FREE NBDE Microbiology and Pathology Questions and Answers

Question 1

A 5-year-old child presents with a fever, sore throat, and small, painful ulcers primarily located on the soft palate and tonsillar pillars. The child's hands and feet appear normal with no rash or lesions. Based on these findings, what is the most likely diagnosis?

Accepted Answer

Herpangina

Answer

Herpangina, caused by the coxsackievirus, is characterized by ulcers and sores located in the posterior part of the mouth, such as the soft palate and tonsils. Hand, Foot, and Mouth Disease, also caused by coxsackievirus, presents with oral lesions but is distinguished by the additional presence of a rash on the hands and feet. Primary Herpetic Gingivostomatitis typically involves more widespread oral lesions, including the gingiva, and Erythema Multiforme has characteristic 'target' lesions.

Question 2

A patient presents with a chronic, non-healing, draining sinus tract on the skin of the jaw. A purulent discharge from the tract contains small, yellowish particles. Histopathological examination of these particles would most likely reveal tangled masses of filamentous bacteria. Which microorganism is the most probable causative agent?

Accepted Answer

Actinomyces israelii

Answer

The clinical presentation of a cervicofacial draining sinus tract with 'sulfur granules' (yellowish particles) is a classic sign of Actinomycosis. The causative agent is typically Actinomyces israelii, a gram-positive, filamentous anaerobic bacterium. These sulfur granules are not composed of sulfur but are masses of the causative bacteria.

Question 3

A routine radiographic examination reveals a well-demarcated, unilocular radiolucency surrounding the crown of an unerupted mandibular third molar. The tooth is asymptomatic. This radiographic finding is most characteristic of which of the following?

Accepted Answer

Dentigerous (Follicular) Cyst

Answer

A dentigerous cyst, also known as a follicular cyst, is a developmental odontogenic cyst that forms from the accumulation of fluid between the reduced enamel epithelium and the crown of an unerupted tooth. Radiographically, it appears as a well-defined, unilocular radiolucency attached at the cementoenamel junction of the unerupted tooth. Radicular cysts are associated with the apex of a non-vital tooth, and OKCs and ameloblastomas can have a more varied and sometimes multilocular appearance.

Question 4

A middle-aged female patient complains of a burning sensation and soreness in her mouth. Clinical examination reveals bilateral, interlacing white lines (Wickham's striae) on the buccal mucosa. Some areas appear erythematous and eroded. This clinical presentation is most indicative of which condition?

Accepted Answer

Oral Lichen Planus

Answer

Oral Lichen Planus (OLP) is a chronic inflammatory autoimmune disease that affects the oral mucosa. The reticular form, the most common type, is characterized by the pathognomonic Wickham's striae, which are fine, lacy, white lines. Symptomatic forms, like erosive OLP, present with erythema and ulceration, causing pain and burning.

Question 5

Which of the following bacteria is most strongly implicated as the primary initiator of enamel caries due to its ability to produce acid and synthesize extracellular polysaccharides from sucrose, which facilitates its adherence to the tooth surface?

Accepted Answer

Streptococcus mutans

Answer

Streptococcus mutans is considered a major etiological agent in the initiation of dental caries. It is highly acidogenic (acid-producing) and aciduric (able to survive in an acidic environment). Crucially, it metabolizes sucrose to produce insoluble extracellular glucans, which help it adhere firmly to the tooth surface and form a biofilm (plaque), creating a localized acidic environment that demineralizes enamel.

NBDE - National Board Dental Examination Practice Test

NBDE - National Board Dental Examination Practice Test

FREE NBDE Microbiology and Pathology Questions and Answers