- Open Access
Comparison of measurements of mandible growth using cone beam computed tomography and its synthesized cephalograms
© Lin et al.; licensee BioMed Central Ltd. 2014
- Received: 29 May 2014
- Accepted: 30 August 2014
- Published: 10 September 2014
The current study aimed to compare the measurements of the mandible morphology using 3D cone beam computed tomography (CBCT) images with those using 2D CBCT-synthesized cephalograms; to quantify errors in measurements based on 2D synthesized cephalograms; and to clarify the effects such errors have on the description of the mandibular growth.
Mandibles of six miniature pigs were scanned monthly using CBCT over 12 months and the data were used to reconstruct the 3D bone models. Five anatomical landmarks were identified on each bone model, and the inter-marker distances and monthly distance changes were calculated and taken as the gold standard. Synthetic 2D cephalograms were also generated for each bone model using a digitally reconstructed radiography (DRR)-generation method. Errors in cephalogram measurements were determined as the differences between the calculated variables in cephalograms and the gold standard. The variations between cephalograms and the gold standard were also compared using paired t-tests.
While the inter-marker distance increases varied among the marker pairs, all marker pairs increased their inter-marker distances gradually every month, reaching 50% of the total annual increases during the fourth and fifth months, and then slowing down in the subsequent months. The 2D measurements significantly underestimated most of the inter-marker distances throughout the monitoring period, in most of the monthly inter-marker distance changes during the first four months, and in the total growth (p < 0.05).
Significant errors exist in the measurements using 2D synthesized cephalogram, underestimating the mandibular dimensions and their monthly changes in the early stages of growth, as well as the total annual growth. These results should be considered in dental treatment planning at the beginning of the treatment in order to control more precisely the treatment process and outcome.
- Mandible growth
- Miniature pigs
Dental treatments are often performed while the mandible bone is still growing. This is especially true during the process of orthodontic treatment planning or the assessment of the outcome of craniomandibular surgery. Since the data of the growth of the mandible are difficult to obtain via human experiments, physicians have to rely on current images to infer future growth of the mandible in planning treatments and assessing their efficacy. Studies on the influence of factors related to the mandibular growth on the treatment outcome are not yet available. Therefore, including growth-related factors in the treatment plan at the beginning of the treatment in order to control more precisely the treatment process and outcome will be helpful for improving the quality of treatment.
The use of cephalograms for long-term, in vivo measurement of human mandible growth would require multiple exposures to radiation over the monitoring period, which is not feasible for ethical reasons. A limited number of in vivo studies attempted to image mandible shape changes at limited time instances with unequal intervals but failed to describe long-term growth [1, 2]. Predictive mathematical models may be helpful for resolving the above-mentioned difficulties but, to the best knowledge of the authors, no such mathematical models have been reported. Their experimental validations before their clinical applications present another problem. However, long-term follow-up experiments on animal bone-growth can shed light on the growth of the mandible, and can also be useful in the construction and experimental validation of predictive mathematical models. Therefore, considering the medical ethics, animal experiments are indeed necessary. Many of the previous studies on the mandible have used pigs as animal models because their anatomy, physiology, circulatory system, mastication system and teeth germination are very similar to those of humans [3–5]. This is especially true for mini-pigs in which the size and shape of the jaw, occlusion and bone metabolism rate are similar to those of humans [6–9]. Compared to other pig breeds, mini-pigs are small in body size and relatively easy to manipulate in experiments, making them much more feasible for use as subjects in mandible studies.
The purposes of this study were to compare the measurements of mandible morphology using 3D CBCT data with those using CBCT-synthesized 2D images; to quantify the errors in measurements using CBCT-synthesized 2D images; and to clarify whether such errors would affect the description of the changes of mandibular growth.
