Localised irradiance distribution found in dental light curing units

• Published in: Journal of dentistry Vol. 42; no. 2; pp. 129 - 139
• Main Authors: Michaud, Pierre-Luc, Price, Richard B.T, Labrie, Daniel, Rueggeberg, Frederick A, Sullivan, Braden
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.02.2014; Elsevier Limited
• Subjects: Beam uniformity; Bond strength; Curing; Curing Lights, Dental - classification; Dentistry; Equipment Design; Free radicals; Humans; Irradiance; Irradiance beam profile; Light; Light curing units; Localised spectral emission; Materials Testing; Photometry; Radiation Dosage; Resin photopolymerisation; Spectrum Analysis; Surface Properties; Wavelengths; Light curing units; Irradiance beam profile; Resin photopolymerisation; Beam uniformity; Localised spectral emission
• ISSN: 0300-5712; 1879-176X
• DOI: 10.1016/j.jdent.2013.11.014

Abstract Objective To measure the localised irradiance and wavelength distributions from dental light curing units (LCUs) and establish a method to characterise their output. Methods Using a laboratory grade integrating sphere spectrometer system (Labsphere and Ocean Optics) the power, irradiance, and spectral emission were measured at the light tips of four LCUs: one plasma-arc (PAC) unit, one single peak blue light-emitting diode (blue-LED) unit, and two polywave LED (poly-LED) units. A beam profiler camera (Ophir Spiricon) was used to record the localised irradiance across the face of the light tips. The irradiance-calibrated beam profile images were then divided into 45 squares, each 1 mm2 . Each square contained the irradiance information received from approximately 3200 pixels. The mean irradiance value within each square was calculated, and the distribution of irradiance values among these 45 squares across the tip-ends was examined. Additionally, the spectral emission was recorded at various regions across each light tip using the integrating sphere with a 4 - mm diameter entrance aperture. Results The localised irradiance distribution was inhomogeneous in all four lights. The irradiance distribution was most uniformly distributed across the PAC tip. Both the irradiance and spectral emission from the poly-LED units were very unevenly distributed. Conclusions Reporting a single irradiance value or a single spectral range to describe the output from a curing light is both imprecise and inappropriate. Instead, an image of both the irradiance distribution and the distribution of the spectral emission across the light tip should be provided. Clinical significance The localised beam irradiance profile at the tip of dental LCUs is not uniform. Poly-LED units may deliver spectrally inhomogeneous irradiance profiles. Depending on the photoinitiator used in the RBC and the orientation of the LCU over the tooth, this non-uniformity may cause inadequate and inhomogeneous resin polymerisation, leading to poor physical properties, and premature failure of the restoration.