加壓及注射式熱聚合樹脂與數位切削列印技術製成下顎義齒之應變分布評估 - 體外實驗

Evaluation of the strain distribution of mandibular denture fabricated by compression molded, injection molded, CAD/CAM milled and 3D printed techniques. - An In Vitro Study

周桂蓮(Kuei-Lien Chou)

指導教授 ： 楊宗傑

共同指導教授 ： 林立德(Li-Deh Lin)

國立臺灣大學/醫學院/臨床牙醫學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202101836

摘要

實驗目的：本研究目的在檢測樹脂熱聚合加壓及注射方式與數位化技術電腦設計切削及3D列印所製作之下顎全口活動義齒基底及咬合堤，在受力後的應變分布，及3D列印所製作之下顎咬合堤強化加工後對應變分布的影響。
材料與方法：基於本研究團隊[1]先前研究製作出的下顎鈷鉻合金( cobalt-chrome alloy )金屬參考模，以透明壓克力樹脂翻製成測試模型，並以2 mm厚之矽膠印模材製作出軟組織墊片置於測試模型上，用以模擬下顎無牙嵴之黏膜構造。而後，依據金屬參考模之組織面，分別採用下列三種製程、各二種材料( 共計六種材料 )製備出下顎全口活動義齒基底及咬合堤：(1) 樹脂熱聚合製程[(注射成型( injection molding, IM group )、加壓成型( compression molding, CM group )]；(2) CAD/CAM切削製程( 由樹脂塊POLYWAX完成的，簡稱CCM-P group；由樹脂塊YAMAHACHI完成的，簡稱CCM-Y group )；(3) 3D列印製程( 由可列印樹脂( printable resin )BV005或BB base完成的，簡稱3DP-B group；由可列印樹脂( printable resin )Nextdent完成的，簡稱3DP-N group )，每種材料各包含五個樣品，共計30個下顎全口活動義齒基底及30個咬合堤以供測試。義齒基底及咬合堤完成後，於拋光面黏貼應變規( strain gauge )，以測得CH1：唇繫帶切跡( labial notch )、CH2：舌繫帶切跡( lingual notch )、CH3：左側頰繫帶切跡( left buccal notch )、CH4 CH5：左側齒槽脊前緣及後緣( left anterior and posterior ridge crest )、CH6：左側頰棚( left buccal shelf )、CH7：左側下頷舌骨脊( left mylohyoid ridge )、CH8 CH9：縱向及橫向臼齒後墊( left retromolar pad – axial and transverse )等九處不同走向或位置之受力應變。就義齒基底及咬合堤受力後之應變分布，採取之測試方式為：將測試模型固定於萬能試驗機( universal testing machine )上，並將待測試之義齒基底放置於測試模型上，施以5公斤重垂直定力後，記錄應變數值，完成初始測量；而在3D列印咬合堤( 3DP-B group、3DP-N group )金屬強化加工後之受力應變測試方法為：在咬合堤的舌側拋光面切削出平滑的長方形凹槽，用鎳鉻金屬鑄造出符合長方形凹槽的金屬支架並黏著在咬合堤，再按照前述咬合堤受力應變之測試方法，完成金屬強化後之應變測量。本研究之統計方式使用Mann-Whitney U test進行樹脂熱聚合、CAD/CAM切削與3D列印三種製程中兩種不同材料的比較，及相同材料的義齒基底及咬合堤的比較。另以Kruskal -Wallis test進行三種製程間的比較，及咬合堤的樹脂熱聚合、CAD/CAM切削與3D列印金屬強化加工後的比較，同時採Dunn’s test進行事後檢定( post-hoc test )。最後以Wilcoxon signed rank sum test來評估3D列印咬合堤金屬強化加工前後應變值是否有差異，有意義水準設於p小於0.05。
實驗結果：無論是義齒基底或咬合堤受力應變測量時，同種製程之兩種材料大多呈現同為拉伸應變( Tensile strain, 簡稱拉應變 )或是壓縮應變( compressive strain, 簡稱壓應變 )等相類似的應變分佈，但相近程度會受到不同製程影響，樹脂熱聚合製程及CAD/CAM切削製程內的兩種不同材料應變分佈相當接近，在3D列印製程內的兩種不同材料有最大的差異，此現象在義齒基底更為明顯。無論是義齒基底或咬合堤受力應變測量時，在三種製程中，樹脂熱聚合製程與CAD/CAM切削製程的受力後應變分佈較接近，而3D列印製程與另外兩種製程間差異較大且應變較大，此現象在義齒基底更為明顯。樹脂熱聚合製程及CAD/CAM切削製程義齒基底在九個位置中的最大應變皆出現在義齒中線，分別依序出現在舌繫帶切跡( CH2 )及唇繫帶切跡( CH1 )，3D列印製程義齒基底的3DP-B group和3DP-N group在九個位置中最大應變則分別出現在左側下頷舌骨脊( CH7 )和左側齒槽脊前緣( CH4 )。同一種材料的義齒基底和咬合堤相比較時，在同一個位置上，義齒基底的應變大多大於咬合堤的應變，且義齒基底資料離散性也較大，義齒基底和咬合堤在九個位置中最大應變位置有關聯性，除3DP-N group外，其餘五種材料的咬合堤在九個位置中前兩大應變位置都有左側頰繫帶切跡( CH3 )以及該種材料義齒基底在九個位置中最大應變位置。而最後的金屬強化測試，結果顯示3D列印製程咬合堤在金屬加工後會出現受力後應變下降的趨勢。
結論：樹脂熱聚合製程、CAD/CAM切削製程及3D列印製程的義齒基底及咬合堤相比，樹脂熱聚合及CAD/CAM切削的受力後應變分佈較接近，且製程內的兩種不同材料應變分佈也較接近。隨著材料體積的增加，無論何種製程，咬合堤的應變數值皆小於義齒基底。3D列印咬合堤經金屬強化後，會出現受力後應變下降的趨勢。

