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1 Accuracy of reformatted cone beam CT image for the preoperative treatment planning of dental implants Sang-A Eun The Graduate School Yonsei University Department of Dental Science

2 Accuracy of reformatted cone beam CT image for the preoperative treatment planning of dental implants A Dissertation Thesis Submitted to the Department of Dental Science and the Graduate School of Yonsei University in partial fulfillment of the requirements for the degree of Doctor of Philosophy of Dental Science Sang-A Eun December 2007

3 This certifies that the dissertation thesis of Sang-A Eun is approved. Thesis Supervisor : Chang-Seo Park Kee-Deog Kim Kyoo-Sung Cho Jae-Ho Lee Hee-Jin Kim The Graduate School Yonsei University December 2007

4 감사의글 졸업을하고치과방사선과에수련을받기시작한게어제일만같습니다. 수련을받으면서진로와학문에대한고민을하면서도좀더공부하고싶었습니다. 그러나진료를하면서논문을쓴다는것은생각처럼쉽지않아서어떻게하지도못하고있었습니다. 이러한때에병원에서다시일할기회를주시고격려해주시고좋은논문을위해질책을아끼지않으신박창서선생님께깊은감사를드립니다. 작은것에도세심하고예리하게지도해주시고새로운일도열정을갖고즐겁게하시는김기덕선생님께많은감동을받았습니다. 좋은결론을낼수있도록매번수정할때마다결과를물어봐주신조규성선생님의관심에감사드립니다. 세심하게봐주시고중재해주시고조언해주신이제호선생님께감사드립니다. 논문을보여드렸는데흥미롭다고하신김희진선생님말씀에힘을얻어이과정을즐겁게잘마칠수있었습니다. 논문의아이디어때문에고민하고있었는데박혁선생님께서들어주시고중요한부분에아이디어를주셨습니다. 여러일을도맡아서도와주시고어려움을이해해주시고항상배려해주시는정호걸선생님께감사드립니다. 전국진선생님과함께할수있어서모든일을쉽게할수있었습니다. 항상도와주시겠다고격려해주신선경훈선생님께감사드립니다. 새로운열의를가지고활기를주었던조준용선생님께감사드립니다. 매일의일상에서함께기쁨을나누었던구강악안면방사선학교실의여러선생님들과직원분들께감사드립니다. 자료의대부분을일산리빙웰치과병원에도움을구했는데적극적으로협조해주신김현철원장님께감사드리고좋은선배님이신이장렬원장님께감사드립니다. 바쁜중에도자료를찾는수고를기꺼이해주신손효정선생님, 정성순선생님의도움을잊을수가없습니다. 그림의수정과편집에한숨을쉬고있었는데갑자기민정이가나타나놀라운손놀림으로해결해주었고정말그때하나님의손길같았습니다. 급하게성남이에게들이밀며영어를좀도와달라고했는데마다하지않고해주었습니다. 이런저런얘기도다받아주고함께해주었던병욱이가너무힘이되었지요. 은경이가있으면항상즐거운데빨리다시만나보고싶습니다. 지혜로운조언을해주고급할때도움을주었던현실언니와주령이와정렬이에게참고마웠습니다. 명은이의논문을몇번씩다시보며부러워하고참고하고했었습니다. 또혜승이의논문은감동을주기위해쓴게아니라고하지만그노력과수고를생각하니도전받고감동을받지않을수없었습니다. 소중한친구들영은이, 태민이, 원경언니, 진아, 유경이, 민희언니와함께배우고울고웃으며치과의사로살아가는것이기쁨이됩니다. 저에게소중하고아름다운시간들이고이과정을통해서도움을주신많은분들이떠올라서사는것이참행복하다는생각이듭니다. 저를받아주시고사랑해주시는엄마, 아빠, 동생, 그리고생명을주신하나님께한없이감사와사랑을드립니다. 2007년 12월저자씀

5 Table of Contents Abstracts (English) ⅶ I. Introduction 1 II. Materials and Methods 6 1. Materials 6 2. Methods 7 1) Archiving the images 7 2) Measurement of the expected possible distance of implantation 8 3) The reproducibility of measurement in different methods. 14 4) Differences between measurements of different imaging modalities 15 5) The contribution factors of the difference between Method 3 and Method ) The difference between Method 3 and Method 2 by edentulous sites 16 7) Statistical Analyses 16 III. Results 18 1) Measurement of the expected possible distance of implantation 18 2) The reproducibility of measurement in different methods 21 3) Differences between measurements of different imaging modalities 22 4) The contribution factors of the difference between Method 3 and Method ) The difference between Method 3 and Method 2 by edentulous sites 24 IV. Discussion 25 V. Conclusion 31 References 32 Abstract (Korean) 35 v

