In a study conducted in the US on adults 25 and older, 4 out of 10 people were found to be living with the type of tooth sensitivity resulting from exposed dentin, typically caused by overbrushing.  If you have sensitive teeth make sure you're not brushing too hard as it can cause abrasion to your teeth and gums while wearing down your tooth enamel.  This exposes the next layer of your tooth and causes gum recession.  To avoid further damage to your teeth; brush properly with a soft toothbrush, floss regularly to help your gums stay healthy, reduce gum recession, and dentin exposure to keep your oral health in great shape.