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Perio Reports  Vol. 24, No. 2
Perio Reports provides easy-to-read research summaries on topics of specific interest to clinicians.
Perio Reports research summaries will be included in each issue to keep you on the cutting edge
of dental hygiene science.
Bacteria Involved in the Caries Process

For several reasons, mutans Streptococci (MS) are generally considered the primary pathogenic bacteria in biofilm responsible for acid production leading to dental caries. First, MS are frequently isolated from carious lesions. Second, laboratory studies repeatedly show that MS can produce caries in animals fed a high sucrose diet. And third, MS are both acidogenic (acid forming) and aciduric (can live in a highly acidic environment).

A researcher from the Tohoku University in Japan, and one from the University of Aarhus in Denmark, collaborated on a review of the literature regarding caries-associated bacteria and their roles in the caries process on smooth tooth surfaces. An extension of the ecological plaque hypothesis proposes three reversible stages in caries to explain the dynamic demineralization and remineralization process prior to cavitation.

Stage 1 is Dynamic Stability with biofilm dominated by non-mutans Streptococci and Actinomyces. Acid production is mild and infrequent in this stage with the balance of demin/remin shifting to a net mineral gain. Next comes the Acidogenic stage when sugar is eaten frequently and acid production becomes moderate and frequent. Increased acid in the biofilm encourages selective replication of “lowpH” non-mutans Streptococci and over time encourages bacteria that don’t usually produce acid to begin producing acid.

Under severe and prolonged acidic conditions, aciduric bacteria dominate, making this the Aciduric stage. Mutans Streptococci and Lactobacilli as well as aciduric strains of non-mutans Strep, Actinomyces, Bifidobacteria and yeasts dominate the biofilm. Many acidogenic and aciduric bacteria take part in the caries process.

Clinical Implications: The pH of biofilm will dictate which bacteria will proliferate and if they will produce acids.

Takahashi, N., Nyvad, B.: The Role of Bacteria in the Caries Process: Ecological Perspectives. J Dent Res 90(3):294-303, 2011.



Taste Genes Influence Caries Rates in Children

Dental caries is a chronic disease affecting people worldwide and is the most prevalent childhood disease. Caries is influenced by many factors: bacterial flora, dietary habits, fluoride exposure, oral hygiene, salivary flow, salivary composition and tooth structure. Recent research evaluating caries susceptibility in twins suggests genetics should also be considered.

Researchers from the University of Pittsburgh and West Virginia University in Morgantown, West Virginia, collaborated with researchers at the Center for Oral Health Research in Appalachia where an ongoing study pairs parents and children for long-term oral health evaluations. It was hypothesized that genes associated with taste might play a role in the caries process, since dietary habits are a significant risk factor in caries.

DNA samples were collected from blood, buccal cheek tissue or saliva from 496 children with primary dentition, 562 children with mixed dentition and 1,391 adults. Caries assessments were done on all subjects by trained and calibrated dentists and hygienists.

Specific amino acid substitutions on the genes were analyzed relative to taste. Those highly sensitive to bitter tastes are called “super tasters.” Those insensitive to bitter tastes are called “non-tasters.” Each presents with different amino acid patterns. In relation to caries levels, these genes seem to influence caries rates in children and not adults. Those with genes indicative of “super tasters” seem to experience a caries protective effect. Those with genes of “nontasters” are associated with increased caries risk.

Clinical Implications: The future might bring testing to identify “super tasters” and “non-tasters” in young children leading to targeted caries preventive measures.

Wendell, S., Wang, X., Brown, M., Cooper, M., DeSensi, R., Weyant, R., Crout, R., McNeil, D., Marazita, M.: Taste Genes Associated with Dental Caries. J Dent Res 89 (11): 1198-1202, 2010.
Genetic Markers for Caries Identified



Genetic factors might account for 40 to 65 percent of the risk for dental caries. Defensins are elements of the innate immune system that provide a broad spectrum of defense against pathogenic bacteria. Beta defensin 1 (DEFB1) is a chemoattractant for T-cells and dendritic cells of the acquired immune system. Research evaluating the genetic markers for DEFB1 suggests it might predict susceptibility to dental caries.

Researchers at the University of Pittsburgh evaluated saliva samples of 296 individuals. Three fairly uncommon polymorphisms on the genes for DEFB1 were studied. When the DEFB1 G-20A polymorphism was present, caries levels increased five-fold. When a different pattern is evident, DEFB1 G-52A, the caries rate is decreased two-fold. These are important genetic markers.

DEFB1 is located on chromosome 8, where other researchers also found signals relating to increased susceptibility to caries. These polymorphic variants on the chromosomes provide important risk information.

Clinical Implications: Dentists and dental hygienists providing prevention and periodontal therapy will impact both the oral health and the general health of those with DM.

Lamster, I., Lalla, E., Borgnakke, W., Taylor, G.: The Relationship Between Oral Health and Diabetes Mellitus. J Am Dent Assoc 139: Suppl 5, 19S-24S, 2008.
Root Caries in Periodontal Patients

The rate of root caries in adults is reported between 43 to 63 percent. High salivary levels of Strep mutans and Lactobacilli, reduced salivary flow and buffering capacity, smoking and poor oral hygiene are risk factors for root caries. The root caries index (RCI) is calculated by dividing the number of exposed root surfaces by the total number of decayed or filled root surfaces to determine a percentage. For example: six decayed/filled surfaces divided by 60 root surfaces equals 0.1 x 100 equals a RCI of 10 percent. Past studies show RCI rates between six and 10 percent.

Researchers in Holland evaluated 45 periodontal maintenance patients to determine RCI and risk factors. The average age of this group was 55 years and the average RCI was eight percent. The actual number of root surface lesions per patient ranged from zero to 19, with an average of 4.3 per patient. The number of exposed root surfaces ranged from 10 to 119 with an average of 65 per patient. The average number of coronal caries/fillings was 42, ranging from nine to 83. The number of coronal caries/fillings did not correlate to root caries levels.

High levels of salivary Strep mutans correlated with root caries incidence, while Lactobacilli counts did not. Poor oral hygiene was significantly correlated. Average plaque levels were 29 percent on facial surfaces, 45 percent on approximal surfaces and 50 percent on lingual surfaces. The overall average plaque score was 41 percent ranging from eight to 88 percent.

Clinical Implications: Periodontal therapy exposes root surfaces, increasing the risk for root caries.

Reiker, J., van der Velden, U., Barendregt, D., Loos, B.: A Cross-Sectional Study Into the Prevalence of Root Caries in Periodontal Maintenance Patients. J of Clin Perio 26: 26, 1999.
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