Perception Threshold Research Articles

Ankle torque variance is a better indicator of balance control performance than plantar perceptual sensitivity threshold.

We explored whether ankle torque variability or plantar perceptual threshold explains human balance control more effectively. We hypothesized that ankle torque variance is a better indicator of center of pressure (COP) velocity variance than plantar perceptual sensitivity. Two conditions were tested: loaded (23-kg vest added) and unloaded, as loading should diminish plantar sensitivity and increase COP velocity variability. We created a linear feedback model to assess the noise change in the sensorimotor loop induced by loading. Plantar sensitivity was quantified using a psychophysical approach while participants stood barefoot. A linear motor applied a force impulse on the participant's heel. A "yes-no" method of limits was selected to identify plantar sole sensory thresholds in both conditions. We observed reduced plantar sensitivity in loaded compared with unloaded conditions. In the loaded condition, participants exhibited greater COP velocity variance, with significant positive Pearson's correlations confirming a substantial association between ankle torque and COP velocity variances for both loaded [variance accounted for (VAF): r2 = 44.56%, P = 0.018] and unloaded conditions (VAF: r2 = 58.83%, P = 0.004). No significant correlation existed between COP velocity variance and plantar sensitivity threshold for both loaded (VAF: r2 = 0.002%, P = 0.99) and unloaded conditions (VAF: r2 = 21.81%, P = 0.35). The model confirmed an ∼88% rise in sensorimotor loop noise in the loaded condition. Ankle torque variance assesses the precision of nonperceptual and perceptual detection mechanisms in evaluating whole body motions and the accuracy in converting sensory cues into ankle torque.NEW & NOTEWORTHY Plantar cutaneous information contributes to balance control by modulating motor commands, but plantar perceptual sensitivity is a suboptimal indicator of balance performance. Multiple sensory cues encode whole body dynamics, guiding sensorimotor mechanisms to minimize body sway variability. Ankle torque variance is proposed as a superior measure for explaining balance control performance and evaluating the sensorimotor loop's functioning in balance control.

The Conflict between Top-down and Bottom-up Impairments in Consciousness Disorder in Schizophrenia

Introduction: Schizophrenia, a complex psychiatric disorder, is often associated with consciousness disorders, typically characterized by an elevated threshold of conscious perception. Over the years, a multitude of research has been dedicated to uncovering the primary cause of these disorders, leading to the development of several theories. Methods: In this article, two central answers to this problem have been reviewed. For this, the articles that were more related to the topic were selected. Based on the relevance to the subject of research, the main ideas of targeted articles are reordered to be comprehensible for the readers. Finally, the judgment and conclusion of the authors about the discussed problem are presented in this study. Discussion: The first theory, which we will explore in this article, suggests that the root cause of these disorders lies in defects within bottom-up processes. These processes, fundamental to our understanding of the world, involve the progression of sensory information from low-level perception to high-level awareness. In individuals with schizophrenia, these processes are believed to be compromised, leading to a distorted perception of reality. The second theory, in contrast, attributes the cause to impairments in top-down processes. These processes, which refer to the influence of high-level cognitive functions on lower-level sensory perception, are also considered dysfunctional in schizophrenic patients. This dysfunction is thought to disrupt the integration of sensory information, thereby affecting the individual's consciousness. However, a third perspective has emerged, suggesting the coexistence of impairments in both bottom- up and top-down processing. This perspective argues that to fully comprehend the nature of consciousness disorders in schizophrenia, it is crucial to determine the type and severity of both bottom-up and top-down impairments. Conclusion: In this review, we delve into these theories, examining the evidence supporting each and discussing their implications for our understanding of schizophrenia. Considering both bottom-up and top-down impairments, the third perspective offers a more holistic explanation for these disorders. We further argue that this perspective underscores the need for a more nuanced approach to studying schizophrenia. It suggests that future research should not only focus on these processes in isolation but also explore their interaction and the potential synergistic effects of their impairment. By doing so, we can hope to gain a more comprehensive understanding of consciousness disorders in schizophrenia, which could ultimately lead to more effective treatment strategies.

Postural control in episodic ataxia type 2: no evidence for increased vestibular excitability.

