# Dental Microstructural Imaging: From Conventional Radiology to In Vivo Confocal Microscopy
## 1 Introduction  
The oral cavity displays the entry path into the human organism, and it is a complex system unit involved in several disorders of both soft and hard oral tissues [1]. Dental tissues can be subject to various pathological processes caused by environmental or genetic factors [2]. Enamel defects, for example, are commonly verifiable in clinical practice; they may be aberrations in the quality and quantity of dental enamel causing early damage to the enamel organ, predisposing to plaque accumulation and caries [3]. Among them, _Enamel Hypomineralization_ is a qualitative defect of systemic origin with reduced mineralization, which shows discolored enamel with standard thickness and regular shape of the involved teeth [4]. Histologically, enamel hypomineralization shows a picture of less distinct prismatic shells and a lack of arrangement of the enamel crystals [5]. The demineralized enamel has lower mechanical properties, as the hardness and elastic modulus have lower values than those found in normal enamel, requiring complex management fortooth restoration [6]. In comparison, _Enamel Hypoplasia_ is a quantitative defect predisposing dimpled teeth with reduced enamel thickness, but enamel quality is unaffected [7]. Furthermore, a very high rate of deciduous teeth, ranging from 10% to 80%, may result in dental erosion, which determines altered dental shape and aesthetics and the loss of occlusal vertical dimension [8]. A broad picture of hereditary disorders, such as _osteogenesis_ and _amelogenesis imperfecta_, may also affect oral hard tissues, thus leading to bone and dentin defects [9]. Certainly, tooth decay is the most common dental disease in children and young adults, severely affecting their quality of life. Dental caries recognizes bacterial plaque as the major etiological factor, organized as a biofilm matrix that can damage several host tissues [10]. Furthermore, recent investigations seem to suggest interesting data regarding some microorganism salivary levels and general health: the oral microbiota is increasingly assumed to play an important role in clinical and scientific interests, hosting a vast complexity of microorganisms, namely bacteria, archaea, protozoa, fungi, and viruses [11]. With the increasing definition and profiling of the oral microbiota, growing evidence has emerged regarding the bidirectional association between systemic and oral pathologies; for example, the correlations between osteoporosis and peculiar oral dysbiosis are supported by some cariogenic or periodontal pathogenic bacteria [12]. Salivary flow plays a crucial role in maintaining microbiome homeostasis; altered salivary secretion could generate an imbalance between the host and microbiota, thus leading to dysbiosis and dysfunctional anomalies [13]. Thus, the microorganisms' crucial role has always shown a considerable weight in both periodontal and endodontic disorders [14]. The most demanding challenge for clinicians lies in correctly identifying the most appropriate diagnosis to better manage patients suffering from those disorders [15]. For this purpose, dentistry has constantly renewed how to classify caries, its direct effects on the stomatognathic apparatus, and its indirect effects on the patient's and their family's well-being [16]. In recent decades, caries detection and assessment have been standardized by an international team of caries researchers that developed an integrated clinical scoring system called ICDAS (International Caries Detection and Assessment System) [17]. The ICDAS is helpful in clinical practice, research, and epidemiological purposes, simplifying caries management and its outcomes. Parallel to the research and development of scoring systems and clinical assessment, a strong interest has been raised in the empowerment of technological tools in diagnosing dental affections. In fact, clinically similar lesions of the dental crown surface can underlie completely different conditions that require different therapeutic approaches.