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PMC Dentistry Licensure practice questions

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Question 1Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

During a mandibular nerve block, the needle passes near the structure that provides general sensation to the anterior two-thirds of the tongue. Which cranial nerve carries these fibers?

  1. Facial nerve (CN VII)
  2. Glossopharyngeal nerve (CN IX)
  3. Hypoglossal nerve (CN XII)
  4. Lingual branch of the trigeminal nerve (CN V3) Correct answer.

Explanation

General sensation from the anterior two-thirds of the tongue travels via the lingual nerve, a branch of the mandibular division of the trigeminal nerve. Taste from the same region is carried by the chorda tympani, which travels along with the lingual nerve but is a facial nerve branch. Distinguishing general sensation from special taste is the key clinical point.

Question 2Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient's blood pressure is recorded as 118/76 mmHg. Which vascular event corresponds to the second number in this reading?

  1. Passive recoil of the arterial wall during ventricular relaxation Correct answer.
  2. Peak pressure generated during ventricular ejection
  3. Ventricular depolarization recorded on ECG
  4. Closure of the semilunar valves at end of systole

Explanation

Diastolic pressure reflects the elastic recoil of the large arteries while the ventricles are relaxed and filling. Systolic pressure, the higher value, reflects peak ventricular ejection. The difference between them, the pulse pressure, depends largely on stroke volume and arterial compliance.

Question 3Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A child is brought in with a sore throat and a greyish pseudomembrane adhering to the tonsils. The causative organism is a Gram-positive, club-shaped rod. Which organism is most likely responsible?

  1. Corynebacterium diphtheriae Correct answer.
  2. Streptococcus pyogenes
  3. Neisseria gonorrhoeae
  4. Candida albicans

Explanation

Corynebacterium diphtheriae is a Gram-positive, pleomorphic, club-shaped rod that produces an exotoxin causing a firmly adherent grey pseudomembrane. The toxin can damage the myocardium and peripheral nerves. Streptococcus pyogenes produces a different picture with exudative pharyngitis and does not form this characteristic adherent membrane.

Question 4Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

An enzyme follows Michaelis-Menten kinetics. At a substrate concentration equal to twice the Km, what fraction of Vmax is observed?

  1. Three-quarters
  2. Two-thirds Correct answer.
  3. One-half
  4. One-third

Explanation

Applying the Michaelis-Menten equation, v = Vmax[S]/(Km+[S]). Substituting [S]=2Km gives v = Vmax(2Km)/(3Km), so the velocity equals two-thirds of Vmax. This illustrates that the reaction approaches but never reaches Vmax at finite substrate concentrations.

Question 5Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which component of the periodontium is primarily responsible for transmitting occlusal forces from the tooth to bone?

  1. Gingival epithelium
  2. Periodontal ligament Correct answer.
  3. Alveolar bone proper
  4. Cementum

Explanation

The periodontal ligament is a dense connective tissue containing collagen fiber bundles that suspend the tooth in the alveolus and transmit and dissipate occlusal forces. Its oblique principal fibers convert vertical forces into tension on bone. Cementum anchors these fibers but does not itself absorb force.

Question 6Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient taking warfarin presents for an extraction. Which laboratory test best reflects the anticoagulant effect of this drug?

  1. International normalized ratio (INR) Correct answer.
  2. Platelet count
  3. Activated partial thromboplastin time (aPTT)
  4. Bleeding time

Explanation

Warfarin inhibits vitamin K-dependent carboxylation of factors II, VII, IX, and X, prolonging the extrinsic pathway. The INR standardizes prothrombin time, which measures this pathway, and is the appropriate monitoring test. The aPTT reflects the intrinsic pathway and is used for heparin monitoring.

Question 7Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which cell type is the principal producer of collagen fibers in healing gingival connective tissue?

  1. Plasma cell
  2. Fibroblast Correct answer.
  3. Macrophage
  4. Osteoblast

Explanation

Fibroblasts are the dominant cells of the periodontal connective tissue and synthesize collagen, elastin, and ground substance during repair. They also participate in collagen turnover through matrix metalloproteinases. Osteoblasts produce bone matrix, not gingival collagen.