Patients with episodic ataxia type 2 (EA2) suffer from recurrent paroxysmal episodes of vertigo and oscillopsia. Pathophysiologically, altered neuronal excitability has been suspected. Vestibular excitability in 22 EA2 patients and 22 age-matched healthy participants was compared. Galvanic vestibular stimulation (GVS) was used to assess vestibular excitability by vestibular motion perception thresholds and mean postural sway velocity during various visual and proprioceptive conditions in the two groups. Control stimuli using sham and no GVS were established to identify the specificity of GVS-induced postural sway. In the baseline condition, EA2 patients showed larger postural instability. However, motion perception thresholds and the increase in mean postural sway velocity during vestibular stimulation (stimulation ratio) did not differ between groups. Postural sway during suprathreshold GVS increased with the vestibular motion perception threshold in EA2 patients, in contrast to healthy participants. The larger postural unsteadiness of EA2 patients probably reflects their progressive cerebellar degeneration. It is not related to abnormal visual (Romberg's ratio) or proprioceptive control of stance. Postural unsteadiness during vestibular stimulation does not indicate altered vestibular excitability in EA2 patients. However, vestibular stimulation increasingly destabilized postural control of EA2 patients with higher motion perception thresholds when proprioceptive information was diminished. This conclusion, however, is restricted to the postural control of EA2 patients in the interval between the vestibulo-cerebellar episodes.

Perceptual discrimination of action formidableness and friendliness and the impact of autistic traits

The ability to determine whether the actions of other individuals are friendly or formidable are key decisions we need to make to successfully navigate our complex social environment. In this study we measured perceptual performance when discriminating actions that vary in their friendliness or formidableness, and whether performance was related to the autistic traits of individuals. To do this, we developed an action morphing method to generate novel actions that lied along the action quality dimensions of formidableness and friendliness. In Experiment 1 we show that actions that vary along the formidableness or friendliness continua were rated as varying monotonically along the respective quality. In Experiment 2 we measured the ability of individuals with different levels of autistic traits to discriminate action formidableness and friendliness using adaptive 2-AFC procedures. We found considerable variation in perceptual thresholds when discriminating action formidableness (~ 540% interindividual variation) or friendliness (~ 1100% interindividual variation). Importantly, we found no evidence that autistic traits influenced perceptual discrimination of these action qualities. These results confirm that sensory enhancements with autistic traits are limited to lower level stimuli, and suggest that the perceptual processing of these complex social signals are not affected by autistic traits.

Color Ranges and Distribution of Human Teeth: A Prospective Clinical Study.

This study investigated the in vivo color range of human teeth using a research-grade noncontact spectroradiometer, analyzing the effects of gender, age, ethnicity, and lifestyle factors, including diet, smoking, and oral hygiene. A total of 1004 participants were recruited at two research sites and stratified by gender, age, and ethnicity, and data on their dietary and oral habits were collected. Noninvasive color measurements of an upper central incisor were performed using a spectroradiometer and a fiber-coupled Xe-Arc light source. Color differences were computed using the CIELAB and CIEDE2000 color difference formulas, statistically analyzed, and interpreted through comparisons with 50:50% perceptibility (PT) and acceptability (AT) thresholds for dentistry. CIELAB and CIEDE2000 color coordinate values varied significantly. Female teeth appeared lighter and less yellow than men's. Age correlated with darker, more chromatic teeth, stabilizing only after Age 46. Significant ethnic differences were observed, particularly between African-American and Asian participants. Coffee consumption impacted teeth yellowness and chromaticity, while tea had no significant effect. Frequent tooth brushing led to lighter teeth, and tooth whitening considerably influenced color, emphasizing the effect of cosmetic dental treatments. Smoking showed minimal impact, with slight discoloration noted among light smokers compared to nonsmokers. Color coordinate values by gender, age, and ethnicity exhibited statistically significant differences and, in most cases, noticeable color differences. With exceptions, the dietary/oral habits of the patient had a significant impact on the color of human teeth. The findings from this study provide detailed information and understanding of the color range and distribution of human teeth, which can help enhance the esthetic outcome of dental care and, consequently, the patient's satisfaction.

