Abstract: In the field of dental care, diagnoses have been and being made by means of X-ray images, visual observation, explorer, palpation, fluorometery, insertion of a pocket probe and observation, observation by means of a root canal meter and the use of a Doppler flood flowmeter. However, such diagnoses are invasive and not very clear and three-dimensional X-ray CT apparatus that are being used for diagnoses are very large and complex. Additionally, OCT apparatus for obtaining optical tomographys by using reflection light that are being used by ophthalmologists give rise to problems because of the profile of the detection probe and operability when such an apparatus is used in an oral cavity that contains hard tissues such as teeth and soft tissues such as gingiva for dental care. The present invention dissolves the above identified problems and provides a non-invasive and high resolution dental optical diagnostic apparatus.

Abstract: A coating material for a pressure-sensitive recording sheet comprises both microcapsules A and microcapsules B, wherein the microcapsules A contains a solvent S.sub.1 which dissolves a colorless dye for a pressure-sensitive recording sheet, and the microcapsules B contains a dye-free solvent S.sub.2 which has no ability of dissolving dye and which has a lower boiling point than the solvent S.sub.1. The pressure-sensitive recording sheet using this coating material provides an improved thermal smudge without the deterioration of the image density, etc.