Effect of light intensity and exposure duration on cure of resin composite

Medical College of Georgia, School of Dentistry, Department of Restorative Dentistry, Augusta 30912-1264.
Operative Dentistry (Impact Factor: 1.67). 01/1994; 19(1):26-32.
Source: PubMed


Of the many factors under their control, clinicians can manipulate light-exposure duration but must deal with a set intensity of light emitted from the dental curing unit. This research investigates the interdependence of exposure duration and source intensity on resin cure at various depths within a simulated light-cured resin composite restoration. This wafers of composite were obtained from a simulated cylindrical restoration such that the wafer could be removed from the top or from a distance of 1, 2, and 3 mm beneath the surface. The composites used in this study were a microfill and hybrid of Universal and Gray shades. All the data concerning filler type and shade were pooled so that generalized statements could be made regarding curing of light-activated composite in general. Specimens were cured using various source intensities and for different durations at each level within the cured cylinder. The cure of the specimens resulting from the different treatments was determined using infrared spectroscopy. The results indicate a dramatic effect of depth on the cure of composite. At depths greater than 2 mm, poor cure results, and polymerization is very susceptible to changes in light intensity and exposure duration. From these results, routine exposure times of 60 seconds are recommended using light-source intensities of at least 400 mW/cm2 as measured with a commercial dental light intensity meter. Incremental layer thickness should not exceed 2 mm, with 1 mm being ideal. Sources with intensity values less than 233 mW/cm2 should not be used because of their poor cure characteristics.

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    • "Thus several factors affect the DC of resin composites when applied clinically. These include operator-related factors, such as thickness of each layer, irradiance of the light curing unit, and proximity of light curing tip to the restoration [22] [23] [24]. "
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    ABSTRACT: Objective: Since bulk-fill (BF) resin composites should cure efficiently to a depth up to 4mm, the aim of the study was to determine the time-dependence of degree of conversion (DC) at that depth during 24h post-irradiation. Methods: Eight representative BF resin composites were studied [x-tra base (XTB), Venus Bulk Fill (VBF), Tetric EvoCeram Bulk Fill (TECBF), Sonic Fill (SF), Filtek Bulk Fill (FBF), everX Posterior (eXP), Beautifil-Bulk Flowable (BBF), Beautifil-Bulk Restorative (BBR)]. Specimens were fabricated in white Delrin moulds of 4mm height and 5mm internal diameter directly on an attenuated total reflectance (ATR) accessory attachment of an (FTIR) spectrometer (Nicolet iS50, Thermo Fisher, Madison, USA). Upper specimen surfaces were irradiated in situ for 20 s with an LED curing unit (Elipar S10 with average tip irradiance of 1200 mW/cm(2)). Spectra from the lower surface were recorded continuously in real-time for 5min and then at 30 and 60min and 24h post irradiation. Results: Mean ranges of DC4mm (%) of the materials at 4mm depth were 39-67; 48-75; 45-74; and 50-72 at 5, 30 and 60min and 24h respectively. DCs for XTB, VBF, TECBF, FBF, BBR increased significantly 30min after irradiation (p<0.05) and were not affected by subsequent time up to 24h (p>0.05). DC for SF was not affected by subsequent time after 5min (p>0.05). For eXP and BBF, DC increased 24h after irradiation (p<0.05). The data were described by the superposition of two exponential functions characterising the gel phase (described by parameters a, b) and the glass phase (described by parameters c and d). Significance: Post polymerization impact of bulk-fill composites is material dependent. Five materials exhibited their maximum DC4mm already 30min after starting the irradiation while DC4mm for two materials optimized after 24h. BF materials were found to exhibit after 24h a DC between 50 and 72% at 4mm depth under the stated irradiation conditions.
    Dental materials: official publication of the Academy of Dental Materials 08/2015; 31(10). DOI:10.1016/ · 3.77 Impact Factor
    • "Omitting any description of the method or an analysis of the light received by the RBC, many simply state that the restoration was light cured for xx seconds. Light curing an RBC is more complicated than this statement implies (Ferracane 2013; Leprince et al. 2013; Strassler 2013; Price, Rueggeberg, et al. 2014), and certain aspects of the process have been shown to greatly affect the outcome (Rueggeberg et al. 1994; Ferracane et al. 1997; Fan et al. 2002; Vandewalle et al. 2004; Xu et al. 2006; Rueggeberg et al. 2009; Ferracane et al. 2013; Leprince et al. 2013; Shortall et al. 2013; Bortolotto et al. 2014; Price, Rueggeberg, et al. 2014; Shimizu et al. 2015). Adequate photocuring is required for light-activated RBC restorations to reach their manufacturer's intended properties and is believed to be a basic requirement for predictable longterm clinical success (Bayne 2012; Leprince et al. 2013; Shortall et al. 2015), but establishing a direct relationship between inadequate photopolymerization of the RBC and the premature failure of the restoration in a clinical trial would be ethically problematic. "
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    ABSTRACT: For improved interstudy reproducibility, reduced risk of premature failures, and ultimately better patient care, researchers and dentists need to know how to accurately characterize the electromagnetic radiation (light) they are delivering to the resins they are using. The output from a light-curing unit (LCU) is commonly characterized by its irradiance. If this value is measured at the light tip, it describes the radiant exitance from the surface of the light tip, and not the irradiance received by the specimen. The value quoted also reflects only an averaged value over the total measurement area and does not represent the irradiance that the resin specimen is receiving locally or at a different moment in time. Recent evidence has reported that the spectral emission and radiant exitance beam profiles from LCUs can be highly inhomogeneous. This can cause nonuniform temperature changes and uneven photopolymerization within the resin restoration. The spectral radiant power can be very different between different brands of LCUs, and the use of irradiance values derived from dental radiometers to describe the output from an LCU for research purposes is discouraged. Manufacturers should provide more information about the light output from the LCU and the absorption spectrum of their resin-based composite (RBC). Ideally, future assessments and research publications should include the following information about the curing light: 1) radiant power output throughout the exposure cycle and the spectral radiant power as a function of wavelength, 2) analysis of the light beam profile and spectral emission across the light beam, and 3) measurement and reporting of the light the RBC specimen received as well as the output measured at the light tip. © International & American Associations for Dental Research 2015.
    Journal of dental research 07/2015; 94(9). DOI:10.1177/0022034515594786 · 4.14 Impact Factor
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    • "The Physical and mechanical properties of dental composites are directly influenced by the degree of conversion achieved during polymerization [23]. Lower degree of conversion provides composites with an inferior mechanical properties and greater discoloration and degradation [24] and as a result, restorations with poor wear resistance and poor color stability [25]. "
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    ABSTRACT: The aim of this study was to evaluate the degree of conversion and surface hardness of two bulk-fill composites and one incremental-fill composite.
    03/2015; 98(2). DOI:10.1016/j.tdj.2015.01.003
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