Previous studies of dental pain have indicated a maximum intensity of pain at around 8 hours following third molar extractions. On a 100 mm visual analogue scale the mean (S.D.) pain score was 40.9 (24.4). At a pain score of 27.3 the S.D. was 17.2. We estimate that 17 patients are required for a power of 80% and a 50% decrease in pain.