18: The periapical tissues

The periapical tissues

Introduction

This chapter explains how to interpret the radiographic appearances of the periapical tissues by illustrating the various normal appearances, and describing in detail the typical changes associated with apical infection and inflammation following pulpal necrosis. To help explain the different radiographic appearances, they are correlated with the various underlying pathological processes. In addition, there is a summary of the other, sometimes sinister, lesions that can affect the periapical tissues and may simulate simple inflammatory changes.

Fig. 18.13 A Part of a panoramic radiograph showing a round, well-defined area of radiolucency – a likely radicular cyst (arrowed), associated with the poorly root-filled . B Same patient 6 months later following successful root filling at . Note the bony fill-in in the apical area.

Normal radiographic appearances

A reminder of the complex three-dimensional anatomy of the hard tissues surrounding the teeth in the maxilla and mandible, which contribute to the two-dimensional periapical radiographic image, is given in Fig. 18.1.

Fig. 18.1 A Sagittal section through the maxilla and central incisor showing the hard tissue anatomy. B (i) Sagittal and (ii) coronal sections through the mandible in the molar region showing the hard tissue anatomy.

The appearances of normal, healthy, periapical tissues vary from one patient to another, from one area of the mouth to another and at different stages in the development of the dentition. These different normal appearances are described below.

The periapical tissues of permanent teeth

Fig. 18.2 Periapical radiographs of A , B , C showing the normal radiographic anatomy of the periapical tissues in different parts of the jaws. Note the continuous radiolucent line of the periodontal ligament shadow and the radiopaque line of the lamina dura outlining the roots.

The three most important features to observe are:

• The radiolucent line that represents the periodontal ligament space and forms a thin continuous black line around the root outline

• The radiopaque line that represents the lamina dura of the bony socket and forms a thin, continuous, white line adjacent to the black line

• The trabecular pattern and density of the surrounding bone:

– In the mandible, the trabeculae tend to be relatively thick and close together, and are often aligned horizontally

– In the maxilla, the trabeculae tend to be finer, and more widely spaced. There is no predominant alignment pattern.

These features hold the key to the interpretation of periapical radiographs, since changes in their thickness, continuity and radiodensity reflect the presence of any underlying disease, as described later.

Important points to note

• There is considerable variation in the definition and pattern of these features from one patient to another and from one area of the jaws to another, owing to variation in the density, shape and thickness of the surrounding bone.

• The limitations imposed by contrast, resolution and superimposition can make radiographic identification of these features particularly difficult, hence the need for ideal viewing conditions and digital image enhancement software.

The periapical tissues of deciduous teeth

Fig. 18.3 Periapical radiograph of in a 4-year-old child, showing normal periapical tissues. Note the confusing shadows created by the radiopaque crowns and radiolucent crypts (arrowed) of the developing permanent incisors.

The important features of normality (thin lamina dura and periodontal ligament shadows) are the same as for permanent teeth, but can be complicated by:

• The presence of an underlying permanent tooth and its crypt, the shadows of which may overlie the deciduous tooth apex

• Resorption of the deciduous tooth root during the normal exfoliation process.

The periapical tissues of developing teeth

Fig. 18.4 Periapical radiographs showing the normal periapical tissues of developing teeth. A , B . Note the circumscribed areas of radiolucency of the radicular papillae (arrowed) and the funnel-shaped roots.

The important features of normal apical tissues where the root is partially formed and the radicular papilla still exists include:

• A circumscribed area of radiolucency at the apex

• The radiopaque line of the lamina dura is intact around the papilla

• The developing root is funnel-shaped

• Only after root development is complete does the thin continuous radiolucent line become evident.

The effects of normal superimposed shadows

Normal anatomical shadows superimposed on the apical tissues can be either radiolucent or radiopaque, depending on the structure involved.

Radiolucent shadows

Examples include:

• The maxillary antra

• The nasopalatine foramen

• The mental foramina.

Such cavities in the alveolar bone decrease the total amount of bone that would normally contribute to the final radiographic image, with the following effects:

• The radiolucent line of the periodontal ligament may appear MORE radiolucent or widened, but will still be continuous and well demarcated.

• The radiopaque line of the lamina dura may appear LESS obvious and may not be visible.

• There will be an area of radiolucency in the alveolar bone at the tooth apex (see Figs 18.5 and 18.6).

Fig. 18.5 Periapical of showing normal healthy apical tissues but with the radiolucent shadow of the antrum superimposed (the antral floor is indicated by the open arrows). As a result the radiolucent line of the periodontal ligament appears widened and more obvious around the apices of the canine and premolar, but it is still well demarcated, while the radiopaque line of the lamina dura is almost invisible (solid arrows).

Fig. 18.6 Diagrams of showing the anatomical tissues that the X-ray beam passes through to reach the image receptor. A Without a normal anatomical cavity superimposed. B With the antral cavity in the path of the X-ray beam. The different resultant radiopaque (white) and radiolucent (black) lines of the apical lamina dura and periodontal ligament are shown on the image receptor (arrowed).

Important points to note:

• The fact that the radiopaque lamina dura shadow may not be visible does not mean that the bony socket margin is not present clinically. It only means that there is now not enough total bone in the path of the X-ray beam to produce a visible opaque shadow. Since the bony socket is in fact intact, it still defines the periodontal ligament space. Thus, the radiolucent line representing this space still appears continuous and well demarcated.

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Tags: Radiography and Radiology for Dental Care Professionals 3e

Jan 12, 2015 | Posted by mrzezo in Oral and Maxillofacial Radiology | Comments Off

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