Subjects and experimental procedure
Bone model reconstruction and morphological parameters
Anatomical landmarks on the mandible utilized in this study
LP: lateral pole of condyle
The most protruding point on the lateral side of the mandibular condyle
CP: Coronoid process
The most protruding point on the Coronoid
The most posterior and inferior point at the mandibular angle
AMF: Anterior mental foramen
The most anterior edge of the export of the mental nerve
PMF: Posterior mental foramen
The most posterior leading edge export of the mental nerve
Generation of and measurement on synthesized cephalograms
On each DRR-generated synthesized cephalogram, the same anatomical landmarks on the 3D volumetric bone model were also identified by the same experienced dentist (HSL) using a self-developed program (MATLAB, Mathwork Inc., USA). The repeatability of this procedure was determined from the same dentist’s repeated operation, giving a very good intra-rater reliability (ICC > 0.93) .
Definitions of the variables for the description of the mandibular growth
Distance between two bony landmarks measured from CBCT data
Inter-marker distance error
The differences between 3D and 2D inter-marker distance
Monthly distance change
The difference in the inter-marker distances between the current and the previous month
Monthly distance change error
The difference between the 3D and 2D monthly distance change
Apart from descriptive statistical analysis of the calculated variables, paired t-tests were also performed to compare 2D measurements with the 3D gold standard of each of the inter-marker distances, monthly distance changes and total annual increases using SPSS version 13.0 (SPSS Inc., Chicago, IL, USA). A significance level of 0.05 was selected. Considering the resolution of the CBCT (0.25 mm), errors less than 0.25 mm were considered clinically non-significant even if statistical significance (p < 0.05) was found.
Means (standard deviations) of the total annual increase of the inter-marker distances †
This study aimed to compare the measurements of mandible morphology made on 3D CBCT data (gold standard) with those on CBCT-synthesized 2D cephalograms; to quantify the errors in measurements made on CBCT-synthesized cephalograms; and to clarify whether such errors would affect the description of the changes in mandibular growth. While the increases of the inter-marker distances varied among the marker pairs, all marker pairs increased their inter-marker distances gradually every month, reaching 50% of the total annual increases during the fourth and fifth months, and then slowed down in the subsequent months (Figure 6). The errors in 2D measurements caused significant underestimations in most of the inter-marker distances throughout the monitoring period (Figure 8), in most of the monthly inter-marker distance changes during the first four months (Figure 9), and in the total growth (Table 3). These results showed that significant errors were prevalent in the 2D measurements of the dimensions and their monthly changes in the early stage of growth, as well as in the total growth of the mandible.
The measurement errors using 2D imaging are related to the fundamental characteristics of the image formation which is based on the projection of X-rays from a point source through the mandible onto the image plane (Figure 1). With point X-ray projections, the centerline of the imaging source is perpendicular to the image plane. The magnification ratio is dependent upon the ratio of the distance between the source and the imaging plane, and the distance between the source and the object. Thus, reducing the distance between source and object will increase the magnification ratio, and vice versa. For a 3D solid object with a complicated geometry and thickness, the projection is the result of non-uniform magnification. These characteristics largely explained the observed 2D measurement errors.The errors in the 2D distance measurements appeared to be affected by the inter-marker distances, and the angles between the inter-marker segments and the image plane (projection angle). For example, since GO-CP and LP-GO were on the ramus that was close to a flat plate and nearly parallel with the projection plane, and since these segments were not the longest ones, they were found to have the smallest errors (<1.5 mm) among all the marker pairs (Figure 8). On the other hand, since LP-CP had the greatest projection angle (>30° for both sides), it had considerable errors (2.3-5.2 mm) even though it was the shortest segment (13–32 mm). Marker pairs with similar distances and projection angles had similar magnitudes of inter-marker distance errors (Figure 8).The large errors in measuring inter-marker segments located between the mental foramen and the outer edge of the ramus could also be explained by the distance and angle factors determined largely by the anatomy. Since the mandibular body resembles a “V”-shape in the transverse plane, each side of the body formed an angle with the image plane, contributing to the errors in the inter-marker segments on the mandibular body. Therefore, being the longest segments on the mandible (length 65–170 mm) with projection angles in the range of 15°-20°, LC-AMF and GO-AMF were found to have the largest measurement errors (3.6-7.1 mm). With similar projection angles, shorter segments on the mandible body in space would thus produce smaller errors, between 1.1 and 5.4 mm (Figure 8).
