NBDHE Scientific Basis of Practice 2

Question 1

Which immunoglobulin class is the most abundant in gingival crevicular fluid (GCF) and plays a primary role in local periodontal defense?

Accepted Answer

IgG

Answer

IgG is the predominant immunoglobulin in GCF, derived from plasma cells in the inflamed gingival connective tissue and periodontal ligament, where it functions in opsonization and complement activation against periodontal pathogens.

Question 2

In research design, a randomized controlled trial (RCT) is considered the gold standard because it:

Accepted Answer

Randomly assigns subjects to experimental and control groups, minimizing selection bias and confounding variables

Answer

Randomization ensures that both known and unknown confounding variables are distributed equally between groups by chance, making the RCT the most powerful design for establishing causality.

Question 3

The cariogenic bacterium Streptococcus mutans produces which key virulence factor that enables its colonization of smooth tooth surfaces?

Accepted Answer

Glucosyltransferases (GTFs) that synthesize insoluble glucans from sucrose for biofilm adhesion

Answer

S. mutans produces glucosyltransferases (GTFs) that catalyze the synthesis of insoluble glucan polymers from sucrose, enabling firm adhesion to smooth tooth surfaces and forming the scaffold of cariogenic biofilm.

Question 4

When calculating the sensitivity of a diagnostic test for periodontitis, which value represents the percentage of people WITH the disease who test positive?

Accepted Answer

True positive / (True positive + False negative) × 100

Answer

Sensitivity = TP / (TP + FN) × 100 — the proportion of diseased patients correctly identified as positive; high sensitivity minimizes false negatives.

Question 5

The Gram stain differentiates bacteria based on cell wall composition. Which characteristic is the basis of the Gram-positive reaction (purple/violet staining)?

Accepted Answer

A thick peptidoglycan cell wall that retains the crystal violet-iodine complex during decolorization

Answer

Gram-positive bacteria have a thick, multilayered peptidoglycan cell wall that traps the crystal violet-iodine mordant complex during the alcohol decolorization step, resulting in a purple/violet color.

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NBDHE Scientific Basis of Practice 2