1. Department of Endodontology and Oral Diagnosis, Faculty of Odontology, Göteborg University, Box SE 40530, Göteborg, Sweden
2. Department of Endodontology and Oral Diagnosis, Faculty of Odontology, Göteborg University, Box SE 40530, Göteborg, Sweden, Department of Endodontics, Faculty of Dentistry, Tokyo Medical and Dental University 5-45, Yushima 1-chome, Bunkyo-ku, Tokyo 11 3, Japan