Editorial Type:
Article Category: Research Article
 | 
Online Publication Date: 25 Aug 2017

Effectiveness of high irradiance for short-time exposures on polymerization of composite under metal brackets

,
,
, and
Page Range: 834 – 840
DOI: 10.2319/051817-338.1
Save
Download PDF

ABSTRACT

Objective:

To evaluate the effect of different curing modes available in a dental light-curing unit on degree of conversion (DC) of a composite photoactivated under a metal orthodontic bracket.

Materials and Methods:

The average irradiance and total energy delivered by three curing modes (standard, high, and extra power) of a multiwave LED unit (Valo Cordless, Ultradent Products, South Jordan, Utah) were measured using the longest time available for each mode (20, 4, and 3 seconds, respectively). Brackets (n = 3/group) were bonded to molar epoxy resin replicas using each curing mode. Mesiodistal sections, 0.5 mm thick, were assessed using an infrared spectrometer microscope. Spectra of composite beneath the brackets were sequentially collected using the mapping tool in near-infrared (NIR)-transmittance mode. Composite conversion was mapped between the mesial and distal edges of the bracket base using 400-μm steps for a total of 10 measurements per specimen. Data from irradiance and total energy were analyzed by one-way ANOVA, while data of DC were analyzed with two-way repeated measures ANOVA (α = 0.05).

Results:

The highest DC values were observed for standard power (mean 56%, P < .05), while no difference was observed between high (50%) and extra power (49%) modes. Regarding the site of measurement, higher DC was observed close to the bracket edges (52%, P < .05).

Conclusions:

The use of high irradiance for a short time slightly reduced the DC. The small magnitude of reduction suggests that use of a high irradiance protocol is a clinically valid approach when bonding metal brackets.

Keywords: Orthodontic bracket; Polymerization

INTRODUCTION

Efficacy of orthodontic treatment using fixed appliances is strongly dependent on reliable bonding of brackets.1,2 Bracket rebonding requires additional appointments, delaying the treatment and potentially compromising the results.3 Orthodontic brackets are often bonded using resin-based, light-cured composites due to greater control of working time relative to chemically cured composites.4,5 Light activation occurs when the photons emitted by the light-curing unit reach the photoinitiators of the composite, generating free radicals that initiate the polymerization reaction.6 Accordingly, the degree of polymerization of light-cured composites depends on the amount of energy reaching the material, as well as on the proper match between the wavelength emitted by the light-curing unit and that absorbed by the photoinitiator.7–11

Most resin-based materials used in dentistry contain camphorquinone/amine as the photoinitiator system, with a light absorption maximum of around 470 nm (blue light).6–11 This absorption peak of camphorquinone is overlapped by LED curing units available in dentistry, resulting in ample ability to polymerize the composites when exposure to light is not a concern. In orthodontic applications, as well as in some prosthetic situations, the composite cement can be fully covered by metal such that during light activation, the amount of light reaching the composite is compromised.12 Reduced light intensity reaching the composite can jeopardize polymerization and ultimately reduce bond strength to enamel.1,12–14 Therefore, for composites developed specifically to bond orthodontic brackets, the manufacturers' recommendations are usually very prescriptive in terms of time required to light-activate the composites, based on the irradiance of the light-curing unit and the type of bracket (ceramic or metal).

Regarding the time required to light-cure the composite during bracket bonding, shorter times are preferred by clinicians to enhance chair-time efficiency. Thus, light-curing units emitting high irradiance have been marketed to clinicians under the premise that higher irradiances will allow adequate polymerization to be achieved in shorter exposure times.11 Indeed, some LEDs reaching irradiances of 3000 mW/cm2 are commercially available, with exposure times as short as 3 seconds recommended by the manufacturer. It remains unclear whether the light-activation using high irradiance for short times is comparable with lower irradiance for longer times to properly polymerize the resin composite. Therefore, the aim of this study was to evaluate the effect of irradiance and exposure duration on the degree of conversion (DC) of a composite light cured under a metal orthodontic bracket. The hypothesis of the study is that high irradiance for shorter times of light activation results in reduced DC.

MATERIALS AND METHODS

Experimental Design

This investigation was conducted to evaluate the effect of three levels (standard, high, and extra power) of curing mode of a multiwave LED on the degree of conversion (DC) of a composite measured in ten locations under orthodontic brackets. The wavelength emission profile, the irradiance, and total energy emitted by each curing mode were also evaluated.