6 List of Figures Figure 1. The measurement of possible expected path for implantation from the panoramic radiography 8 Figure 2. The procedure of re-orientation of CBCT multiplanar images 11 Figure 3. The measurement of possible expected path for implantation from the CBCT of original orientation 12 Figure 4. Three representative angles of the teeth and face from the CBCT synthesized Cephalograms 16 Figure 5. The prediction of the path for implantation compared with 3 methods 20 Figure 6. The reproducibility of each method 21 List of Tables Table 1. The expected possible distances from each imaging method 19 Table 2. Differences between measurements of imaging methods 22 Table 3. The angles to the occlusal plane 23 Table 4. The comparison between preimplant sites 24 vi

7 ABSTRACT Accuracy of reformatted cone beam CT image for the preoperative treatment planning of dental implants When evaluating the bony quantity and quality for implantation, a more precise distance and width can be measured if a precise plane parallel to the expected implant pathway can be obtained. An estimation of the distance for implantation on a partially edentulous mandible was archived using conventional panoramic radiography. The images reconstructed from the CT data by image reformation softwares implemented on a CT workstation as well as a personal computer could be helpful in both the diagnosis and planning for implantation. However, the images reconstructed from CT data using those softwares showed the preexisting axial plane and multiplanar plane as being perpendicular to the preexisting axial plane. This was not the optimal cutting plane for an implant because the real axis of the tooth or planned axis of the implant would not be the same as the plane perpendicular to those preexisting axial. The aim of this study was to reconstruct the plane on the implant axis to be aligned with the tooth contrary to the traditionally viewing plane perpendicular to the occlusal plane. This study analyzed the diagnostic imaging methods used to visualize and measure the distance for implantation on mandibular partial edentulous sites. A more accurate path of placement for vii

8 implantation can be expected by comparing the measurements from the panoramic radiography and cone beam computed tomography(cbct). An oral and maxillofacial radiologist examined in 13 patients. The expected possible distances for implantation were measured using three methods. The first was measured in panoramic radiography. The second and third were measured in the CBCT. The DICOM images were imported into the Accurex (CyberMed Inc., Seoul, Korea) software program to acquire the multiplanar images and multiplanar reconstruction. The second method employed the original reference scan orientation. The third method used the reoriented scanning plane to be perpendicular to tooth axis. The differences between methods, reproducibility, and correlated factors were examined. The largest difference was between panoramic radiography and CBCT (1.83±1.12 mm). For the reproducibility of methods, average coefficient of variance (C.V) was 5.80%. There was no significant correlation between the measurement differences with the angles, as represented by teeth or skeletal angles. There were differences in the expected distances for implantation determined using the different imaging methods. However, the differences in measurement were quite small, which might increase the risk of injury to the mandibular nerve. Therefore, these differences should be considered in order to prevent injury to the anatomic structures. Key Words : cone beam computed tomography(cbct); multiplanar image reconstruction viii

9 Accuracy of reformatted cone beam CT image for the preoperative treatment planning of dental implants Sang-A Eun, D.D.S. Department of Dental Science Graduate School, Yonsei University (Directed by prof. Chang-Seo Park, D.D.S., M.S.D., PhD.) Ⅰ. INTRODUCTION CT is the most commonly available and accurate imaging modality for evaluating preimplant sites 1-6. When evaluating the bone quantity and quality for implantation, a more precise distance and width might be measured if a very precise plane parallel to the expected implant pathway, i.e. the optimal cutting plane specific to each implant to be planned, can be obtained 1-2. An estimation of the distance for implantation on partial edentulous mandible is normally achieved using conventional panoramic radiography on account of its ease of use, low cost and versatility. The images reconstructed from the CT data using DentaScan (General Electric, - 1 -

10 Milwaukee, Wis., USA) image reformation software implemented on a CT workstation were used to determine the distance from the preimplant site without any magnification error. In addition, those SimPlant (Materialise Inc., Glen Burnie, MD, USA), V-implant (CyberMed Inc., Seoul, Korea), and Accurex (CyberMed Inc., Seoul, Korea) image reformation software implemented on a personal computer might be helpful in providing an individual diagnosis and treatment plan by clinicians themselves. However the images reconstructed from the CT data using computer-aided software show the preexisting axial plane and multiplanar plane determined to be perpendicular to the preexisting axial plane. This is not the optimal cutting plane for an implant to be installed because the real axis of a tooth or planned axis of an implant is not the same as the plane perpendicular to those axial planes from the plane parallel to the occlusal plane 1-2. Nowadays, the advances in imaging technology and computer technology has brought in a revolution in reconstructed 3D/2D virtual images, simulation of surgery, rapid prototyping modelling to guide the operative surgical phase, navigation systems etc. CT-based surgical guidance templates can predict the expected installation of an implant, and also deliver the implant accurately ahead of time using transferring devices. This can simplify the surgical process and allow practice before surgery. The transfer system needs to accurately deliver the preliminary plan for implantation by supplying surgical guidance templates and prototyping model 6. However, it is not always be possible because the additional media occupy the space within the limited mouth opening and replication of preliminary implantation causes another procedure. It is well known that images from the CT data can determine the appropriate plane for implantation from the estimated distance and width, and that those are necessary for a preimplant. There is some discrepancy between the preexisting alveolar ridge and residual - 2 -

