(a) before etching {b) after etching for 10 seconds in 2.5• lactic acid Figure ,5 Electron micrograph of enamel specimen after polishing with ¬ micron diamond paste followed by brushing in water for 5,000 double brush strokes Facing page 398

(a) surface etched with 2.5 •o lactic acid and brushed for 5,000 double strokes with dentifrice 'M' (b) surface etched with 2.5 • lactic acid for 10 seconds and brushed for strokes with dentifrice 'C' 5,000 double Figure 6 Effect of dentifrice on etched enamel surfaces Facing page 399

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