Dynamic Attending in percussionists and wind players

Percussionists have been shown to have superior temporal perception, but the underlying mechanisms for this advantage deserve further investigation. Dynamic Attending Theory, which posits the way attention aligns with rhythmic temporal structure, may explain why percussionists exhibit superior temporal perception. Percussionists may entrain more strongly to periodic stimuli than other musicians, and possibly at multiple hierarchical levels as opposed to only the tactus. To test these hypotheses, we asked a total of 41 musicians, 20 percussionists, and 21 wind players to complete a target detection task. Participants listened to periodic bursts of noise ( priming bursts) and tried to detect target bursts of noise at different temporal positions, some in phase and some out of phase with the initial noises. Target-burst amplitudes were calibrated to be at each participant’s perceptual threshold. We analyzed the hit rates at the different temporal positions, as well as the Fourier transform of those hit rate curves. No discernible difference between groups was found in the time domain, but in the frequency domain the percussionist group showed stronger fluctuation at a frequency that matched the priming bursts, but not at other hierarchical levels (specifically, double that frequency). Our findings help explain percussionists’ perceptual advantages, although questions about entrainment at different hierarchical levels deserve further consideration.

Impact of Speed Sintering on Translucency, Opalescence and Microstructure of Dental Zirconia with a Combination of 5 mol% and 3 mol% Yttria-Stabilized Zirconia

Optical characteristics and microstructure of multilayered zirconia with different yttria contents in each layer can be influenced differently with a layer after speed sintering. The layer-wise translucency and opalescence of dental zirconia (E.max, E.max ZirCAD prime; Cercon, Cercon ht ML) after conventional (control) and speed sintering were analyzed using a spectrophotometer (n = 5). Specimens were subjected to microstructural analyses (n = 2) using field-emission scanning electron microscopy (FE-SEM) and phase analyses (n = 1) using high-resolution X-ray diffraction (HRXRD) and Rietveld refinement. The translucency parameter (TP) and opalescence parameter (OP) were analyzed using a 3-way ANOVA, followed by Scheffé’s post hoc test (α = 0.05). The average grain size was analyzed using the Welch’s t-test and Kruskal–Wallis test, followed by the Bonferroni–Dunn post hoc test (α = 0.05). Changes to the TP and OP after speed sintering were only observed in the dentin layers. Although the TP of E.max increased (p < 0.05), the difference was below the 50:50% perceptibility threshold (ΔE00 = 0.8). The OP of E.max decreased slightly, whereas that of Cercon increased slightly (p < 0.05). The microstructure and phase fraction of both zirconia barely changed. Therefore, speed sintering is considered to have a negligible clinical impact on the optical characteristics and microstructure.

Glucose-lowering medication associated with weight loss may limit the progression of diabetic neuropathy in type 2 diabetes.

Obesity is a major risk factor for diabetic peripheral neuropathy (DPN) in type 2 diabetes (T2D). This study investigated the effect of glucose lowering medication associated with weight change on DPN. Participants with T2D were grouped based on whether their glucose lowering medications were associated with weight gain (WG) or weight loss (WL). They underwent clinical, metabolic testing and assessment of neuropathic symptoms, vibration perception threshold (VPT), sudomotor function and corneal confocal microscopy (CCM) at baseline and follow-up between 4 and 7 years. Of 76 participants, 69.7% were on glucose lowering medication associated with WG, and 30.3% were on glucose lowering medication associated with WL. At baseline, participants in the WG group had a significantly longer duration of diabetes (p < .01), higher douleur neuropathique en 4 (DN4) score (p < .0001) and VPT (p = .01) compared with those in the WL group. Over a 56-month period, participants in the WG group showed no significant change in body weight (p = .11), HbA1c (p = .18), triglycerides (p = .42), DN4 (p = .11), VPT (p = .15) or Sudoscan (p = .43), but showed a decline in corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD) and corneal nerve fiber length (CNFL) (p < .0001). Participants in the WL group showed a reduction in weight (p = .01) and triglycerides (p < .05), no change in DN4 (p = .30), VPT (p = .31) or Sudoscan (p = .17) and a decline in the corneal nerve branch density (p < .01). Participants treated with glucose lowering medication associated with weight gain had worse neuropathy and greater loss of corneal nerves during follow-up, compared to patients treated with medication associated with weight loss.

