Public Health · patient case question
Which factor does NOT act DIRECTLY on remineralisation of an early enamel lesion?
Patient case: Root caries in a dry mouth
Patient: Male, 70 years old
Chief Complaint: “My teeth are decaying at the gumline and my mouth is always dry.”
Background: Takes amlodipine, sertraline and oxybutynin. Generalised gingival recession following treated periodontitis.
Vital Signs: BP 136/80 mmHg · HR 70 bpm
Findings: Multiple soft, leathery lesions on the exposed root surfaces of several teeth. Unstimulated salivary flow is markedly reduced. One molar has long-standing deep occlusal caries; a section of an extracted tooth from the same mouth shows a translucent zone beneath the lesion and dark bands within the dentine.
Show answer and explanation
Correct answer: D. Salivary immunoglobulin A
- A. Fluoride acts directly in two ways: it drives precipitation of FLUORAPATITE, which is markedly less soluble than hydroxyapatite, and it is incorporated into the remineralising lattice at the crystal surface. It also inhibits bacterial enolase, but the direct mineral effect is the point here.
- B. Saliva is SUPERSATURATED with calcium and phosphate with respect to hydroxyapatite, and those ions are the raw material from which the lesion is rebuilt. Their concentration is a direct determinant of how much remineralisation occurs.
- C. Buffering capacity — principally the bicarbonate system, with phosphate and protein contributing — determines how quickly plaque pH returns above the critical value after an acid challenge, and therefore how much of the day is spent in net remineralisation rather than net demineralisation.
- D. CORRECT as the exception. Secretory IgA acts on the BACTERIA, not on the mineral. It agglutinates organisms and interferes with their adhesion to the acquired pellicle, and the clumped bacteria are then washed from the mouth and swallowed. That reduces the acid challenge, so IgA influences the balance INDIRECTLY — but it contributes no mineral ion and takes no part in the redeposition itself.
Note: The direct-versus-indirect distinction is the specific twist this item adds. Saliva's full protective repertoire: lubrication, clearance, buffering, mineral supply, and an antimicrobial package of lysozyme, lactoferrin, salivary peroxidase, histatins and secretory IgA.