[1] Oslo Univ Hosp Ulleval, Dept Maxillofacial Surg, POB 4956 Nydalen, N-0424 Oslo, Norway
[2] Oslo Univ Hosp, Finance Dept, Oslo, Norway
[3] Univ Oslo, Dept Oral Biol, Fac Dent, Oslo, Norway
[4] Univ Oslo, Oslo Ctr Biostat & Epidemiol, Res Support Serv, Oslo, Norway
[5] Oslo Univ Hosp Ulleval, Dept Anesthesiol, Div Emergencies & Crit Care, Oslo, Norway