Cavities occur when these bacteria eat sugar for energy and produce acid as a waste. This acid dissolves the mineral crystals that enamel is made of. If acid attacks are not frequent and the person's saliva is able to neutralize the acid, the saliva contains minerals that can be returned to the damaged enamel crystals - repairing the damage. If demineralization is greater than re-mineralization for any reason a cavity is formed that is beyond natural repair. By the time a cavity is visible it is beyond natural repair.
The cavity causing Streptococcus Mutans bacteria infects children usually between 19 and 31 months of age but infection has been found in children as young as 6 months and in 60 percent of 15 month-old children. Our body's immune system is present even in gum tissue around teeth and in our saliva. Our immune system attempts to eliminate Streptococcous Mutans bacteria when we are infected but resistant strains of the bacteria persist.
Many, if not most, children are infected by cavity causing bacteria from their mothers. Current genetic DNA identification techniques have allowed researchers to "fingerprint" specific strains of bacteria and trace the path of infection.
Treating active dental disease in children's' mothers and fathers reduces the reservoir of decay-causing bacteria and reduces the likelihood that they'll transmit their bacteria to their child. This may be important knowledge because combined with the above knowledge about the age at which children become infected, we may find that by providing certain preventive treatments to mothers and fathers of young children, infection of their children by resistant strains to them might be avoided.
One study demonstrated that when women in their seventh month of pregnancy rinsed daily with two rinses, one being fluoride and the other a disinfectant called chlorhexidine; bacterial colonization of their children's mouths was delayed by an average of 4 months. This delay may be significant in allowing the children to develop their own immunity against other bacterial strains.
Other preventive treatments can include chewing gum with xylitol (Extra, Trident) and professional application of time-release fluoride varnishes. Additionally, we need to appreciate that decay susceptibility runs in families, owing to a combination of factors and that children in decay-susceptible families should be identified as being at risk. Since the hereditary factors can't be changed, the controllable factors of bacteria, diet, brushing and flossing need to be concentrated on.