Pediatric Dentistry - a Clinical Approach, 3ed.

CHAPTER 8. Radiographic Examination and Diagnosis

Hanne Hintze and Ivar Espelid

Radiographic examination in children is essential for diagnosis, treatment planning, and monitoring of a number of changes and pathologies related to teeth and jaws. However, since no exposure to X‐rays can be considered completely free of risk, a radiographic examination should be performed only when it is likely that it will benefit the patient; for example, to improve the diagnosis and/or result in a more appropriate treatment considered more beneficial to the patient.

Indications for radiographs in children and adolescents

Before ordering a radiographic examination of a patient the clinician should consider the parameters listed in Box 8.1.

Box 8.1 Parameters to be assessed prior to deciding on radiography, modified from Hintze and Poulsen [31]

Specific parameters

·     Patient’s symptoms and history

·     Information obtained from clinical examination

General parameters

·     Prevalence in the general population of the disease/anomaly for which the radiographic examination might be required

·     The probability of obtaining additional information from thorough radiographic examination

·     The consequence of an undiagnosed and thereby untreated disease/anomaly

·     The influence of a radiographic finding on the course of the disease or the patient’s prognosis

·     Alternative diagnostic methods involving no or lower X‐ray exposure

In general, exposure to X‐rays must not be undertaken without a previous clinical examination [1]. This requirement has been introduced to ensure that radiographs are exposed on the basis of individual prescriptions rather than generalized approaches not taking into consideration individual patient history and clinical findings.

Principles for interpretation of radiographs

Before image interpretation, the quality of the image should be assessed. Important criteria to be evaluated in this connection are listed in Box 8.2.

Box 8.2 Criteria to be assessed in relation with evaluation of radiographic image quality

·     Region of interest: is the region imaged sufficiently?

·     Density and contrast: are these parameters optimal for assessment of the problem?

·     Geometric appearance of the examined structures: is it good enough for correct interpretation?

·     Sharpness: is it sufficient?

·     Artefacts: are such located in areas where they can interfere with image interpretation?

In the case of radiograph being of poor quality, a new radiograph with a higher quality should be exposed before image interpretation can begin. When a radiograph is ready for interpretation it should ideally be observed under proper viewing conditions. For details see Box 8.3.

Box 8.3 Important viewing conditions for radiographic images.

Mounting

·     Intraoral film radiographs should be mounted and stored in frames.

·     Intraoral digital radiographs should be mounted in templates ensuring arrangement in an anatomic identifiable way with a proper orientation (rotation might be necessary).

Displaying

·     Film radiographs should be viewed on a lightbox emitting a homogeneous light intensity across the entire surface, and the size of the box should match the size of the radiograph (a large light box can be reduced in size by a sheet of opaque material).

·     X‐ray viewer with magnification should be used.

·     Digital radiographs should be viewed on a quality monitor using software with facilities for image enhancement for keeping the radiation dose as low as possible, and for making the image subjectively more appealing in relation to various diagnostic tasks (image enhancement that improves the quality for one specific task might reduce the quality for another task). However, subjectively optimal enhanced images do not necessarily result in improved accuracy of the image interpretation.

·     Ambient room light should be turned off or reduced.

Source: Hellén‐Halme et al. 2007 [32]. Reproduced with permission of Elsevier.

The best way to start the analysis of a radiograph is to use a systematic viewing procedure including a standard examination sequence ensuring assessment of the different tissues (periapical and alveolar crest bone, number and localization of teeth, each tooth subdivided into crown, root, pulp, etc.) in all parts of the radiograph. The next step is to perform an interpretation including a differentiation between normal and abnormal structures, and a diagnostic decision concerning the latter. The optimal endpoint is a definitive interpretation and a definitive diagnosis.

Radiographic anomalies and pathologies in children and adolescents

Box 8.4 lists the most frequent reasons for radiographic examination in children.

Box 8.4 The most frequent reasons for radiographic examination of dentomaxillary structures in children and adolescents

·     Caries and sequelae

·     Trauma to teeth and supporting tissue

·     Developmental and acquired dental anomalies

·     Systemic diseases and syndromes

·     Treatment planning prior to:

o  orthodontics

o  surgery (most often removal or exposure of impacted teeth)

Caries and its sequelae

Using radiographs it is possible to identify approximal enamel and dentin caries lesions and occlusal dentin lesions and to disprove the presence of such lesions. In general, it is recommended to perform a radiographic caries examination when the preceding clinical examination has not resulted in sufficient information for a final diagnosis or for the planning of treatment. This implies that radiography is considered most useful in surfaces that are not easily accessible with conventional methods such as visual inspection and careful probing.

