Radiographs in the diagnosis of periodontal disease

Radiographic diagnosis is a challenging task in periodontics. This is primarily because the conventional radiographs provide us the two dimensional image of a three dimensional object. Thus, it becomes essential that the patient is diagnosed on the basis of combined information obtained from clinical and radiographic findings 1. The radiographs are broadly classified as extraoral or intraoral radiographs. Intraoral radiographs provide us the radiographic image of a few teeth, whereas the extraoral radiographs can provide us the information about many teeth or the whole of the dentition. However, each of them has their own advantages and disadvantages. In the following sections we shall discuss in detail the radiographic techniques used in periodontics with their clinical applications and limitations.

Radiographic techniques:

X-rays were discovered in 1895 by professor Wilhelm Conrad Röntgen and Dr. Otto Walkhoff is credited with the first dental radiograph. As already stated, radiographs can be divided into intraoral and extraoral radiographs. The intraoral radiographs can be further divided into bite-wing, periapical and occlusal radiographs. The intraoral periapical (IOPA) radiographs are commonly done radiographs for a part of the dentition (Figure 40.1 a) whereas bite-wing radiographs are usually done for the posterior teeth except for size 1 bite-wing that can be used for the anterior teeth (Figure 40.1 b). The occlusal radiographs are used to find out the buccolingual or buccopalatal positions of the impacted canines or third molars and to determine the extent of diseases like cysts and to measure the changes in size and shape of the mandible.

Figure 40.1 (a) An intraoral periapical radiograph (IOP A) demonstrating the periapical areas of the teeth, (b) Bite-wing radiograph showing the crestal bone of teeth in maxillary and mandibular arch

Periapical radiograph

(a)

Bite-wing radiograph

(b)

Intraoral radiographic techniques:

As already stated, there are three types of intraoral radiographs: intraoral periapical radiographs (IOPA), bite-wing radiographs and occlusal radiographs.

Positioning guidelines for intraoral radiographs:

Appropriate positioning of the x-ray film inside the oral cavity is essential to avoid distortion of the image. There are two techniques for intraoral radiography: paralleling and bisecting technique (Figure 40.2).

Figure 40.2 Diagrammatic representation of principle of paralleling (a) and bisecting angle (b) radiographic technique.

Radiographic techniques

Paralleling technique:

This technique can be used for both IOPA and bite-wing radiographs. It is the most accurate technique for taking intraoral radiographs. In this technique, the x-ray film is kept parallel to the teeth and the x-ray beam is directed at right angles to the teeth and x-ray film. In both IOPA and bitewing x-ray, the film/sensor is kept parallel to the teeth with the help of holders (position indicating divice) (Figure 40.3 a, b). A bitwing radiograph is easy to take because it is placed between the upper and lower teeth, so can be easily kept in the mouth. However, IOPA radiographs are used for teeth in one arch only, so in patients with shallow palate keeping the film parallel to the teeth becomes difficult.

Figure 40.3 (a) The positioning device used to hold the film/sensor in paralleling radiographic technique, (b)Positioning of the x-ray film/sensor holder in the oral cavity of the patient.

X-ray Sensor holder

(a)

Placement of X-ray sensor holder

(b)

Bisecting technique:

This technique is used for IOPA radiographs. In this case, the receptor is placed diagonally to the teeth and the X-ray beam is directed at a right angle to a plane that is midway between (bisects) the x-ray film or sensor and the teeth. This technique is not as accurate as the paralleling technique, but is a useful alternative technique when ideal receptor placement cannot be achieved due to shallow palate or shallow floor of the mouth and narrow arch widths or anatomic obstacles such as tori.

Extraoral radiographic techniques:

There are various extraoral radiographic techniques which give us a larger view of the oral and surrounding structures. Out of all the extraoral techniques the most common radiographic technique used for periodontal purposes is orthopantomogram (OPG). An OPG provides us a complete bilateral view of dentition, maxilla, mandible and temporomandibular joint (TMJ) (Figure 40.4). A detailed description of OPG is available in chapter 85 “Diagnostic imaging in Implantology”.

Anatomical landmarks on a Panoramic radiograph

Figure 40.4 Orthopentomogram of a patient showing various landmarks. 

Obtaining standardized radiographic images:

In periodontics, standardized, reproducible techniques are required to obtain reliable radiographs for pre-treatment and post-treatment comparisons. The main purpose of using position indicating devices is generating a standardized radiographic image of an area that can be compared with another radiograph later on. Standardization of exposure and development time, type of film, and x-ray angulation minimizes the image distortions. The radiographic comparison of crestal bone levels before and after the treatment is a routine procedure that gives us the information regarding the alteration in bone levels. A grid calibrated in millimeters can be used over the radiograph to calculate the bone levels in radiographs taken under similar conditions.