The error on the side of the mandible further away from the image source was mostly much greater than that on the side closer to the source. In the current study, 2D projection measurements were made on images calibrated back to the median plane. This caused a magnification effect for the side of the mandible closer to the image source but a shrinking effect for the side further away from the source. As indicated in the aforementioned information, the angle formed by the inter-marker segments and the projection plane often led the 2D measurement methods towards a trend of underestimating the true segment length as determined by the 3D methods. Therefore, considering the relative positions of the mandible, image source and image plane, it appears that the magnification effects would compensate for the errors in results for the side closer to the image source while further underestimation of the true length would be expected. It was also observed from the results of the current study that the error of LP-GO on the side of the mandible further away from the image source was greater than that on the side closer to the source, and the difference increased with time.
For many years, the 2D cephalogram has been used by orthodontists as the standard method for assessing the changes of facial bone morphology. Two-dimensional cephalogrametric measurements have also been used to describe the growth of the facial bones. However, the facial bones are three-dimensional objects. Therefore, many details cannot be measured accurately. The superposition of the images of the bones can also lead to measurement errors owing to human misinterpretation. It would be even more difficult to use 2D images for measuring patients who exhibit non-symmetrical or deformed facial morphology. The current study used low radiation CBCT so it was possible to obtain 3D anatomical measurements over the growth process.
The current study was the first in the literature to evaluate the errors associated with 2D measurements over the growth process. This is in contrast to previous studies on the differences in measurements between 2D and 3D image-based methods using a single object at a set growth point in time. While the current study showed that similar bone growth patterns could be obtained using 2D measurements, the measured amount and rate of change of the bone morphology over time were found to be affected by the errors associated with 2D measurements. Two-dimensional measurements caused significant and different underestimations of the inter-marker distances throughout the monitoring period, of the monthly inter-marker distance changes during the first four months and of the total growth. These errors are difficult to eliminate because of their non-homogeneous and non-linear nature. The measurement errors were proportional to the inter-marker distances and their projection angles that were non-homogeneous within the bone and also related to the non-linear growth of the mandible over time . The current results suggest that 2D measurements of the dimensions and their monthly changes during the early stage of growth, as well as the total growth of the mandible, should be interpreted cautiously.
In the current study the amount of growth recorded in the pigs was approximately equivalent to the growth in humans from birth to the age of nine years. The results suggest that the misinterpretation owing to 2D image errors must be taken into account for dental treatment or craniofacial surgery in a growing mandible. Although the current approach cannot be performed on humans due to ethical considerations, in the future, if radiation doses and costs could be reduced, a 3D image-based method could replace the 2D image-based method in providing more accurate measurement parameters. The viewpoint raised in the current study should be included in clinical considerations when drawing up plans for treatment, taking into consideration the effects of growth time-points in interpreting imaging results.
Significant errors exist in the measurements using 2D imaging methods, underestimating the mandibular dimensions and their monthly changes in the early stages of growth, as well as total annual growth of the mandible. These results should be considered in dental treatment planning at the beginning of the treatment in order to control more precisely the treatment process and outcome.
