The analgesic effects of aspirin and placebo on experimentally induced tooth pulp pain.

We examined the relative analgesic potency of aspirin and placebo in a within-subject-repeated-measure experiment using a precision tooth pulp stimulation technique with long-term stability (r = 0.93) for more than two months between measures. The attenuation of pain perception was evaluated using a standardized magnitude estimation procedure and constructing an individual psychophysical function for each trial. The data were fit equally well by either a straight line (Y = mX + b) or a power function (Y = mXa + b). Using the line fit and distribution insensitive conservative statistical tests, the effect of each treatment was compared to baseline and the treatments were compared to each other. In randomized, double-blind trials we found reliable effects of both aspirin (p less than 0.001) and placebo (p less than 0.001) but no difference (p = 0.08) between these two treatments. However, on an individual basis, 12 of 17 subjects displayed a larger analgesic response to aspirin than to placebo (p less than 0.05).