저작자표시-비영리-변경금지 2.0 대한민국 이용자는 아래의 조건을 따르는 경우에 한하여 자유롭게
l 이 저작물을 복제, 배포, 전송, 전시, 공연 및 방송할 수 있습니다. 다음과 같은 조건을 따라야 합니다:
l 귀하는, 이 저작물의 재이용이나 배포의 경우, 이 저작물에 적용된 이용허락조건 을 명확하게 나타내어야 합니다.
l 저작권자로부터 별도의 허가를 받으면 이러한 조건들은 적용되지 않습니다.
저작권법에 따른 이용자의 권리는 위의 내용에 의하여 영향을 받지 않습니다. 이것은 이용허락규약(Legal Code)을 이해하기 쉽게 요약한 것입니다.
Disclaimer
저작자표시. 귀하는 원저작자를 표시하여야 합니다.
비영리. 귀하는 이 저작물을 영리 목적으로 이용할 수 없습니다.
변경금지. 귀하는 이 저작물을 개작, 변형 또는 가공할 수 없습니다.
치의학석사 학위논문
Methodology for measuring volumetric change of bone after
dental implant installation in computed tomography
전산화 단층촬영을 이용한 임플란트 식립 전후의 치조골의 체적 변화 측정 방법
2015 년 2 월
서울대학교 치의학대학원
치의학과임 영 욱
전산화 단층촬영을 이용한 임플란트 식립 전후의 치조골의 체적 변화 측정
방법
지도교수 임 영 준
이 논문을 치의학 석사 학위논문으로 제출함
2014 년 10 월서울대학교 치의학대학원
치의학과임 영 욱
임영욱의 석사 학위논문을 인준함
2014 년 11 월위 원 장 권 호 범 (인) 부 위 원 장 임 영 준 (인) 위 원 김 명 주 (인)
Abstract
Methodology for measuring volumetric change of bone after
dental implant installation in computed tomography
(Directed by Professor Young Jun Lim)
Young-Wook Lim Department of Dentistry School of Dentistry Seoul National University
Introduction: Computed tomography(CT) could be the solution for the limitations of 2-D X-ray because CT provides 3-D image, bone resorption pattern and radiolucency around implant fixture can be observed in all direction around implant fixture. In this study, a method for measuring volumetric change of alveolar bone after dental implant installation in CT is proposed. Volumetric change of alveolar bone of maxilla during first year after installation is measured using this proposed method.
Materials and Methods: The volume of the alveolar bone around a implant fixture is measured as follows: 1) A cylinder which is made up of points have same distance from axis of implant, defined as
main cylinder, is established 2) Another cylinder which is made up of points have same distance from axis of implant, defined as error correction cylinder, is established. 3) The volume of alveolar bone is the number of voxels which have H.U. of bone in volume obtained by subtracting error correction cylinder from main cylinder.
Volumetric change is difference between the volumes measured immediately after installation and 1-year installation. Using proposed method, 40 implants in 21 partially edentulous patients were selected. They were subjected to take CTs immediately after dental implant installation and 1-year after installation.
Results: The average of volumetric change was –0.011cc and the standard deviation was 0.016cc. Negative average means volumetric increase. According to paired t-test, the volume of alveolar bone around implant fixture is statistically increased after dental implant installation (p<0.05).
Conclusions: A method for measuring volumetric change of alveolar bone after dental implant installation in CT is proposed. For the assessment of marginal bone change, volumetric change of alveolar bone around the coronal part of implant fixture would be a better criterion.
