Amnesia for dental procedures and mood change following treatment with nitrous oxide or midazolam

Fifty-eight patients undergoing restorative dental treatment at Guy's Hospital had been previously allocated on the basis of clinical assessment, including that of their dental anxiety, to treatment under local anaesthetic alone or in combination with i.v. midazolam or inhalation nitrous oxide. They were tested before and after dental treatment to determine their memory of dental procedures and changes in mood and bodily symptoms. The patients allocated to the midazolam treatment had significantly higher pre-treatment scores on the Bond & Lader mood factors of "anxiety" and "discontent". All the groups showed significant pre- to post-treatment reductions in sweating, palpitations, restlessness, dry mouth, muscular tension, nausea, loss of appetite and upset stomach and the extent of these reductions were not different for the different treatments. Midazolam treatment resulted in significantly greater reductions in self-ratings of bodily symptoms of anxiety, shaking and trembling compared with the control (local anaesthetic) group. Nitrous oxide resulted in a significant reduction in irritability, compared with controls. Both midazolam and nitrous oxide significantly reduced the patients' memory of the dental procedures and the impairments in memory were independent of any changes in anxiety or sedation. Of the items remembered there were no differences between the groups in their ratings of how well explained, how pleasant or unpleasant, or how painful the procedures were.