Component SB · Scientific Basis for Dental Hygiene Practice · 61 of 200 discipline-based items
NBDHE scientific basis practice questions
15 original questions from the DHPrep NBDHE preview, with the correct answer and a rationale for every option.
Scientific Basis for Dental Hygiene Practice is 61 of the 200 discipline-based items on the NBDHE specifications DHPrep treats as in force. The free preview holds 15 of its 50 questions here. None of those 15 needs a radiograph, so all 15 are printed on this page.
The items are spread across anatomic sciences, physiology, biochemistry and nutrition, pathology, and pharmacology. They ask you to use a science fact on a patient fact. A definition by itself is not the task.
How to work this set. Name the science claim the stem depends on before you look at the options. If two options share that claim, the one that also fits the patient’s age, drug, or finding is the key. Write the claim in your own words after you check the answer.
Anatomic sciences
4 standalone questions in the free set.
Question 1
Which type of oral mucosa is characterized by the presence of keratinized stratified squamous epithelium and is found on the hard palate and attached gingiva?
- A. Specialized mucosa
- B. Alveolar mucosa
- C. Masticatory mucosaCorrect answer
- D. Lining mucosa
Answer
C. Masticatory mucosa
Masticatory mucosa is keratinized and found on the hard palate and attached gingiva, providing resistance to mechanical forces.
Rationale
Masticatory mucosa is characterized by a keratinized stratified squamous epithelium, making it tough and well-suited to withstand the forces of mastication. This mucosa covers the hard palate and attached gingiva. In contrast, lining mucosa (non-keratinized) covers regions like the buccal and labial mucosa. Specialized mucosa is restricted to the dorsum of the tongue and includes taste buds, while alveolar mucosa is a subset of lining mucosa but is not keratinized.
Why each option lands where it does
- A. Specialized mucosa contains taste buds and is only on the dorsum of the tongue.
- B. Alveolar mucosa is mobile, non-keratinized, and found just apical to the attached gingiva.
- C (correct). Correct. Masticatory mucosa is keratinized and covers the hard palate and attached gingiva.
- D. Lining mucosa is non-keratinized and found on the inside of cheeks, lips, and floor of the mouth.
Decision rule. Look for keratinized oral mucosa found where heavy function takes place.
Takeaway. Masticatory mucosa is keratinized and supports the hard palate and attached gingiva.
Common miss. Some believe all gingiva is non-keratinized, but attached gingiva is keratinized.
Question 2
A patient asks which part of the tooth is hardest. Which dental tissue contains the highest percentage of hydroxyapatite crystals by weight?
- A. Dentin beneath the enamel
- B. Enamel covering the crownCorrect answer
- C. Cementum on the root
- D. Pulp tissue in the center
Answer
B. Enamel covering the crown
Enamel is the most mineralized dental tissue, with the highest hydroxyapatite content, making it the hardest tissue in the body.
Rationale
Enamel consists of about 96% inorganic hydroxyapatite by weight, making it extremely hard and resilient to mechanical forces. Dentin and cementum also contain hydroxyapatite but at lower concentrations, which makes them softer. Pulp is soft connective tissue lacking significant mineral content.
Why each option lands where it does
- A. Dentin is mineralized but not as hard as enamel.
- B (correct). Enamel is 96% hydroxyapatite by weight, giving it exceptional hardness.
- C. Cementum is less mineralized than enamel or dentin.
- D. Pulp is soft connective tissue, not mineralized.
Decision rule. Choose the tissue with the greatest mineral content for maximum hardness.
Takeaway. Enamel's high hydroxyapatite content makes it the hardest tissue in the human body.
Common miss. Sometimes, dentin or cementum is confused with enamel in terms of hardness.
Question 3
A patient is observed chewing food during an oral exam. Which muscle primarily elevates the mandible to close the jaw in this process?
- A. Lateral pterygoid muscle
- B. Temporalis muscleCorrect answer
- C. Mylohyoid muscle
- D. Digastric muscle
Answer
B. Temporalis muscle
The temporalis muscle elevates the mandible to close the jaw during mastication.
