Dental MCQ
Cleaning and shaping · Endodontics · INBDE Patient Cases

Access & Canal Instrumentation INBDE Patient Cases

By Dr. Isaac Sun, DDS

7 ADA INBDE-format patient cases on access & canal instrumentation. Each case is a shared patient box (chief complaint, history, medications, allergies, exam) followed by linked multiple-choice questions with full distractor explanations. Practice the way the real exam is structured.

7 patient cases35 linked questionsADA INBDE formatFull distractor explanations

Seven ADA INBDE-format patient cases on endodontic access and canal instrumentation: a maxillary molar that fails because the second mesiobuccal (MB2) canal was missed, determining working length to the apical constriction with an apex locator and radiograph, a separated nickel-titanium instrument in a curved canal from cyclic fatigue with its prevention and management, ledge formation in a curved canal from forcing a stiff file and how a glide path and patency prevent it, over-instrumentation past the apex causing a postoperative flare, a sodium hypochlorite accident from a wedged needle with supportive management and prevention, and a furcal perforation recognized by bleeding and an apex locator and repaired with mineral trioxide aggregate. Topics include access cavity design and straight-line access, working length and patency, hand and rotary instrumentation, irrigation, and procedural errors.

Case Coverage Map
What each case is testing
A maxillary molar that won't settle after a root canal:
The missed MB2 canal, why a missed canal causes failure, finding canals with magnification and anatomy, retreatment, and access design.
Deciding exactly where to stop:
Working length to the apical constriction, apex locator plus radiograph, why the constriction (not the radiographic apex), and apical patency.
A file tip left in a curved canal:
Separated NiTi instrument from cyclic fatigue, prevention (glide path, limited cycles, no forcing), management factors, prognosis, and referral.
Losing the path in a curved canal:
Ledge formation from forcing a stiff file, prevention by glide path/patency/precurving, negotiating past a ledge, and the cost of an uncleaned apex.
Severe ache the night after instrumentation:
Over-instrumentation past the apex, lost apical stop, accurate working length, conservative flare management, and how crown-down limits extrusion.
A sudden swelling during irrigation:
Sodium hypochlorite accident, the wedged-needle cause, supportive management, prevention (side-vented needle, gentle pressure, short of length), and why NaOCl is still preferred.
An unexpected bleed through the floor:
Furcal perforation, recognition by bleeding and apex locator, MTA repair, prognosis factors, and the role of magnification and referral in difficult anatomy.
Patient case: A maxillary molar that won't settle after a root canal
0 of 5 answered, 0 correct
Patient
Female, 45 years old
Chief Complaint
"My upper back tooth still hurts months after the root canal."
Background and/or Patient History
  • Root canal completed on a maxillary first molar several months ago
  • Persistent tenderness and a lingering lesion
  • Records show three canals were treated
Allergies
NKDA
Medications
  • None
Current Findings
  • Persistent apical radiolucency on the mesiobuccal root
  • Reassessment suggests an untreated canal in the mesiobuccal root
  1. Question 1
    Moderate
    The untreated canal most likely responsible is the:
  2. Question 2
    Moderate
    A missed canal causes failure because it:
  3. Question 3
    Moderate
    What most helps locate a canal like the MB2 during access?
  4. Question 4
    Moderate
    Treating the persistent lesion now generally involves:
  5. Question 5
    Moderate
    A correctly designed access cavity would have helped by:

Reset this case?

This clears your answers for this patient case only.

Patient case: Deciding exactly where to stop
0 of 5 answered, 0 correct
Patient
Male, 36 years old
Chief Complaint
Root canal in progress on a mandibular molar.
Background and/or Patient History
  • Mid-treatment; the canal has been negotiated to the apical third
  • An apex locator reading and a working-length radiograph are being compared
  • The clinician is setting the final working length
Allergies
NKDA
Medications
  • None
Current Findings
  • Apex locator indicates the apical constriction; the radiograph shows the file near the radiographic apex
  • Canal is patent and negotiable to length
  1. Question 1
    Moderate
    The preparation should ideally terminate:
  2. Question 2
    Moderate
    How should the apex locator and radiograph be used together?
  3. Question 3
    Hard
    Why is the apical constriction the preferred endpoint rather than the radiographic apex?
  4. Question 4
    Moderate
    If the file is taken beyond the constriction to length, the risk is:
  5. Question 5
    Moderate
    Keeping a small file passing the constriction throughout shaping is called:

Reset this case?

This clears your answers for this patient case only.

Patient case: A file tip left in a curved canal
0 of 5 answered, 0 correct
Patient
Female, 41 years old
Chief Complaint
Root canal on a molar with sharply curved roots.
Background and/or Patient History
  • A nickel-titanium rotary file separated in the apical third of a curved canal
  • The file had been used in several previous cases
  • The fragment is lodged short of the working length
Allergies
NKDA
Medications
  • None
Current Findings
  • Separated instrument fragment confirmed on radiograph
  • Sharply curved canal anatomy
  1. Question 1
    Hard
    The most likely contributing cause of the file separation is:
  2. Question 2
    Moderate
    A key strategy that helps prevent instrument separation is:
  3. Question 3
    Moderate
    Management of a separated instrument depends largely on:
  4. Question 4
    Hard
    If the fragment cannot be removed, the prognosis is best when:
  5. Question 5
    Moderate
    A complex case like this (sharp curvature, separated file) is also a reasonable point to consider:

Reset this case?

