Polymerization Kinetics Stability, Volumetric Changes, Apatite Precipitation, Strontium Release and Fatigue of Novel Bone Composites for Vertebroplasty

Purpose: The aim was to determine effects of diluent monomer and monocalcium phosphate monohydrate (MCPM) on polymerization kinetics and volumetric stability, apatite precipitation, strontium release and fatigue of novel dual-paste composites for vertebroplasty. / Materials and methods: Polypropylene (PPGDMA) or triethylene (TEGDMA) glycol dimethacrylates (25 wt%) diluents were combined with urethane dimethacrylate (70 wt%) and hydroxyethyl methacrylate (5 wt%). 70 wt% filler containing glass particles, glass fibers (20 wt%) and polylysine (5 wt%) was added. Benzoyl peroxide and MCPM (10 or 20 wt%) or N-tolyglycine glycidyl methacrylate and tristrontium phosphate (15 wt%) were included to give initiator or activator pastes. Commercial PMMA (Simplex) and bone composite (Cortoss) were used for comparison. ATR-FTIR was used to determine thermal activated polymerization kinetics of initiator pastes at 50-80 °C. Paste stability, following storage at 4-37 °C, was assessed visually or through mixed paste polymerization kinetics at 25 °C. Polymerization shrinkage and heat generation were calculated from final monomer conversions. Subsequent expansion and surface apatite precipitation in simulated body fluid (SBF) were assessed gravimetrically and via SEM. Strontium release into water was assessed using ICP-MS. Biaxial flexural strength (BFS) and fatigue properties were determined at 37 °C after 4 weeks in SBF. / Results: Polymerization profiles all exhibited an inhibition time before polymerization as predicted by free radical polymerization mechanisms. Initiator paste inhibition times and maximum reaction rates were described well by Arrhenius plots. Plot extrapolation, however, underestimated lower temperature paste stability. Replacement of TEGDMA by PPGDMA, enhanced paste stability, final monomer conversion, water-sorption induced expansion and strontium release but reduced polymerisation shrinkage and heat generation. Increasing MCPM level enhanced volume expansion, surface apatite precipitation and strontium release. Although the experimental composite flexural strengths were lower compared to those of commercially available Simplex, the extrapolated low load fatigue lives of all materials were comparable. / Conclusions: Increased inhibition times at high temperature give longer predicted shelf-life whilst stability of mixed paste inhibition times is important for consistent clinical application. Increased volumetric stability, strontium release and apatite formation should encourage bone integration. Replacing TEGDMA by PPGDMA and increasing MCPM could therefore increase suitability of the above novel bone composites for vertebroplasty. Long fatigue lives of the composites may also ensure long-term durability of the materials

SPACE CLOSURE IN BIALVEOLAR DENTAL PROTRUSION CASES - A COMPARATIVE COMBINATION METHOD

Objective: To measure and compare the amount, rate and anchor loss after the en masse retraction of all anteriors with titanium mini-implant anchorage and conventional molar anchorage.Methods: This comparative clinical study sample comprised 12 patients (10 females, 2 males; mean age between 16 and 22 years). The implants were placed in the maxillary and mandibular arches. Preretraction and post retraction lateral cephalograms were taken for measuring the amount, rate and anchor loss after the retraction.Results: Mean en masse retraction amounts, the rate of movement per month, and horizontal and vertical anchor loss at the maxillary implant site were 4.79 mm, 0.58 mm, 0 mm, and 0 mm, respectively. In the mandible, on implant sides were 4.66 mm, 0.56 mm, 0 mm, and 0 mm. Mean en masse retraction amounts, the rate of movement per month, and horizontal and vertical anchor loss at the maxillary conventional molar anchor side were 4.08 mm, 0.49 mm, 2.91 mm, and 1.66 mm. In the mandible, on conventional anchor sides were 3.54 mm, 0.48 mm, 3.12 mm, and 1.95 mm.Conclusion: En masse retraction had a faster rate of space closure with mini-implants as anchor units than the conventional molar anchorage preparation.Â

Small vessel disease disrupts EEG postural brain networks in 'unexplained dizziness in the elderly'

Objective: To examine the hypothesis that small vessel disease disrupts postural networks in older adults with unexplained dizziness in the elderly (UDE). / Methods: Simultaneous electroencephalography and postural sway measurements were undertaken in upright, eyes closed standing, and sitting postures (as baseline) in 19 younger adults, 33 older controls and 36 older patients with UDE. Older adults underwent magnetic resonance imaging to determine whole brain white matter hyperintensity volumes, a measure of small vessel disease. Linear regression was used to estimate the effect of instability on electroencephalographic power and connectivity. / Results: Ageing increased theta and alpha desynchronisation on standing. In older controls, delta and gamma power increased, and theta and alpha power reduced with instability. Dizzy older patients had higher white matter hyperintensity volumes and more theta desynchronisation during periods of instability. White matter hyperintensity volume and delta power during periods of instability were correlated, positively in controls but negatively in dizzy older patients. Delta power correlated with subjective dizziness and instability. / Conclusions: Neural resource demands of postural control increase with age, particularly in patients with UDE, driven by small vessel disease. / Significance: EEG correlates of postural control saturate in older adults with UDE, offering a neuro-physiological basis to this common syndrome

Perceived state of self during motion can differentially modulate numerical magnitude allocation.