Corneal nerve loss in adolescents with obesity and acanthosis nigricans.

Obesity and related metabolic abnormalities in adults are associated with peripheral neuropathy. Acanthosis nigricans (AN) is associated with insulin resistance, fatty liver, hyperlipidemia and glucose intolerance, all of which are risk factors for neuropathy. The aim of this study was to investigate if obese adolescents with AN have evidence of small nerve fiber damage. Adolescents with obesity with and without AN underwent body composition analysis, assessment of vibration perception threshold (VPT), monofilament sensitivity and corneal confocal microscopy (CCM) to quantify corneal nerve fiber density (CNFD), branch density (CNBD), length (CNFL) and inferior whorl length (IWL). Forty-six participants with obesity with (n = 31) and without (n = 15) AN aged 15(14-17) years were compared to 20 healthy controls aged 13(12-14) years. There was no difference in VPT, monofilament sensitivity and CCM measures between adolescents with obesity and controls. However, adolescents with AN had a significantly higher weight (P = 0.022), fat% (P = 0.029) and fat-muscle ratio (P = 0.012) with a lower CNFD (P = 0.045) compared to those with obesity without AN. Adolescents with obesity and acanthosis nigricans have a higher fat mass and small nerve fibre loss, indicative of a sub-clinical neuropathy.

Emerging Perspectives: The Interplay of Taste Perception and Oral Microbiota Composition in Dietary Preferences and Obesity.

Recent advancements in sensory research have brought to light the intricate relationship between taste perception and the oral microbiota, prompting investigations into their influence on human health, particularly in the context of dietary preferences and obesity. This review aims to update the current understanding of how oral microbiota influence taste perception and dietary choices, elucidating shared metabolic pathways between food processing and oral bacteria. Further, this review outlines the mechanisms underlying taste perception, emphasizing the role of taste receptors and taste buds in shaping sensory experiences influenced by genetic and environmental factors. Notably, we explore the bidirectional relationship between oral microbiota and taste sensitivity, highlighting the potential impact of microbial composition on taste perception thresholds and implications for dietary habits and health outcomes, such as obesity and dental caries. However, significant research gaps remain, particularly in the understanding of the molecular mechanisms linking oral microbiota with taste sensitivity, as well as the long-term effects of microbiota-targeted interventions. Future research should focus on longitudinal studies and experimental interventions to explore these connections more deeply, offering insights into potential strategies for promoting healthier dietary behaviors and managing diet-related non-communicable diseases.

Hand’s Vibration Perception Thresholds—A Systematic Review

The term vibration perception threshold (VPT) refers to the minimum amplitude required for a vibration to be consciously perceived. Knowledge of VPTs can be used to aid in the diagnosis of various pathologies, or to support design decisions during human-machine interface development. However, several factors affect VPT measurements (e.g., contactor size and pressure), thus, comparing VPT results from multiple studies should not be done without considering both the similarities and differences between said studies. This paper presents a systematic review on VPT results obtained across multiple studies, taking into consideration the different factors affecting the values reported in the literature. We intended to answer the following question: “What are the Vibration Perception Thresholds assessed on the glabrous skin of the hands and fingers of healthy humans?” To the best of our knowledge, this is the first attempt at conducting a systematic review focused specifically on numerical VPT results. Starting from 936 records, VPT results from 37 studies were organized according to various factors (gender, age, probe size, contact pressure, psychophysical method, room temperature, skin temperature, and hand location). This data was organized into a table, the Organization Table that is available for readers. This review can help future researchers and developers working on or working with the topic of human perception of vibrations by examining the factors that affect VPTs and discussing strategies to address them. We offer recommendations for future research and insights on how design engineers can utilize VPTs in the development of new haptic devices.

The Influence of Diffuse-Field Equalization on the Perception of Spatial Aliasing Introduced by Spherical Microphone Arrays

When a sound field is sampled by a finite number of microphones, the upper-frequency range of the recorded content is affected by spatial aliasing. The frequency beyond which aliasing-induced artifacts occur is related to the distance between a microphone and its nearest neighbors. In this study, ambisonics signals of order N = 7 were encoded from simulated recordings made by virtual spherical microphone arrays of varying characteristics (radius, sampling scheme, and sampling grid order). A diffuse-field equalization, the role of which is to lessen the aliasing-induced spectral coloration, was also considered in the tested conditions. These aliased stimuli were then compared with unaliased stimuli of order N = 7. Results showed that the diffuse-field equalization had a great impact on the perceived differences. A perceptual threshold was calculated in order to determine whether aliasing artifacts are likely to be audible based on the amount of aliasing-induced encoding error.

