使用高加速寿命实验评价纤维桩修复体：力学平衡的再思考

Ideally a balance between the post length within root and the coronal extension should exist. Some have advocated the use of the longest post possible as long as the apical seal is not disturbed. Others have advocated that the post be longer than the crown or that the post should be a certain fraction of the length of the root. The conventional post length has been equal to 2/3-3/4 of the root length from half a century ago. Most of these studies have emphasized the post length requirements in order to achieve sufficient retention and rigidity for coronal restoration. However, the dental materials are evolving with each passing day, with the use of fiber post and resin cement, stress distribution and post retention are improved over conventional metal post and zinc phosphate or glass-ionomer cement. Therefore, it is theorized that with improved retention of these bonded posts, the post length within root should be minimized but still able to maintain sufficient coronal rigidity. At this moment there is no unambiguous guideline for optimal design of the post-and-core system in the construction. Factors that play a role in fracture resistance balance of a post-and-core system include the amount of Ferrule height(FH), Post length in root(PLIR), Post length in bone(PLIB), and Abutment height(AH). In view of the above, this current study focuses on the cyclic impact load, evaluates the durability and fatigue life of fiber posts in the anterior area using highly accelerated life test (HALT), the static test and the finite element method. The aim of this study is to provide a new way and the theoretical basis for the design of fiber post.

桩的根内长度与冠部长度应存在一个理想的平衡点。一些学说提倡在不破坏根尖封闭的前提下桩应该尽可能长。另一些学说认为桩长应该大于冠长或与根长成一定比例。从半个世纪前开始，教科书中桩长一直是牙根长度的2/3-3/4。这些学说大都强调依靠桩的长度来增加冠部修复体的固位力。然而，近年来口腔材料学的发展日新月异，纤维桩树脂核代替金属桩核，树脂类水门汀代替传统的磷酸锌﹑玻璃离子水门汀，桩的应力分布和固位力得到改良。因此有理由认为对于粘结力强的纤维桩，桩长应在保持足够固位力的前提下最小化。但目前桩核的最佳设计缺乏理论指导。牙本质肩领长度，桩在根内长度，牙槽骨内桩长度，预备体长度这4个因子在维持桩核力学平衡中有重要意义。据此，本研究着眼于循环荷载，拟利用高加速寿命实验法和静态强度实验结果，评估前牙区纤维桩的耐久性和疲劳寿命，建立可靠性分析模型，并结合有限元方法，为纤维桩的设计提供新思路和理论依据。

从半个世纪前开始，教科书中桩的长度一直是牙根长度的2/3-3/4。然而，近年来口腔材料学的发展日新月异，纤维桩树脂核代替了金属桩核，树脂类水门汀代替了传统的磷酸锌﹑玻璃离子水门汀，桩的应力分布和固位力得到改良。因此有理由认为对于粘结力强的纤维桩，桩长应在保持足够固位力的前提下最小化。但目前纤维桩核的最佳设计缺乏理论指导。本研究着眼于循环荷载，使用静态破坏荷载实验，高加速寿命实验和有限元法，评估纤维桩修复根管治疗牙的抗折性能和耐久性。.选择192颗完整的离体上颌前磨牙并行根管治疗。按照桩长度（7.5, 11 and 15 mm）和预备体高度（3 and 5 mm）随机分为6组，每组32颗。所有离体牙均采用玻璃纤维桩和二氧化锆全冠修复。实验1：1/4的试件(n=8)进行冷热循环后在和牙长轴成135°方向测定抗折力。实验2：剩余的试件在冷热循环后进行高加速寿命试验，并使用有限元法对上颌前磨牙纤维桩修复进行建模分析。.实验1结果表明：纤维桩长度对抗折性能有显著影响（P＜0.01），预备体高度对抗折性能无显著影响（P＞0.05）。抗折力最大的是桩长度15mm，预备体高度5mm组（2080.82±705.22 N），这与抗折力最小的桩长度7.5mm，预备体高度5mm组（1268.02±282.68 N）间的差别有统计学意义。实验2结果表明：纤维桩长度对耐久性能有显著影响（P＜0.01），纤维桩越长修复体寿命衰减越慢。预备体高度对耐久性能无显著影响（P＞0.05）。.综上所述，在静态荷载和高加速冲击荷载条件下，纤维桩长度与抗折力和疲劳寿命成正相关关系。预备体高度对抗折力和疲劳寿命影响有限，而预备体高度较短组牙冠脱落的失败频率增加，断裂形态趋向于可修复破坏。.我们发现磨牙也可形成类似前牙和前磨牙的平衡关系。磨牙桩核受体积影响大于长度影响，这能使桩核平衡理论从二维拓展到三维，在理论系统化方面更进一步。嵌体、髓室固位冠等可成为磨牙桩核的特例进行分析。本项目也带动了纤维材料在口腔新技术、新方法的研究，如纤维加强复合树脂粘结桥，髓室固位冠等微创修复方式的临床应用。