The Effect of Palatal Coverage and Metal Reinforcement on Maxillary Implant Overdenture - An In Vitro Study

實驗目的: 本研究目的在探討在垂直受力的情況下，上顎覆蓋的有無與增加金屬支架強化對上顎植體覆蓋式義齒的應力影響 材料與方法: 以PMMA樹脂製作上顎無牙及全口義齒的模型，共製作五組義齒模型。分別在雙側犬齒、第一大臼齒區埋入四根植體 (3.75x10mm, Mark III, Nobel Biocare™, Sweden)，上面再接Locator® (Zest Anchors, USA)附連體。之後分別在義齒的中線顎側、中線頰側、附連體上方、及上顎左後粗隆處(tuberosity)黏上四個雙軸應變規(biaxial strain gauges, KFG-2-120-D16-11 L1M2S, Kyowa, Japan) 去測量義齒上這四個不同區域在垂直受力情況下所受的應力，每個應變規可測得兩個方向的受力，共有八個頻道的應變數值。之後將上顎覆蓋移除(without palatal coverage)，在相同條件下再測量上述四個區域所受的應力，之後再加入金屬支架再測量一次。靜態垂直力100牛頓施加在橫跨義齒雙側後牙區的樹脂板上(bite plate) ，三種情況都各測量二十次，之後比較三種情況之間應變數值的差異，(P<0.05)，共有五組samples。 實驗結果: 最大應力出現在義齒中線顎側，第二大應力出現在附連體上方的位置，其它無統計上差異。去除上顎覆蓋後與增加金屬支架後，應力的分布趨勢是類似的。三種情況相比，去除上顎覆蓋後，在中線顎側與附連體上方應力是增加的，加入金屬支架後，應力皆有下降。 結論: 在本實驗有限的條件下，上顎四根植體支持覆蓋式義齒在中線顎側與附連體上方的義齒表面，在沒有上顎覆蓋的情形下，加入金屬支架可有效減少應力。Objective: The aim of this study was to investigate the effect of palatal coverage and metal reinforcement on maxillary implant overdenture under vertical loading. Materials and Methods: An edentulous maxilla model and complete dentures were fabricated with polymethyl methacrylate(PMMA) resin. Four implants (3.75x10mm, Mark III, Nobel Biocare™, Sweden) were embedded at bilateral canine, and first molar areas connected with Locator®(Zest Anchors, USA) attachments. Four biaxial strain gauges(KFG-2-120-D16-11 L1M2S, Kyowa, Japan) were attached to the midline palatal, midline buccal, the palatal surface above the attachment, and left tuberosity on each denture to measure the bending strains on the four areas. On the same denture, the palatal coverage was removed and the strains on the above four areas were measured again. Then the metal framework was embedded into the denture for reinforcement and strains on the same areas were recorded for comparison. A vertical static load of 100N was applied to the denture on one biting plate cross bilateral posterior occlusion rims for 20 times in each condition.(P<0.05) Results: The largest strain was observed at the midline palatal area, followed by the area above the attachment. There was no significant difference between other channels. Without palatal coverage, the strains on the above two areas got larger and decreased when metal reinforcement was added into the denture. Conclusions: Within the limitation of the study, the rigidity of 4-implant-supported maxillary overdenture could be reinforced by adding metal framework into the dentur