Emission Profile, Irradiance, and Total Energy

The tip of an LED light-curing unit (Valo Cordless, Ultradent Products, South Jordan, Utah) was positioned over the sensor of a portable spectrometer-based instrument (CheckMARC, BlueLight Analytics, Halifax, NS, Canada). Three curing modes of a Valo light-curing unit were used: standard power for 20 seconds, high power for 4 seconds, and extra power for 3 seconds. The average irradiance and total energy received by the sensor of a UV spectrometer (CheckMARC) over the period of activation were measured for each curing mode. The wavelength emission profile of each mode was also recorded.

Specimen Preparation

In order to create a standardized substrate to bond the brackets, impressions were made of the buccal surface of a noncarious human third molar using a polyvinyl siloxane impression material (Aquasil Ultra, Dentsply Caulk, Milford, Del). The molds were filled with epoxy resin (Buehler Epoxide, Lake Bluff, Ill) to produce replicas of the buccal surface. Approximately 3 mL of the light-cured composite Transbond XT (3M Unitek, Monrovia, Calif) was placed onto the bracket base (Ormco, Glendora, Calif) and spread using a sickle scaler to cover the entire base. The bracket was hand-pressed onto the center of the buccal surface, followed by removal of excess composite. Light activation was carried out on two sides of the bracket (mesial and distal), with the tip of the LED positioned at 45° and as close to the base of the bracket as possible, using one of the three curing modes described previously. Three brackets were bonded for each curing mode. During photoactivation, the specimens were maintained over a black opaque background to avoid any light reflection that could intervene and affect cement polymerization. The specimens were stored in 100% relative humidity for 24 hours at 37°C. Previous research has shown that after 24 hours, there is no significant increase in conversion.12 After storage, the bonded brackets were encased in epoxy resin (Buehler), and sectioned in a mesiodistal plane parallel to the occlusal surface of the base, using a diamond saw blade (Accutom-5, Struers, Cleveland, Ohio) to obtain four parallel slices per specimen, 0.5 mm in thickness, which were then averaged to obtain the conversion value for each location.

Degree of Conversion Measurement

Individual slices were positioned over the platform of an inverted infrared microscope (Nicolet Continuμm FTIR Microscope, Madison, Wis) connected to a spectrometer Nicolet 6700 (ThermoFisher, Madison, Wis). The area (4 mm in length, 0.5 mm in depth) corresponding to the area of the composite under the bracket was selected on specimens under magnification of 10× (Figure 1). Spectra were sequentially collected from specimens using the mapping tool in NIR-transmittance mode. The spectra were collected starting from the surface corresponding to the mesial or distal edge of bracket, moving toward the opposite side with 400-μm steps (aperture of 100 μm) totaling 10 different locations in the composite. Three spectra were collected at each site, corresponding to depth locations closer to the bracket, the tooth surface, and midway in between. The average of these three measurements was used to describe the DC for each mesiodistal location. The ratio between peak areas at 6165 cm−1 (methacrylate vinyl overtone) and 4473 cm−1 (aromatic C=C), used as an internal standard, was calculated for each spectrum collected. Spectra of the unpolymerized material were also collected to be used as a reference for the DC calculations. The DC was calculated based on the ratio of the polymerized vs unpolymerized material following standard techniques.13

