Enamel cracks generated in the anterior teeth not only affect the function but also the aesthetics of the teeth. Chair-side tooth enamel crack detection is essential for clinicians to formulate treatment plans and prevent related dental disease. This study aimed to develop a dental imaging system using a near-IR light source to detect enamel cracks and to investigate the relationship between anterior enamel cracks and age in vivo. A total of 68 subjects were divided into three groups according to their age: young, middle, and elderly. Near-infrared radiation of 850 nm was used to identify enamel cracks in anterior teeth. The results of the quantitative examination showed that the number of enamel cracks on the teeth increased considerably with age. For the qualitative examination, the results indicated that there was no significant relationship between the severity of the enamel cracks and age. So, it can be concluded that the prevalence of anterior cracked tooth increased significantly with age in the young and middle age. The length of the anterior enamel cracks tended to increase with age too; however, this result was not significant. The silicon charge-coupled device (CCD) with a wavelength of 850 nm has a good performance in the detection of enamel cracks and has very good clinical practicability.

A holey optical fiber (HOF) wavelength division multiplexing (WDM) coupler, which divides optical waves according to their wavelengths, has been made by using the Fused Biconical Tapered (FBT) method. The transmission band of the proposing HOF WDM coupler could be easily tuned by adjusting the pulling length during the FBT process. The HOF used for the WDM coupler was designed to be bending insensitive, which could withstand a bending radius of up to 6 mm. Interestingly, it was observed that the air hole structure of the HOF should be maintained to have the property of a WDM coupler. The cross sectional SEM images of the implemented HOF WDM coupler are presented along with the light intensity distribution at the coupling region. The proposed HOF couplers may find applications as optical CWDM (coarse wavelength division multiplexing) filters and as optical fiber sensors also.