NBDE Periodontics and Endodontics Questions and Answers — Questions and Answers
Question 1: A 45-year-old patient presents with a chief complaint of a "gummy smile." Clinical examination reveals probing depths of 2-3 mm, minimal bleeding on probing, and a gingival margin located significantly coronal to the CEJ. Bone sounding reveals a distance of 5 mm from the gingival margin to the alveolar crest. What is the most likely diagnosis?
- Chronic Periodontitis
- Medication-induced Gingival Hyperplasia
- Altered Passive Eruption (Correct answer)
- Aggressive Periodontitis
Correct answer: Altered Passive Eruption
Altered passive eruption occurs when the gingival margin fails to migrate apically to the CEJ after tooth eruption, resulting in short clinical crowns and excessive gingival display. The key diagnostic finding here is the excessive gingival tissue coronal to the CEJ despite normal probing depths, which rules out periodontitis. The significant distance from the gingival margin to the alveolar crest confirms an excess of supracrestal soft tissue.
Question 2: Which of the following is the primary purpose of using 17% Ethylenediaminetetraacetic acid (EDTA) as an irrigant during root canal therapy?
- To dissolve organic pulpal tissue remnants.
- To provide broad-spectrum antimicrobial activity.
- To remove the inorganic component of the smear layer. (Correct answer)
- To act as a lubricant for rotary instruments.
Correct answer: To remove the inorganic component of the smear layer.
EDTA is a chelating agent that specifically binds with calcium ions in dentin. Its primary function in endodontics is to remove the inorganic, mineralized component of the smear layer created during canal instrumentation. This action unplugs the dentinal tubules, allowing for better adaptation of obturating materials and deeper penetration of disinfectants like sodium hypochlorite, which dissolves the organic tissue.
Question 3: A clinician is evaluating a maxillary molar with a Nabers probe. The probe passes completely through the furcation from the buccal to the mesiopalatal aspect, and the entrance to the furcation is clinically visible due to significant gingival recession. According to Glickman's classification, what is the correct classification for this furcation involvement?
- Class II
- Class IV (Correct answer)
- Class I
- Class III
Correct answer: Class IV
Glickman's classification defines a Class IV furcation as a through-and-through involvement that is clinically visible because of gingival recession. A Class III furcation is also a through-and-through defect, but it is covered by soft tissue and not clinically visible. Class I is incipient involvement, and Class II is partial penetration into the furcation.
Question 4: A 22-year-old patient reports sharp, lingering pain in tooth #30 that lasts for several minutes after a cold stimulus is removed. The pain also occurs spontaneously and has awakened the patient from sleep. Percussion and palpation tests are within normal limits. A periapical radiograph shows a deep composite restoration but no periapical radiolucency. Based on these findings, what are the most likely pulpal and periapical diagnoses?
- Symptomatic Irreversible Pulpitis and Normal Apical Tissues (Correct answer)
- Reversible Pulpitis and Normal Apical Tissues
- Symptomatic Irreversible Pulpitis and Symptomatic Apical Periodontitis
- Necrotic Pulp and Asymptomatic Apical Periodontitis
Correct answer: Symptomatic Irreversible Pulpitis and Normal Apical Tissues
The key signs of symptomatic irreversible pulpitis are spontaneous pain and lingering pain to thermal stimuli. Since the percussion and palpation tests are normal and there is no radiographic evidence of periapical pathosis, the diagnosis for the periapical tissues is Normal Apical Tissues. Symptomatic Apical Periodontitis would present with pain on percussion, indicating inflammation has reached the periapical ligament.
Question 5: Which of the following clinical scenarios is most indicative of a primary periodontal lesion with secondary endodontic involvement?
- A non-vital tooth with a deep, isolated, narrow periodontal pocket that traces to the apex.
- A vital tooth with generalized severe bone loss and a wide, conical periodontal pocket. (Correct answer)
- A non-vital tooth with a small sinus tract that traces directly to the apex of the tooth.
- A vital tooth with a history of trauma presenting with internal root resorption radiographically.
Correct answer: A vital tooth with generalized severe bone loss and a wide, conical periodontal pocket.
A primary periodontal lesion begins with marginal periodontitis. This would be characterized by generalized bone loss and wide pocketing around a tooth that initially tests vital. The infection can then progress apically to involve the pulp via lateral canals or the apical foramen, causing a secondary endodontic lesion where the pulp becomes necrotic. A deep, isolated pocket on a non-vital tooth suggests a primary endodontic lesion draining coronally.
Question 6: A periodontist prescribes a subantimicrobial dose of doxycycline (20 mg twice daily) for a patient with chronic periodontitis as an adjunct to scaling and root planing. What is the primary mechanism of action for this specific therapy?
- To exert a bactericidal effect on key periodontal pathogens.
- To inhibit the activity of host-derived collagenase (matrix metalloproteinases). (Correct answer)
- To stimulate osteoblastic activity and promote alveolar bone formation.
- To directly reduce the depth of periodontal pockets through epithelial reattachment.
Correct answer: To inhibit the activity of host-derived collagenase (matrix metalloproteinases).
At subantimicrobial doses, doxycycline's primary therapeutic effect is not antibiotic. Instead, it acts as a host modulatory agent by inhibiting the activity of matrix metalloproteinases (MMPs), particularly collagenase, which are enzymes responsible for the breakdown of periodontal connective tissue. This helps to reduce the destruction of the periodontium that is part of the host's inflammatory response to bacterial plaque.
NBDE Periodontics and Endodontics Questions and Answers
A 45-year-old patient presents with a chief complaint of a "gummy smile." Clinical examination reveals probing depths of 2-3 mm, minimal bleeding on probing, and a gingival margin located significantly coronal to the CEJ.
Bone sounding reveals a distance of 5 mm from the gingival margin to the alveolar crest.
What is the most likely diagnosis?