# All of the following are contraindications for root planing except: A. deficient or overhanging margins of amalgam restorations B. erosion and/or abrasion C. recession D. root caries # While sharpening curettes and sickles, the internal angle of ________ must be preserved between the face and lateral surface. A. 50-60 B. 60-70 C. 70-80 D. 80-90