Dental caries Study Guide

📖 Core Concepts Dental caries = demineralization of enamel, dentin, or cementum caused by acids from bacterial metabolism of fermentable carbs. Cariogenic triad – tooth surface, cariogenic bacteria (e.g., Streptococcus mutans, S. sobrinus, lactobacilli), fermentable sugars, and time for acid production. Demineralization‑remineralization balance – caries occurs when acid‑driven mineral loss > natural remineralization (saliva + fluoride). Critical pH – enamel begins to dissolve at pH ≈ 5.5; dentin/cementum dissolve at a higher pH (more vulnerable). Caries progression – early (chalky white spot) → brown discoloration → cavitation → dentin exposure → pulp involvement. --- 📌 Must Remember Key risk factors: frequent simple‑sugar intake, reduced salivary flow, poor oral hygiene, poverty, gingival recession (root exposure). Acid exposure duration: each bout can keep minerals dissolved for ≈ 2 h. Root caries progress 2.5× faster than enamel caries. Fluoride concentration: toothpaste ≥ 1 000 ppm reduces decay 25 %; > 1 000 ppm gives marginal added benefit. DMF/DMFT index counts decayed, missing, filled teeth – underestimates prevalence because radiographs aren’t included. Hall Technique: seals decay with a pre‑formed stainless‑steel crown, no tooth prep or anaesthesia. Silver diamine fluoride (SDF) arrests lesions by killing bacteria and hardening the surface (black staining). --- 🔄 Key Processes Biofilm formation Acquired pellicle forms → bacteria adhere → mature plaque (biofilm). Acid production cycle Sugar → bacterial glycolysis → lactic acid → pH drop → enamel demineralization. Demineralization‑Remineralization Acid dissolves hydroxyapatite → Ca²⁺/PO₄³⁻ released → saliva/fluoride supply Ca²⁺/PO₄³⁻ + F⁻ → remineralization (fluorapatite formation). Lesion assessment Visual inspection → air‑dry → identify white spot → probe texture → radiograph if needed → classify (incipient, cavitated, arrested). Restorative decision flow Non‑cavitated & active → diet + fluoride ± SDF → monitor. Cavitated (enamel only) → resin‑based composite/glass ionomer. Cavitated into dentin → composite, inlay/onlay, or crown. Non‑restorable → extraction. --- 🔍 Key Comparisons Enamel vs Dentin vs Cementum Enamel: highest mineral content, critical pH 5.5, slower progression. Dentin: lower mineral, tubules → sensitivity, faster progression once exposed. Cementum: least mineral, exposed by recession → fastest progression (2.5×). Fluoride sources Systemic (water, salt): low, continuous exposure; modest effect. Topical (toothpaste, varnish, gels): direct contact → greater remineralization & bacteriostatic/bactericidal effect. Restorative materials Composite resin: aesthetic, fluoride‑release (if glass‑ionomer), technique‑sensitive. Amalgam: high strength, less aesthetic, declining use. Glass ionomer: fluoride release, good for primary teeth & cervical lesions. Non‑operative vs Operative Non‑operative: early, non‑cavitated, active – diet, hygiene, fluoride, SDF. Operative: cavitated, dentin involvement – removal + restoration. --- ⚠️ Common Misunderstandings “White spots are harmless.” – They are early demineralization; if untreated they progress to cavities. “Fluoride causes decay.” – Fluoride replaces OH⁻ in hydroxyapatite → fluorapatite, which is more resistant to acid. “Only sugar frequency matters.” – Both frequency and amount matter; each acid episode can last 2 h. “All caries need drilling.” – Early lesions can be arrested with fluoride or SDF; drilling is reserved for cavitated lesions. “Sealants protect forever.” – Sealants need periodic check‑up; loss of sealant re‑exposes pits/fissures. --- 🧠 Mental Models / Intuition “Acid‑time balance” – Picture a seesaw: acid attacks (time × frequency) on one side, saliva + fluoride on the other. When the acid side stays down > 24 h (multiple meals), demineralization wins. “Caries as a fire” – Sugar = fuel, bacteria = spark, acid = flame, saliva = fire‑extinguisher. Remove fuel or boost the extinguisher → fire dies. --- 🚩 Exceptions & Edge Cases Root caries: Occur even with good oral hygiene if gingival recession exposes cementum. Dry‑mouth (xerostomia) patients: Even with low sugar intake, reduced buffering → high caries risk. Heavy metal exposure (e.g., lead) can increase caries risk independent of oral hygiene. Children < 3 y: Use only a smear of fluoride toothpaste to avoid fluorosis. --- 📍 When to Use Which Fluoride toothpaste vs varnish – Use toothpaste daily for maintenance; apply varnish/gel in high‑risk patients (frequent sugar, xerostomia). Sealants vs fluoride alone – Seal pits/fissures of newly erupted permanent molars and maintain fluoride regimen. SDF vs conventional restoration – Choose SDF for non‑cooperative patients, medically compromised, or when aesthetics are not a priority. Hall Technique vs traditional crown – Hall Technique for primary molars with occlusal caries where patient cooperation is limited. --- 👀 Patterns to Recognize White spot → brown → cavity sequence on the same surface. Pain triggered by thermal/sweet stimuli → dentin exposure; constant dull ache + pressure sensitivity → pulp involvement. “Hidden caries” on radiograph – radiolucency under intact enamel surface. Root surface lesions in patients with recession, dry mouth, or periodontal disease. --- 🗂️ Exam Traps Distractor: “Fluoride works only systemically.” – Wrong; topical fluoride is the primary preventive agent. Distractor: “Caries only affect enamel.” – Incorrect; dentin and cementum are also vulnerable, especially with recession. Distractor: “All sugar types are equally cariogenic.” – False; sucrose is most cariogenic because it fuels dextran synthesis for plaque adherence. Distractor: “A single episode of sugar intake causes caries.” – Misleading; repeated/long‑lasting acid exposure is needed. Distractor: “If a lesion is non‑cavitated, no treatment is needed.” – Not true; active non‑cavitated lesions require dietary/fluoride interventions. ---