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.

Andrés Fernando Montenegro Arana,Michele De Oliveira Sugahara,Andrés Dávila-Sánchez,Cesar Arrais,Barbara Justus,Paulo Vitor Farago,Ulisses Coelho

doi:10.1590/2177-6709.26.1.e2119150.oar

Abstract

ABSTRACTIntroduction: 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.

Highlights

Third generation of LED light curing units might be used in short exposure periods for orthodontic brackets bonding
This study evaluated the effect of the different radiant exposure (RE) values: Manufacturers’ instructions (MI), 1⁄2 MI, 1/4 MI and Turbo mode
In an attempt to simulate the clinical scenario where light-curing units (LCU) tip is placed on the mesial and distal profile and microhardness of orthodontic composite under ceramic and metallic brackets portion of the metallic bracket, the LCU tip was placed in two directions, so light was delivered for half exposure period in each side

Summary

Introduction

Third generation of LED light curing units might be used in short exposure periods for orthodontic brackets bonding. Some are light-cured materials, others are self-cured resins, and there are dual-cured OCs, which have both photoinitiators and self-curing components in their composition.[3] these products have shown acceptable mechanical proprieties,[4] the use of light-curing units (LCU) is required regardless of the OC type, to ensure that brackets are bonded without wasting chairtime, once photo-activated polymerization is considerably faster than self-cured polymerization.[5,6] in order to provide optimal degree of conversion (DC) and mechanical properties of OCs, the radiant emittance values must be considerably high.[7] In this regard, recently, third generation light-emitting diode (LEDs) curing units have become available for dental practitioners.[8] known as multi-peak LCUs, these LED devices are capable of emitting light with varying wavelength ranging from 390 nm to 490 nm.[8,9]

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