What would a periodontist use to record the depth of periodontal pockets, duration involvement and tooth mobility?

A periodontal probe

Explanation:

A periodontist is a dentist who's specialty is the diagnosis, treatment and prevention of periodontal diseases. One of the instruments used by the periodontist in the examination of the gums and teeth, is the periodontal probe.

The periodontal probe is a long, thin instrument, blunted at the end. It is used to measure spaces around the teeth and gums known as pocket depths so as to assess the state of health of the periodontium.

The periodontist measures the pocket depths by placing the probe between the tooth and the gum. He checks to see if the pocket depth is greater than 3mm which is might signify the disease condition called periodontitis.