關鍵字

CAD/CAM切削 ； 3D列印 ； 熱聚合樹脂 ； 下顎全口活動義齒 ； 應變 ； 強化加工測試

並列摘要

Purpose: The purpose of this in vitro study was evaluation of strain distribution between mandibular denture which were fabricated by conventional heat polymerized resin ( compression/injection molding ) method, CAD/CAM milled and 3D printed after the static force loading and the effects of strain distribution of metal reinforcement in the 3D printed mandibular occlusal rim.
Materials and methods: Based on the research by our research team [1], the metal cobalt-chrome alloy reference model was converted into a test model which made with transparent acrylic resin. A 2mm artificial gingiva made with silicon impression material was placed on the test model to simulate the structure of the mandibular edentulous mucosa. According to the intaglio surface of the metal reference model, the following three different process method containing two materials each ( six materials in total ) were used to fabricated the denture base and the occlusal rim of the mandibular denture : (1) conventional heat-polymerized resin process [ injection molding group ( IM group ), compression molding ( CM group )]; (2) CAD / CAM milled process ( made from POLYWAX PMMA disc, named CCM-P group; made from YAMAHACHI PMMA disc, named CCM-Y group ); (3) 3D printing process ( made from BV-005 or BB base printable resin, named 3DP-B group; made from Nextdent printable resin 3DP-N group ), five denture bases were fabricated for each material ( 30 denture base and 30 occlusal rim ). Since the denture base were completed, nine strain gauges were then attached on the polishing surface in different position and direction as the follow: CH1: labial notch, CH2: lingual notch, CH3: left buccal notch, CH4 CH5: left anterior and posterior ridge crest, CH6: left buccal shelf, CH7: left mylohyoid ridge, CH8 CH9: left retromolar pad – axial and transverse. Strain distribution data with static loaded denture base were collected by following method: fixed the test model on the universal testing machine, place the denture base to be tested on the model, apply an axial static load of 5 kg and record the strain value, complete the initial measurement. Test method of strain distribution of metal reinforcement in the 3D printed ( 3DP-B group, 3DP-N group ) occlusal rim: Rectangle groove smoothly surface over occlusal rim lingual surface was made. Ni-Cr alloy metal framework whose shape matching the rectangle groove was casted and bonded to the occlusal rim. Following the previous step to collect the strain distribution data after metal reinforcement. Statistically, we use Mann-Whitney U test to compare two materials in the same process method and compare denture base and occlusal rim in the same material. Kruskal-Wallis test were used to compare the three process methods and compare conventional heat-polymerized resin process, CAD / CAM milled process and 3D printed occlusal rim after metal reinforcement, with Dunn's test method for post-hoc test. Last, Wilcoxon signed rank sum test were used to evaluated the 3D printed occlusal rim the difference between initial and after metal reinforcement. The significant difference level is set at p <0.05.
Results: About the strain measurement of denture base and occlusal rim, two materials of the same process method showed similar strain tendency mostly, especially in the conventional heat-polymerized resin process and CAD/CAM milling process. Two materials of 3D printing process showed more different compared with the other two process, more significant in the denture base than occlusal rim. The strain distribution trend of the conventional heat-polymerized resin process and CAD/CAM milling process were similar, but the trend of the 3D printing process was quite different, and the standard deviation of 3D printing showed the largest data deviation, more significant in the denture base than occlusal rim. The largest strain in the nine measured position presented in the denture base fabricated by conventional heat-polymerized resin process and CAD/CAM milling process were both in the midline of the denture base, respectively labial notch (CH1) and lingual notch (CH2). The largest strain in the nine measured position presented in the denture base fabricated by 3DP-B group and 3DP-N group were left mylohyoid ridge (CH7) and left anterior ridge crest (CH4), respectively. While comparing the same position between denture base and occlusal rim in the same material, we could see the strain in denture base was mostly larger than occlusal rim, and the standard deviation of denture base showed larger than occlusal rim. The largest strain in the nine measured position in denture base was related to which in occlusal rim. Except for 3DP-N group, occlusal rim of the other group in which the largest two strain position in the nine measured position containing left buccal notch (CH3) and the largest strain position in the denture base of the same material. Moreover, 3D printed occlusal rim present decreased strain after metal reinforcement.
Conclusion: About the strain distribution of denture base and occlusal rim fabricated by conventional heat-polymerized resin process, CAD/CAM milling process and 3D printing process, conventional heat-polymerized resin process and CAD/CAM milling process showed similar strain tendency, and in both processing, two materials of the same process method showed similar strain tendency mostly. As the volume increased, strain in the occlusal rim was larger than in the denture base. 3D printed occlusal rim present decreased strain after metal reinforcement.

並列關鍵字

CAD/CAM milled ； 3D printing ； Heat-polymerized resin ； Mandibular denture ； Strain distribution ； Metal reinforcement

參考文獻

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