Radmila Jančić Heinemann

Influence of pastes containing casein phosphopeptide-amorphous calcium phosphate on surface of demineralized enamel.

Purpose The purpose of the study was to evaluate the surface characteristics of demineralized enamel after treatment with pastes containing casein phosphopeptide–amorphous calcium phosphate (CPP-ACP) or casein phosphopeptide–amorphous calcium fluoride phosphate (CPP-ACFP) and to compare their efficacy with that of 0.05% NaF. Methods Following formation of the artificial carious lesion, enamel slabs were divided into 4 groups (CPP-ACP, CPP-ACFP, 0.05% NaF and control) and submitted to a chemical caries model. Remineralization potential was examined using scanning electron microscope, energy-dispersive spectroscopy (EDS) and microhardness test. Scanning electron microphotographs were analyzed for area, minimal, maximal and mean diameter, perimeter, roundness and number of enamel defects and percentage of tooth surface affected by defects. Results Treatment with 0.05% NaF partly reduced the appearance of enamel defects when compared with irregular demineralized enamel. Treatment with CPP-ACP or CPP-ACFP resulted in occlusion of defects which produced more flattened enamel surface. Image analysis revealed reduction of the dimensions of the defects in the 3 experimental groups. Treatment with CPP-ACFP decreased the number of enamel defects when compared with demineralized enamel. The EDS analysis did not show differences in Ca/O, P/O and Ca/P ratios between the groups (P>0.05). Microhardness test revealed significant effects of CPP-ACP and CPP-ACFP (P<0.05). Conclusions Pastes containing CPP-ACP or CPP-ACFP showed potential to remineralize enamel surface lesions.

Optimizing the thermal gradient and the pulling speed in a thermoplastic pultrusion process of PET/E glass fibers using finite element method

A thermoplastic pultrusion process was examined using commercial fiber roving of PET/E glass, to determine the optimum pulling speed and optimal zonal temperatures. Finite element analysis predicted heat transfer through the commingled fibers and air in the pultrusion die. The cross-section of obtained rods was examined, and image analysis was carried out to obtain information about the degree of fiber impregnation, number of voids and uniformity of fiber distribution. Optimizing the temperature field for the pultrusion of poly (ethylene terephthalate) is of significant importance. The pulling speed has the same importance. These two parameters are closely related as evidenced by the analysis of images.

The influence of alumina particle modification on the adhesion of the polyacrylate matrix composite films and the metal substrate

ABSTRACT Adhesion behavior between the composite films, consisting of UV cured Bis-GMA (Bisphenol A glycidylmethacrylate)/TEGDMA (triethylene glycol dimethacrylate) as a matrix and the ferrous oxide doped alumina particles, Al2O3 Fe, modified with 3-aminopropyl)tri – methoxysilane (AM) and methyl esters of linseed oil fatty acids (biodiesel – BD) used as a reinforcement, and metallic surface was investigated in this study. Al2O3 Fe-BD particles showed pronounced hydrophobicity and hydrolytic stability of alumina surface. Adhesive and mechanical properties of prepared composites, containing 0.5, 1.5 and 3 wt. % of surface modified Al2O3 Fe-AM and Al2O3 Fe-BD particles, were compared to the neat polymer matrix. Adhesion parameter was evaluated using the micro hardness testing method. The comparison of determined contact angle with adhesive parameter, obtained from micro hardness measurements, was discussed in relation to structural effect of reinforcement used.

Numerical simulation of temperature field in the vertical Bridgman method crystal growth

The mathematical model for heat transfer during the Bridgeman crystal growth, using the finite element method and the obtained result аre presented. Some modifications to the method were introduced in order to incorporate the data obtained experimentally. Solving the model enabled comparison of the experimental and numerical data and to obtain sufficient accuracy. The model was used to calculate the temperature gradient in the sample and the calculated gradient was in accordance with the observed crystal growth regime.