Question 8Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which vitamin deficiency classically causes impaired collagen cross-linking and therefore bleeding gums and delayed wound healing?

  1. Vitamin A
  2. Vitamin C Correct answer.
  3. Vitamin D
  4. Vitamin K

Explanation

Vitamin C is a cofactor for prolyl and lysyl hydroxylase, enzymes required for collagen cross-linking. Deficiency impairs collagen synthesis, producing gingival bleeding, poor wound healing, and scorbutic changes. Vitamin K deficiency instead impairs synthesis of clotting factors.

Question 9Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A dental patient with poorly controlled type 1 diabetes develops rapid periodontal destruction. Which mechanism best explains this increased susceptibility?

  1. Increased salivary pH
  2. Enhanced neutrophil chemotaxis
  3. Advanced glycation end-product accumulation Correct answer.
  4. Reduced capillary basement membrane thickness

Explanation

Chronic hyperglycemia drives non-enzymatic glycation of proteins, forming advanced glycation end-products that bind receptors on macrophages and fibroblasts. This amplifies inflammatory cytokine release and impairs collagen turnover, accelerating periodontal breakdown. Diabetes also impairs neutrophil function rather than enhancing it.

Question 10Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A local anesthetic is formulated with epinephrine. Which mechanism explains why epinephrine prolongs the anesthetic effect?

  1. It raises the pKa of the anesthetic molecule
  2. It causes local vasoconstriction reducing anesthetic clearance Correct answer.
  3. It increases nerve membrane permeability to sodium
  4. It blocks potassium channels in the axon

Explanation

Epinephrine stimulates alpha-adrenergic receptors in local vessels, producing vasoconstriction that slows removal of the anesthetic from the injection site. This prolongs duration and reduces systemic absorption and toxicity. It does not alter the anesthetic's channel-blocking mechanism or its pKa.

Question 11Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A lesion on the lateral border of the tongue shows dysplastic squamous epithelium confined above the basement membrane. What is the most appropriate diagnosis?

  1. Verrucous carcinoma
  2. Squamous cell carcinoma in situ Correct answer.
  3. Pleomorphic adenoma
  4. Invasive squamous cell carcinoma

Explanation

When dysplastic squamous epithelium remains confined above an intact basement membrane, the lesion is carcinoma in situ. Invasion through the basement membrane into underlying connective tissue defines invasive carcinoma. Recognizing this boundary is critical because it determines staging and treatment.

Question 12Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which structure separates the submandibular space from the sublingual space and influences the spread of dental infection?

  1. Mylohyoid muscle Correct answer.
  2. Buccinator muscle
  3. Palatoglossus muscle
  4. Masseter muscle

Explanation

The mylohyoid muscle forms the floor of the mouth and divides the sublingual space above from the submandibular space below. Infections from mandibular molars can spread into the submandibular space along this boundary. This anatomy explains why submandibular swelling may develop from a lower molar abscess.

Question 13Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient hyperventilates during a stressful procedure. Which acid-base change is expected?

  1. Respiratory acidosis
  2. Respiratory alkalosis Correct answer.
  3. Metabolic acidosis
  4. Metabolic alkalosis

Explanation

Hyperventilation increases alveolar ventilation and eliminates carbon dioxide faster than it is produced, lowering arterial PCO2. The resulting fall in carbonic acid shifts the bicarbonate-to-carbonic acid ratio upward, producing respiratory alkalosis. Compensation is renal and occurs slowly.

Question 14Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A 45-year-old reports recurrent episodes of intense throbbing pain in the lower face triggered by cold drinks and touch, with pain-free intervals. Which diagnosis is most consistent?