Visual pathways functioning in healthy pre-term adolescents: Sex but not gestational age effect.

Visuo-spatial and visuo-perceptual functioning is widely studied in preterm child and is strongly sex-specific. However, little to no data is available regarding male-female differences in preterm children and adolescents and about the interaction effect between sex and preterm birth. We studied 30 adolescents born preterm with normal cognitive and clinical neurological outcomes and 34 age-matched controls to investigate the interaction between levels of prematurity and sex in predicting the outcome of visual pathways functioning and to explore the relation between psychophysiological perceptive processing and neuropsychological performance. In the presence of prematurity, a greater female vulnerability in central visuo-cognitive processing (Form Coherence Task), but not in neuropsychological accuracy (Street Completion Test and Visual Object and Space Perception battery), seems to be more evident. Moreover, the psychophysical threshold is correlated to neuropsychological accuracy only in preterm females and not in males. These results support the idea that the male vulnerability in cognitive functioning described in prematurity-related developmental conditions is negligible during school age in children-adolescents with normal cognitive and clinical neurological outcomes. Visuo-perceptual functioning is widely studied in prematurity. However, few data are available about the interaction effect between sex and preterm birth in predicting visuo-perceptual functioning. We evidenced that in females born preterm with preserved cognitive abilities, the efficiency of the psychophysical visuo-perceptual threshold is reduced, but not related to the neuropsychological performance. Females may implement compensation strategies to achieve good performance regardless of the perceptual threshold. The present study addresses an important gap in literature, suggesting possible sex-specific outcomes in visuo-perceptual ability among preterm children and adolescents with normal intelligence and neurological outcomes.

Tinnitus Suppression with Electrical Stimulation at the Most Basal Contact of the Cochlear Implant Electrode as a Model for Round Window Stimulation.

The objective of this research was to test whether efficient tinnitus suppression could be achieved by electrical stimulation of the single most basal electrode contact of a cochlear implant. This approach simulates the effects of electrical stimulation using a round-window electrode. The study was performed in 10 adult cochlear implant patients showing complete or almost complete tinnitus suppression during electrical stimulation with their standard fitting-MAP. In all patients, tinnitus appeared again when the implant was switched off. Five Nucleus implant (1 CI532, 4 CI24RE CA) users and 5 Mi12xx series with FLEX28 electrodes with at least 6 months of CI experience were included. Two types of stimulation were presented at the most basal CI contact: a constant pulse train and a modulated pulse train. The variation in pulse rates was low rate (100-300 pps) and high (≥900 pps), and the current level ranged from the C-level to less than the T-level for both stimulation types. The effect of acute electrical stimulation at the most basal electrode contact was compared to the effect obtained with multichannel stimulation with the patient's current fitting MAP. Electrical stimulation was paused between tests with different stimulation types until tinnitus returned to baseline intensity. Patients reported Visual Analog Scale (VAS) scores for tinnitus loudness and intrusiveness during normal CI use and for each single contact stimulation type. Eight participants perceived complete suppression with one or more stimulation patterns. In 2 patients, suppression was less efficient than full-band CI stimulation. Louder stimuli are generally perceived as annoying and less effective in reducing tinnitus. In FLEX28 patients, it was also possible to obtain full tinnitus suppression with current amplitudes under the thresholds for auditory perception (this was not tested in patients with the Nucleus device). In 8 of the 10 included patients, we were able to obtain complete or almost complete tinnitus suppression with electrical stimulation at only 1 most basal electrode contact. Therefore, round-window stimulation with a single electrode may be a potential treatment for tinnitus in patients with significant residual hearing. The long-term effects of this therapy should be confirmed in future studies.

Perceptual sensitivity to labeling stereotyped emotion expressions: Associations with age and subclinical psychopathology symptoms from childhood through early adulthood.

