Veterinary Medicine - July 2008 - (Page 364)

Dental Corner PEER-REVIEWED 1. A complicated crown fracture of the left maxillary canine tooth in a dog (A). Also note the abrasion on the right maxillary canine tooth (B) caused by chewing on a cage. This pattern of abrasion has been called cage chewer’s syndrome and can predispose the teeth to fracture, as has happened in this case. 2A. An uncomplicated crown fracture of the right maxillary fourth premolar tooth (carnassial tooth) in a dog. It was not known how long the tooth had been fractured. Note that there is no direct pulp exposure. The dark area (arrow) is tertiary or reparative dentin. 2B. A dental radiograph of the fractured tooth in Figure 2A. The periapical radiolucent areas indicate endodontic disease, illustrating the need for dental radiography even when the pulp is not exposed. DENTAL ANATOMY Enamel, the tooth structure that covers and protects the crown (the part of the tooth above the gum line), is the hardest substance in the body. Its composition is 96% inorganic calcium hydroxyapatite crystals and 4% water and collagen.8 The inorganic component is arranged in prisms surrounded by a collagen sheath. Enamel cannot regenerate after trauma. Beneath the enamel is a layer of dentin that surrounds the hollow pulp chamber (root canal), which contains the pulp tissue. Dentin and pulp can be considered the same organ. Although morphologically different, the histologic boundary is not distinct. The pulp consists of connective, vascular, and nervous tissues along with reserve mesenchymal tissue, ﬁbroblasts, and specialized cells called odontoblasts. Located at the periphery of the pulp, these cells continuously produce additional dentin, called secondary dentin, as long as the pulp is vital. Odontoblasts also send cytoplasmic processes into channels located in the dentin. These channels, called dentinal tubules, run at right angles to the complex of the dentin and pulp and the dentin and enamel. In addition to the odontoblastic process, an ultraﬁltrate of blood is in the dentinal tubule as free ﬂuid. Because of blood pressure gradients, there is constant outward ﬂow of this ﬂuid.9 The dentinal tubules in dogs are 0.9 to 2.5 µm in diameter, with 20,000 to 90,000 dentinal tubules per square millimeter of exposed dentin. The width and number of dentin tubules depend on the distance from the pulp and the cusp of the crown.8,10 The pulp tissue in human teeth communicates with the body’s vascular system through a single foramen, the apical foramen, located at the root apex. However, in dogs and cats, an apical delta exists where the pulp enters and exits the tooth root.11 As the pulp extends through the root apex, it branches several times, like a river delta. From there, it communicates with the periodontal ligament, periapical bone, and the vascular and lymphatic systems. FRACTURE CLASSIFICATION A dental fracture classiﬁcation system has been adopted by the American Veterinary Dental College.12 The key diagnostic questions to ask are 1) What is the anatomical extent of the fracture? 2) Is the pulp exposed? 3) Is there radiographic evidence of pathology? • Enamel infraction An incomplete fracture (crack) of the enamel without loss of tooth substance • Enamel fracture A fracture with loss of crown substance conﬁned to the enamel • Uncomplicated crown fracture A fracture of the crown that does not expose the pulp (Figures 2A & 2B) • Complicated crown fracture A fracture of the crown that exposes the pulp (Figure 3) • Uncomplicated crown-root fracture A fracture of the crown and root that does not expose the pulp • Complicated crown-root fracture A fracture of the crown and root that exposes the pulp 364 July 2008 VETERINARY MEDICINE

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Veterinary Medicine - July 2008 Contents Leading Off Practical Matters Idea Exchange Clarification Dental Corner The Diagnostic Approach to Hematuria Guidelines for Evaluating Hypercalcemic Cats CE Form Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - July 2008

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