  1. Acute pulpitis
  2. Atypical odontalgia
  3. Trigeminal neuralgia Correct answer.
  4. Temporomandibular joint disorder

Explanation

Trigeminal neuralgia produces paroxysmal, lancinating pain in a trigeminal distribution triggered by innocuous stimuli such as touch or cold, with symptom-free intervals. The pain is not typically provoked by a specific carious tooth and does not follow a pulpitis pattern of continuous thermal sensitivity. Clinical examination and imaging help exclude odontogenic causes.

Question 15Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which immunoglobulin is the main antibody in saliva that limits microbial colonization of mucosal surfaces?

  1. IgM
  2. IgG
  3. IgA Correct answer.
  4. IgE

Explanation

Secretory IgA is produced by plasma cells near mucosal surfaces and transported across epithelium with a secretory component. It agglutinates bacteria and blocks adhesion to oral mucosa, a key innate-adaptive barrier. IgG predominates in serum and gingival crevicular fluid rather than whole saliva.

Question 16Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

During the cardiac cycle, which event immediately follows closure of the atrioventricular valves?

  1. Ventricular filling
  2. Atrial systole
  3. Isovolumetric ventricular contraction Correct answer.
  4. Aortic valve opening

Explanation

Closure of the atrioventricular valves marks the start of ventricular systole. Because both the AV and semilunar valves are closed, the ventricles contract without changing volume, a phase called isovolumetric contraction. Once ventricular pressure exceeds aortic pressure, the semilunar valves open.

Question 17Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A drug that inhibits cyclooxygenase-1 in the stomach most directly reduces which protective factor?

  1. Bicarbonate secretion
  2. Prostaglandin-mediated mucosal protection Correct answer.
  3. Gastric acid secretion
  4. Mucus secretion

Explanation

COX-1 produces prostaglandins that stimulate mucus and bicarbonate secretion and maintain mucosal blood flow. Inhibiting COX-1 reduces this prostaglandin-mediated protection, predisposing to ulceration. Acid secretion itself is driven mainly by histamine, gastrin, and acetylcholine acting on parietal cells.

Question 18Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

In a patient with chronic kidney disease, accumulation of which substance most directly causes secondary hyperparathyroidism?

  1. Increased phosphate and decreased calcitriol Correct answer.
  2. Increased calcium and increased calcitriol
  3. Decreased phosphate and increased calcitriol
  4. Increased calcitonin and decreased phosphate

Explanation

Failing kidneys retain phosphate and reduce 1-alpha-hydroxylation of vitamin D, lowering calcitriol. The resulting hypocalcemia and hyperphosphatemia stimulate parathyroid hormone release, producing secondary hyperparathyroidism and bone resorption. This is relevant to jawbone changes in renal osteodystrophy.

Question 19Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which bacterial product is primarily responsible for the tissue destruction seen in aggressive periodontitis through direct cytotoxicity and immune activation?

  1. Lipopolysaccharide Correct answer.
  2. Tetanospasmin
  3. Streptolysin O
  4. Cholera toxin

Explanation

Lipopolysaccharide from Gram-negative periodontal pathogens such as Porphyromonas gingivalis activates toll-like receptor 4 on host cells, triggering cytokine release and matrix metalloproteinase production. This indirect host response drives most connective tissue and bone destruction. Streptolysin, cholera toxin, and tetanospasmin are unrelated toxins.

Question 20Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient with a history of rheumatic fever is scheduled for periodontal scaling. Which preventive measure is most appropriate?

  1. Prescribe topical antifungal rinse
  2. Delay all dental treatment indefinitely
  3. Antibiotic prophylaxis before the procedure Correct answer.
  4. No prophylaxis is needed for scaling

Explanation

Current guidelines recommend antibiotic prophylaxis before invasive dental procedures for patients with specific cardiac conditions, including a history of infective endocarditis or prosthetic valves, and some cases of rheumatic heart disease with valvular damage. The goal is to prevent bacteremia-related endocarditis. Decisions should follow current cardiology guidance and the patient's cardiac status.

Question 21Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which nerve is most at risk during surgical removal of an impacted mandibular third molar, producing temporary or permanent lingual sensory loss?

