The ornamental design for a dentalinstrument, as shown and described.
FIG. 1 is a side view of a dental instrument that has the design.
FIG. 2 is another side view of the instrument.
FIG. 3 is an enlarged side view of FIG. 1, with the upper portion removed for ease of illustration.
FIG. 4 is a perspective view of the instrument.
FIG. 5 is an exploded view of the instrument.
FIG. 6 is another perspective view of the instrument; and,
FIG. 7 is an enlarged perspective view of the instrument.
The broken lines in the figures are included for the purpose of illustrating a portion of the dental instrument that forms no part of the claimed design.