Dental MCQ
Electrolyte and ECG safety · Renal & GI · INBDE Patient Cases

Fluid & Electrolytes INBDE Patient Cases

By Dr. Isaac Sun, DDS

9 ADA INBDE-format patient cases on fluid & electrolytes. 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.

9 patient cases45 linked questionsADA INBDE formatFull distractor explanations

Nine ADA INBDE-format patient cases on fluid, electrolyte, and acid-base balance in the dental setting: post-thyroidectomy hypoparathyroidism with perioral tingling and a Chvostek sign, primary hyperparathyroidism with hypercalcemia and a brown tumor found on a panoramic radiograph, drug-induced hyponatremia causing confusion in an elderly patient on a thiazide and an SSRI, hyperkalemia with peaked T waves after missed dialysis, diabetic ketoacidosis with Kussmaul breathing and acetone breath, failure of an inferior alveolar nerve block in acidic infected tissue, diuretic-related volume depletion and orthostatic hypotension before sedation, hypomagnesemia causing refractory hypokalemia in a patient with heavy alcohol use, and acute fluoride ingestion in a child causing hypocalcemia. Topics include body fluid compartments, sodium and potassium balance, calcium and magnesium regulation, parathyroid hormone and calcitriol, the anion gap, metabolic acidosis and alkalosis, and respiratory compensation.

Case Coverage Map
What each case is testing
Lips tingling weeks after thyroid surgery:
Post-surgical hypoparathyroidism and hypocalcemia, perioral tingling and the Chvostek sign, QT prolongation, and deferral with referral.
Kidney stones, fatigue, and odd jaw bone on X-ray:
Primary hyperparathyroidism with hypercalcemia, the parathyroid adenoma, the lab pattern, the brown tumor, and medical referral.
An elderly patient suddenly confused:
Drug-induced hyponatremia in the elderly, confusion and consent, deferral, and the danger of over-rapid correction.
Missed dialysis and now the heart feels funny:
Hyperkalemia after missed dialysis, peaked T waves, canceling care for an emergency, and drugs that raise potassium.
Toothache plus thirst, nausea, and fruity breath:
Diabetic ketoacidosis, high anion gap acidosis, Kussmaul breathing and acetone breath, and activating emergency care.
The numbing shot won't work on an infected tooth:
Why local anesthesia fails in acidic infected tissue, the un-ionized base, blocking away from the infection, and source control.
Dizzy and dry-mouthed before sedation:
Diuretic-related volume depletion, orthostatic hypotension, sedation risk, and rehydrating before treatment.
Cramps and weakness with heavy alcohol use:
Hypomagnesemia driving refractory hypokalemia and hypocalcemia, arrhythmia risk, alcohol-related bleeding, and medical coordination.
A child swallowed the fluoride rinse:
Acute fluoride toxicity binding calcium, early GI symptoms, milk as a binder, and urgent care with poison control.
Patient case: Lips tingling weeks after thyroid surgery
0 of 5 answered, 0 correct
Patient
Female, 45 years old
Chief Complaint
"My lips and fingertips have been tingling, and my face feels twitchy."
Background and/or Patient History
  • Presented for a routine restorative visit
  • Total thyroidectomy six weeks ago
  • Reports tingling around the mouth and in the fingers
  • Occasional hand cramps
Allergies
NKDA
Medications
  • Levothyroxine
  • Calcium and vitamin D supplements (admits she often forgets them)
Current Findings
  • Tapping over the facial nerve in front of the ear triggers a brief facial twitch
  • No local anesthetic given today
  • Vitals normal
  1. Question 1
    Moderate
    Her perioral tingling and facial twitch most likely reflect:
  2. Question 2
    Moderate
    The most likely cause after her recent surgery is:
  3. Question 3
    Moderate
    The facial twitch elicited by tapping the facial nerve is called a:
  4. Question 4
    Moderate
    Which finding would you also expect with significant hypocalcemia?
  5. Question 5
    Moderate
    The appropriate dental response is to:

