A dentist in a big metropolitan city like Bangalore or Mumbai or Delhi would never use non sterile instruments. I think u r referring to the Scaler tips. All are autoclaved and sterilised these days. Don't worry.. Only a highly negligent doctor would do such a blunder of not sterilizing his equipment.
The chances of HIV or hepatitis transmission through used needles is very very high, but practically speaking, no doctor in today's time will ever use a needle twice..... the cost of the needle is very nominal and the emphasis that is put on sterilization and disinfection during our training is enough to deter any doctor from reusing needles or even gloves and masks...... if it is the scaler tip that you are referring to as the needle, then please understand that it is not disposable but it is sterilized by autoclaving which is the best sterilization modality in the world as of now.... Regards.....
U need not worry about it. Scaling (cleaning) needles are sterilized by dentists with basic sterilization process, so there are very less chances of getting infected.
But still if you have a doubt you can ask a dentist or any health professional to disclose his/her sterilization procedure for instruments used and the dentist will be happy to explain his / her procedure as it is your right to know about it.
You must be talking about the cleaning tip that your dentist would have used for your scaling. They aren't disposable. They need to be autoclaved/sterilised before any treatment. The risk of HIV is definitely high if the instruments are not sterilised. But no dentist will do this blunder of using an unsterilised cleaning tip on any patient.
Did the dentist inject you with the needle? Are you talking about the scaling tip? The scaling tips are sterilized on a regular basis. The risk factor for hepatitis/ HIV on used needles being re-used is high but, the chances of that happening are very less. Trained health professionals would never do that unless they are unsound of mind.
In Todays World, this is almost impossible. The needle which you call on a cleaning machine is an extension of the scaling(Cleaning) iinstrument, the scaler. It is detachable and is autoclavable(Sterilised). It is not disposable.Almost all dentists all over the world follow strict sterilisation procedures, understanding the risk of various infections. Considering that you should not have too many reasons to worry.