  1. Facial nerve
  2. Hypoglossal nerve
  3. Lingual nerve Correct answer.
  4. Glossopharyngeal nerve

Explanation

The lingual nerve runs close to the lingual cortex of the mandible in the third molar region and can be injured during retraction or bone removal. Injury causes loss of general sensation and taste on the anterior tongue. The inferior alveolar nerve is also at risk but is a separate structure.

Question 22Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient presents with unilateral facial paralysis, inability to close the eye, and loss of taste on the anterior tongue. Which nerve is affected?

  1. Trigeminal nerve
  2. Glossopharyngeal nerve
  3. Facial nerve Correct answer.
  4. Optic nerve

Explanation

The facial nerve supplies the muscles of facial expression and carries taste from the anterior two-thirds of the tongue via the chorda tympani. A lesion produces ipsilateral facial weakness and taste loss. The trigeminal nerve supplies sensation but not facial motor function.

Question 23Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient with a history of infective endocarditis requires dental treatment. Which organism is most commonly implicated in bacteremia from oral procedures?

  1. Streptococcus viridans Correct answer.
  2. Escherichia coli
  3. Mycobacterium tuberculosis
  4. Clostridium tetani

Explanation

Viridans group streptococci are normal oral flora and are the most common cause of subacute infective endocarditis following dental procedures. They adhere to damaged endocardium and form vegetations. Enteric organisms, anaerobes, and mycobacteria are less typical in this setting.

Question 24Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient with a known deficiency of vitamin B12 presents with glossitis and megaloblastic anemia. Which biochemical role of B12 explains these findings?

  1. Cofactor for methionine synthase and methylmalonyl-CoA mutase Correct answer.
  2. Substrate for fatty acid oxidation
  3. Inhibitor of folate absorption
  4. Cofactor for pyruvate dehydrogenase

Explanation

Vitamin B12 is a cofactor for methionine synthase, which regenerates tetrahydrofolate for DNA synthesis, and for methylmalonyl-CoA mutase, which converts methylmalonyl-CoA to succinyl-CoA. Deficiency causes megaloblastic anemia and neurologic dysfunction. The tongue changes reflect epithelial turnover impairment.

Question 25Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient with a history of gastric surgery develops iron-deficiency anemia. Which mechanism best explains this?

  1. Increased transferrin saturation
  2. Increased hepcidin production
  3. Reduced erythropoietin secretion
  4. Reduced gastric acid impairing iron absorption Correct answer.

Explanation

Gastric acid converts dietary ferric iron to the more absorbable ferrous form and aids its uptake in the duodenum. After gastric surgery, reduced acid and altered anatomy impair iron absorption, leading to iron-deficiency anemia. Hepcidin and erythropoietin are not the primary cause in this setting.

Question 26Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which enzyme converts angiotensin I to angiotensin II, the peptide that raises blood pressure and stimulates aldosterone release?

  1. Cyclooxygenase
  2. Aldosterone synthase
  3. Angiotensin-converting enzyme Correct answer.
  4. Renin

Explanation

Angiotensin-converting enzyme (ACE) is a carboxypeptidase located mainly on the luminal surface of pulmonary and renal endothelium that cleaves angiotensin I into the active octapeptide angiotensin II. Angiotensin II is a potent vasoconstrictor and stimulates aldosterone secretion from the adrenal zona glomerulosa. This pathway is relevant to dentistry because patients on ACE inhibitors may develop dry cough and, more rarely, angioedema of the lips and tongue.

Question 27Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

In the glycolytic pathway, which enzyme catalyzes the rate-limiting step and is inhibited by ATP and citrate while activated by fructose-2,6-bisphosphate?

  1. Glucose-6-phosphatase
  2. Pyruvate kinase
  3. Hexokinase
  4. Phosphofructokinase-1 Correct answer.

Explanation

Phosphofructokinase-1 catalyzes the committed, rate-limiting step of glycolysis, phosphorylating fructose-6-phosphate to fructose-1,6-bisphosphate. It is allosterically inhibited by high ATP and citrate, signaling abundant energy, and activated by fructose-2,6-bisphosphate and AMP. Understanding this regulation matters clinically because ischemic or hypoxic dental pulp shifts toward anaerobic glycolysis and lactate accumulation.

