It would be an excellent option to get your tooth removed, rather than getting into the whole hassle of opening your mouth so wide that your jaw hurts, the doctor trying all possible ways to clean up and fill the cavity. It’s not a problem to get fillings done on your 3rd molar, but it’s a hassle on an impacted one and also, your toothbrush won’t reach the tooth good enough to clean all of it’s surfaces and you might have to get it extracted at one point when there’s a new cavity which goes unnoticed on the back side of the tooth (towards your throat) as it has one cavity already. It might be susceptible to more.

Hello, it depends on the mouth opening and accessibility of the instrument to reach there. If filling can't be done you can undergo topical flouride application from dentist to arrest the profession of the caries.

Hello It would be better if you can go for the tooth extraction