Although a direct relationship between numerical-allocation and spatial-attention has been proposed, recent research suggests these processes are not directly coupled. In keeping with this, spatial attention shifts induced either via visual or vestibular motion can modulate numerical allocation in some circumstances but not in others. In addition to shifting spatial attention, visual or vestibular motion-paradigms also (i) elicit compensatory eye-movements which themselves can influence numerical-processing and (ii) alter the perceptual-state of-"self", inducing changes in bodily self-consciousness impacting upon cognitive mechanisms. Thus, the precise mechanism by which motion modulates numerical-allocation remains unknown. We sought to investigate the influence that different perceptual experiences of motion have upon numerical magnitude allocation whilst controlling for both eye-movements and task-related effects. We first used optokinetic visual-motion stimulation (OKS) to elicit the perceptual experience of either "visual world" or "self"-motion during which eye movements were identical. In a second experiment we used a vestibular protocol examining the effects of perceived and subliminal angular rotations in darkness, which also provoked identical eye movements. We observed that during the perceptual experience of "visual-world" motion, rightward OKS biased judgments towards smaller numbers, whereas leftward OKS biased judgments towards larger numbers. During the perceptual experience of "self-motion", judgments were biased towards larger numbers irrespective of the OKS direction. Contrastingly, vestibular motion perception was found not to modulate numerical magnitude allocation, nor was there any differential modulation when comparing "perceived" versus "subliminal" rotations. We provide a novel demonstration that magnitude-allocation can be differentially modulated by the perceptual state of-self during visual-motion. This article is protected by copyright. All rights reserved

Polymerization kinetics stability, volumetric changes, apatite precipitation, strontium release and fatigue of novel bone composites for vertebroplasty

PURPOSE: The aim was to determine effects of diluent monomer and monocalcium phosphate monohydrate (MCPM) on polymerization kinetics and volumetric stability, apatite precipitation, strontium release and fatigue of novel dual-paste composites for vertebroplasty. MATERIALS AND METHODS: Polypropylene (PPGDMA) or triethylene (TEGDMA) glycol dimethacrylates (25 wt%) diluents were combined with urethane dimethacrylate (70 wt%) and hydroxyethyl methacrylate (5 wt%). 70 wt% filler containing glass particles, glass fibers (20 wt%) and polylysine (5 wt%) was added. Benzoyl peroxide and MCPM (10 or 20 wt%) or N-tolyglycine glycidyl methacrylate and tristrontium phosphate (15 wt%) were included to give initiator or activator pastes. Commercial PMMA (Simplex) and bone composite (Cortoss) were used for comparison. ATR-FTIR was used to determine thermal activated polymerization kinetics of initiator pastes at 50-80°C. Paste stability, following storage at 4-37°C, was assessed visually or through mixed paste polymerization kinetics at 25°C. Polymerization shrinkage and heat generation were calculated from final monomer conversions. Subsequent expansion and surface apatite precipitation in simulated body fluid (SBF) were assessed gravimetrically and via SEM. Strontium release into water was assessed using ICP-MS. Biaxial flexural strength (BFS) and fatigue properties were determined at 37°C after 4 weeks in SBF. RESULTS: Polymerization profiles all exhibited an inhibition time before polymerization as predicted by free radical polymerization mechanisms. Initiator paste inhibition times and maximum reaction rates were described well by Arrhenius plots. Plot extrapolation, however, underestimated lower temperature paste stability. Replacement of TEGDMA by PPGDMA, enhanced paste stability, final monomer conversion, water-sorption induced expansion and strontium release but reduced polymerization shrinkage and heat generation. Increasing MCPM level enhanced volume expansion, surface apatite precipitation and strontium release. Although the experimental composite flexural strengths were lower compared to those of commercially available Simplex, the extrapolated low load fatigue lives of all materials were comparable. CONCLUSIONS: Increased inhibition times at high temperature give longer predicted shelf-life whilst stability of mixed paste inhibition times is important for consistent clinical application. Increased volumetric stability, strontium release and apatite formation should encourage bone integration. Replacing TEGDMA by PPGDMA and increasing MCPM could therefore increase suitability of the above novel bone composites for vertebroplasty. Long fatigue lives of the composites may also ensure long-term durability of the materials