Question 28Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A Gram-positive coccus grows in chains on blood agar and produces a zone of complete (beta) hemolysis. Which organism is most consistent with this description?

  1. Staphylococcus epidermidis
  2. Streptococcus pneumoniae
  3. Streptococcus pyogenes Correct answer.
  4. Enterococcus faecalis

Explanation

Streptococcus pyogenes is a group A beta-hemolytic streptococcus that grows in chains and causes pharyngitis, impetigo, and scarlet fever. Beta hemolysis reflects complete lysis of erythrocytes via streptolysin S and O. This organism is clinically relevant to dentistry because untreated streptococcal pharyngitis can lead to rheumatic fever, which affects antibiotic prophylaxis decisions.

Question 29Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient with chronic periodontitis undergoes scaling, and a small amount of bacteria enters the bloodstream. Which immune process most directly neutralizes circulating bacterial antigens before they can cause systemic effects?

  1. Formation of antigen-antibody immune complexes cleared by the spleen
  2. Activation of cytotoxic T lymphocytes
  3. Opsonization by complement C3b followed by phagocytosis Correct answer.
  4. Degranulation of mast cells with histamine release

Explanation

Opsonization coats bacteria with complement fragment C3b and antibodies, enabling recognition and phagocytosis by neutrophils and macrophages. This is the principal mechanism for clearing transient bacteremia after dental procedures. Mast cell degranulation and cytotoxic T cells do not directly neutralize circulating bacteria in this setting.

Question 30Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient taking a beta-blocker for hypertension develops bronchospasm during a dental visit. Which pharmacologic property most explains this adverse effect?

  1. Direct histamine release from mast cells
  2. Blockade of beta-2 receptors in bronchial smooth muscle Correct answer.
  3. Nonselective blockade of beta-1 receptors in the heart
  4. Alpha-1 receptor antagonism causing vasodilation

Explanation

Beta-2 receptors mediate bronchodilation in airway smooth muscle; nonselective beta-blockers block these receptors and can precipitate bronchospasm, especially in patients with asthma. Cardioselective agents are preferred when a beta-blocker is required. This is a key consideration when reviewing a dental patient's medication list before administering epinephrine-containing local anesthetics.

Question 31Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient on long-term aspirin therapy for cardiovascular protection reports easy bruising. Which mechanism best explains the prolonged bleeding time?

  1. Irreversible acetylation of platelet cyclooxygenase-1, reducing thromboxane A2 Correct answer.
  2. Direct lysis of fibrin clots
  3. Inhibition of vitamin K-dependent clotting factor synthesis
  4. Activation of antithrombin III

Explanation

Aspirin irreversibly acetylates platelet cyclooxygenase-1, blocking thromboxane A2 synthesis and impairing platelet aggregation for the life of the platelet, about 7 to 10 days. This prolongs bleeding time while coagulation tests such as PT and aPTT remain normal. Dentists must consider this before surgical procedures because platelet function recovers only as new platelets are produced.

Question 32Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

Which structure passes through the parotid gland and is at risk during parotid surgery, with injury causing paralysis of the muscles of facial expression?

  1. Glossopharyngeal nerve (cranial nerve IX)
  2. Trigeminal motor root (cranial nerve V)
  3. Facial nerve (cranial nerve VII) Correct answer.
  4. Hypoglossal nerve (cranial nerve XII)

Explanation

The facial nerve exits the stylomastoid foramen and traverses the parotid gland, dividing into temporal, zygomatic, buccal, marginal mandibular, and cervical branches. Injury during parotid surgery causes ipsilateral facial palsy. The trigeminal motor root supplies muscles of mastication, while the hypoglossal and glossopharyngeal nerves supply the tongue and pharynx respectively.

