“…The observed effects have been confirmed in different studies after correction for a variety of potential cofounders such as socioeconomic status, education, and oral hygiene. Despite the existence of these potential confounding factors, the impact of smoking is not obscured when all factors accounted for (Feldman et al 1983, Bergström & Eliasson 1987a,b, Feldman et al 1987, Haber & Kent 1992, Horning et al 1992, Bolin et al 1993, Martinez-Canut et al 1995, Bergström et al 2000a,b, Calsina et al 2002, Khader et al 2003, Teng et al 2003, Razali et al 2005, Apatzidou et al 2005.…”