Research Article Transmission of Curing Light through Moist, Air-Dried, and EDTA Treated Dentine and Enamel E. Uusitalo, 1 J. Varrela, 1,2,3 L. Lassila, 4 and P. K. Vallittu 1,2,4 1 Institute of Dentistry, University of Turku, 20520 Turku, Finland 2 City of Turku Division of Welfare, 20520 Turku, Finland 3 Department of Oral Development and Orthodontics, University of Turku, 20520 Turku, Finland 4 Department of Biomaterials Science and Turku Clinical Biomaterials Centre (TCBC), 20520 Turku, Finland Correspondence should be addressed to E. Uusitalo; erheuu@utu.f Received 7 March 2016; Revised 16 May 2016; Accepted 5 June 2016 Academic Editor: Evandro Piva Copyright © 2016 E. Uusitalo et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Objective. Tis study measured light transmission through enamel and dentin and the efect of exposed dentinal tubules to light propagation. Methods. Light attenuation through enamel and dentin layers of various thicknesses (1 mm, 2 mm, 3 mm, and 4 mm) was measured using specimens that were (1) moist and (2) air-dried (=5). Measurements were repeated afer the specimens were treated with EDTA. Specimens were transilluminated with a light curing unit (maximum power output 1869mW/cm 2 ), and the mean irradiance power of transmitting light was measured. Te transmission of light through teeth was studied using 10 extracted intact human incisors and premolars. Results. Transmitted light irradiance through 1 mm thick moist discs was 500 mW/cm 2 for enamel and 398 mW/cm 2 for dentin ( < 0.05). Te increase of the specimen thickness decreased light transmission in all groups ( < 0.005), and moist specimens attenuated light less than air-dried specimens in all thicknesses ( < 0.05). EDTA treatment increased light transmission from 398 mW/cm 2 to 439 mW/cm 2 (1 mm dentin specimen thickness) ( < 0.05). Light transmission through intact premolar was 6.2 mW/cm 2 (average thickness 8.2 mm) and through incisor was 37.6 mW/cm 2 (average thickness 5.6 mm). Conclusion. Light transmission through enamel is greater than that through dentin, probably refecting diferences in refractive indices and extinction coefcients. Light transmission through enamel, dentin, and extracted teeth seemed to follow Beer-Lambert’s law. 1. Introduction Light transmission through human tooth became a matter of interest when resin based light cured orthodontic adhesives spread in common use and due to the increased use of indirectly luted restorations which are bonded with dual- curing resin composite luting cements [1]. Indirect luting is used especially in prosthodontics but could also be used in orthodontics. In dual-curing resin, composite light is typically used to coinitiate polymerization and in order to achieve proper curing, light irradiation through the curing process is ofen needed. Polymerization occurs when free radicals are generated, and this can be due to chemical process or curing light initiation [2]. Ceramic inlays, onlays, and veneers are usually bonded with dual-curing cements, which requires light transmission through the ceramic material. In dual-curing resins the cement includes chemical activator, which increases the amount of free radicals when the curing light is insufcient and photoinitiators are unable to produce free radicals required for polymerization [3]. Because the light initiated adhesives are also used in orthodontics to bond brackets, it is important to study the light transmission through the tooth to evaluate the possibility of light curing with transillumination. Light curing adhesives are used under orthodontic appli- ances, such as stainless steel brackets that do not let any light pass through [4]. A common way to cure the adhesive under the bracket is to cure 20 s from both mesial and distal side of the bracket. Tis method may provide clinically satisfactory bond strengths, but there is a risk that the adhesive is polymerized only from the edges of the bracket leaving the center incompletely polymerized [5]. Furthermore the curing Hindawi Publishing Corporation BioMed Research International Volume 2016, Article ID 5713962, 6 pages http://dx.doi.org/10.1155/2016/5713962