不同金屬床設計對上顎植體支持覆蓋式義齒的影響:應變分析

Abstract

實驗目的：本研究探討上顎植體支持覆蓋式義齒(implant overdenture, IOD)在受力的情況下，補強結構設計與顎覆蓋範圍等理想的補綴物設計。 材料與方法：以PMMA樹脂製作上顎全口無牙模型及全口義齒，並分別在兩側犬齒及第一大臼齒區域埋入四根植體(3.75x10mm, Nobel Biocare)，接上Locator (Zest Anchors) 附連體(attachment system)。在義齒的中線顎側、中線頰側、附連體正上方及突隆處黏貼雙軸應變規(strain gauge; KFG-020120-C1, Kyowa)，測量在垂直受力下產生的應變量。實驗分成兩部分，實驗一:測量顎覆蓋範圍對IOD應變量影響，上顎模型從incisive papilla延伸到fovea palatine畫出假想直線，分成四等份，以模擬或測試檢討100%、75%、50%及25%顎覆蓋情況下應變量變化。實驗二:探討顎覆蓋範圍縮小的條件下(維持顎覆蓋25%)，不同金屬支架(Co-Cr alloy)設計對義齒應變量的影響。測試包含 (1)全樹脂顎覆蓋25% (對照組) (2)顎部金屬支架不延伸至牙嵴 (3)金屬支架簍空於附連體 (4)金屬支架蓋過附連體之U-shape metal frame-work design。靜態垂直力100牛頓施加於雙側後牙區的樹脂板上(bite plate)，紀錄受力時黏貼微電阻應變計位置所產生的應變值。實驗數據以one-way ANOVA合併post hoc Tukey事後檢定來檢定有意差(SPSS 21, IBM)，有意水準設於ｐ<0.05。藉由結果比較，評估各項因子間對應力結果影響的情形。 實驗結果：當兩邊同時受力的情況下，隨著顎覆蓋範圍由100%、75%至50%逐漸縮減，義齒應變量有增加的趨勢；再者，當顎覆蓋範圍減少至25%時，義齒應變量和其他組別相比顯著增加，達統計上差異。另外，相較於全樹脂顎覆蓋範圍25%對照組，垂直受力時加入金屬支架設計之IOD義齒應變量降低；又針對不同金屬支架設計相比較，當金屬支架設計覆蓋附連體正上方時，能夠最有效降低義齒形變。 結論：本實驗在有限的條件下發現，上顎IOD顎覆蓋面積減少時會增加義齒內應變量。此時，藉由合適的金屬支架設計能有效降低義齒內形變。

Objective: The aim of this study was to investigate the ideal maxillary implant overdenture design regarding palatal coverage areas and metal framework types under vertical loading. Materials and Methods: An edentulous maxilla model and complete dentures were fabricated with polymethyl methacrylate(PMMA) resin. Four implants (3.75x10mm, Nobel Biocare) were embedded at bilateral canine, and first molar areas connected with Locator (Zest Anchors) attachments. Four biaxial strain gauges (strain gauge; KFG-020120-C1, Kyowa) were attached to the midline palatal, midline buccal, the top of the attachment, and left tuberosity on each denture to measure the bending strains on these areas. The experiment included two parts. First, from the area between incisive papilla to fovea palatine, the areas of palatal coverage on IOD were fabricated and divided into 100%, 75%, 50% and 25%. Part two was to investigate the effect of different metal framework design on the denture strain of IOD under the condition of 25 % palatal coverage. Control group was IOD with fully PMMA resin (25% palatal coverage). Testing groups were Co-Cr alloy metal framework embedded including U-shaped palatal plate only, palatal plate with and without covering the top of attachments. 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. Comparisons of the bending strains were made by an analysis of variance (P<0.05). Results: As the decrease of the IOD palatal coverage area from 100%、75% , 50% to 25%, the values of strain increased under loading. Furthermore, the values of strain increased significantly and dramatically in 25 % palatal coverage area comparing to the other groups. Additionally, under the 25 % palatal coverage of IOD, metal framework embedded decreased the strain on denture in all test groups, compare to the control group. Moreover, the most effective metal framework design was the one which covered the top of attachment. Conclusions: Within the limitation of the study, the denture strain increased while the extension of IOD palatal coverage decreased. Moreover, in the decrease of palatal coverage, the metal-framework design with the covering over the top of the attachments decreased the strain on denture under loading.