Endodontics · patient case question
Which bacterial species is most strongly implicated in the initiation of dental caries?
Patient case: Generalized Caries and a Throbbing Lower Left
Patient: 41-year-old male
Chief Complaint: “The bottom left throbs for twenty minutes every time I drink anything cold.”
Background: No dental care in 6 years. Drinks four sweetened sodas daily. Healthy, no medications, no allergies. Smokes occasionally at social events only.
Medications: None
Vital Signs: BP 122/78 mmHg · HR 74 bpm · RR 16 · T 98.4°F
Findings: Generalized caries. Tooth #19: deep distal caries, exaggerated and lingering response to cold lasting 20 seconds, no percussion tenderness, no periapical radiolucency. Tooth #18: subgingival distal caries with a narrow vertical bony defect on the distal; would require both crown lengthening and root canal treatment to restore. A full mouth radiographic series shows dark bands running across the premolar film.
Show answer and explanation
Correct answer: C. Streptococcus mutans
- A. Incorrect. P. gingivalis is a keystone pathogen of chronic periodontitis, a gram-negative anaerobe of the red complex. It is asaccharolytic and plays no role in caries.
- B. Incorrect. A. actinomycetemcomitans is associated with localized aggressive periodontitis, particularly in adolescents, and produces a leukotoxin.
- C. Correct. S. mutans is acidogenic, aciduric, and able to synthesize extracellular glucans from sucrose that anchor it firmly to the enamel pellicle. That triad makes it the principal initiator of the carious lesion. Lactobacillus species dominate later, in the progression of established lesions.
- D. Incorrect. A. israelii causes actinomycosis, a chronic suppurative infection with characteristic sulfur granules. Actinomyces species contribute to root caries but are not the primary initiator.