Lekholm and Zarb classification based on bone macrostructure: Q1, almost the entire jaw is comprised of homogenous compact bone; Q2, a thick layer of compact bone surrounds a core of dense trabecular bone; Q3, a thin layer of cortical bone surrounds a core of dense trabecular bone; Q4, a thin layer of cortical bone surrounds a core of low-density trabecular bone. Misch classification based on the clinical drilling resistance of the bone: D1, oak or maple wood; D2, white pine of spruce wood; D3, balsa wood; D4, styrofoam. n: number of implant sites.