The ornamental design for a pet dental chew, as shown and described.
FIG. 1 is a perspective view of a pet dental chew showing the new design;
FIG. 2 is a front view thereof;
FIG. 3 is a back view thereof;
FIG. 4 is a left-side elevation view thereof;
FIG. 5 is a right-side elevation view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines illustrate a break in length in the pet dental chew that forms no part of the claimed design. The surface between the break does not form part of the claimed design.