of brackets and polymerization of composites is limited to the edges
The one-way analysis of variance (ANOVA) test showed that there was a significant difference among shear bond strength amounts in groups (F(5,10) = 719.394, p < 0.05)
The highest mean bond strength was seen in group 2 (40-s curing from the buccal aspect with the intensity of 800 mW/cm2)
Summary
Using light-cured composites for bonding orthodontic brackets has become increasingly popular, curing light cannot penetrate the metallic bulk of brackets and polymerization of composites is limited to the edges. The purpose of this study was to evaluate the clinical effectiveness of trans-illumination technique in bonding metallic brackets to premolars, using different light intensities and curing times of an LED light-curing unit. Acid etch technique was first introduced by Buonocore in 1955 [1], and since it has become increasingly popular among dentists due to its numerous advantages It has been introduced by Newman [2] in the field of orthodontics and used for direct bonding of brackets for many years. The polymerizing process begins immediately after mixing; limited time is available for positioning the brackets Another disadvantage of this method is the possibility of air bubble lockup into the adhesive during mixing that would reduce the bond strength of orthodontic brackets. It has been demonstrated that the initial bond strength of brackets would be higher by using lightpolymerizing composites rather than self-polymerizing materials [4]
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