Figure 1. Mapping of degree of conversion in the specimens. (A) In this infrared spectrometer microscope image, the white square represents the area of composite measured in the specimen. Note that the darkest area corresponds to the metal bracket and the white, serrated area to the epoxy resin. (B) Spectra collection from specimen. In the isolated region of the composite, the cross in the left image indicates where the spectrum is being collected, and this area is visualized at higher magnification on the right side. During the experiment, the cross was moved along the x- and y-axes in 400-μm steps to map the conversion in the entire specimen. (C) A representative spectrum collected. The black arrow indicates the peak at 6165 cm−1 (methacrylate vinyl overtone), and the white arrow shows the peak at 4473 cm−1 (aromatic C=C) used as an internal standard in calculating the DC.Figure 1. Mapping of degree of conversion in the specimens. (A) In this infrared spectrometer microscope image, the white square represents the area of composite measured in the specimen. Note that the darkest area corresponds to the metal bracket and the white, serrated area to the epoxy resin. (B) Spectra collection from specimen. In the isolated region of the composite, the cross in the left image indicates where the spectrum is being collected, and this area is visualized at higher magnification on the right side. During the experiment, the cross was moved along the x- and y-axes in 400-μm steps to map the conversion in the entire specimen. (C) A representative spectrum collected. The black arrow indicates the peak at 6165 cm−1 (methacrylate vinyl overtone), and the white arrow shows the peak at 4473 cm−1 (aromatic C=C) used as an internal standard in calculating the DC.Figure 1. Mapping of degree of conversion in the specimens. (A) In this infrared spectrometer microscope image, the white square represents the area of composite measured in the specimen. Note that the darkest area corresponds to the metal bracket and the white, serrated area to the epoxy resin. (B) Spectra collection from specimen. In the isolated region of the composite, the cross in the left image indicates where the spectrum is being collected, and this area is visualized at higher magnification on the right side. During the experiment, the cross was moved along the x- and y-axes in 400-μm steps to map the conversion in the entire specimen. (C) A representative spectrum collected. The black arrow indicates the peak at 6165 cm−1 (methacrylate vinyl overtone), and the white arrow shows the peak at 4473 cm−1 (aromatic C=C) used as an internal standard in calculating the DC.
Figure 1. Mapping of degree of conversion in the specimens. (A) In this infrared spectrometer microscope image, the white square represents the area of composite measured in the specimen. Note that the darkest area corresponds to the metal bracket and the white, serrated area to the epoxy resin. (B) Spectra collection from specimen. In the isolated region of the composite, the cross in the left image indicates where the spectrum is being collected, and this area is visualized at higher magnification on the right side. During the experiment, the cross was moved along the x- and y-axes in 400-μm steps to map the conversion in the entire specimen. (C) A representative spectrum collected. The black arrow indicates the peak at 6165 cm−1 (methacrylate vinyl overtone), and the white arrow shows the peak at 4473 cm−1 (aromatic C=C) used as an internal standard in calculating the DC.

Citation: The Angle Orthodontist 87, 6; 10.2319/051817-338.1

Statistical Analysis

Data from average irradiance and total energy measured for each curing mode were analyzed by one-way ANOVA and Tukey‘s post hoc multiple comparison test. The specimens were used as experimental units instead of the slices. Therefore, averages of DC calculated for data from the four slices per specimen were subjected to statistical analysis. Data from DC were analyzed with 2-way repeated measures ANOVA (location as a repetition factor) followed by Tukey's test. All analyses were performed using the SigmaStat v.3.5 statistical software package (Systat Software Inc, Chicago, Ill) with a significance level set at α = 0.05.

RESULTS

One-way ANOVA showed a significant effect of the curing mode on both average irradiance (P < .001) and total energy (P < .001; Table 1). The extra power mode resulted in the highest average irradiance followed by high power. Regarding total energy, using standard power for 20 seconds provided the highest total energy, whereas the lowest values were observed for high power for 4 seconds. The profile of light emission is presented in Figure 2.

Table 1. Means (Standard Deviation) of Average Irradiance and Total Energy Achieved With Each Curing Mode*
Table 1.
Figure 2. Profile of light emission obtained with each curing mode showing three peaks of light emission and differences in the absolute irradiance for each mode.Figure 2. Profile of light emission obtained with each curing mode showing three peaks of light emission and differences in the absolute irradiance for each mode.Figure 2. Profile of light emission obtained with each curing mode showing three peaks of light emission and differences in the absolute irradiance for each mode.
Figure 2. Profile of light emission obtained with each curing mode showing three peaks of light emission and differences in the absolute irradiance for each mode.

Citation: The Angle Orthodontist 87, 6; 10.2319/051817-338.1

Two-way repeated measures ANOVA showed that both curing mode (P < .001) and location (P < .001) significantly affected the DC; whereas interaction between the factors was not significant (P = .086; Figure 3 and Table 2). The standard mode resulted in the highest DC values, and no difference was observed between the other modes evaluated. Regarding the location, a small but significantly higher DC was observed close to the bracket's edge, with a tendency for reduction toward the center of the specimen.