Question 33Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient with a history of infective endocarditis requires a dental extraction. Which organism is most commonly implicated in native-valve endocarditis following transient bacteremia of oral origin?

  1. Streptococcus viridans Correct answer.
  2. Clostridium tetani
  3. Mycoplasma pneumoniae
  4. Escherichia coli

Explanation

Viridans group streptococci, such as Streptococcus mutans and Streptococcus sanguinis, are normal oral flora and are the most common cause of subacute native-valve endocarditis after dental procedures. They adhere to damaged endocardium and form vegetations. This is why antibiotic prophylaxis is considered for high-risk cardiac patients before invasive dental procedures.

Question 34Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient with a known deficiency of vitamin B12 presents with glossitis and megaloblastic anemia. Which biochemical role of vitamin B12 best explains the megaloblastic changes?

  1. Activation of vitamin K-dependent carboxylase
  2. Cofactor for prolyl hydroxylase in collagen synthesis
  3. Cofactor for methionine synthase, needed to regenerate tetrahydrofolate for thymidylate synthesis Correct answer.
  4. Direct incorporation into hemoglobin heme

Explanation

Vitamin B12 is a cofactor for methionine synthase, which converts homocysteine to methionine and regenerates tetrahydrofolate. Without tetrahydrofolate, thymidylate synthesis fails, causing impaired DNA replication and megaloblastic anemia. This explains why B12 deficiency produces the same megaloblastic picture as folate deficiency.

Question 35Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

During the action potential of a ventricular cardiac myocyte, which ion influx is primarily responsible for the plateau phase?

  1. Chloride influx through ligand-gated channels
  2. Potassium efflux through inward rectifier channels
  3. Calcium influx through L-type channels Correct answer.
  4. Sodium influx through fast channels

Explanation

The plateau phase of the ventricular action potential results from slow inward calcium current through L-type calcium channels, balanced by potassium efflux. This prolongs the action potential and refractory period, preventing tetanic contraction. Calcium channel blockers used for hypertension reduce this current and depress contractility.

Question 36Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient with a history of peptic ulcer disease is prescribed a nonsteroidal anti-inflammatory drug after dental surgery. Which mechanism most directly explains the gastric mucosal injury?

  1. Enhanced mucus production with bicarbonate trapping
  2. Increased gastric acid secretion from histamine release
  3. Direct stimulation of parietal cell proton pumps
  4. Inhibition of cyclooxygenase-1 reduces protective prostaglandin synthesis Correct answer.

Explanation

Cyclooxygenase-1 produces prostaglandins that increase mucus and bicarbonate secretion and maintain mucosal blood flow. NSAIDs inhibit COX-1, reducing these protective factors and predisposing to gastritis and ulceration. This is why selective COX-2 inhibitors or gastroprotection are considered in at-risk patients.

Question 37Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A surgical biopsy of a gingival lesion shows increased mitotic figures, nuclear pleomorphism, and loss of polarity with an intact basement membrane. Which term best describes this change?

  1. Atrophy
  2. Hypertrophy
  3. Dysplasia Correct answer.
  4. Metaplasia

Explanation

Dysplasia describes disordered growth with cytologic atypia, including pleomorphism, hyperchromasia, and increased mitoses, while the basement membrane remains intact. It is a premalignant change seen in oral leukoplakia and is graded as mild, moderate, or severe. Invasion through the basement membrane would define carcinoma rather than dysplasia.

Question 38Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient with chronic kidney disease develops secondary hyperparathyroidism. Which sequence best explains the underlying pathophysiology?

  1. Increased calcium absorption causes hypercalcemia and suppressed parathyroid hormone
  2. Reduced phosphate excretion leads to hyperphosphatemia, low ionized calcium, and increased parathyroid hormone Correct answer.
  3. Primary parathyroid adenoma causes calcium-independent parathyroid hormone secretion
  4. Reduced calcitonin secretion causes hypocalcemia and parathyroid stimulation

Explanation

Failing kidneys cannot excrete phosphate, producing hyperphosphatemia, which lowers ionized calcium and also reduces calcitriol synthesis. The resulting hypocalcemia stimulates parathyroid hormone release, causing secondary hyperparathyroidism and renal osteodystrophy. Dentists may see jaw changes such as ground-glass bone or loss of lamina dura in these patients.

