Employee was installing propel motor on P&H 2800 shovel. Employee tightened feet bolts with impact wrench. Injured worker was verifying that he had all the bolts tightened by using 2-1/4"" slap wrench and sledge hammer. As employee attempted the bottom foot bolt, the slap wrench came off the nut, striking the employee in the mouth, chipping the top right central incisor.