Biomedical subjects
Publications and source records attributed to H M Rootare.
The relationship between the wear of three composite resins and the hardness of the abrasive was studied by a two-body abrasion test. The wear rates of the composites increased linearly with abrasive hardness from 530 to 2080 KHN. Measurement of the slope of the wear rate versus abrasive hardness over this range provided a sensitive method for ranking the composites.
Synthetic HAP made in the laboratory as 'synthetic bone' may be a possible replacement or repair material, since the mineral phase of dental hard tissue and bone is essentially hydroxyapatite in form. Hydroxyapatite or modified compositions of HAP appear to offer possibilities as a substitute for the original material provided by nature. A high surface area (70.4 m2/g) commercially available hydroxyapatite (HAP) of poor crystallinity was converted to a highly crystalline HAP through sintering at 1200 degrees C in an atmosphere of steam and nitrogen. Compacts were made of the powdered HAP from 500 to 25,000 psi and sintered under the same conditions. The changes in the resulting pore volumes, pore sizes, pore size distributions, densities, and surface areas of the sintered compacts were determined by mercury porosimetry. A 20-fold reduction in open pore volume for sintered compacts was observed. For compacts made at pressures above 5000 psi, the reduction in open pore volume was compensated for by the formation of closed pore volume. The sintering mechanism was attributed mainly to neck formation, growth between particles, diffusion, and plastic deformation.
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The free energies of immersion for three hydroxyapatite samples of different origin and method of preparation were determined from water adsorption isotherms at 20 and 25 C. The free energies varied with the temperature of the isotherm, changing linearly with the outgassing temperature in the range of 20 and 300 C. The samples outgassed at 300 C yielded free energy of immersion values of 365, 432, and 476 ergs/cm2 for the VIC-, NBS-, and TVA-HAP, respectively. Work of adhesion and work of spreading were calculated for water on these samples.
Water vapor adsorption isotherms were determined gravimetrically on three hydroxyapatite sampel differing in preparation and with surface areas of 70.4, 22.5, and 3.0 M2/gm, respectively. Heats of adsorption for the first layer of water were found to be 13.3, 13.2, and 13.9 kcal/mole on these hydroxypatites. From repeated thermal desorption and adsorption cycles of water, stepwise adsorption was observed which diminished with each outgassing cycle until it disappeared after the fourth cycle. Cross-sectional area of adsorbed water molecule on hydroxyapatite surface was estimated at 11.5 A2. Standard free energies, isosteric heats, changes in enthalpy, and entropy of adsorption of water on HAP samples outgassed at 300 C were determined.
Pure gutta-percha was heat-treated in a differential thermal analyzer. The high melting form crystallized on cooling when gutta-percha was heated to 70 C or less. Above 74 C, crystallization into the low melting form predominated. Either polymorph can be selectively crystallized by control of the heat-treatment temperature before cooling.
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A sintered hydroxyapatite (HAP) ceramic for use in wear studies was prepared from a commercial tricalcium phosphate. The sintered HAP had physical properties close to those of human enamel. The coefficient of friction and wear of the sintered HAP ceramic as characterized by tangential force, track width, and surface failure data, approximated those of human enamel.