Coevolution between heat and cold tolerance in endotherms.

Whether the heat and cold tolerance of endotherms evolve independently or correlatively remains unresolved. Both physiological trade-offs and natural selection can contribute to a coevolutionary pattern of heat and cold tolerance in endotherms. Using a published database, we tested the correlation between upper and lower thermal limits across endothermic species with multi-response generalized linear mixed models incorporating phylogenies. We found a positive correlation between upper and lower thermal limits, which suggested a coevolutionary pattern of heat and cold tolerance. Specifically, this relationship between heat and cold tolerance is phylogenetically constrained for tropical endotherms but not for temperate endotherms. The correlated evolution between heat and cold tolerance may have a significant influence on endotherms' evolution and ecology and needs to be further investigated.

Prolonged Standing-Induced Low Back Pain Is Linked to Extended Lumbar Spine Postures: A Study Linking Lumped Lumbar Spine Passive Stiffness to Standing Posture.

Postural assessments of the lumbar spine lack valuable information about its properties. The purpose of this study was to assess neutral zone (NZ) characteristics via in vivo lumbar spine passive stiffness and relate NZ characteristics to standing lumbar lordosis. A comparison was made between those that develop low back pain during prolonged standing (pain developers) and those that do not (nonpain developers). Twenty-two participants with known pain status stood on level ground, and median lumbar lordosis angle was calculated. Participants were then placed in a near-frictionless jig to characterize their passive stiffness curve and location of their NZ. Overall, both pain developers and nonpain developers stood with a lumbar lordosis angle that was more extended than their NZ boundary. Pain developers stood slightly more extended (in comparison to nonpain developers) and had a lower moment corresponding to the location of their extension NZ boundary. Overall, in comparison to nonpain developers, pain developers displayed a lower moment corresponding to the location of their extension NZ boundary which could correspond to greater laxity in the lumbar spine. This may indicate why pain developers have a tendency to stand further beyond their NZ with greater muscle co-contraction.

Energetic costs of bill heat exchange demonstrate contributions to thermoregulation at high temperatures in toco toucans (Ramphastos toco).

Body temperature regulation under changes in ambient temperature involves adjustments in heat production and heat exchange rates between the animal and the environment. One mechanism involves the modulation of the surface temperature of specific areas of the body through vasomotor adjustment. In homeotherms, this thermoregulatory adjustment is essential for the maintenance of body temperature over a moderate temperature range, known as the thermal neutral zone (TNZ). The bill of the toco toucan (Ramphastos toco) has been described as a highly efficient thermal window and hypothesized to assist in the thermal homeostasis of this bird. Herein, we directly evaluated the contribution of heat exchange through the bill of the toco toucan and role of the bill in the delimitation of the TNZ. To do this, we measured metabolic rate (MR), via oxygen consumption, over a range of ambient temperatures from 0 to 35°C. MR measurements were made in birds with the bill intact and with the bill insulated. The limits of the TNZ did not differ between treatments, ranging from 10.8 to 25.0°C. The MR differed among treatments only at elevated temperatures (30 and 35°C), reaching 0.92±0.11 ml O2 g-1 h-1 (mean±s.d.) for the intact group and 1.13±0.13 ml O2 g-1 h-1 for the insulated group. These results indicate that although heat dissipation through the bill does not contribute significantly to widening of the TNZ, it may well be critically important in assisting body temperature regulation at higher temperatures extending above the upper limit of the TNZ.

A study to investigate the effectiveness of the application of virtual reality technology in dental education.

BACKGROUND: Today, the use of virtual reality (VR) technology as an educational tool in dental education has expanded considerably. This study was aimed to evaluate the effectiveness of using VR technology in teaching neutral zone and teeth arrangement. METHODS: This randomized trial was conducted at Kermanshah University of Medical Sciences, Iran in 2019. The study sample consisted of 50 six-year dental students who were randomly divided into experimental (n = 25) and control (n = 25) groups. Students' performance in both groups was assessed using tests. A questionnaire was used to assess the usability of VR technology and students' satisfaction with it. RESULTS: All faculty members confirmed the usability of VR technology in dental education. The majority of students (76%) were highly satisfied with the use of this technology in their learning process. The mean score of students was significantly higher in the experimental group (16.92 ± 1.12) than in the control group (16.14 ± 1.18). CONCLUSION: In general, it can be argued that VR technology is useful and effective in the teaching-learning process. Therefore, its use in medical and dental schools can play an effective role in creating a dynamic, attractive, and successful learning environment.

