We know that caries can occur on any tooth surface. However, it is generally accepted that caries occurs under plaque and is the direct result of bacterial acids. The primary acid that causes caries is lactic acid, a byproduct of the breakdown of fermentable carbohydrates (primarily sugar) by plaque bacteria. While the most dominant bacteria responsible for caries are S. mutans, other bacteria, such as lactobacillus, have also been suggested as contributors to various aspects of the caries process.45,46
Erosion, on the other hand, is a result of the direct action of extrinsic, dietary acids; such as those found in carbonated drinks and fruit juices or intrinsic acids, such as from GERD. Dietary acids include phosphoric, citric, and other acids commonly used to impart the tart, tangy flavors we associate with acidic foods and beverages. Although “diet” drinks are generally “sugar free,” and thus more acceptable from a caries standpoint, the acid content of the diet beverages is no different from their sugar-containing counterparts. From the standpoint of acid content, “sugar free” drinks offer no advantage when it comes to their potential to cause dental erosion.