INBDE Biomedical Sciences Practice
Exam 2026 | 100 Questions & Answers
with Detailed Rationales | Integrated
National Board Dental Examination
Prep & Study Guide
1. A patient with severe ketoacidosis has an arterial pH of 7.12 and a markedly
decreased serum bicarbonate concentration. Which compensatory
response is expected?
A. Decreased respiratory rate
B. Increased renal bicarbonate secretion
C. Increased alveolar ventilation
D. Increased hydrogen ion secretion by the lungs
Answer: C. Increased alveolar ventilation
Rationale: Metabolic acidosis stimulates peripheral and central respiratory
mechanisms, producing hyperventilation that lowers PaCO₂ and partially
compensates for the reduced bicarbonate concentration.
2. A mutation prevents osteoclasts from effectively acidifying their resorption
lacunae. Which process will be most directly impaired?
,A. Osteoblast-mediated osteoid formation
B. Mineral dissolution during bone resorption
C. Collagen synthesis by osteoblasts
D. Vitamin D synthesis
Answer: B. Mineral dissolution during bone resorption
Rationale: Osteoclasts secrete hydrogen ions into the resorption lacuna,
creating an acidic environment that dissolves hydroxyapatite. Impaired
acidification therefore reduces mineral resorption.
3. A patient has a mutation affecting the β-globin gene that substitutes valine
for glutamic acid. Which structural level of hemoglobin is directly altered?
A. Quaternary structure only
B. Primary structure
C. Secondary structure only
D. Tertiary structure only
Answer: B. Primary structure
Rationale: A change in the amino acid sequence represents an alteration of
primary protein structure. In sickle cell disease, the β-globin substitution
subsequently affects hemoglobin behavior and higher-order structure.
4. Which vitamin deficiency most directly impairs hydroxylation of proline and
lysine residues during collagen synthesis?
A. Vitamin A
B. Vitamin B12
C. Vitamin C
D. Vitamin K
Answer: C. Vitamin C
Rationale: Vitamin C is required for prolyl and lysyl hydroxylases involved in
collagen maturation. Deficiency produces defective connective tissue and
impaired wound healing.
, 5. A patient receives a drug that competitively inhibits acetylcholinesterase.
Which effect is most likely at the neuromuscular junction?
A. Reduced acetylcholine concentration
B. Prolonged acetylcholine activity
C. Reduced presynaptic calcium entry
D. Irreversible blockade of nicotinic receptors
Answer: B. Prolonged acetylcholine activity
Rationale: Acetylcholinesterase normally rapidly hydrolyzes acetylcholine within
the synaptic cleft. Inhibition prolongs acetylcholine action at both muscarinic
and nicotinic receptors.
6. Which embryologic structure gives rise to the enamel organ?
A. Dental papilla
B. Dental follicle
C. Oral ectoderm
D. Neural tube
Answer: C. Oral ectoderm
Rationale: The enamel organ develops from oral ectoderm through the dental
lamina. In contrast, the dental papilla and dental follicle are derived primarily
from ectomesenchyme.
7. A patient has damage to the myelin surrounding peripheral nerves. Which
cell is primarily responsible for producing this myelin?
A. Astrocyte
B. Oligodendrocyte
C. Schwann cell
D. Microglial cell
Answer: C. Schwann cell
, Rationale: Schwann cells myelinate peripheral nervous system axons.
Oligodendrocytes perform the analogous function in the central nervous system.
8. Which immunoglobulin is most abundant in normal saliva and provides
important mucosal immune protection?
A. IgM
B. IgG
C. IgE
D. Secretory IgA
Answer: D. Secretory IgA
Rationale: Secretory IgA is the predominant immunoglobulin in saliva and other
mucosal secretions. It inhibits microbial adherence and helps neutralize
pathogens without producing extensive inflammatory damage.
9. A patient has a lesion affecting the parasympathetic fibers traveling with
cranial nerve III. Which finding is most likely?
A. Miosis with accommodation
B. Mydriasis and loss of accommodation
C. Increased lacrimation
D. Constricted pupil with preserved accommodation
Answer: B. Mydriasis and loss of accommodation
Rationale: Parasympathetic fibers associated with CN III constrict the pupil and
mediate accommodation. Their disruption produces a dilated pupil and impaired
near vision.
10.Which enzyme is considered the rate-limiting enzyme of glycolysis?
