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                                         CT Scan Technology
             An Evolving Tool for Avoiding Complications and Achieving
                  Predictable Implant Placement and Restoration

                                                      SCOTT D. GANZ, DMD / USA

          Implant dentistry, one of the most predictable treatment       cessary tools to avoid potential complications associated
       alternatives offered to patients who are missing teeth can be     with implant dentistry.
       enhanced by thorough pre-surgical diagnosis and treat-               The purpose of this paper was to identify valuable aspects of
       ment planning efforts by all members of the implant team.         interactive CT through documentation and identification of
       Conventional radiologic techniques including periapical           several important issues; (1) revealing difficult to detect patho-
       and panoramic radiographs are limited by the two dimen-           logy, (2) correct assessment of bone trajectory to avoid iatro-
       sional interpretation of existing hard and soft tissue. The in-   genic damage, (3) use of CT scan / surgical templates to relate
       herent distortion factor can misrepresent bone topography         tooth-to-bone relationship, (4) choosing appropriate implant
       in critical areas associated with vital anatomy or potential      shape to fit residual bone, and (5) appreciation of sinus anatomy
       implant sites. Advances in diagnostic radiological techni-        post augmentation procedures. It was concluded that inter-
       ques improved with the introduction of CT scan technology         active CT scan software applications provide state-of-the-art
       for dental applications. The enhanced diagnostic range of         diagnostic tools which create the confidence to benefit both pa-
       this evolving technology empowers the clinician with ne-          tient and clinician in the quest for achieving predictable results.

                Introduction                      20 years resulting in the need for im-         of the bone for either maxillary or
                                                  proved methods to ensure the most fa-          mandibular arches. The advent of CT
       Dental implants provide clini-             vorable surgical position to restore           Scan film technology allowed for an
    cians with an expanded set of treat-          the patient properly. Problems asso-           accurate assessment of bone height
    ment options to offer their patients.         ciated with implant failure or patient         and width, identification of soft and
    Implant dentistry can replace miss-           dissatisfaction are often related to           hard tissue pathology, location of
    ing teeth in a known, acceptable,             poor diagnostic and treatment plan-            anatomical structures such as the in-
    and highly predictable mode which             ning methods. Advanced diagnostic              ferior alveolar canal, and for measur-
    has dramatically improved quality of          aids such as tomography, digital ra-           ing the vital qualitative dimensions
    life for millions of people. The con-         diography, and CT Scan film allow for          necessary for proper implant place-
    ventional approach to treatment               a more accurate presurgical evalua-            ment.
    planning dental implants includes             tion. Perhaps the most important                  Conventional periapical, panor-
    thorough clinical examination, pan-           technological advancement which                amic, or tomographic images contain
    oramic radiography, diagnostic wax-           dramatically enhanced the clinician’s          an inherent distortion factor which if
    up and mounted study models.                  ability to diagnose and treatment plan         unrecognized can lead to incorrect
    Other diagnostic aids may include             dental implants has been the CT scan.          diagnosis. This distortion was vir-
    cephalometric films, periapical ra-           Although CT scans (Computerized                tually eliminated through advance-
    diographs, and tissue or bone-mapp-           Tomography) have been available                ments in CT Scan imaging techni-
    ing techniques for assessment of              for medical use since 1973 it was              ques1. In 1988 Columbia Scientific,
    implant sites. Until recently the             not until 1987 that this innovative            Inc.(Columbia, Maryland, USA) de-
    greatest emphasis was directed to the         technology became available for                veloped 3D dental software that
    surgical aspect of implant place-             dental application. After referral to a        worked through standard GE CT
    ment, with less consideration for soft        radiologist, specially formatted diag-         Scanners. The addition of an inter-
    tissue, anatomical contour, emer-             nostic images were created from CT             mediate computer workstation call-
    gence profile, occlusion, tooth mor-          scan data to determine potential sites         ed an Imagemaster -101™ (introdu-
    phology, or final prosthetic outcome.         for placement of dental implants. The          ced in 1990) allowed for further de-
       Demand for dental implants has in-         resultant radiographic films offered           velopment and refinement of the
    creased substantially during the past         true, three dimensional visualization          diagnostic tools available to CT

