[1] Univ Gothenburg, Dept Periodontol, Sahlgrenska Acad, Inst Odontol, S-40530 Gothenburg, Sweden
[2] Postgrad Dent Educ Ctr, Dept Oral Radiol, Orebro, Sweden
[3] Univ Gothenburg, Dept Oral & Maxillofacial Radiol, Sahlgrenska Acad, Inst Odontol, S-40530 Gothenburg, Sweden
[4] MRC, Social & Publ Hlth Sci Unit, Glasgow, Lanark, Scotland