Micro & Immunology · patient case question
A radiograph of another tooth shows a root-surface carious lesion. Which organism is most closely associated with root caries?
Patient case: Abandoned periodontal therapy with pain at tooth #29
Patient: Female, 55 years old
Chief Complaint: Pain in the lower right premolar region.
Background: Began scaling and root planing two years ago but never completed the course and did not return for review.
Current Findings: Generalised heavy subgingival calculus with profuse bleeding on probing. Deep pockets and generalised horizontal bone loss. A panoramic shows a periapical radiolucency associated with tooth #29 continuous with the marginal bone loss. Tooth #29 has no caries and no restoration.
Show answer and explanation
Correct answer: C. Actinomyces species
- A. Lactobacillus species are associated with the PROGRESSION of established lesions rather than initiation — they thrive in the acidic environment of a deep cavity.
- B. Porphyromonas gingivalis is a periodontal pathogen of the red complex and has no role in caries.
- C. Actinomyces species — particularly A. naeslundii and A. viscosus — are the organisms classically implicated in ROOT-SURFACE caries. They colonise exposed cementum and dentine readily and are prominent in the root caries microflora of older adults with recession.
- D. Streptococcus mutans is the principal INITIATOR of coronal enamel caries. It is present in root lesions too, but Actinomyces is the association specifically tested for root caries.
Note: ⚑ This one is contested and the group should be aware. Some sources key root caries to S. mutans and Lactobacillus, and both are certainly present. The Actinomyces association is the classic and the one this recall tests. Keep both in mind on exam day.
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