Figure 3. Heat maps of the average DC measured with the curing unit's three power modes. Although higher conversion values were recorded for the standard mode and closer to bracket edges within each mode, the conversion ranged from 0.48% to 0.57%, demonstrating relatively narrow variation in curing.Figure 3. Heat maps of the average DC measured with the curing unit's three power modes. Although higher conversion values were recorded for the standard mode and closer to bracket edges within each mode, the conversion ranged from 0.48% to 0.57%, demonstrating relatively narrow variation in curing.Figure 3. Heat maps of the average DC measured with the curing unit's three power modes. Although higher conversion values were recorded for the standard mode and closer to bracket edges within each mode, the conversion ranged from 0.48% to 0.57%, demonstrating relatively narrow variation in curing.
Figure 3. Heat maps of the average DC measured with the curing unit's three power modes. Although higher conversion values were recorded for the standard mode and closer to bracket edges within each mode, the conversion ranged from 0.48% to 0.57%, demonstrating relatively narrow variation in curing.

Citation: The Angle Orthodontist 87, 6; 10.2319/051817-338.1

Table 2. Means (Standard Deviation) for Degree of Conversion According to Curing Mode and Distance From Edges of Bracket (n = 3)a
Table 2.
Table 2. Extended
Table 2.

DISCUSSION

Bracket retention to enamel is largely dependent on the degree of polymerization of the resin composite cement, with efficient light activation being paramount in achieving this goal.3,14–20 Despite clinicians' preferences for reduced time with bonding procedures, a prior study reported low bond strengths with brackets bonded to enamel when the composite was light cured with a monowave LED (irradiance ≈ 800 mW/cm2) for a shorter exposure time of 5 seconds.19 In the same study, increasing the light-curing time to 20 seconds resulted in twofold higher bond strength. On the other hand, another study using a similar LED reported only a slight improvement (around 20%) in bond strength when the light-curing time was increased from 5 to 15 seconds.20 An explanation for this difference might be in the positioning of the LED tip during light activation. While in the former study the LED tip was positioned parallel to the base of the bracket, in the second study the LED was positioned at 45° to the base, demonstrating that this position seems to favor composite polymerization. Therefore, in the present study, the LED tip was positioned 45° to the base of the bracket to optimize the light-curing procedure.

The composite used in our study contained camphoroquinone as the photoinitiator, which is the most common initiator used in light-cured, resin-based materials in dentistry. Camphoroquinone is an α-diketone requiring amine coinitiators to produce free radicals to initiate polymerization.7 In order to achieve efficient excitation of the photoinitiator, the wavelength emitted by the light-curing unit must overlap the absorption range of camphoroquinone, or approximately 400 to 500 nm with a maximum excitation of around 470 nm.6–10 The light-curing unit used in the present study is a multiwave emission LED, with three peaks of light emission (Figure 2), overlapping the emission absorption range of camphoroquinone. Therefore, it was expected that the light-curing unit used would properly polymerize the composite irrespective of the curing mode and that differences in the DC achieved with each curing mode would relate only to the irradiance and the total energy provided by each mode.

The highest irradiance values were observed for the extra-power mode as expected because this mode exhibited more than twice the irradiance as that measured for the standard mode. Using high power resulted in intermediate irradiance values, around 37% lower than extra power and 39% higher than the standard mode. However, despite the lowest irradiance values for standard mode, the longer time of exposure used with this curing mode resulted in the highest total energy. Light curing the composite for 20 seconds with standard mode provided almost three times as much energy as that obtained with extra power mode for 3 seconds and 3.6 times as much energy as that achieved using high power for 5 seconds. If the law of exposure reciprocity holds, then the polymerization of a given material would be related solely to the total energy received from the light-curing unit.9 Thus, high irradiance used for shorter times would result in a DC similar to that produced when a low irradiance is used for longer times, assuming that the total energy delivered is the same.

Previous studies have demonstrated that the reciprocity law cannot totally explain the DC when methacrylate monomers are used due to the complexity of the polymerization reaction.21 It has been demonstrated that, as irradiation intensity is increased, the overall dose required to achieve full conversion is also increased.22 Thus, using the high power or extra power mode would require more total energy than that provided by the standard mode to achieve similar conversion. In accordance with the previous studies, the current results have demonstrated that the highest DC values were obtained when the composite was light cured using the standard mode for 20 seconds. Another observation regarding the results of DC relates to the location of the measurement: Higher values were found close to the bracket edge, closest to where the light-curing unit tip was positioned. Due to higher irradiance close to the light-source tip, the proximity also increases heating of the composite, favoring DC improvement.23,24 However, despite the statistical differences, it is important to note that the DC values observed for all curing modes were relatively close in range, varying from 48% to 56%, irrespective of the measurement site. Therefore, it is unlikely that differences in clinical behavior would be expected based on the relatively small differences currently measured.5 Consistent with the current results, a prior study on bond strength by Cerekja and Cakirer found that light curing composite with a high-irradiance halogen lamp (≈ 3000 mW/cm2) for 2, 3, or 6 seconds produced bond strengths similar to those achieved using a polywave LED (≈ 1200 mW/cm2) for 10 or 20 seconds.25

CONCLUSIONS

  • The curing modes of the LED light-curing unit had significant effects on the total energy available to light-activate the composite, whereas the differences observed on energy delivered only minimally affected the DC of the composite used to bond metal orthodontic brackets.