11 edentulous ridge due to resorption and remodeling of the surrounding alveolar bone after the loss of teeth 5. Therefore, clinicians wanted to plan for the most functional and esthetic suitable position for implantation. You and Kim stated that there were differences in the length of the implanted gutta percha cone when measured in reformatted view between the variable reference lines for taking axial computed tomogram 7. The Gutta percha cone was implanted into the extraction sockets of a premolar and the molar on a dry mandible. Six variable scan protocols were applied, such as, 3 gantry angles, and 2 different inclinations of the dry mandible. They reported that the measurement error decreased with decreasing difference between the occlusal plane and reference line. The authors suggested the closest inclination or parallel the occlusal plane 7. However, that study was carried out using a dry skull mandible and the tooth was extracted artificially. Actually, after the loss of teeth, the edentulous ridge has changed as a result of a bony resorption process. It is possible that the expected path of placement for the impanation of an implant is neither parallel nor the same as the extraction socket that has not been remodeled 7. Kohavi et al. compared the measurements in different transaxial planes, which deviated from the lower border of the edentulous mandible and that of the actual bone length. As the angulation of the deviation increased, the maximal range of differences increased to ±30% 8. The reference line is a basic plane parallel to the gantry of the CT equipment when axial views taken. As it was changed, the axial views were verified, and the cross-sectional and panoramic plane perpendicular to them was confirmed. This change influenced the measurement. Acceptable results can be obtained when the patient s mandibular position that determines the reference line makes a mandibular canal parallel to the scanning plane. Clinicians have used the mandibular canal or inferior border of a mandible, the occlusal plane of a mandible as a reference line in various studies or practices. The variation in the length - 3 -

12 measurements due to the different mandibular reference lines and changes in the gantry angle has been reported Kim et al suggested that care should be taken when setting a mandibular position 11. Dantas et al announced that within 19 of the mandibular position, it takes differences < 10% from the length as the standard position, which would not result in significant error 11. One method for obtaining the same cross-sectional plane as the real implant axis to be installed is to obtain CT acquisition using a stent or devices so that the axial views can be taken perpendicular to the tooth axis 9. Another way is to set the re-orientation of the preexisting axial images from the standard mandibular position 1,2. Indeed, the mandibular natural tooth axis is aligned with the curve of Spee and the curve of Wilson. When restoring missing teeth, it should be noted that those curves are peculiar to the patient, and each tooth in those curves have a characteristic inclination and tip 9, 13,14. In mandibular partial edentulous patients, it can be possible to obtain the same plane as the real tooth axis using the first method if there are few missing teeth. However, when there is several successive losses of teeth, considering their own peculiar tooth axis, it might difficult or impossible to take the correct axial images of each different variable tooth axis for an accurate measurement. Cucchara R et al. proposed the versatile DentalVox (Era Scientific, Italy) software that can provide the appropriate cross-sectional plane automatically for each tooth axis in only one CT acquisition 1,2. The Accurex program can also rotate the transaxial plane, and change the multiplanar planes to the reoriented transaxial plane. Advances in CT technology have allowed picturing implantation for accurate implantation, computer-guided simulation preoperatively or CT-based image-guided navigation systems intraoperatively as well as computer-guided 3-dimensional functional for esthetic prostheses 6. The use of autogenous and allogenous bone has led to many advances in bone grafting - 4 -

13 procedures. Hence, there does not appear to be a need to maintain sufficient alveolar bone length, as was previously the case. These alternative methods negate the requirement for the clinician to measure the length for implantation. However, the length of the implant needs to be chosen before simulating an implantation procedure. Therefore, predicting the length for implantation will be helpful. It is expected that the possible distance of an implant to be installed in a very precisely selected plane and the identification of the extent of error between measured and real distance would be very important. Barthling R et al. suggested that selected implants be located 2 mm above the inferior alveolar canal based on the panoramic images and 1 mm based on CT images 15. This study examined the different diagnostic imaging methods for visualizing and measuring the possible distance for implantation on mandibular partial edentulous patients. The aim of this study was to reconstruct the plane on the implant axis to be aligned with the tooth contrary to the traditionally viewing plane perpendicular to the occlusal plane. This study analyzed the diagnostic imaging methods used to visualize and measure the distance for implantation on mandibular partial edentulous sites. A more accurate path of placement for implantation can be expected by comparing the measurements from the panoramic radiography and cone beam computed tomography (CBCT)

