In the presence of acute pericoronitis of mandilbular third molar, antibiotic therapy and early incision and drainage are the method of choice, followed by definitive surgical extraction of the tooth as soon as it becomes subacute. If excision of the overlying tissues is decided on, it should be done adequately. All overlying tissues must be throughly excised, and the crown portion of the unerupted tooth should be completely exposed. After excision has been completed, the wound should be managed with a surgical dressing. This should be allowed to remain approximately 7 days. And then, surgical extraction of the impacted mandibular third molar can be done usually. In this operation, there are many complications, such as, postoperative bleeding, infection, trismus, dysphasia and paresthesia. The surgeon are discredited and medicolegal problem may be occurred in the presence of many distressed complications. Therefore, the relatively nonsurgical treatment is the method of choice. So, authors selected the conservative treatment methods of incision and drainage, primary endodontic drainage, operculectomy without surgical extraction of the mandibular third molars. The results were more favorable without the postoperative complication in Wonju old offender prison.