Figure 5-2. - Impaction.

Figure 5-3. - Attrition.

biting foreign objects such as a pipestem, thread, or bobby pins. Other mechanical actions such as a poorly fitted clasp of partial dentures or acid from food debris can cause abrasion.

EROSION

Erosion is a loss of tooth substances from a chemical process that does not involve bacteria. It occurs usually on the facial surfaces at the gingival third of the crown and often involves the maxillary incisors. The enamel and dentin on the floor of the lesion are smooth, hard, and glistening. Some types of lesions are called idiopathic erosion because the factors producing this condition are unknown or may occur from a known acid source such as people who have bulimia (who vomit frequently).