14 Ⅱ. MATERIALS AND METHODS 1. Materials The subjects were 13 patients who had missing mandibular molar teeth. Of the edeutulous areas, the mandibular first and second molar was missing in 14 and 11 areas each. The average number of missing teeth was 1.9 and the average age of the patients was 45 years. The expected implantation distance was examined by one oral and maxillofacial radiologist. The patients who had missing the mandibular molars visited the Livingwell dental hospital. They were examined using CBCT and panoramic radiography for implantation in the mandibular posterior edentulous area. Sites with any pathologic conditions were excluded. Of the preimplant cases, some cases did not require reorientation of preexisting axial planes to adjust the reference tooth to align the right angle to the axial plane. 25 cases that required reorientation of the axial planed by set axis of Accurex were selected for this study. However, the implantation was planned in each edentulous site not considering the economic, or systemic or other disturbances. Depending on the bone available, there are other treatment choices for implant restoration and in some cases, the restoration will not be possible by implantation only. However, in this study, the aim was to predict the preimplant distance on a partial edentulous mandible. It was presumed there was a plan for implantation after the loss of a tooth without considering other options

15 2. Methods 1) Archiving the images 1 Panoramic radiography The panoramic radiography was taken using Orthopantomograph OP 100 (Imaging. GE healthcare, Tuusula, Finland) to plan the implant treatment for the edentulous areas. 2 Cone beam CT Cone beam computed tomography was taken using I-CAT CBCT (Imaging Sciences International, Hatfield, USA). The FOV was 16cm 22cm, the conditions were 120kVp, 3~8mA, voxel size=0.4mm. It took 20 seconds to archive the data and turn around 360. The patient s data was reconstructed into DICOM images. The patient was sitting in the chair of the CBCT with the head position parallel to the occlusal plane of the mandible with a floor. Simultaneously, the teeth were in the centric occlusion position naturally. Because the stent of the mandible was not used often, that position was guided easily

16 2) Measurement of the expected possible distance of implantation 1 Method 1: From the panoramic radiography The expected possible distance for implantation on the mandibular partial edentulous sites was measured as follows. The expected implantation drilling sites were at least 3mm apart from the adjacent teeth. When several implants were planned, the distance between the drilling sites was at least 7 mm. If there were missing teeth areas that had two adjacent teeth on each mesial and distal side, the center area was selected as the drilling sites of the implant. The guidelines followed the general principles of implantation 16, 17. The expected possible distance from the alveolar crest to the superior aspect of a mandibular canal was determined. That distance axis was chosen parallel to the adjacent teeth or considering the reference controlateral teeth axis (Figure 1.). The distance was measured and then adjusted using the default magnification ratio of the image, 1.3. The calculated value was the expected possible distance planned by the panoramic radiography. Figure 1. The measurement of possible expected path for implantation from the panoramic radiography - 8 -

17 2 Method 2: From the CBCT of original orientation The DICOM images were imported into the Accurex (CyberMed Inc., Seoul, Korea) software program to obtain multiplanar images and multiplanar reconstruction. Accurex was a powerful reconstruction software that can run on Intel-based Personal computer but not on a CT workstation. Therefore, systems such as Intel Pentium4 CPU 3.00 GHz, under the Microsoft Window XP Service Pack2, 1,023 MB physical RAM operating system are needed. The original reference scan orientation was when the occclusal plane was parallel to the base (Figure 2(a)). The data was converted into DICOM format, and Accurex was used to visualize and take the measurements. The dental reformat module of Accurex provides multiplanar images, such as axial, bucco-lingual cross-sectional, panoramic planes. In the cross sectional planes, the implantation drilling site was selected as the edentulous area. In planning the pathways, we referred to the general implantation guidelines 16, 17. The expected implantation drilling site was at least 3mm apart from the adjacent teeth, When several implants were planned, the a distance between drilling sites was at least 7 mm. If there were edentulous areas with two adjacent teeth on each mesial and distal side, the middle area was selected as the drilling sites of the implant. When the drilling plane was selected, the angulation of the path of placement was determined. Several guidelines were followed considering the adjacent natural teeth and opposite teeth. Diseased teeth with defects or tilted angulation could not be used as a reference. The natural angulation of the adjacent teeth was used, If there were two adjacent teeth mesially and distally, the angulation of the two was considered, and the average was determined. Considering the angulation of the opposite teeth, a line was drawn from the palatal cusp of the opposite teeth to - 9 -

18 the middle of the alveolar bone width. The middle of the edentulous ridge of the maxilla was used instead if there were no opposite maxillary teeth. Therefore, the expected path for placement in the preimplant site had contained the corresponding angulation of the adjacent mandibular and opposite maxillary teeth. Finally, the bucco-lingual position of the expected placement path was planned in the middle of the edentulous ridge where the angulation had been planned. There were different circumstances on a case by case basis. The distance on that path of placement was measured from the upper most edentulous ridge to the superior cortical layer of the mandibular canal (Figure 3)

