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Table of Contents   
ORIGINAL RESEARCH  
Year : 2013  |  Volume : 24  |  Issue : 3  |  Page : 294-297
Evaluation of horizontal magnification on panoramic images


1 Oral and Dental Diseases Research Center, Department of Endodontics, Kerman University of Medical Sciences, Kerman, Iran
2 Department of Oral and Maxillofacial Radiology, Kerman University of Medical Sciences, Kerman, Iran
3 Oral and Dental Diseases Research Center, Kerman University of Medical Sciences, Kerman, Iran

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Date of Submission03-Apr-2012
Date of Decision12-Apr-2012
Date of Acceptance06-Feb-2013
Date of Web Publication12-Sep-2013
 

   Abstract 

Aims: This study evaluated the horizontal magnification of images taken from adults and pediatrics with PM 2002 CC Planmeca analogue machine.
Materials and Methods: A series of 120 panoramic radiographs were obtained of 60 adults and 60 pediatrics. For all patients, negative impressions were used to make positive casts of the teeth. A caliper was used to measure the maximum mesiodistal length of the buccal surface of all teeth except canines on both casts and radiographs. The horizontal magnification factor was calculated for incisor, premolar, and molar regions by dividing the values obtained from the casts by the values obtained from the radiographs.
Statistical Analysis: Independent t-test and one-way analysis of variance (ANOVA) were used.
Results: The results indicated that with regard to adults, maxillary and mandibular incisor regions, unlike the other two sessions, didn't show significant difference of the mean magnification of horizontal dimension (P = 0.5). In pediatrics, the comparison between mean magnification factors of all subgroups showed significant difference (P < 0.0001). Despite the adults' radiographs, the results of pediatrics' radiographs showed significantly higher magnification than the index listed by the manufacturer of the radiographic machine used.
Conclusion: The present study results point to the fact that PM 2002 CC Proline panoramic machine makes possible precise measurements on radiographs of adults' jaws in the horizontal dimension.

Keywords: Horizontal magnification, measurement, panoramic, radiography

How to cite this article:
Raoof M, Haghani J, Ebrahimi M. Evaluation of horizontal magnification on panoramic images. Indian J Dent Res 2013;24:294-7

How to cite this URL:
Raoof M, Haghani J, Ebrahimi M. Evaluation of horizontal magnification on panoramic images. Indian J Dent Res [serial online] 2013 [cited 2019 Oct 23];24:294-7. Available from: http://www.ijdr.in/text.asp?2013/24/3/294/117989
Conventional Panoramic radiographs are still used extensively by dentists. Markis et al., in their survey, concluded that there was no significant difference in the quality of images obtained with both conventional film-based and digital panoramic devices. [1]

One of the greatest problems associated with panoramic images include unequal magnification which may obscure useful information and compromise diagnosis. [2],[3]

The aim of the present study was to evaluate the horizontal magnification of the images taken from adults and children with PM 2002 CC Planmeca analogue machine.


   Materials and Methods Top


This descriptive study was approved by the research ethics committee at Kerman University of Medical Sciences (Protocol n. KA/86/70). The study consisted of a population of 120 patients who sought treatment at Kerman dental school, Iran and were referred to the Radiology department for taking panoramic radiography images. Out of the 120 patients, 60 were adults who had no extracted tooth apart from their third molars and all their permanent teeth were erupted and 60 of them were pediatrics with deciduous teeth; and if they had removed a tooth or had a tooth that had fallen out, it wasn't long that this had occurred. The mean age of adults was 35.5 years (range 16-55 years) and as for the pediatrics, it was 6 years (range 3-8 years). Patients who agreed to take part in this study were to sign a consent form by themselves or their parents. The patients needed radiographs for their treatment and no more additional radiographs were taken for the study. One radiologist took all radiographs, in the department of oral radiology using T-MAT film (Kodak, NY, USA) in a cassette with Kodak Lanex Regular screen (Eastman Kodak Company, Rochester, NY) and exposed in a Planmeca X-ray unit (PM 2002 CC, Planmeca, Helsinki, Finland). Exposure settings were 70 kV, 7 mAs, 18 s for adults and 60 kV, 4 mAs, 18 s for children.

