The ornamental design for a holder for dentalresin, as shown and described.
FIG. 1 is a perspective view of a holder for dental resin, showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof;
FIG. 6 is a right side view thereof; and,
FIG. 7 is a cross-sectional view thereof taken along lines 7-7 shown in FIG. 2.
A left side view of the holder for dental resin is omitted as it is symmetric in appearance to the right side view of FIG. 6. The broken line showings of FIGS. 1-7 are environmental only and not part of the claimed design.