NBDHE Test Scientific Basis of Practice 1 — Questions and Answers
Question 1: Which triad of bacteria comprises the 'red complex,' most strongly associated with deep periodontal pockets and clinical attachment loss in chronic periodontitis?
- Actinobacillus actinomycetemcomitans, Prevotella intermedia, and Fusobacterium nucleatum
- Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola (Correct answer)
- Streptococcus sanguinis, Actinomyces viscosus, and Veillonella parvula
- Campylobacter rectus, Eikenella corrodens, and Peptostreptococcus micros
Correct answer: Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola
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?
- 20%
- 80% (Correct answer)
- 40%
- 60%
Correct answer: 80%
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?
- Fluoride kills Streptococcus mutans directly by disrupting its cell membrane integrity
- Fluoride substitutes for hydroxyl ions in hydroxyapatite, forming fluorapatite with a lower critical pH (~4.5) (Correct answer)
- Fluoride binds salivary glycoproteins to block acquired pellicle formation on enamel
- Fluoride inhibits salivary amylase, reducing fermentable carbohydrate availability for plaque bacteria
Correct answer: Fluoride substitutes for hydroxyl ions in hydroxyapatite, forming fluorapatite with a lower critical pH (~4.5)
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?
- Type I — IgE-mediated immediate hypersensitivity
- Type II — cytotoxic antibody-mediated hypersensitivity
- Type III — immune complex–mediated hypersensitivity
- Type IV — T-cell–mediated delayed hypersensitivity (Correct answer)
Correct answer: Type IV — T-cell–mediated delayed hypersensitivity
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?
- Prostaglandin I2 (prostacyclin)
- Prostaglandin E2 (PGE2) (Correct answer)
- Thromboxane A2 (TXA2)
- Prostaglandin D2 (PGD2)
Correct answer: Prostaglandin E2 (PGE2)
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.
Question 6: When evaluating literature to support a clinical guideline on subgingival scaling frequency, which study design provides the HIGHEST level of evidence?
- A well-conducted cohort study following 500 patients over 5 years
- A single randomized controlled trial with blinded outcome assessment
- A systematic review with meta-analysis of multiple randomized controlled trials (Correct answer)
- A cross-sectional survey of periodontists' current treatment preferences
Correct answer: A systematic review with meta-analysis of multiple randomized controlled trials
The evidence hierarchy places systematic reviews with meta-analysis of RCTs at the apex because they synthesize findings across multiple high-quality trials, reducing random error, increasing statistical power, and improving generalizability. A single RCT, while strong, ranks below this pooled synthesis of the best available individual studies.
