KACD
Articles
- Page Path
- HOME > Restor Dent Endod > Volume 41(4); 2016 > Article
- Research Article Effects of radiant exposure and wavelength spectrum of light-curing units on chemical and physical properties of resin cements
- Adriano Fonseca Lima1, Stephanie Ellen Ferreira Formaggio2, Lígia França Aires Zambelli2, Alan Rodrigo Muniz Palialol3, Giselle Maria Marchi3, Cintia Helena Coury Saraceni1, Marcelo Tavares de Oliveira4
-
Restorative Dentistry & Endodontics 2016;41(4):271-277.
DOI: https://doi.org/10.5395/rde.2016.41.4.271
Published online: September 26, 2016
1Dental Research Division, School of Dentistry, Paulista University, Sao Paulo, SP, Brazil.
2Nove de Julho University, São Paulo, SP, Brazil.
3Department of Restorative Dentistry, Piracicaba Dental School, University of Campinas, Piracicaba, SP, Brazil.
4Department of Restorative Dentistry, Nove de Julho University, São Paulo, SP, Brazil.
- Correspondence to: Adriano Fonseca Lima, DDS, MS, PhD. Professor, Dental Research Division, School of Dentistry, Paulista University, Rua Doutor Bacelar, 1212, Sao Paulo, SP, Brazil 04026-002. TEL: +55-11-5586-4000; FAX: +55-11-5586-4010; lima.adf@gmail.com
• Received: March 22, 2016 • Accepted: July 5, 2016
©Copyrights 2016. The Korean Academy of Conservative Dentistry.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
- 17 Views
- 0 Download
Abstract
-
Objectives In this study, we evaluated the influence of different radiant exposures provided by single-peak and polywave light-curing units (LCUs) on the degree of conversion (DC) and the mechanical properties of resin cements.
-
Materials and Methods Six experimental groups were established for each cement (RelyX ARC, 3M ESPE; LuxaCore Dual, Ivoclar Vivadent; Variolink, DMG), according to the different radiant exposures (5, 10, and 20 J/cm2) and two LCUs (single-peak and polywave). The specimens were made (7 mm in length × 2 mm in width × 1 mm in height) using silicone molds. After 24 hours of preparation, DC measurement was performed using Fourier transform infrared spectrometry. The same specimens were used for the evaluation of mechanical properties (flexural strength, FS; elastic modulus, E) by a three-point bending test. Data were assessed for normality, after which two-way analysis of variance (ANOVA) and post hoc Tukey's test were performed.
-
Results No properties of the Variolink cement were influenced by any of the considered experimental conditions. In the case of the RelyX ARC cement, DC was higher when polywave LCU was used; FS and E were not influenced by the conditions evaluated. The LuxaCore cement showed greater sensitivity to the different protocols.
-
Conclusions On the basis of these results, both the spectrum of light emitted and the radiant exposure used could affect the properties of resin cements. However, the influence was material-dependent.
Introduction
For many years, the halogen lamp was the main light source used for curing dental resin composites. These devices produce light through a thin tungsten filament at high temperatures,1,2 emitting a broad spectrum of wavelengths. However, some factors might jeopardize the performance of these light-curing devices and thereby promote light degradation.3 Therefore, other technologies, such as light-emitting diodes (LEDs), have been introduced as alternatives to the use of the halogen lamp. Semiconductors produce light after receiving an electric current,1,4 consuming less radiant exposure and having lower degradation than the halogen light devices.3 In the first generation, LEDs used in dental procedures had a reduced irradiance, which allowed the curing of resins without heating. However, despite their capacity to cure the resin materials, the efficiency of the first-generation LEDs was reduced as compared to the quartz-tungsten halogen lamps.5 Thus, the second-generation LEDs were developed, emitting a narrow spectrum of wavelengths similar the first-generation LEDs, but with higher irradiance allowing better polymerization of dental resins.5
To improve the polymerization of dental resins, due to the availability of materials with different compositions related to monomers and initiators, polywave LEDs have been introduced.6 These LEDs have the similar capacity of conventional single-peak devices to activate camphorquinone (CQ); however, they present a great advantage since these units emit a broad spectrum of wavelengths, allowing the activation of alternative photoinitiators, such as phenyl-1,2-propanedione (PPD, 393 nm),7 bisacylphosphine oxide (BAPO, 370 nm),8 or monoacylphosphine oxide (MAPO, 380 nm).9
Material polymerization can be related to the light source,3,10 and this characteristic is linked to the clinical performance of the materials.11,12,13 As previously demonstrated, radiant exposure, irradiance, wavelength, and distance of the light-curing tip can influence the degree of conversion (DC) of resin materials.11,14,15,16
Minimally invasive dentistry has resulted in an increased number of adhesive procedures17 involving dental adhesives, resin composites, and resin luting agents. The latter materials cited might be classified by the mode of polymerization, such as chemical, light, or dual curing (presenting both chemical and light-curing modes in the same product).18,19,20 With respect to the light-curing process, CQ is the most commonly used photoinitiator in dental resins, presenting an absorption peak at 470 nm, corresponding to the blue light spectrum.6,21 However, because of the yellow appearance of CQ, alternative initiators have been inserted into the resin agents to obtain nearly white materials,6 allowing the restoration of bleached teeth.
