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The Influence of Distance on Radiant Exposure and Degree of Conversion Using Different Light- Emitting-Diode Curing Units

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The Influence of Distance on Radiant Exposure and Degree of Conversion Using Different Light- Emitting-Diode Curing Units ÓOperative Dentistry, 2019, 44-3, E133-E144 The Influence of Distance on Radiant Exposure and Degree of Conversion Using Different Light- Emitting-Diode Curing Units AO Al-Zain GJ Eckert JA Platt Clinical Relevance It may be necessary to double or triple exposure times when polymerizing at increasing clinically relevant distances from the base of the preparation. SUMMARY specimens (5 3 5 3 2 mm) were cured at each Objectives: To investigate the influence of distance (n=6/LCU/distance). Irradiance and curing distance on the degree of conversion DC (micro-Raman spectroscopy) were deter- (DC) of a resin-based composite (RBC) when mined for the top and bottom surfaces. The similar radiant exposure was achieved using effect of distance and LCU on irradiance, six different light-curing units (LCUs) and to radiant exposure, and DC as well as their explore the correlation among irradiance, ra- linear associations were analyzed using anal- diant exposure, and DC. ysis of variance and Pearson correlation coef- ficients, respectively (a=0.05). Methods and Materials: A managing accurate resin curing-resin calibrator system was used Results: While maintaining a similar radiant to collect irradiance data for both top and exposure, each LCU exhibited distinctive pat- terns in decreased irradiance and increased bottom specimen surfaces with a curing dis- curing time. No significant differences in DC tance of 2 mm and 8 mm while targeting a values (63.21%-70.28%) were observed between consistent top surface radiant exposure. the2-and8-mmdistances,exceptfora Square nanohybrid-dual-photoinitiator RBC multiple-emission peak LCU. Significant *Afnan O Al-Zain, BDS, MSD, PhD, King Abdulaziz Univer- differences in DC were detected among the sity, Faculty of Dentistry, Restorative Dentistry Department, LCUs. As expected, irradiance and radiant Jeddah, Saudi Arabia exposure were significantly lower on the George J Eckert, MS, Indiana University School of Medicine, bottom surfaces. However, a strong Division of Biostatistics, Indianapolis, IN, USA correlation between irradiance and radiant Jeffrey A Platt, DDS, MS, Indiana University, Department of exposure did not necessarily result in a Biomedical and Applied Sciences, Indianapolis, IN, USA strong correlation with DC. *Corresponding author: PO Box 80209, Jeddah 21589, Saudi Arabia; e-mail: [email protected] Conclusions: The RBC exhibited DC values .63% when the top surface radiant exposure DOI: 10.2341/18-004-L was maintained, although the same values “Used by permission. © Operative Dentistry, Inc. Transmission or reproduction of protected items beyond that allowed by fair use requires the written permission of Operative Dentistry, Inc.” E134 Operative Dentistry were not reached for all lights. A moderate- curing time combinations and different light sources strong correlation existed among irradiance, at one curing distance.2,9,14-18 Determining curing radiant exposure, and DC. protocols remains complicated because of variations in RBCs and the complexities of polymerization INTRODUCTION kinetics. The literature recommends that manufac- turers provide curing protocols identifying the The polymerization effectiveness of light-cured res- 9,14 in-based composite (RBC) depends on its composition required energy for each RBC. Unfortunately, and the light’s spectral characteristics.1,2 An RBC detailed curing protocols at clinically relevant dis- should receive the necessary power at the appropri- tances to effectively activate polymerization are ate wavelengths for a sufficient amount of time to rarely provided, and clinicians are left to subjectively effectively activate polymerization.1-5 The amount of determine appropriate exposure times. Determining energy needed varies according to the RBC’s compo- the curing effectiveness for different distances based sition, shade, and translucency.1-5 on radiant exposure calculations from the irradiance and curing time provided by the manufacturer was Manufacturers do not typically disclose all of their worth investigating. product components and concentrations. The manu- facturer-recommended RBC curing time is typically The aims of this study were 1) to investigate the based on testing the material in ideal laboratory influence of distance on the degree of conversion conditions, in which a light-curing unit (LCU) guide (DC) of an RBC when similar radiant exposure is tip is positioned as close as possible to the specimen, achieved using multiple light-emitting-diode (LED) commonly at a distance of 0 mm.5 However, in a curing units and 2) to explore the correlation among clinical setting, a 0-mm distance between the light irradiance, radiant exposure, and DC for multiple guide and the restoration surface or cavity floor is LED units at two clinically relevant distances. not often attained. For example, the distance between the light guide tip and the cervical floor of METHODS AND MATERIALS 3 a class II proximal