The ornamental design for a dental handle instrument, as shown and described.
FIG. 1 is a front perspective view of a dental handle instrument with tools shown in broken lines and extending from opposite ends.
FIG. 2 is a first side plan view thereof.
FIG. 3 is a second side view thereof.
FIG. 4 is a top view thereof; and,
FIG. 5 is a bottom view thereof.
The broken line showing of the tools is included for the purpose of illustrating environmental structure and forms no part of the claimed design. The other side views of the handle of a dental handle instrument (with or without the tools shown in broken lines) are similar or symmetrical to the illustrated first side plan view of FIG. 2.