Interpreting dental radiographs for periodontal disease

The information gained by interpretation of intraoral dental radiographs is essential to the practice of veterinary dentistry.

Figure 1: Periodontal anatomy: (A) alveolar margin (B) lamina dura; (C) periodontal ligament.

Dental radiographs, when correlated with clinical examination and case history, allow the practitioner to see where he cannot feel or probe. In the May 2004 edition of DVM Newsmagazine , intraoral dental indications, equipment, positioning and processing were discussed. This will be the first installment of a multipart series on dental film interpretation as it applies to clinical case management. The images in this series were taken with the ImageVEt 70 Plus and the AFP Imaging EVA-Vet digital senor system.

Stages of periodontal disease

Periodontal disease can be classified from Stages 1 to 4 based on severity of radiographic and clinical signs. Normally, interdental bone appears 1-2 mm apical (toward the root) to the cementoenamel junction (CEJ) (Figure 1). The bone level in periodontal disease decreases as inflammation extends and bone is resorbed. The radiograph is used indirectly to determine the amount of bone loss. Forty percent of the bone must be destroyed before bone loss can be radiographically visualized. Distribution of bone loss is classified as either localized or generalized, depending on the number of areas affected. Localized bone loss occurs in isolated areas. Generalized bone loss involves the majority of the crestal bone. Bone loss is a crude determination of support level. The actual level of periodontal support can be less than the radiographic bone height.

Figure 2: Loss of the normally sharp angles between the lamina dura and the alveolar margins and vertical bone loss of a dog's second mandibular molar typical of Stage 2 periodontal disease.

Gauging attachment loss

Stage1

, gingivitis, occurs when the gingiva appears inflamed. In Stage 1 disease, there is no periodontal support loss or radiographic changes.

Stage 2

, early periodontitis, occurs when attachment loss is less than 25 percent of the root, as measured from the CEJ to the apex. Clinically, early periodontitis is typified by pocket formation or gingival recession. Radiographically,

Stage 2

disease appears as blunting (rounding) of the alveolar margin. The continuity of the lamina dura at the level of the alveolar margin might show a loss in Stage 2 (Figure 2).

Figure 3: Twenty-five to 40 percent horizontal bone loss around the second and third mandibular premolar tooth roots typical of Stage 3 periodontal disease.

Stage 3 , established periodontitis, is diagnosed when 25-50 percent of attachment loss occurs (Figure 3). The direction of bone loss can be horizontal or vertical (angular).

• Horizontal bone loss radiographically appears as decreased alveolar marginal bone around adjacent teeth. Normally, the crestal bone is located 1-2 mm apical to the cementoenamel junction. With horizontal bone loss, both the buccal and lingual plates of bone, as well as interdental bone, have been resorbed. Clinically, horizontal bone loss is typified by suprabony pockets, which occurs when the epithelial attachment is coronal to the bony defect (Figure 4).

Figure 4: Horizontal bone loss around the mandibular fourth premolar and first molar.

• Vertical bone loss, resulting from infrabony (intrabony if three-walled) defects, occurs when the walls of the pocket are within a bony housing. Periodontal disease can cause a vertical defect to extend apically from the alveolar margin. At first, the defect is surrounded by three walls of bone: two marginal (lingual or palatal and facial) and a hemisepta (the bone of the interdental septum that remains on the root of the uninvolved adjacent tooth).

As disease progresses, two-, one-, and no-walled (cup) defects can occur. Radiographically, vertical bone defects are generally V-shaped and are sharply outlined (Figure 5).

Figure 5: Vertical bone loss along distal root of the mandibular second molar.

Stage 4 , advanced periodontal disease is typified by deep pockets and/or marked gingival recession, tooth mobility, gingival bleeding and purulent discharge. Attachment loss is greater than 50 percent of the root height (Figure 6).

Figure 6: Stage 4 periodontal disease with greater than 50-percent bone loss around the second and third mandibular molars.

Furcation exposure

The furcation is where multiple tooth roots divide at the trunk of the tooth. The furcation is a normal structure usually filled with bone. Furcation exposure results from intraradicular (between the roots) bone loss due to advanced periodontal disease. It is sometimes difficult to determine whether the intraradicular space is involved unless there is a radiographic radiolucent area in the region of the furcation. Lack of radiographically detectable furcation involvement is not confirmation of the absence of periodontal destruction (Figure 7). Advanced furcation exposures, where both cortical plates are resorbed, are easily recognized on radiographs.

Figure 7: Normal appearance of the furcation of the maxillary fourth premolar.

• Class I (incipient) furcation involvement exists when the tip of a probe can just enter the furcation area. Bone partially fills the area where the roots meet. Radiographically, there is a decreased density of the bone at the furcation (Figure 8).

Figure 8: Radiograph of a Class I furcation exposure.

• Class II (definite) furcation exposure exists when the probe tip extends horizontally into the area where the roots diverge, but it does not exit on the other side. Radiographically, there will be bone loss at the furcation.

• Class III (through-and-through) exposure lesions exist secondary to advanced periodontal disease with extensive osseous destruction. Alveolar bone has resorbed to a point that an explorer probe passes through the defect unobstructed. Radiographically, there will be an area of complete bone loss (Figure 9).

Figure 9: Radiograph of class III furcation involvement.

Feline chronic alveolar osteitis

Feline chronic alveolar osteitis (buccal bone expansion) clinically appears as bulging alveoli around one or both maxillary and/or mandibular canines.

Figure 10: Bulging areas around the maxillary canines caused by feline chronic alveolar osteitis.

Radiographically, this lesion appears as bone loss around the root and expansile alveolar canine bone growth (Figures 10, 11).

Figure 11: Bone loss around the canine roots is caused by feline chronic alveolar osteitis and root resorption.

Feline supereruption

Feline supereruption (extrusion) occurs when one or more of the canine teeth appear longer than normal. Radiographically, the affected teeth have marked loss of periodontal support (Figure 12).

Figure 12: Loss of lamina dura from tooth affected by periodontal disease in feline supereruption syndrome.