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REVIEW ARTICLE
Year : 2021  |  Volume : 9  |  Issue : 2  |  Page : 45-51

Effectiveness of orthopantomograph in vertical mandibular measurements: A systematic review


1 Department of Orthodontics and Dentofacial Orthopaedics, Subharti Dental College, Meerut, Uttar Pradesh, India
2 Department of Public Health Dentistry, Subharti Dental College, Meerut, Uttar Pradesh, India

Date of Submission07-Apr-2021
Date of Decision07-May-2021
Date of Acceptance03-Aug-2021
Date of Web Publication30-Aug-2021

Correspondence Address:
Anupriya Srivastava
KM-22, SF-2, Kavi Nagar, Ghaziabad, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jomr.jomr_9_21

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  Abstract 


Objective: The purpose of this study is to review the literature to provide a better understanding of effectiveness of orthopantomogram in determining mandibular vertical measurements. Materials and Methods: A systematic review was conducted through the Medline database (Entrez PubMed), Web of Science, and Scopus. All the articles in which the primary objective was to investigate the effectiveness of orthopantomograph in diagnosing mandibular asymmetry in the vertical plane were included in the meta-analysis. Results: Out of 100 potentially relevant articles, only 18 met all the inclusion criteria. The rest all other articles were excluded that were not filling the initial selection criteria, and which did not actually address the accuracy of panoramic radiograph in assessing asymmetry with reasons. Conclusion: Caution is advised when using conventional or digital panoramic images to assess vertical measurements. Vertical measurements are usually more accurate than horizontal measurements and angular measurements, but still they are not the true representation of the real objects. Therefore, understanding the limitations of every form of panoramic imaging is required. Future studies with panoramic images generated from three-dimensional data are required to determine whether they overcome the limitations of conventional and digital panoramic images.

Keywords: Condyle, mandibular asymmetry, panoramic radiograph


How to cite this article:
Srivastava A, Raghav P, Pradhan S. Effectiveness of orthopantomograph in vertical mandibular measurements: A systematic review. J Oral Maxillofac Radiol 2021;9:45-51

How to cite this URL:
Srivastava A, Raghav P, Pradhan S. Effectiveness of orthopantomograph in vertical mandibular measurements: A systematic review. J Oral Maxillofac Radiol [serial online] 2021 [cited 2021 Dec 1];9:45-51. Available from: https://www.joomr.org/text.asp?2021/9/2/45/325044




  Introduction Top


Improvement in the beauty and harmony of facial appearance has been the main intention of orthodontic treatment since the beginning of orthodontic practice.[1] The facial complex consist of variable constituent parts and harmony among these parts determines the overall symmetry.[2]

Clinically, symmetry refers to balance, while significant asymmetry denotes imbalance. Symmetry can be defined as equality or correspondence in the form of parts distributed around a center or an axis, at the two extreme poles, or on the two opposite sides of the body. A difference in the pace of development of right and left sides of the mandible may result in asymmetrical function and activity of the jaw.[2]

Asymmetry in the lower third of the face referred to as “mandibular asymmetry” causes esthetic and functional problems. Condylar asymmetry is the disproportion of vertical condylar between left and right mandibular condyles. Condylar asymmetries are thought to be one of the most important causes of mandibulofacial asymmetries.[3]

It has been shown that malocclusions have a remarkable effect on mandibular condyle morphology, resulting in asymmetrical growth of the left and right sides of the mandible. Thus resulting in asymmetrical function and activity of the jaws.[4]

Two hypotheses are given to explain mandibular asymmetry. The first one is that observed asymmetries are simple facts of fluctuating morphological asymmetry. The second is a functional and mechanical one. The theory states that the functional masticatory forces from the mandible to the cranium suggest the magnitude of joint loading over time to be related to condylar size.[5]

Mandibular asymmetry has been diagnosed by a combination of tools. These include clinical examination followed by extraoral photographs of frontal and side views. Radiographic aids include two-dimensional (2D) radiographs such as lateral and posteroanterior cephalograms[6] and also oblique radiographs of the mandible taken at 45 unit and panoramic radiographs.[7]

Many techniques to assess condylar asymmetry have been developed, some of which are based on standardized panoramic radiography measurements.[8] The popularity of this technique may be because of its simplicity of operation, its low radiation dosage in comparison with conventional full mouth periapical survey, and the wide field of projected structures with minimal superimposition of intervening tissues. However, the disadvantage of the orthopantomograph (OPG) technique regarding the insecure interpretation of such wide areas as the temporomandibular joint (TMJ) condyles and the two mandibular rami, questions the value of an OPG. The study focus on the accuracy of bilateral information about structures such as the TMJ condyles when using the OPG image from a vertical point of view.[9]

A difference of more than 6% in vertical dimensions between the left and right sides of the condyle are supposed to be noted in an OPG.[10]

Therefore, this study aims to compare the vertical dimensions of the condyles and ramus in the OPG images, without craniomandibular complaints, focusing on their respective magnitude of vertical symmetry.