Key words: dental implant, computed tomography, CT, alveolar bone, volumetric change, bone resorption, installation
Student number: 2011-22480
Table of Contents
1. Introduction ··· 1
2. Materials and Methods ··· 4
3. Results ··· 7
4. Discussion ··· 8
5. Conclusion ··· 12
6. Reference ··· 13
국문초록 ··· 22
Lists of Tables
[Table 1] ··· 16
List of Figures
[Figure 1] ··· 17[Figure 2] ··· 17
[Figure 3] ··· 18
[Figure 4] ··· 18
[Figure 5] ··· 19
[Figure 6] ··· 19
[Figure 7] ··· 20
[Figure 8] ··· 20
[Figure 9] ··· 21
Introduction
Dental implants have been regarded as a treatment option for people who have lost a tooth or teeth due to periodontal disease, an injury, or some other reasons. Dental implants are clearly becoming a choice of treatment in edentulous patients, and its indication is expanding from partially edentulous to fully edentulous patients.
Various success criteria for dental implant were proposed by many researchers such as Schnitman and schulman, Cranin et al., and McKinney et al. [1-3]. Success criteria for dental implants were proposed by Albrektsson, et al in 1986 :
(1) Individual unattached implant that is immobile when tested clinically
(2) Radiography that does not demonstrate evidence of peri-implant radiolucency
(3) Bone loss that is less than 0.2 mm annually after the implant′
s first year of service
(4) No persistent pain, discomfort or infection
(5) By these criteria, a success rate of 85% at the end of a 5 year observation period and 80% at the end of a 10 year period are minimum levels for success [4].
Adell proposed that the success of implant therapy should be judged after 1 year of service because most of the bone loss occurred during the 12 months following abutment connection [5].
Adell et al. also reported that alveolar bone loss during the first year after abutment connection averaged 1.2 mm, and annual bone loss thereafter remained at approximately 0.1 mm for both the maxilla and the mandible [6].
Radiographic examination is useful for the assessment of success
- 2 -
of dental implants. However, 2-dimensional radiographs such as panoramic radiograph and periapical radiograph have revealed limitations in evaluating success criteria for dental implants. It is unable to not only evaluate bone change of bucco-lingual direction but also show exact mesio-distal bone change.
CT allows applicable evaluation of bone quality and adjacent anatomic structures such as maxillary sinus and inferior alveolar nerve which can be used as efficient diagnostic tool for dental implantation. CT image has a lot of advantages over conventional radiographic and single CT slice. First, superimposed structures are eliminated to make the targeted anatomic layer more apparent.
Second, high contrast resolution allows distinguishment of physical density by less than 1% when conventional radiographic image requires approximately 10% of physical density difference. Third, multiplanar reformatted imaging technique combines images to allow viewing in various approaches such as in transverse sections, longitudinal sections, or sagittal planes [7].
Computed tomography(CT) could be the solution for the limitations of 2-dimensional X-ray. Because CT provides 3-dimentional image, bone resorption pattern and radiolucency around implant fixture can be observed in all direction around implant fixture, therefore bone change pattern after implant installation can be observed more accurately. Moreover, it is possible to analyze volumetric change of alveolar bone with CT.
There are many researches about alveolar bone resorption after implant installation, after loading or related with other factors [8-11]. However, there is no volumetric analysis of bony change after dental implant installation.
In this study, a method for measuring volumetric change of alveolar bone after dental implant installation in CT is proposed.
Volumetric change of alveolar bone of maxilla during first year after installation is measured using this proposed method.
- 4 -
Materials and Methods
Materials40 implants in 21 partially edentulous patients, aged 50 to 75 years, with fixture installed from July, 2012 to March, 2014, were selected. Patients who had clinical symptoms or mobility of fixture were excluded. The subjects included 15 males and 5 females with all implants in maxilla. Types of implants used included 10mm-long 16 internal fixtures from the Straumann(Straumann Dental Implant System, Waldenberg, Switzerland), as well as 10mm-long 24 fixtures from implants(Neobiotech Co., Seoul, Republic of Korea).
They were subjected to take CTs immediately after dental implant installation and 1-year after installation for analyzing volumetric change of the alveolar bone after installation at Department of Oral and Maxillofacial Radiology, SNUDH. The CT scans were taken by Somatom Sensation 10(Siemens AG, Forchheim.,Germany) with following parameters; slice thickness 1mm;T1, 0.75s; 120kV; and 100mA/s.
