Dental and oral is body organ located on the face, so that the health of the teeth and mouth is very important. Some of people fell fear to dentist because it take times and expensive cost. Knowledge improvement could assist expert to insert, update and delete data diseases so that the system remains accurate and up to date. Fuzzy logic method is used to obtain the user's trust value (wi), while the certainty factor method is used to get an answer from the system diagnostics. After the user has answered about 27 questions, then the system displays the result of diagnosis based on the users answers. The diagnosis results are used to obtain the accuracy of the system based on comparison of the results of the expert diagnosis with the diagnosis results. Accuracy of Expert System with Dental and Oral Disease with Fuzzy and Certainty Factor obtained the result is 94,627%.