I think you will find that the PVG will show convictions, impending prosecutions, and any other information that the police hold which is relevant to the application (PVG is the Scottish equivalent to a DBS check in England and Wales, for those who do not know) An application for employment as a dental nurse implies access to drugs (Lidocaine) for pain relief, therefore whilst the investigation into the drink driving may not be relevant, the cocaine driving element certainly IS relevant.
If you do not disclose this now and try to bluff your way through it, I feel this will involve suspension and probable dismissal when it does come to light, not just because of the offence involving drugs but your failure to disclose the investigation.
I think you have to ask yourself,” how will I perform at work knowing this is hanging over me and the likely outcome?” Are you looking for a career, or a few months “works experience”, because that is all this would probably be, even if the arrest did not immediately show up.
The difference between a PVG and a DBS is that if a DBS check is clear, you would escape notice until the next one is done, whereas with a PVG check your case remains ‘live’ and as soon as you get a conviction your employer is updated almost straight away on a continual basis.
‘Fess up, and the anxiety you feel about what will happen will be resolved.