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Micro & Immunology · patient case with 3 questions

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.

Question 1

What is the MOST likely sequence of events producing this lesion?

  1. An independent endodontic lesion unrelated to the periodontal disease
  2. A primary endodontic lesion with secondary periodontal involvement
  3. A vertical root fracture
  4. A primary periodontal lesion with secondary endodontic involvement
Show answer and explanation

Correct answer: D. A primary periodontal lesion with secondary endodontic involvement

  • A. Coincidental independent lesions do occur, but here the periapical lucency is continuous with the marginal bone loss and the tooth has no independent cause of pulpal death.
  • B. A primary endodontic lesion begins in a necrotic pulp and drains coronally through the periodontal ligament, producing a NARROW, isolated probing defect at one point on a tooth that is otherwise periodontally sound. Neither the tooth nor the mouth fits that description.
  • C. A vertical root fracture produces a narrow J-shaped or halo radiolucency along the root with an isolated deep probing defect, usually in a root-filled or heavily restored tooth. This tooth is unrestored.
  • D. CORRECT. The tooth has no caries and no restoration, so there is no coronal route by which bacteria could have reached the pulp. What there IS is long-standing untreated periodontitis. Deep pocketing and progressive attachment loss expose lateral and accessory canals, and eventually the apical foramen, allowing bacteria and their products to reach the pulp from the periodontium. That is a primary periodontal lesion with secondary endodontic involvement.

Note: Sequence the treatment accordingly: address the ENDODONTIC component first (it heals predictably and quickly), then re-evaluate the periodontal response after non-surgical therapy before committing to periodontal surgery. Prognosis in a true combined lesion is governed by the PERIODONTAL component.

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Question 2

How many bacterial species are typically implicated in a periapical lesion?

  1. Two
  2. One
  3. Three
  4. More than three
Show answer and explanation

Correct answer: D. More than three

  • A. Two species does not reflect the observed microbial diversity of the necrotic canal.
  • B. Single-organism endodontic infection is essentially unknown. Even a lesion apparently dominated by one species has others present.
  • C. Three understates it. The community is characteristically larger, and its complexity increases with the duration of the infection.
  • D. CORRECT. Endodontic infections are POLYMICROBIAL. Culture and molecular studies typically recover four to twelve species from an infected canal, predominantly obligate anaerobes acting in synergy — one organism's metabolic products become another's substrate, which is why the community is far more pathogenic than any single member.

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Question 3

A radiograph of another tooth shows a root-surface carious lesion. Which organism is most closely associated with root caries?

  1. Lactobacillus species
  2. Porphyromonas gingivalis
  3. Actinomyces species
  4. Streptococcus mutans
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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