Enamel Microcracks Induced by Simulated Occlusal Wear in Mature, Immature, and Deciduous Teeth

Enamel wear, which is inevitable due to the process of mastication, is a process in which the microcracking of enamel occurs due to the surface contacting very small hard particles. When these particles slide on enamel, a combined process of microcutting and microcracking in the surface and subsurface of the enamel takes place. The aim of this study was to detect microscopic differences in the microcrack behavior by subjecting enamel specimens derived from different age groups (immature open-apex premolars, mature closed-apex premolars, and deciduous molars) to cycles of simulated impact and sliding wear testing under controlled conditions. Our findings indicated that the characteristics of the microcracks, including the length, depth, count, orientation, and relation to microstructures differed among the study groups. The differences between the surface and subsurface microcrack characteristics were most notable in the enamel of deciduous molars followed by immature premolars and mature premolars whereby deciduous enamel suffered numerous, extensive, and branched microcracks. Within the limitations of this study, it was concluded that enamel surface and subsurface microcracks characteristics are dependent on the posteruptive age with deciduous enamel being the least resistant to wear based on the microcrack behavior as compared to permanent enamel.

Wear-Resistant Properties of TiC/Fe Ceramic Composite Coating on Steel Plate via Combustion Synthesis

The highly dense TiC/Fe ceramic coating was fabricated on Q235 steel surface by self- propagating high-temperature synthesis combined with pseudo hot iso-static pressing. The wear-resistant properties were examined by means of ball-on-disk contact wear test. The microstructure of TiC/Fe cermets coating was investigated. The results show that TiC/Fe cermets coating has an excellent wear-resistant property. There is little mass loss after 1200s under 30N loading under the condition of dry sliding wear testing. The major wear mechanisms are described by the following stages: sticking friction, grain abrasion and stripping of hard phase.

Investigation of the Nanomechanical and Tribological Properties of Tooth-Fillings Materials

This study utilizes novel characterization techniques nanoindentation and nanoscratch for testing both the human enamel and dentine together with two biocompatible dental filling materials; epoxy nanocomposite and silver amalgam. Nanoindentation tests were performed to obtain accurate hardness and reduced modulus values for the enamel, dentin and two different fillers. We utilized Nano-scratch tests to obtain critical load in scratch test and resistance to sliding wear. Testing showed the silver amalgam filling has a higher modulus of elasticity, hardness and wear resistance compared to the nanocomposite. The novel mechanical characterization techniques utilized might assist in better understanding the mechanical behavior of the dental fillers and thus facilitate the design of robust fillers with excellent mechanical properties.

Wear Resistance of Super Alloys at Elevated Temperatures

This paper provides the results of an extensive sliding wear testing program to evaluate wear resistance of several material couples currently used for high temperature applications such as ground based gas turbines and aircraft engines. Nickel and cobalt base superalloys and iron base stainless steels were tested in different combinations, and their wear rates compared to determine optimal wear resistance. The results show that an alloy’s wear resistance is highly dependent on operating temperature and its coupling with another material. The influences of friction, hardness, and oxide formation on the alloy’s wear resistance are also presented and discussed.