10.59987/ads/2010.3-4.33-38
Aim. A successful implant therapy is based on an accurate assessment of the anatomy of the jaws. The aim of our study was to evaluate the reliability of magnetic resonance imaging (MR) compared with computed tomography (CT) for dental implant planning in respect to bone measurements and to observe and analyze the differences.
Method. We have studied 30 cases in which scans were performed with CT and MR. The images provided by the MR and CT examinations were delivered to three specialists in oral and maxillofacial radiology to measure the bone height at the specific sites.The measurements obtained by the specialists in MR and CT images were compared using the ANOVA test with a 0.05 significance level.
Result. In all 30 cases examined, MR images appeared perfectly comparable to CT images. The differences between the measurements from the MR and CT exams varied from 0.04 to 1.1 mm. There were no statistically significant differences (P=0.9).
Conclusion. The MR, when compared with CT, shown to be reliable in respect to bone measurements for dental implant planning. However, further studies are necessary to determine the technical advantages of Resonance at lower fields, compared with those of CT and MR with medium or high magnetic field.
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1971-1441
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Annali di stomatologia
implant planning
A comparative study of Magnetic Resonance (MR) and Computed Tomography (CT) in the pre-implant evaluation
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Research Article
2022-08-18
2022-08-18
2010-12-01
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Ann Stomatol (Roma)
S. Di Carlo
2010
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1971-1441
3-4
implant planning
en
38
A comparative study of Magnetic Resonance (MR) and Computed Tomography (CT) in the pre-implant evaluation
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1
    A comparative study of Magnetic Resonance (MR)
    and Computed Tomography (CT) in the pre-implant
    evaluation




                                                                                                  i
                                                                                                al
                                                                                              on
    Valentina Pompa, MD1                                         Introduction
    Sabrina Galasso, PhD2
    Michele Cassetta, MD2                                        A successful implant therapy is based on an accurate
    Giorgio Pompa, MD2                                           evaluation of the patient’s anatomy of jams.
    Francesca De Angelis, PhD2                                   Proper patient selection and careful pre-surgical planning




                                                                                            zi
    Stefano Di Carlo, MD2                                        are essential to the success of implant therapy. They are
                                                                 essentially based on the evaluation of the quality and
                                                                 quantity of the bone and on the location of anatomical




                                                                     na
    “Sapienza” University of Rome, Rome (Italy)                  structures that might be limiting the implant such as the
    1 Department of Radiology
                                                                 mandibular canal, mental foramen, maxillary sinus, sur-
    2 Department of Odontostomatological
                                                                 face of nasal pit and the incisive canal. This evaluation
    and Maxillofacial Sciences,                                  can only be complete if the acquired information interests
    Prosthetic Rehabilitation Unit                               all three dimensions of space and faithfully reproduces




                                                                   er
                                                                 natural dimensions.
                                                                 Methods used in the past for implant programs only allo-
    Corresponding author:                                        wed bi-dimensional and inexact analyses. Only more re-
                                                                 cently, some instruments are able to provide stratigraphic
    Prof. Giorgio Pompa
    Via Caserta 6
    00161 Rome (Italy)
    Phone: 0649976614 - 3805152572
                                                           nt    images whose use is limited to individual implant sites,
                                                                 while the cranial radiography in lateral projection repre-
                                                                 sents a partial solution in the study of the anterior portion
                                                  iI
                                                                 of the jaw.
                                                                 The selection, especially in the case of multiple implants,
                                                                 is based on computed tomography (CT) which allows us
                                                                 to have images in section of vital structures and three-di-
                                         on

    Summary                                                      mensional reconstructions.
    A comparative study of Magnetic Resonance (MR) and           All these radiographic techniques expose the patient to
    Computed Tomography (CT) in the pre-implant evaluation.      ionizing radiations that can be harmful to the body; in the
                                                                 case of CT this exposure is significant.
    Aim. A successful implant therapy is based on an accu-
                               i


                                                                 CT analyses are also more prone to artefacts due to me-
    rate assessment of the anatomy of the jaws. The aim of
                            iz



