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Dental caries is a widespread disease that affects many children. Through a concerted effort by the parents, dentist, and child, the decay process can be arrested/reversed by non-surgical means via fluoride therapy, antimicrobial rinses, dietary changes, or low-intensity laser irradiation. However, success of these preventative measures depends to a great extent on the early detection of the decay process. Traditionally, dentists have utilized tactile and visual techniques to detect caries, but unfortunately these methods have a low sensitivity. Conventional radiography (x-rays) is adequate for large, cavitated lesions; however, it does not have sufficient sensitivity for the detection of early, non-cavitated caries, root surface caries, or secondary caries. Moreover, due to the distinct morphology of the primary dentition, including thin enamel, proportionally thinner dentin, and large pulp chambers, the progression of caries is intensified. Therefore, new methods for early caries detection are necessary. Recently, new technology has been approved for the diagnosis of decay, e.g. the DIAGNOdent and QLF, but these devices detect caries in its late stages when surgical intervention is usually necessary. Moreover, these devices do not provide depth-resolved images of the caries and therefore, cannot be used to assess the effectiveness of properly implemented preventative measures. Polarization-sensitive optical coherence tomography (PS-OCT) is a non-invasive imaging technique which utilizes near-infrared (NIR) light to produce depth-resolved images of dental enamel and has the potential to monitor early enamel caries. The scattering of light in the sound enamel and dentin is sufficiently strong in the visible range to obscure light transmission through the tooth. However, in the near-IR at 1310nm, enamel is highly transparent. The tissue contrast with devices utilizing near-IR light arises from changes in tissue scattering as opposed to conventional radiography, which is based on variations in tissue density. Therefore, this method can be more sensitive than x-rays in detecting early caries lesions 25. The potential of NIR imaging of early caries lesions in primary teeth has not been investigated. These methods do not require exposure to ionizing radiation, deciduous teeth are smaller and more accessible, and the dentist can avoid the difficult procedure of placing x-ray films in uncooperative children. However, primary teeth differ in composition and structure from the permanent dentition and therefore, their optical properties are expected to be different. The overall objective of this research is to develop non-invasive optical devices for the detection and diagnosis of early dental caries in deciduous teeth. The objectives of this study will be achieved through the following specific aims:AIM # 1: To test the hypothesis that the scattering coefficient of sound deciduous enamel is orders of magnitude less at 1310 nm than in the visible range. AIM # 2: To test the hypothesis that trans-illumination with NIR can discriminate carious enamel from sound enamel with high contrast.AIM # 3: To test the hypothesis that PS-OCT can image and quantify occlusal caries lesions.