| Abstract: | 近年，隨著牙科陶瓷材料的不斷改良以及研發出CAD╱CAM 系統，全瓷牙冠已經應用於牙科贗復治療。牙科陶瓷材料具有很好的生物相容性、美觀性、穩定的化學性和熱性質。但全瓷牙冠較容易受到陶瓷材料固有的脆性和弱彎曲強度的影響，陶瓷材料的機械性質對於牙科贗復物的使用期很重要的，尤其是需要有適合的抗疲勞性質。最近研發出一些新型的抵抗破裂增殖的牙科陶瓷材料。本研究的目的是評估三種CAD╱CAM系統的牙科全陶瓷材料（Pro CAD, e.maxCAD 和e.max ZirCAD）的雙軸彎曲強度，模擬口腔咀嚼情況，探討全陶瓷的疲勞壽命。試片的形狀為圓盤狀（12 mm x 1.2mm），按照ISO 6872 標準進行雙軸彎曲強度測試以及在水的環境和反覆機械作用下的動態疲勞測試。之後對三種陶瓷材料的雙軸彎曲強度值作韋伯統計分析。結果顯示e.max ZirCAD 的雙軸彎曲強度值1000.2MPa 明顯的高於ProCAD 和 e.maxCAD(123.4 MPa 和 394.7 MPa) 的強度，用One-way ANOVA 統計分析三種全陶瓷材料的雙軸彎曲強度間存在顯著的差異(p<0.05)。三種陶瓷材料的韋伯模數範圍在4.5 至14.5。當負載為50N，機械循環次數為20,000 次或100,000 次的條件下，ProCAD 和 e.maxCAD 的疲勞強度有少量改變，但機械循環作用之前、後的雙軸彎曲強度沒有統計學上的差異(p>0.05)。在疲勞試驗中當循環作用64,000 次，ProCAD和 e.maxCAD 試片破斷時所能承受的應力減少，只有原來強度的76％及42％。此外，浸泡在人工唾液中測試的ProCAD 和e.maxCAD 試片的疲勞壽命也明顯減少。結論是三種應用於CAD╱CAM 系統的全陶瓷材料的雙軸彎曲強度存在顯著的差異。陶瓷材料自身的穩定性受到循環作用力以及水的環境的影響，隨著循環作用的增加，抗疲勞的強度下降。
In recent years all-ceramic crown has been used as dental ceramics restoration because of improved dental ceramic materials, as well as newly developed computer-assisted design╱computer-assisted manufacture (CAD╱CAM) ceramic system. The dental ceramics exhibit their biocompatibility, aesthetics, chemical stability, and thermal stability. However, the all-ceramic crown is also susceptible to brittle fracture with the low flexural strength. Because the mechanical properties of all-ceramic materials play a crucible role in the long-term restorative dentistry, it is worthy to exam the fatigue behavior of all-ceramics. A variety of all ceramic materials have been developed to prevent inner crack propagation that can cause crown to failure. The aim of this study was to evaluate the biaxial flexural strength (BFS) of three all-ceramic systems (Pro CAD, e.max CAD and e.max ZirCAD) used for CAD╱CAM. To simulate oral mastication the cycle loading was performed to investigate fatigue lifetime of all-ceramic. The disc-type specimen of each material (12 mm * 1.2 mm) was fabricated. The specimens were tested in BFS test followed ISO 6872 standard, and dynamic fatigue test under aqueous and cyclic loading was also measured. The calculation of BFS and data were also analyzed with the Weibull distribution function. The results of mean BFS revealed that e.max ZirCAD had a significantly higher value of 1000.2 MPa than those of ProCAD and e.maxCAD (123.4 MPa and 394.7 MPa). One-way analysis of variance (ANOVA) showed significant difference in BFS among the three groups (p<0.05). Weibull modulus ranged from 4.5 to 14.5. Mechanical cycling for 20,000 or 100,000 cycles under 50N in water, small changed the BFS for both ProCAD and e.max CAD but it was not statistically significant (p>0.05). For specimens of ProCAD and e.max CAD the cycle loading stress lower than 76% (94 MPa) and 42% (165 MPa) of the BFS value (123 and 395 MPa), respectively, when both specimens fractured with mechanical cycling for 64000 cycles in water. Additionally, a marked decrease in fatigued lifetime of ProCAD and e.max CAD was recorded in artificial saliva. The results suggested that there were significant differences in BFS among the three all-ceramic system. The stability of all-ceramic bodies was affected by the cyclic loading, and an aqueous environment, with a remarkable decrease in the strength as the number of cycles increased. |