  Materials and Methods Top


This systematic review was reported following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses checklist.[11]

Inclusion criteria

Articles in which the primary objective was to investigate the effectiveness of OPG in diagnosing mandibular asymmetry in the vertical plane were included in the study.

Exclusion criteria included

(1) Case reports, reviews, letters, and personal opinions and (2) studies that evaluated other imaging methods were excluded from the study.

A literature search was performed utilizing the Medline database (Entrez PubMed), Web of Science, and Scopus covering the period from January 1967 to December 2019.

A two-phase selection of the articles was conducted. In Phase 1, two authors independently reviewed the titles and abstracts of all references. All the articles that did not appear to meet the inclusion criteria were excluded from the study. In the second phase, full texts were independently reviewed and screened accordingly. Any disagreement was resolved by means of discussion.

Out of the two authors, one author extracted data from the selected studies that included study characteristics (authors, year of publication, and country), sample characteristics (sample size, observers, number, and type), diagnostic assessment methods (in situ, panoramic radiography, and computed tomography [CT] or cone-beam CT [CBCT]), and outcome characteristics (frequency). Second author cross-checked all the retrieved information. Again, any mistyping was resolved through discussion.


  Result Top


A total of 100 potentially relevant articles were selected using Medline database

(Entrez Pubmed), web of science and scopus. In search strategy, 17 articles met all the inclusion criterias [Figure 1]. Included studies were of medium or low methodological quality with serious shortcomings and the results were contradictory. But the majority of studies suggested that OPG has proved a good and reliable diagnostic aid in determining vertical measurements. The included studies have been summarized in [Table 1]
Table 1: Summary of Articles included in the literature

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Figure 1: Flowchart showing search strategy for article selection

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The goal of this study is to gain some clarity regarding the diagnosis of mandibular asymmetry with panoramic radiographs.[7] Diagnosing mandibular asymmetry is a complex problem. Although the precise differentiation of these conditions may be confusing, the clinical environment requires radiographic impressions at first hand before any other data are available.

Tronje et al.[12],[13] mathematically calculated the accuracy of measurements on panoramic radiographs. Under certain limits, the panoramic film can be used for vertical measurements in clinical practice if the patient is properly positioned. They also concluded that the horizontal dimension is unreliable.

Laster et al.[14] compared vertical and horizontal measurements of anatomic points on 30 skulls imaged with ideal, for 7 mm laterally shifted, and 10° rotation around a vertical axis positioning in a Sirona Orthophos Plus Panoramic Unit with measurements obtained by software on digital images. The purpose of this study was to assess the changes in both in symmetry ratios on panoramic radiographs and linear measurements. They found that horizontal cephalograms showed the greatest differences between the panoramic image and the actual skull. Manufacturer reported that magnification was consistently less than the calculated magnification. Accuracies for detecting asymmetry on the panoramic image were 67% for ideal, 70% for rotated, and 47% for shifting. Therefore, one should be cautious when making absolute measurements or relative comparisons.

Larheim and Svanaes[15] divided 31 patients into three groups and imaged each patient with a panoramic machine on two occasions. For Group 1, the two exposures were done by the same operator using identical machine settings and head position recording. Group 2 had two operators, and the exposure was also done using identical machine settings and head position recording. Group 3 had two operators with identical machine settings but without any idea of the head position used by the first operator. Besides, five dried skulls with metal pins placed at various reference points were imaged in different orientations using panoramic machines. They concluded that, although, the change in imaging condition reduced the reproducibility of the horizontal linear measurements, but the vertical linear measurements and angular variables were consistently reproducible in all three groups. The change in imaging condition reduced the reproducibility of the horizontal linear measurements, but no differences in precision were identified between the left and right sides. The dry skull component of the research showed a magnification factor of 18%–21% for the vertical, but gonial angle skulls were identical to those measured on the panoramic image.

