Elite Perio Probe/Explorer PE1/23 Hollow Handle Combination of Probe and Shepherd's Hook Explorer 23. Periodontal Probe – used to measure the pocket depth of the gums around each tooth. A healthy gum will have less than 2 mm of pocket depth. Explorers – used to detect decay in the tooth's surface. If the explorer sticks in the surface of the tooth, the tooth may have some decay that needs to be removed.