| Summary: | 碩士 === 中國醫藥大學 === 牙醫學系碩士班 === 97 === 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.
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