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Patient case: Kidney stones, fatigue, and odd jaw bone on X-ray
0 of 5 answered, 0 correct
Patient
Female, 60 years old
Chief Complaint
"I'm here for a checkup; I've also had kidney stones and feel tired."
Background and/or Patient History
  • Routine new-patient exam with a panoramic radiograph
  • History of recurrent kidney stones
  • Reports fatigue, constipation, and bone aches
  • No chronic kidney disease, not on dialysis
Allergies
NKDA
Medications
  • None
Current Findings
  • Panoramic film shows generalized loss of the lamina dura and a ground-glass trabecular pattern
  • A well-defined radiolucency in the mandible
  • No carious cause for the findings
  1. Question 1
    Hard
    Combined with stones, fatigue, and bone aches, the radiographic changes suggest:
  2. Question 2
    Hard
    Because she has no kidney disease and is not on dialysis, the most likely mechanism is:
  3. Question 3
    Hard
    Her laboratory pattern would most likely show:
  4. Question 4
    Hard
    The well-defined mandibular radiolucency most likely represents a:
  5. Question 5
    Moderate
    The most appropriate dental action is to:

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Patient case: An elderly patient suddenly confused
0 of 5 answered, 0 correct
Patient
Female, 78 years old
Chief Complaint
Daughter: "She's more confused than usual today and seems out of it."
Background and/or Patient History
  • Brought by her daughter for a denture adjustment
  • Treated for hypertension with a thiazide diuretic
  • Recently started on an antidepressant (SSRI)
  • Increasingly drowsy and disoriented over two days
Allergies
NKDA
Medications
  • Hydrochlorothiazide
  • Sertraline
Current Findings
  • Disoriented to time and place
  • BP 128/76, afebrile
  • No focal weakness or facial droop
  1. Question 1
    Moderate
    Her confusion, given her medications, is most concerning for:
  2. Question 2
    Moderate
    Both of her medications can lower sodium because they promote:
  3. Question 3
    Moderate
    The safest immediate step is to:
  4. Question 4
    Easy
    A key reason not to proceed is that she cannot:
  5. Question 5
    Hard
    Correcting severe hyponatremia too quickly is dangerous because it can cause:

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Patient case: Missed dialysis and now the heart feels funny
0 of 5 answered, 0 correct
Patient
Male, 50 years old
Chief Complaint
"I missed my dialysis this week, and now I feel weak and my heart feels funny."
Background and/or Patient History
  • Presented for an urgent extraction
  • End-stage renal disease on hemodialysis
  • Missed his last two dialysis sessions
  • Reports generalized weakness and palpitations
Allergies
NKDA
Medications
  • Antihypertensives
  • Phosphate binder
Current Findings
  • Looks unwell, with mild muscle weakness
  • An office ECG shows tall, peaked T waves
  • BP 150/92
  1. Question 1
    Moderate
    The peaked T waves and weakness after missed dialysis most likely indicate:
  2. Question 2
    Moderate
    The most appropriate action is to:
  3. Question 3
    Easy
    Untreated, severe hyperkalemia most dangerously leads to:
  4. Question 4
    Moderate
    Which medication would be especially harmful to give him now?
  5. Question 5
    Moderate
    Once stabilized, invasive dental care for this patient is best done:

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Patient case: Toothache plus thirst, nausea, and fruity breath
0 of 5 answered, 0 correct
Patient
Male, 24 years old
Chief Complaint
"My tooth hurts, but honestly I've been feeling terrible, thirsty and nauseated."
Background and/or Patient History
  • Presented for a painful tooth
  • Type 1 diabetes; admits he ran out of insulin a few days ago
  • Excessive thirst, frequent urination, nausea, and abdominal pain
  • Rapid, deep breathing noted in the waiting room
Allergies
NKDA
Medications
  • Insulin (recently missed doses)
Current Findings
  • Fruity odor on the breath
  • Deep, rapid (Kussmaul) respirations
  • Dry mucous membranes and a rapid pulse
  1. Question 1
    Moderate
    His presentation is most concerning for:
  2. Question 2
    Moderate
    His acid-base disturbance is a:
  3. Question 3
    Moderate
    His deep, rapid breathing is:
  4. Question 4
    Easy
    The fruity odor is due to:
  5. Question 5
    Moderate
    The correct dental response is to:

