Dents are depressed layers of wood caused by hard impacts. They can be raised back to original level by steam. Place several layers of damp fabric or damp, brown wrapping paper over the dent. Touch the fabric or paper with a warm iron. The steam will cause the wood fibers to swell back into place. It may be necessary to repeat this process until the dented area is level with the surface around it. Allow the area to dry.
Since the steam opens the wood pores, sand the area thoroughly to "repack" the grain. If you don't, the area will absorb more stain and have an uneven color.
NOTE Don't use this treatment on veneers. The steam can soften the glue under the veneer and cause it to come loose. Also, be careful when applying steam near joints because the glue there can soften, also. When an impact has been great enough to cut through the wood fibers, steam and heat will not repair the damage. Fill the dent with a wood filler to make it level. Follow directions on the package.