Effect of framework design on crown failure

Abstract

This study evaluated the effect of core-design modification on the characteristic strength and failure modes of glass-infiltrated alumina (In-Ceram) (ICA) compared with porcelain fused to metal (PFM). Premolar crowns of a standard design (PFMs and ICAs) or with a modified framework design (PFMm and ICAm) were fabricated, cemented on dies, and loaded until failure. The crowns were loaded at 0.5 mm min(-1) using a 6.25 mm tungsten-carbide ball at the central fossa. Fracture load values were recorded and fracture analysis of representative samples were evaluated using scanning electron microscopy. Probability Weibull curves with two-sided 90% confidence limits were calculated for each group and a contour plot of the characteristic strength was obtained. Design modification showed an increase in the characteristic strength of the PFMm and ICAm groups, with PFM groups showing higher characteristic strength than ICA groups. The PFMm group showed the highest characteristic strength among all groups. Fracture modes of PFMs and of PFMm frequently reached the core interface at the lingual cusp, whereas ICA exhibited bulk fracture through the alumina core. Core-design modification significantly improved the characteristic strength for PFM and for ICA. The PFM groups demonstrated higher characteristic strength than both ICA groups combined.

The influence of zirconia coping designs on the fracture load of all-ceramic molar crowns

“…Bonfante et al 8) showed the effect of modified coping design on the fracture load. On the other hand, Lorenzoni et al 18) reported that framework modification did not improve the fatigue life of the crown.…”

“…To reduce this problem, zirconia coping design was modified. One of the suggestion of coping design modification that might reduce the chipping troubles are shown some researchers 2,8,13,17) , changing tensile loads to compressive loads on the occlusal porcelain were important when designing the copings. From these points of view, in this study, four kinds of models were designed; a: uniform thickness of the coping with sharp marginal area which has been conventionally used (control), b: uniform thickness of the coping which has been conventionally used, and marginal area of the coping is strong enough compared to design a, and c: two inclined cusp planes, which might change the tensile loads to compressive loads (lateral load), and at the cervical margin area is designed the same with design a, and d: supporting configuration against the vertical load, and at the cervical margin area is designed the same with design a.…”

“…However, they do not have long-term clinical results to conclude. Furthermore, Bonfante et al 8) showed the effectiveness of core-design modification of In-Ceram crown on the fracture load when applying vertical load at the central fossa, whereas Lorenzoni et al 18) reported that there are no effect of core-design modification of Y-TZP coping crown applying cyclic loading.…”

“…There may be some reasons to fail of veneered porcelain; flexural strength 4) , bond strength between coping and porcelain 5) , excessive load 6) , porosities and surface conditions of the porcelain 7) , improper coping design 8) , and thermal stress when firing porcelain 9) . In clinical case, there might have sever contact under some situations, if there are no coping support of veneered porcelain, chipping problems will increase.…”

Deği̇şi̇k Yöntemlerle Hazirlanan Metal Alt Yapilar Üzeri̇ndeki̇ Veneer Porselenleri̇ni̇n Kirilma Di̇renci̇ne Farkli Kenar Bi̇ti̇m Şeki̇lleri̇ni̇n Etki̇si̇ni̇n İncelenmesi̇≠

“…6 Metal alt yapılı restorasyonlarda en sık karşıla-şılan başarısızlıklar arasında veneer porselenindeki minör kırıklar ve veneer porseleninin alt yapıdan ayrılması sayılabilir. 7,8 Veneer porselenindeki kırıklara; preparasyon şekli, alt yapı materyali ve şekli gibi faktörler sebep olabileceği gibi kırılma dayanıklılığını etkileyen bir diğer faktör ise kenar bitim şeklidir. Sabit protetik restorasyonlarda kenar bitimi (basamak); künt (shoulder), oluk biçimli (chamfer) ve bıçak sırtı (knifeedge) olmak üzere üç şekilde hazırlanabilmektedir.…”