Rationale
The temporalis muscle originates in the temporal fossa and inserts on the coronoid process of the mandible, functioning to elevate and retract the jaw. The lateral pterygoid instead depresses and protrudes the mandible. The digastric acts to open the mouth by depressing the mandible, while the mylohyoid elevates the floor of the mouth but does not close the jaw. The temporalis is major for closing the jaw.
Why each option lands where it does
- A. The lateral pterygoid muscle primarily assists in opening the jaw and moving it side to side.
- B (correct). The temporalis muscle contracts to raise the mandible, closing the jaw during chewing.
- C. The mylohyoid muscle forms the floor of the mouth and does not elevate the mandible.
- D. The digastric muscle assists in depressing the mandible, not elevating it.
Decision rule. Choose the muscle that performs elevation of the mandible during chewing.
Takeaway. Know the function of each muscle of mastication for better understanding of jaw movement.
Common miss. Some confuse the temporalis and masseter; both elevate the mandible, but the temporalis is often overlooked.
Question 4
During the administration of an inferior alveolar nerve block for tooth #30, a patient develops temporary facial paralysis. Which anatomical structure was most likely inadvertently anesthetized?
- A. Facial nerve within the parotid glandCorrect answer
- B. Lingual nerve in the pterygomandibular space
- C. Buccal nerve at the mandibular ramus
- D. Mylohyoid nerve on the medial mandible
Answer
A. Facial nerve within the parotid gland
Temporary facial paralysis following IAN block is most often caused by anesthetic deposited too far posteriorly, reaching the facial nerve inside the parotid gland.
Rationale
The facial nerve passes through the parotid gland and controls facial muscles. If anesthetic is injected too far posteriorly during an IAN block, it can reach the parotid gland and affect the facial nerve, causing temporary paralysis. The lingual, buccal, and mylohyoid nerves do not control facial expression muscles.
Why each option lands where it does
- A (correct). Anesthetizing the facial nerve in the parotid gland can cause temporary facial paralysis.
- B. Lingual nerve involvement would cause loss of tongue sensation, not facial paralysis.
- C. Buccal nerve anesthesia affects buccal mucosa sensation, not facial musculature.
- D. Mylohyoid nerve innervates mylohyoid and anterior digastric, not facial expression muscles.
Decision rule. Associate the onset of facial paralysis with improper IAN block technique and facial nerve anatomy.
Takeaway. Facial nerve anesthesia via parotid gland involvement can cause temporary facial paralysis after IAN block.
Common miss. Students often believe the IAN block can only affect nerves within the mandible, overlooking the facial nerve.
Biochemistry and nutrition
1 standalone question in the free set.
Question 5
A 6-year-old with a vegan diet and no fortified foods has delayed eruption and enamel banding on permanent first molars. Which deficiency is most likely responsible?
- A. Vitamin K deficiency
- B. Vitamin B12 deficiency
- C. Vitamin E deficiency
- D. Vitamin D deficiencyCorrect answer
Answer
D. Vitamin D deficiency
Vitamin D deficiency is most likely, resulting in delayed eruption and enamel defects in developing teeth.
Rationale
Strict vegan diets lacking fortified foods may lead to vitamin D deficiency, as natural plant sources are limited. Vitamin D is crucial for calcium absorption and mineralization of tooth structures, with deficiency causing delayed eruption and enamel defects. Vitamin B12 is implicated in anemia and neural issues; vitamin K in clotting; vitamin E in antioxidation, none directly causing these dental findings.
Why each option lands where it does
- A. Vitamin K deficiency primarily affects blood clotting and is not associated with delayed tooth eruption or enamel defects.
- B. Vitamin B12 deficiency may cause oral mucosal changes but does not lead to enamel defects or delayed eruption.
- C. Vitamin E deficiency is rare and does not typically cause dental developmental issues.
- D (correct). Vitamin D is essential for normal tooth mineralization and eruption; deficiency can cause enamel defects and delayed eruption.
Decision rule. Identify clinical signs suggesting hypomineralization and relate them to likely nutrient deficiencies in vegan diets.
Takeaway. Vitamin D is required for normal mineralization and eruption of teeth during childhood.
Common miss. Candidates might assume B12 deficiency, which doesn't present with tooth mineralization issues.
