[1] Kings Coll London, Inst Dent, Div Populat & Patient Hlth, London SE5 9RW, England
[2] Natl Inst Hlth & Welf, Helsinki, Finland
[3] Univ Eastern Finland, Inst Dent, Dept Oral Publ Hlth, Kuopio, Finland
[4] Kuopio Univ Hosp, Dept Oral & Maxillofacial Surg, SF-70210 Kuopio, Finland
[5] Oulu Univ Hosp, Oral & Maxillofacial Dept, Oulu, Finland