The Neutral Zone Approach with CAD-CAM Record Bases.

Lack of adequate retention, support, and stability in the complete denture can be attributed to a poor fit or incorrect shape of the polished surfaces. This article presents a case using the neutral zone technique effectively with the fabrication of computer-aided design and computer-aided manufacturing (CAD-CAM) record bases in an edentulous patient with severely resorbed alveolar ridges and discusses the overall treatment steps and clinical implications of this technique. A stable neutral zone and an accurate jaw relation were recorded using CAD-CAM record bases and stability of complete denture was optimized by arranging denture teeth and reforming polishing surfaces in the neutral zone. A new complete denture was fabricated for a patient with atrophic alveolar ridges by a technique utilizing the neutral zone with CAD-CAM record bases.

Mechanical Consequence of Induced Intervertebral Disc Degeneration in the SPARC-Null Mouse.

Intervertebral disc (IVD) degeneration is associated with low back pain (LBP) and accompanied by mechanical changes to the spine. Secreted protein acidic and rich in cysteine (SPARC) is a protein that contributes to the functioning and maintenance of the extracellular matrix. SPARC-null mice display accelerated IVD degeneration and pain-associated behaviors. This study examined if SPARC-null mice also display altered spine mechanics as compared to wild-type (WT) mice. Lumbar spines from SPARC-null (n = 36) and WT (n = 18) mice aged 14-25 months were subjected to cyclic axial tension and compression to determine neutral zone (NZ) length and stiffness. Three separate mechanical tests were completed for each spine to determine the effect of the number of IVDs tested in series (one versus two versus three IVDs). SPARC-null spine NZs were both stiffer (p < 0.001) and smaller in length (p < 0.001) than WT spines. There was an effect of the number of IVDs tested in series for NZ length but not NZ stiffness when collapsed across condition (SPARC-null and WT). Correlation analysis revealed a weak negative correlation (r = -0.24) between age and NZ length in SPARC-null mice and a weak positive correlation (r = 0.30) between age and NZ stiffness in WT mice. In conclusion, SPARC-null mice had stiffer and smaller NZs than WT mice, regardless of the number of IVDs in series being tested. The increased stiffness of these IVDs likely influences mobility at these spinal joints thereby potentially contributing to low back pain.

The biomechanical effect of single-level laminectomy and posterior instrumentation on spinal stability in degenerative lumbar scoliosis: a human cadaveric study.

OBJECTIVEDegenerative lumbar scoliosis, or de novo degenerative lumbar scoliosis, can result in spinal canal stenosis, which is often accompanied by disabling symptoms. When surgically treated, a single-level laminectomy is performed and short-segment posterior instrumentation is placed to restore stability. However, the effects of laminectomy on spinal stability and the necessity of placing posterior instrumentation are unknown. Therefore, the aim of this study was to assess the stability of lumbar spines with degenerative scoliosis, characterized by the range of motion (ROM) and neutral zone (NZ) stiffness, after laminectomy and placement of posterior instrumentation.METHODSTen lumbar cadaveric spines (T12-L5) with a Cobb angle ≥ 10° and an apex on L3 were included. Three loading cycles were applied per direction, from -4 Nm to 4 Nm in flexion/extension (FE), lateral bending (LB), and axial rotation (AR). Biomechanical evaluation was performed on the native spines and after subsequent L3 laminectomy and the placement of posterior L2-4 titanium rods and pedicle screws. Nonparametric and parametric tests were used to analyze the effects of laminectomy and posterior instrumentation on NZ stiffness and ROM, respectively, both on an individual segment's motion and on the entire spine section. Spearman's rank correlation coefficient was used to study the correlation between disc degeneration and spinal stability.RESULTSThe laminectomy increased ROM by 9.5% in FE (p = 0.04) and 4.6% in LB (p = 0.01). For NZ stiffness, the laminectomy produced no significant effects. Posterior instrumentation resulted in a decrease in ROM in all loading directions (-22.2%, -24.4%, and -17.6% for FE, LB, and AR, respectively; all p < 0.05) and an increase in NZ stiffness (+44.7%, +51.7%, and +35.2% for FE, LB, and AR, respectively; all p < 0.05). The same changes were seen in the individual segments around the apex, while the adjacent, untreated segments were mostly unaffected. Intervertebral disc degeneration was found to be positively correlated to decreased ROM and increased NZ stiffness.CONCLUSIONSLaminectomy in lumbar spines with degenerative scoliosis did not result in severe spinal instability, whereas posterior instrumentation resulted in a rigid construct. Also, prior to surgery, the spines already had lower ROM and higher NZ stiffness in comparison to values shown in earlier studies on nonscoliotic spines of the same age. Hence, the authors question the clinical need for posterior instrumentation to avoid instability.