It is important to understand the influence of the current LEDs on commercial resins, since such an understanding allows clinicians to proceed in the best possible way when using different materials and devices, and establishing an effective protocol for each luting agent. Therefore, the aim of this study was to evaluate the influence of different radiant exposures of single-peak and polywave LEDs on the DC, elastic modulus (E), and flexural strength (FS) of resin cements. The null hypothesis of the present study was that the spectrum of wavelengths and different radiant exposures would not influence the chemical and physical properties of the resin cements tested.
Materials and Methods
In the present study, three luting agents were used (RelyX ARC, 3M ESPE, St. Paul, MN, USA; Variolink, Ivoclar Vivadent, Schaan, Liechtenstein; LuxaCore Dual, DMG Chemisch Pharmazeutische Fabrik GmbH, Hamburg, Germany). The experimental groups were established according to the light-curing units (LCU) used and the radiant exposures tested (Table 1). In the present study, we used a single-peak LED (Bluephase 16i, Ivoclar Vivadent) and a polywave LED (Bluephase G2, Ivoclar Vivadent). The output power (mW) of the LCUs was measured using a calibrated power meter (Ophir Optronics, Har Hotzvim, Jerusalem, Israel). The light irradiance was determined by dividing the output power by the tip area (mW/cm2). Spectral distributions were obtained using a computer-controlled spectrometer (USB2000, Ocean Optics, Dunedin, FL, USA) with a 0.35 nm resolution linear array detector, over a wavelength range of 340 to 1,100 nm. The spectral distribution and irradiance data were integrated using the Origin 6.0 software (OriginLab, Northampton, MA, USA) and are shown in Figure 1.
Eight specimens were prepared for each group according to the manufacturer's instructions. For the evaluation of DC, E, and FS, a silicone mold was used for preparing a bar-shaped specimen with the following dimensions: 7 mm in length × 2 mm in width × 1 mm in height.11 These sample dimensions were adapted for the microflexural test to enable single-step polymerization instead of several light activations at different points, according to the ISO 4049 specifications.
Prior to light activation, a microscope glass slide (0.15 mm thick) was placed over the mold in an attempt to obtain a flat sample surface and avoid the formation of an oxygen-inhibited layer. The resin cements were irradiated immediately after the manipulation, according to the groups with the respective LCU, from the surface of the specimens. After curing, the glass slide was removed and the specimens were stored in light-proof vials for 24 hours at 37℃.
After 24 hours of storage, DC was measured for five specimens by using a Fourier transform infrared spectroscope (FTIR, Spectrum 100 Optica, PerkinElmer, Cambridge, MA, USA), equipped with an attenuated total reflectance (ATR) device with a horizontal ZnSe crystal (Pike Technologies, Madison, WI, USA). The specimens were kept in contact with the horizontal face of the ATR cell.
A preliminary reading for the uncured material was recorded under the following conditions: frequency range of 1,665 – 1,580 cm-1, 32 scans, resolution of 4 cm-1, and Happ-Genzel apodization in the absorbance mode. DC was calculated using a baseline technique based on the band ratios of 1,638 cm-1 (aliphatic carbon-to-carbon double bond) and 1,608 cm-1 (aromatic component group) as an internal standard between the polymerized and the uncured samples.22
After the DC analysis, the specimens were subjected to a three-point bending test to measure the FS and E at a crosshead speed of 0.5 mm/min in a universal testing machine (Instron model 4411, Instron Corp., Canton, MA, USA). Prior to the test, the dimensions of each specimen were recorded using the Bluehill 2 software (Instron Corp.), which calculated the E (GPa) and FS (MPa) values according to the specimen dimensions and tension.