The manufacturer's instruction on patient positioning were precisely followed.Films were developed in an automatic processor (Velopexe, ExtraXmedien, UK) using champion developer and fixer solutions (Champion photochemistry, Iran). According to the instructions the manufacturer gave out, alginate impressions were made (Alginoplast Bayer dental D5090 Leverkusen) using plastic impression trays. Upon removal from the teeth, the impressions were carefully inspected for voids and errors and were rinsed for a few seconds to remove any saliva. Using dental stone type IV (Velmix stone, Kerr, Italy), all impressions were first poured, where type III stone (DE Deyussa stone type III, Germany) was used for the base. To ensure the flow of the stone into critical areas, each impression was carefully poured with slight vibration. After 24 hours, when the casts were set, they were then separated from the impressions and trimmed to an almost uniform height.

A caliper was used to measure the distance between mesial and distal height of the contour of all teeth except canines on both casts and radiographs. All casts and radiographs assessed by a board-certified radiologist. The images were viewed and evaluated on a light-viewing box (Shayanteb, Iran) under normal operating illumination in a quiet room. No particular time was set for viewing.The observer was allowed a rest period whenever he felt tired. A set of 10 randomly selected radiographs wasused for calibrating the reader. This was repeated for the mean range of all measurement till the difference did not exceed 0.1 mm. All the measurements were done twice with an interval of 10 days. The magnification factor for each tooth was calculated. This was done by dividing the values obtained from the casts by the values obtained from the radiographs. The magnification of horizontal dimension was analyzed using Statistical Product and Service Solutions (SPSS) software, V 11.5. In order to compare the magnification of the horizontal dimension between the regions, independent t-test and one-way analysis of variance (ANOVA) were used. Intra-observer reliability of the measurements was calculated by Pearson correlation-coefficient test.


   Results Top


In all cases, the maximum mesiodistal size on the radiograph was greater than the size measured on the cast. It means that we had magnification in all specimens. [Table 1] and [Table 2] show the magnification factors for each measurement using the mean, the standard deviation, and the 95% confidence intervals.
Table 1: t-test comparisons of horizontal magnification in different maxillary and mandibular regions for adult and pediatric panoramics taken by PM 2002 CC planmeca machine

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Table 2: t‑test* and one way ANOVA comparisons of horizontal magnification in different regions in maxilla and mandible for adult and pediatric panoramics taken by PM 2002 CC Planmeca machine

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In adults, for maxillary and mandibular central and lateral incisor regions, unlike the other two sessions, the difference of the mean magnification of horizontal dimension was not statistically significant (P = 0.5).

In children, the comparison between mean magnification factors of all subgroups showed significant difference (P < 0.0001). The mean horizontal measurements calculated from central and lateral incisors were greater than molars in both arches.

Intra-class correlation coefficient was 0.96 that indicated low intra-observer error.


   Discussion Top


Distortion and magnification are considerable disadvantages of panoramic images. Image size magnification varies considerably among films from different panoramic units and even within regions of the same film. [4],[5] Such inherent magnification in panoramic images may lead to erroneously dental and maxillofacial treatment plans. For example, the clinician must consider the magnification factor when calculating the dimensions of the bone at the implant size. [2] This is the first study to evaluate the magnification factor in different areas in both jaws and also in adults and pediatrics.

All measurements were performed by a single observer who was experienced in radiographic diagnosis. This eliminates inter-observer variation and measurement errors were, therefore, presumed to be consistent with the single examiner. It is obvious that different measurement methods will produce noticeably different intra-observer errors, [6] but it is generally agreed that the performance of a single observer with any method is relatively reproducible. [7],[8]

