Radiographic Diagnosis of Periodontal Disease

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Inverse radiograph outlining
(white) periodontal ligament

The most common disease in small animals older than five years is periodontal disease. Treatment may include supragingival and subgingival scaling, periodontal surgery, tooth resection, or total extraction. Radiography plays an important role in determining the extent of periodontal disease and therapy. Radiographs are evaluated for alveolar bone changes, interdental bone height, presence of the lamina dura, trabecular patterns, periodontal ligament space, and severity of bone loss.

Radiographs show two dimensional representation of three dimensional structures. At times, radiographs may not adequately show the severity of disease. Early destructive bone lesions sometimes are not radiographically observable. Buccal and lingual alveolar bone are particularly difficult to evaluate because of superimposition and summation. In addition to the radiographic findings, the clinician should rely on clinical examination, including sulcular depths, tooth mobility, and appearance of the attached gingiva in order to decide on the diagnosis and treatment plan.

Normal radiographic anatomy

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Normal alveolar bone
support around maxillary

Normal, healthy alveolar bone has characteristic appearance on radiographs. The alveolar crests are situated approximately 2 to 3 mm apical to the cementoenamel junction of the teeth. The shape of the alveolar crests may vary from rounded to flat. The alveolar crest will normally lie 1-2 millimeters below the cementoenamel junction (CEJ). Between incisor teeth, the alveolar crest will usually appear pointed. Between premolar and molar teeth the alveolar crest will be parallel to a line between the adjacent CEJs -- where the enamel thins and disappears. The alveolar crest will be continuous with the lamina dura of the adjacent teeth. When viewing the lamina dura and the periodontal ligament, only the interproximal portions are visible. The buccal and lingual areas are not seen in the radiograph. Widening of the periodontal ligament space and loss of lamina dura can be interpreted as resorption of the alveolar bone.

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Normal alveolar bone support around
canine and premolars

The overall height of the alveolar crestal bone in relationship to the cementoenamel junction gives evidence of whether loss of bone has occurred. The 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. Initially, periodontitis develops as a localized erosion of the alveolar crest. Bony changes cannot be radiographically detected until they are advanced. As the severity of the periodontitis increases, more alveolar bone is destroyed and the process becomes generalized.

Radiographic bone changes in periodontal disease

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Moderate bone loss around
mandibular incisors secondary
to grade 3 periodontal disease

Bone level

Normally the crest of interdental bone appears 1-2 millimeters below the cementoenamel junction. Bone level in periodontal disease is lowered as the inflammation is extended and bone is resorbed.

Shape of the remaining bone

When the crest of the bone is parallel with a line between the cementoenamel junctions of two adjacent teeth, it is called horizontal bone loss. It is usually caused by inflammation. When the amount of remaining bone is fairly evenly distributed throughout the dentition, it is described as generalized horizontal bone loss. If confined to a specific area, localized horizontal bone loss is used.

Irregular reduction in the height of crestal bone is termed angular or vertical bone loss. With vertical bone loss, there will be greater bone loss on the mesial surface on one tooth than on the adjacent tooth. Usually, inflammation and trauma from occlusion are combined in causing the destruction and irregular shape of the bone.

Crestal Lamina Dura

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Minimal bone loss between
adjacent teeth due to grade 3
periodontal disease

Normally a radiopaque line covers the alveolar socket and extends on top of the interdental bone. Because the facial and lingual bony plates are obscured by dense root structure, radiographic evaluation of bone changes in periodontal disease is based mainly on the interdental septa. The septum is presented as a thin radiopaque border, adjacent to the periodontal ligament and the crest, referred to as the lamina dura. It appears radiographically as a continuous white line. With periodontal disease, the crestal lamina due is indistinct, irregular, fuzzy, and radiolucent.

Periodontal ligament space

The periodontal ligament is composed of connective tissue. In cases where periodontal disease is not present, the periodontal ligament appears as a fine, black, radiolucent line next to the root surface. On its outer side, is the lamina dura, the bone lining the tooth socket, which appears radiopaque. With disease, the periodontal ligament space may appear at varying thicknesses, which can show that the disease involvement is not consistent around the entire root.

