Abfractions are thought to be v-shaped notches around the gingival margins of the teeth.  It's their unique sharp angles that differentiate it from abrasion and erosion lesions that tend to be more u-shaped from slow tooth loss over time.

It is suspected that abfractions are a result of buccolingual flexure of the enamel from significant bruxism.  Essentially, the patient is grinding their teeth so hard that the clinical crown moves while the root does not, creating pressure at the gingival margin level of the tooth.  This causes cracks in the enamel and dentin that eventually chip out.

It is difficult to say an abfraction lesion is solely a result of bruxism as there are often a combination of abfraction, abrasion, and/or erosion.

TREATMENT

The common treatment for most abfraction lesions is to place a class V composite restoration.  It is wise to create some grooves for retention inside the lesion and place a bevel onto the surrounding tooth structure in hopes of gaining both mechanical and chemical retention.