Loss of Tooth Structure

Both enamel and cementum may be lost either gradually or suddenly from the tooth surface. The sudden exposure of dentin will elicit more acute hypersensitivity since gradual dentin exposure over time allows for the development of protective measures such as smear layer, sclerosis, and proliferation of secondary/ reparative dentin.

Enamel is less susceptible than cementum to erosion or abrasion, since it is thicker and more highly mineralized. At the area of the cementoenamel junction there may be only a thin layer of enamel, making this area particularly susceptible to loss of tooth structure. Because the layer of cementum is thin and not highly mineralized, it easily can be abraded or eroded in this area. In approximately 10% of teeth, the enamel and cementum do not meet, leaving an area of exposed dentin. When gingival recession is also present, this is a mechanism by which sensitivity occurs.43

Tooth wear, leading to loss of enamel or root surface, may result from abrasion or attrition. Attrition is tooth-to-tooth contact, which results from occlusal function or para-function, such as bruxism, and can cause loss of tooth structure on the occlusal surfaces and incisal edges. Neither abrasion nor attrition usually results in hypersensitivity due to the force-created smear layer, which obturates dentin tubules.44 Both of these gradual traumatic processes stimulate the development of natural protective measures, such as secondary dentin and sclerosis. This can be observed in older individuals who show more exposed dentin, but less sensitivity than their younger counterparts.45

Erosion is thought to be the major source of tooth wear, and has been defined as tooth dissolution by acids that are not of bacterial origin.46 Erosion from dietary acids is thought to work in combination with abrasion from toothbrushing and toothpaste, leading to more loss of tooth structure than would be possible with either effect alone.47-49 That is why brushing with toothpaste after consuming acidic food or drinks can be damaging.1 The additive combined effects of abrasion and erosion may not always lead to hypersensitivity since protective measures may develop over time. Protective measures can be enhanced by the burnishing effects of the toothbrush or toothpick which may stimulate secondary dentin, and the toothpaste abrasives which may serve to obliterate dentinal tubules (Figure 6).

Abfraction is another mechanism that can lead to loss of tooth structure. An association has been demonstrated between cervical dentin hypersensitivity and abfractive lesions.50 These cervical lesions, caused by occlusal stresses, lead to weakening of the cervical tooth structure and can cause enamel, cementum, or dentin to chip away from the cervical aspect of the tooth (Figure 7). The appearance of the lesion is a V-shaped cervical notch (Figure 8). Abfraction is most likely a co-factor with abrasion or erosion in tooth structure loss, since abfraction has not been identified as a sole cause of hypersensitivity.51 In fact, enamel loss rarely results from a single agent but rather from a combination of two or three contributing factors.1,3