The widely held opinion within dentists that bleaching is harmless is disputed; by the study findings of Dr. Irwin Smigel, President of American Society for Dental Aesthetics. His findings are valuable, owing to problems associated with this teeth-whitening procedure.

Dr. Smigel's study findings
a. Bleaching teeth at a moderate level, does not pose any problem. But over bleaching leads to breakdown of enamel and teeth color turns blue gray or even blue.
b. Research has shown that over bleaching, lead to tooth discoloration making them look unnatural and sometimes may lead to a different color.
c. Smigel has also advised against the use of teeth whitening trays. Many of the teeth whitening trays do not cover the gums properly and this leads to damage of gums.