|Year : 2016 | Volume
| Issue : 1 | Page : 22-26
Positioning errors in digital panoramic radiographs: A study
A Cicilia Subbulakshmi1, N Mohan2, R Thiruneervannan1, S Naveen3, Sabitha Gokulraj2
1 Department of Oral Medicine and Radiology, KSR Institute of Dental Sciences, Trichengodu, Tamil Nadu, India
2 Department of Oral Medicine and Radiology, Vinayaka Missions Sankarachariyar Dental College, Salem, Tamil Nadu, India
3 Department of Conservative Dentistry and Endodontics, Vinayaka Missions Sankarachariyar Dental College, Salem, Tamil Nadu, India
|Date of Web Publication||6-May-2016|
Dr. A Cicilia Subbulakshmi
6/3, Chaithanya Apartments, 5th Cross, Brindhavan Road, Fairlands, Salem - 636 016, Tamil Nadu,
Source of Support: None, Conflict of Interest: None
Panoramic radiography is a unique and a very useful extraoral film technique that allows the dentist to view the entire dentition and related structures, from condyle to condyle, on one film. Capturing a wide range of structures on a single film grounds the odds of errors in the digital panoramic radiographs. Improper positioning of the patient complicates it more, reducing the diagnostic usefulness of these radiographs. Wide knowledge about the common positioning errors and the ways to rectify it benefits the dentists in interpretation and diagnosis. Aim: This study is aimed at analyzing the 10 common positional errors (anteriorly positioned, posteriorly positioned, head tilted upwards, head tilted downwards, head twisted to one side, head tipped, overlapping of spine in lower anterior region, tongue not placed close to palate, patient movement, and ghost images) in 200 digital panoramic radiographs selected randomly. Materials and Methods: Two hundred digital panoramic radiographic images of the patients above 6 years of age were selected randomly from the stored data in the system, projected on the white screen, and studied. The radiographs were analyzed by two oral medicine and radiology specialists, by recording separately, and then the results were analyzed. Results: The most common error was failure to place the tongue close to the palate, which leads to the presence of radiolucent airspace obscuring the roots of the maxillary teeth.
Keywords: Panoramic imaging, patient positioning in orthopantomogram (OPG) etc., positioning errors
|How to cite this article:|
Subbulakshmi A C, Mohan N, Thiruneervannan R, Naveen S, Gokulraj S. Positioning errors in digital panoramic radiographs: A study. J Orofac Sci 2016;8:22-6
|How to cite this URL:|
Subbulakshmi A C, Mohan N, Thiruneervannan R, Naveen S, Gokulraj S. Positioning errors in digital panoramic radiographs: A study. J Orofac Sci [serial online] 2016 [cited 2019 Dec 11];8:22-6. Available from: http://www.jofs.in/text.asp?2016/8/1/22/181922
| Introduction|| |
Since the introduction of panoramic radiographs by Numeta and Patero in early 1960s,  it has gained considerable popularity as a diagnostic tool. It is a radiographic procedure that produces a single tomographic image of the facial structures including both the maxillary and mandibular arches and their supporting structures.  Panoramic images are most useful clinically for diagnostic problems requiring broad coverage of the jaws and for those tasks that do not require high resolution and sharp details available on intraoral images. 
Other problems associated with panoramic radiographs include unequal magnification and geometric distortion across the image and occasionally the presence of overlapping structures such as cervical spine that can hide lesions in the anterior region. The simple method of operation, wider scope of examination, display of anatomic structures, and low radiation dose are the reasons for its continuously growing popularity. 
The value of panoramic radiograph is reduced when they are of poor diagnostic quality.  The poor quality is not a result of an inherent limitation with the equipment but rather is a result of errors made by the operator during patient positioning or during exposure or during film processing in case of conventional radiographic techniques.
To obtain diagnostically useful panoramic radiographs, it is necessary to prepare patients properly and position their heads carefully in the image layer.  Image layer is nothing but a three-dimensional curved zone or "focal trough" where the structures lying within this layer are reasonably well defined on the final panoramic image.  Image distortion and ghost image formation due to positioning errors can mask an existing pathology. Ability to recognize various errors plays a vital role in correct interpretation of the panoramic radiographs.
| Materials and Methods|| |
Two hundred panoramic radiographs, taken using Planmeca Romexis digital panoramic machine in the department during the time period of 2010-2011, were selected randomly from the stored patient data files. However, the radiographs of children less than 6 years of age were excluded from the study. Radiographs of edentulous patients were also included in the study. The radiographs were selected at random, reviewed, and then numbered from 1 to 200. After collection, all radiographs were projected on a white screen and were analyzed for the presence of positioning errors by two oral medicine and radiology specialists with more than 15 years of experience.
