Noncontact, nondestructive elasticity evaluation of sound and demineralized human dental enamel using a laser ultrasonic surface wave dispersion technique

Abstract

Laser ultrasonic nondestructive evaluation (NDE) methods have been proposed to replace conventional in vivo dental clinical diagnosis tools that are either destructive or incapable of quantifying the elasticity of human dental enamel. In this work, a laser NDE system that can perform remote measurements on samples of small dimensions is presented. A focused laser line source is used to generate broadband surface acoustic wave impulses that are detected with a simplified optical fiber interferometer. The measured surface wave velocity dispersion spectrum is in turn used to characterize the elasticity of the specimen. The NDE system and the analysis technique are validated with measurements of different metal structures and then applied to evaluate human dental enamel. Artificial lesions are prepared on the samples to simulate different states of enamel elasticity. Measurement results for both sound and lesioned regions, as well as lesions of different severity, are clearly distinguishable from each other and fit well with physical expectations and theoretical value. This is the first time, to the best of our knowledge, that a laser-based surface wave velocity dispersion technique is successfully applied on human dental enamel, demonstrating the potential for noncontact, nondestructive in vivo detection of the development of carious lesions.

Scanning laser-line source technique for nondestructive evaluation of cracks in human teeth

“…Reducing the line width can increase the bandwidth of generated SAW, but this will also increase the energy density of irradiating laser at the same time. According to the studies of Wang et al [26] there is damaging to the enamel, and the P peak is controlled under 1.0 × 10 8 W∕cm 2 to ensure that the ultrasonic wave is generated in the thermo-elastic mechanism and our experiments are nondestructive. A photodiode with a rise time of ∼100 ps receives the laser beam reflected by a beam splitter and triggers the TDS3054B digital oscilloscope to record signals.…”

“…Blodgett [24] has used the LU technique for determining the characterization of the internal structure of teeth. Wang et al [25,26] have done some qualitative experimental researches on evaluation for elastic properties of human sound teeth and carious teeth by the LU technique. However, to the best of our knowledge, there is no literature reporting that the LU technique has been used for evaluating cracks in human teeth.…”

Laser ultrasonic evaluation of human dental enamel during remineralization treatment

“…In the current study, the usable frequency bandwidth of the generated SAW (i.e. those frequency components with sufficient signal-to-noise ratio for reliable measurement) typically spanned from 1 ~25 MHz [13], equivalent to a probing depth of 3 ~0.1 mm for wave speed of ~3000 m/s. The bandwidth of the generated SAW could be further increased by reducing the line-source width but this unavoidably raises the irradiating power density, potentially to a level that may damage the specimen surface.…”

“…In previous studies we have demonstrated a non-contact, non-destructive elastic evaluation technique utilizing the dispersion of laser generated and detected SAW [12] and validated its effectiveness for evaluating the state of elastic response of both sound and demineralized human dental enamel [13,14]. …”

Frequency Domain Characteristics of Laser Surface Acoustic Waves in Healthy Incisor and Initial Dental Caries

“…Toda, 10) as well as others, has measured the thickness of enamel and dentin with the help of Leaky Lamb Wave and echo wave technique. Hsiao 11) and his teams from Sydney University have employed laser ultrasonic technique to assess teeth. Laser is used to excite SAW in human teeth in vitro, and then they probe SAW in healthy teeth and dental caries in early stage by means of light interferometer.…”