                                                                 tallic dental materials and to those in correspondence
    our study was to evaluate the reliability of magnetic res-
                                                                 with the dense cortical bone (1). DentaScan was intro-
    onance imaging (MR) compared with computed tomog-
    raphy (CT) for dental implant planning in respect to
                                                                 duced to reduce the excessive dose of radiations to the
           Ed




    bone measurements and to observe and analyze the dif-        eyes and the thyroid gland. It has a special software to
    ferences.                                                    draw out thin layers that are orthogonal to the dental arch,
    Method. We have studied 30 cases in which scans were         in each point, and similar layers in orthopantomography.
    performed with CT and MR. The images provided by the         (2,3).
    MR and CT examinations were delivered to three spe-          Magnetic Resonance images (MR), instead, use the prin-
    cialists in oral and maxillofacial radiology to measure      ciple of nuclear magnetic resonance to give cross sec-
    the bone height at the specific sites.The measurements       tional images with a high spatial resolution without the
IC




    obtained by the specialists in MR and CT images were         use of ionizing radiations. These evaluations led us to use
    compared using the ANOVA test with a 0.05 significance       the MR in the quantitative and qualitative tridimensional
    level.                                                       evaluation of the alveolar bone crest.
    Result. In all 30 cases examined, MR images appeared         The aim of this study has been to evaluate and compare
C




    perfectly comparable to CT images. The differences be-       the results in identifying a correct pre-implant treatment
    tween the measurements from the MR and CT exams              using MR rather than CT DentaScan.
    varied from 0.04 to 1.1 mm. There were no statistically
    significant differences (P=0.9).
    Conclusion. The MR, when compared with CT, shown to
©




                                                                 Magnetic resonance (MR)
    be reliable in respect to bone measurements for dental
    implant planning. However, further studies are neces-
    sary to determine the technical advantages of Reso-          The acquisition of MR images is based on a set of physi-
    nance at lower fields, compared with those of CT and         cal principles completely different from those that cha-
    MR with medium or high magnetic field.                       racterize radiographic techniques.
                                                                 A special feature of the MR is the use of electromagne-
    Key words: Magnetic Resonance Imaging, dental im-            tic fields and radiofrequency waves, which, except for few
    plant,computed tomography, implant planning.                 recognized cases, are not believed to be harmful to the

    Annali di Stomatologia 2010; I (3-4): 33-38                                                                            33
    G. Pompa et al.


    body (4,5). This relative biological safety is the key ele-       cosa, away from the interface with air.
    ment that leads to testing its clinical applications.             It was suggested that a partial solution might be to apply
    All the data employed to create the final image come from         a gel between the mucosa and radiological template in
    the study of hydrogen atoms, particularly suitable for their      order to remove the air and reduce the artefact. Howe-
    high concentration in the human body and for the favou-           ver, this does not solve the problem in the upper jaw,




                                                                                                          i
    rable physics of their nuclei (4).                                where the interface between air and Schneider mucosa




                                                                                                        al
    These atomic nuclei, properly stimulated, first absorb and        remains unchanged. It is also important to note that the
    then give out energy that is detected in the form of elec-        geometric distortion is greatly reduced if you employ
    trical signals. A computer collects and processes this si-        scanners that use a magnetic field of lower intensity. Gray
    gnal, transforming it through a series of mathematical            et al. (5) have obtained favourable results using tomo-




                                                                                                      on
    algorithms in an MR image                                         graphy dedicated to the study of joints that uses fields of
    The different signal intensity is represented in the MR           a considerably reduced intensity (0.2 Tesla) if compared
    image by a change in the grayscale: white corresponds to          to the usual (0.5-1.5 Tesla).
    a high signal, grey corresponds to an intermediate signal,        Further improvements can be achieved by changing,
                                                                      when appropriate, the protocol of image acquisition and




                                                                                                    zi
    and black corresponds to absence of signal. The signal of
    each frame depends on the sequence used. Sections                 using receiving coils specifically designed for the single
    with a detectable flow, such as blood in the lumen, are           application. In implantology when you are faced with com-
    usually identified as sections that do not emit any signal,       plex cases, where there are very few points of reference,




                                                                          na
    because their nuclei leave the studied body section be-           the use of a template is recommended. Once routinely
    fore these can be spotted (1).                                    radiographic examinations (Fig. 1) and diagnostic wax-
    Depending on the parameter which is taken into consi-             up are performed, a modified template can be built, simi-
    deration there will be images weighted in proton density          lar to the traditional radiological template, but without