Ongkosuwito et al.[16] also showed no significant differences in the magnification factor of the left and right sides of the mandible. Compared with other 2D radiographic techniques, the OPG had comparable reliability in measuring mandibular measurements condylion-gonion, gonion-menton, and condylion-menton.

The above studies clarify that horizontal measurements are unreliable because of there is nonlinear variation in the magnification at different object depths, whereas vertical measurements are relatively reliable.[17]

Habets et al.[10],[11],[12],[13],[14],[15],[16],[17] took nine pantomographic radiographs by altering the central position of a synthetic mandible up to 10 mm in the horizontal plane of a Siemens OPG 5. The authors suggested that the 6% observed difference between left and right condylar height measured on the panoramic film might be a result of technical errors. The differences >6% can be considered true vertical asymmetry.

Kjellberg et al.[18] imaged two dry skulls in six positions with three panoramic units. They found that the manufacturer's listed magnification for the panoramic unit might not be correct for all areas of the panoramic radiograph because different panoramic machines provide different measurements.

On the other hand, some studies suggest that OPG is not recommendable and one cannot rely on its diagnostic qualities for linear measurements.

A study done by Markic et al.[19] showed that all diagnostic radiography techniques for the Condyle and ramus showed similar ranges of agreement between magnetic resonance imaging, CT, and CBCT (maximum 6.4 mm) but higher ranges for OPG. Therefore, understanding the limitation of panoramic radiography is required.

Schulze et al.[20] assessed the precision and accuracy of panoramic measurements using digital panoramic software. They imaged a dry skull ten times in seven positions with an Orthophos DS panoramic system. Two metal pins and a metal sphere were fixed to the premolar region of the mandible in skull. One pin was kept parallel to the Frankfort horizontal plane, and the other was positioned in the vertical plane. Both the digital and actual measurements of the metal pins and spheres were compared with both actual measurements and the other digitized images. They concluded that vertical measurements were less reproducible as compared to the horizontal measurements.

Türp et al.[21],[22] imaged 25 macerated skulls with a Seimans OPG 5 unit and compared measurements of condylar and rami heights directly on the skulls and on the panoramic radiograph. A low degree of correlation among the data, with Pearson correlations coefficient of 0.26 (condyle and ramus height), 0.06 (ramus height), and 0.26 (condyle height) was reported. The study concluded that the panoramic radiographs are not appropriate source for exact vertical measurements such as condylar and ramus heights, or a combination, to assess mandibular asymmetry.

Akcam et al.[23] found that panoramic radiographs can provide information on the vertical dimensions of craniofacial structures; however, they are not reliable enough to give acceptably accurate additional information as compared with lateral cephalograms.

Nohadani and Ruf[24] compared longitudinal vertical facial and dentoalveolar changes on panoramic radiographs with measurements on lateral cephalometric radiographs and reported that OPG delivers a moderate approximation to the situation depicted on lateral cephalogram, one cannot recommend panoramic radiographs cannot be recommended for evaluating vertical facial parameter changes during time.

Batenburg et al.[25] imaged five edentulous mandibles in nine positions using a Siemens orthophos orthopanoramic unit. All the measurements were made by using parallel vertical bars transecting the alveolar ridge at various points along the mandible. The objective of their study was to determine the effects of mandibular angulation, position, and shape on the panoramic image distortion. They found that by tilting the mandibles 20°, the length of the bars was changed both on top of and inside the mandible. Therefore, they concluded that orthopantomography is not a reliable technique to evaluate alveolar bone height in an edentulous mandible.

Kumar et al.[26] concluded that panoramic radiography can be used to determine the ramus height as accurately as another 2D radiography. However, clinicians should be careful when predicting horizontal measurement from OPGs.

Xie et al.[27] took panoramic radiographs (Planmeca PM 2002) of 5 dry skulls in 9 different orientations that included 5 mm forward or backward shifting and 5° up or down movement in the sagittal plane of the orthopantomogram. Vertical measurements were calculated on the distal surfaces of the first premolar and molar, the mental foramen bilaterally, and the midline on panoramic radiograph. All these measurements were when compared with actual measurements from the mandibles, they found that, if the head was only slightly misaligned (5 mm horizontal or 5° vertical rotation), vertical measurements were not significantly affected as long as the reference lines were in the same vertical path as the teeth. Hence, it was suggested that vertical measurements should be made using reference points located anatomically, directly above or below the point being measured.

