Pain relief with nitrous oxide (aka laughing gas)in dental patients can be enhanced by suggestions or hypnosis; say scientists from University College London.

The study showed that people are more suggestible under the influence of gas. This suggests that dental patients may benefit from being coached to relax while undergoing sedation.

A number of dentists have been trained in hypnosis and find that their patients respond well to being spoken to in a quiet, hypnotic manner.

For the study, the researchers recruited thirty participants, who took part in two sessions. They were given a mask from which they breathed in air or 25 per cent nitrous oxide. The mask was scented to disguise the sweet smell of the laughing gas.

During each session, participants were given a series of mental imagery tests and were asked to rate their response according to a scale of 1-7, where 1 was 'as clear and vivid as the real thing' and 7 was 'no image present at all'.

The participants were asked to close their eyes and imagine tasting oranges or smelling roast beef, feeling linen or hearing the honk of a car horn.

The volunteers were also put through a series of 'imaginative suggestibility' tests based on suggestions given to them while under the gas.

The participants were asked to experience hallucinated sensations.

For instance, they were told to imagine a sour taste in their mouth, and were told that after a while they would actually begin to experience a sour taste in their mouth, and that this would become stronger and stronger.