6                                                                                              INTERNATIONAL MAGAZINE OF ORAL IMPLANTOLOGY 1/2001
                                                                                                                                  NEW TECHNIQUES

scans for dental implants. Interfaces                nosis and treatment planning. This                     Enhancements offered by these
were then developed to process CT                    innovative software program allows                  software packages enable the clini-
data from most CT Scanners avail-                    the clinician to easily and quickly                 cian to dramatically improve diag-
able today.                                          visualize all of the images which may               nostic ability in a manner superior
   The original limitations of CT Scan               exist in the film version of the CT                 than the original radiographic film.
film were overcome in July of 1993                   Scan. Advanced 3-D reformatting                     Clinicians can quickly scan through
when SIM/Plant™ for Windows was                      techniques permit highly refined, ac-               all relevant graphical images with-
                                                                                                         out the need for a room full of light
                                                                                                         boxes. The interactive specifications
                                                                                                         of the software allow for “scrolling”
                                                                                                         through the distortion-free slices
                                                                                                         usually set at 1mm intervals for axial,
                                                                                                         cross-sectional, and panoramic
                                                                                                         views. Innovative digital tools have
                                                                                                         been developed to enhance the dia-
                                                                                                         gnostic quality of each image and
FIGURE 1 Conventional panoramic radiograph           FIGURE 2 CT Axial 40 reveals anterior lesion (red
revealing advanced periodontal disease.              arrow), posterior lesion (blue arrow), and pa-      improve the relationship between
                                                     thology in left maxillary sinus (yellow arrow).     imaging and practical aspects of sur-

FIGURE 3 Cross-sectional slice 107 reveals a         FIGURE 4 Cross-sectional slice 136 indicates        FIGURE 5 The extent of the soft tissue prolifera-
magnified view of the ovoid, calcified anterior      the buccal plate (blue arrows) and the well-cir-    tion in the maxillary left sinus is measured at over
lesion (red arrow).                                  cumscribed posterior lesion (red arrow).            16mm as seen in cross-sectional slice 15.

released as an intuitive, user-friendly              curate assessment of the CT Scan                    gical intervention on patients. To
software interface for dentists to                   data in a manner which exceeds in-                  achieve predictable results CT Scan
harness the power of CT technology                   formation gleaned from film alone.                  technology is a tool which should be
for their patients. This interactive                 This state-of-the-art software offers               used by both the surgical and resto-
program fueled by improvements in                    the clinician an improved interactive               rative members of the implant team.
the personal computer hardware                       diagnostic tool, superior to conven-                It is the purpose of this paper to iden-
and software provided by the Win-                    tional CT Scan film. Significantly,                 tify valuable aspects of this exciting
dows® platform revolutionized the                    film cannot relate information on                   diagnostic modality through docu-
world of diagnostic imaging.                         bone density which is an important                  mentation and discussion of several
SIM/Plant™ for Windows® enabled                      factor in determining an adequate lo-               important issues; (1) revealing diffi-
the clinician to examine the CT Scan                 cation for osseointegration to occur.               cult to detect pathology, (2) correct
data in an environment which sur-                    Since      the    development      of               assessment of bone trajectory to
passed the limited information                       SIM/Plant™ other similar applica-                   avoid iatrogenic damage, (3) use of
afforded by CT Scan film alone.                      tions have been introduced in the                   CT scan / surgical templates to relate
   Once loaded into the doctor’s                     marketplace for the purposes of mak-                tooth-to-bone relationship, (4)
computer SIM/Plant™ opened a                         ing CT scan technology available to                 choosing appropriate implant shape
whole new world of interactive diag-                 clinicians around the world.                        to fit residual bone, and (5) apprecia-

INTERNATIONAL MAGAZINE OF ORAL IMPLANTOLOGY 1/2001                                                                                                              7