Methods
OnDemand3D software(CyberMed, Seoul, Republic of Korea) was used for analysis of the volumetric change alveolar bone.
The volume of the alveolar bone around a implant fixture is measured as follows:
(1) Draw the dental arch shape and place the installed dental implant model on axial view (Figure 1).
(2) Adjust location of implant model on axial, cross-sectional and panorama view. This is coarse adjustment of position of implant (Figure 2).
(3) Adjust position of implant model finely at the verification tab (Figure 3). Rotational angle of a implant model can be controlled in 0.1 degree intervals, position can be controlled in 0.05mm intervals, respectively.
(4) A cylinder which is made up of points have same distance(r+d) from axis of implant, defined as main cylinder, is established (Figure 5, 6).
(r : radius of implant, d+r : radius of main cylinder)
(5) In order to observe the volumetric change of alveolar bone of area of interest, determine the height of the main cylinder, defined as ‘h’ (Figure 5).
(6) Another cylinder which is made up of points have same distance(r+dc, dc<d) from axis of implant, defined as error correction cylinder, is established (Figure 6).
(r+dc : radius of error correction cylinder)
Error correction cylinder should be established because there is radiolucency around radiopaque implant fixture and it introduces error in evaluating volumetric change of alveolar bone after installation (Figure 7). The height of error correction cylinder is set to the same value as that of main cylinder.
(7) The volume of alveolar bone is the number of voxels which have H.U.(Hounsfield scale, CT number) of bone in volume obtained by subtracting error correction cylinder from main cylinder. In other words, volumetric change of alveolar bone, defined as Vd, was calculated by subtracting volume certain period after implant installation from volume measured immediately after installation.
Values of variables can be changed at the control panel, in OnDemand3D software as shown in Figure 8.
- 6 -
Statistical Analysis
Paired t-test was used for statistical analysis: p<0.05 was considered to be significant. For these analyses, SPSS v20 software(SPSS, Chicago, Il, USA) was used.
Results
Radiographic CT data were collected retrospectively from 40 implants in 21 partially edentulous patients who were subjected to take CTs immediately after dental implant installation and 1-year after installation.
‘d’ was set to 3mm, ‘dc’ to 1mm, and range(minimum and maximum value) of H.U. from 385 to 2560, and ‘h’ to 3mm, respectively. The cylinder extended from the top of the fixture to the coronal portion. Volumetric changes of alveolar bone around the coronal part of fixture was observed.
Measurement results of the volumetric change of alveolar bone, Vd, 1-year after implant installation are summarized in Table 1 and plotted in Figure 9.
The average was –0.011cc and the standard deviation was 0.016cc.
Negative average means volumetric increase. According to paired t-test, the volume of alveolar bone around implant fixture is statistically increased after dental implant installation (p<0.05).
- 8 -
Discussion
There were many researchers who studied marginal implant bone loss after dental implant installation in periapical radiographs. It differs from 0.1 to 0.25mm. Behneke A. et al reported that mean annual bone loss a year after installation was 0.1mm. According to Levy et al, it was 0.17mm and it was 0.25mm by becker's study [8-11]. Kitamura et al studied marginal bone resoption around implant fixture using 3-dimensional finite element analysis [12].
However, until now, there is no clinical analysis or report of volumetric change of alveolar bone after implant installation.
Volumetric changes of alveolar bone after implant installation in CT is not a bone loss in a specific direction just like bucco-lingual, or mesio distal direction, but it is a reflection of bone loss in every direction. It can also show not only crestal bone loss, but also alveolar bone change including horizontal bone loss. If apex of implants were the focus of interests, alveolar bone change around apex of implant can also be observed. Therefore, it could be a good index reflecting general change of alveolar bone loss around implants. It could also be a meaningful tool of finding correlation among studies regarding marginal bone loss and volumetric change.