As caries prevalence decreases in a population there is a continuous need for reassessment of a strategy to take radiographs of individuals where no clinical signs of caries or previous caries experience are present. To do such reassessments, the clinician needs to know the characteristics of the method. Such characteristics are sensitivity and specificity. These parameters are essential in evaluating new methods which are launched to “improve” the caries diagnosis. To determine sensitivity and specificity of a caries diagnostic method a “gold standard” has to be established for every surface included in the study. Often, a histologic reference standard is made during sectioning of teeth and thereafter microscopic validation is performed [2–4].

Evidence‐based reports on caries diagnosis frequently exclude or give a poor‐quality rating to studies due to major imperfections in the study design [5,6]. In Table 8.1 sensitivity and specificity values from a number of studies judged to fulfill the general principles for good study design are listed. From the table it appears that sensitivity (true‐positive ratio) is low in contrast to a relatively high specificity. This means that the radiographic method misses lesions in enamel and even in dentin. On the other hand, relatively few false‐positives will occur since the specificity is relatively high. Whether these values, which are obtained mainly under in vitro study circumstances, are also valid in patients is not well researched.

Table 8.1 Sensitivity and specificity values and ranges in parentheses for radiographic diagnosis of caries based on a systematic review.

 

Diagnostic accuracy

 

Sensitivity

N

Specificity

N

Approximal caries in:

 

Enamel

0.39 (0.22–0.68)

10

0.87 (0.67–0.97)

10

Dentin

0.45 (0.13–0.61)

9

0.96 (0.89–1.00)

9

Occlusal caries in:

 

Dentin

0.58 (0.03–0.96)

17

0.85 (0.71–1.00)

17

Note: in some studies macroscopic methods were used for validation (the gold standard), but microscopic methods were more commonly used. N denotes the number of studies which were included after a quality assessment of the literature dealing with the subject.

Source: Swedish Council on Technology Assessment in Health Care, 2007 [6]. Reproduced with permission of SBU.

Clinical examination (visual and tactile) is always the prerequisite before any other type of additional examination should be considered. The primary type of supplementary examination should then be the radiographic method. A radiographic image is a good documentation for the dental record and is useful for several purposes including assessment of the caries experience and current activity if undertaken longitudinally. Methods such as fiberoptic transillumination, electrical resistance measurements and laser‐induced fluorescence (DIAGNOdent) have to be considered as additional techniques that may be used in cases of doubt, but thus far cannot replace the radiographic caries examination.

The recommended radiographic technique for caries diagnostics is the bitewing projection. A bitewing radiograph must have a dark density and a good contrast as these factors have a significant influence on the diagnostic outcome [7]. A rule of thumb says that good density for caries diagnostics is when image areas representing soft tissue and “air” are intensely black (not dark gray). Usually this will also result in a good contrast. A good contrast ensures optimal differentiation of the various tissues, e.g., that enamel is clearly different from dentin, that demineralized enamel is clearly different from sound enamel, etc. In radiographs with a light density and poor contrast many existing lesions will remain undetected, resulting in false‐negative diagnoses. The opposite—that nonexistent lesions are detected—may be the case in radiographs with a very dark density [7]. This results in false‐positive diagnoses, which may lead to unnecessary treatment (overtreatment).

Deep caries may cause pulp involvement and lead to necrosis of the pulp. Radiographic examination of teeth with pulp involvement may be useful for the detection of internal and external root resorptions and periradicular ostitis. In the primary molars the first sign of necrosis may be a radiolucent zone close to the bifurcation or trifurcation area.

Intervals between bitewing examinations

How often radiographs should be performed for caries detection depends on several factors:

·     The post‐eruptive age of the tooth with a lesion

·     In which tooth and surface types lesions are present

·     Lesion depth at baseline

·     Risk of surface cavitation

·     Previous caries experience

·     Caries/filling status of neighboring approximal surfaces.

Caries progression through the permanent enamel will take on average several years, but some surfaces and newly erupted teeth are at a higher risk [8,9]. Enamel lesions may arrest, but it is less likely that dentin lesions will, and it is a fact that caries progression in dentin is much faster than in enamel [8].

There are no rules for how often bitewings should be repeated in any patient category. It is generally agreed that the decision to take bitewing radiographs for detecting caries should be based on the benefit to the individual patient in relation to the risks associated with low‐dose radiation exposure and the costs. There is incomplete knowledge about the effectiveness of various methods for selecting individuals who will benefit from bitewing examination and therefore different strategies are in use.

