RESUMO
The development of dental implantology is based on the detailed study of the interaction of implants with the surrounding tissues and methods of osteogenesis stimulation around implants, which has been confirmed by the increasing number of scientific publications presenting the results of studies related to both the influence of the chemical composition of dental implant material as well as the method of its surface modification on the key operational characteristics of implants. The main materials for dental implant manufacturing are Ti and its alloys, stainless steels, Zr alloys (including ceramics based on ZrO2), and Ta and its alloys, as well as other materials (ceramics based on Al2O3, Si3N4, etc.). The review presents alloy systems recommended for use in clinical practice and describes their physical-mechanical and biochemical properties. However, when getting into the body, the implants are subjected to various kinds of mechanical influences, which are aggravated by the action of an aggressive biological environment (electrolyte with a lot of Cl- and H+); it can lead to the loss of osteointegration and to the appearance of the symptoms of the general intoxication of the organism because of the metal ions released from the implant surface into the biological tissues of the organism. Since the osteointegration and biocompatibility of implants depend primarily on the properties of their surface layer (it is the implant surface that makes contact with the tissues of the body), the surface modification of dental implants plays an important role, and all methods of surface modification can be divided into mechanical, physical, chemical, and biochemical methods (according to the main effect on the surface). This review discusses several techniques for modifying dental implant surfaces and provides evidence for their usefulness.
RESUMO
Ti-TiN-(Y,Ti,Al)N coatings with a three-layer architecture (adhesive Ti layer, transition TiN layer, and wear-resistant (Y,Ti,Al)N layer) were studied. When depositing coatings, three arc current values of the yttrium cathode were used: 65, 85, and 105 A. The yttrium contents in the coatings were 30, 47, and 63 at. %, respectively. When turning 1045 steel, a coating with 30 at. % yttrium showed better wear resistance compared to a commercial (Ti,Cr,Al)N coating. The coating with 63 at. % yttrium did not show an increase in wear resistance compared to the uncoated sample. Nanolayers with a high yttrium content are oxidized more actively compared to nanolayers with a high titanium content. Phase analysis shows partial retention of the initial phases (Y,Ti,Al)N and (Ti,Y,Al)N during the formation of the Y2O3 oxide phase in the outer layers of the coating and the presence of only the initial phases in the deep layers. Coating nanolayers with high contents of aluminum and yttrium lose their original structure to a greater extent during oxidation compared to layers without aluminum.
RESUMO
The article deals with the problems of cracking in the structure of multilayered coatings under the conditions of stochastic loading process. A mathematical model has been proposed in order to predict the crack propagation velocity in the coating while taking the influence of interlayer interfaces into account. A technique for calculating the probability density distribution of the coating fracture (failure rate) has been developed. The probability of a change in the crack growth direction is compared with the experimental data that were obtained as a result of the studies focused on the pattern of cracking in the Zr,Nb-(Zr,Nb)N-(Zr,Nb,Al)N and Ti-TiN-(Ti,Cr,Al)N coatings under the conditions of the real stochastic loading of cutting tools during the turning. The influence of the crystalline structure of the coating on the cracking pattern has been studied. The investigation has found the significant effect of the crystalline structure of the coating layers on the cracking pattern.
