57.有關金屬瓷修復體（metal-ceramic restoration），下列敘述何者正確？
(A)瓷粉在燒成（firing）過程中，其體積收縮（volumetric shrinkage）通常大於20%
(B)金屬的熱膨脹係數（coefficient of thermal expansion）最好小於瓷
(C)瓷內部最好維持於抗張應力（tensile stress）的狀態
(D)金屬與瓷之間的氧化層（oxide layer）厚度愈厚愈好

答案：登入後查看
統計： A(361), B(116), C(169), D(7), E(0) #1633843

詳解 (共 5 筆)

#5549809

瓷對抗張應力（tensile stress ）之抵抗力較弱，對壓縮應力（compressive stress ）抵抗力較強 
 應避免多餘的抗張應力產生
(C) 應改為內部最好維持於壓縮應力（compressive stress ）的狀態

可以透過在材料表面引入壓縮應力來提高材料的斷裂強度( fracture strength)
參考
Pocket Dentistry
Metal-Ceramic and All-Ceramic Restorations

" Complex stresses develop in the mouth. The maximum pressure appears at the surface of the restoration. Therefore, surface inclusions are especially important in judging the strength of a ceramic. Removing or reducing the number of surface inclusions can result in a considerable improvement of the fracture resistance. This is one of the reasons why it is necessary to polish and glaze dental ceramics. The fracture strength of the material can be improved in two ways:

—through introducing a compressive stress within the material surface, and

—through interrupting crack propagation in the material. "



(B) 金屬膨脹係數若小於瓷  會產生過多抗張應力 導致斷裂
參考
Ceramic Fracture in Metal-Ceramic Restorations: The Aetiology

ㅤㅤ
" coefficient of thermal contraction of metal and ceramic, where ceramic contracts more than the metal, can generate excessive tensile stresses in the ceramic layer, thus promoting fracture " 



補充考題
104年 - 104-1 專技高考_牙醫師（二）：牙醫學（五）
47.有關瓷金屬修復體（metal-ceramic restoration）之敘述，下列何者正確？
答案:(C)
(A) 切端部瓷之厚度應該大於2.0 mm
(B) 金屬薄蓋冠（metal coping）之表面應儘可能粗糙
(C) 長徑距牙橋（long span bridge）用合金應有較大之彈性係數（modulus of elasticity）
(D) 瓷對壓縮應力（compressive stress）之抵抗力較弱，對抗張應力（tensile stress）抵抗力 較強
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