This study investigates (a) age-related differences in how the intensity of stereotyped facial expressions influence the emotion label children, adolescents, and adults assign to that face and (b) how this perceptual sensitivity relates to subclinical symptoms of psychopathology. In 2015-2016, 184 participants aged 4-25 years viewed posed stereotypes of angry, fearful, sad, and happy expressions morphed with neutral expressions at 10%-90% intensity. Thin plate regression smoothing splines were used to chart nonlinear associations between age and the perceptual threshold participants needed to assign the emotion label expected based on cultural consensus. Results suggest that sensitivity to labeling stereotypical happy faces as "happy" peaked by age 4. Sensitivity to perceiving stereotypical angry faces as "angry" increased from ages 4 to 7 and then plateaued. In contrast, sensitivity to perceiving stereotypical fearful and sad faces demonstrated protracted development, not reaching a plateau until ages 15 and 16, respectively. Reduction in selecting the "I don't know" response was the primary driver of these age-related changes. Stereotyped fear expressions required the highest intensity to be labeled as such and showed the most marked change in perceptual threshold across development. Interestingly, lower intensity morphs of stereotypical fear faces were frequently labeled "sad." Furthermore, perceiving lower intensity fear morphs was associated with fewer internalizing and externalizing symptoms in participants aged 7-19. This study describes the development of perceptual sensitivity to labeling stereotypical expressions of emotion according to cultural consensus and shows that how people perceive and categorize ambiguous facial expressions is associated with vulnerability to psychopathology. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Using biothesiometer, Neuropathy Symptom Score, and Neuropathy Disability Score for the early detection of peripheral neuropathy: A cross-sectional study.

Patients with peripheral neuropathy could have damaged peripheral nerves, which leads to sensory and motor dysfunction. Diabetes, infections, and trauma are the major causes of peripheral neuropathy. Vibratory perception threshold (VPT) tools are commonly used to detect peripheral neuropathy. This study aims to determine the assessment of peripheral neuropathy through the different diagnostic tools in the community in Malaysia. A total number of 1283 participants were recruited from the seven retail pharmacies located in Selangor, Malaysia. The peripheral neuropathy test was conducted based on VPT tools on both feet using the digital biothesiometer. Following that, Neurological Symptom Score (NSS) and Neurological Disability Score (NDS) were taken from the participants to assess the neurological symptoms. Participants had an average age of 40.6 ± 12.9 years and were mostly of Chinese ethnicity (54.1%). The findings show that increasing age was associated with more severe peripheral neuropathy across the various assessment tools, but gender differences were found with the biothesiometer test and ethnicity has severity in the biothesiometer and disability scores. The sensitivity and specificity of the biothesiometer test were 0.63 and 0.84, respectively. The combined tool NSS and NDS had high specificity and a high positive predictive value, suggesting that it could be a reliable indicator of peripheral neuropathy when both scores are elevated. The findings show that the biothesiometer test, NSS, and NDS are considered screening VPT tools for diagnosing peripheral neuropathy. However, further evaluation and diagnostic testing are necessary in cases of a positive test result.

Microsaccadic suppression of peripheral perceptual detection performance as a function of foveated visual image appearance.

Microsaccades are known to be associated with a deficit in perceptual detection performance for brief probe flashes presented in their temporal vicinity. However, it is still not clear how such a deficit might depend on the visual environment across which microsaccades are generated. Here, and motivated by studies demonstrating an interaction between visual background image appearance and perceptual suppression strength associated with large saccades, we probed peripheral perceptual detection performance of human subjects while they generated microsaccades over three different visual backgrounds. Subjects fixated near the center of a low spatial frequency grating, a high spatial frequency grating, or a small white fixation spot over an otherwise gray background. When a computer process detected a microsaccade, it presented a brief peripheral probe flash at one of four locations (over a uniform gray background) and at different times. After collecting full psychometric curves, we found that both perceptual detection thresholds and slopes of psychometric curves were impaired for peripheral flashes in the immediate temporal vicinity of microsaccades, and they recovered with later flash times. Importantly, the threshold elevations, but not the psychometric slope reductions, were stronger for the white fixation spot than for either of the two gratings. Thus, like with larger saccades, microsaccadic suppression strength can show a certain degree of image dependence. However, unlike with larger saccades, stronger microsaccadic suppression did not occur with low spatial frequency textures. This observation might reflect the different spatiotemporal retinal transients associated with the small microsaccades in our study versus larger saccades.