19 Figure 2. The procedure of re-orientation of CBCT multiplanar images It is a Set axis of Accurex that can adjust the scan plane. The drawn dotted line indicates the axis of reference tooth. A Set axis window of Dental reformat module: in original scan plane, the axis of reference tooth was inclined. The axial scan plane was adjusted to get axial views perpendicular to tooth axis in the Set axis window of Dental reformat module

20 (a) (b) (a) (c) (b)

21 Figure 3. The measurement of possible expected path for implantation from the CBCT of original orientation Of the multiplanar reconstruction, the bucco-lingual cross-sectional plane was appropriate to set path of placement. On the appropriate cross-sectional plane, the expected possible distance of implant is designed The angulation parallel with tooth axis that drawn from the serial section of adjacent reference tooth. The angulation formed from opposite maxillary palatal cusp to middle of alveolar bone width The expected possible distance for implantation has harmonized angulation of and, and that angulation has been positioned bucco-lingually to be directed to the palatal cusp of the maxillary tooth. the measurement of the expected possible distance for implantation was determined from the upper most edentulous ridge to superior cortical layer of the mandibular canal

22 3 Method 3: From the CBCT of re-orientation. In the Dental Reformat module of the Accurex, Set axis key was used to re-orientate the original scan position. After observing the lateral view of the face, the scanning plane was rotated to obtain the axial planes of the perpendicular tooth axis (Figure 2(b)). This procedure produced new CBCT images lying on different planes, which can visualize the re-oriented CBCT reconstruction data to multiplanar images. In the re-oriented CBCT multiplanar reconstruction, the path of placement for the implant could be planned following the same guidelines for measuring in the original orientation plane. The drilling site was chosen, the angulation and position of the implantation path was determined, and the distance was measured. 3) The reproducibility of measurement in different methods. The reproducibility of the three different diagnostic imaging techniques were compared. Four preimplant edentulous sites were chosen randomly for the reproducibility test. The possible implantation distances were measured at five time intervals in each different imaging technique. The distances in randomly selected 4 preimplant sites were measured 5 times. The time interval was at least 7 days. The mean and standard deviations were obtained, and the absolute difference ( measured value-mean value ) was divided by the mean value. The coefficient of variance(c.v) each imaging method was compared

23 4) Differences between measurements of different imaging modalities The distances measured by the three different imaging methods on preimplant sites were measured. The absolute value of the difference ( measured value by one method- measured value by another method ) was calculated. The absolute differences between Method 2 and Method 1, Method 3 and Method 1, Method 3 and Method 2 were compared. The values between methods and between differences were analyzed. 5) The contribution factors of the difference between Method 3 and Method 2 It was supposed that 3 angles from the teeth and maxillofacial area represent the facial angle, angulation of the teeth, inclination of the teeth. These angles were easily obtained from the lateral and frontal x-ray images. This study used the X-ray Generator module of Accurex to obtain the lateral and frontal reconstructed images. There may be some differences between conventional Cephalogram and the CBCT synthesized cephalograms. However, it was reported that it can be used with similar precision and accuracy as a conventional Cephalogram 18. The three angles are as follows: an angle composed by mandibular plane and occlusal plane, an angle by the occlusal plane and the related teeth axis of the edentulous site from the lateral view, and an angle by the occlusal plane and related teeth axis of the edentulous site from the frontal view (Figure 4). The correlation of the angles with the difference between the Method 2 and 3, were analyzed using correlation coefficient equations

24 6) The difference between Method 3 and Method 2 by edentulous sites The preimplant sites were divided by missing teeth into the first molar and second molar groups. We examined whether or not the differences are related to to the missing teeth area. (a) (b) (c) Figure 4. Three representative angles of the teeth and face from the CBCT synthesized Cephalograms Angle composed by mandibular plane and occlusal plane Angle by occlusal plane and related mandibular teeth axis from the lateral view Angle by occlusal plane and related mandibular teeth axis from the frontal view. 7) Statistical Analyses The statistical analysis were carried out on SAS 9.1 (SAS Institute, Inc., Cary, NC, USA). Three measuring methods were analyzed by Repeated measures of analysis of variance(anova) if there is any difference between the methods. The mean and standard deviation of the measurement differences between imaging methods were calculated and analyzed by ANOVA. From the 4 selected preimplant sites, the reproducibility was calculated

25 and tested using a Kruskal-Wallis Test. The correlation between the measurement differences in the imaging methods and factors, such as the skeletal and dental angles, was analyzed using a Pearson correlation coefficients test. The groups classified according to teeth or orientation were compared using a t-test. For all analyses, a p value 0.05 was considered significant

