Went to a dentist due to discomfort in upper premolar. he took x-rays and seemed certain there was no cavity. but he did not i guess the word is probe with a sharp instrument for signs of decay like previous dentists. is this ok?

The discomfort, if not a cavity, could be from gum disease, causing a sensitivity to tooth. Also a small fracture could be present, but seen on an x-ray, but possible seen on a probe. If discomfort continues, have an x-ray taken at a different angle, and a probing and tapping on the tooth done. You could have a piece of food lodged in between your tooth.

A dental explorer (sharp instrument) is used to probe the nooks, crannies, pits, and fissures of teeth for incipient decay. That decay would not cause sensitivity on the tooth. Do you have a sinus condition (allergy, cold, stuffy nose, etc)? Many times an inflamed sinus will result in a maxillary tooth sensitivity when no actual problem exists with the tooth.