Robust mechanical property measurements of fibrous parylene-C thin-film substrate via moiré contouring technology

Effect of preparation design on the fracture behavior of ceramic occlusal veneers in maxillary premolars

OBJECTIVES

The fracture strengths of four types of occlusal veneers and a traditional full crown ceramic restoration and the influence of preparation design on the stress of restorations were examined.

METHODS

Forty intact maxillary premolars randomly divided into five groups were prepared based on the demands of type O (occlusal surface coverage), OF (occlusal and lingual surface coverage), POF (occlusal, lingual, and mesial surface coverage), and POFP (occlusal, lingual, mesial, and distal surface coverage) veneers and full crown, and then restored by glass ceramic. Specimens were subjected to fracture resistance tests after cyclic loading. The fracture strengths and modes were analyzed statistically. The level of significance was set at α = 0.05. One maxillary premolar was prepared for type O, OF, POF, POFP veneer and full crown, and then scanned to establish finite element models. The mean fracture load was applied vertically to calculate the maximum principal stress on the ceramic.

RESULTS

Type O veneer showed higher fracture strength than type POF and POFP veneers (P < 0.05). Both type O and OF veneers exhibited higher fracture strength than full crown (P < 0.05). No significant difference in failure mode was observed. The maximum principal stress for type O, OF, POF, POFP veneers, and full crown increased progressively and concentrated at the bonding surface directly beneath the loading area.

CONCLUSIONS

Four types of occlusal veneer showed fracture strengths that considerably exceeded normal biting forces. They represent conservative alternatives to full crowns and present a viable treatment for severely worn teeth.

CLINICAL SIGNIFICANCE

The occlusal veneers with different preparation designs, including type O, OF, POF and POFP veneers, show higher fracture resistances than traditional full coverage crowns that considerably exceed the normal biting forces. Therefore, these represent conservative alternatives to crown restorations and present a viable treatment for restoring severely worn teeth.

The biomechanics of the umbilical cord Wharton Jelly: Roles in hemodynamic proficiency and resistance to compression

The umbilical cord is a complex structure containing three vessels, one straight vein and two coiled arteries, encased by the Wharton Jelly (WJ) a spongy structure made of collagen and hydrated macromolecules. Fetal blood reaches the placenta through the arteries and flows back to the fetus through the vein. The role of the WJ in maintaining cord circulation proficiency and the ultimate reason for arterial coiling still lack of reasonable mechanistic interpretations. We performed biaxial tension tests and evidenced significant differences in the mechanical properties of the core and peripheral WJ. The core region, located between the arteries and the vein, resulted rather stiffer close to the fetus. Finite element modelling and optimization based inverse method were used to create 2D and 3D models of the cord and to simulate stress distribution in different hemodynamic conditions, compressive loads and arterial coiling. We recorded a facilitated stress transmission from the arteries to the vein through the soft core of periplacental WJ. This condition generates a pressure gradient that boosts the venous backflow circulation towards the fetus. Peripheral WJ allows arteries to act as pressure buffering chambers during the cardiac diastole and helps to dissipate compressive forces away from vessels. Altered WJ biomechanics may represent the structural basis of cord vulnerability in many high-risk clinical conditions.