Biomedical subjects
Publications and source records attributed to J R Heath.
This article considers first, factors influencing the need and demand for removable partial dentures (RPDs) and second, the particular requirements and problems of elderly patients related to such treatment.
Melatonin production in the pineal gland is high at night and low during the day. This rhythm reflects circadian changes in the activity of serotonin N-acetyltransferase [arylalkylamine N-acetyltransferase (AA-NAT); EC 2.3.1.87], the penultimate enzyme in melatonin synthesis. The rhythm is generated by an endogenous circadian clock. In the chick, a clock is located in the pinealocyte, which also contains two phototransduction systems. One controls melatonin production by adjusting the clock and the other acts distal to the clock, via cyclic AMP mechanisms, to switch melatonin synthesis on and off. Unlike the clock in these cells, cyclic AMP does not appear to regulate activity by altering AA-NAT mRNA levels. The major changes in AA-NAT mRNA levels induced by the clock seemed likely (but not certain) to generate comparable changes in AA-NAT protein levels and AA-NAT activity. Cyclic AMP might also regulate AA-NAT activity via changes in protein levels, or it might act via other mechanisms, including posttranslational changes affecting activity. We measured AA-NAT protein levels and enzyme activity in cultured chick pineal cells and found that they correlated well under all conditions. They rose and fell spontaneously with a circadian rhythm. They also rose in response to agents that increase cyclic AMP. They were raised by agents that increase cyclic AMP, such as forskolin, and lowered by agents that decrease cyclic AMP, such as light and norepinephrine. Thus, both the clock and cyclic AMP can control AA-NAT activity by altering the total amount of AA-NAT protein. Effects of proteosomal proteolysis inhibitors suggest that changes in AA-NAT protein levels, in turn, reflect changes in the rate at which the protein is destroyed by proteosomal proteolysis. It is likely that cyclic AMP-induced changes in AA-NAT protein levels mediate rapid changes in chick pineal AA-NAT activity. Our results indicate that light can rapidly regulate the abundance of a specific protein (AA-NAT) within a photoreceptive cell.
Nanoparticles deposited at the air-water interface are observed to form circular domains at low density and stripes at higher density. We interpret these patterns as equilibrium phenomena produced by a competition between an attraction and a longer-ranged repulsion. Computer simulations of a generic pair potential with attractive and repulsive parts of this kind, reproduce both the circular and stripe patterns. Such patterns have a potential use in nanoelectronic applications.
A 36-item questionnaire was used to investigate the stress perceived by students at Manchester Dental School to potential stressors, grouped under the headings of living accommodation, personal factors, educational environment, academic work and clinical factors. The stressors producing the highest ratings for perceived stress varied throughout the course but high values were allocated to examinations, fear of failing the course or year, shorter and fewer holidays than other university students and--for clinical students--approachability of staff and completing the required quantity and variety of work within a limited time. Female students experienced greater stress than their male counterparts. Since high levels of perceived stress can reduce student performance, dental schools should consider courses in stress management.
Ordered arrays, or superlattices, of metallic, insulating, or semiconducting quantum dots, represent an exciting new class of materials. These superlattices are often referred to as artificial solids, in which the nanocrystals take the place of atoms in traditional solids, and the packing arrangement of the nanocrystals determines the unit cell parameters of the superstructure. In this review, we discuss various approaches toward assembling nanocrystal superlattices and we discuss their physical properties.
This case report demonstrates a method of adding composite to a tooth to move a high survey line closer to the gingival margin. The purpose of this modification is to facilitate clasping.
The tensile and shear adhesive bond strengths of two addition cured silicones (Provil and Express) and a polyether (Impregum) impression material to brass, poly(methylmethacrylate) and visible light-cured (VLC) tray resin were determined. Adhesive application significantly increased the bond strength; Provil and Express adhered most strongly to brass; whilst the Impregum-VLC combination produced the strongest bond. Indeed, VLC resin generated greater adhesion than acrylic resin. Exchanging the adhesives specified for each silicone material generally resulted in higher bond strengths. No correlation was established between speed of separation of the test surfaces and bond strength. For optimum clinical performance, the impression material (adhesive) tray material giving the highest bond strength should be utilized.