Bone destruction in periodontal disease

Patterns of bone loss

The interdental septa may be reduced in height with the crest horizontal and perpendicular to the long axis of the adjacent teeth, or there may be vertical or angular bone loss. A reduction of only 1.0 mm in the thickness of the cortical plate is sufficient to permit radiographic visualization of destruction of the inner cancellous trabeculae.

Amount of bone loss

Radiography is an indirect method for determining the amount of bone loss in periodontal disease. It shows the amount of remaining bone rather than the amount lost.

Stages of periodontal disease


Periodontal disease is also classified from stages 1 to 4 based on the severity of radiographic and clinical signs. Stage 1 is referred to as gingivitis. Clinically, the gingiva appears and swollen inflamed. In stage 1 disease, no bone loss has occurred, and dental radiographs appear normal.

Early periodontitis

Stage 2 disease refers to early periodontitis, and signifies the first appearance of radiographic abnormalities. The loss of alveolar supporting bone is accompanied by an apical migration of the gingival fiber apparatus and the junctional epithelium. The loss of osseous support can occur either as a generalized horizontal loss involving some or all surfaces of the teeth.

The earliest radiographic sign of periodontitis is a loss of definition of the crestal bone. The alveolar crest loses its distinct sharp appearance and becomes blunted. The bony margin becomes diffuse and irregular, and may show areas of localized erosion. In the incisor regions, there will be a blunting of the alveolar crests. In the premolar and molar regions, there may also be loss of the normally sharp angle between the lamina dura an the alveolar crest.

Established periodontitis

Marked bone loss around
distal root of mandibular
fourth premolar

Stage 3 periodontal disease is typified by pocket formation. Radiographically, the bony destruction usually extends to the buccal or lingual alveolar bony plate or both. There may also be horizontal or vertical defects. Horizontal bone loss is used to describe the radiographic appearance of the loss of bone height in the region of several adjacent teeth. Horizontal bone loss may be classified as localized or generalized, depending on the regions involved, and as mild (less than 10% bone loss), moderate (10-30%), or severe (>30%), depending on the extent of bone loss. In horizontal bone loss, both the buccal and lingual plates of bone as well as the interdental bone have been resorbed.

Vertical bone defects-are also called proximal intrabony defects. The defect extends apically from the alveolar crest, and 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, following destruction of either the distal or mesial portion of the interproximal bone septum). As the disease progresses, a two walled defect may occur. Radiographically, the vertical bone defect is generally V shaped and sharply outlined. It is immediately adjacent to the root surface of the affected tooth, and the adjacent bone has a normal radiographic appearance. It is important to understand that intrabony defects may not be identified on the radiograph if the defect is relatively small. Radiography of a gutta-percha point inserted into the pocket may be helpful to evaluate the extent of the defect.

Inconsistent bony margins

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Inconsistent bony

Inconsistent bony margin is result of an uneven resorption of the alveolar cortical plate on lingual or facial surfaces. This finding is typical of established periodontitis where marginal bone is thin, and may be incompletely removed by the inflammatory process. The radiographic appearance of inconsistent margins are not easy to identify at times. The lesions may be superimposed on the root of the effected tooth.

Advanced periodontal lesions

Stage 4 periodontal disease is represented by deep pockets, tooth mobility, gingival bleeding, and pustular discharge. Bone loss is extensive.

Furcation exposure comes from bone loss at the furcation of multirooted teeth. Furcation exposure may occur before advanced periodontal disease. It is sometimes difficult to determine radiographically, whether the interradicular space is involved, unless there is a radiolucent area in the region of the furcation. Only advanced furcation exposures where both cortical plates are gone will be easily recognized on radiographs. Class 1 (incipient) furcation exposure exists when the tip of a probe can just (<1 mm) enter the furcation area. Bone still fills most of the area where the roots meet. Class II (definite) furcation exposure exists when the probe tip extends more than one millimeter horizontally into the area where the roots converge. Class III (through and through) lesions exist secondary to advanced periodontal disease. The alveolar bone has eroded to a point that the explorer probe passes through the defect unobstructed.

Alveolar dehiscence exists when the alveolar cortical bone is resorbed along the entire length of the root. Radiographically, there will be a radiolucency surrounding the effected root.


This page last updated on October 31, 2000
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Jan Bellows, DVM
All Pets Dental Clinic
17100 Royal Palm Blvd.
Weston, FL 33326
(954) 349-5800