Currently medical accidents suits are growing with increase of concern to oral health and dental office utility. Nevertheless this increase of medical accidents suits, the study on their cures are few. The purpose of this study was to investigate causes and preventive methods using case study of medical accidents. Cases were collected by the interview with dental practitioners in dental office. Collected cases were classified to seven fields of dental practice, four steps of dental practice, several causes, and methods of solution. Medical accident cases in field of oral and maxillofacial surgery were 58 cases, 53.4%. The accident cases in dental care step of dental practice were 78 cases, 70.3%. Also technical insufficiency and carelessness of dental practitioner during dental care were 26 cases, and 25 cases, 56 cases were solveded by reconciliation between dental patient and dentist.