concept of remineralization and is particularly apt when addressing smooth surface lesions.4 Among the keys to successfully addressing caries is proper patient assessment. One approach has been termed caries management by risk assessment or CAMBRA, as described by Feather- stone.5 In this model, the patient’s hygiene, diet, caries activity, and salivary function are assessed and weighed against protective factors, such as fluoride exposure. Caries risk assess- ment systems such as CAMBRA help support preventive care and minimally invasive treatment, and also facilitate breaking the cycle of continuous restoration. Caries and Demineralization Enamel structure is composed of approximately 96% inorganic material, 3% water, and 1% organic material. The inorganic component consists of tightly packed calcium-hydroxyap- atite (HA) crystals secreted in a rod-interrod formation. Due to the formation and arrange- ment of the enamel rod crystals, a porous diffusible space is created between the crystal interfaces. In addition, there is variability within enamel itself, which becomes more porous toward the dentinoenamel junction. Caries is the result of a continuous process involving repeated challenges of demineralization and remineraliza- tion. A lesion develops when the dynamic changes involved in this cycle shift toward demineralization,4 which is a natural destructive process of hydroxyapatite crystals initiated by a local decrease in pH of the oral cavity. The pH at the outer enamel surface is impacted by the pH of the surrounding environment — saliva, plaque and the acquired enamel pelli- cle. Organic acids produced by metabolic microbial action on dietary carbohydrates decrease the local pH on the tooth surface and create a concentration gradient for the dis- solution of calcium and phosphate ions out of superficial hydroxyapatite crystals. The critical initiation pH for the demineralization of enamel is 5.5 (Figure 1). A decrease in pH in the biofilm and surrounding saliva initiates an acid attack, causing an imbalance in the equilib- rium of ions within hydroxyapatite crystals, and their supersaturated content in saliva. Cal- cium and phosphate ions diffuse from the tooth surface, causing ions to leach into the surrounding biofilm and saliva. This loss is the beginning of the decalcification process, and, if not interrupted, results in the early stages of lesion development. Demineralization begins within the crystalline structure of the enamel and will progress toward the dentin. The lesion advances through the entire enamel layer, damaging the hydrox- yapatite crystals in a tapered funnel-like shape. Once demineralization reaches dentin, the process progresses rapidly. The critical pH for the initiation of demineralization in dentin is 6.2 to 6.4, which is higher than that of enamel (Figure 2). Thus, dentin is much more susceptible to demineralization than enamel at similar pH levels. The rate of caries progression depends on a host of factors. Smooth surface caries progresses to cavitation in anywhere from 18 months4 to four years.6 Enamel Remineralization Remineralization of enamel occurs naturally in the oral cavity, although the process is much slower than enamel demineralization. This is a natural and continuously occurring phenome- non related to the foods and fluids consumed and the natural mechanism to repair minute damage that might arise from contact with these substances. The remineralization process relies on a neutral pH and is driven by the precipitation of calcium and phosphate ions from saliva, plaque and biofilm back into the enamel. Fluoride facilitates remineralization once the pH exceeds 5.5, assisting in the repair of demineralized enamel or incipient lesions.6 As the SECTION 2 WILLIAM R. BACHAND, DDS, is a professor in the Department of Restorative Sciences at the Dental College of Georgia at Augusta University, where he serves as director of the Advanced Education in General Dentistry Residency. He can be reached at [email protected]. OLIVIA L. FRASER, DMD, MBA, is a general dentist in the United States Army stationed at Fort Gordon in Augusta, Georgia. JANE N. PARK, DMD, is a resident in the Advanced Education in General Dentistry Program at East Carolina University School of Dental Medicine in Greenville, North Carolina. The authors have no commercial conflicts of interest to disclose. dimensionsofdentalhygiene.com January/February 2024 • Dimensions OF DENTAL HYGIENE 43 FIGURE 1. PROCESS OF DEMINERALIZATION. FIGURE 2. REMINERALIZATION/DEMINERALIZATION MODEL. pH 8.0 Formation of calculus 6.8 Critical pH of dentin HA 6.4 Production of HA and FA calcium and phosphate in saliva 6.2 6.8 6.5 6.0 Critical pH of enamel HA 5.5 5.0 Critical pH of enamel FA 4.5 FA forms if fluoride is available in the saliva and/or biofilm 5.5 5.0 4.5 Caries 4.0 4.0 3.5 3.0 Acid dissolution of HA crystals 3.5 3.0 Erosion
