The ornamental design for the dental patient guard, as shown and described.
FIG. 1 is a front perspective view of the dental patient guard according to the present invention.
FIG. 2 is a front view of the dental patient guard.
FIG. 3 is a side view of the dental patient guard.
FIG. 4 is a top view of the dental patient guard; and,
FIG. 5 is a rear view of the dental patient guard.
The broken line showing of portions of the dental patient guard is for the purpose of illustrating environment and forms no part of the claimed design.