Pathology
4 standalone questions in the free set.
Question 6
A 42-year-old reports a non-healing, indurated ulcer on the lateral tongue with pain and no improvement after two weeks of local care. What is the best next step for the dental hygienist to recommend?
- A. Advise saltwater rinses longer
- B. Prescribe topical antifungal rinse
- C. Recommend biopsy by oral surgeonCorrect answer
- D. Refer for foreign body removal
Answer
C. Recommend biopsy by oral surgeon
A persistent, indurated ulcer with concerning features should be biopsied to rule out malignancy.
Rationale
Non-healing oral ulcers with induration and lasting more than two weeks may indicate oral squamous cell carcinoma or other serious pathology. Early biopsy is essential for diagnosis and improved outcomes. Symptomatic remedies or antimicrobials delay necessary diagnosis and management. Foreign body removal is inappropriate without evidence of one. Proper referral is aligned with professional standards and protects the patient.
Why each option lands where it does
- A. Delaying further with saltwater rinses risks missing a serious diagnosis.
- B. Topical antifungals are not indicated without evidence of fungal infection.
- C (correct). Biopsy is necessary for persistent, indurated oral ulcers to assess for malignancy.
- D. No evidence suggests a foreign body is present in this case.
Decision rule. Refer any non-healing oral ulcer lasting over 2 weeks with induration for biopsy.
Takeaway. Persistent oral lesions with concerning features require prompt biopsy referral.
Common miss. Some believe all oral ulcers are benign and will resolve with time or home care.
Question 7
A 62-year-old man has a persistent ulcer on the ventral tongue and reports daily tobacco and alcohol use for 40 years. Which factor most strongly raises suspicion for malignancy in this patient?
- A. Patient's age over 60
- B. Combined use of tobacco and alcoholCorrect answer
- C. Ulceration lasting over two weeks
- D. Location on ventral tongue
Answer
B. Combined use of tobacco and alcohol
Concurrent use of tobacco and alcohol significantly increases oral cancer risk, synergistically elevating concern for malignancy in persistent tongue lesions.
Rationale
While each factor increases cancer risk, the combination of tobacco and alcohol use acts synergistically, dramatically multiplying the risk for oral squamous cell carcinoma. The ventral tongue is a high-risk site, patient’s age also matters, and non-healing ulceration over two weeks is concerning. However, the synergistic effect of combined tobacco and alcohol use is most critical, as it greatly magnifies malignant potential compared to either risk factor alone.
Why each option lands where it does
- A. Older age is a risk factor, but not as significant as the combined use of tobacco and alcohol.
- B (correct). Tobacco and alcohol together have a synergistic effect, greatly increasing oral cancer risk compared to either alone.
- C. Ulcer duration is concerning, but the combined habits are more critical for malignancy risk.
- D. While the ventral tongue is a high-risk site, the combined exposure is a stronger risk factor.
Decision rule. Choose the factor that most strongly magnifies malignancy risk due to synergy, not just presence of individual risks.
Takeaway. Concurrent use of tobacco and alcohol exponentially increases oral cancer risk beyond individual factors.
Common miss. Students may focus on site or chronicity, but the synergy of combined risk factors is most critical statistically.
Question 8
A patient’s saliva sample is analyzed to determine which antibody provides primary immune defense in the oral cavity. Which immunoglobulin is most prevalent in these secretions?
- A. Immunoglobulin ACorrect answer
- B. Immunoglobulin M
- C. Immunoglobulin E
- D. Immunoglobulin G
Answer
A. Immunoglobulin A
Immunoglobulin A (IgA) is the most abundant antibody in saliva, providing the first immune defense in the oral cavity.
Rationale
Secretory IgA is specially adapted for secretion in saliva, tears, and mucosal linings, where it neutralizes pathogens before they invade tissues. IgE is minimal in saliva and is linked with allergic responses. IgM and IgG are more prevalent in serum than in secretions. IgA's structure enables it to function effectively in protecting oral mucosa.
Why each option lands where it does
- A (correct). IgA is the dominant immunoglobulin in saliva and other secretions, protecting mucosal surfaces.
