One of the most challenging aspects of dentifrice development is to ensure that they continue to meet the changing needs of consumers. One example of this is the increased prevalence of dental erosion that has been reported on a global basis.87 Most researchers believe that excessive consumption of acid-containing foods and beverages is a primary cause of this emerging issue.88-90 Excessive ingestion of acid from any source can eventually overwhelm the pellicle coating on exposed tooth surfaces, the natural protective mechanism that is designed to protect teeth against damage due to acid intake.91 Enamel erosion has become an important issue with the increased consumption of sports and energy drinks, soft drinks, and citric juices.107 Dental professionals have been successful in steering consumers away from sugar laden beverages that can lead to caries. However, diet soft drinks, sports and energy drinks although better from a standpoint of sugar, contain essentially all of the acid contained in their sugared counterparts. From the standpoint of erosive potential, there is little to no difference between the two varieties of beverage.93 All of these products have a pH below the critical level for dissolving dental enamel. In this context, the enamel erosion benefits of existing dentifrice ingredients has become more relevant. 108-110
As a result of this drop in pH, teeth can become softened, and any abrasive action on these tooth surfaces while they are softened can result in permanent loss of the affected tooth mineral. Even the repetitive movement of the tongue over these acid-challenged surfaces has been noted as a potential source of abrasive activity.92
Figure 13: Surface Softening Leading to Tooth Erosion
Credit: Lussi A, Schlueter N, Rakhmatullina E, Ganss C: Dental Erosion – An Overview with Emphasis on Chemical and Histopathological Aspects. Caries Res 2011;45(suppl 1):2-12. doi: 10.1159/000325915
Since fluoride is well known for its ability to strengthen enamel, significant research has been done to determine whether or not fluoride is able to strengthen teeth to sufficiently protect them against erosive acid damage. Erosion is characterized by the dissolution and loss of mineral and removal of the tooth enamel surface under highly acidic conditions. When the localized pH drops below approximately 4.5, the pellicle cannot protect the enamel surface, and irreversible erosive damage can occur.
Many of these studies have found that fluoride, in general, does provide some level of benefit. However, there is an increasing body of research that has demonstrated unique benefits attributable to stannous fluoride over all of the other fluoride sources used. Although all fluorides help form stronger mineral within the tooth structure after a caries challenge, under plaque, dental erosion primarily occurs on smooth surfaces of the teeth, in the absence of plaque. Thus, the type of acid challenge is much different than one that occurs during caries formation. The level of challenge and the concentration and volume of acid are generally much higher during an erosive acid challenge. Stannous fluoride is different from other fluorides in that it deposits, in addition to the caries preventative F- ion, an invisible, protective barrier layer onto exposed tooth surfaces that consists of stannous (tin) precipitates. This barrier layer is highly acid resistant and provides the tooth surface with an extra layer of protection against erosive acid challenges.
The first clinical trial that demonstrated the preventive benefits of a stabilized, SnF2 toothpaste (Crest PRO-HEALTH) against the initiation and progression of dental erosion was published in 2007.95 A special issue of the International Dental Journal (2014) presented a range of studies that confirmed the erosive protective benefits of stabilized stannous fluoride dentifrice.95-101 Interestingly, one study demonstrated the erosion protection potential of a stabilized SnF2 dentifrice was significantly greater than that provided by some of the most popular prescription level (5000 ppm F) fluoride treatments available.102 More recently, several additional human in situ clinical studies have demonstrated enhanced erosion protection benefits of stabilized stannous fluoride over other formulations tested.103-106 Thus, formulations are now available that provide not only all of the major benefits generally attributable to toothpaste, but are also proven to provide a new benefit that meets the ever-changing needs of consumers by preventing the loss of mineral. A recent meta-analysis of Gluconate chelated stannous formulations demonstrated an 83% reduction in enamel surface loss vs sodium fluoride or arginine.147
While it is unlikely that dental professionals will be able to get consumers to stop drinking acid-containing beverages, it is comforting to know that therapies are available to help protect these consumers against things that are difficult for them to control. Stannous fluoride provides enhanced protection against the initiation and progression of dental erosion compared to other fluoride sources commonly used.
Figure 14. Testing the Erosion Prevention Effects of Different Fluoride Sources.