Kambylafkas et al.[28] evaluated the ability of panoramic radiographs to assess side-to-side differences in condyle and ramus height. By using a phantom marked with radiopaque steel balls representing either right or left side of the mandible, two sets of panoramic films were created with an OPG OP 100. They found a 2.1% average variation in the total height of the mandible. Laminograph is recommended as the gold standard for measuring posterior vertical mandibular asymmetry. The correlation between the laminography and panoramic measurements is 0.92 for total height and 0.39 for condylar height.

Catić et al.[29],[30] studied the precision of dimensional measurements made on panoramic images, considering the orthopantomographic unit's manufacturer's reported magnification index. Metal markers were placed on 25 dry mandibles imaged in the panoramic unit. Distances between metal markers were measured on both the mandible and the panoramic radiographs. Five vertical, 5 horizontal, 3 oblique, and 2 angular measurements were made. They found that all horizontal distances measured on the OPG crossing the midline and extending between the right and left condylar processes were much larger than those distances measured directly on the dry skull (1.45–1.85 times). Vertical measurements, even in the midline, were precise. Measurements which do not cross the midline were significantly lower than the magnification index reported by the manufacturer and thus considered precise. Catić et al.[29] found that the gonial angle measurement from the panoramic radiograph was accurate (magnification factor 1.05), but the angle B values, defined as the tangent of right/left a corpus of the left/right mandible and the line that connects the lower border of the mandible in a sagittal line with the highest point of the right/left condylar process, were much lower than those from the dry skull. Therefore, they concluded that any linear, vertical, horizontal, or oblique measurements can be made precisely on an orthopantomographic radiograph as long as the distance is only on 1 side of the mandible and does not transverse the midline.

Fuentes et al.[31] analyzed whether the X-ray method of measuring condylar asymmetries in orthopantomography presents a minor tendency to error due to slight displacements of the head in the horizontal plane. Thirty patients between 18 and 25 years of age were assessed. Each of them underwent three panoramic X-rays in three different positions: orthoradial and at 5° and 10° horizontal angles. No significant difference was observed when the 0° and 5° angles were compared. By contrast, significant differences were found in all patients at 0° and 10° in condylar ramal height.


  Discussion Top


Rotational panoramic radiography is used in clinical dentistry on wide scale because it is simple and the radiation dosage is low. The measurements in panoramic radiographs, however, include considerable methodologic errors. In the sharply depicted focal trough, the image is free of distortion, which means that the magnification factor is the same in both the vertical and the horizontal plane. Objects outside this layer, however, will appear distorted in the image owing to the difference between the velocity of the film and the velocity of the projection of the object on the film. The panoramic image is therefore affected by both magnification errors and displacement.[12],[13],[14],[15],[16],[17],[18],[19],[20],[21],[22],[23],[24],[25],[26],[27],[28],[29],[30],[31],[32] The horizontal distances are particularly unreliable as a result of the nonlinear variation in the magnification at different object depths, whereas vertical distances are relatively reliable.[12],[15],[33] For this reason, Ramstad et al.[34] suggest that quantitative measurements on panoramic radiographs should not be encouraged. However, other authors[12],[15] find that the reproducibility of vertical and angular measurements are acceptable provided if the patient's head is correctly positioned in the equipment.


  Conclusion Top


  • Inspite of the ease and accuracy of pantomograph, caution is advised while using panaromic machines for vertical measurements.
  • More of the accuracy has been observed in vertical measurements than horizontal and angular measurements, but still they are not the true representation of the real objects.
  • Therefore, understanding the limitations of every form of panoramic imaging is required.
  • Future studies with panoramic images generated from 3-dimensional data are required to determine whether they overcome the limitations of conventional and digital panoramic images.


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Laster WS, Ludlow JB, Bailey LJ, Hershey HG. Accuracy of measurements of mandibular anatomy and prediction of asymmetry in panoramic radiographic images. Dentomaxillofac Radiol 2005;34:343-9.  Back to cited text no. 14
    
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Ongkosuwito EM, Dieleman MM, Kuijpers-Jagtman AM, Mulder PG, van Neck JW. Linear mandibular measurements: Comparison between orthopantomograms and lateral cephalograms. Cleft Palate Craniofac J 2009;46:147-53.  Back to cited text no. 16
    
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