NBDHE Test Scientific Basis of Practice 1

Question 1

Which triad of bacteria comprises the 'red complex,' most strongly associated with deep periodontal pockets and clinical attachment loss in chronic periodontitis?

Accepted Answer

Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola

Answer

Socransky's landmark cluster analysis identified P. gingivalis, T. forsythia (formerly B. forsythus), and T. denticola as the red complex — the bacterial group most strongly correlated with clinical measures of periodontitis severity such as increased probing depth, bleeding on probing, and attachment loss.

Question 2

A new salivary biomarker test for early caries detection yields 80 true negatives and 20 false positives among 100 disease-free individuals. What is the specificity of this test?

Accepted Answer

80%

Answer

Specificity = TN / (TN + FP) = 80 / (80 + 20) = 80%. Specificity measures how accurately a test identifies those WITHOUT disease (the true negative rate), thereby minimizing false positives and avoiding unnecessary treatment.

Question 3

Which mechanism BEST explains how fluoride reduces enamel susceptibility to acid dissolution by cariogenic bacteria?

Accepted Answer

Fluoride substitutes for hydroxyl ions in hydroxyapatite, forming fluorapatite with a lower critical pH (~4.5)

Answer

Fluoride substitutes for hydroxyl groups in the hydroxyapatite crystal lattice to form fluorapatite, which has a critical pH of approximately 4.5 compared to 5.5 for hydroxyapatite. This structurally more stable mineral is significantly more resistant to acid attack from bacterial metabolic byproducts.

Question 4

A dental hygienist develops erythema and vesicles on her hands 48 hours after contact with latex gloves. This reaction is BEST classified as which type of hypersensitivity?

Accepted Answer

Type IV — T-cell–mediated delayed hypersensitivity

Answer

The 48-hour delay and contact dermatitis presentation are hallmarks of Type IV (delayed-type) hypersensitivity, mediated by sensitized CD4+ T lymphocytes rather than antibodies. Contact dermatitis to latex chemical additives follows this timeline, in contrast to Type I reactions (urticaria, anaphylaxis) triggered by latex proteins within minutes.

Question 5

Which prostaglandin is considered the PRIMARY lipid mediator of alveolar bone resorption in chronic inflammatory periodontal disease?

Accepted Answer

Prostaglandin E2 (PGE2)

Answer

PGE2 is the predominant prostaglandin detected at elevated concentrations in gingival crevicular fluid at active periodontitis sites. It stimulates osteoclast differentiation and activity by upregulating the RANK/RANKL pathway, making it the principal arachidonic acid–derived mediator of bone destruction in periodontal disease.

NBDHE Test Practice Test

NBDHE Test Practice Test

NBDHE Test Scientific Basis of Practice 1