過去的研究中發現，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，但我門假設認為牙齒本身為一黏彈性材料，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，因此容易產生斷裂。本實驗利用模態測試測量五顆上顎第一小臼齒在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)。此實驗結果顯示，在動態力量作用下牙齒的黏滯性可能可以改變應力傳遞時間與最大應力值，因此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 an 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. However, the viscosity properties on the stress responses of an impacted tooth was ignored in biomechanical studies. In this study, we hypothesized that damping ratio of teeth in the different endodontic treatment stages, such as 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 intact 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). These results indicated that the transduction and distribution of the stress in teeth may change when altering the damping ratio values of the teeth. In conclusion, for fracture resistance analysis, teeth viscosity is an important properties for stress distribution and should not be ignored.