Optical characterization of bisphenol-A-glycidyldimethacrylate–triethyleneglycoldimethacrylate (BisGMA/TEGDMA) monomers and copolymer

Lehtinen, Janne; Laurila, Toni; Lassila, Lippo V.J.; Vallittu, Pekka K.; Räty, Jukka; Hernberg, Rolf

doi:10.1016/j.dental.2008.02.012

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Volume 24, Issue 10 , Pages 1324-1328, October 2008

Optical characterization of bisphenol-A-glycidyldimethacrylate–triethyleneglycoldimethacrylate (BisGMA/TEGDMA) monomers and copolymer

Janne Lehtinen
- Tampere University of Technology, Institute of Physics, Optics Laboratory, Tampere, Finland 33720
- Corresponding author. Tel.: +358 3 7418883; fax: +358 3 31152090.
Toni Laurila
- Tampere University of Technology, Institute of Physics, Optics Laboratory, Tampere, Finland 33720
Lippo V.J. Lassila
- University of Turku, Institute of Dentistry, Department of Prosthetic Dentistry and Biomaterials Science, Turku, Finland
Pekka K. Vallittu
- University of Turku, Institute of Dentistry, Department of Prosthetic Dentistry and Biomaterials Science, Turku, Finland
Jukka Räty
- University of Oulu, Measurement and Sensor Laboratory, Kajaani, Finland
Rolf Hernberg
- Tampere University of Technology, Institute of Physics, Optics Laboratory, Tampere, Finland 33720

Received 16 October 2006; received in revised form 30 January 2008; accepted 11 February 2008.

Abstract

Objective

The fundamental optical characteristics of dental polymers as a function of curing time are exiguously reported in the literature. In this work the refractive index [1] and the extinction coefficient [2] of bisphenol-A-glycidyldimethacrylate–triethyleneglycoldimethacrylate (BisGMA/TEGDMA)-based polymers of different volume fractions have been studied as a function of the curing time. A comparison between the measured index of refraction and theoretical calculation based on molar refraction is made. Also the temporal behavior of both the refractive index and extinction coefficient is compared.

Methods

Index of refraction: BisGMA/TEGDMA monomer samples were cured with a commercial light-curing unit by using camphorquinone and DMAEMA as the photoinitiator system. Curing times of 0, 40, 60, 300, 900 and 1800s were used. The refractive indices were determined with a refractometer at 470nm wavelength, where the peak absorption of the camphorquinone photoinitiator is located. Extinction coefficient: BisGMA/TEGDMA samples having different lengths were cured and the relative attenuation of light at 470nm was measured as a function of the curing time (0, 40, 60, 300, 900, 1800s).

Results

The results show that in general the index of refraction increases during the photopolymerization process in a time frame from 0 to 40s and then approaches a steady-state value, which depends on the original composition of the admixture. The detailed refractive index change depends on the volume fractions of the constituent substances. The extinction coefficient decreases in a time frame from 60 to 900s and reaches a steady-state value thereafter.

Significance

Knowledge of the fundamental optical characteristics of commonly used dental polymers is essential in the development of advanced light-initiated curing methods.

Keywords: BisGMA, TEGDMA, Optical properties, Optical characterization, Dental composites, Dental polymer, Monomer, Refractive index, Extinction coefficient