Unification of disease name notation and its code is important to promote medical activities and using standards have been strongly encouraged. Although online medical insurance claims service is improving, we still have problems that unregistered disease names, coded as “0000999” with free style texts, are transferring online in medical and dental treatment fee claims. In this study, we analyzed unregistered disease names for dentistry provided from Health Insurance Claims Review & Reimbursement Services in Japan. About 23 percent of unregistered disease names was fully matched with disease names, index words or synonyms that were already registered in the Japanese standard disease code for dentistry. About 16 percent of them was also fully matched with abolished disease names, and 25 percent of them was matched with standardized disease names if brackets, arrows or spaces were removed from the term. These results suggested that careful investigation of the standard code tables that contain correspondence data, index term data, modifier data, and supplementary comments might reduce the ratio of transferring unregistered disease names from medical/dental institutions online.