以不同製程技術製作全口義齒時，固持力與密合度及義齒後緣型態之相關評估：體外實驗

Abstract

實驗目的： 本研究目的在測試以以不同製程技術製作全口義齒時，固持力與密合度及義齒後緣型態之相關評估。 材料與方法： 使用上顎全口無牙組織模擬模型，以 2 mm 厚之矽膠印模材模擬口內軟組織，並定義此模型為標準模型。調拌藻膠印模材並置於印模托上後放入模型上印模，待硬化完成後取下。將初始模型倒出後，製作上顎客製化印模托，以上顎初始模型作為標準，其延伸範圍到上顎前庭最深處往內 2mm。將客製化印模托塗佈接著劑後以矽膠印模材進行精確印模，待印模材完全硬化後取下。以 3D 桌掃機掃描模型，並由 CAD 模擬設計軟體設計厚度為 2mm 之義齒基底試品，並調整邊緣及拋光面(polishing surface)型態。後續以 CAD/CAM 切削(CAD/CAM Milling) (CCM 組)、熱聚合方式(Compression molding) (CM 組) 以及 3D 列印(3D printing) (又以列印角度不同分為 3DP 0-degree 組、3DP 45-degree 組) 進行義齒基底之製作，每組上顎各製作 7 個義齒試品 (Model 1 ~ Model 7，四組共計 28 個義齒基底試品)。使用萬能測試機 (universal testing maching)作為將上顎全口義齒基底板拉離標準模型之施力裝置。測試時將標準模型固定於牽引裝置之水平平台，上顎組織面朝下擺放。並將丙三醇之水溶液塗布於上顎全口義齒基底板與標準矽膠模型之間作為口內唾液的模擬。在全口義齒基底板的重心位置裝置一個環鉤，牽引裝置對此環鉤施予垂直向上拉力，拉伸速率設定為 50mm/min。以基底板脫離上顎標準模型時最大量測數值作為固持力大小。每一組進行七次檢測並去除最大及最小之值各一，將剩餘五次的數值進行平均得到固持力大小。之後將各組義齒基底後側邊緣修短至顎凹(palatini fovea)前方 4mm 處，並將修短過後之義齒基底以前述同樣方式進行拉力測試，並比較修短前後固持力之差距。修短前後的固持力之間比較使用 Kruskal-Walist test 進行無母數統計分析，若組之間有顯著差異再使用 Dunn’s test for post hoc test 進行事後檢定。考量到密合度可能是造成固持力差距之因素，將製成之 CCM, CM , 3DP義齒基底(共 28 個)使用桌掃機進行掃描，得到義齒基底之立體結構檔案(STL 檔)，並進行義齒基底之組織面與初始設計檔差距之比較。使用疊合軟體將義齒基底之組織面與設計檔進行疊合，先於軟體中定義出組織面貼合之範圍，而後將設計檔之組織面以及義齒基底組織面進行最佳疊合(best fit alignment)。疊合之後以軟體分析兩者之間的立體空間差距，並以均方根誤差(root mean square)代表誤差大小。誤差大小使用 Kruskal-Walist test 進行無母數統計分析，若組之間有顯著差異再使用 Dunn’s test for post hoc test 進行事後檢定。並將不同組測得均方根誤差數值與拉力測試數值進行相關性評估 (使用 Spearman correlation)，其絕對值愈接近 1 表示關聯性愈大，正負值代表兩變數之間的趨勢變化。 實驗結果： 在固持力測試的結果中，以電腦切削義齒基底有最大的固持力中位數(CCM 組,1603gw)，其次是熱聚合義齒基底(CCM 組, 1217gw)，以 3D 列印製程為最差(3DP 0-degree 組 , 447gw ; 3DP 45-degree 組 , 427gw)。CCM 組相較於 3DP 組較佳、CM 組相較於 3DP-45degree 組較佳且有統計上的意義 (P<0.05) 。在後側邊緣修短後，各組所測得之固持力皆有下降且具統計上的意義 (P<0.05)，下降幅度為20~52 %。 以電腦疊合後立體空間的差距表示義齒基底和模型之間的間隙，結果顯示義齒基底與模型貼合程度以 CCM 組為最佳 (RMS = 0.04mm), 其次是 CM 組 (RMS = 0.09mm), 以 3DP 組為最差(3DP – 0 degree 組, RMS=0.25mm ; 3DP – 45 degree 組, RMS=0.19mm)。將疊合得到的空隙大小與固持力進行比對分析後，發現固持力較好的組別空隙也較小，反之固持力較差之組別空隙也較大，相關係數 R 值為-0.77504 ( p < 0.0001)，表示兩組之間具明確相關性。 結論： 在本實驗有限的條件下，對於全口義齒基底在固持力的檢測的結果，CCM 組有最大的固持力，其次是 CM 組，而 3DP 組之固持力最差，3DP 組中 0 度列印與45 度列印組之間無統計上顯著差異。在義齒基底後側邊緣修短條件下，對於固持力的下降有影響，後緣面積減少 4.8 %，固持力下降 21% ~ 52%。密合度方面以 CCM 組有最佳之密合度，其次為 CM 組，以 3DP 組密合度為最差，在 0 度列印與 45 度列印組之間無統計上顯著差異。在固持力與密合度的關係比較之下，越高的固持力同時也具備較貼合的組織面，兩者呈現正相關。

