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.