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Enamel Etching Mechanism — NDEB AFK MCQ

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ModerateRestorative DentistryEnamel Etching MechanismNDEB AFK

Which of the following correctly describes the mechanism of acid etching enamel with 37% phosphoric acid?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: C — It selectively dissolves the inorganic hydroxyapatite crystals creating a microporous surface for micromechanical retention

37% phosphoric acid selectively dissolves hydroxyapatite crystals from the enamel prism cores and/or periphery (depending on the etch pattern type I, II, or III), creating a microporous surface with a depth of approximately 5-50 μm. When unfilled resin (bonding agent) is applied, it flows into these microporosities by capillary action and polymerises in situ, forming resin tags that provide micromechanical retention (bond strength 20-50 MPa). Etching time is 15-30 seconds for enamel.

Reference: Heymann – Sturdevant's Art and Science of Operative Dentistry, 7th ed., 2019