Strategy 1. Bitewing radiographs are prescribed on the basis of a clinical examination of the individual patient. It may be a challenge for the dentist precisely to decide the time interval for the next bitewing examination since caries activity is never constant but changes through life often depending on the individual’s lifestyle and changes in lifestyle (e.g., dietary, social and familiar environment, stability of dental hygiene routines, etc.). During a patient’s first visit it may be difficult to overview all factors relevant for deciding the optimal time for the next bitewing examination, but if seeing the patient regularly (which is the case in many Western countries) this may become easier. High caries risk factors and/or the presence of lesions with increased risk of fast progression, e.g., lesions in outer dentin in high‐risk surfaces or in recently erupted teeth, will call for repeated bitewings at short intervals (e.g., yearly) whereas clinical observation of the presence of caries risk factors under control and the presence of a sound gingival status in combination with no signs of active lesions will call for repeated bitewings at longer intervals.

Strategy 2. To overcome the difficulties with individual timing for the next bitewing examination, some authors [10] and dental organizations [11] have proposed that children are allocated to different caries risk categories each operating with fixed time intervals for repeated bitewings. Guidelines for such a selective screening procedure nave been suggested by Mejàre [10] based on longitudinal studies on caries progression in a group of children followed from the age of 11–13 years to young adulthood [12]. The mentioned guidelines are based on child ages in combination with radiographic characteristics at certain key ages and are illustrated in Table 8.2. According to these guidelines children are allocated to a low‐risk or high‐risk group on the basis of findings obtained from bitewings exposed in all children at the age of 5 years—constituting the baseline reference. If the child has no radiographically diagnosed caries lesions at this early age there is low probability that lesions will develop over the next 3–4 years. However, radiographic caries experience at the age of 5 years indicates a greater future risk and therefore repeated bitewings should be taken with short intervals. At the age of 8–9 years it is reasonable to obtain new radiographs because caries might then have developed in the first permanent molars and the distal aspect of the second primary molars. At ages from 12–13 years the approximal contacts of premolars and permanent molars have been established for some years and it may be reasonable to take bitewings to check caries‐prone clinically non‐accessible surfaces. Thereafter, the time interval between repeated bitewings should not exceed 2 years, since the teenager still has relatively many newly erupted teeth and runs a considerable risk of caries development and should therefore be followed regularly. At the age of 15–16 years bitewings may be useful for making sure that the teenager is allocated to the correct risk group since large difference in time interval between repeated bitewings is present for the two groups.

Table 8.2 Individual key ages for bitewing radiography and proposed time intervals between radiographic examinations].

Source: Mejàre 2005 [10]. Reproduced with permission of George Warman Publications (UK) Ltd.

Key age (years)

Time interval in years between bitewing examinations

In low‐risk individuals

In high‐risk individuals

5

3–4

1

8–9

3–4

1

12–13

2

0.5

15–16

3

0.5

While fixed time intervals for repeated bitewings according to risk assessment seem attractive, it is important to remember that such an approach is no excuse for not seeing the patient more frequently for a clinical examination. At each clinical examination it is then up to the dentist to assess whether the patient is allocated to the correct caries risk group or should be moved to another one to be certain that the time for the next bitewing examination is adjusted to fit with the patient’s actual risk level. Moving to a lower risk level should imply bitewings at longer time intervals as opposed to moving to a higher risk level which should imply bitewings at shorter intervals. The aim with repeated bitewings of active lesions is often to monitor if the lesions respond as expected to the applied treatment and, in case of progression, to be in due time to change treatment strategy to avoid further lesion progression. However, it should be remembered that radiographs should not be used as the sole criterion in making treatment decisions.

Trauma to teeth and supporting tissue

In children exposed to an acute mechanical trauma of the oral region, radiography is very useful for assessing the extent of possible damage such as displacement of tooth fragments and position of foreign bodies in the soft tissue, root and jaw fractures, tooth displacements, and possible damage to the permanent tooth germs. Patients with moderate to manifest traumas are usually received at an emergency department in a hospital where they will undergo the radiographic examinations specified in the hospital’s trauma protocol. Often, such a protocol recommends computed tomography (CT) for severe and multi‐traumatized patients. Patients exposed to mild traumas that primarily cause damage to teeth and supporting marginal bone only are usually seen in a dental clinic where the radiographic examination should depend on the patient’s individual history and clinical appearance.