Question 39Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A patient with poorly controlled diabetes develops severe periodontal disease. Which mechanism best explains the increased susceptibility?

  1. Advanced glycation end products promoting inflammation and impaired wound healing Correct answer.
  2. Upregulation of collagen synthesis in the periodontium
  3. Enhanced neutrophil chemotaxis and phagocytosis
  4. Increased salivary flow diluting bacterial toxins

Explanation

Chronic hyperglycemia forms advanced glycation end products that bind receptors on macrophages and endothelial cells, increasing inflammatory cytokines and oxidative stress while impairing collagen synthesis and wound healing. Neutrophil function is also depressed, worsening periodontal destruction. This explains the bidirectional relationship between diabetes and periodontitis.

Question 40Basic Medical Sciences relevant to dentistry (anatomy, physiology, biochemistry, pathology, microbiology, pharmacology)

A 24-year-old woman reports that her gums bleed when she brushes and that small purple spots have appeared on her legs. Examination shows swollen, bleeding gingival papillae and petechiae over both shins. Her diet for the past several months has consisted almost entirely of white bread and canned meat. Which biochemical defect best explains her gingival findings?

  1. Deficiency of vitamin K–dependent gamma-carboxylation of clotting factors
  2. Impaired hydroxylation of proline and lysine residues in collagen Correct answer.
  3. Impaired absorption of iron leading to microcytic anemia
  4. Defective conversion of pyruvate to acetyl-CoA by pyruvate dehydrogenase

Explanation

Vitamin C (ascorbic acid) is the reducing cofactor for prolyl and lysyl hydroxylase, enzymes that hydroxylate proline and lysine in procollagen so that the triple helix can form stable cross-links. Without it, collagen is weak and blood vessels leak, producing the classic gingival bleeding, petechiae, and poor wound healing of scurvy. The restricted diet lacking fresh fruit and vegetables fits this deficiency.

Question 41Head and Neck Anatomy, Oral Biology and Oral Histology

Which cranial nerve provides general sensory innervation to the anterior two-thirds of the tongue before it exits the skull?

  1. Glossopharyngeal nerve (CN IX)
  2. Hypoglossal nerve (CN XII)
  3. Trigeminal nerve (CN V), via the lingual branch of the mandibular division Correct answer.
  4. Facial nerve (CN VII)

Explanation

General sensation from the anterior two-thirds of the tongue travels with the lingual nerve, a branch of the mandibular division of the trigeminal nerve. The facial nerve only joins the lingual nerve briefly to carry taste fibers, and it does so via the chorda tympani rather than supplying general sensation itself.

Question 42Head and Neck Anatomy, Oral Biology and Oral Histology

The parotid duct (Stensen duct) opens into the oral cavity at which location?

  1. The floor of the mouth beside the lingual frenum
  2. The sublingual caruncle
  3. The buccal mucosa opposite the maxillary second molar Correct answer.
  4. The soft palate near the uvula

Explanation

Stensen duct traverses the buccinator muscle and opens at a papilla on the buccal mucosa adjacent to the crown of the maxillary second molar. The submandibular duct, by contrast, opens at the sublingual caruncle in the floor of the mouth.

Question 43Head and Neck Anatomy, Oral Biology and Oral Histology

Which muscle of mastication is the primary depressor of the mandible and is innervated by a branch of the mandibular division of the trigeminal nerve?

  1. Masseter
  2. Medial pterygoid
  3. Temporalis
  4. Lateral pterygoid Correct answer.

Explanation

The lateral pterygoid pulls the condyle forward and downward, producing opening of the mouth, and it is supplied by the mandibular nerve. The other three muscles of mastication are elevators of the mandible.