26 Ⅲ. RESULTS Variable diagnostic methods can show differences in the measurements of the possible expected implant distance. Several sets of equipment have been used in the diagnosis of preimplant sites, panoramic radiography, computed tomography, CBCT. To this computer technology, such as multiplanar image reconstruction, simulation of implantation, navigation, CAD/CAM, can be added to the techniques for diagnosis and treatment of implants. 1) Measurement of the expected possible distance of implantation. This study examined 3 diagnostic imaging techniques, from which the path of placement was set and the possible distance for implantation was measured. The prediction of the path for implantation was carried out using the 3 methods on the same site. The predicted measurements varied according to imaging methods. From the orientation, 25 cases required re-orientation of the axial-plane to obtain a more precise implantation plane(table 1). The distances of the placement path measured in the same edentulous site using the 3 methods were compared using 25 cases. There were no significant differences between Methods 2 and 3, but there were significant differences between Methods 1 and 2, and between Methods 1 and 3(Figure 6)

27 Table 1. The expected possible distances from each imaging method (mm) Case Method 1 Method 2 Method 3 Implant site Average st st nd nd st st st st nd nd st st st st st st st nd nd nd nd nd nd st nd 6.7 Method 1: The measurement from the panoramic radiography Method 2: The measurement from the CBCT of original orientation Method 3: The measurement from the CBCT of reorientation

28 By the absence of tooth, the implant sites are classified into 1st (first molar group) and 2nd (second molar group). Average means the average measurements of Method 1, Method 2, and Method 3. The cases are followed by descending order of Average. distance(mm) Measure 1* Measure 2 Measure 3 Average case Figure 5. The prediction of the path for implantation compared with 3 methods (n=25) Method 1: The measurement from the panoramic radiography Method 2: The measurement from the CBCT of original orientation Method 3: The measurement from the CBCT of reorientation The cases are followed by descending order of average of measurements. * There were significant differences between Method 1 and Method 2, also Method 1 and Method 3 (p 0.05)

29 2) The reproducibility of measurement in different methods. On selected sites for reproducibility test, the calculated C.V was compared in each modality. The largest C.V was Method 2, followed by Methods 3 and 1. The average C.V was 5.80%. The median(range)s for Methods 1, 2 and 3 were 4.40(2.42~9.17), 5.85(3.62~9.98), 5.74(2.36~10.03), respectively. Method 1 was the lowest of all three techniques. However, the difference of C.V between the three Methods was not significant. (p> 0.05) (Figure 7). C.V(%) Method 1 Method 2 Method 3 Figure 6. The reproducibility of each method Method 1: The measurement from the panoramic radiography Method 2: The measurement from the CBCT of original orientation Method 3: The measurement from the CBCT of reorientation Upper limit of the box was one fourth rank of the measured values, middle bar meant median, lower limit of the box was three fourth rank, + meant average value. All graph covered the whole range of the values

30 3) Differences between measurements of different imaging modalities. There were differences between the measurements using the different imaging modalities. The largest difference was between Methods 1 and 2, 1.83±1.12 mm ranging from 0.3 ~ 4.5mm. The smallest difference was between Methods 2 and 3, 1.09±1.04 mm ranging from 0.1 ~ 3.5 mm. The maximum difference was 4.5 mm between modalities. The difference between Methods 1 and 2 was significantly different from the difference between Methods 2 and 3. (Table 2.) Table 2. Differences between measurements of imaging methods. (Mean±S.D., mm) Differences between measurements (n=25) (Mean±S.D., mm) Tukey grouping Method 2 and ±1.12 A Method 3 and 1 1.7±1.11 A B Method 3 and ±1.04 B Method 1: The measurement from the panoramic radiography Method 2: The measurement from the CBCT of original orientation Method 3: The measurement from the CBCT of reorientation A, B : Same letters indicate no significant difference at p=

31 4) The contribution factors of the difference between Method 3 and Method 2. The tooth axis was not perpendicular to the occlusal plane from the lateral and frontal views. The teeth had angulated to mesially and lingually with its occlusal plane slightly. The occlusal plane had average 20.9 with the mandibular inferior border from the lateral view. (Table 3) The correlation between the difference and the following three angles was examined: the angle of the occlusal and mandibular planes, the angle of the reference teeth shown in the lateral view, and the angle of the reference teeth shown in the frontal view. There was no significant correlation between the difference and the angles. Table 3. The angles to the occlusal plane (degree) Contribution factor OP/MP angle Lateral tooth axis Frontal tooth axis Average Max Min OP/MP angle: The angle of occlusal plane and mandibular plane Lateral tooth axis: the angle of reference teeth shown in the lateral view Frontal tooth axis: the angle of reference teeth shown in the frontal view

32 5) The difference between Method 3 and Method 2 by edentulous sites. The measurements according to the tooth groups were compared. The 1st molar group showed a larger difference than the 2nd molar group. However, there was no significant differences between the groups(table 4). Table 4. The comparison between preimplant sites (Mean± S.D., mm) Tooth group 1st molar (n=14) 2nd molar (n=11) Difference between Method 3 and Method ± ±0.71 Method 2: The measurement from the CBCT of original orientation Method 3: The measurement from the CBCT of reorientation

