Hillar M. Rootare

Vapor Phase Adsorption of Water on Hydroxyapatite

Water vapor adsorption isotherms were determined gravimetrically on three hydroxyapatite samples differing in preparation and with surface areas of 70.4, 22.5, and 3.0 M 2/gm, respectively. Heats of adsorption for the first layer of water were found to be 13.3, 13.2, and 13.9 kcallmole on these hydroxyapatites. 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 Å2. Standard free energies, isosteric heats, changes in enthalpy, and entropy of adsorption of water on HAP samples outgassed at 300 C were determined.

Characterization of the compaction and sintering of hydroxyapatite powders by mercury porosimetry

Abstract Mercury porosimetry was used to measure the bulk and real densities, pore volumes and pore size distributions of compacts of hydroxyapatite before and after sintering. The hydroxyapatites were prepared by two different methods and had widely different surface areas. The properties were determined as a function of compaction force and sintering temperature. Densities from porosimetry were in good agreement with geometric densities. A linear relation was found between pore volume and log of the applied force. There was also a linear relationship between bulk volume and pore volume of the compacts. A bimodal pore size distribution was observed for the high surface area hydroxyapatite which disappeared with increasing compaction loads. Pressurization and depressurization measurements indicated that the main body of the pores in the compacts attained a more regular “spherical” shape with increasing compaction force than did the “necks”. The pore volume, percent porosity, and bulk density of the compacts remained unchanged up to 600°C; however, the surface area and the average pore diameter changed at 400°C. The distribution of pores became more uniform, narrower in distribution, and larger in size as the sintering temperature increased. The change in pore area with pore volume indicated that two mechanisms were operating during sintering. The pore area proved to be the most sensitive indicator of changes during sintering.

Sintered Hydroxyapatite Ceramic for Wear Studies

A sintered hydroxyapatite (HAP) ceramic for use in wear studies was prepared from a commerical 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.

Wear of Composites by Abrasives of Varying Hardness

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.

Thermal analysis of experimental and commercial gutta-percha

Abstract Differential thermal analysis and penetration analysis were used to study the effects of heat treatment and plasticizers on the structure and resistance to penetration of commercial and experimental gutta-percha formulations. Penetration of commercial cones was related to the amount of gb and y crystalline polymorphs of gutta-percha and could be changed by heat treatment. The addition of waxes to experimental formulations of gutta-percha with barium sulfate and zinc oxide lowered the resistanceto penetration more than the addition of resins.

Determination of Phase Transitions in Gutta-Percha by Differential Thermal Analysis

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.

A computer program for pore volume and pore area distribution calculations from mercury porosimeter data on particulate or porous materials

Abstract A computer program in Fortran IV is described for rapidly determining pore size and pore area distribution calculations from the high pressure mercury porosimeter data. The listing of the program is reproduced as well as the printout of the sample data. Illustrations of the graphic representation of the processed data are given for two samples of fine crystalline precipitated hydroxyapatite and one carbon black—Spheron 6.

Free Surface Energy Change for Water Adsorbed on Hydroxyapatite

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.

Heats of Solution of Apatites, Human Enamel and Dicalcium-Phosphate in Dilute Hydrochloric Acid

The solubility of hydroxyapatite and dental enamel in water and various buffered solutions has been studied extensively by many investigators and only a few will be listed in the references1–12. Heats of wetting and heats of immersion have been measured for water on synthetic hydroxyapatite and ground tooth structure by Tsuchitani, et al.13,14 and Brauer and Huget15,16. The latter authors17,18, as did Pitt19, studied the degree of surface modification produced by various ions and functional groups in an aqueous environment by measuring the heats of immersion.

Thermal Analysis of Dental Gutta Percha

A variety of materials have been used in the endodontic practice of dentistry as root canal filling materials.1–3 Only two, gutta-percha and silver points have survived the test of time. The introduction of gutta-percha to dentistry dates back to the middle of the nineteenth century,4 when Dr. Jose D’Almeida5 brought samples of gutta-percha to London’s Royal Asiatic Society in 1843. However, until recently very little work has been done to evaluate the physical and mechanical properties of gutta-percha as used in dentistry.6–9