Introduction

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 along with the surrounding structures of the dentition. However, each of these techniques have their own advantages and disadvantages. In the following sections we shall discuss in detail various radiographic techniques used in periodontics with their clinical applications, advantages 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 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. The occlusal radiographs are used to ……. Contents available in the book ……. Contents available in the book……. Contents available in the book……. Contents available in the book ……

An intraoral periapical radiograph (IOPA) demonstrating the periapical areas of the teeth
An intraoral periapical radiograph (IOPA) demonstrating the periapical areas of the teeth



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.

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). A bitwing radiograph is easy to take because the film 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.

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


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 an useful ……. Contents available in the book ……. Contents available in the book……. Contents available in the book……. Contents available in the book ……

 

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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 commonly used radiographic technique for periodontal purposes is orthopantomogram (OPG). An OPG provides us a complete bilateral view of dentition, maxilla, mandible and temporomandibular joint (TMJ). It is a commonly used radiograph especially in cases with widespread periodontal destruction. Multiple IOPA X-rays can be avoided with this radiographic technique. However, it may not give a very clear details of small areas as compared to IOPAs.

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 to generate 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.

The positioning device used to hold the sensor in paralleling radiographic technique
The positioning device used to hold the sensor in paralleling radiographic technique


Positioning of the x-ray sensor holder in the oral cavity of the patient.
Positioning of the x-ray sensor holder in the oral cavity of the patient.



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 following figure, teeth are surrounded by a thin radiolucent space that 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 parallel to the line joining the CEJ of the adjacent teeth. The interdental bone is thin between the anterior teeth due to less interdental space and wide between the posterior teeth due to wide interdental space. When there is bone resorption of interdental bone due to periodontal disease, the crest of the Interdental ……. Contents available in the book ……. Contents available in the book……. Contents available in the book……. Contents available in the book ……


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 on 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 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 cancellous bone is obscured by the dense buccal and lingual/palatal cortical plates on a radiograph. The cancellous bone loss becomes obvious only when there is involvement of at least one cortical plate. It has been observed that a minimum of 0.5-1 mm reduction in the level of cortical plate is required to permit the radiographic visualization of bone loss of the cancellous bone 6. One old method to determine the morphology of the osseous defect is packing gutta-percha around the tooth and then taking the radiograph but this method does not give accurate information about defect morphology. The best method to check for defect morphology is surgical exposure of the area 1.

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 ……. Contents available in the book ……. Contents available in the book……. Contents available in the book……. Contents available in the book ……

     In localized Grade C periodontitis with molar-incisor pattern, the bone loss is observed in the maxillary and mandibular incisor and/or first molar areas, usually bilaterally with a vertical, arc-like destructive pattern. As the disease progresses, the bone loss may become generalized. However, premolar areas demonstrate less severe bone loss as compared to other areas of dentition. In generalized Grade C periodontitis, the bone loss is severe with a horizontal or vertical destruction pattern; however, angular bone loss is more commonly observed. In Grade A/B periodontitis, usually horizontal bone loss is observed with crestal bone, demonstrating well-demarcated margins. There are many factors that affect radiographic appearance of periodontal defects. These include,

  1. The thickness, width, and angulation of the alveolar crest.
  2. Thickness of lingual and facial alveolar bone plates.
  3. Presence of fenestration and dehiscence.
  4. Tooth alignment in the jaw.
  5. Root and root trunk anatomy.
  6. Root position within the alveolar process.
  7. Proximity with another tooth surface.

     It must be noted here that radiograph is only able to detect bone loss following loss of 30% – 40% of bone density 9. Thus, initial bone loss is not visible on the radiographs.

Furcation involvement on a radiograph

Furcation involvement most often affects the lower first molars, followed by mesial furcation of the upper first molars, whereas the upper premolars are the least frequently involved. The prognosis of furcation involvement in three-rooted teeth tends to be poorer, especially when the distal root has been compromised. On the other hand, lower molars have a somewhat better prognosis. It is evident from the literature that loss of molars with age is more frequent in patients who have been treated for furcation involvement as compared to the patients who have no furcation involvement.

     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 ……. Contents available in the book ……. Contents available in the book……. Contents available in the book……. Contents available in the book ……



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 and a patient should be assessed clinically to identify periodontal abscess.

Radiographic changes in trauma from occlusion

Trauma from occlusion is tissue injury that results when the occlusal forces exceed the adaptive capacity of the periodon-tium. 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 (“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. Also, 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 the periodontium, in an attempt to adapt to the new functional demand.

