You may have a case of Oral Submucous Fibrosis. The right approach for you would be to completely abstain from supari, tobacco etc which you have been rightly doing. Not eating spicy food is the right approach too. Avoiding alcohol will also be beneficial. You should have food rich in Vitamin A, B,C, and iron. As a supplement you can take Zincovit Tablet. As for mouth opening, it is restricted by fibrous bands formed inside the mouth due to your previous habits. The treatment involves balanced diet
, supplements as mentioned above, injections inside the buccal mucosa, or surgical incisions if it's a progressive and severely limiting condition. Try to keep a good oral hygiene by brushing twice daily and using mouthwashes I would suggest you to get yourself evaluated soon for this condition as well as the teeth problems you have mentioned.