The homogeneity and homoscedasticity of the values obtained were analyzed, after which the data for the DC, E, and FS of the resin cements were analyzed using two-way analysis of variance (ANOVA), with 'radiant exposure' and 'LCU' as the main variables. All post hoc multiple comparisons were performed using Tukey's test. The statistical significance was set at α = 0.05. The resin cements were not compared.
Results
1. Elastic modulus
The cements Variolink and RelyX ARC were not influenced by the variables tested. In the case of LuxaCore, the effects of the variables 'LCU' and 'radiant exposure' were statistically significant (p = 0.0001 and p = 0.0013, respectively). However, the interaction effect between the factors was not significant (p = 0.1723). The polywave LED promoted higher values of E than the single-peak LED. The radiant exposure of 5 J/cm2 resulted in lower E values (p < 0.05), and the doses of 10 and 20 J/cm2 promoted similar results, superior to those of 5 J/cm2 (p < 0.05, Figure 2).
2. Flexural Strength
From the viewpoint of FS, the cement Variolink was not influenced by the experimental conditions. For LuxaCore and RelyX ARC, the effect of the variable 'LCU' was significant (p = 0.0142 and p = 0.0053, respectively), with higher values obtained with the single-peak LED (p < 0.05, Figure 3). The interaction between the factors was not significant for any resin cement.
3. Degree of conversion
The results of DC are presented in Figure 4. As for the mechanical properties, the resin cement Variolink was not influenced by the different experimental conditions. In the case of the LuxaCore dual-cure cement, the effect of the radiant exposure was significant (p = 0.0360), promoting a higher DC with 10 and 20 J/cm2 and lower values obtained with 5 J/cm2 (p < 0.05). Only the DC of RelyX ARC was influenced by LCU, with a higher conversion obtained with the polywave LED (p = 0.0270). The interaction between the factors was not significant for any resin cement.
Discussion
In clinical practice, several systems are available for the cementation of indirect restorations and/or intraradicular posts. Dual-cure resin cements are more commonly used because of their suitable conversion and mechanical properties, presenting both chemically and light-activated cures.23,24 Therefore, the wavelength of the LCU and the radiant exposure applied can influence several properties of these materials.
Three radiant exposures were evaluated in this study, from 5 J/cm2 to the one 4 times higher (20 J/cm2). Despite the fact that the power of the LCU used in clinical practice is high, these reduced powers were analyzed since some situations, such as post-fixation or cementation of indirect restorations, can drastically reduce the light that reaches the resin materials. On the basis of the obtained results, the null hypothesis was partially rejected, since all the considered resin cements were influenced by the experimental conditions, except for the Variolink cement.
According to the study protocol, the resin cements were not compared, as the aim of this study was to find the best protocol for each material, not the best material. Although the numerical results obtained for the three cements tested were similar, statistical comparisons among them might cloud the main analyses, masking results, since the compositions of the materials differ significantly and can influence all the results.
The mechanical properties of the Variolink system, as well as the DC, were not influenced by the experimental conditions. The system based on bisphenol a-diglycidyl methacrylate (Bis-GMA), urethane dimethacrylate (UDMA), and triethylene glycol dimethacrylate (TEGDMA) exhibited the same behavior between after curing with 20 J/cm2 and after curing with just 5 J/cm2. Despite the large amount of Bis-GMA (around 60 - 70 wt%), the presence of the agent TEGDMA can reduce the viscosity of the system,25,26 allowing a high-viscosity monomer25 to obtain the high DC observed (70 - 75%) and improving the mechanical properties of the material even with reduced radiant exposure. It should be noted that this cement and the LCUs tested belong to the same manufacturer. Factors such as initiators and co-initiators,7,27,28 as well as the selected filler particles and the respective refractive indices29 can influence the polymerization of the system positively, favored by the characteristics of the LCU, such as wavelength spectrum emitted and the beam profile, resulting in a relatively high compatibility between the resin system and the LCU.
In the case of RelyX ARC, the polywave LED promoted a higher DC. According to the manufacturer's specifications, there is no mention of alternative photoinitiators other than CQ in the composition of the cement. In addition, although the peak of the second-generation LED coincides with the absorption peak of the CQ (468 nm), the broad-spectrum wavelength emitted by the polywave LED can have more excited molecules of the photoinitiator, favoring monomer conversion and thereby improving the DC. However, the FS values of the specimens cured by the polywave LED were lower than those with the single-peak unit probably due to the different polymer network formed because of the differences in the wavelength emission and irradiance among the LCUs.
