We need to evaluate the cavity, if it's not deep then normal filling can be done, injections may not require for filling... But if the cavity is deep, need to do a Root Canal Treatment, the numbness injection will be given... But don't have to worry about injection it won't be painful... Just a feel of prick you will get, it will be bearable pain...

Get a dental check up and fill the cavities asap. You may feel slight sensitivity but no pain if the cavities are not deep. Local anesthetiser injections are pretty painless so don’t worry. If required your Dr will give you a local anaesthetic to make you comfortable during the procedure

Filling of cavity is not a painful procedure. However if the cavity is deep and has affected the tooth nerve root canal treatment maybe required which requires the dentist to give you numbing injection to make the procedure painless along with a course of antibiotics. Regards Fusion Dental