Endodontics
This domain tests diagnosis, canal anatomy, shaping and disinfection, obturation and the management of failure - the sequence that determines whether a tooth is retained or lost.
Diagnosis first
Establish pulpal status (normal, reversible pulpitis, irreversible pulpitis, necrotic, previously treated) and apical status (symptomatic or asymptomatic apical periodontitis, acute or chronic apical abscess, condensing osteitis). Cold testing and electric pulp testing assess pulp vitality; percussion and palpation assess the periapex; a sinus tract is traced with gutta-percha to its source. Radiographs supplement but never replace sensibility testing.
Anatomy you must recall
- Maxillary first molar: second mesiobuccal canal (MB2) is present in the large majority and missed in most failures.
- Mandibular first molar: usually three canals, but a second distal canal is common.
- Mandibular incisors: a second canal is present in a substantial minority.
- Mandibular second molar: C-shaped anatomy is a recognised variant, especially in East Asian populations.
Shaping, irrigation, obturation
Establish patency and working length with an apex locator confirmed radiographically, create a glide path, then shape with rotary nickel-titanium files using crown-down principles and copious irrigation. Sodium hypochlorite (0.5–5.25%) dissolves organic tissue and is antimicrobial; 17% EDTA removes the smear layer and chelates; never mix hypochlorite and chlorhexidine directly because a precipitate forms. Activation improves penetration. Obturation with gutta-percha and sealer, warm vertical or cold lateral condensation, must be followed by a coronal seal.
Worked example
A patient returns two years after root canal treatment of an upper first molar with tenderness to percussion and a periapical radiolucency; the access is through a crown and the original obturation looks short with an unfilled second mesiobuccal canal. Reasoning: post-treatment apical periodontitis with a likely missed canal and inadequate length. Orthograde retreatment - remove the coronal restoration as needed, negotiate MB2, re-instrument and re-obturate - is preferable to apical surgery here because the aetiology is intraradicular.
Traps that cost marks
- Extruding hypochlorite beyond the apex, causing severe pain and swelling.
- Accepting a working length short of the apical constriction and leaving uninstrumented apical biofilm.
- Using a radiograph alone to declare a pulp necrotic.
- Obturating without a coronal seal, which invites reinfection.