Wisdom tooth: my dentist suggested me to remove all of my wisdom tooth. one of them has a large cavity (bottom left) and the other is growing inwards. the one with cavity pains but the other is alright. is it necessary to get all four removed?

Unknown: So many variables in your post. The one that is erupting lingually, is that the lower right? You may be impacting bacteria and food around it, affecting the second molar. Once the lowers are removed, the maxillary third molars are useless since there are no antagonists. Your dentist knows your mouth better than anyone on the internet. If you value his/her opinion, then extract them.

Wisdom teeth: The best person to advise you is your Dentist, the professional that knows you best. There are many good and just reasons for removing wisdom teeth besides infection, including malposition, inability to properly clean, conduit for bacteria, improper occlusion, etc. It sounds as if your Dentist is being prudent. Ask to be referred to a wisdom tooth specialist, an Oral Surgeon, for treatment.