Orthopentomogram of a patient showing various landmarks
Orthopentomogram of a patient showing various landmarks (1: Middle cranial fossa, 2: Orbit, 3: Zygomatic Arch, 4: Palate, 5: Styloid process, 6: Maxillary tuberosity, 7: External oblique ridge, 8: Angle of the mandible, 9: Hyoid bone, 10: Glenoid Fossa, 11: Articular eminenance, 12: Mandibular condyle, 13: Vertebra, 14: Coronoid process, 15: Pterygoid plates, 16: Maxillary sinus, 17: Ear Lobe, 18: Mandibular canal, 19:Mental foramen.)


Radiological findings of specific diseases in maxilla and mandible

Osteosclerosis:

In this condition, the jaw bones demonstrate homogeneous radiodense areas that have a sharp interface with the surrounding bone, although some may fade into the surrounding bone. The mandible has found to be affected more as compared to the maxilla. 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 ……. Contents available in the book ……. Contents available in the book……. Contents available in the book……. Contents available in the book ……

 

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Paget’s disease (Osteitis deformans):

Paget disease of bone, also known as osteitis deformans, was first described in a small group of patients in 1877 by Sir James Paget. The disease is characterized by excessive and abnormal remodeling of bone, with both active and quiescent phases. Three phases have classically been described: the lytic phase (incipient-active), in which osteoclasts predominate; the mixed-phase (active), in which osteoblasts begin to appear superimposed on osteoclastic activity and eventually predominate; and finally, the blastic phase (late-inactive), in which osteoblastic activity gradually declines. In the lytic phase, osteolysis dominates and the lesion is radiolucent. In the mixed phase, 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 blastic phase, osteoblastic apposition continues and osteoclastic activity subsides. The bone becomes homogeneously dense. When the jaws are involved, the teeth often show hypercementosis. The anatomic distribution of Paget disease usually is asymmetric and most commonly affects the lumbar spine (30-75%), pelvis (30-75% of cases), sacrum (30-60%), femur (25-35%), and cranium (25-65%).

Fibrous dysplasia:

Fibrous dysplasia is a relatively common, benign skeletal disorder, typically encountered in adolescents and young adults. It is a developmental anomaly in which the normal medullary space of the affected bone is replaced by fibro-osseous tissue. The disease may affect a single bone (monostotic fibrous dysplasia) or many bones (polyostotic fibrous dysplasia). Yellowish or brownish non-elevated patches of cutaneous pigmentation (cafe-au-lait spots), situated predominantly on the trunk of the patient’s body, are coexistent findings in one-third to one-half of patients affected with polyostotic 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 radio-density, the so called “ground-glass” appearance. The lesions are well-circumscribed with no periosteal reaction.

Cherubism:

Cherubism is a rare disease of autosomal dominant inheritance characterized by painless, frequently symmetrical, enlargement of the jaws as a result of the replacement of bone with fibrous tissue. It is usually diagnosed in children aged 2 to 7 years, with the observation of exacerbation of its manifestations within the first 2 years after diagnosis and of stabilization or even regression after puberty. Boys are more affected than girls at the proportion of 2 : 1. Clinically, cherubism is characterized by bilateral enlargement of the mandible and/or maxilla, causing a rounded face and swollen cheeks accompanied by upward-looking eyes. The osseous ……. Contents available in the book ……. Contents available in the book……. Contents available in the book……. Contents available in the book ……



Langerhans cell histiocytosis:

This disease is a result of the clonal proliferation of immuno-phenotypical and functionally immature Langerhans cells, as well as eosinophils, macrophages, lymphocytes, and occasionally, multinucleated giant cells. Clinical presentations of the disease vary widely, from an asymptomatic solitary bone lesion to a multisystem life-threatening affliction. Any organ or system of the human body can be involved, but the skeleton, the skin and the central nervous system are more commonly affected. 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 also known as marble bone disease was described originally in 1904 by Albers-Schonberg. It is a rare bone disorder characterized by defective osteoclastic resorption of primary spongiosa of the bone result in dense sclerotic bone. Persistence of this primitive tissue, interferes with the formation of mature adult bone with a normal medullary canal, which results in abnormally dense but brittle bones. This disease is also known as marble-bone disease and 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:

Scleroderma or systemic sclerosis, is a rare connective tissue disorder. Although the etiology is not fully elucidated, syste-mic sclerosis is considered to be an autoimmune disease. The condition is characterized by a variable degree of systemic manifestations, including fibrosis (affecting multiple organs system); and telangiectasias and abnormalities of the digestive system.The periodontal findings associated with this disease include uniform widening of PDL space at the expense of surrounding alveolar bone. This finding was first reported by Austin 11 and was later confirmed by others 12-14. The exact ……. Contents available in the book ……. Contents available in the book……. Contents available in the book……. Contents available in the book ……


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 article.

References

References are available in the book.

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