Endodontics · patient case with 3 questions
Full-mouth series in a patient with several root-treated teeth
Patient: Male, 52 years old
Chief Complaint: New patient examination. Intermittent vague discomfort in the upper right quadrant.
Background: Several root canal treatments completed at different times by different clinicians.
Current Findings: A full-mouth radiographic series has been taken. On the periapical below, one root-filled tooth shows an obturation that stops well short of the radiographic apex, with a small periapical radiolucency (arrow).
Question 1
Which finding indicates that this tooth requires retreatment?
Show answer and explanation
Correct answer: C. An obturation short of the apex WITH an associated periapical radiolucency
- A. Slight extrusion of sealer or gutta-percha in an asymptomatic tooth with no periapical lesion is a technical imperfection, not a failure. Extruded material is often tolerated and resorbed.
- B. Obturation ending 0.5–2 mm short of the radiographic apex is the intended endpoint, since the apical constriction lies coronal to the radiographic apex. With no lesion, this tooth is a success.
- C. CORRECT. A short fill leaves the apical few millimetres of canal uninstrumented and unsealed. When that is accompanied by a periapical radiolucency, the two findings together mean persistent apical periodontitis from residual intracanal infection — the definition of a failing root canal treatment and the indication for retreatment.
- D. A sound restoration with no periapical change is a successful outcome. Coronal seal is in fact one of the strongest predictors of long-term endodontic success.
Question 2
Retreatment will require re-establishing straight-line access. What is the principal ADVANTAGE of straight-line access?
Show answer and explanation
Correct answer: C. Instruments can reach the apical third of curved canals
- A. Irrigation is indispensable regardless of access. Sodium hypochlorite dissolves tissue and kills bacteria in regions no file ever touches.
- B. Straight-line access necessarily REMOVES more tooth structure. That is its acknowledged trade-off, not its advantage.
- C. CORRECT. Straight-line access removes the coronal interferences — overhanging dentine, unroofed pulp horns, the cervical bulge — so files enter the canal without deflection. The instrument then follows the canal's own curvature rather than being restrained at the orifice, which is what allows the apical third of a curved canal to be reached and shaped. It also reduces ledging, transportation and instrument separation.
- D. Access design does not change how many canals exist. Good access makes them easier to FIND, but the number is fixed by the anatomy.
Note: Straight-line access: reduces ledging, removes unsupported dentine, unroofs the pulp horns, and gives adequate access to the apical third. Its one disadvantage: more tooth structure is removed.
Question 3
Which anatomical landmark is used to locate the apex of the MESIOBUCCAL root of a maxillary first molar?
Show answer and explanation
Correct answer: B. The mesiobuccal cusp tip
- A. The mesiolingual cusp overlies the PALATAL root — and the MB2 canal orifice is found in the groove running from the MB orifice toward the mesiolingual cusp.
- B. CORRECT. Each root apex of a maxillary molar lies approximately beneath its own cusp tip. The mesiobuccal cusp tip therefore overlies the mesiobuccal root apex — useful for angling a radiograph, for locating the apex during surgery, and for orienting the access cavity.
- C. The buccal developmental groove is a surface feature between the buccal cusps; it does not correspond to a root apex.
- D. The central groove runs between the cusps in the middle of the occlusal table and does not overlie any single root apex.