Objective: This in vitro study was to evaluate the effects of fabrication techniques (compression molding, CAD/CAM milling, and 3D printing), regarding adaptation, and posterior border design on the retention of the denture base. Material and methods An edentulous maxilla model using a 2 mm thick silicone impression material to simulate the soft tissue was regarded as a standard model. Impressions were taken in the individual tray using the PVS impression material (Express XT Light body, 3M ) for seven times, and then poured out seven casts(Model 1 to Model 7). Scanning the models with a 3D table scanner(3Shape, Copenhagen, Denmark), and a denture base sample with a thickness of 2 mm was fabricated by CAD simulation design software (3Shape dental system,3Shape) by using different fabrication techniques and materials: CAD-CAM milled (CCM), compression molding (CM), 3D printed (3DP; 3DP - 0 degree build angle, 3DP – 45 degree build angle). Each group had 7 denture samples (28 denture bases in total). A universal testing machine was used as a force-applying device for pulling the denture base denture away from the standard model. The pulling force was recorded the maximum retention force. A glycerol solution was applied between the denture base and the standard silicone model as a simulation of intraoral saliva. Before the test, press the denture base for five seconds to fit the model to make the glycerin distributed evenly, and stop the pressure for five seconds to allow the silicone material to rebound. A loop was installed at the center of the denture base and the traction device exerts a vertical upward pulling force on it. The crosshead speed was set at 50 mm/min. Each group was tested for seven times, and the largest and smallest divergent values were removed. The remaining five values of retention force were averaged. Afterward, the posterior edge of the denture bases was shortened to 4 mm in front of the palatini fovea, and had taken retention test again in the same manner. The difference between the retention force before and after the denture base shortening was calculated. To evaluate the adaptation, all the denture bases were scanned with a table scanner to obtain the three-dimensional structure file (STL file). After superimposing between the denture base file and the initial design file, the three-dimensional space gap was analyzed by image analysis software (Geomagic Control X 2020), and the root mean square was calculated to represent the adaptation error. Results In the retention force test results, the CCM group(1603gw) had the largest median retention force, followed by the CM group (1217gw), and the 3D printing process was the lowest ( 3DP 0-degree group, 447gw ; 3DP 45-degree group, 427gw) with statistical significance (P<0.05) . The results of adaptation showed that the CCM group had the best adaptation (RMS = 0.04mm), followed by the CM group (RMS = 0.09mm), with the 3DP group as the lowest (3DP – 0 degree group, RMS=0.25mm; 3DP – 45 degree group, RMS=0.19mm) with statistical significance (P<0.05). The correlation coefficient R value between retention force and RMS is -0.77504 , which is highly correlated. (p < 0.0001) Conclusions Within the limitation of the study, the conclusions are 1. The CAD/CAM milled denture process presented with higher retention force, followed by the CM group, while the 3DP group was the lowest. 2. With the shortened posterior border, the retention force of the denture base decreased. 3. The better the tissue surface of denture base, the higher the retention force was present. Retention force and denture adaptation were positively correlated.