- Krarup S, Darvann TA, Larsen P, Marsh JL, Kreiborg S: Three-dimensional analysis of mandibular growth and tooth eruption. J Anat 2005, 207: 669–682. 10.1111/j.1469-7580.2005.00479.xView ArticleGoogle Scholar
- Reynolds M, Reynolds M, Adeeb S, El-Bialy T: 3-d volumetric evaluation of human mandibular growth. Open Biomed Eng J 2011, 5: 83–89. 10.2174/1874120701105010083View ArticleGoogle Scholar
- Huh K-H, Yi W-J, Jeon I-S, Heo M-S, Lee S-S, Choi S-C, Lee J-I, Lee Y-K: Relationship between two-dimensional and three-dimensional bone architecture in predicting the mechanical strength of the pig mandible. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006, 101: 363–373. 10.1016/j.tripleo.2005.06.024View ArticleGoogle Scholar
- Ström D, Holm S, Clemensson E, Haraldson T, Carlsson GE: Gross anatomy of the mandibular joint and masticatory muscles in the domestic pig (Sus scrofa). Arch Oral Biol 1986, 31: 763–768. 10.1016/0003-9969(86)90009-9View ArticleGoogle Scholar
- Langenbach GEJ, Zhang F, Herring SW, Hannam AG: Modelling the masticatory biomechanics of a pig. J Anat 2002, 201: 383–393. 10.1046/j.0021-8782.2002.00108.xView ArticleGoogle Scholar
- Obrez A: Mandibular molar teeth and the development of mastication in the miniature pig (Sus scrofa). Acta Anat (Basel) 1996, 156: 99–111. 10.1159/000147834View ArticleGoogle Scholar
- Koppe T, Rossmann P, Ohkawa Y, Schumacher GH, Nagai H: The course of the mandibular canal in the growing miniature pig. Okajimas Folia Anat Jpn 1997, 74: 39–52. 10.2535/ofaj1936.74.1_39View ArticleGoogle Scholar
- Kuboki T, Shinoda M, Orsini MG, Yamashita A: Viscoelastic properties of the pig temporomandibular joint articular soft tissues of the condyle and disc. J Dent Res 1997, 76: 1760–1769. 10.1177/00220345970760110701View ArticleGoogle Scholar
- Ide Y, Nakahara T, Nasu M, Matsunaga S, Iwanaga T, Tominaga N, Tamaki Y: Postnatal mandibular cheek tooth development in the miniature pig based on two-dimensional and three-dimensional X-ray analyses. Anat Rec 2013. doi:10.1002/ar.22725Google Scholar
- Moyers RE, Bookstein FL, Hunter WS: Analysis of the Craniofacial Skeleton: Cephalometrics. In Handbook of Orthodontics. Edited by: Moyers RE. Chicago: Year Book Medical; 1988:247–309.Google Scholar
- Athanasiou AE: Orthodontic Cephalometry. London: Mosby Wolfe; 1997.Google Scholar
- Halazonetis DJ: From 2-dimensional cephalograms to 3-dimensional computed tomography scans. Am J Orthod Dentofac 2005, 127: 627–637. 10.1016/j.ajodo.2005.01.004View ArticleGoogle Scholar
- Papadopoulos MA, Jannowitz C, Boettcher P, Henke J, Stolla R, Zeilhofer H-F, Kovacs L, Erhardt W, Biemer E, Papadopulos NA: Three-dimensional fetal cephalometry: an evaluation of the reliability of cephalometric measurements based on three-dimensional CT reconstructions and on dry skulls of sheep fetuses. J Cranio-MaxilloFac Surg 2005, 33: 229–237. 10.1016/j.jcms.2005.02.003View ArticleGoogle Scholar
- Broadbent BH: A new X-ray technique and its application to orthodontia: the introduction of cephalometric radiography. Angle Orthod 1981, 51: 93–114.Google Scholar
- Adams GL, Gansky SA, Miller AJ, Harrell WE Jr, Hatcher DC: Comparison between traditional 2-dimensional cephalometry and a 3-dimensional approach on human dry skulls. Am J Orthod Dentofac 2004, 126: 397–409. 10.1016/j.ajodo.2004.03.023View ArticleGoogle Scholar
- Nalçaci R, Öztürk F, Sökücü O: A comparison of two-dimensional radiography and three-dimensional computed tomography in angular cephalometric measurements. Dentomaxillofac Radiol 2010, 39: 100–106. 10.1259/dmfr/82724776View ArticleGoogle Scholar