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Since the government introduced the loan scheme for university students in 1990, it has become abundantly apparent that students are falling increasingly into debt. This paper describes the results of two studies undertaken by Manchester undergraduate dental students into the level and consequences of debt on dental students.
OBJECTIVES: This paper aims to identify which groups of elderly people living in residential institutions are in particular need of dental care and advice. Comparison of different types of residential institution allows identification of elderly in greatest need of dental assistance. METHODS: A postal survey of carers in 250 residential homes for elderly people in Manchester, UK, was undertaken to determine the frequency of dental visits, arrangements for dental care of the residents' teeth and denture cleansing and appliance-wearing patterns and, also, the carers' knowledge and practice of simple dental and oral maintenance procedures for residents. Comparisons were undertaken using the SPSS software package of: social service and private homes, large and small homes, homes where regular visits were undertaken and those not regularly visited, and also homes which maintained records of their clients' dental state with those which did not. RESULTS: Residents' oral health tended to be more at risk in smaller or privately managed homes, in those where no dentist visited regularly and where no records of dental care were kept. CONCLUSION: The dental profession needs to especially target homes where care is less well organized, not only to examine and treat residents, but also to instruct carers in simple mouth care techniques, in order that dental disability in an increasingly dentate population can be minimized.
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Chick pineal cells in dispersed cell culture display a persistent, photosensitive, circadian rhythm of melatonin production and release. Light pulses have at least two distinguishable effects on these cells, i.e., acute suppression of melatonin output and phase shifts (entrainment) of the underlying circadian pacemaker. Previous results linked calcium influx through voltage-sensitive calcium channels in the plasma membrane to acute regulation of melatonin synthesis but denied a role for such influx in entrainment. Those experiments did not, however, address the role of intracellular calcium metabolism. Here we describe the effects of pulses of caffeine, thapsigargin, and EGTA on the melatonin rhythm, and their interactions with the effects of light pulses. Caffeine had two distinguishable effects on these cells, acute enhancement of melatonin output (attributable to phosphodiesterase inhibition) and phase shifts of the circadian pacemaker with a light-like pattern (attributable to effects on intracellular calcium). Phase shifts induced by light and caffeine were not additive. Thapsigargin (which specifically blocks the pump that replenishes intracellular calcium stores, thereby increasing cytoplasmic calcium and depleting intracellular stores) had no phase-shifting effects by itself but reduced the size of the phase advances induced by caffeine or light. Low calcium solution acutely suppressed melatonin output without inducing phase shifts or affecting those induced by caffeine or light. However, addition of EGTA (which specifically chelates calcium, thereby lowering cytoplasmic calcium and depleting intracellular stores) did reduce the size of phase advances induced by caffeine or light, in normal medium or in low calcium solution, without inducing a phase shift by itself at that phase. Taken together, these results point toward a role for intracellular calcium fluxes in entrainment of the circadian pacemaker.
We report the first structural characterization of the triplet isomer of C6. Forty-one rovibrational/fine structure transitions in the nu 4(sigma u) antisymmetric stretch fundamental of the C6 cluster have been measured by diode laser absorption spectroscopy of a supersonic carbon cluster beam. The observed spectrum is characteristic of a centrosymmetric linear triplet state with cumulene-type bonding. The measured ground state rotational constant B0 = 0.048 479 (10)cm-1 and the effective bond length r(eff) = 1.2868 (1) angstroms are in good agreement with ab initio predictions for the linear triplet (3 sigma g-) state of C6.
