Dental MCQ
Cell structure and genetics · Microbiology · INBDE Patient Cases

Bacterial Structure & Function INBDE Patient Cases

By Dr. Isaac Sun, DDS

7 ADA INBDE-format patient cases on bacterial structure & function. 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 connecting bacterial structure and function to dentistry: bacterial endospores and why dental instruments are autoclaved and spore-tested rather than wiped, the Gram-negative outer membrane and lipopolysaccharide (lipid A) endotoxin that drives the inflammation of a necrotic pulp, plasmids and conjugation spreading antibiotic resistance and the case for stewardship, the low-oxygen niche that lets obligate anaerobes drive a spreading odontogenic space infection (Ludwig angina), the peptidoglycan cell wall as the penicillin target with beta-lactamase resistance and clavulanic acid, the antiphagocytic capsule and why a walled-off abscess needs incision and drainage, and the mycolic-acid acid-fast cell wall of Mycobacterium tuberculosis with airborne precautions and standard precautions. Topics include Gram staining and the cell wall, the capsule, pili, flagella and endospores, oxygen requirements and growth, and bacterial genetics and horizontal gene transfer.

Case Coverage Map
What each case is testing
A handpiece that was only wiped down:
Endospores as the most resistant form, disinfection versus sterilization, the autoclave, and spore-test verification.
A throbbing tooth with a swollen face:
Gram-negative anaerobes in a necrotic pulp, LPS (lipid A) endotoxin driving inflammation, and source control over antibiotics.
"Just call in some antibiotics":
Plasmids and conjugation spreading resistance, selection pressure, and antibiotic stewardship for a localized problem.
Spreading swelling and trouble swallowing:
Polymicrobial anaerobic deep-space infection, the low-oxygen niche, recognizing an airway-threatening Ludwig angina, and diabetes.
Why amoxicillin for the abscess:
Penicillin blocking peptidoglycan cross-linking, action on growing cells, beta-lactamase resistance, and clavulanic acid.
Why the abscess won't clear on its own:
The antiphagocytic capsule, why pus and the abscess wall defeat host defenses and drug penetration, and incision and drainage.
A persistent cough on the medical history:
The mycolic-acid acid-fast wall of Mycobacterium tuberculosis, airborne spread, deferring elective care, and standard precautions.
Patient case: A handpiece that was only wiped down
0 of 5 answered, 0 correct
Patient
Female, 34 years old
Chief Complaint
"Is it safe? I saw them just wipe the drill from the last patient."
Background and/or Patient History
  • Presented for a routine restoration
  • Noticed the assistant wipe the handpiece with a disinfectant cloth between patients
  • Asks how instruments are made safe
  • Healthy, no medical conditions
Allergies
NKDA
Medications
  • None
Current Findings
  • Cooperative and well informed
  • Office uses an autoclave with weekly spore testing
  1. Question 1
    Moderate
    The most resistant microbial form that instrument processing must destroy is the:
  2. Question 2
    Moderate
    Wiping the handpiece with a disinfectant cloth is best described as:
  3. Question 3
    Easy
    Reliable sterilization of the handpiece between patients is achieved by:
  4. Question 4
    Moderate
    The weekly spore test (biological indicator) works by checking whether the autoclave:
  5. Question 5
    Easy
    The best response to reassure this patient is that:

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Patient case: A throbbing tooth with a swollen face
0 of 5 answered, 0 correct
Patient
Male, 41 years old
Chief Complaint
"This tooth has been throbbing and now my face is swelling."
Background and/or Patient History
  • Several days of severe throbbing pain in a lower molar
  • Now with facial swelling and general malaise
  • Tooth had a large untreated cavity
  • Otherwise healthy
Allergies
NKDA
Medications
  • None
Current Findings
  • Temperature 38.3 C
  • Tooth non-responsive to cold (likely necrotic pulp)
  • Tender localized vestibular swelling
  1. Question 1
    Moderate
    The necrotic pulp space of this tooth most likely harbors a predominance of:
  2. Question 2
    Hard
    A major driver of the inflammation here is endotoxin, which is structurally:
  3. Question 3
    Hard
    Unlike a secreted exotoxin, endotoxin is:
  4. Question 4
    Moderate
    Given a non-restorable necrotic tooth with localized swelling, the primary treatment is:
  5. Question 5
    Moderate
    Antibiotics would be most clearly indicated in this patient because of:

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Patient case: "Just call in some antibiotics"
0 of 5 answered, 0 correct
Patient
Male, 52 years old
Chief Complaint
"Can you just phone in an antibiotic? It usually settles things down."
Background and/or Patient History
  • Mild discomfort around a lower molar for two days
  • Has taken leftover antibiotics for dental pain several times before
  • Requests a prescription over the phone, wants to avoid coming in
  • No fever, no swelling reported
Allergies
NKDA
Medications
  • Occasional ibuprofen
Current Findings
  • On exam, a localized reversible pulpitis from a leaking restoration
  • No swelling, no fever, no spreading infection
  1. Question 1
    Moderate
    Antibiotic-resistance genes most often spread between bacteria on:
  2. Question 2
    Moderate
    The transfer of a resistance plasmid through direct cell-to-cell contact is:
  3. Question 3
    Moderate
    Taking an antibiotic when it is not needed promotes resistance by:
  4. Question 4
    Moderate
    For this localized reversible pulpitis with no systemic signs, the appropriate management is:
  5. Question 5
    Moderate
    When an antibiotic is genuinely needed for an odontogenic infection, stewardship favors:

