Caries Detection Methods Based on Changes in Optical Properties between Healthy and Carious Tissue

Abstract

A conservative, noninvasive or minimally invasive approach to clinical management of dental caries requires diagnostic techniques capable of detecting and quantifying lesions at an early stage, when progression can be arrested or reversed. Objective evidence of initiation of the disease can be detected in the form of distinct changes in the optical properties of the affected tooth structure. Caries detection methods based on changes in a specific optical property are collectively referred to as optically based methods. This paper presents a simple overview of the feasibility of three such technologies for quantitative or semiquantitative assessment of caries lesions. Two of the techniques are well-established: quantitative light-induced fluorescence, which is used primarily in caries research, and laser-induced fluorescence, a commercially available method used in clinical dental practice. The third technique, based on near-infrared transillumination of dental enamel is in the developmental stages.

Figure 1

The electromagnetic spectrum.Wavelengths of interest in this paper are the visible light spectrum from 400 nm to 700 nm and the range of near-infrared light from 750 nm to 1500 nm.

Figure 2

Light interactions with a tooth. How waves can interact with the dental hard tissue; (a) reflection, the wave rebounds; (b) scattering, the incident wave enters the tooth and changes direction. The photons then leave the tooth either as backscattering, where the photons leave through the surface by which they entered, or through another surface (scattering with diffuse transmission); (c) transmission, the wave is illuminated through the tooth and refracts on the surfaces; (d) absorption with heat production; (e) absorption with fluorescence. Most interactions of waves are a combination of these processes.

Figure 3

(a) Light of certain wavelengths is led by an optic fibre from the light source to a hand piece with a micro-Charge Couple Device video camera. (b) The image can be captured and saved for later analysis. Computer program: QLF 1.97e Inspector Research System BV, Amsterdam, The Netherlands.

Figure 4

(a) The LF device operates with light from a diode laser transmitted through a descendent optic fibre to a hand held probe with a fibre optic eye. The emitted fluorescence is collected through the tip, passes into ascending fibres, and is finally processed and presented on the display as an integer between 0 and 99. (b) In the presence of carious tooth substance, fluorescence increases.

Figure 5

Transillumination (TI) with Near-Infrared (NIR) light. experimental set-up of the TI system. The tooth is illuminated with NIR light. Polarizers are used to experimentally block out the ambient light from saturating the detector, a Charge Couple Device (CCD).