This in vitro study investigates whether the surface smoothness of a finished composite resin is a function of the time at which it is trimmed. Five materials were studied. Visiodispers (VIS) is a sintered microfine, the remainder were hybrid formulations: Miradapt (MIR), Command Ultrafine (COM) and two experimental formulations-'EXP (2)' and 'EXP (15)'-with larger filler particles. All except MIR were photo-activated. Samples were placed and cured in holes machined in Perspex rods, ensuring excess of material and moulded to shape with cellulose acetate matrix strip. The strips were removed immediately after light curing and after 5 min in the case of MIR. Sample groups were finished after the following intervals: 10, 15, 30, 45s, 1, 2, 3, 4, 5 min, dry, and after 1 and 7 days in 37 degrees C water. The finishing procedure used plain-cut tungsten-carbide burs and coarse, medium and fine finishing discs, which were applied for standardized times, directions and pressures. Surface roughness was assessed visually and with a surface profilling instrument. COM and VIS materials significantly improved in surface finish when the procedure was delayed for 7 days. However, EXP (2), EXP (15) and MIR surface finishes were independent of finishing time. This may result from a rapid attainment of optimum surface hardness, whereas with COM and VIS incomplete curing leads to smearing of resins and filler across the surface.
The bases of occlusal rims and trial dentures should fit both the cast and the mouth accurately. The retention of shape and dimension of strips and sheets of grey and pink shellac, filled cold cure acrylic resin and wax were tested following moulding over stylised upper edentulous casts. The thermoplastic materials were softened over a flame or in a water bath. Specimens were prepared with and without folding along the long axes of the strips. The angles formed by the strips, the gap between the palate of the baseplates and casts and the linear dimension of the sheets were measured after moulding, after immersion in water at 37 and 45 degrees C and after 24 h at room temperature. The least angular change was shown by unfolded grey shellac, softened over a flame and moulded by finger pressure over an unwarmed cast, followed by folded specimens softened in water and moulded with the fingers over a prewarmed cast. The least gap developed beneath pink shellac softened in water and moulded by finger pressure over a warmed cast. The smallest dimensional change was shown by grey shellac softened in water and moulded by finger pressure over a warmed cast. Thus, optimally manipulated shellac materials exhibit less change after moulding than cold cure acrylic resin or modelling wax.
The bases of occlusal rims and trial dentures may sorb water during disinfection procedures, adjustment in the mouth and rinsing and cooling under running water. Such sorped water may adversely affect the properties of the baseplate materials. The room temperature water sorption of sheets of grey and pink shellac and cold cure acrylic resin was determined over 10 weeks by weighing. The Wallace surface hardness, linear dimension and transverse strength were also measured each week. Specimens were reweighed each week as they dried at room temperature. At the conclusion of the tests, the materials showed a change after soaking in weight, hardness, linear dimension and transverse strength, and change after drying relative to original mass for grey shellac of +1.5%, -48%, +0.7%, -58%, +0.33%; for pink shellac of +2.0%, -56%, +0.9%, -65%, +0.4%; and for acrylic resin of +1.2%, +10%, +0.4%, -30%, -2.1% respectively. The acrylic resin material was thus less affected by water sorption than the grey and pink shellac materials.
A postal survey of 250 residential homes in the Manchester area was undertaken in late spring 1991. The 152 questionnaires returned gave information about 3757 residents. In spite of an apparently adequate understanding of the importance of dental care, carers did not appear to provide as effective a service as they thought necessary. Ninety-one percent of carers realised dentures do not last indefinitely and 77.4% thought dentures should be checked every 2 years. Yet, in over 50% of homes, there was no provision for regular dental checks and in only 42.8% were residents seen every 2 years. It was pleasing to note that 70.7% of respondents welcomed the suggestion of a half-day educational workshop. Suggestions are made for assisting homes with areas of particular concern. The importance of good rapport with local dental surgeons is stressed.
The baseplate material that best reproduced the most grooves in a gypsum cast was filled cold cure acrylic resin, followed in turn by modelling wax, grey shellac and finally the pink shellac material. These latter three thermoplastic materials performed best when softened in a water bath and subsequently adapted to a prewarmed cast.