Nitrous oxide alternatives

Hello!

I'm working with some NHS dental units that are currently commissioned to provided dental procedures under light sedation. They predominantly use nitrous oxide at present, but I was wondering whether there are any alternatives being used in other units around the country? 

I've seen that they use penthrox in australia, but that doesn't seem to be used in dentistry in the UK and is only used in emergency departments. 

Any info on this greatly appreciated!

Lauren