It has been suggested that removal of occlusion contacts will prevent or reduce postoperative endodontic pain during treatment. However, this theory has not been tested in clinical experiments. In this study, after endodontic instrumentation, the treated posterior tooth randomly received occlusal relief or mock-occlusal relief. Mean pain levels and the incidence of pain to occlusal pressure at various time intervals were recorded on questionnaire postcards by all patients, as was the duration of discomfort. Comparison of pain experienced by the occlusal treatment groups through statistical analysis gave the following conclusions: Spontaneous pain levels in the mock-occlusal relief and occlusal relief groups were not significantly different; Spontaneous pain levels in the mock-occlusal relief and occlusal relief groups did significantly relate to preoperative pain; Pain incidence from occlusal pressure in the mock-occlusal relief and occlusal relief groups did not significantly differ; Pain from occlusal pressure in both occlusal treatment groups did not significantly relate to preoperative pain; Duration of discomfort was not related to the occlusal treatment provided. The theory may be invalid that prophylactic removal of occlusal contacts is a pain preventive measure.