Dmt crystals of different shapes could be the result of different  conformational isomers making up the crystal lattice  - or maybe not.

Rotatable carbons as benzyme said will always rotate in solution / gaseous phase in which case all possible rotational coformations are equally possible at a given instance. But in a crystal latice there are constrains and fixed conformational isomers can be found. But melt or dissolve the crystal and this effect is lost.

The term conformational isomers is meaningful in larger molecules like proteins or nucleic acids; for dmt, not really.