Micro & Immunology · single question
Which organism is the PREDOMINANT species found in ROOT surface caries?
Show answer and explanation
Correct answer: C. Actinomyces species
- A. Lactobacillus is strongly associated with the PROGRESSION of established deep lesions rather than being the predominant root-caries species.
- B. S. mutans initiates and predominates in CORONAL (enamel) caries — it is also recovered from root lesions, but it is not the predominant species there.
- C. Correct. ACTINOMYCES (gram-positive anaerobic rods that normally inhabit healthy gingiva) are the predominant organisms in root-surface caries. Root caries occurs on exposed cementum/dentin, which demineralizes at a higher critical pH (~6.7) than enamel (~5.5).
- D. P. gingivalis is a red-complex periodontal pathogen of chronic periodontitis, not a cariogenic organism.
Note: Two-part rule for the exam: S. mutans = initiation of coronal/enamel caries; Lactobacillus = progression; Actinomyces = root caries.
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