Dental caries, commonly known as a cavity, results from a destructive disease process in the tooth structure. While the decay itself is not contagious like a cold, the specific bacteria responsible for initiating the decay can be passed between people. The transfer of these acid-producing microorganisms allows them to colonize a new host’s mouth and potentially lead to tooth decay.
Understanding the Bacterial Culprit
The primary microbial agents associated with initiating tooth decay are members of the mutans streptococci group, most notably the species Streptococcus mutans. These bacteria naturally inhabit the oral cavity, but their presence in high concentrations promotes disease. Decay begins when these bacteria consume fermentable carbohydrates, particularly sugars like sucrose, left on the tooth surface.
As the bacteria metabolize these sugars, they produce organic acids, primarily lactic acid. This acid lowers the pH level in the environment of the tooth, causing the protective mineral structure of the enamel to dissolve, a process called demineralization. Streptococcus mutans is adept at surviving in this low-pH, acidic environment. The bacteria also use sucrose to produce a sticky substance that helps them adhere to the tooth surface and form dental plaque, a resilient biofilm that shelters the bacteria from saliva and oral hygiene efforts.
How Transmission Occurs Through Saliva Exchange
The mechanism by which these cavity-causing bacteria spread is through the exchange of saliva between individuals. This transfer is categorized as either vertical or horizontal transmission, with vertical transmission being the most significant in early life. Vertical transmission occurs when the bacteria are passed from a primary caregiver, typically the mother, to an infant or young child.
This transmission often happens during daily interactions that involve salivary contact. Common examples include:
- Sharing eating utensils with the child.
- Tasting food before feeding it to them.
- Blowing on a child’s food to cool it down.
- Cleaning a dropped pacifier or bottle nipple by putting it into the adult’s mouth.
- Kissing a child on the mouth.
The period between 19 and 33 months of age is often referred to as the “window of infectivity,” as this is a common time for initial colonization to occur. The bacterial strains found in the child often genetically match those found in the mother, confirming this direct transfer. Horizontal transmission involves the transfer of bacteria between individuals of similar age, such as siblings or children in a daycare setting, usually through shared toys or cups.
Stopping the Spread to Children
Given that the caregiver is the most frequent source of bacterial transmission, reducing the adult’s bacterial load is a primary preventative strategy. Caregivers should prioritize their own oral health by treating any active cavities and gum disease, which lowers the concentration of harmful bacteria available for transfer. Regular dental check-ups and professional cleanings are important for maintaining a low bacterial count.
Parents should consciously avoid saliva-sharing habits with their children, including pre-tasting food and sharing drinking cups or utensils. Chewing xylitol-sweetened gum two to three times daily is an effective preventative measure for adults, as xylitol significantly reduces the level of mutans streptococci in the saliva. For the child, oral hygiene should begin before the first tooth erupts by gently wiping their gums after feedings. Once the first tooth appears, it should be brushed twice daily with fluoride toothpaste, and the child should establish a “dental home” by their first birthday.