Surface porosity of enamel white spot lesions and penetration of fluorapatite nanocrystals into their subsurface: proof-of-concept study.

OBJECTIVES: In this study, we used atomic force microscopy (AFM) to quantify the size of surface pore apertures of enamel white spot lesions and then demonstrated the penetration of fluorapatite nanocrystals (nFA) into the subsurface of these lesions. METHODS: For the porosity study, enamel lesions were created on three sound human teeth using a demineralizing gel for 8 days. The interface between sound enamel and the artificial lesion was analyzed by AFM. To visualize the penetration of nFA tagged with a calcium-binding fluorophore (Fluo-4) into the subsurface of white spot lesions, we used two-photon microscopy. Sixteen extracted human teeth with either active, natural, or in vitro-created carious lesions in enamel were randomly divided into three groups. The teeth were treated for 2 min with either a suspension of tagged nFA crystals, Fluo-4 alone, or deionized water, and left for 30 min before being washed with distilled water and examined microscopically. RESULTS: A greater concentration of surface pores with larger areas was observed on the in vitro demineralized enamel (29 % of pores greater than 1.0 µm2) when compared with the adjacent sound enamel (8 % of pores greater than 1.0 µm2) (p=0.012, Fisher exact test). In vitro and natural lesions treated with tagged nFA showed fluorescence at depths ranging from 50 to 170 µm, demonstrating penetration of the nFA into the lesion subsurface. The lesions treated with Fluo-4 alone with no crystals showed mostly surface fluorescence (restricted to the outer 25 µm), while those treated with deionized water showed minimal (restricted to the outer 20 µm) to no fluorescence. CONCLUSION: We have demonstrated the use of AFM to quantify the surface pore apertures and two-photon microscopy to visualize nFA crystals in the subsurface of non-cavitated enamel lesions. CLINICAL SIGNIFICANCE: The restoration of the subsurface of non-cavitated caries lesions is a clinical challenge. This study demonstrated that a 2 min application of nFA could penetrate through the surface apertures of non-cavitated enamel lesions into their subsurface.

Validity and User Experience in an Augmented Reality Virtual Tooth Identification Test.

By leveraging emerging technologies in augmented reality (AR) and virtual reality (VR), a Virtual Dental Library and AR virtual tooth identification test were developed at a U. S. dental school. The AR virtual tooth identification test is a vision- based AR application that uses three-dimensional models of extracted human teeth as test items. The aims of this study were to investigate the validity of the AR virtual tooth identification test and evaluate the users' experience with the virtual testing method. The AR virtual tooth identification test scores were compared with real tooth identification tests, scores on three quizzes, final exam, and final grade for the course to assess its validity. In addition, a survey was used to assess students' perceptions of the AR tool. In 2018, all 109 first-year dental students who had completed the dental anatomy course were invited to participate in the study. Of the 93 participants, 61 (56% of total students) were included in the correlation analysis (32 were excluded due to incomplete test answer sheets or missing criterion measures). All 93 could respond to the survey and provide comments. In the results, the AR virtual tooth identification test had a positive correlation with the real tooth identification test (r=0.410, p<0.01), a combined score of two real tooth identification tests (r=0.545, p<0.01), the final exam (r=0.489, p<0.01), and overall grade for the dental anatomy course (r=0.661, p<0.01). On the tests, the students had some difficulty in viewing and manipulating the images and experienced technical difficulties related to their smartphones, and their survey responses expressed little support for the AR tool. Nevertheless, this study demonstrated criterion validity of the AR virtual assessment tool for tooth identification.