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(a,c) Widening drill (depth 4 mm and diameter 4.1 mm) with countersink (depth 0.5 mm and diameter 5.5 mm). (b,d) Conical guide drill (depth 3 + 4 mm and diameter 3.1 mm), which is described in detail in patent [35]. All drills are made of hardened stainless steel (WS 1.4197). Pictures taken with the Carl ZEISS Vario700 microscope, 6.5× magnification; focal length 225–235 mm.
