根管治療後的牙齒會受到牙根狀態、根柱種類與設計的影響。現有根柱材料，包括金屬與非金屬材質。其中非金屬纖維根柱，彈性係數與牙本質較相近，可將力量平均傳導於牙根中。另外多篇研究報告也指出，齒槽骨高度會對根管治療牙齒的預後造成影響。本篇研究目的，是探討不同的根柱材料應用於不同齒槽骨高度牙齒經循環壓力測試前後，牙冠與牙齒密合度的影響及破裂的強度與形式。
研究中測試玻璃根柱Parapost® Fiber Lux，鈦金屬根柱Parapost XT 配合樹脂冠心與鑄造式根柱冠心等三種材料。以兩種包埋高度來模擬齒槽骨喪失的情況。收集60顆單根牙根的牙齒分為六組，經根管治療後依組別置入三種不同根柱冠心系統，並裝置金屬牙冠。牙根包覆矽膠模擬牙周韌帶，以壓克力樹脂包埋至牙冠邊緣6 mm與2 mm模擬齒槽骨喪失或正常。以CCD記錄牙齒於100N壓力下的位移，並以數位影像相關系統(DIC)計算位移量。牙齒再進行溫度壓力循環(3000次5℃~60℃溫度循環，3000次10N~100N壓力循環)，於溫壓循環前後以電子顯微鏡觀察牙套邊緣密合度。最後施予15°斜向力直到牙冠或是牙根發生破壞為止，並記錄下破壞強度與模式。
研究結果顯示，受壓側(顎側咬頭)位移量比頰側來的顯著，而齒槽骨喪失的牙齒位移量也較大。正常齒槽骨高度下，使用纖維根柱復形的牙齒產生較明顯的彎曲現象。使用鑄造式金屬根柱冠心的牙套，其邊緣密合度下降量會比纖維與鈦金屬根柱來的少。比較頰舌處的邊緣密貼度可發現頰側的邊緣密貼度下降量比顎側處明顯。破壞強度方面，使用根柱冠心與金屬牙套復形的牙齒強度較正常牙齒高；相同齒槽骨高度下使用纖維根柱復形牙齒的強度，比鈦金屬與鑄造金屬根柱復形牙齒的強度來的差。齒槽骨高度的改變也會影響破壞強度，除了鑄造根柱沒有顯著差異之外，纖維根柱與鈦金屬都有明顯差異。破壞形式上，自然牙多半破壞於牙冠處。齒槽骨高度正常時，金屬牙套多會產生鬆脫並造成牙根斷裂，纖維根柱復形的破壞中九成是可修復性的，相對於鈦金屬與鑄造金屬根柱，則各只有七成與六成是可修復的。齒槽骨高度降低時，幾乎所有的牙齒都會發生不可修復性的破壞。
根據本篇的研究結果顯示，齒槽骨喪失的牙齒整體位移量較為明顯。齒槽骨正常時，若以纖維根柱復形，其彎曲變形現象會比金屬根柱明顯。對於根管治療後的牙齒更應該用根柱冠心外加牙套加以保護。根管治療後的牙齒在正常齒槽骨高度時，建議以纖維根柱復形，以避免不可修復性的破壞產生。但是在齒槽骨高度喪失的情況下，不管使用哪一種根柱皆易造成不可修復性破壞，則建議以強度較高的鑄造式根柱來復形。

The survival of endodontically treated teeth depends on the apical status, tooth destruction, occlusal loading conditions, types and designs of posts. Current posts can be classified as cast posts, prefabricated metal posts and non-metal posts. Fiber posts exhibited elastic modulus similar to dentin, thus they were considered to distribute the force evenly in the restored tooth. In another aspect, previous studies reported that alveolar bone loss may lead to an increased risk for root fracture. The purpose of this study was to compare the crown fitness and fracture resistance of teeth restored with different posts and under the different alveolar bone conditions.
The posts chosen to be tested were a glass fiber post Parapost® Fiber Lux,, a titanium post Parapost XT with composite cores, and a cast post to restore teeth with two bone heights. 60 teeth with a single root were collected and divided into six groups (n=10). After endodontic treatments, the teeth were restored with post-core systems and metal crowns were cemented respectively. Subsequently the roots were covered with a layer of silicone to imitate the periodontium, the teeth were embedded in acrylic resin either 2 mm or 6 mm below the crown margin. The tooth displacements under a 100 N static force were recorded by a CCD camera and analyzed with a digital-image-correlation (DIC) method. These teeth were subjected to thermocycling and mechanical loading (TCML) test. Marginal adaptation was evaluated before and after TCML under a scanning electron microscope. At last, the teeth received an oblique load to examine the fracture strength and modes.
The results showed that the horizontal displacements on the palatal side were greater than those on the buccal side. For the reduced bone groups, the tooth displacements were greater than normal bone groups. The fiber post restored teeth showed a bending tendency under normal bone condition. The effect of TCML on marginal quality was quantified as the decrease in acceptable margin ratio (DAMR). The cast post groups showed lower DAMR than titanium or fiber post groups. DAMR on the buccal side was higher than that on the palatal side. Results of the fracture test showed that all post restored teeth had higher fracture strength than intact teeth. With the normal bone height, fiber post restored teeth exhibited lower fracture strength than titanium and cast post restored teeth. For the same post systems, the fracture strength is associated with the bone level except the cast post groups. The fracture modes of intact teeth were mostly the dentine fracture on the crown. In the condition of normal bone, both metal crowns loosening and root fracture were found. Most (90%) of the fiber post restored teeth were reparable, comparably 70% and 60 % of teeth in titanium and cast post groups were reparable. As the bone level reduced, most teeth were non-reparable.
In this study, the fiber post/normal bone teeth showed bending deformation compared to the rigid post groups. As the bone level reduced, body movement of the tooth was apparent. Endodontically treated tooth should be restored with post-core systems and covered with crown. For endodontically treated teeth with normal bone height, fiber posts are suggested to decrease the non-reparable failure modes. On the other hand, using cast post is suggested to increase the fracture strength and prevent non-reparable failure under reduced bone condition.

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