Influence of acid washing on the surface morphology of ionomer glasses and handling properties of glass ionomer cements.

Acid washing is known to influence the handling properties of ionomer glasses used in glass ionomer cements due to the production of an ion depleted-zone on the surface of the glass particles. The influence of acid washing on the particle size distribution and surface area of four glasses was examined by scanning electron microscopy (SEM), particle size analysis (PSA) and accelerated surface area porosimetry (ASAP) and the working and setting times of cements, produced from the glasses, correlated to changes in surface morphology. A linear relationship was found between the specific surface area of acid-washed SiO(2)-Al(2)O(3)-XF(2)-P(2)O(5) glasses (X being either calcium or strontium) and their cement working and setting times. These changes directly correlated with increases in the mesopore volume. However, the influence of acid washing on the surface morphology was also found to be glass composition-dependent with the addition of sodium into the glass network resulting in no significant change in the surface area or mesopore volume despite changes in the working and setting time. Through examination of the influence of acid washing and glass composition on the specific surface area improvements in the control of the working and setting times of glass ionomer cements may be achieved.

The influence of capsule geometry and cement formulation on the apparent viscosity of dental cements.

OBJECTIVES: This work examines the influence of specific aspects of capsule design and cement formulation on the handling properties of the extruded glass polyalkenoate cement (GPC) pastes. METHODS: A commercial metal reinforced GPC, HiDense, and experimental GPCs were extruded using a tensometer at loads and rates maintained within end-user limits and the apparent viscosity of the cement paste was determined by applying Poiseuille's law. The influence of the extrusion procedure (mixing time and ram speed), capillary geometry (length and diameter) and cement composition (powder: liquid (P:L) ratio, tartaric acid content and poly(acrylic acid) molar mass) on the apparent viscosity of the cement paste was evaluated. RESULTS: The examined GPCs behaved as non-Newtonian, pseudoplastic materials and exhibited a yield stress. Variation of the geometry of the capsule capillary resulted in the apparent viscosity of HiDense increasing by 7% as the length increased from 5 to 15mm whilst halving the capillary diameter from 2 to 1mm resulted in a 63% decrease in the apparent viscosity and a 600% increase in the extrusion load. The apparent viscosity of the experimental GPCs was increased by an increase in the P:L ratio and, in general, by the PAA molar mass, whilst the concentration-dependent effect of (+)-tartaric acid (TAA) indicates a working time dependence on TAA content. CONCLUSIONS: Using this approach optimisation of the rheological properties can be achieved by manipulation of the capsule design and cement formulation due to the dependency of the apparent viscosity on the capillary diameter, TAA content, P:L ratio and poly(acrylic acid) molar mass.

A histologic study of retrodiscal tissues of the human temporomandibular joint in the open and closed position.

Specialized roles for the different components of the retrodiscal tissues have been previously postulated. This study compared the histologic features of the retrodiscal tissues of temporomandibular joints, taken from human cadavers, in the open and closed position; it was concluded that the primary role of these components was to provide a volumetric compensatory mechanism for pressure equilibration. This mechanism was still active in joints that demonstrated disc displacement and degenerative changes. Elastin was found in the upper and lower strata of the retrodiscal tissues, as well as in the central zone. The concept of an elastic upper stratum that has a recoil mechanism to control disc movement was not supported by this study, as the upper stratum was folded on itself in the closed position and only became stretched near maximal opening.

Prevention of nosocomial respiratory syncytial virus infections through compliance with glove and gown isolation precautions.

To determine whether increased compliance with a policy of glove and gown isolation precautions could reduce the high rate of nosocomial respiratory syncytial virus (RSV) infection on an infant and toddler ward, we conducted a longitudinal intervention trial during three RSV seasons, from 1982 to 1985, with an intervention to increase compliance introduced midway through the second season. The risk of acquiring RSV infection in the hospital was adjusted for the intensity of nosocomial exposure to the virus by assigning each study week to one of five strata, defined by the proportion of hospital days on which virus was shed by children on the ward. Overall, 37 patients acquired nosocomial RSV infections during 7547 days at risk. The adjusted relative risk, comparing the infection rate in the period before the intervention (when compliance with isolation precautions was noted in only 38.5 percent of the observed patient contacts) with the infection rate in the postintervention period (when compliance more than doubled) was 2.9 (95 percent confidence interval, 1.5 to 5.7). Rates of nosocomial RSV infection increased linearly with increasing levels of exposure to patients shedding virus, but the rise in the infection rate with increasing exposure was less than one fourth as great (P less than 0.001) in the period after the intervention as it was before. We conclude that glove and gown precautions can substantially reduce the nosocomial transmission of RSV, particularly with increasing exposure to patients shedding the virus.

Interlibrary loan of audiovisual materials in the health sciences: how a system operates in New Jersey.

An audiovisual loan program developed by the library of the College of Medicine and Dentistry of New Jersey is described. This program, supported by an NLM grant, has circulated audiovisual software from CMDNJ to libraries since 1974. Project experiences and statistics reflect the great demand for audiovisuals by health science libraries and demonstrate that a borrowing system following the pattern of traditional interlibrary loan can operate effectively and efficiently to serve these needs.