Mutans streptococci (MS) are the group of microorganisms most associated with the dental caries process and key to the understanding of caries in preschool children.  MS are believed to contribute to caries because of their ability to adhere to tooth surfaces, produce copious amounts of acid, and survive and continue metabolism at low pH conditions.  Pre-school children with high colonization levels of MS have been shown to have greater caries prevalence, as well as a much greater risk for new lesions than those children with low levels of MS.  Additionally, colonization with MS at an early age is an important factor for early caries initiation.  Several studies have shown that the earlier MS is detected in children, the higher the caries experience.

Colonization of the oral cavity with MS in children is generally the result of transmission of these organisms from the child’s primary care giver, usually the mother.  The exact method of transmission is not known, but it is suspected to be due to close maternal-child contact, and sharing of food and utensils.  Factors found which influenced colonization were frequent sugar exposure in the infants and habits that allowed salivary transfer from mother to infants. 

Lack of enamel maturation or the presence of developmental structural defects in enamel may increase the caries risk in preschool children.  Such defects enhance plaque retention, increase MS colonization, and in severe cases, the loss of enamel enables greater susceptibility to tooth demineralization.  Enamel defects in the primary dentition are most associated with pre-, peri- or post-natal conditions such as low birth weight, and child’s or mother’s malnutrition or illness. 

There is abundant epidemiological evidence that dietary sugars are the major dietary factor affecting dental caries prevalence and progression.  Sucrose appears to be the most cariogenic sugar, not only because its metabolism produces acid, but also because MS utilize this sugar to produce the extracellular polysaccharide glucan.  Glucan polymers are believed to enable MS to both adhere firmly to teeth and to inhibit diffusion properties of plaque.  The intensity of caries in preschool children may be due, in part, to frequent sugar consumption.  High frequency sugar consumption enables copious acid production by cariogenic bacteria that are adherent to teeth.  This acid can demineralize tooth structure depending on the absolute pH decrease, as well as the length of time that the pH is below the “critical pH” level.  If demineralization over time exceeds remineralization, an initial carious lesion, the so-called white spot lesion, can develop and may further progress to a frank cavity.