Quick answer
Internationally trained dentists need Grade B (350) in each of the four OET sub-tests for GDC (UK), ADC (Australia), and equivalent regulators. No Grade C+ concession applies for dentists. Writing is the most retaken sub-test — typically due to Genre & Style losses when adapting register from colleague-dentist to non-dentist addressee (e.g. GP, family member). Tooth notation systems (FDI, Universal, Palmer) require adjustment to the addressee.