# Dental Microstructural Imaging: From Conventional Radiology to In Vivo Confocal Microscopy
## 5 Discussion  
This work aimed to overview the existing literature on conventional dental imaging techniques and to report the current knowledge on innovative methods, focusing on the ones that not only promise to pursue the early and less invasive detection of dental disorders but also those that could be applied in clinical practice. The meaningful characteristics of the most representative promising in vitro and in vivo techniques are summarized in Table 1.  
Although conventional radiology is still the gold standard for caries detection in the clinical setting, it is an invasive instrumental investigative method due to the use of ionizing radiations, thus presenting a series of clinical limitations [34]. Furthermore, enamel defects or early caries are not allowed to be detected with conventional radiology. This is also true when aiming to determine responsiveness to remineralizing agents or the microscopic gaps between the tooth and restorative treatments, which require ex vivo evaluation for research purposes, meaning radiology is not appliable in clinical practice for establishing the actual condition of every single case in every single patient. Hence, dental research is currently investigating a series of alternative technologies that can be applied in clinical practice to overcome these limitations. Despite the encouraging results from in vitro studies, most of the techniques described are not suitable for clinical use, mainly based on their principle of works, the need for thin sectioning, or the damage caused to living cells. This is the case of SEM and TEM, whose electrons may damage living tissues, and Raman spectroscopy, where examination may be affected by salivary fluid and imperceptible movements of the human being during the examination. Among the techniques potentially applicable in vivo, laser speckle imaging systems have already proven their feasibility of evaluating the blood flux in gingivitis, and the pulse-echo ultrasonic technique could be considered to measure enamel and dental thickness in vivo. However, these hypotheses need to be concretized by expensive efforts in the research and development of handheld devices for clinical use, which are still never investigated to date. DIAGNOdent remains the only unique device already available in this field, but there is a sizeable and contrasting body of work on its real and practical usefulness in recognizing caries; ICDAS seems to provide comparable or better results, which could discourage its use. Among the investigated technologies, OCT and RCM seem to be the most promising and complementary to each other to offer a complete evaluation of the hard dental tissues at microscopic resolution in vivo. Indeed, both CM and RCM allow non-invasive real-time examination, are proven to be well tolerated by patients, are short-lasting, and are relatively simple for a trained operator [91]. Furthermore, OCT and RCM have already demonstrated their applicability in vivo on patients, including pediatric ones, with good collaboration and remarkable results from the image quality and monitoring of dental treatments. However, despite the feasibility of the procedures and the quality of the microscopic images, significant concerns related to the non-adaptability of these specific tools to image every oral cavity surface for limited access remain, thus limiting the potential use of existing de facto devices for the evaluation of the sole anterior teeth. Furthermore, these are costly devices and require a long learning curve, so their diffusion is unlikely, thus limiting their applications for research purposes or in hospitals and universities. Last, the literature provides no data or publications on the specificity or reliability of these imaging modalities in clinical or research projects.