                                                                        er
    (PD), T1 or T2, which are different and must be interpre-         metal or gutta-percha landmarks (Fig. 2).
    ted differently.                                                  The template for MR (scanning template) consists of a
    The MR T1 images show high quality and anatomical re-             mask of transparent acrylic resin, in which holes of 2 mm
    solution, so as to look like actual anatomical drawings:          in diameter, with a proper slope, are dug through poten-
    the dense cortical bone looks very dark; the trabecular
    bone, rich in medullary adipose tissue is very clear; the
    mucous membrane, the periosteum and the neurova-
    scular structures also appear very clear; the air is black.
                                                                nt    tial implant sites. The holes are filled with a solution of 2
                                                                      ml of Gd-DTPA (Magnevist, Schering AG, Berlin, Ger-
                                                                      many) (11) in 1000 ml of saline and then sealed with
                                                                      acrylic resin (Fig. 3). The resin appears as a dark area,
                                                      iI
    T2 images have lower spatial resolution but sometimes,            with low signal, and produces no artefacts. Magnevist II
    due to their high intrinsic contrast, they assume particu-        contains metal ion gadolinium, a paramagnetic substance
    lar value in discriminating normal and pathological struc-        that, by reducing the T1 of the protons of the water of the
                                       on

    tures (6).                                                        solution, increases the signal (12). In T1-weighted ima-
    The image is determined by the sequence of acquisition
    which is used. Choosing the type of sequencing is the
    main way for the operator to optimize the signal received
    by the system under consideration (7). MR is, like CT, a
                              i


    type of tomography: it allows the formation of represen-
                           iz



    tative images only of the structures formed in layers that
    have been pre-selected, and pre-oriented in space (2,3).
    It is possible directly scan each plane of interest, without
           Ed




    the need for further reconstruction of the image, contrary
    to what happens with CT DentaScan (8).


    MR in implantology
                                                                      Figure 1 - Panorex.
    Until recently, MR, mainly used in dentistry in the study of
IC




    the temporo-mandibular joints (9,10), was believed not to
    be suitable for applications in the field of implantology.
    Faithfully reproduced data in all dimensions (necessary
    for implant diagnosis) seemed threatened by the fact that
C




    any alteration of the homogeneity of the applied magne-
    tic field results in a geometric distortion of the image. This
    alteration occurs in presence of ferromagnetic elements,
    such as metal dental restorations or radiological markers
©




    of the template, but also in tissue-air interface (4).
    It was then observed (11) that the artefact to ferroma-
    gnetic elements is extremely localized and does not bring
    a significant problem, since the edentulous implant site
    is still relatively distant. Furthermore, the difference in ma-
    gnetic behaviour between tissues and air, responsible for
    the distortion, affects the implant assessments, since the        Figure 2 - Modified template, similar to the traditional radiologi-
    angle and depth measurements are taken under the mu-              cal template, but without metal or gutta-percha landmarks.


    34                                                                                       Annali di Stomatologia 2010; I (3-4): 33-38
    A comparative study of Magnetic Resonance (MR) and Computed Tomography (CT) in the pre-implant evaluation




                                                                                                           i
                                                                                                         al
                                                                                                       on
    Figure 3 - Holes filled with a solution of 2 ml of Gd-DTPA in 1000




                                                                                                     zi
    ml of saline and then sealed with acrylic resin.




                                                                             na
                                                                         Figure 5 - The marker of the template scan are located through




                                                                           er
                                                                         a set of axial images.



                                                                         coronal and sagittal), low resolution, with a fast gradient-



    Figure 4 - The scanning template modified into a surgical tem-
                                                                   nt    echo sequence test-scan is carried out: this provides the
                                                                         images needed to control the alignment of the patient; the
                                                                         scan time is 6 -14 seconds. The sagittal test scan is used
                                                        iI
    plate.                                                               to prepare a set of axial images aligned to the mandible
                                                                         or maxilla as needed. The edentulous sites or the marker
                                                                         of the template scan are located through this set of axial
                                         on

                                                                         images (Fig. 5). On the basis of data from the axial refe-
    ges, the markers that are accordingly obtained are cle-              rence image the orientation of the next set of orthoradial
    arly visible, and therefore offer clear reference points that        pictures is determined.
    allow you to make the measurements necessary to turn                 In the event that a template scan has been used, poten-
    the scanning template into a surgical template (Fig. 4).             tial sites are indicated by landmarks labelled with Gd-
                               i


