Using an Optical Reflectometer to Measure Caries Lesion Activity on Enamel

Background: Specular reflection can be used to quantify dental erosion, and might also provide similar results for caries. This study assessed the possibility of using specular reflection intensity (SRI; quantitative lesion activity assessment) to measure the progression of initial enamel caries lesions. Methods: Two hundred native enamel specimens and flat ground enamel specimens (n=100 each) were subjected to a 4-species biofilm caries model during 2, 4, 6, 8, and 10 weeks (n=20 each), to induce ‘active’ enamel caries lesions. Afterwards, to induce ‘inactive’ lesions, all specimens were continuously remineralized and brushed twice daily for 2, 4, 6, 8, and 10 weeks. Change in specular reflection intensity (%SRI), visual caries detection (ICDAS) and visual caries severity assessment were performed for all active lesions and during the remineralization phase. Scanning electron microscopy (SEM) images were taken for qualitative analysis. Results: For active lesions, %SRI dropped from 100% to about 80% in native enamel, and to about 15% in polished enamel. Remineralization/brushing increased %SRI in native enamel, but not in polished enamel. The comparison with visual caries scores yielded a better linear relationship of %SRI with early enamel lesion where caries was induced for up to 6 weeks. Conclusion: The use of the optical reflectometer for the assessment of caries lesion activity seemed to work better for early caries lesions and for polished specimens.

Reducing the measurement error of signal propagation delays using an optical reflectometer with picosecond resolution

The problems requiring high-precision measurements of signal propagation delays in optical fibers are considered. Design features of a pulsed optical reflectometer with a picosecond resolution designed for measuring propagation delays of a signal are considered. It is shown that the error of such a reflectometer includes the additive and multiplicative components. A method for determining the additive component of the optical reflectometer error based on measurements of signal delays introduced by individual optical fiber coils and the total delay introduced by series-connected coils is proposed. The requirements to the measurement conditions are formulated and the results of the error estimation of the proposed method are presented. To exclude the multiplicative component of the reflectometer error, a method for determining corrections to the reflectometer readings is proposed. The method is based on measuring the propagation delays of the signal in the coils of the optical fiber, first using reference equipment (installation for measuring the propagation delay of the signal), and then using an optical reflectometer, and then calculating the differences of the obtained measurement results. The scheme of installation for measurements of a propagation delay of signal in a coil of optical fiber is presented, the principle of operation of measuring installation is described. The results of the estimation of the error in determining the corrections to the reflectometer readings by the proposed method are presented. It is shown that the exclusion of the additive and multiplicative components of the error will reduce the error of optical reflectometers to values less than ± 100 ps.

Sub-Terahertz Quasi-Optical Reflectometer for CFRP Surface Inspection

Quasioptical reflectometer based on hollow dielectric beamguide (HDB), terahertz beamguide components and elements has been developed. The reflectometer has been analyzed in terms of its application for nondestructive method for surface and subsurface contamination of carbon fiber reinforced plastic (CFRP). Sub-terahertz (0.1…0.2 THz) measurement results of CFRP samples with different surface contaminations are presented.