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Dentistry: Interpreting Dental Radiographs continued... There are numerous theories as to eitiology; however none have been proven at this time. Odontoclastic resorption occurs at some point on the root surface and progresses at varying rates until in some cases no identifiable tooth remains. Type 1 TRs are typically associated with inflammation such as gingivostomatitis or periodontal disease; therefore, they are commonly seen in conjunction with periodontal bone loss. The teeth will have normal root density in some areas and a well defined periodontal space in areas not affected by the lesion. In addition, there is often a definable root canal in the intact part of the tooth. Therefore, they will have resorption of the teeth and roots which is not replaced by bone. (Figure 5) Type 2 TRs (Figure 6) are usually associated with only localized gingivitis. These teeth will have a different radiographic density as compared to normal teeth, as they have undergone significant replacement resorption. Radiographic findings typically include areas with no discernable periodontal space (dentoalveolar ankylosis) or root canal. In the late stages, there will be little to no discernable root structure (ghost roots). In these cases, the lost root structure will be replaced by bone. The importance of dental radiography in TR cases cannot be overstated. Type 1 lesions typically retain a viable root canal system, and will result in pain and endodontic infection if the roots are not completely extracted. However, the concur- rent presence of a normal periodontal ligament makes these extractions easier. With type 2 lesions, there are areas lacking a normal periodontal ligament (ankylo- sis) which also demonstrate varying degrees of root resorption. In these cases, ex- traction by conventional elevation is difficult to impossible. Therefore, these may be treated with crown amputation if the following rules are satisfied. l No evidence of endodontic disease l No evidence of periodontal disease l Significant to complete root replacement l No radiographically visible periodontal ligament l No radiographically visible endodontic system l Not treating stomatitis (caudal mucositis) It is this author's opinion that teeth with an identifiable root canal on dental radiographs MUST be extracted completely, while teeth with no discernable root canal may be treated with crown amputation. If there is any question, always err on the side of complete extraction. (Learn the techniques of extraction and crown amputation at the San Diego Vet Dental Training Center). Cysts and Neoplasia Neoplasia is defined as a growth of abnormal cells that is not responsive to normal growth control. Neoplasms can be further classified by their biologic behavior as benign or malignant. Benign neoplasia: Benign neoplastic growths often have no bony involvement on dental radiographs. If bone involvement does occur with a benign growth it will typically be expansive (Figure 7). This is because benign oral soft tissue neoplasms do not generally directly invade/infiltrate bone. This pattern of growth will result in the bone "pulling away" from the advancing tumor leaving a decalcified soft tissue filled space in the tumor site. Bony margins are usually distinct and there is often tooth movement. Cysts: Cystic structures will appear as a radiolucent area with smooth bony edges. Similar to other benign growths, they grow by expansion and thus displace the other structures (e.g. teeth). Dentigerous cysts are typically seen as a radiolucent structure centered on the crown of an unerupted tooth (Figure 8). Malignant neoplasia: Malignant oral neoplasms invade bone early in the course of 42 Butler Schein Animal Health™ ph: (888) My1-BSAH (691-2724) | fx: (888) 329-3861 | www.ButlerSchein.com disease and result in irregular, ragged bone destruction. Initially, the bone will have a irregularly mottled "moth eaten" appearance (Figure 9), but radiographs late in the disease course will reveal a complete loss of bone in the area (the teeth will ap- pear to float in space) (Figure 10). Pathologic Mandibular Fractures Proper radiographic interpretation is critical in the area of the mandibular first molar in older small and toy breed dogs, as pathologic fractures are quite common. This occurs when the mandible has been severely weakened by endodontic or more commonly periodontal disease thus leading to the fracture (Figure 10). Standard radiographic resolution is often inadequate for the diagnosis of small periapical or periodontal lesions which contributed to the fracture. The increased detail of dental radiographs is required for proper diagnosis. Finally, if a mandibular fracture is not responding to what is considered proper therapy, dental radiographs may elucidate the cause of the non-union (Figure 11). It is impossible to perform proper dental therapy without dental radiology. Appropriate exposure technique and interpretation will greatly improve the quality of dental care within the practice. The examples and descriptions in this article provide a base for the novice practitioner; however it did not cover the majority of pathologies as well as the variations of the diseases presented. The reader is di- rected to continuing education programs and/or www.vetdentalrad.com for advice on atypical cases. Further reading: Niemiec, BA: Small animal dental, oral, and maxillofacial disease, a color handbook London, Manson, 2010 (available at www.vetdentalrad.com). Mulligan TM, Aller MS, Williams CE. Atlas of Canine and Feline Dental Radiography. Trenton, Veterinary Learning Systems. 1998. Dupont GG, Debowes LJ. Atlas of Dental Radiography in Dogs and Cats. Saunders,