Mechanisms of Atomization from Rotary Dental Instruments and Its Mitigation.

Since the onset of coronavirus disease 2019, the potential risk of dental procedural generated spray emissions (including aerosols and splatters), for severe acute respiratory syndrome coronavirus 2 transmission, has challenged care providers and policy makers alike. New studies have described the production and dissemination of sprays during simulated dental procedures, but findings lack generalizability beyond their measurements setting. This study aims to describe the fundamental mechanisms associated with spray production from rotary dental instrumentation with particular focus on what are currently considered high-risk components-namely, the production of small droplets that may remain suspended in the room environment for extended periods and the dispersal of high-velocity droplets resulting in formites at distant surfaces. Procedural sprays were parametrically studied with variables including rotation speed, burr-to-tooth contact, and coolant premisting modified and visualized using high-speed imaging and broadband or monochromatic laser light-sheet illumination. Droplet velocities were estimated and probability density maps for all laser illuminated sprays generated. The impact of varying the coolant parameters on heating during instrumentation was considered. Complex structured sprays were produced by water-cooled rotary instruments, which, in the worst case of an air turbine, included droplet projection speeds in excess of 12 m/s and the formation of millions of small droplets that may remain suspended. Elimination of premisting (mixing of coolant water and air prior to burr contact) resulted in a significant reduction in small droplets, but radial atomization may still occur and is modified by burr-to-tooth contact. Spatial probability distribution mapping identified a threshold for rotation speeds for radial atomization between 80,000 and 100,000 rpm. In this operatory mode, cutting efficiency is reduced but sufficient coolant effectiveness appears to be maintained. Multiple mechanisms for atomization of fluids from rotatory instrumentation exist, but parameters can be controlled to modify key spray characteristics during the current crisis.

A review of gagging problems in dentistry: aetiology and classification.

Some people have a pronounced gag reflex that can be a severe limitation to their ability to accept dental care and the clinician's ability to provide it. It can compromise all aspects of dentistry, from diagnostic procedures to active treatment and can be distressing for all concerned. Many techniques have been described that attempt to overcome the problem. Dentists will undoubtedly see patients with gagging problems and knowledge of a variety of management strategies is necessary to aid the delivery of dental care. This first paper looks at the background to gagging problems and their classification and categorization prior to clinical treatment. The second article will look at the clinical assessment of the patient presenting for dental treatment with a history of gagging problems. It will also review methods used to manage patients with gagging reflexes during dental treatment.

A review of gagging problems in dentistry: 2. Clinical assessment and management.

A pronounced gag reflex can be a severe limitation to a patient's ability to accept dental care and for a clinician's ability to provide it. It can compromise all aspects of dentistry from diagnostic procedures to active treatment and can be distressing for all concerned. Many 'management' techniques have been described. This paper describes the different categories of treatment used to manage people with pronounced gag reflexes.

A review of gagging problems in dentistry: 2. Clinical assessment and management.

A pronounced gag reflex can be a severe limitation to a patient's ability to accept dental care and for a clinician's ability to provide it. It can compromise all aspects of dentistry from diagnostic procedures to active treatment and can be distressing for all concerned. Many 'management' techniques have been described. This paper describes the different categories of treatment used to manage people with pronounced gag reflexes.

A review of gagging problems in dentistry: I. Aetiology and classification.

Some people have a pronounced gag reflex that can be a severe limitation to their ability to accept dental care and the clinician's ability to provide it. It can compromise all aspects of dentistry, from diagnostic procedures to active treatment and can be distressing for all concerned. Many techniques have been described that attempt to overcome the problem. Dentists will undoubtedly see patients with gagging problems and knowledge of a variety of management strategies is necessary to aid the delivery of dental care. This first paper looks at the background to gagging problems and their classification and categorization prior to clinical treatment. The second article will look at the clinical assessment of the patient presenting for dental treatment with a history of gagging problems. It will also review methods used to manage patients with gagging reflexes during dental treatment.

Pursuit and optokinetic responses in latent/manifest latent nystagmus.