- B. IgM is primarily found in blood and is not the main antibody in secretions.
- C. IgE is mainly involved in allergic responses and is not abundant in saliva.
- D. IgG is the most common antibody in serum, but not in saliva.
Decision rule. Select the antibody class best adapted for mucosal and secretory environments.
Takeaway. IgA is the dominant immunoglobulin in saliva, protecting the oral cavity.
Common miss. Some may confuse IgG or IgM as dominant due to their role in blood-borne immunity.
Question 9
A patient with a history of chronic hepatitis exhibits generalized jaundice, petechiae, and easy bruising during a dental exam. Which of the following complications should the dental hygienist anticipate during treatment?
- A. Onset of hypoglycemic episodes
- B. Development of oral candidiasis
- C. Sudden hypertensive crisis
- D. Increased risk of hemorrhageCorrect answer
Answer
D. Increased risk of hemorrhage
The patient is at increased risk for hemorrhage due to impaired liver function and decreased synthesis of clotting factors.
Rationale
Chronic hepatitis leads to impaired liver function, reduced synthesis of clotting factors, and abnormal bleeding. This is evident in the patient's jaundice (bilirubin buildup), petechiae, and easy bruising. Oral candidiasis and hypoglycemia can occur in other systemic conditions, but the signs point most directly to coagulopathy. Hypertensive crisis is unrelated to hepatitis.
Why each option lands where it does
- A. Incorrect. Hypoglycemia is not a primary complication of hepatitis without diabetes or medication errors.
- B. Incorrect. While immune compromise can predispose to candidiasis, this patient's main issue is bleeding.
- C. Incorrect. There is no evidence for hypertensive crisis in chronic hepatitis.
- D (correct). Correct. Impaired liver function diminishes clotting factors, elevating bleeding risk.
Decision rule. Anticipate hemorrhagic complications in patients with liver dysfunction and clinical bleeding signs.
Takeaway. Chronic liver disease increases bleeding risk due to clotting factor deficiencies.
Common miss. Jaundice alone does not predict bleeding, but when paired with petechiae and bruising it suggests coagulopathy.
Pharmacology
2 standalone questions in the free set.
Question 10
A 54-year-old man with a long tobacco history has a firm, non-healing ulcer on the left tongue near tooth #20 for 7 weeks. What should the dental hygienist recommend next?
- A. Suggest improved oral hygiene
- B. Recommend immediate biopsy referralCorrect answer
- C. Schedule two-week follow-up
- D. Advise over-the-counter rinse
Answer
B. Recommend immediate biopsy referral
Immediate biopsy referral is indicated for a persistent indurated ulcer in a high-risk patient.
Rationale
A non-healing ulcer on the lateral tongue in a long-term smoker is highly suspicious for malignancy, particularly oral squamous cell carcinoma. Delaying care by suggesting follow-up, oral rinses, or improved hygiene is inappropriate, as early diagnosis is critical for prognosis and management. Biopsy is essential to confirm diagnosis and guide further treatment. The dental hygienist should recognize the red-flag features and facilitate prompt specialist referral.
Why each option lands where it does
- A. Improved oral hygiene does not address the risk of malignancy in this clinical scenario.
- B (correct). A persistent indurated ulcer in a high-risk patient requires urgent biopsy referral to rule out cancer.
- C. Delaying referral could postpone diagnosis of a potentially serious lesion.
- D. Over-the-counter rinses are not appropriate for a suspicious persistent ulcer.
Decision rule. Prioritize urgent referral over symptomatic management when red-flag malignancy features are present.
Takeaway. Any persistent indurated oral ulcer, especially in high-risk patients, requires immediate referral for biopsy.
Common miss. Some may believe oral ulcers should be monitored before referral, but certain features demand immediate specialist assessment.
Question 11
A patient with a history of asthma is scheduled for scaling and root planing. Which local anesthetic should be avoided due to increased risk of allergic reaction in asthmatic patients sensitive to sulfites?
- A. 2% lidocaine with epinephrineCorrect answer
- B. 2% chloroprocaine
- C. 3% mepivacaine plain
- D. 4% prilocaine plain
Answer
A. 2% lidocaine with epinephrine
2% lidocaine with epinephrine contains sulfite preservatives that may trigger reactions in sensitive asthmatic patients.
