International Journal of Dentistry dentition, when demineralization passes from the outer enamel tooth layer to the more highly organic dentin layer, caries progression is rapid, and restorative dentistry is often required. The body’s natural repair mechanism for dental caries, or demineralization, is called remineralization, a process whereby minerals from saliva diﬀuse back into the porous subsurface region of the demineralized lesion. The cycle of demineralization and remineralization continues through- out the day. When ﬂuoride is present in saliva, it is strongly adsorbed to the demineralized surface of the tooth and protects its crystal surface against acid dissolution. Whether a lesion will progress, remain the same, or becomes reversed is determined by the balance between protective factors and pathological factors, which is called the “caries balance” [16]. 4. Risk Factors 4.1. Microbiological Risk Factors. ECC is an infectious dis- ease, and mutans streptococci (MS), including the species Streptococcus mutans and Streptococcus sobrinus, are the most common causative agents. Lactobacilli also participate in the development of caries lesions and play an important role in lesion progression, but not its initiation [17]. Diet also plays an important role in the acquisition and clinical expression of this infection. Early acquisition of MS is a key event in the natural history of the disease [18]. Vertical transmission of MS from caregiver to child has been reported [19]. The major reservoir of MS is the mother, from whom the child acquires it during a window period of around 2 years of age. At this time, the child is probably most susceptible to acquiring MS [19]. Successful infant colonization of maternally transmitted MS may be related to several factors, which include the magnitude of the inoculum, the frequency of small-dose inoculations, and the minimum infective dose. Mothers with dense salivary reservoirs of MS are at high risk of infecting their infants very early in life [20]. Thus, poor maternal oral hygiene and higher daily frequencies of snacking and sugar exposure increase the likelihood of transmission of the infection from mother to child [21]. In addition to maternal transmission of MS, father-to-child transmission has been studied [22]. Horizontal transmission was also examined; transmission of microbes may occur between members of a group (e.g., siblings, toddlers at a nursery) [20]. According to a recent study, neonatal factors may also increase the risk for early acquisition of S. mutans via vertical transmission. Infants delivered by cesarean section acquire S. mutans earlier than vaginally delivered infants. The investigators hypothesized that vaginal delivery may expose newborns to early protection against S. mutans colonization. That is, by being exposed to numerous bacteria earlier and with great intensity, the pattern of microbial acquisition is aﬀected. Cesarean infants are delivered in a typically more aseptic manner, resulting in an atypical microbial environment that may increase susceptibility to subsequent early S. mutans colonization [23]. 3 The time span between MS colonization and caries lesion development is approximately 13–16 months. In more high-risk children (preterm and/or low-birth-weight infants, with hypomineralized teeth), the duration is likely to be much shorter. Considerable presumptive evidence exists that malnutrition/undernutrition during the prenatal and perinatal periods causes hypoplasia. A consistent association has been reported between enamel hypoplasia and ECC [21, 24]. 4.2. Dietary Risk Factors. In addition to heavy infection with MS, children with ECC typically experience frequent and prolonged consumption of sugared beverages [25– 27]. Sugared beverages are readily metabolized by MS and lactobacilli to organic acids that can demineralize enamel and dentin. The use of nursing bottles enhances exposure to lactose. Cow milk in a nursing bottle is often assumed, incor- rectly, to be a primary causative agent in the induction of ECC [28]. Available experimental evidence in vivo and in vitro clearly shows that cow milk has negligible cariogenicity. Indeed, cow milk is essentially noncariogenic because of its mineral content and low level of lactose [25, 26, 28–30]. Saliva production decreases during sleep, and the protracted presence of a teat or nipple can result in promoting the cariogenic potential of the ﬂuid part of an infant’s diet. Thus, water should be the only drink given to a child during the night [1]. The cariogenicity of human milk is the subject of some controversy. A systematic review of epidemiological evidence suggests that breast feeding for longer than 1 year and at night may be associated with an increased prevalence of dental decay [31]. Also, a study demonstrated that human milk promoted the development of smooth- surface caries and was signiﬁcantly more cariogenic than cow milk. However, no signiﬁcant diﬀerence in the caries scores of the sulcal surfaces of the cow milk and human milk groups was detected [26]. Moreover, an epidemiological study demonstrated that breast feeding and its duration were independently associated with an increased risk for ECC and a greater number of decayed or ﬁlled tooth surfaces among children aged 2–5 years in the United States [32]. However, it should also be noted that these children were living in poverty. 4.3. Environmental Risk Factors. A systematic review con- cluded that children were most likely to develop caries if MS was acquired at an early age, although this may be partly compensated for by other factors, such as good oral hygiene and a noncariogenic diet [3]. Development of oral hygiene habits may be sensitive to the economic environment in which children live. Such environmental factors include caregivers’ social status [33–35], poverty, ethnicity, depriva- tion, number of years of education, and dental insurance coverage. Despite the widespread decline in caries prevalence and severity in permanent teeth in high-income countries over recent decades, disparities remain, and many children still develop dental caries [36, 37]. This relatively new area