Sharpness can be determined by visual inspection. The serrated surface of a sharp blade viewed under intense light (such as that from a dental unit- or head-light) has a matte finish. The sharp serrations diffuse light and result in a matte finish. Under a magnifying lens, this effect is more discernible. On the other hand, a dull edge, from which discreet metal particles have been worn away, has worn down serrations and appears shiny under these same conditions. Shiny light is reflected off the blade surface that has become dull from use (Figure 1).
A plastic test stick is designed specifically to differentiate a sharp instrument from a dull one. A sharp blade edge will “bite” into the plastic surface whereas a dull one will glide along the surface without engagement. Furthermore, a sharp blade edge produces a metallic clicking sound (Figure 2).