The resin cement LuxaCore DC was the most influenced by the experimental conditions. E increased when this cement was cured by the polywave LED. However, compared with the FS, the single-peak LED exhibited higher results. The single-peak LED may have promoted the formation of a polymer with slightly reduced crosslink chains, through a lower reaction speed, because of the narrow wavelength and the amount of photoinitiator excited, forming a more flexible polymer with higher FS. The radiant exposure was an important factor relevant to the DC of LuxaCore. Higher values were obtained after exposure to 10 and 20 J/cm2, with lower values at 5 J/cm2, showing that this cement requires at least 10 J/cm2 for optimal performance, with respect to not only mechanical properties but also the DC.
The present study demonstrated that the radiant exposure and the wavelength spectrum might influence the chemical and mechanical properties of resin cements. This was not true only for Variolink, which presented similar properties for all the radiant exposures tested, even a low radiant exposure (5 J/cm2). As discussed, the same manufacturer produces this resin cement and the LCUs analyzed, and this factor can be relevant in the selection of products, as compatibility between the devices and products seems to be important for achieving the best possible performance.
The influence of the light source on resin materials has been demonstrated in other studies.30,31,32 However, in the present study, the authors would like to test and establish a suitable protocol for the resin cements tested and indicate the best dose and device to be used according to the material. Despite the fact that the materials tested have not been described in the composition of any initiator other than CQ, the use of a polywave LED unit can allow the activation of a higher number of molecules of the CQ sensitizer, because of the broad spectrum of absorption of this initiator. This point along with the addition of alternative initiators in other commercially available resin materials explains the fact that new LCUs present a polywave peak to guarantee the curing of any resin material present in the market.
The results of this study are important not only for clinicians but also for manufacturers as they demonstrate the importance of adding, in the instructions for use of the materials, information on the wavelength spectrum as well as the minimal radiant exposure required to obtain the best possible performance, thereby alerting users to the possible flaws in the procedure if the recommendations are not followed.
Conclusions
According to the results of the present study, both the wavelength spectrum and the radiant exposure can influence the materials tested. A relatively low radiant exposure (5 J/cm2) can form a polymer with inferior mechanical properties only in the case of the LuxaCore resin cement. Further, the properties of the resin cement Variolink were not influenced by the experimental conditions tested, showing that the influence is material-dependent.
Acknowledgment
This study was partially supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (Fapesp, grant # 2013/02928-0).
-
Conflict of Interest: No potential conflict of interest relevant to this article was reported.
ARTICLE INFORMATION
- 1. Carvalho AP, Turbino ML. Analysis of the microtensile bond strength to enamel of two adhesive systems polymerized by halogen light or LED. Braz Oral Res 2005;19:307-311. ArticlePubMed
- 2. Dunn WJ, Taloumis LJ. Polymerization of orthodontic resin cement with light emitting diode curing units. Am J Orthod Dentofacial Orthop 2002;122:236-241. ArticlePubMed
- 3. Arrais CA, Pontes FM, Santos LP, Leite ER, Giannini M. Degree of conversion of adhesive systems light-cured by LED and halogen light. Braz Dent J 2007;18:54-59. ArticlePubMed
- 4. Jiménez-Planas A, Martin J, Abalos C, Llamas R. Developments in polymerization lamps. Quintessence Int 2008;39:e74-e84. PubMed
- 5. Jandt KD, Mills RW. A brief history of LED photopolymerization. Dent Mater 2013;29:605-617. ArticlePubMed
- 6. Santini A, Miletic V, Swift MD, Bradley M. Degree of conversion and microhardness of TPO-containing resin-based composites cured by polywave and monowave LED units. J Dent 2012;40:577-584. ArticlePubMed