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Patient case: The numbing shot won't work on an infected tooth
0 of 5 answered, 0 correct
Patient
Male, 36 years old
Chief Complaint
"This back tooth is throbbing and the numbing shot isn't working."
Background and/or Patient History
  • Presented with a severe toothache on a lower molar
  • Swelling and acute infection around tooth #30
  • Two inferior alveolar nerve blocks have failed to achieve profound anesthesia
  • No medical conditions
Allergies
NKDA
Medications
  • None
Current Findings
  • Localized swelling and erythema near tooth #30
  • Tooth tender to percussion
  • Patient still feels sharp pain on access
  1. Question 1
    Hard
    A common physiologic reason local anesthesia fails in acutely infected tissue is that the tissue is:
  2. Question 2
    Hard
    Local anesthetics block nerves only after the un-ionized (base) form:
  3. Question 3
    Moderate
    A practical way to achieve anesthesia here is to:
  4. Question 4
    Moderate
    Definitive relief for this acutely infected tooth also requires:
  5. Question 5
    Moderate
    Why might an antibiotic alone fail to relieve his pain?

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Patient case: Dizzy and dry-mouthed before sedation
0 of 5 answered, 0 correct
Patient
Male, 74 years old
Chief Complaint
"I felt dizzy standing up, and my mouth is really dry."
Background and/or Patient History
  • Scheduled for an extraction with oral sedation
  • Takes a diuretic for blood pressure and heart failure
  • Ate and drank little today and skipped his usual fluids
  • Felt lightheaded when standing
Allergies
NKDA
Medications
  • Furosemide
  • Lisinopril
Current Findings
  • Dry oral mucosa
  • BP 118/74 sitting, dropping to 96/60 on standing
  • Pulse rises on standing
  1. Question 1
    Moderate
    His dizziness on standing and dry mouth most likely reflect:
  2. Question 2
    Moderate
    Orthostatic hypotension here is best explained by:
  3. Question 3
    Moderate
    Adding oral sedation now would be risky mainly because it can:
  4. Question 4
    Moderate
    The most appropriate plan is to:
  5. Question 5
    Moderate
    His diuretic may also have caused an electrolyte problem, most likely:

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Patient case: Cramps and weakness with heavy alcohol use
0 of 5 answered, 0 correct
Patient
Male, 52 years old
Chief Complaint
"My muscles keep cramping and I feel weak."
Background and/or Patient History
  • Presented for multiple extractions
  • Long history of heavy alcohol use and poor diet
  • Reports persistent muscle cramps and weakness
  • His physician notes potassium that stays low despite supplements
Allergies
NKDA
Medications
  • Potassium supplement (potassium stays low)
Current Findings
  • Generalized weakness
  • Poor oral hygiene with several non-restorable teeth
  • Reports easy bruising
  1. Question 1
    Hard
    His potassium that will not correct despite supplements most likely reflects coexisting:
  2. Question 2
    Hard
    Low magnesium can also cause:
  3. Question 3
    Moderate
    His low potassium and magnesium together increase the risk of:
  4. Question 4
    Moderate
    His easy bruising in the setting of heavy alcohol use should prompt concern about:
  5. Question 5
    Moderate
    The most appropriate approach before his extractions is to:

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Patient case: A child swallowed the fluoride rinse
0 of 5 answered, 0 correct
Patient
Female, 4 years old, accompanied by parent
Chief Complaint
Parent: "She swallowed a big gulp of the fluoride rinse and now she's drooling and vomiting."
Background and/or Patient History
  • At the office for a routine pediatric visit
  • Swallowed a large amount of a concentrated fluoride product
  • Now nauseated, vomiting, and complaining of stomach pain
  • Drooling and looks distressed
Allergies
NKDA
Medications
  • None
Current Findings
  • Vomiting and abdominal pain
  • Hypersalivation
  • Alert but uncomfortable
  1. Question 1
    Moderate
    Acute fluoride ingestion is dangerous partly because fluoride binds:
  2. Question 2
    Moderate
    Early symptoms of acute fluoride toxicity are mainly:
  3. Question 3
    Moderate
    A reasonable immediate measure in the office is to give:
  4. Question 4
    Moderate
    If a large amount was swallowed, the appropriate action is to:
  5. Question 5
    Easy
    This case reinforces which preventive practice with high-concentration fluoride products?

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Keep studying
Fluid & Electrolytes core recall

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

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