The development of caries is dependent on the interaction of four primary factors. These are a host (tooth surface), a substrate (food), the presence of oral bacteria, and time. Caries will not develop if any of these four primary factors are not present.
Each of the four primary factors can be further divided into sub-factors that also influence the likelihood of caries (Figure 1).
Figure 1. The factors and sub-factors that influence caries development.
Host (tooth surface): The sub-factors that influence caries development are age (the enamel of the deciduous teeth of children is more susceptible to acid demineralization), if fluoride has been used, tooth morphology (which varies within the mouth and from person to person), root surface exposure due to gum recession, nutrition (if tooth-strengthening nutrients are consumed), and saliva flow rate and buffering capacity.
A tooth is more susceptible to caries if it has less acid resistant enamel due to age or low fluoride intake, or if the roots have been exposed by gum recession. Caries risk is also higher if the diet is low in nutrients (such as magnesium and vitamin D) that are necessary for healthy tooth development, and/or when an individual’s saliva flow rate is low or has a low buffering capacity. Pit-and-fissure demineralization is more likely to develop in teeth with numerous and exaggerated grooves. Teeth are less prone to caries activity in situations where tooth enamel has been strengthened by fluoride, a diet of tooth-strengthening nutrients is consumed, and/or the buffering capacity of saliva is high.
Substrate (food): The sub-factors that influence caries development are oral clearance (if food is retained or not in the mouth after eating), oral hygiene (if, after eating, food is actively removed with a sharp instrument such as a toothpick), eating frequency, food detergency (if consumed food can clean teeth), consumption of carbohydrates, and the cariogenicity of consumed carbohydrates (sucrose is more cariogenic than glucose and fructose).
When food is retained in the mouth and not actively removed after eating, is consumed more frequently, and/or more sugars, sucrose-containing foods, and sticky foods (like toffee) are consumed, there is higher risk of caries. On the other hand, when remaining food particles are actively removed after eating, food is consumed less frequently, fewer sugars, sucrose-containing foods, and sticky foods are consumed, and/or more tooth-cleaning foods (like apples) are eaten, the likelihood of caries is lower.
Oral bacteria: The development of caries depends on microbial load (how much bacteria is present), plaque composition (with some types of plaque microbes being more cariogenic than others), plaque acidogenicity (how much acid can be produced by the plaque that is present), plaque aciduricity (how well plaque can survive in acidic conditions), oral hygiene (how often the microbial load is reduced by brushing or prophylaxis), and if fluoride is present in plaque.
The likelihood of caries development is higher when the microbial load is high, as indicated by excessive plaque, when more caries-linked bacteria are present in plaque, when plaque produces more acid, when more plaque bacteria can survive in acidic conditions, and/or when plaque is not regularly removed by brushing. The odds that caries will develop are lower when the microbial load is low as indicated by little plaque, present plaque has fewer bacteria associated with caries or that can withstand highly acidic conditions, plaque acid production is low, and/or plaque is regularly removed by brushing or flossing.
Time: While the shift in microflora can occur over a fairly short period, a significant amount of time is needed for demineralization to lead to the development of white-spot and/or carious lesions. Acid production does not instantly trigger tooth decay, and in the early stages, remineralization can restore enamel, keeping the effects of dental caries at bay.
In summary, bacterial fermentation of consumed sugars produces acid in the tooth’s immediate environment. This acid demineralizes tooth enamel and, over time, this dissolution of tooth structure leads to the development of carious lesions. Because the combination of factors and sub-factors include unavoidable situations, dental caries can be very difficult to prevent.