    The purpose of this study was to evaluate and compare                DTPA, clearly visible on T1-weighted images. The same
                            iz



    the ability to conduct a proper pre-implant treatment iden-          axial reference image is then used to program the oblique
    tified through the use of MR rather than CT DentaScan.               sagittal sections, tangential to the jaw line in the posterior.
                                                                         The orthoradial (Figs. 6-7) images provide excellent
           Ed




                                                                         cross-sectional information of the depth and, together
    Materials and methods                                                with the oblique sagittal images obtained by performing
                                                                         cuts parallel to the hypothetical axis of implantation, allow
    We selected 30 patients with monoedentulism or partial               a quantitative three-dimensional assessment.
    edentulism requiring the insertion of osseointegrated im-            However, if the oblique sagittal set of images is not pro-
    plants. After the usual routine radiographic examinations,           perly oriented, the quantity of available bone is over-or
    the group underwent both CT DentaScan and MR of the                  underestimated because of the wrong perspective. For
IC




    jaws. In more complex cases a diagnostic wax-up was                  this purpose, a cross-evaluation with the set of orthoradial
    carried out and a template was built: this was first used as         images is useful in order to reduce the risk of error. The
    a template for CT DentaScan and later modified in the                images provided by the MRI and CT examinations were
    template scan for MR, replacing the metal or gutta-percha            delivered to three specialists in Oral and Maxillofacial Ra-
C




    landmark with a solution of gadolinium or 0.2% saline.               diology to measure the bone height at the specific sites.
    The CT DentaScan was performed for each patient ac-                  The measurements obtained by the specialists in MRI
    cording to standard procedures. The MR of the jaws, for              and CT images were compared using the ANOVA test
    implant evaluation purposes, was performed by acquiring              with a 0.05 significance level.
©




    images PD, T2-weighted and Tl-weighted. The MR exa-                  The measurements on the available bone can be made
    mination was performed using a scanner with 1.5-magnet               by using the centimeter grade scale available on the prin-
    and a coil head, which is dedicated to the study of the              ted copy. If necessary, a reference grid can be laid over
    head and the neck.                                                   the image for measurement. The numbering of the single
    Spin-echo sequences were used: these require about                   cuts must be shown on the axial reference image or set-
    three minutes for each acquisition with a slice thickness            up and on the Panorex type image, to allow a quick iden-
    of 3 mm and a space between each layer and the other                 tification of significant cuts. It is advisable that the set up
    of 0.3 mm. During the initial MR a (scout) triplanar (axial,         image with the numbers be printed on film along with the

    Annali di Stomatologia 2010; I (3-4): 33-38                                                                                      35
    G. Pompa et al.




                                                                                                             i
                                                                                                           al
                                                                                                         on
                                                                                                       zi
                                                                         Figure 8 - Differences between the measurements from the MR
                                                                         and CT exams.




                                                                             na
    Figure 6 - Orthoradial and sagittal images.




                                                                           er
                                                                   nt
                                                        iI
                               i         on
                            iz



    Figure 7 - Orthoradial images parallel to the hypothetical axis of
    implantation.
           Ed




    images of the cuts, in order to allow the surgeon to orient
    the images according to a correct plan, and to prevent in-
    voluntary reverses to the opposite side of the maxilla.
IC




    Results                                                              Figure 9 - X-ray control of implant position.

    In all cases, it was possible to plan the placement of os-
    seointegrated implants using both CT DentaScan and
C




    MR of the jaws (Fig. 8).                                             In MR the production of artefacts is minimal and locali-
    The differences between the measurements from the MR                 zed. It was found exclusively around ferromagnetic struc-
    and CT exams varied from 0.04 to 1.1 mm. There were no               tures like the old small metal dentin pins. This is a good
    statistically significant differences (P=0.9).                       result if compared to CT where there is less image de-
    Being able to clearly identify nerves and vessels the sa-            gradation in correspondence with amalgam fillings, but
©




    fety of those operating systems is substantial, and im-              the degradation is potentially important since it occurs
    plants can be safely and securely placed in sites (Fig. 9)           near the region of interest, and also there is a difference
    where it would otherwise be dangerous if using bi-di-                in magnetic susceptibility between bone and soft tissues
    mensional radiographic techniques. In the MR images the              and between tissues and air; this also sets changes in
    cortical and medullary bone are easily distinguished, thus           the magnetic field which can cause a distortion of the MR
    allowing us to anchor the apical cortical bone for optimal           image.
    implant osseointegration.                                            The effects at the bone-tissues interface are really negli-

