Question

Which bacterium is primarily responsible for initiating root caries?

• A. Streptococcus mutans
• B. Actinomyces viscosus
• C. Staphylococcus aureus
• D. Lactobacillus acidophilus

Hint:

Enamel caries initiation → Streptococcus mutans.
Root caries initiation → Actinomyces species.

Answer 1

The Correct Option is B

Step 1: Understanding Root Caries.
Root caries occurs on exposed root surfaces, usually due to gingival recession.
Unlike enamel caries, root surfaces are covered by cementum and dentin, which are less mineralized and more susceptible to acid dissolution.
Step 2: Microbial Etiology of Root Caries.
The initiation of root caries is primarily associated with Actinomyces species, especially Actinomyces viscosus and Actinomyces naeslundii.
These bacteria colonize root surfaces and are capable of adhering to cementum.
They ferment carbohydrates to produce acids, leading to demineralization of root structure.
Step 3: Comparison with Other Organisms.
(A) Streptococcus mutans — Primarily associated with initiation of enamel caries, particularly in pits and fissures.
(C) Staphylococcus aureus — Not a primary cariogenic organism.
(D) Lactobacillus acidophilus — Associated with progression of deep dentinal caries rather than initiation.
Step 4: Clinical Correlation.
Root caries is more common in elderly patients due to gingival recession and xerostomia.
Actinomyces species thrive in these conditions and initiate lesion formation on root surfaces.
Step 5: Conclusion.
Therefore, the bacterium primarily responsible for initiating root caries is Actinomyces viscosus.