    tion of sinus anatomy post augmen-                 nasal concha clearly visible at the              diagnostic work-up which includes
    tation procedures.                                 midline. The red arrow indicates                 mounted study casts, and a formula-
                                                       what appears to be a calcified lesion            tion of the restorative plan. From this
         Clinical Documentation                        located in the anterior aspect of the            plan, an acrylic template is fabrica-
                                                       right maxillary sinus. The blue arrow            ted to incorporate a radiopaque sub-
      The conventional panoramic ra-                   points to a second lesion in the pos-            stance (usually barium sulfate)
    diograph remains as an excellent                   terior aspect of the right maxillary si-         which can be easily identified on the
                                                                                                        CT scan image, and sometimes the
                                                                                                        addition of tubes of titanium for di-
                                                                                                        rectional guidance4,5,6. A full con-
                                                                                                        tour wax-up or the patient’s existing
                                                                                                        denture if appropriate can be dupli-
                                                                                                        cated in clear acrylic, with missing
                                                                                                        teeth replaced by the barium sulfate/
                                                                                                        acrylic mixture (figure 6). The patient
                                                                                                        should be instructed to wear this
    FIGURE 6 A clear acrylic template with full con-   FIGURE 7 Reformatted panoramic view of
    tour teeth which incorporate radiopaque ba-        missing mandibular first molar in radiopaque     template during the process of CT
    rium sulfate for visualization on the CT scan.     template.                                        scan imaging. The radiopaque teeth
                                                                                                        will then appear in the CT image as
    tool to assess hard and soft tissues of            nus. The yellow arrow shows an al-               indicators to potential implant sites.
    the oral cavity. However, the two-di-              most complete occlusion of the left                 Upon evaluation of the CT scan
    mensional panoramic radiograph                     maxillary sinus by a non-calcified or            image incorporating a properly fab-
    delivers an inherently distorted                   soft tissue-type lesion. The cross-              ricated radiopaque template, the
    image which can lead to incorrect                  sectional images reveal radiopaque,              underlying bony anatomy can be
    diagnosis leading to incorrect treat-              well-circumscribed, calcified lesions            visualized in direct relationship to the
    ment1. A conventional panoramic                    which are ovoid in shape and at-                 desired tooth position. In the follow-
    radiograph presented in figure 1 re-               tached to the walls of the sinus by a            ing example, a single mandibular first
    veals an advanced case of periodon-                soft tissue connection (figure 3, Slice          molar was missing leaving a mesial-
    tal disease in both maxillary and                  107 – anterior lesion and figure 4,              distal space of approximately 14 mil-
    mandibular arches. On closer in-                   Slice 136 – posterior lesion). The               limeters (figure 7). Cross-sectional sli-
    spection, a radiopaque area was                    near occlusion of the left maxillary             ces, one millimeter apart reveal the
    noted superior to the apical roots of              sinus represents soft tissue polyps              full buccal-lingual dimension, incli-
    the maxillary right premolars. After a             which were measured at over 16 mm                nation, trajectory of the bone within
    complete examination and diagnos-                  in height from the sinus floor (figure           the framework of the missing tooth to
    tic work-up the preliminary treat-                 5). As this patient was scheduled for            be replaced (figure 8). For such a wide
    ment plan called for extraction of all             a bilateral sinus augmentation post-             space it was anticipated that two im-
    the maxillary teeth followed by pla-               extractions, the radiographic find-              plants would be better utilized than a
    cement of an immediate transitional                ings obtained through the CT scan                single implant to avoid any potential
    complete denture. To regain the lost               were significant to alter the plan of            cantilever forces. Cross-sectional sli-
    dentition it was planned to complete               treatment.                                       ces 110 – 112 indicate the relation-
    bilateral sinus augmentation proce-                   Certainly the advanced images af-             ship in the area where the first anterior
    dures to create the necessary foun-                forded by the three dimensional CT               implant could be placed. The blue ar-
    dation for later fixture placement. To             scan offer the clinician further insight         row representing the straight line ana-
    facilitate the diagnostic phase of the             into the anatomical structures neces-            tomy of the lingual cortical plate. Im-
    treatment plan work-up the patient                 sary for proper diagnosis, treatment             plant placement parallel to the lin-
    was instructed to obtain a CT scan of              planning and execution of proposed               gual cortical plate, surrounded by
    the maxillary arch, and was referred               treatment. To further enhance the                adequate bone could be achieved
    to a radiology center for imaging.                 practical application of this evolving           guided by the template position.
       The reformatted CT scan series re-              technology, CT scan templates can                However, within a few millimeters
    vealed significant pathology unde-                 be fabricated to help guide the pla-             posterior (slices 116 – 118) the straight
    tected by the panoramic radiograph.                cement of endosteal implants. Tooth              line changed representing the lingual
    The CT axial 40 view represented in                position should be the ultimate guide            concavity which is usually present in
    figure 2 slices the maxilla superior to            in determining implant placement,                the posterior molar region of the man-
    the floor of the nose. The outline of              as implant dentistry is a restoratively          dible (figure 9). This concavity, if
    the nose can be seen at the top of the             driven entity2,3. To that end, tem-              overlooked can result in perforation
    image with the inferior aspect of the              plates are fabricated from a complete            of the lingual cortical plate during the