There are four controllable variables in proposed method. Distance between outer contour of implant and outer contour of main cylinder, ‘d’, is related to region of interest of volumetric change of bone. If 'd' was set too big, final data could include not only the focus area of this study, alveolar bone change around implant fixture, but also change of surrounding alveolar bone that should not be included in this study. However if 'd' was too small, final data could be acquired that is not sufficient to include overall alveolar
bone change. Therefore, 'd' was set as 3mm as not to be influenced by other anatomical structures.
Distance between outer contour of implant and outer contour of error correction cylinder, ‘dc’, which should be less than ‘d’, determines the size of error correction cylinder. Radiolucent rim around implant fixture could be formed by following reasons; 1) radiolucency which appears around implant fixture with strong radiopacity 2) bone defect caused by drilling or fixture installation immediately after dental implant installation, which decreases bone volume measured immediately after installation therefore bony change caused by installation could not be observed accurately.
Therefore it could be necessary to set ‘dc’ big enough to reduce possible error that might occur. However, as ‘dc’ value increases, error correction cylinder might also get bigger, and this could compromise the final data. So it is necessary to set ‘dc’ value low enough to eliminate major error factor to see alveolar bone change closed to implant fixture. In this study, because 1mm width of radiolucency around implant fixture was observed in CT image, ‘dc’ was set to 1mm.
Range of H.U determines boundary of H.U. value of bone. Range of H.U. of bone is different according to previous studies [13-15].
In this study, range of HU was set from 385 to 2560 to consider H.U. higher than that of soft tissue's as bone.
‘d’ value sets the horizontal range of the focus area of this study and the height of cylinder, 'h' sets the vertical range of the focus area. In the case 'h' small, the main cylinder doesn’t include volume of the bone around apex of implant. Therefore it is suitable for observing volumetric change of crestal bone. However, if ‘h’ is too small, volumetric change of apex around implant could not be included in data. To set appropriate value of h, it is necessary to
- 10 - consider bone density in every direction.
According to the results, the volume of alveolar bone around implant fixture is statistically increased 1-year after dental implant installation. It seems to be contradictory to the results of other researches which showed marginal bone resorption after implant installation [8-11], however, it seems it's because of different reasons. In the case bone defect caused by drilling or placement of implant during surgery was not eliminated entirely, volume of bone could be estimated seemingly low and bone could fill in this space with osseointegration, which could make volume seem increased.
Also the value was too small, about 0.01cc, to make any conclusion about volume of bone.
Error could also occur for another reason. CT images taken from right after installation and a year after could not be taken at the same degree and the same angle, so the location of the implant could not be same. Also even if CT images were taken in a way that location of implant were same, it is impossible to place implant model in the exact same place because of software implant model was placed manually. Therefore same area with main cylinder could not be covered with this method.
These error could be reduced by 3-dimensional CT image registration. Won-Jin Yi, et al insisted that it is essential to properly align the 2 images to be evaluated in order to minimize observer dependency [16], and Mattes D, et al proposed an algorithm for three-dimensional positron emission tomography transmission-to-computed tomography registration in the chest, using mutual information as a similarity criterion [17]. After image registration, volumetric change of alveolar bone can be observed through digital subtraction radiography(DSR) process. DSR is a useful method for assessing the small differences on serially taken
radiographs [18].
Proposed method in this study can be applied to other studies calculating volume of bone, analyzing volumetric change of bone. It is not confined to dental researches.
- 12 -
Conclusion
In this study, a method for measuring volumetric change of alveolar bone after dental implant installation in CT is proposed.
Using proposed method, for 40 implants in 21 partially edentulous patients, volumetric change of alveolar bone of maxilla around implant fixtures during first year after installation is measured.