- Chen M-H, Chang JZ-C, Kok S-H, Chen Y-J, Huang Y-D, Cheng K-Y, Lin C-P: Intraobserver reliability of landmark identification in cone-beam computed tomography-synthesized two-dimensional cephalograms versus conventional cephalometric radiography: a preliminary study. J Dent Sci 2014,9(1):56–62. 10.1016/j.jds.2013.02.012View ArticleGoogle Scholar
- Chien P, Parks E, Eraso F, Hartsfield J, Roberts W, Ofner S: Comparison of reliability in anatomical landmark identification using two-dimensional digital cephalometrics and three-dimensional cone beam computed tomography in vivo. Dentomaxillofac Radiol 2009, 38: 262–273. 10.1259/dmfr/81889955View ArticleGoogle Scholar
- Mah J, Hatcher D: Current status and future needs in craniofacial imaging. Orthod Craniofac Res 2003, 6: 10–16. 10.1034/j.1600-0544.2003.230.xView ArticleGoogle Scholar
- Cavalcanti M, Rocha S, Vannier M: Craniofacial measurements based on 3D-CT volume rendering: implications for clinical applications. Dentomaxillofac Radiol 2004, 33: 170–176. 10.1259/dmfr/13603271View ArticleGoogle Scholar
- Hildebolt CF, Vannier MW, Knapp RH: Validation study of skull three-dimensional computerized tomography measurements. Am J Phys Anthropol 1990, 82: 283–294. 10.1002/ajpa.1330820307View ArticleGoogle Scholar
- DeCoster T, Mercer D, Baldwin E: Comparison of the accuracy of X-ray, 2D-CT, 3D-CT, and physical modeling in classification of fractures about the elbow needing operative treatment. UNM Orthopaedic Research Journal 2012,1(1):22–25.Google Scholar
- Cavalcanti MG, Vannier MW: Quantitative analysis of spiral computed tomography for craniofacial clinical applications. Dentomaxillofac Radiol 1998, 27: 344–350. 10.1038/sj.dmfr.4600389View ArticleGoogle Scholar
- Kumar V, Ludlow J, Mol A, Cevidanes L: Comparison of conventional and cone beam CT synthesized cephalograms. Dentomaxillofac Radiol 2007, 36: 263–269. 10.1259/dmfr/98032356View ArticleGoogle Scholar
- Ludlow J, Davies-Ludlow L, Brooks S: Dosimetry of two extraoral direct digital imaging devices: NewTom cone beam CT and orthophos plus DS panoramic unit. Dentomaxillofac Radiol 2003, 32: 229–234. 10.1259/dmfr/26310390View ArticleGoogle Scholar
- Sukovic P: Cone beam computed tomography in craniofacial imaging. Orthod Craniofac Res 2003, 6: 31–36. 10.1034/j.1600-0544.2003.259.xView ArticleGoogle Scholar
- Farman AG, Scarfe WC: Development of imaging selection criteria and procedures should precede cephalometric assessment with cone-beam computed tomography. Am J Orthod Dentofac 2006, 130: 257–265. 10.1016/j.ajodo.2005.10.021View ArticleGoogle Scholar
- Gibbs SJ: Effective dose equivalent and effective dose: comparison for common projections in oral and maxillofacial radiology. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000, 90: 538–545. 10.1067/moe.2000.109189View ArticleGoogle Scholar
- Roberts JA, Drage NA, Davies J, Thomas DW: Effective dose from cone beam CT examinations in dentistry. Brit J Radiol 2009, 82: 35–40. 10.1259/bjr/31419627View ArticleGoogle Scholar
- Lin H-S, Chen Y-J, Li J-D, Lu T-W, Chang H-H, Hu C-C: Measurement of mandibular growth using cone-beam computed tomography: a miniature pig model study. PLOS ONE 2014, 9: e96540. 10.1371/journal.pone.0096540View ArticleGoogle Scholar
- Siddon RL: Fast calculation of the exact radiological path for a three-dimensional CT array. Med Phys 1985, 12: 252–255. 10.1118/1.595715View ArticleGoogle Scholar
- Penney GP, Weese J, Little JA, Desmedt P, Hill DLG, Hawkes DJ: A comparison of similarity measures for use in 2-D-3-D medical image registration. IEEE Trans Med Imaging 1998, 17: 586–595. 10.1109/42.730403View ArticleGoogle Scholar
- Lin H-S, Lu S-L, Chen Y-J, Lu T-W, Huang Y-D: Test-retest reliability of morphological measurements of the mandible on cone-beam computed tomography-synthesized cephalograms. J Dent Sci in pressGoogle Scholar
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