Physical pressure on sciatic nerve for pain relief

INTERVENTION: Physical pressure on the sciatic nerve by squatting down, without any other kinds of intervention before or at the same time. The study is conducted immediately before the the dental procudure. The duration of the pressure is 3 minutes. Patients were randomized to receive placebo or treatment intervention. Each patient is allowed to join the study for one time. CONDITION: Patients at pain with dental diseases. PRIMARY OUTCOME: Pain as measured by VAS scores and assessed statistically. SECONDARY OUTCOME: Nil. INCLUSION CRITERIA: Mental stable; Education high than middle school; patients with pain caused by acute pulpitis, gingivitis and periodontitis.