Evidence from general dental practices
Joana Cunha-Cruz, DDS, PhD; JoAnna Scott, PhD; Marilynn Rothen, RDH, MS; Lloyd Mancl, PhD; Timothy Lawhorn, DDS; Kenneth Brossel, DDS; Joel Berg, DDS, MS; for the Northwest Practice-based REsearch Collaborative in Evidence-based DENTistry
ABSTRACT
Background
Saliva is one of the intraoral host factors that influence caries development. The authors conducted a study to investigate whether salivary characteristics are associated with recent dental caries experience.
Methods
Dentist-investigators and dental staff members collected data pertaining to a two-year cumulative incidence of dental caries (previous 24 months) and salivary characteristics during baseline assessment in an ongoing longitudinal study. The systematic random sample consisted of patients (n = 1,763) visiting general dental practices (n = 63) within the Northwest Practice-based REsearch Collaborative in Evidence-based DENTistry (PRECEDENT). The authors estimated adjusted rate ratios (RRs) by using generalized estimating equations log-linear regression to relate salivary characteristics to coronal carious lesions into dentin.
Results
Low resting pH (≤ 6.0) in the overall sample and low stimulated salivary flow rate (≤ 0.6 milliliter/minute) in older adults (≥ 65 years old) were associated with increased dental caries (RR, 1.6; 95 percent confidence interval [CI], 1.1-2.2; RR, 2.4; 95 percent CI, 1.5-3.8, respectively). Low buffering capacity was associated with decreased dental caries in children and adolescents (RR, 0.3; 95 percent CI, 0.1-1.0; RR, 0.2; 95 percent CI, 0.1-0.7, respectively). A thick, sticky or frothy salivary consistency also was associated with decreased dental caries in adults (RR, 0.6; 95 percent CI, 0.4-1.0). Associations between other salivary characteristics and dental caries for the overall sample and within each age group were not statistically significant.
Conclusions
Salivary characteristics were associated weakly with previous dental caries experience, but the authors did not find consistent trends among the three age groups. Different salivary characteristics were associated with an increased caries experience in older adults and a lowered caries experience in children and adolescents and adults.
Practical Implications
Further investigations are needed in this population setting to understand the study’s conflicting results. The study findings cannot support the use of salivary tests to determine caries risk in actual clinical settings.
Keywords
Saliva; practice-based research; Northwest Practice-based REsearch Collaborative in Evidence-based DENTisty; dental caries. JADA 2013;144(5):e31-e40.
Saliva is the complex mixture of fluids that surrounds the oral tissues, and it originates from major and minor salivary glands and nonglandular sources such as crevicular fluids, oral microorganisms and host cells. The consistency of saliva can be watery, thick, sticky or frothy depending on its composition; the amount of proteins in saliva mainly will determine its thickness or frothiness. A basal unstimulated secretion is produced continuously to moisturize and lubricate the oral tissues for more than 90 percent of the day. The normal resting salivary flow rate ranges from 0.25 to 0.35 milliliter per minute. Mechanical, gustatory, olfactory or pharmacological stimuli increase the production and secretion of saliva. Stimulated saliva represents 80 to 90 percent of daily salivary production, and the stimulated flow rate varies from 1 to 3 mL/minute. The salivary pH and the salivary buffering capacity are determined by the hydrogen bicarbonate balance in saliva. Salivary pH is approximately neutral, and buffering agents, such as inorganic phosphate in resting saliva and undercarbonic acid-bicarbonate system in stimulated saliva, help maintain neutrality.
Among the various protective functions of saliva, including diluting and cleaning the oral cavity, serving as a host defense, and buffering and enabling ion exchange, certain salivary characteristics outside the normal range of values may contribute to the caries process. Dental caries results from the dissolution of minerals from the tooth surface by organic acids formed from the bacterial fermentation of sugars. The capacity of saliva to flush microorganisms and substrates and maintain oral cleanliness may be influenced by its consistency and flow rate. Salivary pH and buffering capacity can contribute to the ion exchanges during re-mineralization and demineralization of enamel, with supersaturation of calcium and phosphate at pH 7 and in the presence of fluoride. The concentration of hydrogen ions (pH) at the tooth surface also will affect the rate of demineralization. The statements above are based primarily on the results of in vitro studies that reveal the biological plausibility for changes in salivary characteristics to contribute to the development of dental caries.
Another source of evidence of the influence of saliva on dental caries is studies conducted in people who have chronic salivary disturbances. Sjögren syndrome, an autoimmune disease, is characterized by a dramatically decreased salivary flow rate, and patients with this syndrome have higher rates of caries experience than those in control participants. The long-term use of some medications with antisialogogue effects, such as b-adrenergic agonists, corticosteroids and psychotropics, also has been shown to be associated with a high rate of caries experience.
However, the effect of saliva on dental caries in people without pathological conditions or chronic salivary gland hypofunction is less well understood. Evidence from epidemiological studies is scarce, and most studies lack statistical power. In a general population in which salivary function typically is within the normal range, the early identification of patients who may develop dental caries may contribute to the use of less invasive treatments. We hypothesize that a low salivary flow rate, low pH and low buffering capacity are associated with a higher dental caries rate.
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