33 Ⅳ. DISCUSSION This study compared the imaging modalities for a preoperative assessment of an implant site. Among the Academy of Oral and Maxillofacial Radiology, the consensus was that panoramic imaging alone is insufficient for imaging of the dental implant sites, whereas tomography, either conventional or computerized, provides the necessary radiographic information such as the height, density, and width of bone 4, 19, 20.. Moreover, this information on the bone anatomy has made a large contribution to the long-term success of dental implants 9. CT-based surgical guidance and CT-based guided navigation systems have been anticipated in dental implantology. Despite the increasing use of implantology in dental practice a small number of clinicians use tomography to evaluate the preimplant site, preferring to limit its use to some cases of diagnosis only for the bony quality and quantity. Therefore, the effectiveness, benefit to cost, applicability, accessibility, scientific evidence need to be evaluated. There is some dispute regarding the position of scanning plane during CT taking. They were suggested that the mandibular occlusal plane, inferior border of the mandible, and mandibular canal. The formed axial images from those scanning planes may lead to dimensional differences according to the inclination of the scanning plane 9. On CT taking of the maxillary teeth, they did not report the necessity of verifying the scanning plane. On the other hand, the change in the inclination of the long axis of dental implant is noticeable when visualizing the mandibular teeth, particularly the posterior mandibular teeth. A reconstruction of single or multiple-dental implants harmonizing esthetics and function is challenging. It is influenced by many factors, including the length, alignment, and bone anatomy of the implants. A radiology evaluation can determine the appropriate length and width as well as the preferred position and orientation 8. When performing a radiologic evaluation for

34 the preimplant sites, there are pitfalls and limitations that need to be considered. The most useful information can be obtained from the most efficient imaging modality. Therefore, the usability of the information depends on the clinician. CBCT has high resolution of bone tissue as well as short scanning and reconstruction times. In addition, it occupies less space and has less installation cost. The use of CBCT for the diagnosis of an implant or oral and maxillofacial bone and teeth is increasing. Therefore, it is expected that CBCT images will be used more frequently. In the facial mode of the CBCT, which has the largest FOV of any other implant or dental mode, the volume data including maxilla and mandible, and craniofacial area, can be obtained in a few seconds. In addition, there is less radiation exposure. Adapting the various computer software packages for diagnostic imaging, the patient s data can be converted into images of different planes and orientation through a multiplanar reconstruction In this study, the Set axis, X-ray generator modules of Accurex were used, the data was reconstructed into various planar images. A more precise length is expected through its ability in orientation from various multiplanar images, which would assist in the clinicians implantation procedure. The general principles of implantation need to be taken into account. Many clinicians suggested the principles from the viewpoint of the long-term success of implants, esthetics and function. There are reference areas, such as the residual edentulous ridge, adjacent teeth, and opposing teeth. Based on these areas, the determination of the position where the stress is well-distributed is considered reasonable. The main question is how to determine the correct position in the diagnostic images of the preimplant sites. It is appropriate to align the position with the missing

35 tooth. However, after a long period of time has passed since loss of teeth, the resorption and remodeling of bone changes the circumstances, such as the occlusion and alignment of teeth. Therefore, the position of the previously missed teeth may not so informative. Another supplemented methods, such as a bone graft and angled abutment can sometimes change the length and path for implantation. A trial to visualize the optimal plane for implantation had been carried out. The aim was to re-orient the axial plane to be perpendicular to the adjacent tooth axis, as expected with the implant path. Set axis control alters the referential plane from the existing CT volume data after CT acquisition. Even in a PC, that function can reconstruct the images well, and reoriented axial plane can be obtained. This study proposed to align the plane on the implant axis to the tooth contrary to the traditionally viewing plane perpendicular to occlusal plane. There were differences in measurement obtained using the different imaging methods. The largest difference was between panoramic radiography and CBCT, 1.83 ±1.12 mm. Using a reorientation for a more precise length and proper orientation, there was a difference from the original CBCT to CBCT-reorientation, 1.09±1.04 mm. The smallest is of differences between imaging modalities. The factors associated with axis of implant are unclear. Knowledge of these factors will allow the selection of cases that require a change in orientation of the scanning plane can be selected. The tooth groups were compared. However, there was no statistically significant difference in the measurement differences between groups. Three angles were suppoosed, which are related with the skeleton, the mesio-distal inclination of the teeth, and bucco-lingual inclination of the teeth, as the relating factors