A. Hexokinase
B. Pyruvate kinase
C. Phosphofructokinase-1
D. Glucose-6-phosphatase
Exam 2026 | 100 Questions & Answers
with Detailed Rationales | Integrated
National Board Dental Examination
Prep & Study Guide
1. A patient with severe ketoacidosis has an arterial pH of 7.12 and a markedly
decreased serum bicarbonate concentration. Which compensatory
response is expected?
A. Decreased respiratory rate
B. Increased renal bicarbonate secretion
C. Increased alveolar ventilation
D. Increased hydrogen ion secretion by the lungs
Answer: C. Increased alveolar ventilation
Rationale: Metabolic acidosis stimulates peripheral and central respiratory
mechanisms, producing hyperventilation that lowers PaCO₂ and partially
compensates for the reduced bicarbonate concentration.
2. A mutation prevents osteoclasts from effectively acidifying their resorption
lacunae. Which process will be most directly impaired?
,A. Osteoblast-mediated osteoid formation
B. Mineral dissolution during bone resorption
C. Collagen synthesis by osteoblasts
D. Vitamin D synthesis
Answer: B. Mineral dissolution during bone resorption
Rationale: Osteoclasts secrete hydrogen ions into the resorption lacuna,
creating an acidic environment that dissolves hydroxyapatite. Impaired
acidification therefore reduces mineral resorption.
3. A patient has a mutation affecting the β-globin gene that substitutes valine
for glutamic acid. Which structural level of hemoglobin is directly altered?
A. Quaternary structure only
B. Primary structure
C. Secondary structure only
D. Tertiary structure only
Answer: B. Primary structure
Rationale: A change in the amino acid sequence represents an alteration of
primary protein structure. In sickle cell disease, the β-globin substitution
subsequently affects hemoglobin behavior and higher-order structure.
4. Which vitamin deficiency most directly impairs hydroxylation of proline and
lysine residues during collagen synthesis?
A. Vitamin A
B. Vitamin B12
C. Vitamin C
D. Vitamin K
Answer: C. Vitamin C
Rationale: Vitamin C is required for prolyl and lysyl hydroxylases involved in
collagen maturation. Deficiency produces defective connective tissue and
impaired wound healing.
, 5. A patient receives a drug that competitively inhibits acetylcholinesterase.
Which effect is most likely at the neuromuscular junction?
A. Reduced acetylcholine concentration
B. Prolonged acetylcholine activity
C. Reduced presynaptic calcium entry
D. Irreversible blockade of nicotinic receptors
Answer: B. Prolonged acetylcholine activity
Rationale: Acetylcholinesterase normally rapidly hydrolyzes acetylcholine within
the synaptic cleft. Inhibition prolongs acetylcholine action at both muscarinic
and nicotinic receptors.
6. Which embryologic structure gives rise to the enamel organ?
A. Dental papilla
B. Dental follicle
C. Oral ectoderm
D. Neural tube
Answer: C. Oral ectoderm
Rationale: The enamel organ develops from oral ectoderm through the dental
lamina. In contrast, the dental papilla and dental follicle are derived primarily
from ectomesenchyme.
7. A patient has damage to the myelin surrounding peripheral nerves. Which
cell is primarily responsible for producing this myelin?
A. Astrocyte
B. Oligodendrocyte
C. Schwann cell
D. Microglial cell
Answer: C. Schwann cell
, Rationale: Schwann cells myelinate peripheral nervous system axons.
Oligodendrocytes perform the analogous function in the central nervous system.
8. Which immunoglobulin is most abundant in normal saliva and provides
important mucosal immune protection?
A. IgM
B. IgG
C. IgE
D. Secretory IgA
Answer: D. Secretory IgA
Rationale: Secretory IgA is the predominant immunoglobulin in saliva and other
mucosal secretions. It inhibits microbial adherence and helps neutralize
pathogens without producing extensive inflammatory damage.
9. A patient has a lesion affecting the parasympathetic fibers traveling with
cranial nerve III. Which finding is most likely?
A. Miosis with accommodation
B. Mydriasis and loss of accommodation
C. Increased lacrimation
D. Constricted pupil with preserved accommodation
Answer: B. Mydriasis and loss of accommodation
Rationale: Parasympathetic fibers associated with CN III constrict the pupil and
mediate accommodation. Their disruption produces a dilated pupil and impaired
near vision.
10.Which enzyme is considered the rate-limiting enzyme of glycolysis?
A. Hexokinase
B. Pyruvate kinase
C. Phosphofructokinase-1
D. Glucose-6-phosphatase