The average of volumetric change of alveolar bone 1-year after implant installation was –0.011cc and the standard deviation was 0.016cc. Negative average means volumetric increase. According to paired t-test, the volume of alveolar bone around implant fixture is statistically increased after dental implant installation (p<0.05). For the assessment of marginal bone change, volumetric change of alveolar bone around the coronal part of implant fixture would be a better criterion.
Reference
1. Schnitman PA, Shulman LB. Recommendations of the consensus development conference on dental implants. J Am Dent Assoc. 1979;98:373–7.
2. Cranin AN, Silverbrand H, Sher J, Salter N. The requirements and clinical performance of dental implants. In: Smith DC, Williams DF, editors.
Biocompatibility of Dental Materials. Vol. 4. Boca Raton: Fla: CRC Press;
1982. p. 198.
3. McKinney R, Koth DL, St DE, k DE. Clinical standards for dental implants. In: Clark JW, editor. Clinical Dentistry. Harperstown: Harper and Row; 1984. pp. 1–11.
4. Alberktsson T, Zarb G, Worthington P, Eriksson AR, The long-term efficacy of currently used dental implants: A review and proposed criteria of success, Int J Oral Maxillofac Implants, 1986;1:11–25.
5. Adell R. Clinical results of osseointegrated implants supporting fixed prostheses in edentulous jaws. J Prosthet Dent 1983;50:251–254
6. Adell R, Lekholm U, Rockler B, Branemark P-I. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Surg 1981;6:387.416.
7. 대한구강악안면방사선학교수협의회, 영상치의학, 4th ed., 나래출판사, 2008
8. Behneke A, Behneke N, D’Hoedt B, Wagner W. Hard and soft tissue reactions to ITI screw implants: 3-year longitudinal results of a prospective study. Int J Oral Maxillofac Implants 1997;12:749.757.
9. Levy D, Deporter D, Pharoah M, Tomlinson G. A comparison of
- 14 -
radiographic bone height and probing attachment level measurements adjacent to porous-coated dental implants in humans. Int J Oral Maxillofac Implants 1997;12:541.546.
10. Becker W, Becker B, Israelson H, et al. One-step surgical placement of Branemark implants: A prospective multicenter study. Int J Oral Maxillofac Implants 1997;12:454.462.
11. Miguel Peñarrocha, Maria Palomar, José María Sanchis, Juan Guarinos, José Balaguer, Radiologic Study of Marginal Bone Loss Around 108 Dental Implants and Its Relationship to Smoking, Implant Location, and Morphology. Int J Oral Maxillofac Implants 2004;19:861–867
12. Kitamura E, Stegaroiu R, Nomura S, Miyakawa O. Biomechanical aspects of marginal bone resorption around osseointegrated implants: considerations based on a three-dimensional finite element analysis. Clin. Oral Impl. Res.
