Some biomaterials including implants have been widely used in dentistry and oral surgery.They work well in many (but not all) cases. The purpose of this study is to reexamine unfavorable cases and to show a concept in dealing with the clinical use of implants. We observed 5 unfavorable cases to which were applied various systems. The patients consisted of three males and two females, 43 to 78 years old. Their chief complaints were painful swelling, abnormal sensation,and mastication difficulty. Clinical symptoms disappeared after the removal of implants. These cases indicated that the success of implantation would depend on the preoperative evaluation of a patient, surgical procedure, postoperative care and etc.