| 摘要: | 研究目的：人工植體周圍骨脊是高應力承受區，人工植體的設計影響著植體周圍骨質的受力形態。本研究目的在探討植體與錐狀支台體間接合形式（part 1），與平台移轉（platform switching）接合式植體於骨脊下不同深度置放位置時（part 2），對植體周圍骨的應力分布影響。材料與方法：Part 1：本研究透過電腦輔助繪圖(Computer Aided Design, CAD)與三維有限元素分析(Finite Element Analysis, FEA)，將植體與錐狀支台體之接合型態之變異因素分為接合寬度（3 mm、3.5 mm、4 mm）、接合深度（4 mm、6 mm、8 mm）、錐狀接合角度（2∘、4∘、6∘、8∘）三種，共建構36組模型，給予170N、45∘斜向力與垂直力二種不同受力測試，紀錄周圍骨脊之應力分布與最大應力值（von-Mises stress）。Part 2：將植體骨脊下置放位置之變異因素分為，與植體接觸皮質骨及未與植體接觸皮質骨。接觸皮質骨厚度0.5~4 mm，以0.5 mm為間隔單位建構8組；未接觸皮質骨厚度0~1.6 mm，以0.2 mm為間隔單位建構9組，兩因素組合後共建構72組模型。於支台體上方平面給予170N、45∘斜向力受力測試，紀錄周圍骨脊之應力分布與最大應力值（von-Mises stress）。Part2另外進行體外實驗，骨質的部分使用人造骨（Sowbones）模型，並與人工牙根搭配，製作出四組模型，包含: 接觸皮質骨厚度2 mm，未接觸皮質骨厚度0與1 mm；與接觸皮質骨厚度3 mm，未接觸皮質骨厚度0與1 mm，四組模型皆進行斜向力受力測試，透過應變規（strain gauge），量測其人工牙根周圍骨質應變並比較其結果。實驗結果：Part 1：結果顯示接合寬度較小與接合深度較深時，不論承受斜向力或垂直力，所得周圍骨脊之最大應力值皆明顯較小（p<0.0001）；而較小之錐狀接合角度在承受垂直力時，周圍骨脊之最大應力值明顯較小（p＝0.0002），但承受斜受力時則無顯著差異（p＝0.83）。三項設計參數中，接合寬度對周圍骨應力之影響性高於接合深度，而接合角度的影響性最小。Part 2：CB與nCB對骨應力之影響皆逹顯著差異（P<.0001），而CB對應力的影響性較大。隨CB厚度提高，其骨質應力呈非線性降低，在CB≦2.5 mm時，CB愈厚則骨應力值降低幅度較大，但CB>2.5 mm，骨應力減低之幅度趨緩。nCB在厚度不足（nCB＝0.2~0.4 mm）的情況下，相較無骨脊下植入之模型（nCB＝0），應力值升高，但厚度較厚（nCB＝0.6~1.6 mm）的情況下則應力值較低。體外實驗方面，壓應力側最大應變值（microstrain），四組模型分別為CB2-nCB0＝-2012，CB2-nCB1＝-1239，CB3-nCB0＝-1630，CB3-nCB1＝-945。相同nCB條件下，CB3較CB2的模型應變值低；而相同CB條件下，nCB1較nCB0的模型應變值低。結論：Part 1：降低人工植體與支台齒間接合寬度與增加接合深度，可幫助植體受力時分散應力，降低周圍骨脊最大應力值。Part 2：平台移轉接合式植體於骨脊下植入時，在足夠厚度的接觸皮質骨（≧2.5 mm）情況下，配合適度的未接觸皮質骨（≧0.6 mm）有助於進一步分散植體周圍骨應力。
Purpose：The aims of this study were to investigate the effects of various implant-abutment connection designs (part 1) and subcrestal-inserting depths (part 2) on the stress in peri-implant crestal bone by using three-dimensional finite element (FE) analysis. Material and methods：Part 1：Thirty-six models with various morse-taper connection designs included different abutment diameters (3 mm, 3.5 mm & 4 mm), and connection depths (4 mm, 6 mm & 8 mm) and conically taper degrees (2∘, 4∘, 6∘& 8∘) between abutment and implant were constructed respectively. Vertical and oblique forces were set as 170N applied on the top surface of the abutment. The maximum values of von-Mises bone stress in the crestal bone around the implant were analyzed statistically by using ANOVA. In addition, the patterns of bone stress around the implant were examined. Part 2：In the crestal region when a morse-tapered implant (which is also one of the platform-switching implant) was subcrestally positioned, two factors were investigated. One is the thickness of cortical bone contacting to implant surface (CB). The other is the depth of subcrestal insertion (nCB). For the models of CB, eights thicknesses from 0.5 to 4 mm were constructed. For nCB, night depths were employed from zero to 1.6 mm. Therefore, a total of 72 FE models were generated. An oblique force of 170N at 45 degree to the long axis of the implant was applied on the top surface of the abutment. The stress distribution and the maximum values of von-Mises stress were recorded and statistically analyzed by using ANOVA. In addition, the experimental strain gauge test was performed to measure the highest strain data of bone around the implant on the four models (CB2-nCB0, CB2-nCB1, CB3-nCB0, and CB3-nCB1; CB2-nCB0 represents 2 mm of CB and 0 mm of nCB). In FE studies of part 1 and part 2, the geometry of bone models was generated based on the cross-section of mandible in the molar region and their material properties were anisotropic, i.e. properties differ in different directions. Results：Part 1： The results demonstrated that implants with smaller abutment diameter and deeper abutment connection did reduce the stresses significantly (p<.0001) in the supporting bone around the implant under oblique or vertical loading. On the other hand, under vertical loading, less taper degrees of implant-abutment connection resulted in less bone stresses significantly (p＝0.0002) around implants. In oblique loading, however, the similar bone stresses were observed (p＝0.83) among the models with different taper-degree connection. As comparing those three factors, abutment diameter had stronger influence on reducing bone stresses than connection depth did, and the influence of conically taper degree was less. Part 2：The bone stresses were significantly different (P<.0001) among the models with different CB and nCB. CB played a major role in reducing bone stresses. The thicker CB was, the lower the maximal von-Mises stresses in the crestal region were, while the thickness of CB was within 2.5 mm. But, following CB increasing more than 2.5 mm, the decrease of stresses slowed down. However, insufficient thickness of nCB (about 0.2 to 0.4 mm), compared with equicrestal position (i.e. nCB is 0 mm), resulted in higher stresses of bone. On the contrary, lower stresses were found while the thickness of nCB was more than 0.6 mm. On in-vitro study, the peak value of minimum principal strain on crestal bone at models of CB2-nCB0, CB2-nCB1, CB3-nCB0, and CB3-nCB1 were 2012, 1239, 1630, and 945 microstrain respectively. The models with CB3 had lower bone strains than the models with CB2. The models with nCB1 had lower bone strains than the models with nCB0. Conclusion：Part 1：Within the limitations of this study, it was suggested that the narrower and deeper implant-abutment connection had the biomechanical advantage to reduce the stress concentration in the crestal region around the implants. Part 2：While the thickness of CB is more than 2.5 mm, adequate thickness of nCB more than 0.6 mm can help to further reduce the bone stresses around the implants. |