    36                                                                                          Annali di Stomatologia 2010; I (3-4): 33-38
    A comparative study of Magnetic Resonance (MR) and Computed Tomography (CT) in the pre-implant evaluation


    gible, while the image distortion caused at the tissue-air        much lower noise produced by these scanners at low
    interface may be more important, especially when the              field, due to the reduced vibration forces acting on the
    depth of the implant placement are measured in the order          coil magnetic field gradient, make this procedure accep-
    of 10 mm. However, current errors are substantially mini-         table.
    mal, since the two points between which the depth of in-          The possibility of using low-field MR with a 0.2 Tesla ma-




                                                                                                         i
    sertion is measured are not directly at the interface with        gnet means costs reduced by half when compared to a




                                                                                                       al
    the air, but are covered by mucosa. The problem of spa-           1 Tesla machine; this equipment is widely available, since
    tial distortion requires further investigation: yet it is im-     it is used in the diagnosis of small joints: there is great
    portant to note that the distortion is highly dependent on        potential for MR to be accessible to implant surgeons.
    imaging protocols that are being used; the spin-echo pro-         All relevant structures (18) are well displayed; however,




                                                                                                     on
    tocols, used by us in the images, minimize these arte-            further studies are necessary to determine the technical
    facts. In all 30 cases examined, MR images appeared               advantages of resonance at lower fields, compared with
    perfectly comparable to CT images. Moreover, the image            those of CT and MR with medium or high magnetic field.
    of the tissues is so exact to show even the formation of          It should, however, be noted that currently the high costs




                                                                                                   zi
    clot in the empty alveolus on the mend.                           of equipment and management, as well as the limited
                                                                      availability of facilities for the realization of this type of dia-
                                                                      gnostic procedures, represent a significant barrier to wi-
    Discussion and conclusions




                                                                          na
                                                                      despread use of MR in practice. In all cases examined,
                                                                      MR images appeared perfectly comparable to CT ima-
    Considering the increasing attention towards the absor-           ges. Moreover, the image of the tissues is so exact to
    ption of ionizing radiation for diagnostic purposes, it be-       show even the formation of clot in the empty alveolus on
    comes increasingly difficult to subject patient to CT if the      the mend.




                                                                        er
    pathology is not very significant. (13). In the dental field      In the future the use of open low-intensity magnetic field
    CT images are usually reconstructed using a software              scanners, could be a solution to reduce costs and extend
    which reduces radiation exposure (14). This procedure,            the application of the technique without exploiting the few
    however, can lead to dimensional errors (7). With the ex-         scanners available for the study of serious diseases .
    ception of few medical counter-effects, MR is a valid al-
    ternative to CT: it is biologically safe (does not use
    ionizing radiation), provides clear images of the implant
    sites and also allows the use in more complex cases of
                                                                nt    References
                                                      iI
    templates (15).                                                    1. Langlais RP, Van Rensburg LJ Guidry J et al. Magnetic Re-
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                                         on

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IC




                                                                       7. Kohavi D, Bar-Ziv J, Marmary Y. Effect of axial plane devia-
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                                                                          tion on cross-sectional height in reformatted computed to-
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                                                                       8. Gray CF, Staff RT, Redpath TW et al. Assessment of maxil-
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©




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    Annali di Stomatologia 2010; I (3-4): 33-38                                                                                      37
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                                                                                                         i
        dental radiology. Eur Radiol 2002; 12(3): 634-7.                  facts in computed tomography caused by fillings in teeth.




                                                                                                       al
    15. Aguiar MF, Marques AP, Carvalho AC, et al. Accuracy of            Neuroradiol 1980; 19(5): 229-34.
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                                                                                                     on
        362-5.                                                            Dentomaxillofac Radiol. 2005; 34(5):285-91.




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    38                                                                                      Annali di Stomatologia 2010; I (3-4): 33-38