Radiographic findings of healthy periodontal structures:

Before we discuss the pathologies related to the periodontium, first let us discuss the radiographic findings of a healthy periodontium. As seen in Figure 40.1 a, teeth are surrounded by a thin radiolucent space surrounding the tooth root which houses the periodontal ligament (PDL). The width of this space should be carefully examined on the radiograph because if the tooth is under occlusal overload, the width of PDL space is increased.

The alveolar bone surrounding the tooth root demonstrates a radiopaque line just adjacent to the PDL space, which is referred to as Lamina dura 2. Radiographically, it appears as a white line, but in fact, it is perforated by numerous small foramina, traversed by blood vessels, lymphatics, and nerves, which pass between the PDL and the bone. Because lamina dura represents the bone surface lining the tooth socket, its continuity and integrity are examined carefully on a radiograph. In healthy periodontium, it is continuous around the root surface just apical to the cementoenamel junction (CEJ). The level of the crest of interdental bone is……………

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Bone loss in periodontal diseases:

Periodontal diseases are characterized by bone loss which is clinically assessed as loss of attachment. The minor bone loss is difficult to visualize on a radiograph because a radiograph provides us a two dimensional view of a three dimensional object. Any minor bone loss on the buccal aspect of the tooth may be overlapped by the intact lingual bone, thus bone loss on one aspect of tooth is camouflaged by bone on the opposite side. Hence, the early signs of periodontitis such as deepening of periodontal pocket or recession are best visualized clinically.

In general, the actual severity of periodontal destruction is more than as shown in a radiograph 3. A radiograph is an indirect method of determination of bone loss. It shows the amount of bone present rather than the amount lost. The amount of bone lost is calculated arbitrarily by estimating the difference between the physiological bone level and the height of the bone remaining. It has been demonstrated that the distance between the CEJ and the alveolar crest in individuals with healthy periodontium is about 2 mm 4, 5.

Assessment of the type of bone loss on a radiograph:

To assess the periodontal status of dentition, the radiographs are examined for levels of interdental bone and its contour, lamina dura, crestal radiodensity and size and shape of the medullary spaces. In periodontal diseases due to bone loss, the crest of the alveolar bone is reduced in height and the contour of the crestal bone may also get altered. The interproximal bone loss may be near parallel to the line joining CEJ of adjacent teeth or may be at an angle to the line joining CEJ of the adjacent teeth. The former condition is called horizontal bone loss and the latter is called as angular or vertical bone loss. It must be noted here that the topography of the bone defect cannot be accurately assessed by a radiograph. The bone destruction that occurs in the……………

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Radiographic features of bone loss in periodontitis:

The most important radiographic feature that can be observed in periodontitis is fuzziness and discontinuity of the lamina dura. It is the result of an extension of inflammation in the alveolar bone, leading to the reduction in calcified tissue and widening of vessel channels in the bone lining the socket. However, it should be remembered that radiographic findings should not be correlated with the clinical findings. An intact lamina dura may indicate periodontal health, but the discontinuity or fuzziness of lamina dura does not necessarily indicate presence of inflammation, bleeding on probing, periodontal pockets, or loss of attachment 7, 8.

Due to bone resorption on the lateral aspect of the interdental septum, a wedge-shaped radiolucent area is formed on the mesial and/or the distal aspect of the tooth with its apex pointing apically. These changes are associated with the widening of PDL space. With the extension of the inflammation in the crestal bone in the interdental septum, areas of bone resorption are formed which may be surrounded by the areas of intact cortical bone. On a radiographic image, these give an appearance of finger-like radiolucent projections that extend from the crest of the bone into the septum. The height of the crestal bone gradually reduced with inflammatory resorption of the bone.

In localized aggressive periodontitis, the bone loss is…………..

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Furcation involvement on a radiograph:

The best method to identify furcation involvement is clinical examination of the suspected tooth with specially designed probe (Naber’s probe). Radiographs are a less accurate method of identification of furcation involvement. As already stated, the actual bone loss is always more than as seen on the radiographs. So, a slight change in the radiodensity in the furcation area should be carefully examined clinically. Any reduction in the radiodensity in furcation area suggests furcation involvement.  Further, if there is a marked bone loss around one root of the molar, it can be assumed that furcation is also involved.

 

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Radiographic appearance of an interdental crater:

Interdental craters cannot be accurately detected on radiographs; however, some radiographic changes can be seen.  The interdental crater is seen as an irregular area of reduced radiopacity on the alveolar bone crests 9. It is generally not sharply demarcated from the rest of the bone, with which it blends gradually. The morphology of an interdental crater cannot be accurately detected on a radiograph and sometimes a deep crater may look like a vertical defect on a radiograph.

 

Radiographic findings of periodontal abscess:

The appearance of periodontal abscess on a radiograph depends on the duration and size of the abscess. The acute periodontal abscess cannot be visualized on a radiograph because of minimal changes in the alveolar bone, whereas a chronic lesion can be visualized, due to marked changes in the bone. Furthermore, periodontal abscess primarily localized to the soft tissue wall of periodontal pocket is less likely to produce radiographic changes than those deep in the supporting tissues. The periodontal abscesses present on the lingual and facial surfaces of the teeth are obscured by the root surface on a radiograph so are less visible. Hence, a radiograph is not a good indicator of periodontal abscess.