HSP70 plays a role in the defense of acute and chronic heat stress in Mongolian gerbils (Meriones unguiculatus).

Mongolian gerbils (Meriones unguiculatus) show a wide thermal neutral zone (TNZ, 26.5-38.9 °C). Whether heat shock proteins (HSPs) are involved in thermal tolerance for gerbils has still been unknown. We investigated the effects of acute and chronic high temperature within and above TNZ on the expressions of HSP70 and HSP90 and oxidative status in Mongolian gerbils, to test the hypothesis that the gerbils need increase the expression in HSPs to defense the acute and chronic heat stress. In experiment I, 50 Mongolian gerbils were exposed to 23 °C, 27 °C, 37 °C, 40 °C and 43.5 °C for 80 min respectively, and then sacrificed 12 h after treatment. HSP70 expression in the liver increased at 40 °C compared to that at 23 °C, but did not change after 27 °C, 37 °C or 43.5 °C exposure. There were no differences in HSP90 expression, oxidative stress parameters such as malonaldehyde (MDA) and hydrogen peroxide (H2O2), or antioxidant parameters such as superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) in the liver. HSP70 and HSP90 expression both in the heart and brain showed no differences among groups. In experiment II, another set of 30 gerbils were acclimated to 23 °C, 27 °C and 37 °C for 21 days, respectively. During chronic acclimation, HSP70 expression increased and H2O2 level decreased in the liver in 37 °C group compared to other two groups. Both H2O2 and SOD in the brain decreased in 37 °C group, but there were no differences in HSP70, MDA or T-AOC in the brain. These data indicate that Mongolian gerbils can maintain basal levels of HSPs after acute exposure to temperatures within the wide TNZ, but rely on increased HSP70 in the liver to protect from heat damage at temperatures above TNZ and during chronic heat acclimation. The increased HSP70 expression in the liver may contribute to keeping from heat damage in desert rodents.

An In Vivo Study to Compare Location of Neutral Zone Recorded with Two Materials.

AIM: To establish a relationship between the crest of the alveolar ridge and neutral zone and to compare its location recorded by two different material. METHODS AND MATERIALS: Thirty subjects were selected, and the location of the neutral zone was compared with the mandibular alveolar ridge crest. For each subject neutral zone was recorded by two different recording materials-Low fusing impression compound and tissue conditioner. After neutral zone recording, the relation between mandibular ridge crest and neutral zone location examined radiographically. The data so collected were checked for normality, descriptive statistics and the Mann-Whitney U test was used. RESULTS: Position of neutral zone was found towards lingual in the posterior, labial side in anterior and almost near to the alveolar ridge crest in premolar region. The thermoplastic flow of the material effects the position of neutral zone but no significant difference was noted in the positions of neutral zone recorded by the two materials in relation to the alveolar ridge crest. CONCLUSION: Location of the neutral zone is not affected by the material used in recording it. CLINICAL SIGNIFICANCE: The location of the neutral zone varies from subject to subject and mainly depends upon their musculature and can be recorded accurately by using correct technique irrespective of the materials used.

Thermal biology of two sympatric gerbil species: The physiological basis of temporal partitioning.

