Generalized Caries and a Throbbing Lower Left

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.

Correct answer: A. Symptomatic irreversible pulpitis

• A. Correct. Pain that lingers well beyond removal of the cold stimulus is the defining feature. The inflammation has progressed beyond the capacity of the pulp to recover, and root canal treatment or extraction is required.
• B. Incorrect. Symptomatic apical periodontitis is a periapical diagnosis characterized by tenderness to percussion and biting. This tooth is not percussion tender.
• C. Incorrect. In reversible pulpitis the response is sharp but resolves within a second or two of stimulus removal. Removing the irritant allows the pulp to heal.
• D. Incorrect. A necrotic pulp gives no response to thermal testing at all. This tooth responds vigorously, which confirms vital tissue remains.

Note: Every endodontic case carries two diagnoses — one pulpal and one periapical. Here the pair is symptomatic irreversible pulpitis with normal apical tissues.

Correct answer: D. Gingival recession

• A. Incorrect — this explains the finding. Percussion tenderness is the cardinal sign of symptomatic apical periodontitis.
• B. Incorrect — this explains the finding. A symptomatic apical abscess produces marked tenderness to percussion from periodontal ligament inflammation and to palpation from inflammation extending into the overlying tissues.
• C. Incorrect — this explains the finding. Excessive occlusal force inflames the periodontal ligament and readily produces percussion tenderness, sometimes with widening of the ligament space radiographically.
• D. Correct — this is the exception. Gingival recession exposes root dentin and produces dentin hypersensitivity: a sharp, brief response to cold, air, or touch on the exposed surface. It does not inflame the periodontal ligament or periapical tissues, so it produces neither percussion nor palpation tenderness.

Note: Interpret the tests separately. Percussion tests the periodontal ligament; palpation tests the buccal or lingual cortical plate and the overlying soft tissue. Together they localize inflammation beyond the confines of the pulp.

Correct answer: B. Root canal treatment

• A. Incorrect. Performing surgery first risks committing to bone removal on a tooth that may prove non-negotiable or non-restorable, after which the surgery was pointless and the bone is gone.
• B. Correct. Endodontic treatment comes first for several converging reasons: it confirms that the canal system can be negotiated and that the tooth is worth retaining before committing to surgery, it eliminates the source of infection, and it allows the final margin position to be planned against a known restorative outcome. A provisional restoration can then be placed while the surgical site matures.
• C. Incorrect. The stem states the tooth is restorable with these two procedures. Extraction discards a restorable tooth.
• D. Incorrect. Crown lengthening requires 8 to 12 weeks of healing before final margin placement, since the gingival margin continues to mature during that period. Definitive preparation at the surgical appointment leads to margin discrepancies.

Note: Flagged as context-dependent. Root canal treatment first is the standard sequence and the expected board answer. The genuine exception is when subgingival caries makes rubber dam isolation impossible — in that situation, crown lengthening or at minimum caries excavation with a build-up must precede endodontic access to permit an adequate seal.

Correct answer: A. The subgingival distal caries acting as a plaque-retentive factor

• A. Correct. Subgingival caries creates an irregular, undercut surface that plaque colonizes and that cannot be cleaned. Localized chronic inflammation follows, producing an isolated vertical defect on that specific surface. The location of the defect matching the location of the caries is the diagnostic clue.
• B. Incorrect. Vitamin D deficiency has been associated with periodontal disease at a population level, but it would not produce a solitary defect on one surface of one tooth.
• C. Incorrect. Occlusal trauma alone does not cause loss of attachment. It can widen the periodontal ligament space and accelerate destruction where inflammation is already present, but it is a co-factor rather than an initiator.
• D. Incorrect. Smoking is a major periodontal risk factor, but it produces generalized rather than isolated tooth-specific destruction, and occasional social smoking is a weak exposure.

Note: Keep vertical root fracture in mind as a classic cause of an isolated narrow vertical or J-shaped defect, especially in an endodontically treated tooth with a post. Here the untreated tooth with matching distal caries points to the caries.

Correct answer: B. Artifact produced by bending the film or sensor

• A. Incorrect. The mandibular canal is a single well-defined radiolucent band with corticated superior and inferior borders, running in a consistent anatomic path, not scattered irregular lines.
• B. Correct. Bending the receptor distorts the geometry between the emulsion and the beam, producing characteristic dark bands or streaks in the resulting image. This is a common finding in a full mouth series where receptors are forced into the palatal vault or the floor of the mouth.
• C. Incorrect. A foreign body would appear radiopaque — white — as a discrete object with definable borders, not as diffuse dark bands.
• D. Incorrect. Cervical burnout is a radiolucent band at the cervical region between the enamel edge and the alveolar crest, caused by differential absorption. It occupies a specific anatomic location rather than crossing the whole image.

Note: Common receptor artifacts to recognize: bending produces dark bands, fingernail pressure produces a crescent-shaped dark mark, static electricity produces branching lines, and double exposure produces two superimposed images.