| 摘要: | 在過去的研究中顯現，根管治療後接受鑄釘治療的牙齒比較容易發生斷裂，一般認為這是因為可能由於治療過程對牙齒破壞導致牙齒強度降低，但牙齒本身為一黏彈性材料，除了剛性物質外，還有黏滯性物質，如牙髓、牙周韌帶等，因此黏彈性質所造成的影響也應考慮。在根管治療與鑄釘治療後可能會使牙齒黏滯性降低，使得傳導到牙齒內部的應力較高，容易產生斷裂，在本實驗中，利用模態測試測量五顆上顎第一小臼齒未修形前、根管清創後利用暫時填補材料填補、根管封填後利用暫時性填補材料填補、根管治療後利用光聚性樹脂填補、鑄釘與牙冠治療等不同療程中，牙齒阻尼比的改變，結果顯示當根管清創後，牙齒的阻尼比從14.42±2.17%下降至8.50±0.53% (p<0.05)、根管封填且咬合面利用樹脂封填後牙齒的阻尼比從8.50±0.53%上升至13.41±1.92% (p<0.05)、施予牙冠鑄釘治療後牙齒阻尼比再從13.41±1.92下降至7.89±1.70% (p<0.05)。此外，本研究建立一個上顎第一小臼齒的二維有限元素模型，模型經收斂分析與可信度確認後，模擬動態咬合力300牛頓作用在咬窩與顎側咬頭上，並分析不同治療步驟中牙齒內部應力的改變。實驗結果發現，動態力量作用下牙齒的黏滯性會改變應力傳遞時間與最大應力值，而在考慮阻尼比與忽略阻尼比的比較中發現，未修形前的牙齒所造成最大應力下降比率較其他治療步驟大，而且頰側最大應力下降比率大於顎側。因此，利用動態力可以更精確模擬口腔內牙齒受力後的狀態，而在分析不同材料對牙齒最大抗斷裂力的影響時，材料的黏滯性質也須在考量中，以達到更精確的結果。
In the past researches, it was found that there exists a high failure rate of a endodontic teeth subjected to a traumatic load. Traditionally, this phenomenon was contributed to the reduction of teeth strength due to endodontic treatment. From biomaterials viewpoint, a teeth is a composite with viscoelastic mechanical property. The viscous materials, such as pulp and PDL, must has effect on the stress transduction and distribution of a tooth subjected to a impact force. However, the viscosity properties on the stress responses of an impacted tooth was ignored in biomechanical studies. In our research, we measured the damping ratio of the teeth in the different endodontic treatment stages, such as before preparation, cleaning& shaping, RCF+IRM filling, RCF+ resin filling, and post& crown treatment. The mean values of the tested samples are 14.42±2.17%, 8.50±0.53%, 10.84±1.70%, 13.41±1.92%, and 7.89±1.70% for before preparation group, cleaning& shaping group, RCF+IRM filling group, RCF+resin filling, and post+ crown, respectively. In addition, significant differences were found among the groups (p<0.05). To test the effect of viscosity on the stress distribution of a impacted teeth. 2D finite element models of maxillary 1st premolar with various endodontic treatment were established. Sequently, dynamic force with a maximum amplitude of 300N, was used to applied to the FE model on central fossa and palatal cusp. The results indicated that the transduction and distribution of the stress was changed when altering the damping ratio values of the FE models. The highest decreasing rate in stress was found in the unprepared group when the viscoelastic properties was simulated. In addition, The decreasing rate in of the buccal side is higher than the palatal side in unprepared group. In conclusion, more precise results regarding the stress response of a endodontic tooth subjected to a dynamic loading was obtained. For fracture resistance analysis of teeth viscosity is an important properties for stress distribution and should not be ignored. |