Sympatric species can coexist through ecological resource partitioning as for example for habitat, food or time. However, a detailed understanding of the basic thermal physiology, crucial for temporal partitioning, is currently lacking, especially for the desert rodents. Here, we compare the physiological performance with regard to thermal energetics and morphological traits of two sympatric gerbils from the Gobi desert of Inner Mongolia, China. The diurnally active Meriones unguiculatus and the nocturnally active M. meridianus. The diurnal M. unguiculatus had more brown adipose tissue (BAT) mass and capacity for non-shivering thermogenesis (NST), a higher resting metabolic rate (RMR) at low ambient temperatures (Ta) and a higher upper critical temperature of the thermal neutral zone (TNZ) than the nocturnal M. meridianus. The overall thermal conductance and lower critical temperatures of M. unguiculatus were also higher than that of M. meridianus, permitting the former to maintain a stable body temperature (Tb) when exposed to high Ta. Laboratory-bred M. meridianus also showed higher daily water intake. We found no differences in body mass, and total evaporative water loss (TEWL) between the two species captured from the natural environment. These results suggest that the diurnal M. unguiculatus have a higher tolerance of high Tas, whereas M. meridianus can save more energy at low Tas. Therefore, from the view point of energy conservation, our results suggest that the nocturnal ecophenotype in M. meridianus is constrained by a lower ability for heat resistance, but this is not the case for the diurnal M. unguiculatus.

Association of Neutral Zone Position with Age, Gender, and Period of Edentulism.

PURPOSE: The changing dynamics of an aging mouth influence the position of the neutral zone (NZ). While the advantage of the NZ concept in complete denture treatment is quite established, what is not clearly understood is its position in relation to the crest of the residual ridge due to conflicting reports from previous studies. The purpose of this study was to investigate the distance and direction of NZ position in relation to crest of the residual ridge in edentulous patients and its association with age, gender, and period of edentulism. MATERIALS AND METHODS: A cross-sectional study was conducted in 133 patients (70 males, 63 females) with a mean age of 58.81 ± 11.78 years. NZ recording was done using admix material by following standard procedures. Two metallic wires were adapted, one on the ridge and another on the center of the occlusal rims, and standardized digital radiographs were made. The position of NZ in relation to the crest of the residual ridge was recorded by noting the direction and measuring the distance between the adapted wires digitally at five locations (right molar, right premolar, incisor, left molar, left premolar regions). RESULTS: Age, gender, and period of edentulism had no significant association with the position of NZ. No specific trend was observed in the in NZ position with a non-significant correlation. CONCLUSIONS: Distance and the direction of neutral zone position in relation to crest of the residual ridge in edentulous patients bear no significant relationship with factors such as age, gender, and period of edentulism.

Lowland biotic attrition revisited: body size and variation among climate change 'winners' and 'losers'.

The responses of lowland tropical communities to climate change will critically influence global biodiversity but remain poorly understood. If species in these systems are unable to tolerate warming, the communities-currently the most diverse on Earth-may become depauperate ('biotic attrition'). In response to temperature changes, animals can adjust their distribution in space or their activity in time, but these two components of the niche are seldom considered together. We assessed the spatio-temporal niches of rainforest mammal species in Borneo across gradients in elevation and temperature. Most species are not predicted to experience changes in spatio-temporal niche availability, even under pessimistic warming scenarios. Responses to temperature are not predictable by phylogeny but do appear to be trait-based, being much more variable in smaller-bodied taxa. General circulation models and weather station data suggest unprecedentedly high midday temperatures later in the century; predicted responses to this warming among small-bodied species range from 9% losses to 6% gains in spatio-temporal niche availability, while larger species have close to 0% predicted change. Body mass may therefore be a key ecological trait influencing the identity of climate change winners and losers. Mammal species composition will probably change in some areas as temperatures rise, but full-scale biotic attrition this century appears unlikely.

Neutral zone or conventional mandibular complete dentures: a randomised crossover trial comparing oral health-related quality of life.

There is widespread consensus that the neutral zone (NZ) concept contributes to improved stability for mandibular complete dentures (CDs). However, little is known about its impact on oral health-related quality of life (OHRQoL) of edentulous patients compared to conventionally (CV) manufactured dentures. In this prospective crossover trial, performed at the Oral Health Centre of the University of the Western Cape, CV and NZ mandibular dentures were made for each patient. Scores from the 20-item oral health impact profile (OHIP-20) for both types of dentures were compared with pre-treatment scores using paired t-tests. Treatment effect size (ES) was established. Associations of OHIP-20 scores and several patient variables (age, gender, period of edentulousness, quality of the denture-bearing tissue, denture dimensions, preference) were performed using the generalised linear model. Significance was set at P = 0·05. Records of thirty-five participants were included in the study (mean age of 62·3 years, range 47-85 years). There were highly significant differences between pre-treatment and both post-treatment OHIP-20 scores with t = 6·470 for CV and t = 6·713 for NZ. Treatment ES was large for both types of dentures (>0·8). Difference of ES between NZ and CV dentures was small (ES < 0·2). None of the patient variables showed significant associations with OHIP-20 scores of the two types of dentures, except for preference and NZ OHIP-20 scores. For this group of patients, both treatment methods improved OHRQoL significantly and patient-related factors did not influence impact on OHRQoL differently for both interventions.