36 There was not significant correlation in the measurement differences between Methods 3 and 2 with angles. Another factor is supposed to be correlated is the curve of Spee of the mandibular dentition. It is important to restore the teeth or implant following the curve of Spee because the teeth are aligned and harmonized with this curve. We wanted to find the correlation of implant axis with the curve of Spee, However, a model of the patients dental arch could not be obtained. A further study on other possible factors, such as the curve of Spee, or curve of Wilsons, will be needed to determine if they correlate with the measurement differences. The mesio-distal inclination of the teeth shown in the lateral view ranged from 60~89.8 (mean 79.9 ) i.e. the average tooth had mesial angulation with the occlusal plane from the lateral view. Therefore, preexisting software that made the cross-sectional plane perpendicular to the occlusal plane could not visualize the precise plane for installing the implant. The axial plane was reorientated to be perpendicular to tooth axis in an attempt to obtain the plane to be installed. Even if the differences were not significant, they may reduce the risk of injury. Moreover, visualization with the precise plane will provide a great deal information. Errors of each imaging modality can influence the differences. The actual length of implant is determined by the distance as well as by the width of the alveolar bone. However, we could not visualize the width of the alveolar ridge bucco-ligually on the panoramic radiograph. In addition, the possible distance of the implantation not the actual length was used. The possible distances for implantation were set from the alveolar crest to the inferior border of the mandibular canal in order to compare the measurements under the same conditions for each imaging modality. In this study, the distances made in each edentulous site were compared between imaging methods. The expected distance and planes for implantation changed according to the imaging modalities and methods used. The errors in measurement depend on the individual error, difficulty in recognition of

37 important anatomy. Because the preferred plan for implant depends on the clinician, the interobserver errors between clinician s is rather the individual treatment choices than the measurement differences in this study. The other observer was excluded and the error was limited to the same clinician s measurement errors. Recognition of the mandibular canal was difficult. In panoramic radiography, superimposition and distortion can blur the canal. In many cases the canals connected the recognized canal area were drawn continuously. In CBCT, despite that there was no superimposition or distortion, the faint or absent cortical bone was not distinct from the empty bone marrow spaces. Some cases had an additional canal or canal of variable width, which influenced the measurement errors. Hanazawa T. et al. reported that the detection accuracy of the mandibular canal, comparing with the tomography images could vary according to the imaging methods and scanning conditions 21. In panoramic radiography, the measuring value was adjusted by a magnification ratio of 1.3. However, the magnification ratio was not consistent, due to positional changes and the imaged area. This measurements from the panoramic radiography had thoses limitations. The intraobsever differences in each modality was compared. Four preimplant sites were selected randomly and the distances were measured 5 times. The time interval was at least 7 days. The largest C.V was CBCT, followed by Panoramic radiography, and CBCT-reorientation. The third method had the smallest C.V. The average of C.V was 5.80%, which means there will be a 5.80% variation in measurements. However, the maximum was approximately % (1.56mm) for all methods considering the range of C.V. There are no problems with the cases having sufficient length for implantation, but there were some cases with insufficient length for implantation. Overall a 10 % variation needs to be taken into account. There were differences in the measured distances depending on the imaging modalities. The

38 largest differences in measurement was observed between panoramic and CBCT imaging. On previous studies of implant imaging, it was reported that CT was more accurate than plane tomography. In addition, the CBCT were comparable in accuracy 22. It is believed that CBCT is accurate but panoramic radiography is used the most. CBCT has accuracy and can help the clinician to make the appropriate position and axis of the implantation using versatile multifunctional imaging modalities and software. CBCT has less exposure and wide field of view (FOV) covering the maxillofacial region. It can take images of both maxilla and mandible simultaneously, and display the inter-arch relationships such as intercuspation between dentitions or edentulous sites and opposing dentition 23. This is easily obtained and the 3- dimensional craniofacial anatomy can be visualized sharply. Compared with conventional whole-body CT, as a diagnosis for preimplant sites is useful due to these advantages, clinicians have accepted this modality as first choice. Taking this drift into account, when diagnosing and making a treatment plan in the craniofacial region, it is expected that imaging diagnosis will employ 3-dimensional computer integrated images. CBCT may be useful not only for implantology, but also in many dental applications 23 on account of its many advantages over conventional plain or CT images 24. This study showed that the expected possible distances for implantation differed according to the imaging methods. The measurement differences were small. However, unless that difference is considered there might be increased risk of injury to the mandibular nerve

39 Ⅴ. CONCLUSION 1. The difference between panoramic radiography and original CBCT was 1.83±1.12mm. The difference between panoramic radiography and reoriented CBCT was 1.7±1.11mm. This measuring difference should be considered when using panorama radiography only. 2. The difference between the original and reoriented CBCTs was 1.09±1.04, which is smaller than the difference between panoramic radiography and CBCT. 3. The mean reproducibility of each modality was 5.80%, which equates to a 0.90mm measurement difference. The difference between the original and reoriented CBCTs was larger than the reproducibility but there was no significant difference. 4. This study could not find the cause for the difference between the original and reoriented CBCTs. The absent tooth sites or angles of the skeleton and tooth did not show a significant correlation with the difference. 5. The measurements between the CBCT methods were not significantly different. For a more precise position and inclination of implantation, the axial plane perpendicular to the cross-sectional plane might need to be reorientated in order to visualize the optimal plane for implantation

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