Using Dentifrices as a Delivery System

The widespread acceptance of using toothpaste for improved oral health has resulted in the use of dentifrices as an effective delivery system for both cosmetic and therapeutic agents. This is evident by the myriad of dentifrice brands and types available at the local supermarket. One of the caveats when using proven caries preventive dentifrices to deliver additional oral health benefits is that the original anticaries benefits of that product must be retained in addition to providing significant new benefits. This has meant significant testing is needed when formulating multi-benefit products to ensure that each ingredient is able to perform in the presence of the others. This is the same situation that faced NaF actives and calcium abrasives in the early dentifrices - compatibility of ingredients. In the development and marketing of new products, each manufacturer has had to test their new formulations in order to ensure the new additive or ingredient does not interfere with the existing “active” while also providing a significant new benefit. Table 1 provides a timeline of significant events in the development of cosmetic and therapeutic dentifrices. One of the more interesting developments was the addition of sodium bicarbonate dentifrices into the market. This product was introduced by Church & Dwight and included baking soda as the abrasive, which was traditionally used by previous generations as a popular tooth cleaner. The popularity of these products resulted in the production of baking soda products by all the other manufacturers as well. The dental care products from Church & Dwight had the greatest amount of baking soda (65%) compared to the Colgate and Crest products which were around 25%. Although it was commonly believed the baking soda abrasive was more aggressive, it ultimately proved to be milder than the more commonly used abrasive formulations.⁶¹

Another product innovation that helped shape the market for years came from the public's desire for whiter teeth. Whitening agents were available in the dental office but not in the drugstore as an over-the-counter product. One of the first claims was the removal of extrinsic stains by existing tartar control agents. These formulas were optimized and tested for stain removal as well as tartar control. Intrinsic stains normally required the use of peroxides or carbamides which have the ability to bleach the teeth and increase "whiteness." Crest Whitestrips marked the advent of consumer applied whitening agents and allowed the individual to brighten their smile at home.⁶² Dentifrice manufacturers were also aware of this public interest in a cosmetic benefit of oral health products and improved formulations for stain removal, stain prevention, tartar reduction, and whitening all became available in the market place. This cosmetic benefit has been a continuing focus in oral care product development since the late 1990s. The whitening effect encompasses the original cleaning function of dentifrices, such as tartar and stain removal, but may also include intrinsic stain removal agents. A dual action whitening technology based on sodium fluoride dentifrices evolved from these early efforts.⁶³ One of the most recent additions into the tooth whitening arena is a two-step product system that provides the unique range of oral care benefits of stabilized SnF₂ dentifrice in Step 1 and a hydrogen peroxide gel in Step 2 to both polish and whiten the teeth. The system delivers gingivitis reductions comparable to chlorhexidine, but with significant whitening benefits.^64-68

As oral care products continue to evolve, we can expect to see even more interesting combinations and approaches in the future, with each iteration intended to deliver either enhanced performance or an increased number of overall oral care benefits. While some of these future products may come from unique combinations of ingredients currently in use, others may include ingredients that are completely new to oral care products. Table 2 lists various benefits and functions of ingredients that are commonly used in modern dentifrice formulations.

Several dentifrice formulations combined selected ingredients and became multi-benefit formulations. One product which had been demonstrated for almost all of the areas listed in Table 2 in a single product was Colgate Total which was introduced in the 1990's and contained 0.3% Triclosan, 2% Gantrez, and 0.243% NaF with a silica abrasive. Extensive clinical testing was performed to receive the ADA Seal of Acceptance for protection against gingivitis, plaque, and caries. More recent versions of this product claimed efficacy with respect to caries, plaque, gingivitis, tooth whitening, calculus and oral malodor.⁶⁹ However, in 2019, in response to global concerns related to the triclosan ingredient, the product was reformulated and now contains SnF2 as the anticaries agent, in addition to stain mitigation technology to help reduce the potential for tooth staining. In contrast to using existing ingredients like the soft silica abrasives for whitening, Procter & Gamble developed a highly efficient stain and tartar removal formulation by using sodium hexametaphosphate (Figure 4), a calcium surface active builder (CASAB). Earlier work to ensure no loss of effectiveness in relation to caries reduction with the new hexametaphosphate (it's not abrasive) polymer was done in vitro,⁵⁹ in situ,⁷⁰ and then in clinical studies.⁷¹ One of the difficulties in formulating products with CASAB agents is their hydrolytic stability in the aqueous phase of conventional dentifrices. The development of dual-phase packaging technology permitted the early use of polypyrophosphate ingredients such as sodium hexametaphosphate.⁷²

Figure 4.

Figure 4.

Sodium hexametaphosphate molecule

Continued development of the dual whitening system resulted in the use of a patented “Polyfluorite” System. The Polyfluorite System contains stabilized stannous fluoride combined with the cosmetic benefits of the sodium hexametaphosphate-CASAB (Figure 5). Thus, the CASAB is used to inhibit calculus, whiten by extrinsic stain removal, and prevent stain formation, while the stannous fluoride in the polyfluorite system fights plaque and gingivitis, provides long-lasting antibacterial action, protects against sensitivity, fights cavities, and helps freshen breath. This formulation is called Crest PRO-HEALTH™ dentifrice. Over 70 studies have been performed to support the Polyfluorite System’s ingredients benefits. A review of this technology is found in an article by Baig and He⁷³ in the online Compendium journal. This technology was the first to combine proven results in caries reduction, plaque reduction, less gingivitis, less sensitivity, and decreased tartar. The ADA granted its Seal of Acceptance to this multi-benefit product in 2006. As stated by the wording of the seal, “The ADA Council on Scientific Affairs‛ Acceptance of Crest PRO-HEALTH™ Toothpaste is based on its finding the product is effective in helping to prevent and reduce tooth decay, gingivitis, and plaque above the gumline, to relieve sensitivity in otherwise normal teeth, and to whiten teeth by removing surface stains, when used as directed.” In 2007, this dentifrice was clinically demonstrated to also provide a significant reduction in halitosis (breath malodor).⁷⁴

Figure 5

Figure 5

Benefits of 0.454% Stabilized Stannous Fluoride and Sodium Hexametaphosphate.

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.⁷⁵ Most researchers believe that excessive consumption of acid-containing foods and beverages is a primary cause of this emerging issue.^76-78 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.⁷⁹ As a result, 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.⁸⁰ Dental professionals have been successful in steering consumers away from sugar laden beverages that can lead to caries. However, diet soft drinks, although better from a standpoint of caries, 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.⁸¹

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. 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 2007.⁸² More recently, mechanistic studies, in vitro performance studies and human in situ clinical studies have all demonstrated enhanced erosion protection benefits of stabilized stannous fluoride over other formulations tested. 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.^83-89 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.⁹⁰ More recently, several additional human in situ clinical studies have demonstrated enhanced erosion protection benefits of stabilized stannous fluoride over other formulations tested.^91-94 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 (Figure 5). 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.

This update has shown the market forces have continued to develop new and improved products for the consumer. The therapeutic dentifrices developed have been responsible for a large portion of the caries reduction in the industrialized world. What new oral care therapies await consumers of the future is open for speculation. Most importantly, research has continued to progress, identifying opportunities to deliver enhanced levels of benefit as well as confirmation of new benefits by focusing on key mechanistic aspects of the various active ingredients. Will nanotechnology become an important component in the future? Will the use of dentifrices as a delivery system increase and expand? Will oral cancer or other systemic diseases find a delivery system from the oral environment? We only have to wait to see what new systems may come to bear in this ever-changing market place. It will be interesting to see what the future of Oral Care will include!