ABSTRACT
The abrasion response of cross sectional areas of enamel was studied by sliding a rounded diamond conical nano-indenter tip across the surface. The nano-indenter tip (radius approximately 1,200 nm) was scanned over a specific squared area with a load of 400 microN. Two different environments were chosen: Hank's balanced salt solution (HBSS) and atmospheric laboratory condition. SEM (Scanning Electron Microscopy) and AFM (Atomic Force Microscopy) were used to characterize the final abraded areas. In addition, single scratches with linear incremented load were performed. The normal load and displacement data were utilized in a complementary manner to support the proposed deformation mechanisms. Greater orientation dependence for the case of the single scratches in relation to the abrasion tests was found. The latter results are discussed in terms of plastic deformation effects. The abrasion mechanisms were found to be the same for both wet and dry measurements and similar to that described in a previous study (Guidoni et al., Wear 266:60-68, 2009; Guidoni, Nano-scale mechanical and tribological properties of mineralized tissues. PhD. Montan University Leoben, Leoben, Austria, 2008). However, scratch deformation under fluid measurements shows greater recovery effects and abrasion resistance.
Subject(s)
Dental Enamel/chemistry , Dental Enamel/drug effects , Nanostructures/chemistry , Stress, Mechanical , Tooth Abrasion , Water/pharmacology , Biocompatible Materials/chemistry , Child , Dental Stress Analysis , Elasticity , Equipment Failure Analysis , Friction , Hardness , Humans , Male , Materials Testing , Microscopy, Atomic Force , Microscopy, Electron, Scanning , Pliability , Surface Properties , Tooth Abrasion/etiology , Tooth Abrasion/pathologyABSTRACT
Flexural strength distributions of standard viscosity and low viscosity bone cements based on Polymethylmethacrylate were obtained by testing the materials in four-point bending according to the ISO 5833 protocol. The cement dough was poured into a mold and was allowed to cure at atmospheric pressure. An additional set of specimens of the standard viscosity cement was prepared under pressure while the cement dough was polymerizing in the mold. Following preparation, test specimens were stored in a 37 degrees C water bath for 48 h. The two-parameter Weibull model, which was used to analyze the data, gave a good representation of the fracture loads distribution. Low viscosity cement displayed a higher mean flexural strength and a slightly lower data scatter than standard viscosity cement. The mean flexural strength of the cement increased about 60% when pressure was applied compared with the same material cured at atmospheric pressure. The Weibull modulus, m, characterizes the scattering in the measured values of strength. For the cement prepared at atmospheric pressure the m value was 8.6 while for the cement cured under pressure it was 12.3, which reveals a reduction in the data scatter. The cement tested in four-point bending displayed lower mean flexural strength compared with the cement tested in three-point bending. The influence of the load type upon the mean flexural strength was satisfactory predicted by Weibull model.