For correct evaluation of fractures and displacements of teeth, a good radiographic overview (e.g., panoramic examination, occlusal projection) supplemented with periapical radiographs of all involved teeth is recommended. Ideally, each traumatized tooth should be examined from at least two different directions at right angles to one another, but when this is not possible, two projections at two different horizontal or vertical angles may be useful (Figure 8.1). The angulation of the beam is essential in order to produce an image of the fracture line. In cases where the suggested radiographs cannot be obtained or they do not provide the needed diagnostic information, cone beam computed tomography (CBCT) should be considered.

Left: 2 Photos of a tooth with root fracture, displaying the tooth in facial and approximal aspects. Arrows depict direction. Right: 2 Radiographs of the tooth displaying fracture as a circle and as a distinct line.

Figure 8.1 A tooth with a root fracture (arrows indicate direction) seen from (a) the facial aspect and (b) an approximal side. On a periapical radiograph this fracture will be shown indistinct or appear (c) as a circle in the case of a steep vertical X‐ray beam angulation and as a distinct line in the case of (d) a flat vertical beam angulation.

Developmental and acquired dental anomalies

The most frequent dental anomalies in the permanent dentition requiring radiographic examination are:

·     tooth agenesis

·     unerupted teeth due to: (a) absent eruption space, (b) blocked eruption path caused by an impacted supernumerary tooth, an odontoma or a dentigourous cyst, and (c) ectopic tooth position (mostly upper jaw canines and lower jaw third molars).

Radiographic examination for the assessment of dental anomalies should be undertaken on the basis of individual selection criteria, and the radiographic technique should fit the actual problem in the individual patient. For assessment of a single to few tooth ageneses, periapical radiographs will be the correct choice, whereas for multiple ageneses a panoramic examination might be more relevant to keep the radiation dose to the patient as low as possible [1]. For assessment of unerupted teeth the same recommendation is valid. However, a panoramic radiograph will be the most obvious choice if larger pathology or manifest ectopic displacement is suspected clinically. Panoramic radiography will also be the choice when the intraoral image receptor cannot be placed correctly, for example, for the examination of impacted lower third molars.

When the buccal–oral placement of an unerupted tooth is to be assessed, localization radiography conducted by intraoral or extraoral techniques (see below) is indicated.

Systemic diseases and syndromes

Systemic diseases and syndromes causing developmental changes in the maxillofacial bone and in teeth usually need to be examined and monitored by radiography. Major changes often require CBCT offering the possibility to view the changes in several anatomical planes.

Treatment planning prior to orthodontics

Radiography prior to orthodontic treatment is essential to establish the diagnosis and treatment plan, and as a reference for follow‐up examinations to monitor the results of the procedure. Traditionally, a panoramic radiograph and a lateral cephalometric skull radiograph are the images required. However, the introduction of CBCT has been shown to be very valuable for the assessment of growth and development [13,14], and some orthodontists seem to prefer a CBCT examination (see section “Computed tomography”) to the traditional panoramic and cephalometric radiographs [15].

Treatment planning prior to surgery

Radiography prior to surgery is usually needed to provide the surgeon with information leading to a realistic treatment plan ensuring that no unforeseen problems occur during the operation. In general, this means that the most convenient access to the operative area, the extent in all planes of the surgical object, and its localization in relation to important neighboring structures should appear from the radiographic examination. In children with a mixed dentition, specific focus on the localization of developing permanent tooth germs is often necessary to avoid any damage during operation. These requirements often imply that the radiographic examination combines intra‐ and extraoral techniques performed in various anatomical planes. In the case of close or uncertain relationship between the surgical object and essential neighboring structures, CBCT will often be preferable.

Intraoral radiographic techniques

Periapical radiographs

Periapical radiographs are indicated when the whole tooth and its supporting tissues are to be examined. For intraoral conventional radiography five film ISO sizes (sizes 0–4) are available on the market. Figure 8.2 shows different sizes of digital image receptors. The rule of thumb is that the size of the image receptor should fit the “size of the problem” in the best possible way to minimize the number of exposures. However, in children especially, this rule should be applied with great caution since the discomfort connected with a large receptor usually will have a negative affect on a child’s cooperation and acceptance of the radiographic procedure, and in the end result in an inferior radiographic quality.

Photo displaying two different sensor sizes (top) and five different phosphor plate sizes with numbers indicating dimensions in millimeters (bottom).

Figure 8.2 Two different sensor sizes and five different phosphor plate sizes. The numbers indicate dimensions in millimeters.

Periapical radiographs can be performed by a paralleling or a bisecting‐angle technique [16]. The paralleling technique is preferable because it is easier to perform and gives a more reliable image of the tooth and surrounding alveolar bone (minimal distortion). However, in a young child this technique might be difficult to practice because it requires a film holder, which often will be difficult to place because of the small dimensions of the oral cavity.