ACKNOWLEDGMENTS

The authors thank BlueLight Analytics for providing the CheckMARC equipment for use in this study.

REFERENCES

  • 1

    Pinto CM.
    Ferreira JT.
    Matsumoto MA.
    Borsatto MC.
    Silva RA.
    Romano FL.
    Evaluation of different LED light-curing devices for bonding metallic orthodontic brackets. Braz Dent J. 2011;22:249–253.

  • 2

    Heravi F.
    Moazzami SM.
    Ghaffari N.
    Jalayer J.
    Bozorgnia Y.
    Evaluation of shear bond strength of orthodontic brackets using trans-illumination technique with different curing profiles of LED light-curing unit in posterior teeth. Prog Orthod. 2013;14:49.

  • 3

    Sfondrini MF.
    Scribante A.
    Fraticelli D.
    Roncallo S.
    Gandini P.
    Epidemiological survey of different clinical techniques of orthodontic bracket debonding and enamel polishing. J Orthod Sci. 2015;4:123–127.

  • 4

    Ahangar Atashi MH, Shahamfar M. Long-term evaluation of clinical performance of direct-bonded brackets: an epidemiologic survey. J Contemp Dent Pract. 2013;14:738–742.

  • 5

    Mohammed RE.
    Abass S.
    Abubakr NH.
    Mohammed ZM.
    Comparing orthodontic bond failures of light-cured composite resin with chemical-cured composite resin: a 12-month clinical trial. Am J Orthod Dentofacial Orthop. 2016;150:290–294.

  • 6

    Neumann MG.
    Schmitt CC.
    Ferreira GC.
    Corrêa IC.
    The initiating radical yields and the efficiency of polymerization for various dental photoinitiators excited by different light curing units. Dent Mater. 2006;22:576–584.

  • 7

    Chen YC.
    Ferracane JL.
    Prahl SA.
    Quantum yield of conversion of the photoinitiator camphorquinone. Dent Mater. 2007;23:655–664.

  • 8

    Ely C.
    Schneider LF.
    Ogliari FA.
    et al. Polymerization kinetics and reactivity of alternative initiators systems for use in light-activated dental resins. Dent Mater. 2012;28:1199–1206.

  • 9

    Schneider LF.
    Cavalcante LM.
    Prahl SA.
    Pfeifer CS.
    Ferracane JL.
    Curing efficiency of dental resin composites formulated with camphorquinone or trimethylbenzoyl-diphenyl-phosphine oxide. Dent Mater. 2012;28:392–397.

  • 10

    de Oliveira DC.
    Rocha MG.
    Gatti A.
    Correr AB.
    Ferracane JL.
    Sinhoret MA.
    Effect of different photoinitiators and reducing agents on cure efficiency and color stability of resin-based composites using different LED wavelengths. J Dent. 2015;43:1565–1572.

  • 11

    Leprince JG.
    Hadis M.
    Shortall AC.
    et al. Photoinitiator type and applicability of exposure reciprocity law in filled and unfilled photoactive resins. Dent Mater. 2011;27:157–164.

  • 12

    Inokoshi M.
    Pongprueksa P.
    De Munck J.
    et al. Influence of light irradiation through zirconia on the degree of conversion of composite cements. J Adhes Dent. 2016;18:161–171.

  • 13

    Stansbury JW.
    Dickens SH.
    Determination of double bond conversion in dental resins by near infrared spectroscopy. Dent Mater. 2001;17:71–79.

  • 14

    Eliades T.
    Eliades G.
    Bradley TG.
    Watts DC.
    Degree of cure of orthodontic adhesives with various polymerization initiation modes. Eur J Orthod. 2000;22:395–399.

