The significance of pH for the inhibiting effect of phosphate buffer on the corrosion processes

Metals Biotribology and Oral Microbiota Biocorrosion Mechanisms

During the last decades, metal-based biomaterials have been extensively explored to be used as biocompatible metals for biomedical applications, owing to their superior mechanical properties and corrosion resistance. Consequently, for long-term implanted medical devices, to assure the biomaterials' reliability, functionality, and biocompatibility, studying the various bio-tribological damage mechanisms to obtain the optimum properties is one of the most important goals. In this review, we consider the most important metal-based biomaterials such as stainless steel, alloys of titanium (Ti), cobalt-chromium (Co-Cr), and Nichel-Titatium (Ni-Ti), as well Magnesium (Mg) alloys and with Tantalum (Ta), emphasizing their characteristics, clinical applications, and deterioration over time. The influence of metal elements on biological safety, including significant effects of metal-based biomaterials in dentistry were discussed, considering the perspectives of surface, mechanical properties, corrosion behaviors, including interactions, bio-mechanisms with tissues, and oral environments. In addition, the role of the oral microbiota was explored due to its role in this erosion condition, in order to further understand the mechanism of metal-based biomaterials implanted on the microflora balance of aerobic and anaerobic bacteria in an oral environment.

Influence of amalgams, bases, and varnish on seal composition at restoration tooth interfaces

Eighty extracted, noncarious premolars were restored with one of 20 different combinations of restorative materials: a high- or low-copper amalgam, unlined or lined with one of five bases, and varnished or unvarnished. The teeth were aged in 1% NaCl and after 3 months and 1 year the seal material deposited on the cut tooth cavity surface and the surface of the amalgam restoration was analyzed by use of energy dispersive x-ray analysis. Atomic weight percentages of marginal seal elements were statistically examined with ANOVA and Tukey's test with significance set at p < 0.05. The results indicated that only one type of seal was formed centered around tin. More marginal seal material was present in the 1-year specimens. Restoration materials used affected the deposition rate of marginal seal material. Low-copper amalgam-restored teeth formed more seal material with significantly greater amounts of chlorine and tin. Less marginal seal material was found in varnished cavities. A calcium hydroxide base produced a thick marginal seal with a significantly different composition of elements compared with the unlined and zinc-based specimens. Tin in Poly-F Plus polycarboxylate cement did not significantly increase the tin content of the marginal seal. Base materials can play a role in determining crevice pH. The findings have bearing on improved longevity of amalgam restorations.

Corrosion of dental amalgam and mercury vapor emission in vitro

Amalgam specimens were immersed for 30 days in 1) water, 2) 0.9% NaCl in water, 3) 0.9% NaCl and 10 mM phosphate buffer in water, and 4) 0.9% NaCl, 7.7 mM phosphate, and 6.1 mM citric acid in water. The solutions were stored in stoppered glass tubes. Hg-drops were immersed in solutions 1, 2, and 3. The concentration of mercury vapor in the air above the solutions was measured once a day. After 30 days the amounts of Cu, Zn, Hg, and Ag in the solutions were analyzed by atomic absorption spectrophotometry. The results showed that 0.9% NaCl alone or in combination with the additives increased the amounts of elements released into the solutions. The concentration of Hg0 in the glass tubes increased with the amount of Hg in the solutions, with the exception of solution No. 3, from which significantly less Hg0 evaporated. The results indicate that the composition of the saliva, oral hygiene and dietary factors may be determinants of Hg0 emission from amalgams in the oral cavity.