In children aged 0–3 years it is in general difficult to obtain periapical radiographs. When necessary due to trauma to the upper front teeth, for example, a dental size 2 image receptor fixed by a needle holder can be placed parallel to the occlusal plane and the X‐ray beam angled perpendicularly to the imaginary line bisecting the angle between the surface of the receptor and the long axis of the front teeth in two identical halves (Figure 8.3). The use of a needle holder makes it easier for a parent to keep the receptor in the correct position during exposure. Another possibility is to place the child backwards on the parent’s knee as shown in Figure 8.4. A needle holder is useful for stabilizing a phosphor plate or a film in the molar region as well, especially in the case of a non‐cooperative child, but cannot be used in combination with a sensor, which is much thicker than phosphor plates and films. If a sensor has to be applied it should to be used in combination with a holder provided with an extraoral beam‐aiming device, offering the possibility for an accompanying person to hold it in position.

Photo of a child with image receptor on his mouth placed by a hand using a needle holder, and X-ray beam orientated perpendicular to long axis of the front teeth in two identical halves.

Figure 8.3 Periapical radiography of the upper front teeth. The image receptor is placed in a needle holder parallel to the occlusal plan and the X‐ray beam is orientated perpendicular to the line dividing the angle between the surface of the receptor and the long axis of the front teeth in two identical halves.

Photo of a woman (parent) with a child placed on her lap, holding the child’s hand with one hand and support the child’s head with the other hand.

Figure 8.4 A young child placed on the lap of a parent during exposure. To avoid the child moving the parent should hold the child’s hands with one hand and support the child’s head with the other. The child’s head should rest against the parent’s shoulder. The legs of very small children can be stabilized between the adult’s legs when necessary.

Figure 8.5 shows the “tell–show–do” technique used to introduce a young child to dental radiography. The accompanying parent should be instructed to support the child during exposure to avoid any sudden movement which increases the risk of image blur and subsequently the need for a retake. Box 8.5 gives a number of suggestions to help to obtain good intraoral radiographs in young children.

Photo displaying a teddy bear place on a chair, facing the head tube of the dental X-ray. Inset: Photo of a child looking up.

Figure 8.5 “Tell–show–do” technique might be useful to obtain good child cooperation. Before exposure of the child the radiographic procedure can be demonstrated on a teddy bear while the child is watching from a “safe” place.

Box 8.5 Suggestions for obtaining good intraoral radiographs in young children

·     Establish good contact with the child.

·     Do not separate the child from the accompanying adult except during radiation exposure if the child feels safe. If not, provide the adult with a lead apron and let him or her stay with the child during exposure.

·     Explain by using the “tell–show–do” technique what you intend to do. Demonstrate the procedures with the image receptor and the radiographic equipment on the child’s doll or teddy‐bear or on the accompanying adult using exposure without radiation (Fig. 8.5).

·     Be sure that the child is well seated in the radiographic chair. If the child is sitting alone, his or her head should be supported optimally by a headrest. If the child is sitting on the accompanying adult’s knee, the child’s head should lean against the adult’s chest and be fixed by the adult’s hand placed on the forehead. This will minimize the risk for patient movement during exposure.

·     Before placing the receptor in the holder intraorally, practice with the holder without the receptor. Instruct the child to close the mouth and bite on the bite piece. When the child manages satisfactorily, mount the receptor in the holder and place them carefully in the mouth without hurting the soft tissue.

·     Use a receptor size which can be tolerated by the child. If the receptor cannot be positioned in direct contact or very near the tooth to be radiographed without hurting the child, move the receptor more centrally in the palate or the floor mouth or perform a sharp bend on one of the corners of a film receptor.

·     Use a size 0 receptor with a paper loop holder or foam rubber bite block if the child cannot tolerate a common bitewing film holder.

·     Involve the child in the procedure, e.g., by breathing through the mouth. Distraction from unpleasant receptor placements can be obtained by counting or letting the child rock one foot calmly.

·     Gagging may be caused by dental anxiety, often combined with tactile stimuli to the posterior part of the mouth. Empathy and a relaxed atmosphere combined with a well‐organized procedure favor quick exposures and minimize gagging. In cases with extreme gagging, the use of an anesthetic ointment or nitrous oxide sedation can be a valuable adjunct.

·     The time with the receptor in the child’s mouth can be reduced when two staff members participate in the radiographic procedure.

·     If the child does not cooperate, give positive reinforcement and tell the child that you believe it will be easier next time.