15, 2004; 401–412
13. Tannaz Shapurian, Petros D. Damoulis, Gary M. Reiser, Terrence J.
Griffin, William M. Rand, Quantitative Evaluation of Bone Density Using the Hounsfield Index, 1. Int J Oral Maxillofac Implants 2006;21:290 –297
14. Ilser Turkyilmaz, Oguz Ozan, Burak Yilmaz, Ahmet Ersan Ersoy, Determination of Bone Quality of 372 Implant Recipient Sites Using Hounsfield Unit from Computerized Tomography: A Clinical Study,Clinical Implant Dentistry and Related Research,2008;10:238-244
15. G. N. Hounsfield, Computerized transverse axial scanning (tomography):
Part I. Description of system, British Journal of Radiology 1973;46:1016-1022
16. Won-Jin Yi, Min-Suk Heo, Sam-Sun Lee, Soon-Chul Choi, Kyung-Hoe
Huh, ROI-based image registration for digital subtraction radiography,Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006;101:523-9
17. David Mattes, David R. Haynor, Hubert Vesselle, Thomas K. Lewellen, and William Eubank, PET-CT Image Registration in the Chest Using Free-form Deformations, IEEE Transactions on Medical Imaging 2003;22:120-128
18. Sam-Sun Lee, Young-June Huh, Ki-Young Kim, Min-Suk Heo, Soon-Chul Choi, Jai-Young Koak, Seong-Joo Heo, Chong-Hyun Han, Won-Jin Yi, Development and evaluation of digital subtraction radiography computer program, Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2004;98:471-5
- 16 -
Table 1. Measurement results of the volumetric change of alveolar bone, Vd, after implant installation for 40 implants
Figure 1. Axial, cross-sectional, panorama and 3-dimensional view after placement of implant model
Figure 2. Axial, cross-sectional, panorama and 3-dimensional view after coarse position adjustment of implant model
- 18 -
Figure 3. Axial, cross-sectional, panorama and 3-dimensional view after fine position adjustment of implant model
Figure 4. The cross section of the main cylinder which is made up of points have same distance(r+d) from axis of implant
Figure 5. The main cylinder (‘h’ = 3mm)
Figure 6. The cross sections of the main cylinder and error correction cylinder
- 20 -
Figure 7. Radiolucency observed around implant fixture in CT images
Figure 8. The control panel in OnDemand3D(Cybermed, Seoul, Republic of Korea). ‘d’ and ‘dc’ can be controlled in ‘Thickness(L/R)’
tab, ‘h’ in ‘Thickness(Apical)’ tab, and Range(minimum and maximum) value of H.U in ‘Density value’ tab.
Figure 9. Measurement results of the volumetric change of alveolar bone, Vd, after implant installation (V_delta = Vd) for 40 implants
- 22 - 서울대학교총장 귀하
국문초록
전산화 단층촬영을 이용한 임플란트 식립 전후의 치조골의 체적 변화
측정 방법
( 지도교수 임 영 준 ) 임 영 욱
서울대학교 치의학대학원 치의학과
목적: 전산화 단층촬영은 3차원적인 이미지를 제공하여 임플란트 지대주 주변의 골변화를 모든 각도에서 관찰할 수 있기 때문에 2차원적인 방사 선 사진의 한계점을 극복할 수 있는 대안이다. 이 연구에서는 임플란트 식립 전후의 치조골의 체적변화를 측정하는 방법을 제안하였다. 이 방법 을 이용하여 식립 1년 후 상악 치조골의 체적변화를 관찰하였다.
재료 및 방법: 임플란트 지대주 주변의 치조골의 체적은 다음과 같이 측 정된다: 1) 임플란트의 축에서 같은 거리만큼 떨어진 점으로 이루어지는 주 원기둥을 설정한다 2) 임플란트의 축에서 같은 거리만큼 떨어진 점 으로 이루어지는 오차보상 원기둥을 설정한다 3) 치조골의 체적은 주 원기둥에서 오차보상 원기둥의 부피를 뺀 부피에서 치조골의 하운스필드 유닛의 값을 가지는 복셀의 수로 계산한다. 체적변화는 식립 직후와 1년 후에 측정된 체적의 차이이다. 이러한 방법을 이용하여 21명의 환자로부 터 40개의 임플란트를 선택하였다. 이들은 식립 직후와 식립 1년 후에
각각 전산화 단층촬영을 수행하였다.
결과: 체적 변화의 평균은 –0.011cc 였으며 표준편차는 0.016cc 였다.
음수 평균은 체적 증가를 의미한다. 대응표본 T 검정에 따르면, 임플란 트 지대주 주변의 치조골의 체적은 통계학적으로 증가하였다 (p<0.05).
결론: 전산화 단층촬영을 이용하여 임플란트 식립 후 치조골의 체적변화 를 측정하는 방법이 제안되었다. 임플란트의 치관부 주위골 손실을 평가 하기 위해서는 임플란트 지대주의 치관부의 체적변화를 관찰하는 것이 더 유용할 것이다.
주요어: 치과용 임플란트, 전산화 단층촬영, 식립 전후, 치조골, 골흡수, 체적 변화
학번: 2011-22480