The observations were tabulated and the positioning error in each of the image was recorded. A simple frequency test was used for the statistical analysis. The frequency table is given that explains the frequency of occurrence of each error with its relative percentage.
The common 10 positioning errors that were considered are anteriorly positioned, posteriorly positioned, head tilted downwards, head tilted upwards, head twisted to one side, head tipped, overlapping of spine in lower anterior region, tongue not placed close to palate, patient movement, and ghost images [Table 1].
| Results|| |
Out of the 200 panoramic radiographs examined, 72 (36%) radiographs did not show any positioning error. And the remaining 128 (64%) radiographs showed one or more positioning errors. The most common error observed among the radiographs was the presence of radiolucency obscuring the roots of maxillary teeth (33%). Sixty-six radiographs showed this error. The second common was the presence of artifacts, reflected and ghost images. Thirty-four (17%) radiographs showed this error. Thirty-one (15.5%) radiographs had the error of patients head tilted upwards. Twenty-one (10.5%) radiographs had the error of overlapping of spine in the lower anterior region due to slumping. The error of positioning - the patient too far back to the image - layer was present in 14 (7%) radiographs. The least common error found was positioning - the patient too forwards in relation to the image layer. Only 1% of the radiographs showed this error. The frequency and percentage of all the 10 errors are given in [Table 2] and their histogram is given in [Figure 1].
The combination of errors was also analyzed. The error of palatoglossal air space Er 8 was present in 48 (24%) radiographs separately and remaining 18 radiographs showed this error in combination with other errors. Nine radiographs had the combination of Er 8 with Er 10, which was the most common combination. Er 8 was also found in combination with other errors like Er 7, 6, 3, 4, 2 in decreasing frequency. Only one (0.5%) radiograph showed the presence of four errors (Er 8, 10, 7, 4) combined.
| Discussion|| |
The panoramic radiograph continues to offer today's dentists a unique patient view, covering the entire dentition and surrounding structures, the facial bones and condyles, and parts of the maxillary sinus and nasal complexes. The equipment used to obtain panoramic radiographs has continued to improve with recent advances including automatic exposure and multiple image programs. In panoramic radiography, the patient's dental arch must be positioned within a narrow zone of sharp focus known as the image layer or "focal trough."  Teeth and structures lying outside this zone of sharp focus will exhibit blurring, distortion, or other artifacts.
Akarslan et al.  evaluated 460 panoramic radiographs for the 20 most common errors. They found that positioning errors were responsible for over 38% of the errors. Errors included improper occlusal plane tilt, blurring, narrowing, and widening of anterior teeth, effects that are largely a result of careless anterior-posterior head positioning.
Rushton et al.  sampled the quality of 1,813 panoramic radiographs. The patient positioning errors appeared in over 85% of the radiographs.
Schiff et al.  reported that 80% of the panoramic radiographs had errors.
A good panoramic radiograph
In a good panoramic radiograph, the mandible is "U" shaped, the condyles are positioned about an inch inside the edges of the film and 1/3 of the way down from the top edge of the film. The occlusal plane exhibits a slight curve or "smile line" upwards. The roots of the maxillary and mandibular anterior teeth are readily visible with minimal distortion.  Magnification is equal on both sides of the midline.  Panoramic images generally show magnification at a ratio that ranges from 10% to 30%. 
Panoramic radiography may not be suitable for some patients because of their physical stature, facial asymmetry, or their inability to follow the instructions properly. These hinder their proper positioning of the patients inside the machine. Here, the panoramic error is inevitable. 
The tongue not placed close to the palate [Figure 2] was the most common error identified in this study. This result is in acceptance with the result obtained in the studies from many investigators. Wafa′a AL-Faleh reported 81.8% of this error in his study. Forty-six percent of the radiographs showed this error according to Akarslan et al.  Seventy-nine percent of the radiographs showed this error according to Granlund et al.  Thirty-three percent of the radiographs in our study showed this error. The percentage of radiographs that showed this error is comparatively less in our study. This error may be due to lack of communication between the dental technician and the patients, and may be because of language difference.  The technician may find difficulty to instruct the patients to swallow and to keep the tongue in the roof of the mouth. Sometimes patients may misunderstand the instructions, putting only the tip of the tongue on the palate, or the patients do not pay much attention to the instructions given by the technician. 
|Figure 2: Tongue not placed close to palate-radiolucent space obscuring the roots of maxillary incisors|
Click here to view
An incorrect tongue position can affect the diagnoses of apical periodontitis and assessments of root anatomy and resorption. 
