Dental caries (cavities) occur when microorganisms build up in deposits of dental plaque and ferment dietary sugars. The byproduct of this fermentation, lactic acid, lowers the pH at the junction of the plaque layer and tooth enamel, and eventually the enamel is eroded (Geddes 1991).
The layer of plaque in the mouth has recently been redefined as “biofilm” (Rudney 2000). Biofilm develops in a predictable pattern, whereby oral bacteria colonize areas of the gums and teeth, then spread, and eventually link with other organisms in a cohesive film. This film can occur both above and below the gum line. If left intact, it may form a hard, mineralized mass called calculus (tartar) (Bernimoulin 2003). This is the hard, yellow substance that dentists scrape off with specialized equipment. Tartar contains masses of bacteria that produce lactic acid and promote tooth decay. Brushing and flossing alone cannot penetrate or remove the tartar.
One novel hypothesis for disrupting the creation of biofilm and preventing tartar involves oral vaccines that may protect the mouth against Streptococcus mutans (S. mutans), the bacteria most commonly responsible for dental caries. Human studies have shown encouraging results with antibodies designed to suppress colonization of S. mutans in the biofilm (Michalek 2004).
The risk of developing cavities differs for each individual, based on factors such as oral hygiene, genetics, the size and shape of the teeth, resistance to infection, retention of dental plaque, and metabolism of sugar (Boraas 1988; Conry 1993). In addition, people with pre-existing conditions such as gum disease have a greater chance of developing cavities, and smoking can accelerate the transformation of plaque into tartar (Feldman 1983). Other risk factors for dental cavities include exposure to lead (Watson 1997), polychlorinated biphenyls (PCBs) (Rogan 1988), and second-hand smoke (Aligne 2003).
Clinically, cavities appear as blemishes on the tooth surface. If not clinically visible, they can still be detected using dental x-rays. Most dentists recommend one set of dental x-rays annually.
Waiting for tooth pain as a reason to visit the dentist is a not a good strategy for preventing cavities. In many cases, cavities are not painful because they affect only the surface layers of the tooth and do not extend into the dental pulp, which is the soft tissue inside the tooth. In more advanced cases, a cavity may extend into the pulp, causing intense pain and pulp disease known as pulpitis. Early pulpitis is generally treatable. If not treated, however, it can advance to pulp death. At this point, the tooth may stop hurting because the nerve has died. By the time a cavity has reached this stage, the tooth will most likely require extraction. Modern preventive dentistry is designed to prevent tooth decay from reaching such advanced stages.
Fluoride: Effective Against Cavities
Fluoride's role in preventing cavities has been extensively documented (Klein 1972). Teeth with adequate fluoride are resistant to acid, and studies have shown a 30 to 50% reduction in decay following the fluoridation of drinking water (Neenan 2004).
The use of fluoride, however, is not without its side effects. The most common side effect is fluorosis. This permanent alteration causes small, barely visible white flecks on adult teeth (Dean 1934). It occurs early during tooth development, when adult teeth are just coming in (Den Besten 1999). To help prevent it, experts recommend:
- Use of low-fluoride water in infant formulas
- Adult supervision of children during brushing
- Rigid application standards when administering fluoride supplements to children (Fomon 2000).
There is, however, little question that fluoride works to prevent cavities. When children between the ages of 5 and 6 years were treated with a 1.2 percent fluoride gel versus a placebo gel twice daily, the fluoride group showed a 40% decrease in cavities compared to the placebo group after a two-year follow-up (Klein 1972).