8                                                                                                     INTERNATIONAL MAGAZINE OF ORAL IMPLANTOLOGY 1/2001

     preparation of the osteotomy or                   adequate width of supporting bone                 casional mistakes occur which
     when the implant is placed7. Additio-             with sufficient vascular supply (fig-             might be avoided with proper diag-
     nally, if too wide an implant is chosen           ure 10B). The desired emergence                   nostics and surgical technique. As
     it can inadvertently create a perfora-            profile can be visualized in the plan-            previously mentioned, perforations
     tion which could result in fistula for-           ning stages with the restorative tools            can occur when the existing bone
     mation or the eventual loss of the fix-           found in the latest version of                    anatomy is not fully appreciated.
     ture (figure 10A). This type of perfo-            SIM/Plant™ (Version 6.03) which is                This unfortunate error is magnified
     ration can occur in the maxillary arch            helpful in fabrication and orienta-               when considering the great effort to
     as well.                                          tion of the guide holes for the actual            regenerate new bone from grafting
        Pre-surgical understanding of                  template to be used during the sur-               procedures to facilitate implant place-
     existing anatomy such as a lingual or             gical procedure.                                  ment. The cross-sectional slice as

     FIGURE 8 Cross-sectional slices 110–112 clearly show the molar tooth in relation to the underlying bone. Blue arrow indicates the straight lingual
     cortical plate.

     FIGURE 9 Cross-sectional slices 116–118 reveal the change in contour of the lingual plate as indicated by the red arrow.

     buccal concavity may lead the clini-                 The sinus augmentation proce-                  illustrated in figure 11A reveals a
     cian to choose an implant shape                   dure has become a very predictable                perforation of the buccal plate by an
     which would maximize the existing                 treatment alternative to gain addi-               implant fixture in a post sinus aug-
     anatomical variation of the bone                  tional sites for subsequent implant               mentation CT scan. The radiopaque
     without sacrificing a wide occlusal               placement and prosthetic recon-                   surgical template seen hovering
     table necessary to support a molar                struction. However few clinicians                 above the alveolar bone, is evi-
     restoration. A tapered implant de-                avail themselves of the imaging                   dence that the bulk of newly gener-
     sign could be used to help avoid                  tools which can give a true 3-D pic-              ated bone was by-passed during
     such a bony concavity and ensure                  ture of the sinus cavity. While most              the surgical placement of the im-
     that the implant is surrounded by an              sinus procedures are successful, oc-              plant. In figure 11 B , a red “triangle”

10                                                                                                     INTERNATIONAL MAGAZINE OF ORAL IMPLANTOLOGY 1/2001

     delineates the cross-sectional area               During surgery on the mandibu-                  be appreciated in the axial view
     of the greatest amount of bone vol-            lar arch the patient’s jaw position                seen in figure 14. The red arrows
     ume which was created in the si-               can be critical especially when an                 indicate the thin residual lingual
     nus. This “triangle of bone” can be            accurate template is not utilized.                 cortical plate, and the blue arrow
     bisected (yellow arrow) to maxi-               What appeared to be a correctly                    pointing to the implant place in the
     mize the positioning of the implant            aligned implant may in actuality be                left mandible. The failures can be
     fixture in the greatest volume of              mal-positioned. When the surgeon                   directly related to the perforation of
     bone as described by GANZ8. For                is incorrectly orientated, it is even              the lingual cortical plate as indica-
     this example, a custom angulated or            possible to perforate the anterior                 ted by figure 15A. The simulated
     angled abutment would be utilized              symphysis of the mandible. Figure                  implant found in figure 12, is posi-
     to re-direct the transmucosal ele-             12 illustrates a reformatted pano-                 tioned to indicate the apparent po-

     FIGURE 10A Wide body implants could     FIGURE 10B A wide emergence plat-       FIGURE 11A Buccal perforation of an implant which missed the
     inadvertently lead to perforation of    form can be maintained with a ta-       sinus augmented bone.
     the lingual plate.                      pered design implant.                   FIGURE 11B The ”triangle of bone” concept illustrates the great-
                                                                                     est bone volume seen in cross-section.