The second most common error was the presence of ghost images [Figure 3] and artifacts, which is in contrast to Akarslan et al.,  a superimposition of the hyoid bone, which was the second most common error according to him and Wafa′a AL-Faleh,  in whose study slumped position of the patient leading to superimposition of the spine in the anterior region of the mandible was the second most common error. Slumping was the fourth most common error in our study [Figure 4].
There is a tendency among patients when holding the hands of the machine to slump. The dental technicians need to make sure that the patients back and spine are erect with the neck extended.  The x-ray beam traverses several cervical vertebrae when the patient is slouched, causing an opaque shadow of the spine to obscure details of the incisor teeth. 
Ghost images could be either anatomic or jewelry ghosts.  Objects that are within the selected image layer are clearly visible in the image, while objects outside the image layer are deliberately blurred out of recognition. The degree to which the blurring of extraneous details is successful is dependent upon a number of factors. 
These factors include:
Ghost image of the mandibular ramus could be clearly demonstrated in magnified form over the contralateral mandibular body. This should not be considered as an error.
- The atomic density of the contents of the object;
- The bulk of the content of the object;
- The proximity of the object to the image layer; and
- The bulk and density of the patient's soft tissues. 
Jewelry has high atomic density, and is generally outside the image layer. It can frequently lead to ghost image formation. At times, unilateral jewelry might be mistaken for an odontoma or other radio-opaque disease entity. Bullets and shrapnel in the soft tissues may also cause ghost images to appear magnified and contralaterally in the panoramic radiographic image. 
The third most common error was tilting of the patients head upwards with the chin placed forward, which is similar to the study by Wafa′a AL-Faleh.  This error can be intentionally created if you wish to see the lower anterior incisors and surrounding bone more clearly, especially with panoramic equipment that allows collimation so that a limited segment of the jaw can be imaged. 
The fifth most common positioning was patient too far back in relation to the image layer [Figure 5].
The anterior portion of the image layer is very narrow, as a result, any flaring of dentition may result in the above error if the patient is positioned correctly in the machine. For these patients, it is advised to move him/her further forward in order to move the apices into the image layer.
The errors due to patient movement and midline asymmetry was present in less than 5% of the radiographs. According to Granlund et al.  25% Of the radiographs showed this error.
There may be an anatomical/pathological reason for a difference in size between right and left. Problem usually lies with the alignment of the midsagittal plane. The tip of the nose and the center of the chin must fall on the reference line. ,, A visual examination of the patient will identify the asymmetric patient. If there is an anatomical variation or a pathological difference in the size of the ramus, the teeth will not display a difference in size between right and left. 
"v" shaped mandible due to downward tilting of mandible was present in 2.5% of the radiographs [Figure 6]. It is better to err with the chin "too far down" than "too far up."  Discrepancies in the height of the condyles and angle of mandible were found in 2% of the radiographs.
|Figure 6: Patient more anteriorly placed to focal trough — "v" shaped mandible|
Click here to view
The least common error found was patient too forwardly placed in relation to the image layer [1%].
In many instances, multiple errors occurred in one image, this could be due to that an inadequate time was spent for patient preparation and positioning. 
Patient positioning 
The midsagittal (horizontal) plane is positioned perpendicular or at a right angle to the floor and centered right to left.
The plane of occlusion (vertical) is positioned parallel to the floor. The Frankfort plane, Tragal-canthus plane, and the Ala-tragus plane are used to align the vertical position of the head.
The anteroposterior plane is aligned between the maxillary lateral incisor and canine contact.
Proper positioning of tongue and lips and remaining still during the exposure.
| Conclusion|| |
An orthopantomogram (OPG) of poor diagnostic quality can lead to unnecessary stress to the patient and the dentist, as it can mask the diagnostic clue, the exact size, extent, location, and nature of the pathology leading to unwanted repeated exposures. Understanding the cause of positioning errors and the importance of patient preparation and positioning can prevent most of the positioning errors in panoramic radiography. It is more important to perfect the panoramic patient positioning technique, than to make unnecessary repeat exposures. The diagnostic value of an excellent panoramic radiograph is far superior to one made under careless quality control.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2]