For a dental hand instrument with a formula of 10-8.5-8-14, the number 10 refers to

The first number is the width of the blade or primary cutting edge in tenths of a millimeter (0.1 mm). The second number of a four-number code indicates the primary cutting edge angle, measured from a line parallel to the long axis of the instrument handle in clockwise centigrades. The angle is expressed as a percent of 360 degrees. The instrument is positioned so that this number always exceeds 50. If the edge is locally perpendicular to the blade, then this number is normally omitted, resulting in a three-number code. The third number (second number of a three-number code) indicates the blade length in millimeters. The fourth number (third number of a three-number code) indicates the blade angle, relative to the long axis of the handle in clockwise centigrades