Which type/form of magnesium is the best for mucle relaxant and TMJ problem? Aspartate?

TMJoint problems. We can't proper advise you without personally examining you and knowing your complete medical and dental history. Nor can we know if muscle relaxants are even indicated for your particular situation.
Meds not answer. Often muscle relaxants are overused for tmj/tmd, as far as I am concerned. Proper physical therapy, exercises and sometimes mouthpieces are more predictable without the side effects.
Need more informatio. Need more information. See a TMJ expert for advice and treatment.