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A dent can develop due to wrong posture while sleeping or due to something pressing on the forehead. An indentation can develop on the forehead in case of mucocele of paranasal sinuses or scleroderma. Indents or furrows can also develop due to wrinkles. Also when the brows sag, this causes indents on the forehead. It is difficult to pinpoint the cause on net. Since a confirmed diagnosis cannot be given on net please discuss these possibilities with your PCP once, if the dent persists.Take care!