Rationale
Vasoconstrictors like epinephrine are preserved with sulfites, which can provoke allergic or asthmatic responses in susceptible individuals. Mepivacaine and prilocaine plain do not contain vasoconstrictors or sulfites, and chloroprocaine is rarely used in dental settings. Choosing an anesthetic without sulfite preservative is critical for these patients.
Why each option lands where it does
- A (correct). Contains epinephrine preserved with sulfites—risky for asthmatics sensitive to these preservatives.
- B. Rarely used in dentistry, but when plain contains no sulfite; not generally a concern for sulfite-sensitive patients.
- C. No vasoconstrictor or sulfite; generally safe for patients with sulfite sensitivity.
- D. Plain prilocaine lacks vasoconstrictor and sulfite preservatives.
Decision rule. Identify drug formulation components, not just active ingredients, relevant to patient allergies.
Takeaway. Asthmatic patients sensitive to sulfites require local anesthetics without vasoconstrictors or sulfite preservatives.
Common miss. Many focus only on anesthetic drugs, but additives like preservatives can pose risks.
Physiology
4 standalone questions in the free set.
Question 12
A patient experiences a sudden drop in blood pressure after standing up quickly. Which physiological response is most likely to occur in order to restore blood pressure to normal levels?
- A. Dilation of coronary arteries
- B. Inhibition of the sympathetic nervous system
- C. Decrease in heart rate
- D. Constriction of peripheral blood vesselsCorrect answer
Answer
D. Constriction of peripheral blood vessels
Constriction of peripheral blood vessels helps return blood pressure to normal after a rapid drop.
Rationale
Orthostatic hypotension—a sudden BP drop after standing—is compensated by baroreceptor reflexes that activate the sympathetic nervous system. This leads to vasoconstriction, increasing peripheral resistance and aiding in BP restoration. The other responses either lower blood pressure further or do not directly affect it in this context.
Why each option lands where it does
- A. Dilation of coronary arteries affects heart muscle blood supply but not systemic blood pressure directly.
- B. Inhibiting the sympathetic nervous system would decrease compensatory responses and lower BP further.
- C. Decreasing heart rate would further lower blood pressure, worsening the problem.
- D (correct). Correct. Vasoconstriction increases resistance and blood pressure, counteracting the drop.
Decision rule. Select the response that would increase, not decrease, blood pressure after a sudden drop.
Takeaway. The body compensates for low blood pressure by vasoconstriction and increasing heart rate.
Common miss. A common error is to confuse vasoconstriction and vasodilation or associate heart rate changes incorrectly.
Question 13
A patient experiences tachycardia and dizziness standing up quickly after a dental procedure. Which physiological response is most likely responsible for stabilizing their blood pressure in this situation?
- A. Baroreceptor-mediated vasoconstrictionCorrect answer
- B. Decreased sympathetic nervous activity
- C. Increased parasympathetic output
- D. Decreased antidiuretic hormone release
Answer
A. Baroreceptor-mediated vasoconstriction
Baroreceptor-mediated vasoconstriction helps stabilize blood pressure after standing quickly.
Rationale
When someone stands quickly, gravity causes blood to pool in the legs, lowering blood pressure. Baroreceptors detect this drop and trigger vasoconstriction and increased heart rate via the sympathetic nervous system to rapidly restore pressure and blood flow to vital organs.
Why each option lands where it does
- A (correct). Baroreceptors adjust vascular tone, maintaining blood pressure during positional changes.
- B. Sympathetic activity increases, not decreases, in response to low blood pressure.
- C. Increased parasympathetic output would slow the heart, worsening hypotension.
- D. Antidiuretic hormone is involved in long-term blood volume, not rapid pressure adjustments.
Decision rule. Identify the short-term regulatory mechanism that acts within seconds during a rapid postural change.
Takeaway. Baroreceptor reflex rapidly compensates for blood pressure drops after standing.
Common miss. Candidates may select a hormone or nervous pathway not involved in immediate blood pressure control.
