NBDE MCQ 2 — Questions and Answers
Question 1: Which cells are primarily responsible for bone resorption during orthodontic tooth movement?
- Osteoblasts
- Osteoclasts (Correct answer)
- Cementoblasts
- Fibroblasts
Correct answer: Osteoclasts
Osteoclasts are multinucleated cells derived from monocyte precursors that resorb bone on the pressure side during orthodontic movement.
Question 2: A patient presents with a periapical abscess. The causative bacteria most commonly involved is:
- Streptococcus mutans
- Porphyromonas gingivalis (Correct answer)
- Fusobacterium nucleatum
- Prevotella intermedia
Correct answer: Porphyromonas gingivalis
Porphyromonas gingivalis is the key pathogen in periapical infections due to its virulence factors including proteases and fimbriae.
Question 3: The mental foramen is most commonly located between which teeth?
- Mandibular central and lateral incisors
- Mandibular lateral incisor and canine
- Mandibular first and second premolars (Correct answer)
- Mandibular second premolar and first molar
Correct answer: Mandibular first and second premolars
The mental foramen is typically positioned between the apices of the mandibular first and second premolars, though location varies among individuals.
Question 4: Which local anesthetic has the longest duration of action for pulpal anesthesia?
- Lidocaine 2%
- Mepivacaine 3%
- Bupivacaine 0.5% (Correct answer)
- Articaine 4%
Correct answer: Bupivacaine 0.5%
Bupivacaine 0.5% with epinephrine provides the longest pulpal anesthesia duration (90–180 minutes) due to its high protein binding and lipid solubility.
Question 5: Enamel matrix proteins that guide enamel crystal formation are primarily secreted by:
- Odontoblasts
- Ameloblasts (Correct answer)
- Cementoblasts
- Stellate reticulum cells
Correct answer: Ameloblasts
Ameloblasts secrete amelogenins, enamelins, and ameloblastins, which organize hydroxyapatite crystal growth during enamelogenesis.
Question 6: A 45-year-old patient has a 6 mm probing depth with bleeding on probing and bone loss on radiograph. This is classified as:
- Gingivitis
- Stage I Periodontitis
- Stage III Periodontitis (Correct answer)
- Stage II Periodontitis
Correct answer: Stage III Periodontitis
Stage III Periodontitis is characterized by probing depths ≥6 mm, bleeding on probing, and radiographic bone loss extending to the middle or apical third of the root.
Question 7: Which instrument is used to detect subgingival calculus by tactile sensation?
- Periodontal probe
- Curette
- Explorer (Correct answer)
- Scaler
Correct answer: Explorer
An explorer (particularly the ODU 11/12 or 3A) provides the best tactile feedback for detecting subgingival calculus deposits.
NBDE MCQ 2
Which cells are primarily responsible for bone resorption during orthodontic tooth movement?