     FIGURE 12 Reformatted panoramic image re-      FIGURE 13 A and B The severe buccal angula-        FIGURE 14 Axial view shows the extent of bone
     vealing two remaining implants and one simu-   tion of the right and left remaining implants.     loss between the buccal and lingual cortical
     lated implant.                                                                                    plates (red arrows). Blue arrow points to re-
                                                                                                       maining left implant.

     ment into the correct position and             ramic image with two remaining                     sitioning of the failed implant figure
     required emergence profile to pro-             implants out of the four originally                15B. This patient was successfully
     duce the final functional and esthe-           placed. The simulated implant has                  rehabilitated after regenerative
     tic restoration. Prior planning and            been added for orientation purpo-                  bone grafting procedures and sub-
     visualization of the relationship be-          ses. Even the reformatted panora-                  sequent placement of four implants
     tween the underlying bone and the              mic image presents difficultly in                  parallel to the true trajectory of the
     desired tooth position is essential to         analyzing the residual bone in the                 remaining bone.
     surgical/ restorative success and              symphysis, or the apparent angula-                    CT scan technology is an evolv-
     avoidance of potential complica-               tion of the implants because this is               ing entity as evidenced by advan-
     tions of fixture perforation. The abi-         still only a two dimensional view.                 ces made possible with the increas-
     lity to evaluate the three-dimensio-           The severe buccal inclination of the               ing speed of personal computing
     nal aspect of sinus cavity topogra-            two remaining implants can be                      power. Faster, improved-perfor-
     phy, or other bone defects has ena-            clearly ascertained in cross-sec-                  mance Pentium-class computer
     bled clinicians to plan and predict            tional images seen in figures 13A                  processors have allowed for the de-
     innovative grafting procedures                 and 13B. This CT scan was taken                    velopment of CAD CAM, three di-
     creating additional treatment solu-            after four of the six implants had                 mensional representations of bone
     tions and restorative alternatives for         failed. The amount of bone de-                     to be manipulated on screen, and
     our patients9,10,11.                           struction (post implant failure) can               when required to produced as ra-

12                                                                                                   INTERNATIONAL MAGAZINE OF ORAL IMPLANTOLOGY 1/2001
                                                                                                                        NEW TECHNIQUES

                                                     CT scan template of proposed tooth        this evolving technology empowers
                                                     restoration. The radiopaque teeth         the clinician with necessary tools to
                                                     (green arrow) can been seen over          avoid potential complications asso-
                                                     the volumetric loss of bone evident       ciated with implant dentistry. This
                                                     by the red arrows. The mental fora-       technology has been found to be
                                                     men is indicated by the yellow ar-        helpful in other areas such as pre-
                                                     row. Newly developed CT scan              surgical planning for bone grafting
                                                     like machines can now image both          procedures. Interactive CT scan soft-
FIGURE 15A The cross-sectional view relates          maxillary and mandibular arches           ware applications provide state-of-
the extent of the perforation caused by the          during one session. These exciting        the-art diagnostic tools which create
failed implant.
FIGURE 15B The simulated implant indicates           new images will allow clinicians to       the confidence to benefit both patient
the previous position of the failed implant.         envision the relationship of the en-      and clinician in the quest for achieving
                                                     tire maxillo-mandibular complex           predictable results.
                                                     (figure 17). As technology advan-
                                                     ces, clinicians will be able to eva-
                                                                                                  Author’s address:
                                                     luate interarch space, vertical di-
                                                                                                  Scott D. Ganz, DMD
                                                     mension, occlusion, TMJ, and pa-
                                                                                                  158 Linwood Plaza – Suite 204
                                                     thology with improved methods for
                                                                                                  Fort Lee, N.J. USA 07024
                                                     more accurate assessments for pre-           Phone: +1-201-592-8888
                                                     surgical and pre-prosthetic plan-            Fax: +1-201-592-8821
                                                     ning.                                        E-mail:

FIGURE 16 A three-dimensional mandibular                Implant dentistry is one of the most                    References
model with green arrow indicating radiopaque
template, red arrows indicating loss of poste-       predictable treatment alternatives
                                                                                                1 Sonick, Michael, ”A Comparison of the Accu-
rior alveolar bone, and yellow area revealing        that can be offered to patients who          racy of Periapical, Panoramic, and Computed
the mental foramen.                                  are missing teeth. Predictability is         Tomographic Radiographs in Locating the Man-
                                                                                                  dibular Canal.“ JOMI, 1994:9:455-460.
                                                     enhanced by thorough pre-surgical          2 Ganz, S.D. What is the Most Important Aspect of
                                                                                                  Implant Dentistry? The Implant Society, inc.,
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                                                                                                  ment with Restoration-Generated Site Develop-
                                                     team. However, radiologic techni-            ment. Compendium, Vol. 16; No. 8, 1995: pp
                                                     ques including periapical and pan-           796–804.
                                                                                                4 Klein, M, Cranin AN, and Sirakian A. A compu-
                                                     oramic radiographs are limited in the        terized tomograph (CT) scan appliance of opti-
                                                                                                  mal presurgical and preprosthetic planning of
                                                     ability to provide clinicians with           the implant patient. Pract Perio and Aesth Dent
                                                     only a two dimensional interpreta-           5(6); 1993:33–39.
                                                                                                5 Amet, E.M., and Ganz, S.D. Functional and
                                                     tion of existing hard and soft tissue.       Aesthetic Acceptance Prior to Computerized
                                                     The inherent distortion factor can           Technology for Implant Placement. Implant
                                                                                                  Dentistry. Vol (6);6, 1997: pp 193–197.
                                                     misrepresent bone topography in            6 N. U. Zitzman, and Marinello, C.P.Treatment
                                                                                                  Plan for Restoring the Edentulous Maxilla with
                                                     critical areas associated with vital         Implant-Supported Restoration: Removable
                                                     anatomy or potential implant sites.          Overdenture versus Fixed Partial Design. J
FIGURE 17 New technology allows for both ma-                                                      Prosthet Dent. 1999:82: 188–196.
                                                     Advances in diagnostic radiological        7 Ganz, S.D. “Utilizing CT Scan Technology to
xillary and mandibular arches to be imaged to-
gether.                                              techniques dramatically improved             Survey Anatomical Sites for Wide Body Implant
                                                                                                  Placement” Paper Presented at the 45th Meeting
                                                     with the introduction of CT scan             of the American Academy of Implant Dentistry.
                                                                                                  Caesar’s Palace. Las Vegas, Nevada. Nov 12,
pid prototype models. These 3-D                      technology for dental applications.          1996. On-Going Research Project.
on-screen models take the visua-                     Limitations in CT scan film have           8 Ganz, S.D. “The Triangle of Bone - A Formula for
                                                                                                  Successful Implant Placment and Restoration”
lization of anatomy to a new level                   been overcome with interactive soft-         The Implant Society, Inc. Vol (5);5, 1995:pp2-6.
of understanding and appreciation.                   ware applications which are avail-         9 Ganz, S.D. Mandibular Tori as a source for on-
                                                                                                  lay bone graft augmentation. A Surgical Proce-
When coupled with properly de-                       able for the desktop or laptop               dure. Pract Perio and Aesth Dent. The Implant
signed templates, diagnosis, treat-                  computer under the Windows®                  Report. Vol (9);9, 1997 pp 973–982.
                                                                                               10 Rothman, Stephen L.G. Computerized Tomo-
ment planning, and execution of                      operating system.                            graphy of the Enhanced Alveolar Ridge. In: Den-
                                                                                                  tal Applications of Computerized Tomography,
the proposed plans can be realized                      Clinical examples were utilized to        Chicago. Quintessence Publishing Co., Inc.
on the computer prior to anyone                      demonstrate the three-dimensional            1998:pp 87–112.
                                                                                               11 Krekmanov L., Placement of Posterior Mandibu-
touching the patient. Figure 16                      capability of interactive CT as it ap-       lar and Maxillary Implants in Patients with Se-
illustrates a three dimensional re-                  plied to practical clinical situations.      vere Bone Deficiency: A Clinical Report of Pro-
                                                                                                  cedure. Int J Oral Maxillofac Implants Vol (15);5,
presentation of a mandible with a                    The enhanced diagnostic range of             2000: pp 722–730.

INTERNATIONAL MAGAZINE OF ORAL IMPLANTOLOGY 1/2001                                                                                                     13

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