This is claimed that PM 2002 CC Proline panoramic X-ray sets new standards in panoramic imaging of its superior imaging quality, low dose, a wide range of exposure possibilities, and ease of operation. [9] So we selected this machine for this study. The manufacturer lists the magnification factor for this machine as 1.2. The present study showed varying amount of horizontal magnification indexes in different sessions. The range was 1.1 to 1.27 for adults. In contrast to the findings of Larheim and Svanaes [10] and Tronje [11] et al., our measurements of horizontal distances had acceptable precision for adults. However, this is in agreement with the results of Catic et al., study. [12] Nishikawa et al., [13] examined the reliability of the distance measurements on panoramic radiographs obtained by Veraviewepocs machine, with the manufacturer reported magnification factor of 1.3, and concluded the distance measurement on panoramic images cannot be recommended. Scarfe et al., evaluated characteristics of the Orthopantomograph OP 100 and reported that the horizontal magnification varied from 1.01 to 1.63. [14] In the study by Yim et al., there was a significant and consistent difference in the magnification ratio depending on the type of panoramic equipment (Ortho stage: 1.27 and promax: 1.17). [15] Overall in this study, images from PM 2002 CC Proline panoramic machine demonstrated acceptable magnification for adults. There are some reasons for this result. The most likely explanation could be its small focal spot (0.5 mm × 0.5 mm), which produces images with excellent resolution. It is likely that the X-ray beam angulation of the PM 2002 CC Proline is not much oblique relative to the long axis of the teeth. Furthermore, the manufacturer's directions for patient positioning were strictly followed for each panoramic radiography. Our finding is consistent with those of Mawani et al., who reported images from PM 2002 CC Proline demonstrated the smallest shape difference. [16]

For pediatrics, the range of magnification factor was from 1.19 to 1.36 that was significantly higher than the manufacturer's magnification index (P < 0.05). So, the horizontal distances are not reliable in pediatrics› panoramic images. It might be as a result of a change in the angle of central beam that was made to compensate for the curvature of the mandible. Moreover, variations in positioning of children may decrease the reliability of distance measurements on panoramic radiographs. Tronje et al., suggested that placing an inclined object uniformly across the focal trough results in differential magnification due to its inclination. [11] It has been shown that patient head positioning is very important in panoramic radiography because poor positioning techniques may result in structures lying outside the focal trough causing images to be distorted. [17],[18] The distortion can create images that are either too wide or too narrow, depending on whether the structures are on the film or source side of the focal trough. [19] Philipp and Hurst observed that when the occlusal plane was located at 6° to the horizontal, there was a minimal amount of distortion, provided the magnification factor remained constant. [20]

In this study, the average magnification was higher in the anterior part of the maxilla and mandible than in the posterior, in pediatric images. However, in adults, data was similar only in mandible. The finding is in line with results of Kim study, [2] whereas Graber found that the average horizontal magnification varied from 19% for the maxillary central incisor to 55% for the second molar. [3] Welander and Wickman found that there was considerable tolerance toward form distortion for the lateral regions of a panoramic image compared to the anterior region. [21] Film speed, the type of machine, number of rotation centers, focal trough shape, and X-ray tube head are some factors that may affect the results in different studies.

Canines are positioned in the angle of both jaws, so while tomographic movement the focal spot position varies on the canine region. In this regard, Like the Xie study we didn't consider canines in this study. [22] To determine the magnification factor in the canine area, modulation transfer function can be calculated which is very expensive and needs special radiology phantom.

Although within the limits of the present study, PM 2002 CC Proline film-based panoramic X-ray unit offers an increasing level of image definition, further studies with different and more precise methods such as using metal markers or dry skulls are suggested. The results of this study can only be applied to the particular model of panoramic radiography unit used.


   Conclusion Top


While panoramic radiography is a valuable tool for clinical assessments, care should be taken to keep the errors inherent in panoramic radiography in mind. Other projections are considered good alternatives whenever an exact assessment of distance is required.

 
   References Top

1.Makris N, Tsiklakis K, Alexiou KE, Vierrou AM, Stefaniotis T. The subjective image quality of conventional and digital panoramic radiography among 6 to 10 year old children. J Clin Pediatr Dent 2006;31:109-12.  Back to cited text no. 1
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2.Kim YK, Park JY, Kim SG, Kim JS, Kim JD. Magnification rate of digital panoramic radiographs and its effectiveness for pre-operative assessment of dental implants. Dentomaxillofac Radiol 2011;40:76-83.  Back to cited text no. 2
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3.Graber TM. Panoramic radiography in orthodontic diagnosis. Am J Orthod 1967;53:799-821.  Back to cited text no. 3
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4.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. 4
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5.Razi T, Moslemzade SH, Razi S. Comparison of linear dimensions and angular measurements on panoramic images taken with two machines. J Dent Res Dent Clin Dent Prospect 2009;3:7-10.  Back to cited text no. 5
    