Abnormalities of foveal smooth pursuit and the monocular optokinetic response (OKR) have often been reported in subjects with latent nystagmus (LN) and manifest latent nystagmus (MLN). This abnormality typically takes the form of a monocular asymmetry with a deficit in the response to nasal-to-temporal (N-T) motion in the visual field. Previous studies have each presented different interpretations of this finding, depending on whether the characteristics of the spontaneous oscillation were considered when analyzing the measured eye movement response: one report has suggested that these asymmetries are in fact the cause of the spontaneous nystagmus. In this study, pursuit and OKRs were examined separately and, when working synergistically and antagonistically, to attempt to overcome this difficulty. Results suggest that pursuit and the OKR could be symmetric in LN and MLN for both binocular and monocular viewing, which leads to the conclusion that the asymmetric patterns of response often reported in LN/MLN result from either shifts in the zone of minimum-intensity oscillation or from non-stimulus-specific increases in the spontaneous nystagmus.

Monochromatic fundus photography of human albinos.

The clinical diagnosis of albinism can often be uncertain, particularly when one is confronted with blond patients with congenital nystagmus. Monochromatic fundus photography was carried out on 31 patients with congenital nystagmus to examine three retinal features: the macular pigment, foveal vasculature, and the retinal pigment epithelium. All subjects who were later classified as albinos did not exhibit any signs of macular pigmentation. Our results imply that monochromatic fundus photography can be a useful aid in the diagnosis of albinism.

The influence of nystagmoid oscillation on contrast sensitivity in normal observers.

Normal observers subjected to retinal image motion equivalent to that experienced by congenital nystagmats were found to display a contrast sensitivity function with characteristics similar to those shown by nystagmat observers. The amplitude, frequency and waveform (and hence foveation time) of nystagmic oscillation were varied, with alteration of the waveform producing the most significant effect on the contrast sensitivity function. The pseudocycloid waveform with the longest percentage foveation time per cycle was commensurate with the best visual resolution of medium-to-high spatial frequency targets. For all waveforms the length of the foveation period showed good correlation with visual resolution of the targets.

Blue light hazard and aniridia.

The fundi of three patients with aniridia were photographed with a 470 nm illuminating light source. No apparent change in contrast was observable throughout the macular region. This would suggest an absence of the macular pigment. The likelihood of aniridics being more susceptible than normal persons to blue light damage is discussed.

Face recognition in age related macular degeneration: perceived disability, measured disability, and performance with a bioptic device.

AIMS: (1) To explore the relation between performance on tasks of familiar face recognition (FFR) and face expression difference discrimination (FED) with both perceived disability in face recognition and clinical measures of visual function in subjects with age related macular degeneration (AMD). (2) To quantify the gain in performance for face recognition tasks when subjects use a bioptic telescopic low vision device. METHODS: 30 subjects with AMD (age range 66-90 years; visual acuity 0.4-1.4 logMAR) were recruited for the study. Perceived (self rated) disability in face recognition was assessed by an eight item questionnaire covering a range of issues relating to face recognition. Visual functions measured were distance visual acuity (ETDRS logMAR charts), continuous text reading acuity (MNRead charts), contrast sensitivity (Pelli-Robson chart), and colour vision (large panel D-15). In the FFR task, images of famous people had to be identified. FED was assessed by a forced choice test where subjects had to decide which one of four images showed a different facial expression. These tasks were repeated with subjects using a bioptic device. RESULTS: Overall perceived disability in face recognition did not correlate with performance on either task, although a specific item on difficulty recognising familiar faces did correlate with FFR (r = 0.49, p<0.05). FFR performance was most closely related to distance acuity (r = -0.69, p<0.001), while FED performance was most closely related to continuous text reading acuity (r = -0.79, p<0.001). In multiple regression, neither contrast sensitivity nor colour vision significantly increased the explained variance. When using a bioptic telescope, FFR performance improved in 86% of subjects (median gain = 49%; p<0.001), while FED performance increased in 79% of subjects (median gain = 50%; p<0.01). CONCLUSION: Distance and reading visual acuity are closely associated with measured task performance in FFR and FED. A bioptic low vision device can offer a significant improvement in performance for face recognition tasks, and may be useful in reducing the handicap associated with this disability. There is, however, little evidence for a correlation between self rated difficulty in face recognition and measured performance for either task. Further work is needed to explore the complex relation between the perception of disability and measured performance.

