The sample calculation will be based on the primary binary outcome (sensitivity risk 24 hours after the procedure) for superiority trial. Power of the test will be set at 80%, considering a type I error of 0.05; risk to tooth sensitivity of 63% (potassium nitrate) and 35% (potassium oxalate), while a reduction around 55% with the treatment will be expected. The calculation resulted in fourty seven patients.