Improper brushing techniques can damage the gums and teeth over time. The aggressive pressure of a toothbrush and even a history of clenching and grinding your teeth can lead to notches evident in these photos. As you can see, the gums have receded exposing the root of the tooth and the protective enamel layer is gone. Not only does it affect the aesthetics of your smile, but it can also lead to sensitivity issues.
These areas can be restored and protected with tooth-colored composite restorations.