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Antioxidants and hydroxyapatite: multifaceted approach to combat dental caries

By Karen Davis, RDH, BSDH

Dental caries continues to be a significant health risk in the United States. It appears that dental caries may be increasing among young children, perhaps as a result of too much dietary sugar, and especially sugary beverages. The end result of this process is often tooth decay, or acid erosion of the enamel.

Differing theories exist about what causes the erosion of the enamel. One school of thought asserts that oral bacteria, Lactobacilli or Streptococcus mutans, metabolize sugars in the mouth to create lactic acid, which dissolves the calcium in the enamel. Another school of thought insists that enzymes from the bacteria break down the enamel, regardless of the acidic environment.

Whatever the biochemical mechanism, dental caries is a complicated process influenced by numerous factors. The main “culprit” in the process is the bacteria Streptococcus mutans, a communicable pathogen that produce acids to create a low pH and a favorable environment to dissolve minerals in tooth enamel.

Calcium in teeth is in the form of hydroxyapatite, or crystalline calcium phosphate, that forms a lattice-like structure. Under normal conditions, teeth go through a cycle of de-mineralization, or loss of hydroxyapatite, followed by a cycle of re-mineralization, when the hydroxyapatite is replenished. Fluoride works by binding with the hydroxyapatite crystals, making them less likely to dissolve, or demineralize. Fluoride also encourages remineralization, bonding with calcium to rebuild the lattice structure.

Controlling bacteria
Over the years, several strategies to combat dental caries have evolved. Most have focused on controlling or eliminating bacteria. Careful oral hygiene is the primary means of controlling bacteria as mechanical processes disrupt and remove the plaque. Also, antimicrobial agents can kill the caries-producing bacteria. These agents include rinses, dentifrices, varnishes, gels and other compounds containing alcohol, triclosan, iodine, and chlorhexidine. Fluoride also has some bacteriostatic effect against the caries-producing bacteria. In addition, chewing gums, candies, lozenges and syrup with non-sucrose sweeteners, such as xylitol, are thought to reduce the nutrients available for S. mutans, that is, to starve them.

Remineralization
Alongside these methods to reduce bacteria, another strategy has proven helpful: remineralization. In addition to fluoride to help replace the calcium and other minerals dissolved or eroded from tooth enamel, other compounds have emerged to help with remineralization. Most of these contain calcium in the forms of tricalcium phosphate, calcium sodium phosphosilicate, casein phosphopeptides, dicalcium phosphate dihydrate, and others. Very recently, scientists have been applying solutions containing nano-hydroxyapatite crystals directly to enamel and found it effective in remineralization.

Acid balance
Still another strategy that is not completely understood is controlling the acid balance in the oral cavity. The cariogenic bacteria S. mutans thrive in an acidic environment, the same pH level of 5.0-5.5 that engenders demineralization. The proper acid balance therefore, limits demineralization, enhances remineralization, and discourages S. mutans. Most of the acid level in the oral cavity is dependent on saliva, and one of the major roles of saliva is neutralizing and buffering acidity.

The importance of saliva in preventing dental caries is gaining attention. Saliva, which is 98 percent water, washes away food particles as the first defense against the residual carbohydrates following a meal. The other 2 percent of saliva contains proteins, electrolytes, enzymes, hormones, and other compounds. A major component of saliva is its rich array of antioxidants, including uric acid, albumin, ascorbic acid, glutathione and antioxidant enzymes. These antioxidants neutralize free radicals and can affect the acid balance in the oral cavity.

Multifaceted approach
Just as the process of dental caries is complex, dealing with caries requires a complex, multifaceted approach. Along with mechanical biofilm removal, antibacterial agents and fluoride as the first line of defense, new technologies are emerging and opening a wide range of research. One area of inquiry should be the effectiveness of topical antioxidants in helping maintain an optimal acid balance in the oral cavity. Research has shown that certain combinations of topical antioxidants can counteract free radicals that are associated with oxidative stress and inflammation.

An emerging field of scientific and clinical study is the interrelationship of antioxidants, dental and oral health, and systemic health. A number of companies have developed products containing antioxidants that counteract oxidation, and topical antioxidants applied to the oral tissues that can help reduce the oxidation associated with inflammation from infection or harmful substances.

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Topical antioxidants can be delivered through gels, toothpastes and mouth rinses to supplement and complement the natural antioxidants found in saliva. PerioSciences recently launched toothpaste with this multifaceted approach in mind containing powerful antioxidants of phloretin, ferulic acid, hesperetin, vitamin-C, herbal extracts along with hydroxyapatite. As these and other novel products emerge in the market, empirical evidence should be accumulated to confirm their efficacy.

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Even though dental caries is still a serious infection in the mouth, science is developing new, innovative approaches, technologies and products to combat the disease.

References
Huang SB, Gao SS, Yu HY. (2009). “Effect of nano-hydroxyapatite concentration on remineralization of initial enamel lesion in vitro.” Biomedical Materials 4:1-6. https://www.carifree.com/dentists/science/documents/Effectofnanohydroxyapatiteconcentrationonremineralizationofinitialenamellesioninviro.pdf [Accessed 31 July 2012].
Hurlbutt M, Novy B, Young D. (2010). “Dental Caries: A pH-mediated disease.” CDHA Journal 25(1):9-14. http://carifree.com/dentists/science/documents/DentalCariesapHMediatedDisease.pdf [Accessed 31 July, 2012].
Kim BI, et al. (2006). “Tooth whitening effect of toothpastes containing nano-hydroxyapatite.” Key Engineering Materials 18:308-311. http://www.scientific.net/KEM.309-311.541 [Accessed 31 July 2012].
Lenander-Lumikari M, Loimaranta V. (2000). “Saliva and dental caries.” Advanced Dental Research 14: 40-47. http://njms2.umdnj.edu/biochweb/education/bioweb/NewsandViews/Dental%20caries.pdf [Accessed 31 July 2012].
Simon L. (2007). “The role of Streptococcus mutans and oral ecology in the formation of dental caries.” Lethbridge Undergraduate Research Journal. 2(2) http://www.lurj.org/article.php/vol2n2/caries.xml [Accessed 31 July 2012].
Southward K. (2011). “The systemic theory of dental caries.” General Dentistry 59(5):367-373. http://www.agd.org/support/articles/?ArtID=9892 [Accessed 31 July 2012].
Tschoppe P, et al. (2011). “Enamel and dentine remineralization by nano-hydroxyapatite toothpastes.” Journal of Dentistry doi:10.1016j.jdent.2011.03.008. https://secure.freigeist.at/www.dp-uni.ac.at/uploads/Kielbassa%20JoD%202011.pdf [Accessed 31 July 2012].
Walsh LJ. (2009). “Contemporary technologies for remineralization therapies: A review.” International Dentistry SA 11(6): 6-16. http://www.moderndentistrymedia.com/nov_dec2009/walsh.pdf [Accessed 31 July 2012].

Karen Davis speaks internationally, is an accomplished author, and has been recognized as a “Top Clinician in Continuing Education” in Dentistry Today. She can be reached at Karen@karendavis.net.

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