box can reach up to 8 mm. Light Characterization Increasing distance decreases the amount of irradi- ance (irradiance [mW/cm2] = power/surface area)1-6 Six LCUs were explored in this study (Table 1). The and radiant exposure (radiant exposure [J/cm2] = irradiance and spectral irradiance for each curing irradiance 3 time)1,2,5,6 received by an RBC. Conse- unit were measured using a managing accurate quently, using the same curing time as instructed by resin curing-resin calibrator (MARC-RC) system the manufacturer when the distance is increased can (BlueLight Analytics, Halifax, Canada). The system result in a lower radiant exposure than required for had custom-designed top and bottom 4-mm cosine sufficient photoinitiator activation.3,7,8 This can lead corrector sensors designed to collect the light output to formation of a polymer network with less than at 1808 to eliminate any optical interference issues ideal properties.2-4,9,10 In addition to decreased associated with the light-collection sampling geom- 19 properties, insufficient polymerization can result in etry. The measurements collected from the top leaching of unreacted monomers into the oral sensor represented the irradiance and radiant environment and compromised restoration longevi- exposure received on the top RBC surface. The ty.3,11-13 Therefore, increasing curing time may be bottom sensor measurements obtained under an needed as the curing distance increases from the RBC increment in real time represented the irradi- RBC. ance and radiant exposure received on the bottom surfaces.8,20-23 When maintaining radiant exposure, some RBCs exhibit similar properties,2,14,15 but others may The irradiance measurements and specimen prep- not.9,16,17 Musanje and Darvell9 reported that calcu- aration were performed in a constant-temperature lations using radiant exposure delivered to a resto- room (218C) with 380- to 520-nm ambient light ration are based on the law of reciprocity, and the filtered from the environment. On the top sensor, calculations do not recognize product behavior. each curing unit position was standardized using a Although this may be true, clinicians need usable mechanical arm, with the guide tip centered over the guidelines when curing RBCs. A recent study sensor. Each unit was positioned at 0, 2, 4, 6, and 8 showed that a better depth-of-cure comparison was mm between the guide tip and the top sensor to achieved when a similar radiant exposure was collect the irradiance and spectral emission (n=6/ delivered.18 In addition, most studies evaluating LCU/distance). The collected irradiance was used to RBC polymerization used different irradiance and adjust the curing times for each tested distance to Al-Zain, Eckert & Platt: Distance and Composite Curing Time E135 Table 1: Light-Curing Units (LCUs) Explored in the Study LCU Type LCU Name Abbreviation Manufacturer Quartz-tungsten-halogen (QTH; control) Optilux 401 O Kerr, Orange, CA, USA Multiple-emission peak light-emitting Bluephase Style (with the updated light guide tip) BS Ivoclar Vivadent, Amherst, NY, USA diode (LED) SmartLight Max SM Dentsply, York, PA, USA Valo Cordless V Ultradent, South Gordon, UT, USA Single-emission peak LED DEMI (with a turbo tip) D Kerr, Orange, CA, USA Demi Ultra DU Kerr, Orange, CA, USA roughly maintain the radiant exposure at 10-11 J/ exposure to light. Specimens were stored dry in a cm2 on the top surface. This was consistent with 378C incubator for 24 hours.26 manufacturer’s irradiance and curing time guide- lines for the dual-photoinitiator RBC (Tetric Evo- DC Measurements Ceram Bleaching shade XL, Ivoclar Vivadent, Am- The top and bottom specimen surfaces were finished herst, NY, Lot No. T25427). Each LED unit was fully using a Struers Rotopol 4 polishing unit with 1200-, charged before collecting measurements, and the 2400-, and 4000-grit SiC abrasive paper and polished quartz-tungsten-halogen (QTH) unit fan was al- using a 1-lm alcohol-based diamond polishing lowed to completely turn off between measurements. suspension (Struers, Ballerup, Denmark) to produce The RBC contained camphorquinone (CQ) and a flat and smooth surface. Specimens were ultrason- diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide ically cleansed for 20 minutes in deionized water to (TPO) photoinitiator systems, with less concentra- produce clean surfaces for DC testing. The DC tion of CQ compared with other Tetric EvoCeram measurements were collected using micro-Raman shades.24 This particular RBC was selected with the spectroscopy (FORAM, CRAIC Technologies, San intent of accentuating potential differences in poly- merization using single- or multiple-emission peak Dimas, CA, USA) with a 785-nm laser excitation. LED units. Five scans for each spectrum measurement were collected and processed with FORAM PC software. Spectra of the uncured and cured RBC were recorded Specimen Fabrication (n=3). The fourth day after specimen preparation, Each LCU was positioned over the bottom MARC-RC DC measurements were collected from the top and sensor in a setup similar to the top sensor. Square bottom surfaces (50/surface) in standardized loca- specimens (5 3 5 3 2 mm) were fabricated using a tions of a 3 3 3-mm checkerboard grid pattern.
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