On July 5, 1995, at 1635 central daylight time, a SAAB-Scania SF340A, N112AE, registered to the AMR Corporation, and operated by Simmons Airlines as American Eagle flight 3710, on a 14 CFR Part 121 scheduled domestic passenger flight from the Draughon- Miller Municipal Airport (TPL), Temple, Texas, to the Dallas/Ft.Worth International Airport (DFW), Texas, sustained minor damage during takeoff. The 3 crewmembers and their 3 passengers were not injured. Visual meteorological conditions prevailed for the flight for which an instrument flight plan was filed. A ground agent observed the outboard tire and wheel assembly separate from the right main landing gear during takeoff roll from runway 33. The flight crew was informed of the wheel separation by company radio 10 minutes after takeoff. According to the pilot, no unusual vibrations were felt nor noises heard during the retraction of the landing gear. The flight continued to DFW where a fly-by confirmed the right main gear outboard wheel/tire was missing. The flight landed on runway 13L without further incident. Examination of the right main landing gear axle revealed that the retaining nut was still attached, and the outboard side of the axle sustained minor damage. According to the operator, the aircraft's right outboard wheel had been replaced the morning of the incident. Inspection of the removed wheel assembly revealed that the spacer was still attached by grease. A check of the maintenance performed revealed that the when the new wheel was installed the required spacer was not put in place.