The stock tray should be _______ mm larger than the ridge.

 # In primary impression, the stock tray should be _________ mm larger than ridge. 

A. 2 mm 

B. 4 mm

C. 6 mm

D. 8 mm

The correct answer is C. 6 mm.

If the tray is too large, it will distort the tissues around the borders of impression. If it is too small, the border tissues will collapse inward onto the residual ridge and thus reduce the support for the dentures.

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