Applications of neuromodulation to explore vestibular cortical processing; new insights into the effects of direct current cortical modulation upon pursuit, VOR and VOR suppression

This is an accepted manuscript of an article published by IOS Press in Journal of Vestibular Research in 2014, available online: https://doi.org/10.3233/VES-140530 The accepted version of the publication may differ from the final published version.Functional imaging, lesion studies and behavioural observations suggest that vestibular processing is lateralised to the non-dominant hemisphere. Moreover, disruption of interhemispheric balance via inhibition of left parietal cortex using transcranial direct current stimulation (tDCS) has been associated with an asymmetric suppression of the vestibulo-ocular reflex (VOR). However, the mechanism by which the VOR was modulated remains unknown. In this paper we review the literature on non-invasive brain stimulation techniques which have been used to probe vestibular function over the last decade. In addition, we investigate the mechanisms whereby tDCS may modulate VOR, e.g. by acting upon pursuit, VOR suppression mechanisms or direct VOR modulation. We applied bi-hemispheric parietal tDCS in 11 healthy subjects and only observed significant effects on VOR gain (tdcs * condition p=0.041) – namely a trend for VOR gain increase with right anodal/left cathodal stimulation, and a decrease with right cathodal/left anodal stimulation. Hence, we suggest that the modulation of the VOR observed both here and in previous reports, is directly caused by top-down cortical control of the VOR as a result of disruption to interhemispheric balance, likely parietal.This work was funded by the UK Medical Research Council (MR/J004685/1).Published versio

A brief review of the clinical anatomy of the vestibular-ocular connections—how much do we know?

This is an accepted manuscript of an article published by Springer Nature in Eye on 21/11/2014, available online: https://doi.org/10.1038/eye.2014.262 The accepted version of the publication may differ from the final published version.The basic connectivity from the vestibular labyrinth to the eye muscles (vestibular ocular reflex, VOR) has been elucidated in the past decade, and we summarise this in graphic format. We also review the concept of ‘velocity storage’, a brainstem integrator that prolongs vestibular responses. Finally, we present new discoveries of how complex visual stimuli, such as binocular rivalry, influence VOR processing. In contrast to the basic brainstem circuits, cortical vestibular circuits are far from being understood, but parietal-vestibular nuclei projections are likely to be involved

A link between frontal white matter integrity and dizziness in cerebral small vessel disease

One in three older people (>60 years) complain of dizziness which often remains unexplained despite specialist assessment. We investigated if dizziness was associated with vascular injury to white matter tracts relevant to balance or vestibular self-motion perception in sporadic cerebral small vessel disease (age-related microangiopathy). We prospectively recruited 38 vestibular clinic patients with idiopathic (unexplained) dizziness and 36 age-matched asymptomatic controls who underwent clinical, cognitive, balance, gait and vestibular assessments, and structural and diffusion brain MRI. Patients had more vascular risk factors, worse balance, worse executive cognitive function, and worse ankle vibration thresholds in association with greater white matter hyperintensity in frontal deep white matter, and lower fractional anisotropy in the genu of the corpus callosum and the right inferior longitudinal fasciculus. A large bihemispheric white matter network had less structural connectivity in patients. Reflex and perceptual vestibular function was similar in patients and controls. Our results suggest cerebral small vessel disease is involved in the genesis of dizziness through its effect on balance

Improving the melting performance in a triple-pipe latent heat storage system using hemispherical and quarter-spherical fins with a staggered arrangement

Data availability statement: The original contributions presented in the study are included in the article/Supplementary Material; further inquiries can be directed to the corresponding author.This study aims to evaluate the melting characteristics of a phase change material (PCM) in a latent heat storage system equipped with hemispherical and quarter-spherical fins. A vertical triple-pipe heat exchanger is used as the PCM-based heat storage unit to improve the melting performance compared with a double-pipe system. Furthermore, the fins are arranged in inline and staggered configurations to improve heat transfer performance. For the quarter-spherical fins, both upward and downward directions are examined. The results of the system equipped with novel fins are compared with those without fins. Moreover, a fin is added to the heat exchanger’s base to compensate for the natural convection effect at the bottom of the heat exchanger. Considering similar fin volumes, the results show that the system equipped with four hemispherical fins on the side walls and an added fin on the bottom wall has the best performance compared with the other cases with hemispherical fins. The staggered arrangement of the fins results in a higher heat transfer rate. The downward quarter-spherical fins with a staggered configuration show the highest performance among all the studied cases. Compared with the case without fins, the heat storage rate improves by almost 78% (from 35.6 to 63.5 W), reducing the melting time by 45%.King Khalid University Deanship of Scientific Research Large Groups [Project under grant number (RGP. 2/142/43)]; Brunel University London