- 7. Dressano D, Palialol AR, Xavier TA, Braga RR, Oxman JD, Watts DC, Marchi GM, Lima AF. Effect of diphenyliodonium hexafluorophosphate on the physical and chemical properties of ethanolic solvated resins containing camphorquinone and 1-phenyl-1,2-propanedione sensitizers as initiators. Dent Mater 2016;32:756-764. PubMed
- 8. Meereis CT, Leal FB, Lima GS, de Carvalho RV, Piva E, Ogliari FA. BAPO as an alternative photoinitiator for the radical polymerization of dental resins. Dent Mater 2014;30:945-953. ArticlePubMed
- 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. ArticlePubMed
- 10. Arrais CA, Giannini M, Rueggeberg FA. Kinetic analysis of monomer conversion in auto- and dual-polymerizing modes of commercial resin luting cements. J Prosthet Dent 2009;101:128-136. ArticlePubMed
- 11. Gaglianone LA, Lima AF, Gonçalves LS, Cavalcanti AN, Aguiar FH, Marchi GM. Mechanical properties and degree of conversion of etch-and-rinse and self-etch adhesive systems cured by a quartz tungsten halogen lamp and a light-emitting diode. J Mech Behav Biomed Mater 2012;12:139-143. PubMed
- 12. Jandt KD, Mills RW, Blackwell GB, Ashworth SH. Depth of cure and compressive strength of dental composites cured with blue light emitting diodes (LEDs). Dent Mater 2000;16:41-47. ArticlePubMed
- 13. Nakamura T, Wakabayashi K, Kinuta S, Nishida H, Miyamae M, Yatani H. Mechanical properties of new self-adhesive resin-based cement. J Prosthodont Res 2010;54:59-64. ArticlePubMed
- 14. Faria-e-Silva AL, Lima AF, Moraes RR, Piva E, Martins LR. Degree of conversion of etch-and-rinse and self-etch adhesives light-cured using QTH or LED. Oper Dent 2010;35:649-654. ArticlePubMedPDF
- 15. Gaglianone LA, Lima AF, Araújo LS, Cavalcanti AN, Marchi GM. Influence of different shades and LED irradiance on the degree of conversion of composite resins. Braz Oral Res 2012;26:165-169. PubMed
- 16. Lima AF, de Andrade KM, da Cruz Alves LE, Soares GP, Marchi GM, Aguiar FH, Peris AR, Mitsui FH. Influence of light source and extended time of curing on microhardness and degree of conversion of different regions of a nanofilled composite resin. Eur J Dent 2012;6:153-157. ArticlePubMedPMC
- 17. Lima AF, Soares GP, Vasconcellos PH, Ambrosano GM, Marchi GM, Lovadino JR, Aguiar FH. Effect of surface sealants on microleakage of Class II restorations after thermocycling and long-term water storage. J Adhes Dent 2011;13:249-254. PubMed
- 18. De Goes MF, Giannini M, Foxton RM, Nikaido T, Tagami J. Microtensile bond strength between crown and root dentin and two adhesive systems. J Prosthet Dent 2007;97:223-228. ArticlePubMed
- 19. Souza-Junior EJ, Prieto LT, Soares GP, Dias CT, Aguiar FH, Paulillo LA. The effect of curing light and chemical catalyst on the degree of conversion of two dual cured resin luting cements. Lasers Med Sci 2012;27:145-151. PubMed
- 20. Yenisey M, Dede Dö, Rona N. Effect of surface treatments on the bond strength between resin cement and differently sintered zirconium-oxide ceramics. J Prosthodont Res 2016;60:36-46. ArticlePubMed
- 21. Usumez A, Ozturk N, Ozturk B. Two-year color changes of light-cured composites: influence of different light-curing units. Oper Dent 2005;30:655-660. PubMed
- 22. Rueggeberg FA, Caughman WF, Chan DC. Novel approach to measure composite conversion kinetics during exposure with stepped or continuous light-curing. J Esthet Dent 1999;11:197-205. ArticlePubMed
- 23. Arrais CA, Rueggeberg FA, Waller JL, de Goes MF, Giannini M. Effect of curing mode on the polymerization characteristics of dual-cured resin cement systems. J Dent 2008;36:418-426. PubMed
- 24. Moraes RR, Faria-e-Silva AL, Ogliari FA, Correr-Sobrinho L, Demarco FF, Piva E. Impact of immediate and delayed light activation on self-polymerization of dual-cured dental resin luting agents. Acta Biomater 2009;5:2095-2100. ArticlePubMed
- 25. Van Landuyt KL, Snauwaert J, De Munck J, Peumans M, Yoshida Y, Poitevin A, Coutinho E, Suzuki K, Lambrechts P, Van Meerbeek B. Systematic review of the chemical composition of contemporary dental adhesives. Biomaterials 2007;28:3757-3785. ArticlePubMed
- 26. Asmussen E, Peutzfeldt A. Influence of selected components on crosslink density in polymer structures. Eur J Oral Sci 2001;109:282-285. ArticlePubMedPDF
- 27. Gonçalves LS, Moraes RR, Ogliari FA, Boaro L, Braga RR, Consani S. Improved polymerization efficiency of methacrylate-based cements containing an iodonium salt. Dent Mater 2013;29:1251-1255. PubMed