Do mandibular complete dentures made using a neutral zone technique improve speech?-A pilot study.

OBJECTIVE: The aim of this study was to evaluate speech sound production (SSP) in older edentulous patients provided with two different types of mandibular complete dentures (MCDs; conventional vs neutral zone). BACKGROUND: Regarding the fact that complete dentures (CDs) affect SSP, it is unknown whether the set-up of the artificial teeth resulting from the neutral zone technique leads to a negative impact on SSP. MATERIALS AND METHODS: For 21 participants, a conventional MCD and a MCD using a modified neutral zone technique (neutral zone dentures) were fabricated. The SSP was described using a phonetically balanced text, which was recorded digitally and evaluated. RESULTS: No significant difference in SSP was observed. CONCLUSION: Within the limits of this study, it can be concluded that the application of the neutral zone technique in the mandible has no considerable impact on SSP.

Ambient temperature influences tolerance to plant secondary compounds in a mammalian herbivore.

Growing evidence suggests that plant secondary compounds (PSCs) ingested by mammals become more toxic at elevated ambient temperatures, a phenomenon known as temperature-dependent toxicity. We investigated temperature-dependent toxicity in the desert woodrat (Neotoma lepida), a herbivorous rodent that naturally encounters PSCs in creosote bush (Larrea tridentata), which is a major component of its diet. First, we determined the maximum dose of creosote resin ingested by woodrats at warm (28-29°C) or cool (21-22°C) temperatures. Second, we controlled the daily dose of creosote resin ingested at warm, cool and room (25°C) temperatures, and measured persistence in feeding trials. At the warm temperature, woodrats ingested significantly less creosote resin; their maximum dose was two-thirds that of animals at the cool temperature. Moreover, woodrats at warm and room temperatures could not persist on the same dose of creosote resin as woodrats at the cool temperature. Our findings demonstrate that warmer temperatures reduce PSC intake and tolerance in herbivorous rodents, highlighting the potentially adverse consequences of temperature-dependent toxicity. These results will advance the field of herbivore ecology and may hone predictions of mammalian responses to climate change.

Optimal foraging behavior and the thermal neutral zone of Peromyscus leucopus during winter: A test using natural and controlled ambient temperatures.

Endotherms foraging at temperatures outside of their thermal neutral zone (TNZ) pay an increased energetic cost. We asked if thermally-induced changes in foraging costs influence quitting harvest rate (QHR) of mice. We predicted that mice foraging during the winter would have a higher QHR in more costly colder conditions. We conducted our study with wild caught Peromyscus leucopus in an enclosure located in West Terre Haute, Indiana. We assayed changes in QHR using the forager's giving up density (GUD), which is the amount of uneaten seeds reaming in a tray after foraging activity. Each night from January 12th to March 13th, we assigned 4 trays as "cold trays" (at ambient temperature), and 4 trays as "hot trays" (trays with a ceramic heat element that increased the temperatures of feeding trays ca. 10-15°C). GUDs (and therfore QHRs) increased as a function of decreasing ambient temperature. Furthermore there was an interaction between tray temperature and ambient temperature; namely, on cool nights mice had lower GUDs in the "hot trays", but on warm nights mice had lower GUDs in the "cold trays". The TNZ for P. leucopus actively foraging during winter may be closer to the environmental average temperature than typically measured in the laboratory. Overall, these results support the idea that QHR is related to an animal's foraging in thermally challenged conditions. We present a unique way of measuring an animal's TNZ in the field using behavioral indicators.

Patient satisfaction with complete dentures fabricated using two neutral zone techniques: a within-subject cross-over pilot study.