Bitewing radiographs

The bitewing projection is very useful for determining the presence and extent of caries in approximal and occlusal surfaces. It also gives information about the status of restorations (overhang, distance to the pulp, secondary caries) and the level of the marginal alveolar bone. The use of a holder device is mandatory in order to place the image receptor correctly in relation to the teeth. A holder with an extraoral beam‐aiming device is usually best if it can be tolerated by the patient. If not, a paper loop or a foam rubber bite block glued directly to the front of the image receptor could be used. In that case the X‐ray beam should be directed perpendicular to the approximal space between the primary first and second molar in young children and between the second premolar and the first permanent molar in older children. The vertical angulation of the X‐ray beam should be +5° to +8°. Figure 8.6 shows different image receptor holders for bitewing radiographs.

Photo displaying image receptor holders for bitewing radiographs, with three on the right side of the photo having an extraoral beam-aiming device.

Figure 8.6 Image receptor holders for bitewing radiographs. The three to the right have an extraoral beam‐aiming device.

In general, bitewing radiographs seem to be tolerated even by very young children. In a study of 161 children of 3–5 years, bitewing radiographs of acceptable quality could be obtained in 97% of them [17].

Three‐dimensional object localization radiographs

The relative buccal–oral position of two objects can be assessed using parallax movement of the X‐ray beam. With a minimum of two intraoral radiographs of the same region taken with different X‐ray beam angulations in the same parallel plane (either the horizontal or the vertical) towards the image receptor, the relative depth localization of objects can be visualized. The principle is that the object positioned most orally (nearest the image receptor) will move in the same direction as the X‐ray tube while the object positioned most buccally (farthest from the image receptor) will move in the opposite direction to the tube. The localization principle in the horizontal direction is illustrated in Figure 8.7. Horizontal tube movement is relevant for the depth assessment of impacted teeth in particular (Figure 8.8), radiopaque pathologies, foreign bodies, etc. Vertical tube movement is most relevant for the assessment of the relationship between the mandibular canal and the root of an impacted lower third molar.

Photo displaying a metal ball positioned on the facial side of the tooth crown and a metal paper collage positioned on the oral side.

Photo displaying of X-ray beam oriented perpendicular at the surface of the image receptor.

Radiograph displaying a tooth, with metallic ball and metal paper collage superimposed.

Photo displaying X-ray beam orientated left-sided excentric at the surface of the receptor.

Radiograph displaying a tooth, with metallic ball and metal paper collage separated from each other.

Figure 8.7 Radiographic principle for three‐dimensional object localization in the horizontal plan. A metal ball positioned on the facial side of the tooth crown and a metal paper collage positioned on the oral side—nearest the image receptor as shown in (a) will appear as superimposed objects on a radiograph (c) exposed with the X‐ray beam orientated perpendicular at the surface of the image receptor (b). On a radiograph exposed with the receptor in the same positioned as in (b) but with the X‐ray beam orientated left‐sided excentric at the surface of the receptor (d), the metal objects appear separated from each other (e). The paper collage—placed nearest to the receptor—has moved in the same direction as the X‐ray beam (to the left) whereas the metal ball—placed nearest to the X‐ray focus—has moved in the opposite direction (to the right).

Two periapical radiographs of the teeth, exposed with X-ray beam orientated perpendicular (left) and mesio-excentric (right) at the region for 13.

Figure 8.8 Horizontal, three‐dimensional object localization of an impacted 13. (a) A periapical radiograph exposed with the X‐ray beam orientated perpendicular at the region for 13. (b) A periapical radiograph exposed with the X‐ray beam orientated mesio‐excentric at the region for 13. Since 13 moves in the same direction as the X‐ray beam (mesially) in relation to the root of 12, it is placed nearest the receptor, which means palatally to the root of 12.

From two projections at right angles to each other, the localization of objects in the jaw can also be established. This technique may be useful in connection with the localization of traumatized teeth such as an intruded primary incisor, a supernumerary tooth, or an odontoma. In such cases a combination of an occlusal and a periapical exposure may provide the information needed. However, from such exposures it may be impossible to determine whether an impacted object has caused resorption damages to neighboring teeth. If this information is important, CBCT should be ordered instead.

Extraoral radiographic techniques

Panoramic examination

A standard panoramic examination shows the lower part of the patient’s face from ear to ear in the horizontal direction and from the inferior point of the chin to the inferior border of the orbit in the vertical direction. Many modern panoramic units are equipped with collimators allowing examination of reduced parts of the area imaged with a standard panoramic examination. Examples of varying panoramic segments can be seen in Figure 8.9. The clinical problem should be decisive for the selection of panoramic segmentation. A small segment requires a smaller radiation dose than a large segment and should be chosen if possible to optimize the radiation protection of the patient.