This clears your answers for this patient case only.

Patient case: Losing the path in a curved canal
0 of 5 answered, 0 correct
Patient
Male, 52 years old
Chief Complaint
Root canal on a molar with a markedly curved mesial root.
Background and/or Patient History
  • During shaping, the file could no longer reach the previously established working length
  • A stiffer file had been pushed without precurving in a curved canal
  • No glide path had been carefully established first
Allergies
NKDA
Medications
  • None
Current Findings
  • An apparent ledge in the curved canal preventing the file from reaching length
  • Working length now short of the original measurement
  1. Question 1
    Moderate
    The artificial blockage preventing the file from reaching length is best described as a:
  2. Question 2
    Moderate
    The technique error that most contributed to the ledge was:
  3. Question 3
    Moderate
    The best prevention of ledges in curved canals is:
  4. Question 4
    Hard
    Once a ledge has formed, regaining the original path often requires:
  5. Question 5
    Moderate
    If the ledge cannot be bypassed and the apical canal stays uncleaned, the consequence is:

Reset this case?

This clears your answers for this patient case only.

Patient case: Severe ache the night after instrumentation
0 of 5 answered, 0 correct
Patient
Female, 29 years old
Chief Complaint
"It was fine, but after the canal appointment it ached badly that night."
Background and/or Patient History
  • Root canal instrumentation completed earlier that day
  • Marked postoperative pain and tenderness to biting overnight
  • During treatment, files were taken slightly beyond the apex
Allergies
NKDA
Medications
  • Ibuprofen
Current Findings
  • Tender to percussion; no spreading swelling
  • Working-length review suggests instrumentation went past the apical terminus
  1. Question 1
    Moderate
    The most likely cause of this flare-up is:
  2. Question 2
    Moderate
    Over-instrumentation also harms the result by:
  3. Question 3
    Moderate
    The best prevention of over-instrumentation is:
  4. Question 4
    Moderate
    Appropriate management of this postoperative flare (no spreading swelling) is generally:
  5. Question 5
    Moderate
    Crown-down instrumentation reduces this kind of flare partly because it:

Reset this case?

This clears your answers for this patient case only.

Patient case: A sudden swelling during irrigation
0 of 5 answered, 0 correct
Patient
Male, 58 years old
Chief Complaint
Sudden severe pain and rapid swelling during canal irrigation.
Background and/or Patient History
  • Mid-treatment irrigation of a maxillary tooth
  • Immediate, intense pain followed by rapid facial swelling and bruising
  • The irrigant was being delivered with the needle wedged in the canal
Allergies
NKDA
Medications
  • None
Current Findings
  • Rapid-onset swelling and severe pain immediately after irrigation
  • Consistent with sodium hypochlorite extrusion past the apex
  1. Question 1
    Moderate
    The sudden severe pain and rapid swelling during irrigation indicate:
  2. Question 2
    Moderate
    The technique factor most responsible was:
  3. Question 3
    Moderate
    Immediate management of a hypochlorite accident includes:
  4. Question 4
    Moderate
    Prevention of a hypochlorite accident centers on:
  5. Question 5
    Moderate
    Sodium hypochlorite is still the preferred irrigant despite this risk because it:

Reset this case?

This clears your answers for this patient case only.

Patient case: An unexpected bleed through the floor
0 of 5 answered, 0 correct
Patient
Female, 49 years old
Chief Complaint
Root canal access on a molar with a calcified, hard-to-read chamber.
Background and/or Patient History
  • While searching for canals, an opening through the pulpal floor was created
  • Brisk bleeding appeared from the site, away from a true canal orifice
  • An apex locator gave a reading consistent with communication to the periodontal tissues
Allergies
NKDA
Medications
  • None
Current Findings
  • A false opening through the chamber floor (furcal perforation)
  • Bleeding and an apex locator signal indicating a perforation, not a canal
  1. Question 1
    Moderate
    A false opening through the pulpal floor into the furcation is a:
  2. Question 2
    Moderate
    Clues that help recognize a perforation include:
  3. Question 3
    Moderate
    The material most commonly used to repair a perforation is:
  4. Question 4
    Moderate
    The prognosis after a perforation repair is generally better when:
  5. Question 5
    Moderate
    A calcified, hard-to-read chamber raised the perforation risk, which supports:

Reset this case?

This clears your answers for this patient case only.

Keep studying
Access & Canal Instrumentation core recall

Refresh the anatomy facts these cases depend on: nerve numbers, foramina, functions, and lesion findings.

← Back to Access & Canal Instrumentation