  • 15

    Mavropoulos A.
    Cattani-Lorente M.
    Krejci I.
    Staudt CB.
    Kinetics of light-cure bracket bonding: power density vs exposure duration. Am J Orthod Dentofacial Orthop. 2008;134:543–547.

  • 16

    Palomares NB.
    Cal-Neto JP.
    Sampaio-Filho H.
    Almeida MA.
    Miguel JA.
    Effect of high-intensity LED units at reduced curing time on in vitro bond strength of orthodontic brackets. World J Orthod. 2008;9:203–208.

  • 17

    Yoshida S.
    Namura Y.
    Matsuda M.
    Saito A.
    Shimizu N.
    Influence of light dose on bond strength of orthodontic light-cured adhesives. Eur J Orthod. 2012;34:493–497.

  • 18

    Lamper T.
    Steinhäuser-Andresen S.
    Huth KC.
    Ilie N.
    Paschos E.
    Does a reduction of polymerization time and bonding steps affect the bond strength of brackets? Clin Oral Investig. 2012;16:665–671.

  • 19

    Gronberg K.
    Rossouw PE.
    Miller BH.
    Buschang P.
    Distance and time effect on shear bond strength of brackets cured with a second-generation light-emitting diode unit. Angle Orthod. 2006;76:682–688.

  • 20

    Dall'Igna CM.
    Marchioro EM.
    Spohr AM.
    Mota EG.
    Effect of curing time on the bond strength of a bracket-bonding system cured with a light-emitting diode or plasma arc light. Eur J Orthod. 2011;33:55–59.

  • 21

    Hadis M.
    Leprince JG.
    Shortall AC.
    Devaux J.
    Leloup G.
    Palin WM.
    High irradiance curing and anomalies of exposure reciprocity law in resin-based materials. J Dent. 2011;39:549–557.

  • 22

    Wydra JW.
    Cramer NB.
    Stansbury JW.
    Bowman CN.
    The reciprocity law concerning light dose relationships applied to BisGMA/TEGDMA photopolymers: theoretical analysis and experimental characterization. Dent Mater. 2014;30:605–612.

  • 23

    Daronch M.
    Rueggeberg FA.
    De Goes MF.
    Giudici R.
    Polymerization kinetics of pre-heated composite. J Dent Res. 2006;85:38–43.

  • 24

    Magne P.
    Malta DA.
    Enciso R.
    Monteiro S Jr.
    Heat treatment influences monomer conversion and bond strength of indirect composite resin restorations. J Adhes Dent. 2015;17:559–566.

  • 25

    Cerekja E.
    Cakirer B.
    Effect of short curing times with a high-intensity light-emitting diode or high-power halogen on shear bond strength of metal brackets before and after thermocycling. Angle Orthod. 2011;81:510–516.

Copyright: © 2017 by The EH Angle Education and Research Foundation, Inc.
<bold>Figure 1.</bold>
Figure 1.

Mapping of degree of conversion in the specimens. (A) In this infrared spectrometer microscope image, the white square represents the area of composite measured in the specimen. Note that the darkest area corresponds to the metal bracket and the white, serrated area to the epoxy resin. (B) Spectra collection from specimen. In the isolated region of the composite, the cross in the left image indicates where the spectrum is being collected, and this area is visualized at higher magnification on the right side. During the experiment, the cross was moved along the x- and y-axes in 400-μm steps to map the conversion in the entire specimen. (C) A representative spectrum collected. The black arrow indicates the peak at 6165 cm−1 (methacrylate vinyl overtone), and the white arrow shows the peak at 4473 cm−1 (aromatic C=C) used as an internal standard in calculating the DC.

<bold>Figure 2.</bold>
Figure 2.

Profile of light emission obtained with each curing mode showing three peaks of light emission and differences in the absolute irradiance for each mode.

<bold>Figure 3.</bold>
Figure 3.

Heat maps of the average DC measured with the curing unit's three power modes. Although higher conversion values were recorded for the standard mode and closer to bracket edges within each mode, the conversion ranged from 0.48% to 0.57%, demonstrating relatively narrow variation in curing.

Contributor Notes

Corresponding author: Dr André Luis Faria-e-Silva, Professor, Departamento de Odontologia, Campus da Saúde, Universidade Federal de Sergipe, Rua Cláudio Batista, s/n Sanatório, Aracaju, SE, 49060-100, Brazil (e-mail: fariaesilva.andre@gmail.com)
Received: 01 May 2017
Accepted: 01 Jul 2017
  • Download PDF