- 28. Andrade KM, Palialol AR, Lancellotti AC, Aguiar FH, Watts DC, Gonçalves LS, Lima AF, Marchi GM. Effect of diphenyliodonium hexafluorphosphate on resin cements containing different concentrations of ethyl 4-(dimethylamino)benzoate and 2-(dimethylamino) ethyl methacrylate as co-initiators. Dent Mater 2016;32:749-755. ArticlePubMed
- 29. Hadis MA, Tomlins PH, Shortall AC, Palin WM. Dynamic monitoring of refractive index change through photoactive resins. Dent Mater 2010;26:1106-1112. ArticlePubMed
- 30. Price RB, Felix CA. Effect of delivering light in specific narrow bandwidths from 394 to 515 nm on the microhardness of resin composites. Dent Mater 2009;25:899-908. ArticlePubMed
- 31. Mainardi Mdo C, Giorgi MC, Lima DA, Marchi GM, Ambrosano GM, Paulillo LA, Aguiar FH. Effect of energy density and delay time on the degree of conversion and Knoop microhardness of a dual resin cement. J Investig Clin Dent 2015;6:53-58.PubMed
- 32. Reginato CF, Oliveira AS, Kaizer MR, Jardim PS, Moraes RR. Polymerization efficiency through translucent and opaque fiber posts and bonding to root dentin. J Prosthodont Res 2013;57:20-23. ArticlePubMed
REFERENCES
Figure 1
Distribution of wavelengths emitted by the two light-emitting diode sources evaluated in the present study.
Figure 2
Elastic modulus (E, GPa) of the specimens, according to the experimental groups. Capital letters and lines indicate the difference between the light-curing units irrespective of the radiant exposure used (two-way analysis of variance [ANOVA] and Tukey's test, α = 0.05). Distinct letters indicate the statistically significant differences. *The resin cements were not compared.
Figure 3
Flexural strength (MPa) of the specimens, in accordance with the light-curing unit and the energy density evaluated. Capital letters and lines indicate the difference between the light-curing units irrespective of the radiant exposure used (two-way analysis of variance [ANOVA] and Tukey's test, α = 0.05). Distinct letters indicate the statistically significant differences. *The resin cements were not compared.
Figure 4
Degree of conversion (%) of the specimens, according to the light-curing unit and the energy density evaluated. Capital letters and lines indicate the difference between the light-curing units irrespective of the radiant exposure used (two-way analysis of variance [ANOVA] and Tukey's test, α = 0.05). Lower-case letters compare the radiant exposures. Distinct letters indicate the statistically significant differences. *The resin cements were not compared.
Tables & Figures
REFERENCES
Citations
Citations to this article as recorded by 
ePub Link
Cite
XML DownloadEffects of radiant exposure and wavelength spectrum of light-curing units on chemical and physical properties of resin cements
Figure 1 Distribution of wavelengths emitted by the two light-emitting diode sources evaluated in the present study.
Figure 2 Elastic modulus (E, GPa) of the specimens, according to the experimental groups. Capital letters and lines indicate the difference between the light-curing units irrespective of the radiant exposure used (two-way analysis of variance [ANOVA] and Tukey's test, α = 0.05). Distinct letters indicate the statistically significant differences. *The resin cements were not compared.
Figure 3 Flexural strength (MPa) of the specimens, in accordance with the light-curing unit and the energy density evaluated. Capital letters and lines indicate the difference between the light-curing units irrespective of the radiant exposure used (two-way analysis of variance [ANOVA] and Tukey's test, α = 0.05). Distinct letters indicate the statistically significant differences. *The resin cements were not compared.
Figure 4 Degree of conversion (%) of the specimens, according to the light-curing unit and the energy density evaluated. Capital letters and lines indicate the difference between the light-curing units irrespective of the radiant exposure used (two-way analysis of variance [ANOVA] and Tukey's test, α = 0.05). Lower-case letters compare the radiant exposures. Distinct letters indicate the statistically significant differences. *The resin cements were not compared.
Figure 1
Figure 2
Figure 3
Figure 4
Effects of radiant exposure and wavelength spectrum of light-curing units on chemical and physical properties of resin cements
