Читать книгу Feline Dentistry - Jan Bellows - Страница 43

Dentin is located beneath the enamel and cementum and composes the majority of the mature tooth mass. Dentin is a specialized connective tissue of mesenchymal origin and is the second hardest tissue in the body after enamel. It is 70% inorganic and 30% organic (water, collagen, and mucopolysaccharide).

Figure 1.33 (a) Suspected fusion of supernumerary mandibular fourth premolars. (b) Radiograph confirmation of fusion.

Dentin is porous; each square millimeter contains over 40 000 dentinal tubules that communicate between the pulp and the dentin‐enamel or dentin‐cementum junctions. If there is near‐pulp exposure from trauma or resorption, bacteria can travel through the exposed dentinal tubules to the pulp. If untreated, inflammation may spread up and/or down the pulp, eventually causing irreversible necrosis. Odontoblast processes extend into the dentinal tubules. Near exposure can also transmit painful stimuli (heat, cold, pressure) due to afferent nerve fibers within the tubules adjacent to the odontoblastic processes. Toxic products from damaged tissue and microorganisms in the tissue perpetuate inflammation.

During pre‐eruptive development and during eruption, the odontoblasts produce primary dentin. Once the tooth has developed to its final length, the odontoblasts produce secondary dentin, causing the dentinal walls to thicken toward the pulp cavity. Primary dentin is deposited until root formation is complete, then secondary dentin accounts for all subsequent dentinogenesis throughout life. This effectively decreases the width of the pulp cavity as the cat ages. Reparative or tertiary dentin is produced in response to thermal, mechanical, occlusal, or chemical trauma to the odontoblasts. The pulp chamber in cats lies closer to the enamel than in dogs. For this reason, any tooth fracture in the cat should be treated aggressively, since most require endodontic therapy or extraction.

Two microscopic features of the dentin known as vasodentin and osteodentin may occasionally exist. Vasodentin is characterized by microscopic vascular inclusions within the outer third of the dentin. It is found to have vascular channels and dentinal tubules coursing through randomly. Osteodentin, unlike vasodentin, is most often found in the dentin adjacent to the root canal. Osteodentin resembles tertiary dentin which occurs secondary to trauma. Previous studies have demonstrated the presence of these two peculiar microscopic structures in cats which have tooth resorption. However, vasodentin and osteodentin have also been found in teeth free of resorption, making a cause‐and‐effect relationship difficult to confirm.