One would expect the £5000 to be with the dentist in a matter of days from release from the loan company. This could easily be arranged. If something happened and the money was not spent immediately on dental surgery then firstly the loan agreement may have been broken and secondly if the money ended up long term in a savings account then the DWP may need to be informed.
David
Nothing on this board constitutes legal advice - always consult a professional about specific problems
