Enamel Micro-crack Inspection Using Near IR Light Trans-illumination With Fluorescence-staining

Objectives: Enamel micro-cracks can be often observed in many teeth of elderly. However, accurate clinical diagnosis for enamel micro-cracks is very difficult. The purpose of this study was to examine the availability of inspection for enamel micro-crack using near infrared light trans-illumination device (DIAGNOcam, KaVo) with fluorescence-staining.
Methods: 10 extracted human upper incisors with typical enamel micro-crack were selected and investigated by four different methods.
The labial surfaces of all tooth specimens were polished with a low-speed rotated polishing-brush. After that, the grayscale picture of each tooth specimen was taken by digital camera (D-5100, Nikon) under visible-light (VL), as control. Every tooth specimen was also inspected by DIAGNOcam (IR). In addition, each tooth specimen was stained by 0.25% indocyanine green solution for 10 sec and then examined by DIAGNOcam (ST), and also photographed by a digital camera under visible-light (ST-VL).
The digital images of all tooth specimens obtained by four different methods were compared with background enamel surface.
The difference in gray-value was measured using image analysis Image J software and data were analyzed using one-way ANOVA and Tukey’s q-test.
Results: The mean gray-values (S.D.) were VL: 44.6(7.6), IR: 91.3(11.2), ST: 111.5(11.1) and ST-VL: 45.9(8.1). The difference in gray-value was influenced significantly by the four methods at p<0.01. The value of ST was statistically larger than others at p<0.01 and IR indicated greater value than VL and ST-VL at p<0.01.
Conclusions: An inspection using near-infrared light trans-illumination with indocyanine green solution was effective to detect the presence of enamel micro-crack. The color of the enamel surface existing micro-crack was not influenced by means of indocyanine green solution application. The new inspection can be one of non-invasive chair-side diagnostic methods and it was effective to detect the presence of enamel micro-crack.