Radiographic diagnosis of periodontal disease

Jan Bellows, D.V.M., Dipl. A.V.D.C., Dipl.A.B.V.P.

Philippe Hennet, D.V. Dipl A.V.D.C.

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

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.

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

Bone level

Normally the crest of interdental bone appears from 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. It 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

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

presents 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 of varying thickness,

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

Gingivitis

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

1disease, 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

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

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 exist 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.