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Etching enamel.

A, Gel etchant dispensed on the enamel portion of the preparation. B, Frosty appearance after etching, rinsing and drying. C, Magnified view of etch pattern with preferential prism periphery etch (type 1). D, Bonding agent revealed after dissolving enamel. E, Mixed etch patterns showing type 1 (light prisms with dark periphery) and type 2 (dark cores with light periphery) etching on same surface