Top left: Dental panoramic radiograph. Top right: Right‐sided panoramic radiograph. Bottom left: Lower jaw panoramic radiograph. Bottom right: Bilateral premolar panoramic radiograph.

Figure 8.9 Different panoramic segments. (a) A dental panoramic radiograph, (b) a right‐sided panoramic radiograph, (c) a lower jaw panoramic radiograph, and (d) a bilateral premolar panoramic radiograph.

Generally, a panoramic examination is comfortable for the patient and can be performed in those patients who are unable to open their mouth due to pain, jaw fixation, unwillingness or inability to cooperate, etc. It requires an effective radiation dose of approximately three to four intraoral radiographs [1] and is rather fast to perform, but it needs the patient to stand still for about 10–20 seconds to avoid moving errors in the image, which makes it unsuitable for diagnostic use. This will often be a problem for children younger than 3–4 years and therefore a very young age might be a contraindication for a panoramic examination. If the radiographer is uncertain of the child’s cooperation a test exposure without radiation should be performed.

Scanography

In some panoramic units, programs for scanography are available. A scanogram is an image of a restricted area obtained using a narrow collimated radiation beam and a moving image receptor, much the same as applied for the panoramic technique. Due to the technique, scanograms have a higher contrast (important for the perception of small details) than traditional intraoral radiographs.

If scanography is undertaken as a stereo examination at least two scanograms with different X‐ray beam angulations towards the same region are obtained (e.g., distoexcentric and ortoradial or ortoradial and mesio‐excentric in the horizontal plane). These images can be viewed as stereoscopic pairs in the same way as intraoral radiographs obtained using the principle of parallax. In comparison with the latter, stereo scanograms are easier and faster to perform for the radiographer and more comfortable for the patient (there is no image receptor in the mouth). The dentist obtains radiographs of a relatively large size, which leads to a good overview. Stereo scanography is excellent for object localization in the buccal–oral direction. Figure 8.10 shows horizontal stereo scanographic images of an impacted upper second premolar. It is easy to see that the impacted tooth is positioned orally to the root of the first premolar.

Two stereo scanograms of the teeth, exposed with X-ray beam orientated disto‐excentric (left) and mesio-excentric (right) at 15.

Figure 8.10 Stereo scanogram for depth localization of an impacted 15. The X‐ray beam orientation at 15 is “disto‐excentric” for the scanogram to the left and “mesio‐excentric” for the scanogram to the right. As 15 moves mesially in relation to the root of 14 on the scanogram to the right compared with the scanogram to the left it is located palatally to the root of 14.

Computed tomography

Computed tomography (CT) can be performed on the basis of the fan beam or cone beam technique [15]. With the fan beam technique the patient is exposed to a fan‐shaped X‐ray beam and the image is produced slice‐by‐slice in the axial plane. Subsequently, the multiple image slices are stacked together and two‐dimensional image reconstructions in all planes (axial, sagittal, coronal, oblique, and curved) and three‐dimensional image models can be generated. Fan beam CT scanners are available mainly in hospitals and not commonly used by dentists because of referring restrictions, high costs, and radiation dose being much higher than the doses traditionally used in dental radiography [18,19].

With the CBCT technique the patient is exposed to a cone‐shaped X‐ray beam rotated around the patient’s head during a 180–360° scan. Single projection images are obtained at certain degree intervals, and subsequently the large number of scans is prepared by the machine’s software and the images are reconstructed in all planes; three‐dimensional image models are available as well. Recently, units for CBCT have been commercially available for dental practice where they have shown to be very useful for the examination of dental and maxillofacial hard tissues [20–22]. A CBCT examination undertaken for assessment of an impacted upper left canine is shown in Figure 8.11.

Radiograph displaying the impaction of 13 and 23 on the frontal part of the teeth.

Radiographs of the coronal, sagittal, and axial plane transposition and 3-Dimensional computer-generated image of the maxillary teeth, displaying odontoma depicted by arrow.

Figure 8.11 (a) Frontal part of a panoramic image showing impaction of 13 and 23. (b) CBCT‐scanning for detailed examination of 23. From 2D‐reconstructed images in the coronal (upper left corner), sagittal (upper right corner) and axial (lower left corner) plane transposition of the impacted 23 with 22 is seen. Palatinally to the crown of 23 a compound odontoma (blue arrow) is present. From the 3D‐model (lower right corner) the odontoma is also visible, and it seems to interfere with the eruption of 23.