Question 44Head and Neck Anatomy, Oral Biology and Oral Histology

Enamel is formed by which cell type, and what is the principal inorganic component of mature enamel?

  1. Ameloblasts; collagen type I
  2. Odontoblasts; calcium carbonate
  3. Odontoblasts; hydroxyapatite
  4. Ameloblasts; hydroxyapatite Correct answer.

Explanation

Ameloblasts secrete the enamel matrix and are lost after tooth eruption, so enamel cannot regenerate. Mature enamel is roughly 96% inorganic, predominantly calcium phosphate in the form of hydroxyapatite.

Question 45Head and Neck Anatomy, Oral Biology and Oral Histology

Which epithelial structure is responsible for the reduced enamel epithelium seen over an erupting tooth?

  1. The stratum intermedium alone
  2. Fused ameloblasts and reduced ameloblasts after enamel formation is complete Correct answer.
  3. Remnants of the dental lamina
  4. The outer and inner enamel epithelium of the enamel organ before mineralization

Explanation

After enamel secretion and maturation, the ameloblasts shorten into reduced ameloblasts and, together with the remnants of the other enamel organ layers, form the reduced enamel epithelium. This layer covers the crown until eruption and later contributes to the junctional epithelium.

Question 46Head and Neck Anatomy, Oral Biology and Oral Histology

Which structure marks the junction between the oral mucosa of the lip and the skin of the face?

  1. Mucogingival junction
  2. Frenulum of the upper lip
  3. Mucobuccal fold
  4. Vermilion border Correct answer.

Explanation

The vermilion border is the sharp transition where the keratinized epidermis of the lip meets the modified lining of the vermilion zone. The mucogingival junction, by contrast, separates attached gingiva from alveolar mucosa.

Question 47Head and Neck Anatomy, Oral Biology and Oral Histology

A patient reports numbness of the lower lip and chin after a difficult mandibular third molar extraction. Which nerve has most likely been injured?

  1. The buccal branch of the mandibular nerve
  2. The inferior alveolar nerve before it exits the mental foramen Correct answer.
  3. The lingual nerve
  4. The mylohyoid nerve

Explanation

The inferior alveolar nerve runs within the mandibular canal and gives off the mental nerve, which supplies the lower lip and chin. Injury proximal to the mental foramen during third molar surgery produces numbness in that distribution.

Question 48Head and Neck Anatomy, Oral Biology and Oral Histology

Which periodontal ligament fiber group is oriented to resist intrusive forces on the tooth?

  1. Apical group
  2. Oblique group Correct answer.
  3. Horizontal group
  4. Alveolar crest group

Explanation

The oblique fibers run from the alveolar bone crest downward and inward to the root, so they are the principal group resisting axial intrusive loading. The apical group mainly resists extrusive forces.

Question 49Head and Neck Anatomy, Oral Biology and Oral Histology

In a histological section of a mature tooth, which tissue shows tubules containing odontoblast processes?

  1. Alveolar bone
  2. Enamel
  3. Dentin Correct answer.
  4. Cementum

Explanation

Dentin is permeated by dentinal tubules that house the odontoblast process and dentinal fluid. These tubules account for dentin sensitivity and are absent in enamel and cementum.

Question 50Head and Neck Anatomy, Oral Biology and Oral Histology

Which feature distinguishes the gingival sulcus epithelium from the junctional epithelium?

  1. The junctional epithelium contains no desmosomes at all
  2. The junctional epithelium is heavily keratinized
  3. The sulcular epithelium forms the epithelial attachment to enamel and cementum
  4. The sulcular epithelium is nonkeratinized and lacks hemidesmosomal attachment to the tooth Correct answer.

Explanation

The sulcular epithelium lines the gingival sulcus, is nonkeratinized, and does not attach to the tooth surface. The junctional epithelium, which does attach via hemidesmosomes to the tooth, is also nonkeratinized and is characterized by wide intercellular spaces and few desmosomes.