Preventive Dental Hygiene and Caries Management
Caries as a dynamic balance
Caries is a biofilm-mediated, diet-modulated process. Demineralization occurs when plaque pH falls below the critical pH (about 5.5 for enamel, 4.5–5.0 for root surfaces); remineralization requires fluoride, calcium, and phosphate. Fermentable carbohydrate frequency matters more than total amount. Saliva is the primary buffer and clearance mechanism, so xerostomia (medications, radiation, Sjögren syndrome) is a major risk factor.
Fluoride concentration questions are common. The topical effect - fluorapatite formation, enhanced remineralization, and bacterial inhibition - is the dominant caries-preventive mechanism. Know these: 5% sodium fluoride varnish = 22,600 ppm; 1.23% APF = 12,300 ppm; 2% NaF = 9,040 ppm; 0.05% daily rinse = 225 ppm; 0.2% weekly rinse = 900 ppm; 1.1% NaF prescription dentifrice = 5,000 ppm. Varnish is applied every 3–6 months for high-risk patients. Avoid APF on porcelain, composites, and sealants because it etches glass filler. Fluorosis risk is greatest in the first six years of life, with the esthetically critical window near 15–30 months for anterior teeth.
Other measures: resin sealants on deep pits and fissures of permanent molars, 38% silver diamine fluoride to arrest cavitated lesions (it stains), CPP-ACP, xylitol 6–10 g/day, and short-term chlorhexidine for specific indications.
Rule of thumb: caries risk assessment drives recall interval and fluoride frequency, and it is reassessed at every visit. Worked example: a high-risk adult with root caries and xerostomia receives 5,000 ppm toothpaste twice daily, varnish every 3 months, a 3-month recall, and diet counseling.