植體數目和位置的差異對上頷覆蓋式義齒受力時應力分佈之影響

Abstract

實驗目的：傳統活動義齒在臨床的應用上，牙醫師常常會面臨到病人抱怨活動義齒太鬆或是不穩等狀況，藉由人工植體的幫忙可以有效解決這些問題。近年來已經有許多的研究指出，在下頷使用兩根植體的覆蓋式義齒應該被列為優先的治療選項，然而，目前針對於上頷覆蓋式義齒的相關研究卻不多。因此，本實驗的研究目的是從力學的角度來探討不同的植體位置和數目，對於上頷覆蓋式義齒受力時應力分佈的影響，使用的測量工具是微電阻應變計和荷重元。 材料與方法：使用聚甲基丙烯酸甲酯製作一個上頷全口無牙模型和三個相同的義齒 (n=3)，將六根植體 (3.75x10 mm, MarkIII, Br&aring;nemark, Sweden)包埋在兩側犬齒、第二小臼齒及第一大臼齒的位置。在模型上第一象限植體的遠心側和第二象限植體的近心側分別貼上一個微電阻應變計 (KFG-02-120-C1-11, Kyowa, Japan)，並在硬顎區放置一個荷重元 (LMA-A-200 N, Kyowa, Japan)。對照組是沒有接上附連體 (Locator, Zest Anchors, Inc., Escondido, Calif., U.S.A)的組別，簡寫為IOD 0。兩側犬齒接上兩個附連體的實驗組簡寫為IOD 2；兩側犬齒及第二小臼齒接上四個附連體的實驗組簡寫為IOD 4(3-5)；兩側犬齒及第一大臼齒接上四個附連體的實驗組簡寫為IOD 4(3-6)；兩側犬齒、第二小臼齒和第一大臼齒接上六個附連體的實驗組簡寫為IOD 6。在義齒後牙區的咬合板上施予100牛頓的定力，每個組別各測量十次。(p<0.05) 實驗結果：有關植體周圍應變量上，平均應變值最大的位置都是位於最後方的植體周圍。此外，將實驗組和對照組做比較，可以看到隨著植體數目的增加和植體分佈的前後距離越遠，硬顎區的荷重元所受到的應力就越少。 結論：在本實驗有限的條件下，實驗結果顯示植體的數目與位置都會對應力的分佈造成影響。當上頷覆蓋式活動義齒的附連體是使用Locator的時候，會希望至少四根以上才會有比較明顯的implant-support效果。而最前方與最後方植體位置分佈的距離如果越大，上頷覆蓋式活動義齒的support狀況會由組織與植體共同支持的覆蓋式義變成完全以植體支持的覆蓋式義齒。

Objectives: Using the conventional complete dentures in clinical application, dentists often face the patient’s complaint about dentures loosening or poor stability. With the help of dental implants, most of these problems can be solved. In recent years, there have been many studies supporting that the use of two-implant overdenture should be the first choice of treatment for the edentulous mandible. However, similar studies about maxillary overdentures are not sufficient to make any recommendation. Therefore, the purpose of this study was to evaluate the influence of implant number and location in maxillary overdenture on load transfer, by miniature strain gauge and load cell methods. Materials and Methods: A maxillary edentulous model with three identical single dentures (n=3) were fabricated by using a polymethyl methacrylate resin. Six implants (3.75x10 mm, MarkIII, Br&aring;nemark, Sweden) were embedded at canine, second premolar and first molar regions bilaterally. A miniature strain gauge (KFG-02-120-C1-11, Kyowa, Japan) was attached on the model adjacent to each implant mesially or distally site. A load cell (LMA-A-200 N, Kyowa, Japan) was placed at the hard palate area. The control group without any attachments (Locator, Zest Anchors, Inc, Escondido, Calif., U.S.A) connected was abbreviated as IOD 0. The group with 2 attachments connected at bilateral canine regions was abbreviated as IOD 2; the group with 4 attachments connected at bilateral canine and second premolar regions was abbreviated as IOD 4(3-5); the group with 4 attachments connected at bilateral canine and first molar regions was abbreviated as IOD 4(3-6); the group with 6 attachments connected at bilateral canine, second premolar and first molar regions was abbreviated as IOD 6. A vertical static load of 100N was applied to the overdenture on a biting plate for 10 times on each group. (p<0.05) Results: Regarding to the strain occurring around implants, the largest strain value was found at the most posterior implant when an attachment was connected. Besides, comparing to the control group, the stress value from load cell decreased as the number of implants increased and the distal implant located more distally. Conclusion: Within the limitation of this study, we concluded: 1. Implant numbers and locations will influence the stress distribution. 2. Four implants may provide sufficient support for maxillary overdentures while Locator attachment using. 3. Increasing the distance between the most anterior and posterior implants resulted in additional support which changed the overdenture from tissue-implant-supported to fully implant-supported.