Drinking and snacking.
Every time we eat or drink, the pH in the mouth becomes acidic. The more often individuals eat and drink, the more frequently the pH becomes acidic in the mouth, giving the cavity-causing bacteria an opportunity to thrive. Our bodies are designed to defend against this pH drop by secreting more saliva. Saliva is designed to buffer the pH back up to healthy levels. The pH of resting saliva is 6.75, while the pH of stimulated saliva is 7.8 to help the mouth recover from the drinking/eating episode. There are also bacteria in a healthy biofilm that function to help raise the pH back to healthy levels immediately following an acidic period. As the pH drops during the drinking/eating episode, when it gets below a pH of 5.5, small amounts of tooth mineral dissolve from the teeth and are trapped in the biofilm on the surface of the teeth. In a healthy mouth, within 15–30 minutes of drinking/eating, the pH recovers and raises above 5.5, and this mineral then returns to the teeth. When the system is in balance, the pH drops, some mineral is lost from the teeth, the pH recovers, and the mineral returns to the teeth. When the system is out of balance, prolonged periods of low pH cause net mineral loss from the teeth. The constant pH balancing act in the mouth has a direct effect on a patient’s risk for cavities, and often is the most common cause of increased dental caries.
Collectively, these studies showed conclusively that it was the low pH generated from sugar metabolism rather than sugar availability that led to the breakdown of microbial homeostasis in dental plaque. 
In order to determine whether what a patient drinks or their dietary habits could be contributing to their caries risk, two questions are asked during a caries risk assessment and near-verbatim questions have been validated in university based trials. These questions are primarily focused on identifying frequency of consumption and oral exposure rather than what type of food and drink the patient is consuming.
- Do you drink liquids other than water more than 2 times daily between meals?
- Do you snack daily between meals?
To maintain a low-risk status, one should eat and/or drink four to five times daily as their daily limit of food and beverage (other than water) intake. As a patient increases the frequency of exposure to food and drink, they are increasing the number of acid attacks their teeth experience. The more acid attacks a patient experiences, the more likely the patient’s biofilm will change from normal healthy bacteria to cavity-causing bacteria, and their teeth are also experiencing demineralization during the acid attacks. Frequent snacking and drinking liquids other than water (including alcohol, which can cause dry mouth) can have a profound effect on a patient’s caries risk.
One area that often becomes a question is the “speed” at which food and drinks are consumed. From a caries-risk standpoint, it is much better to drink three sodas at one meal than to sip on one soda continuously for several hours (See Figure 7). If a patient is going to consume sugary snacks or drinks, it is better to do it during a standard mealtime or consume it quickly to allow their saliva to return their oral biofilm to a healthy pH level. Patients that take small bites of food or sip on beverages over long periods are not giving their oral environment and biofilm the chance to return to a healthier pH level. Ideally, sugary or acidic foods and drinks should be limited as part of a healthy diet if a patient wants to lower their incidence of cavities or their risk of cavities in the future.
For many patients, it is tough for practitioners to explain the increase in caries risk due to frequency of eating and drinking to patients who either “only snack on healthy foods” or are on a frequent meal diet. While frequently snacking on healthy foods or being on a frequent meal diet may be better than snacking on sugary foods or helps improve the patient’s waistline, it does increase a patient’s risk for cavities.
For some patients, their diet is strictly controlled for health reasons, or they are not willing to make dietary changes at this time. For these patients, dental products exist in the forms of gums and sprays that can elevate the pH in the mouth immediately after a food or drink acid attack and contain xylitol, which is a natural sweetener that reduces the growth and acid production of cavity-causing bacteria. Using these products, such as CTx2 Spray, CTx3 Gel, and CTx3 Rinse, regularly can reduce the risk of cavity-causing bacteria taking over a patient’s biofilm and causing cavities.
- P. D. Marsh, “Dental Plaque as a Biofilm: The Significance of pH in Health and Caries,” Compend Contin Educ Dent 30, no. 2 (March 2009):76–8.
- P. D. Marsh, “Dental Plaque as a Biofilm and a Microbial Community—Implications for Health and Disease,” BMC Oral Health 6, Suppl. 1(2006): S14.
- Philip D. Marsh, Michael V. Martin, Oral Microbiology, 5th ed. (2009),15–16.