Enamel and Its Interaction with the Oral Environment

Abstract

Enamel, comprised of hydroxyapatite (HAP) units forming crystallites and rods, constitutes the structure of teeth. HAP is represented by the stoichiometric formula Ca10(PO4)6(OH)2. However, biological HAP, found in enamel, deviates from this stoichiometry due to deficiencies in Ca2+, PO43–, and OH–, and contamination with CO32– and HPO42–, and trace elements within their lattice. Its integrity is influenced by saliva, oral bacteria, fluoride from oral care products, and dietary acids. Salivary glycoproteins form an acquired salivary pellicle on enamel, while oral microorganisms create dental biofilm, which can become cariogenic with increased sucrose levels. The cariogenic biofilm generates acids, which reduces hydroxyl and phosphate groups surrounding enamel, thereby lowering the ion activity product (Ip) of the dental biofilm fluid and saliva and resulting in enamel demineralization. Initial caries appear as subsurface lesions with crystallite dissolution, mitigated by topical fluoride promoting the formation of calcium fluoride-like reservoirs on tooth surfaces and within dental biofilm. Enamel becomes susceptible to irreversible wear with frequent and prolonged dietary acid exposure. Dental erosion, chemically induced below pH 4.5, dissolves fluorapatite and hydroxyapatite predominantly on the surface layer, without subsurface lesions. Understanding these processes is crucial for preventive strategies against dental caries and erosion.