Influence of radiant exposure values from two third generation LED curing units on polymerization profile and microhardness of orthodontic composite under ceramic and metallic brackets

Abstract

Introduction: Third generation of LED light curing units might be used in short exposure periods for orthodontic brackets bonding. Objective: This study evaluated the effect of the different radiant exposure (RE) values: Manufacturers’ instructions (MI), ½ MI, 1/4 MI and Turbo mode. Two third-generation LED curing units were used: VALO® and Bluephase 20i® . The degree of conversion (DC) and Vickers hardness (VHN) of an orthodontic composite (OC) (Transbond XT) under metallic (MB) or ceramic brackets (CB) were measured. Methods: OC was applied to the bracket base, which was then placed over an attenuated total reflectance (ATR) table coupled to an infrared light spectroscope, or to a glass surface for the VHN analysis. The specimens were light-cured and DC values were calculated. The VHN was obtained in a microhardness tester. The data were analyzed with 2-way ANOVA followed by Tukey’s post-hoc test (pre-set α=0.05). Linear regression analysis evaluated the relationship between RE values and dependent variables. Results: CB allowed higher DC and VHN values than MB (p< 0.001). No significant difference was noted among groups when CB were used. For MB, MI groups showed the highest DC and VHN values. A significant, but weak relationship was found between delivered RE values and dependent variables. Conclusions: The decrease in RE values from third generation LED CU did not jeopardize the DC values when CB were used, but can compromise DC and VHN values when MB are used.

Influence of the Bracket Material on the Post-Cure Degree of Conversion of Resin-Based Orthodontic Adhesive Systems

“…Other studies have compared differences in the DC values between metal and ceramic brackets. Reported DC values in the presence of metal brackets were found to be between 48% and 56%, which is lower when compared to ceramic brackets (ranging from 58% to 79%) [2,6,16,18], irrespective of the adhesive system used and the curing time. Shinya et al demonstrated that the presence of metal brackets reduced DC values by 17% to 29% compared to the control group (without brackets) for two commercially available orthodontic adhesive systems [8].…”

“…Most of the available studies on the DC of orthodontic adhesive systems have documented the values immediately after curing [2,6,[15][16][17][18][19], and studies of post-cure DC development are scarce [4]. In the study by Çörekçi et al, no significant difference was observed in DC values measured one day versus 30 days after curing for the tested materials [4].…”