Several studies have compared complete dentures fabricated using conventional and neutral zone (NZ) techniques. However, studies comparing patient satisfaction with complete dentures fabricated using swallowing and phonetic NZ techniques are lacking in literature. To compare patient satisfaction with the complete dentures fabricated using the two NZ techniques. To compare the bucco-lingual dimensions of the NZ records obtained with these techniques. Ten completely edentulous subjects dissatisfied with their existing mandibular complete dentures participated in the study. Five subjects first received the swallowing neutral zone (SNZ) dentures and five the phonetic neutral zone (PNZ) dentures. Tissue conditioner was used as the recording material in both the techniques. After having worn the prosthesis for a minimum of 2 months, subjects responded to a questionnaire that measured their perceptions of various factors associated with the prosthesis. The prostheses were then changed and the procedures repeated. Student t test and non-parametric Mann-Whitney tests were used for statistical analysis. Level of statistical significance was set p < 0.05. There was no statistical significant difference in patient satisfaction with the SNZ and PNZ complete dentures for all the variables assessed. Statistical significant difference was observed for majority of the variables when the two NZ dentures were compared with patients' old dentures. The difference in the mean dimensions of the two NZ records was also found to be statistically insignificant except in the maxillary left premolar region. The study indicated that patient satisfaction with the complete dentures fabricated using SNZ technique did not significantly differ from that of the PNZ technique. Data gathered at the final appointment showed that SNZ dentures were preferred by the patients with regards to esthetics, stability, comfort and ability to chew. For ability to speak, mixed preferences were found.

Refining Complete Dentures: Optimizing Results with Enhanced Phonetics and Esthetics.

Tooth loss and subsequent complete denture rehabilitation can profoundly affect a patient's psychological and social well-being. Dentures play an important role in helping individuals regain a sense of normalcy as well as facilitating communication in today's appearance-conscious society. However, common issues with dentures include discomfort while chewing and dissatisfaction with esthetics and speech. Prosthetic rehabilitation for complete denture patients should aim not just at replacing missing teeth but at fully restoring masticatory functions and appearance. This article outlines a simple, economical, and esthetically pleasing approach to rehabilitating patients with complete dentures, particularly those with resorbed ridges and with difficulty in phonetics. The focus is on comprehensively restoring the patient's orofacial complex.

Comprehensive Approach for Rehabilitation of a Completely Edentulous Patient: A Case Report.

Complete edentulism poses significant challenges to oral function, esthetics, and overall quality of life. The use of complete dentures remains a cornerstone in rehabilitating such patients and restoring masticatory function, phonetics, and facial esthetics. However, to improve patients' function, it is important to restore the stomatognathic system. The rehabilitation process begins with a thorough assessment of the patient's oral health status, including evaluation of the remaining supporting structures and the surrounding soft tissues. Impressions and jaw relation records are meticulously obtained to ensure accurate denture fabrication. Proper denture retention, stability, and occlusion are crucial for successful rehabilitation. Beyond functional aspects, attention to esthetics plays a pivotal role in patient satisfaction and acceptance of complete dentures. Customization of denture teeth in terms of shape, shade, and arrangement is essential to achieve natural-looking smiles and facial harmony. Complete dentures remain a valuable treatment modality for the comprehensive rehabilitation of completely edentulous patients. Through a combination of meticulous treatment planning, advanced techniques, and patient-centered care, we can achieve successful outcomes in restoring oral function and thus improving the overall quality of life for such patients. Thus, this case report outlines a simple, economical, and useful rehabilitation plan for a patient with an edentulous maxillary and mandibular arch with flabby tissue and a resorbed mandibular ridge.

Optimizing Denture Success: A Strategy for Prosthodontic Rehabilitation in a Patient With Compromised Alveolar Ridges.

The ill-fitting and unstable complete denture prosthesis is the most commonly faced problem by patients with compromised resorbed ridge. The retention, support, and stability of dentures are compromised in severely resorbed ridges, leading to difficulty in mastication and swallowing. The flabby tissue can be managed by using appropriate mucostatic impression techniques, and severely resorbed ridges can be managed by the coordination of a complete denture prosthesis with the neuromuscular function using a neutral zone for the arrangement of artificial teeth. This case report presents a combination of the Hobkirk technique and the neutral zone concept for the rehabilitation of the flabby tissue and severely resorbed alveolar ridge.