Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
1
Is any of this happening now?
Call 911
Seek emergency medical care if facial or neck swelling makes it hard to breathe or swallow, is rapidly increasing, or is spreading toward an eye.
Contact local emergency services rather than waiting for a routine dental visit.
Other emergency signs, for anyone
Someone who is struggling to breathe, gasping, choking, or cannot get words out
Someone who has chest pain, tightness or pressure lasting more than a few minutes
Someone who has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
Someone who is unconscious, or cannot be woken
Someone who is bleeding heavily and it will not stop with firm pressure
Someone who has had a seizure that will not stop, or does not wake up afterwards
Someone who has lips or skin that look pale, blue, grey or blotchy
Someone who you believe has taken an overdose or swallowed something poisonous
2
Is any of this happening?
Be seen today
Ask for an urgent dental appointment if you have:
Severe or persistent toothache
Swelling of the gum, face, or jaw
Pus, a bad taste, or a suspected dental abscess
Fever or feeling unwell with dental pain
A broken tooth causing pain or a sharp exposed area
3
Does any of this apply?
Book an appointment
Arrange a routine dental appointment if you notice new sensitivity, a mark or rough area that does not go away, food repeatedly catching, or a lost or damaged filling.
Early decay may not hurt, so pain is not required before seeking assessment.
The article also says
Painkillers may provide temporary relief, but they do not treat the decay or remove an abscess.
Follow the product label and ask a pharmacist or healthcare professional if you are unsure what is safe for you.
Every sign above is quoted from the sofidex article on Tooth decay. If you are not sure, err upward — it is always reasonable to be checked.