The idea that all fake sugars contribute to tooth decay in the same way as traditional table sugar is a common misunderstanding. When consumers choose sugar alternatives to reduce calorie intake, they often wonder if they are simply trading one form of dental risk for another. The impact of sugar substitutes on oral health varies widely, depending entirely on the chemical structure of the sweetener. Most alternatives fail to cause cavities, and some substitutes actually offer protective benefits for the teeth, unlike fermentable sugars.
Defining the Difference: Artificial Sweeteners vs. Sugar Alcohols
The term “fake sugar” broadly covers two distinct groups of compounds with very different effects on the body and the mouth.
Non-nutritive sweeteners (NNS) are the first group, characterized by their high intensity and near-zero calorie count. Compounds like sucralose, aspartame, and saccharin fall into this category, providing sweetness hundreds of times greater than sugar. Because they are not carbohydrates, they pass through the digestive system largely unabsorbed.
The second category is the sugar alcohols, also known as polyols, which are nutritive carbohydrates that are only partially digested. These include compounds such as xylitol, erythritol, and sorbitol, which occur naturally in many fruits and vegetables. Unlike NNS, they do contain some calories, though significantly fewer than table sugar.
The Core Comparison: How Non-Nutritive Sweeteners Affect Teeth
Traditional sugar, specifically sucrose, causes cavities through a well-established biological process involving oral bacteria. The primary culprit, Streptococcus mutans, rapidly ferments sucrose, converting it into organic acids, most notably lactic acid. This acid production lowers the pH in the mouth, leading to the demineralization of tooth enamel, which is the beginning of a cavity.
Non-nutritive sweeteners do not participate in this decay mechanism because they are not fermentable by dental plaque bacteria. Streptococcus mutans cannot use high-intensity sweeteners like sucralose or aspartame as a food source. Therefore, when these sweeteners are consumed, the oral pH does not drop to the acidic level required to damage tooth enamel. This inability to be metabolized by oral bacteria is why NNS are considered non-cariogenic, meaning they do not contribute to the formation of dental caries.
Sugar Alcohols: The Unexpected Dental Benefits
Sugar alcohols offer an oral health advantage that goes beyond mere neutrality. Compounds like xylitol and erythritol are not only non-cariogenic but exhibit active protective qualities, making them cariostatic.
Xylitol, for example, is a five-carbon sugar alcohol that S. mutans attempts to metabolize but cannot complete the process. This futile uptake essentially starves the bacteria, inhibiting their growth, energy production, and ability to adhere to the tooth surface.
Erythritol, a four-carbon sugar alcohol, has shown promising results in some clinical studies. Research indicates that erythritol can reduce dental plaque weight and lower the counts of S. mutans in saliva and plaque more effectively than xylitol or sorbitol. This superior performance is believed to be due to its smaller molecular size and its ability to interfere with the bacteria’s metabolism and adhesion mechanisms.
Acidity and Erosion: A Separate Dental Concern
While the sweetener itself may not cause a cavity, the product it is delivered in can still pose a significant threat to enamel health through a process called dental erosion. This damage is caused by direct chemical dissolution of the tooth surface by acid, independent of bacterial action. Many artificially sweetened products, particularly carbonated beverages and flavored waters, contain high levels of acids to enhance flavor, preserve the product, or provide a necessary tang.
Common ingredients like phosphoric acid, citric acid, and malic acid can lower the beverage’s pH below 5.5. This is the threshold at which tooth enamel begins to demineralize. A diet soda sweetened with a non-cariogenic compound like sucralose can still be highly erosive due to its acidic content. Consumers must consider the acidity of the entire product, rather than just the type of sweetener, when evaluating the risk of enamel erosion.