Congenital idiopathic nystagmus in identical twins.

Using an infrared recording system we examined the nystagmus waveforms of a pair of monozygotic twin girls and found them to be dissimilar. It is proposed that in view of the common mode of inheritance the differences are a result of environmental influences.

Amodiaquine as a prodrug: importance of metabolite(s) in the antimalarial effect of amodiaquine in humans.

Existing analytical methods for assaying the 4-aminoquinoline antimalarial amodiaquine in body fluids are nonspecific and obscure the fact that little or no amodiaquine is present in the blood of dosed persons. We have isolated four metabolites of amodiaquine. The two major metabolites have been identified; one is desethylamodiaquine, and the other has been tentatively identified on the basis of proton nuclear magnetic resonance spectroscopy as 2-hydroxydesethylamodiaquine. We developed a reverse-phase high-performance liquid chromatographic (HPLC) method that separates the two major metabolites from each other and from amodiaquine, allowing separate quantification. The impact of these findings on in vitro sensitivity testing and blood analysis of persons dosed with amodiaquine is discussed.

The elucidation and use of the effect of near fixation in congenital nystagmus.

It has frequently been reported that the spontaneous ocular oscillation in congenital nystagmats is less intense for near viewing than during distance fixation. The reason for this effect was sought, and the influences of monocular adduction, convergence and accommodation acting separately and synergistically were assessed. The frequent assumption that nystagmus intensity (amplitude and frequency) is determined by convergence angle (either symmetrical or asymmetrical) was confirmed, and it was found that binocular viewing was not necessary. An identical effect on nystagmus intensity could be created for distance fixation by the use of base-out prisms, and these were prescribed for constant wear in two congenital idiopathic nystagmats. Although nystagmus intensity was constantly reduced, no concomitant increase in binocular contrast sensitivity or Snellen visual acuity occurred.

Corneal topography of humans with congenital nystagmus.

The refractive status of individuals with congenital nystagmus (albinos and idiopaths) has been examined. Our results indicate that there is a greater than normal incidence of high spectacle astigmatism. This is predominantly with-the-rule and corneal in origin (anterior surface). Partial neutralization by the against-the-rule residual astigmatism is frequent and does not differ significantly from that reported for normal populations. Topographical studies of the anterior corneal surface revealed that there was no statistically significant difference in the mean shape factor values for the albino, idiopath and control populations. The aetiology of the astigmatism is discussed.

The inter-relationship between magnification, field of view and contrast reserve: the effect on reading performance.

For the reading task, contrast reserve is defined as the ratio of the letter contrast of the printed letters, to the reader's contrast threshold. Acuity reserve is the ratio of the print size used for the reading task, to the reader's visual acuity. The effects of low contrast reserve on reading performance were investigated at various magnifications, ranging from 3x to 7.5x, with the field of view systematically controlled. Eye movements were recorded whilst normally sighted subjects read using the magnifiers. It was shown that with adequate contrast reserve, increasing the field of view improved the reading rate because of the resulting increase in forward saccade length. Conversely, reducing the contrast reserve slowed the reading rate by decreasing the length of forward saccades and increasing the mean fixation duration, suggesting that the perceptual span is reduced at low contrast reserve. This study also shows that when the contrast reserve is low, providing magnification higher than that required for letter recognition (that is, increasing the acuity reserve) will not improve the reading performance. Furthermore, even when the contrast reserve was high, reading rates were lower for the magnifications of 5x and higher, because increases in saccade length do not match those of the retinal image size at these magnifications.

The limitations imposed on reading by low vision aids.