Question 14
Following consumption of a carbohydrate-rich meal, insulin is secreted into the bloodstream. Which effect does insulin directly promote in peripheral tissues?
- A. Production of digestive enzymes in the stomach
- B. Mobilization of fatty acids from adipose tissue
- C. Facilitated uptake of glucose by cellsCorrect answer
- D. Inhibition of bone resorption by osteoclasts
Answer
C. Facilitated uptake of glucose by cells
Insulin release after a carbohydrate-rich meal promotes glucose uptake by cells via facilitated diffusion.
Rationale
Insulin is a hormone produced by the pancreas in response to increased blood glucose. Its key role is to facilitate the uptake of glucose into cells, mainly muscle and adipose, via glucose transporters. The other processes are not directly stimulated by insulin: insulin inhibits fat mobilization, bone resorption is regulated by other hormones, and digestive enzyme production is not insulin's function.
Why each option lands where it does
- A. Digestive enzyme production in the stomach is not directly stimulated by insulin.
- B. Insulin inhibits, rather than stimulates, fatty acid release from adipose tissue.
- C (correct). Insulin increases glucose transport into cells, especially muscle and fat, by stimulating glucose transporter proteins.
- D. Insulin does not directly regulate bone resorption by osteoclasts.
Decision rule. Choose the cellular process typically enhanced by insulin.
Takeaway. Insulin primarily increases glucose uptake in target cells after eating.
Common miss. Insulin does not stimulate fat mobilization or digestion directly.
Question 15
A patient presents with tachycardia and anxiety during a routine dental appointment. Which physiological response is most likely contributing to these symptoms?
- A. Increased sympathetic nervous system activityCorrect answer
- B. Suppressed adrenal medulla output
- C. Elevated parasympathetic tone
- D. Enhanced insulin secretion
Answer
A. Increased sympathetic nervous system activity
Activation of the sympathetic nervous system leads to increased heart rate and anxiety, aligning with the patient’s symptoms.
Rationale
The sympathetic nervous system triggers the 'fight or flight' response, manifesting as increased heart rate (tachycardia), heightened anxiety, and other physiological changes. The parasympathetic system has the opposite effect. Suppressed adrenal activity would not cause such symptoms, and insulin secretion relates to glucose metabolism, not acute stress responses.
Why each option lands where it does
- A (correct). Correct. Sympathetic activation causes tachycardia and anxiety as part of the stress response.
- B. Suppressed adrenal medulla output would reduce, not increase, sympathetic effects.
- C. Parasympathetic activation slows the heart and promotes relaxation.
- D. Insulin secretion does not cause tachycardia or anxiety.
Decision rule. Pick the response explaining increased heart rate and anxiety via nervous system function.
Takeaway. Sympathetic nervous system activation is responsible for stress-induced tachycardia.
Common miss. Candidates may wrongly associate parasympathetic activity with anxiety symptoms.
Related reading
- Free NDHCE practice questions
Use the Canadian set only if you are also preparing for the NDHCE. The banks are separate, and the tooth-numbering systems are not the same.
Frequently asked questions
What does the scientific-basis component cover on the NBDHE?
On the specifications in force, it is 61 of 200 discipline-based items: anatomic sciences, physiology, biochemistry and nutrition, microbiology and immunology, pathology, and pharmacology. The free preview prints 15 original questions from that component. Microbiology is part of the component and is not in this 15.
Are tooth numbers on these questions FDI or Universal?
Universal. Permanent teeth are 1 through 32 and primary teeth are A through T. A Canadian FDI number does not transfer by swapping the digits.
Do I need a radiograph for this page?
No. The five free radiograph questions are in Clinical Dental Hygiene Services, on that component’s page, with the image beside the question. Every scientific-basis question here is text.
Practice more with DHPrep
Create a free account to practise this component with a timer, notes, and bookmarks. The account includes the full 50-question preview. A one-time NBDHE pass opens the published US bank and the mock exams.
DHPrep is an independent preparation service. These are original practice questions, not official NBDHE items, and not a prediction of a board result. DHPrep is not affiliated with, endorsed by, or sponsored by the Joint Commission on National Dental Examinations (JCNDE) or the American Dental Association (ADA).