6.Meijer HJ, Steen WH, Bosman F. A comparison of methods to assess marginal bone height around endosseous implants. J Clin Periodontol 1993;20:250-3.  Back to cited text no. 6
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7.McIver FT, Brogan DR, Lyman GE. Effect of head positioning upon the width of mandibular tooth images on panoramic radiographs. Oral Surg 1973;35:698-707.  Back to cited text no. 7
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8.Grondahl K, Sunden S, Grondahl HG. Inter- and intraobserver variability in radiographic bone level assessment at Branemark fixtures. Clin Oral Impl Res 1998;9:243-50.  Back to cited text no. 8
    
9.Available from: http://www.dentaleqpt.com/pr_CC_proline.htm [Last assessed on 2013 July 06].  Back to cited text no. 9
    
10.Larheim TA, Svanaes DB. Reproducibility of rotational panoramic radiography: Mandibular linear dimensions and angles. Am J Orthod Dentofacial Orthop 1986;90:45-51.  Back to cited text no. 10
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11.Tronje G, Welander U, McDavid WD, Morris CR. Image distortion in rotational panoramic radiography. III. Inclined objects. Acta Radiol Diagn (Stockh) 1981;22:585-92.  Back to cited text no. 11
    
12.Catiæ A, Celebiæ A, Valentiæ-Peruzoviæ M, Catoviæ A, Jerolimov V, Muretiæ I. Evaluation of the precision of dimensional measurements of the mandible on panoramic radiographs. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1998;86:242-8.  Back to cited text no. 12
    
13.Nishikawa K, Suehiro A, Sekine H, Kousuge Y, Wakoh M, Sano T. Is linear distance measured by panoramic radiography reliable? Oral Radiol 2010;26:16-9.  Back to cited text no. 13
    
14.Scarfe WC, Eraso FE, Farman AG. Characteristics of the Orthopantomograph OP100. Dentomaxillofac Radiol 1998;27:51-7.  Back to cited text no. 14
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15.Yim JH, Ryu DM, Lee BS, Kwon YD. Analysis of digitalized panorama and conebeam computed tomographic image distortion for the diagnosis of dental implant surgery. J Craniofac Surg 2011;22:669-73.  Back to cited text no. 15
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16.Mawani F, Lam EW, Heo G, McKee I, Raboud DW, Major PW. Condylar shape analysis using panoramic radiography units and conventional tomography. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;99:341-8.  Back to cited text no. 16
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17.Rohlin M, Akerblom A. Individualized periapical radiography determined by clinical and panoramic examination. Dentomaxillofac Radiol 1992;21:135-41.  Back to cited text no. 17
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18.Kaeppler G, Buchgeister M, Reinert S. Influence of the rotation centre in panoramic radiography. Radiat Prot Dosimetry 2008;128:239-44.  Back to cited text no. 18
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19.McDavid WD, Welander U, Brent Dove S, Tronjje G. Digital imaging in rotational panoramic radiography. Dentomaxillofac Radiol 1995;24:68-75.  Back to cited text no. 19
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20.Philipp RG, Hurst RV. The cant of the occlusal plane and distortion in the panoramic radiograph. Angle Orthod 1978;48:317-23.  Back to cited text no. 20
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21.Welander U, Wickman G. Image distortion in narrow beam rotation radiography. A mathematical analysis. Acta Radiol Diagn (Stockh) 1978;19:507-12.  Back to cited text no. 21
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22.Xie Q, Soikkonen K, Wolf J, Mattila K, Gong M, Ainamo A. Effect of head positioning in panoramic radiography on vertical measurements: An in vitro study. Dentomaxillofac Radiol 1996;25:61-6.  Back to cited text no. 22
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Correspondence Address:
Jahangir Haghani
Department of Oral and Maxillofacial Radiology, Kerman University of Medical Sciences, Kerman
Iran
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Source of Support: Research Committee of Kerman University of Medical Sciences, Conflict of Interest: None


DOI: 10.4103/0970-9290.117989

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