INTRODUCTION: The changes that occur in the reading eye movements of normally sighted readers were measured as they used hand magnifiers to identify how these devices contribute to the slow reading of visually-impaired patients. METHODS: Subjects inexperienced in magnifier use read texts containing two sizes of print, using hand magnifiers of two different powers, held at two different eye-to-magnifier distances. The effect of magnification (up to 13.5x) and field-of-view (FOV) (2-45 characters) could be assessed independently. RESULTS: Reading speed decreased with increasing magnification because the size of the saccades did not increase in proportion to the magnification: for a given level of magnification, decreasing the FOV and decreasing the viewing distance both reduce the size of the saccades even further. The overall reading speed is only slowed significantly when the FOV restriction is extreme (two characters' width). CONCLUSIONS: Two mechanisms seem to be used spontaneously by normally sighted readers to mitigate the limitation of reading speed created by the shortened saccades: head movement in the direction of reading and retinal image slip during fixation.

The influence of preexisting oscillations on the binocular optokinetic response.

Full-field binocular optokinetic responses were examined in patients with congenital nystagmus. If the stimulus moved in the same plane as the congenital nystagmus, a gaze-modulated response was recorded for both idiopathic and albino observers. When the congenital nystagmus was almost totally suppressed, neither a gaze-evoked nor a sawtooth response was seen. For stimulus movements in a plane orthogonal to the congenital nystagmus, normal sawtooth optokinetic responses were exhibited by both groups. Experimental evidence supports the hypothesis that the optokinetic response in the meridian of the spontaneous oscillation has been adapted.

A microassay system for measuring esterase activity and protein concentration in small samples and in high-pressure liquid chromatography eluate fractions.

A microtiter plate spectrophotometric system has been used together with the Bradford, Ellman, and van Asperen assays to measure protein concentration (to 0.5 microgram) and the activities of acetylcholinesterase (to 10(-3) units) and carboxylesterase (to 30 micrograms beta-naphthol reaction product) in small samples such as high-performance liquid chromatographic eluate fractions. For 100-microliter samples, at least 300 Ellman acetylcholinesterase or Bradford protein assays can be conducted and read in less than 30 min, and a like number of van Asperen nonspecific esterase assays (including 1-h incubation) run in less than 90 min. The eluate from a single 20-min high-performance liquid chromatographic run of a biological sample can be collected as up to 300 fractions directly into microtiter plate wells, and the three assays run on all fractions in less than 90 min.

Waveform characteristics in congenital nystagmus.

Using infra-red oculography, electro-oculography and fundus video-recordings, waveform characteristics (amplitude, frequency, waveform shape and foveation) were examined in over 150 individuals with congenital nystagmus. For many of the subjects the nystagmus exhibited marked variability in both space and time. The sources of this variability were explored and the state of attention of the observer was found to be a dominant factor. The waveform and precision of foveation were not found to be related to any one classification group (eg. albino or idiopathic).

Spectral sensitivity in patients with dysthyroid eye disease.

The majority of patients with dysthyroid eye disease have an acquired colour vision defect. However, no psychophysical investigation of selective damage to colour or flicker pathways has been carried out. In order to clarify the nature of the visual pathology, we have used a psychophysical technique (spectral sensitivity) to selectively stimulate the chromatic and achromatic mechanisms. Spectral spots of size 1 degree presented at a rate of 1 Hz on a bright 1000 td white background are detected by the chromatic mechanism but a rate of 25 Hz reveals the achromatic mechanism. Fifteen patients (28 eyes) between the ages of 50-70 years were tested. The study showed that all patients had reduced spectral sensitivity, either 1 Hz, 25 Hz or both. The patients with reduced 1 Hz or 25 Hz spectral sensitivity only had a shorter systemic and ocular duration of the condition, had no proptosis, normal intraocular pressures in primary gaze, slightly higher intraocular pressures on upgaze, normal visual field plots and FM 100-Hue error scores higher than the normal age-matched values. The patients with reduced both 1 Hz and 25 Hz spectral sensitivities had a longer systemic and ocular duration of the condition, had proptosis, normal intraocular pressures in primary position, higher intraocular pressures on upgaze and higher FM 100-Hue error scores than the age-matched normals and those in Groups 1 and 2. A total of 50% of patients in Group 3 had defective visual field plots. These data suggest that there is a damage of the large achromatic fibres and small chromatic fibres in dysthyroid eye disease. The mechanism of the damage could be one of ischaemic or mechanical or both.