The three‐dimensional image model obtained from CBCT data may facilitate the clinician’s perception of the separation level between neighboring structures as illustrated in Figure 8.12, where the position of an impacted, lacerated upper central incisor in relation to the neighboring teeth appears clearly, often more unequivocally than on the basis of two‐dimensional images.

Conventional intraoral radiograph displaying an impacted, transversally located 11 (left). 3-Dimensional computer-generate image displaying the impacted 11 being lacerated and placed with crown (right).

Figure 8.12 (a) Conventional intraoral radiograph showing an impacted, transversally located 11. (b) On a three‐dimensional image model from a CBCT examination it is clear that 11 is lacerated and placed with the crown palatally and the root facially to the neighboring teeth.

Compared with conventional fan beam CT, CBCT has a number of advantages such as:

·     easy to request and to refer to (when fully implemented in dentistry)

·     requires a very short scan time

·     requires a significant smaller radiation dose [19]

·     results in fewer relative image artefacts arising from metal objects in the teeth and jaws (fillings, crowns, bridges, implants, bone plate fixtures, etc.)

·     study viewers are free or relatively cheap to buy.

Radiation protection

Patient protection in general

Every patient who undergoes an X‐ray examination is exposed to millions of photons which can cause cell damage due to ionization. Damage to the DNA in a cell’s chromosomes could lead to permanent changes known as mutations. In very rare cases, a mutation may result in the development of a tumor. The risk of a tumor due to a given X‐ray dose can be estimated, and dose and risk have been found to be positively correlated. Therefore, it is recommended that patient doses are kept as low as reasonably achievable [1]. Since the latent period between X‐ray exposure and clinical diagnosis of a resultant tumor is expected to be many years (20–45 years), children are at a higher risk than middle‐aged and elderly adults and therefore should be protected most carefully. Ludlow et al. [23] reassessed patients’ risk related to common dental radiographic exposures using the 2007 ICRP recommendations. These recommendations include tissues such as salivary glands, oral mucosa, and extrathoracic airway tissues in the weighting scheme of radiographic‐sensitive organs. The authors conclude: “Until we have clear evidence for a threshold dose below which our patients are not at risk, we must assume that radiography involves a small, but real, risk to our patients.” However, the authors recommend that the clinician ask the question: “How is this exposure likely to benefit my patient?” When there is an indication for radiography then it is most likely that the benefit will far exceed the risk.

Image receptor sensitivity

Dental films are commercially available in ISO speed groups D, E, and F. The F‐speed film is the most sensitive (20–25% faster than the E‐speed film) and provides a diagnostic quality equal to the other film speed groups and should therefore be used for patient exposures [24–26].

Digital image receptors for intraoral radiographs have previously been much more sensitive and thereby require a significantly lower radiation dose than conventional films [24], but for several of the present digital receptors this characteristic is less pronounced when the diagnostic accuracy of the digital image is comparable with that of films [27,28]. Problems with smaller digital receptor sizes may lead to more than one exposure to cover the area to be examined, and problems with positioning the digital receptor, in particular bulky sensors, may lead to high rejection rates resulting in retakes [29]. These problems could in the end lead to increased patient doses with digital radiography.

For extraoral radiographs, it is unlikely that digital systems will offer any dose reduction when compared to a conventional medium‐speed film‐intensifying screen system.

Beam collimation

For intraoral radiography, a rectangular collimator offers a significant dose reduction to the patient compared with a traditional circular collimator with an opening of maximum size (6–7 cm in diameter) [1]. In addition, a rectangular collimator results in higher image contrast owing to lower scattered radiation.

Lead protection

An apron protects against external scattered radiation but seems to have no effect on the gonad dose [30]. If the apron is supplemented with a thyroid collar, the dose from both primary and scattered radiation to the thyroid gland may be reduced. However, thyroid shielding is not possible in panoramic radiography, for example. For intraoral radiography, a neck shield as shown in Figure 8.13 can be used instead of an apron. The neck shield is placed in contact with the inferior part of the mandible and it offers optimal radiation protection to the thyroid gland. However, the shield may interfere with the X‐ray tube when exposing periapical radiographs of the lower front teeth, making it impossible to use the paralleling technique in this region.

Photo of a neck shield.

Figure 8.13 A neck shield.

Patient cooperation

Dental radiography may be a frightening experience for a child. With intraoral radiography, the X‐ray tube is close to the face and an unpleasant image receptor is placed in the mouth. With extraoral radiography, a young child may find the X‐ray unit large and frightening. Techniques to reduce the child’s fear should be used, and the technicians should be responsible for ensuring a trustful cooperation with the child, since this is important for an acceptable X‐ray examination with a minimum number of retakes.

References

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