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Patient case: Spreading swelling and trouble swallowing
0 of 5 answered, 0 correct
Patient
Male, 38 years old
Chief Complaint
"My jaw and neck are swollen and it hurts to swallow."
Background and/or Patient History
  • Untreated lower molar infection for over a week
  • Swelling has spread under the jaw and into the upper neck
  • Now reports pain on swallowing and a muffled voice
  • Diabetic, not well controlled
Allergies
NKDA
Medications
  • Metformin
Current Findings
  • Temperature 38.7 C
  • Firm, tender bilateral submandibular swelling, elevated floor of mouth
  • Mild difficulty opening the mouth
  1. Question 1
    Moderate
    Deep fascial-space odontogenic infections like this are usually:
  2. Question 2
    Moderate
    Anaerobes thrive in the depths of this infection because that tissue is:
  3. Question 3
    Hard
    The bilateral submandibular swelling with a raised floor of mouth and difficulty swallowing should raise concern for:
  4. Question 4
    Moderate
    The most appropriate next step for this patient is to:
  5. Question 5
    Moderate
    His poorly controlled diabetes is relevant because it:

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Patient case: Why amoxicillin for the abscess
0 of 5 answered, 0 correct
Patient
Female, 29 years old
Chief Complaint
"You said amoxicillin. How does it actually kill the bacteria?"
Background and/or Patient History
  • A localized periapical abscess being treated with drainage
  • Prescribed amoxicillin because of early spreading signs
  • Curious dental hygiene student who asks about the mechanism
  • No drug allergies
Allergies
NKDA
Medications
  • None
Current Findings
  • Localized abscess, drainage established
  • Mild early cellulitis, no airway concern
  1. Question 1
    Moderate
    Amoxicillin (a penicillin) kills bacteria by inhibiting synthesis of the:
  2. Question 2
    Hard
    Penicillins tend to act only on bacteria that are:
  3. Question 3
    Moderate
    Amoxicillin is a reasonable first choice for many odontogenic infections because oral flora include many:
  4. Question 4
    Moderate
    Some bacteria resist amoxicillin by producing beta-lactamase, which:
  5. Question 5
    Moderate
    The agent added to amoxicillin to overcome beta-lactamase is:

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Patient case: Why the abscess won't clear on its own
0 of 5 answered, 0 correct
Patient
Male, 45 years old
Chief Complaint
"I figured my body would just fight it off, but the swelling stayed."
Background and/or Patient History
  • A localized buccal-space abscess from a non-vital tooth
  • Waited two weeks hoping it would resolve on its own
  • Swelling persisted with a pointing, fluctuant area
  • Otherwise healthy
Allergies
NKDA
Medications
  • None
Current Findings
  • Fluctuant, well-localized swelling with pus
  • No fever, no spreading cellulitis
  1. Question 1
    Moderate
    The bacterial surface structure that helps organisms evade phagocytosis is the:
  2. Question 2
    Hard
    Within an established abscess, host defenses are further limited because:
  3. Question 3
    Moderate
    Because of these defenses, the definitive treatment of a fluctuant abscess is:
  4. Question 4
    Moderate
    Antibiotics alone are often insufficient for a walled-off abscess mainly because:
  5. Question 5
    Easy
    The general principle this case illustrates is that for many dental infections:

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Patient case: A persistent cough on the medical history
0 of 5 answered, 0 correct
Patient
Male, 47 years old
Chief Complaint
"I need a cleaning, but I should mention I've been coughing for weeks."
Background and/or Patient History
  • Presented for routine cleaning and a filling
  • Reports several weeks of productive cough, night sweats, and weight loss
  • Recently arrived from a region with high tuberculosis prevalence
  • Not yet evaluated by a physician
Allergies
NKDA
Medications
  • None
Current Findings
  • Appears thin and fatigued
  • Chronic cough; no oral lesions today
  1. Question 1
    Hard
    The organism of concern, Mycobacterium tuberculosis, has a cell wall rich in:
  2. Question 2
    Moderate
    Because of that waxy wall, mycobacteria are identified with which stain?
  3. Question 3
    Moderate
    Active pulmonary tuberculosis spreads chiefly by:
  4. Question 4
    Moderate
    For this patient with possible active tuberculosis, elective dental treatment today should be:
  5. Question 5
    Easy
    The everyday infection-control practice that protects against undiagnosed bloodborne and many other pathogens is:

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Bacterial Structure & Function core recall

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

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