Radiographic changes in trauma from occlusion:

The major radiographic changes in trauma from occlusion are observed in lamina dura, morphology of the alveolar crest, width of the periodontal space, and density of the surrounding cancellous bone. To understand the reason behind these changes, let us first discuss the changes that occur in the periodontal tissue under traumatic occlusal forces.

Under primary occlusal trauma (read chapter 35 “Trauma from occlusion”), compression of the PDL takes place because of which there is a reduction in the diameter of the blood vessels. As a result of this, there is a disorganization of cellular and fiber component of PDL. As a consequence of these changes, there is a release of inflammatory mediators. These chemical mediators have a direct influence on bone remodeling. When these mediators accumulate in high concentration in the connective tissue, they initiate bone resorption, whereas in low concentrations they induce bone formation. Hence, in occlusal trauma, there is bone formation around the tooth to compensate for the increased occlusal forces, which is radiographically visible as the thickening of lamina dura. Along with this, to withstand the increased occlusal forces, there is an increased remodeling of PDL fibers which is radiographically visible as irregular widening of the PDL space. Along with this, there is an increase in the density of adjacent bony trabeculae which is radiographically visible as increased radiopacity.  In the cervical region of PDL, due to the lever effect produced by the tooth under increased occlusal forces, the level of inflammatory mediators may rise to the point of stimulating predominantly the activity of bone resorption. It results in a V-shaped bone loss in the cervical area of the involved tooth. On a radiograph, this type of bone loss may appear as appear as angular bone defect, but there is no periodontal pocket present on periodontal probing. In the advanced traumatic lesion the bone loss may extend till the apical region, producing a wide radiolucent periapical image (cavernous lesion). Furthermore, in the presence of excessive occlusal forces on the tooth, root resorption may also occur. Thus, it can be summarized that all these radiographic findings appear due to the changes in periodontium, in an attempt to adapt to the new functional demand.

Radiological findings of specific diseases in maxilla and mandible:

Osteosclerosis:

The jaw bones demonstrate homogeneous radiodense areas that have a sharp interface with the surrounding bone, although some may fade into the surrounding bone. Osteosclerosis may occur at the site of previous extraction as a result of condensing osteitis or perhaps as a result of the deposition of excessive bone during the course of bone repair. However, in many cases, osteosclerosis cannot be linked with extraction or excessive healing and is considered as developmental malformation.

Paget’s disease (Osteitis deformans):

In the early stage of Paget’s disease, osteolysis dominates and the lesion is radiolucent. In the middle stage, there is deposition of bone and because bone is deposited in the form of isolated islands, “cotton-wool” like densities can be observed on radiographs. In the late stage, osteoblastic apposition continues and osteoclastic activity subsides. The bone becomes homogeneously dense. When the jaws are involved, the teeth often show hypercementosis.

Fibrous dysplasia:

The radiographic features are variable in this disease with case reports demonstrating purely radiolucent to radiopaque appearance.  However, the most common appearance is that of a finely trabeculated radiodensity, the so called “ground-glass” appearance.

Cherubism:

This is the disease of childhood. The osseous lesions in cherubism appear as radiolucent and multilocular lesions on radiographs. The lesions typically begin in the mandibular rami and advance anteriorly. The osseous lesions are bilaterally symmetrical.

Langerhans cell histocytosis:

This disease is a result of the clonal proliferation of immunophenotypical and functionally immature Langerhans cells, as well as eosinophils, macrophages, lymphocytes, and occasionally, multinucleated giant cells. The osseous lesions are invariably radiolucent with a well-defined or indistinct border. Lesions are primarily seen in the tooth bearing areas of the jaws.

Osteopetrosis:

Osteopetrosis is a congenital bone disease caused by malfunctioning osteoclasts. This disease is also known as marble-bone disease, Albers-Schonberg disease. Bones exhibit a homogenous, fine grain density throughout the skeleton with radiographs demonstrating changes related to increased bone density. The bone is homogeneously and finely opaque and in children several teeth that should be erupted are trapped within the bone.

Scleroderma:

The periodontal findings associated with this disease include uniform widening of PDL space at the expense of surrounding alveolar bone.

Conclusion:

Radiographs plays a very important role in the diagnosis of periodontal diseases. They provide us important information regarding alveolar bone loss and the remaining bone. Radiographs also provide us the information regarding the vital structures in orofacial region (mandibular canal in the mandible and floor of maxillary sinus in maxilla) which are important while placing dental implants. However, various recent advances in the field of radiography have been introduced which provide us more accurate information regarding orofacial structures. These advances have been discussed in the next chapter.

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References:

References available in the hard copy of the website

Periobasics: A textbook of periodontics and implantology

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