That depends on the depth of the filling and the individual's tolerance.

Some patients can tolerate fillings without anesthesia, but I am not one of them.

Restoring teeth to normal function without anesthesia generally is uncomfortable.

It all depends upon the size and depth of the decay. Your dentist can usually determine if it is a good idea to try it without anesthesia. Some people can tolerate a little discomfort, others not so much. Some small areas of decay can be done with a laser procedure without anesthesia, however, your dentist would need to make that decision.

Everyone's sensitivity level is different. The depth of the cavity and the health of the nerve affect how sensitive things would be. A well-trained dental professional can keep you very comfortable when they numb you. I recommend numbing for fillings!

Depends on depth of cavity & sensitivity of tooth, some can get away without anaesthesia.

It varies greatly from person to person and cavity to cavity. Sometimes superficial cavities do not require much drilling and can be done with minimal discomfort. Larger, deeper cavities that require drilling into the middle dentin layer of the tooth are typically much more sensitive and are done more comfortably with a local anesthetic such as lidocaine. Ask your dentist prior to your procedure if you could try it without the shot if you are curious or nervous about the injection. 

Sometimes yes and sometimes no.

Fillings are typically done when decay is suspected to have reached the dentin, the layer of tooth beyond the protective outer enamel layer. The dentin layer is highly sensitive and anesthesia is typically required for comfort.

Joseph J. Lee, DDS

It all depends how big the cavity is. For small cavities, we do fillings without anesthesia.