The ornamental design for a dental blankholder, as shown and described.
FIG. 1 is a perspective view of a dental blank holder showing my new design;
FIG. 2 is a perspective view thereof showing the dental blank holder holding exemplary dental blanks;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a cross-sectional view taken along line 7-7 in FIG. 3;
FIG. 8 is a top view thereof;
FIG. 9 is a bottom view thereof; and,
FIG. 10 is a cross-sectional view taken along line 10-10 in FIG. 3.
The short dash broken lines illustrate unclaimed and environmental features that form no part of the claimed design. The long dash-short dash lines represent boundaries of the claimed design.