Influence of preheating and water storage on the color, whiteness, and translucency of modern resin-based composites.

To evaluate the influence of preheating and water storage on color, whiteness, and translucency of one-shaded, group-shaded, and multi-shaded resin-based composites. A total of 270 samples were fabricated from one-shaded (Omnichroma), group-shaded (Optishade MD), and multi-shaded (Enamel Plus HRI) resin-based composites and divided into six groups: no heating (control) and 1-5 heatings (test) (n = 15). The CIE L*, a*, b*, C*, and h° color coordinates were registered over white, black, and gray backgrounds with a spectrophotometer before and after 24, 72, 144 h water storage. Kruskal-Wallis test was used to evaluate differences in the color coordinates, whiteness index, and translucency parameter (α = 0.05). The Mann-Whitney U test was performed with a Bonferroni correction (p < 0.001) for pairwise comparisons. CIEDE2000 color, whiteness, and translucency differences between groups and subgroups were evaluated using their respective 50%:50% perceptibility and acceptability thresholds. Preheating influenced color coordinates, whiteness index, and relative translucency parameters (p < 0.001). Although color differences were below the acceptability threshold for all materials, translucency differences were above the acceptability threshold for Omnichroma. Water storage significantly influenced the whiteness index of Optishade MD (p < 0.001). Preheating had a more considerable effect on the color, whiteness, and translucency of one-shaded resin-based composite, while water storage influenced group-shaded resin-based composite more importantly. Preheating influences the color, whiteness level, and translucency of the resin-based composites, but the variations remain generally clinically acceptable; however, practitioners should be aware that the modifications in translucency for one-shaded resin-based composites could be more important than for group-shaded and multi-shaded resin-based composites.

Effect of Listerine and Chlorhexidine mouthwashes with antidiscoloration system on the colour change of CAD/CAM conventional and novel lithium disilicate ceramics

Background It has been reported that using mouthwashes can discolour the surface of teeth. Their effect on the stainability of newly introduced lithium disilicate ceramics is, however, unknown. Objective: The purpose of this in vitro study was to investigate how mouth washes affected the color change of new and conventional lithium disilicate (LS2) ceramics that were finished using various techniques. Materials and Methods A total of 56 ceramic slices were produced from conventional LS2 (E Max CAD, Ivoclar) and a novel virgilite based LS2 (Cerec Tessera, Dentsply Sirona). According to the finishing method, the specimens were divided into glazed and polished subgroups. Each subgroup was further subdivided into two based on immersion in chlorhexidine (CHXD) or Listerine (LIST) mouth washes. A handheld spectrophotometer was used to measure the color attributes, and color differences (ΔE00) were then counted using specific equation. Data were analyzed using ANOVA and Tukey’s post-hoc tests. Results Significant differences in color change (ΔE00) values were observed between conventional and novel LS2 ceramics, as well as between different finishing methods and mouth-rinse solutions. Chlorhexidine induced higher color differences than Listerine, with average ΔE00 values of 0.959 and 0.885, respectively (p &lt; 0.001). The polished specimens generally exhibited higher ΔE00 values than the glazed specimens, with average values of 1.071 and 0.792 for conventional LS2, and 0.836 and 0.786 for novel LS2 (p &lt; 0.001). However, most color changes did not exceed the perceptibility and acceptability thresholds. Conclusion Using CHXD and LIST mouth washes affected the color change of polished or glazed conventional and novel lithium disilicate ceramics. In general, the stainability of polished specimens was higher than that of glazed ones. There was more discoloration on specimens immersed in CHXD than those immersed in LIST. Bangladesh Journal of Medical Science Vol. 23 No. 04 October’24 Page : 1178-1184

ID: 327963 Clinical Paresthesia Perception Thresholds Decrease with Higher Spinal Cord Stimulation Frequency

ID: 327963 Clinical Paresthesia Perception Thresholds Decrease with Higher Spinal Cord Stimulation Frequency