Feline odontoclastic resorptive lesions
Feline odontoclastic resorptive lesions (FORLs)1,12,20-22 are the result of odontoclastic destruction of feline teeth and are classified as either type 1 (no bone replacement) or
type 2 (bone replacement occurs).21,23 Odontoclastic resorption will occur at some point on the root surface and progress at varying rates until, in some cases,
no identifiable tooth remains.
Studies have reported up to a 65% incidence of FORLs in cats more than 6 years of age.24 Numerous theories on etiology exist, but none have been proven. FORLs are not bacterial in nature, although in some cases
the inflammation that activated the odontoclasts may have been caused by bacteria.23,25
Type 1 FORLs (Figure 16) are typically associated with inflammation such as gingivostomatitis or periodontal disease.23,25 Thus, they are commonly associated with periodontal bone loss on dental radiographs. 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, a definable root canal
in the intact part of the tooth is often present. Type 1 FORLs exhibit resorption of the teeth and tooth roots without bone
replacement (absence of dentoalveolar ankylosis).
Figures 14, 15, 16, 17, 18, 19
Type 2 FORLs (Figure 17) are usually associated with localized gingivitis (which can be severe in some cases) on oral examination, in contrast to
the more widespread inflammation due to periodontal disease or gingivostomatitis seen with type 1 lesions.23,25 In these cases, the gingival inflammation is secondary to the FORL. These teeth have a different radiographic density as
compared with normal teeth, as they have undergone marked replacement resorption. Findings will include areas with no discernable
periodontal space (dentoalveolar ankylosis) or root canal. In the late stages, little to no discernable root structure (ghost
roots) will be present. In these cases, the lost root structure will be replaced by bone.
Differential diagnoses for FORLs include caries (rare in cats), neoplasia, metabolic disease, or trauma.
The importance of dental radiography in FORL cases cannot be overstated.22 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 concurrent presence of a normal periodontal ligament makes these extractions routine.
With type 2 lesions, areas lacking a normal periodontal ligament (ankylosis) also demonstrate varying degrees of root resorption.
In these cases, extraction by conventional elevation is difficult to impossible. If there is marked dentoalveolar ankylosis,
a tooth with a type 2 FORL may be treated with crown amputation therapy.26 It is my 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.
Carious lesions are the result of acidic degradation of the mineralized dental tissues (enamel and dentin).27 They appear radiographically as radiolucent areas in the crown or root of the tooth (Figure 18). They most commonly occur in domestic dogs on the occlusal surfaces of the molar teeth. However, they can also be seen in
interproximal areas, particularly in areas of close tooth proximity. In most cases, an obvious lesion is noted on oral examination.
The extent of tooth structure loss will be clinically evident to a certain extent and, thus, help with treatment planning.
As in periodontal disease, remember that about 40% of the mineral in the tooth must be lost before radiographic changes will
be noticeable. So radiographs underestimate carious loss as well. Since the owner may elect extraction as opposed to root
canal therapy on an endodontically diseased tooth, endodontic involvement must be evaluated before initiation of cavity preparation.
Cysts and neoplasia
Neoplasia is defined as a growth of abnormal cells that is not responsive to normal growth control.1,28-30 Neoplasms can be further classified as benign or malignant.