Dental abrasion is the loss of tooth structure due to mechanical force by a foreign element. The most common source of this wearing is toothbrushes. But it also can be dental floss, toothpicks and any dental appliances.
In this case, the patient came in as an dental emergency, complaining of severe toothache and shooting pain. He brushed so heavily that all the enamel and dentine was brushed away, and eventually exposed the nerve. Unfortunately, he couldn't afford root canal treatment and extraction was performed.
The right thing to do: Use soft toothbrushes or electric ones. Brush gently but thoroughly with little circular motion.