Dental and endodontic-related stress amongst undergraduate students before and during the COVID-19 pandemic: A mixed-methods study.

AIM: To determine and explain the principal sources of stress among preclinical and clinical dental undergraduate students with a particular focus on the stressors linked to endodontics. METHODOLOGY: A mixed-methods study, with an explanatory sequential design, was employed. Volunteer students of second, third and fourth years were asked to complete both the Dental Environment Stress (DES) questionnaire and a bespoke questionnaire for endodontic-related stress assessment, which had 21 questions in common with the DES. The results were analysed by Kruskal-Wallis and Marginal Homogeneity tests. In the second part of the study, a qualitative phase was conducted through focus group interviews of students from each academic year included in the study. Interviews were analysed by inductive content analysis. RESULTS: The DES questionnaire determined that for all years the most stressful domains were 'performance pressure', 'workload' and 'clinical training'. According to the endodontic stress questionnaire, the most stressful domains were 'self-efficacy beliefs', 'endodontic clinical training' and 'faculty and administration' in early years, while they were 'endodontic patient treatment', 'performance pressure in endodontics' and 'clinical training' in later years. Comparing questions common to both questionnaires revealed that the stress score was lower for the endodontic stress questionnaire than in the DES questionnaire for 17 questions, being significantly lower for 13 questions (p < 0.05) and significantly higher for no question. The qualitative study showed that students' dental and endodontic-related stress was linked to different domains: patient, clinical procedure, organization, staff, academic education, evaluation and COVID-19-related issues. Qualitative aspects highlighted the important role that patients and COVID-19 have played in student stress. However, they suggested a possible explanation for the lower endodontic stress observed in this dental university hospital, which was based on: the nature of the teaching in endodontics, the consensus between endodontic supervisors, the use of a logical, progressive procedure and the considerable experience that students gain over the years. CONCLUSION: Students considered endodontics stressful; however, education can play a central role in reducing stress, particularly during the early parts of the undergraduate course.

Development and preliminary validation of an Objective Structured Assessment of Technical Skills (OSATS) for a partial pulpotomy procedure.

AIM: To develop an Objective Structured Assessment of Technical Skills (OSATS) tool for partial pulpotomy and to preliminary assess the validity of this tool. Secondary objectives were to check internal consistency as well as the interrater reliability of this specific checklist and to compare it with the previously validated global rating score (GRS). METHODOLOGY: The study assessed three groups of dental participants (mix of practitioners or students) possessing differing levels of clinical experience (7 novices, 7 intermediates, 7 experts), during a partial pulpotomy procedure on a simulated tooth with deep caries, using a bespoke procedure-specific checklist (PSC) and the GRS. Two independent examiners received the study participants in groups of two, in order to be able to directly observe their actions and grade the different steps of the procedure from 1 to 5 on the PSC and GRS. The internal validity of the specific checklist was assessed using a Cronbach's alpha test. As the construct validity of such a tool can be determined when the tool differentiates performance based on the level of experience, the total score of the PSC of the three groups (e.g., novice group, intermediate group, experienced group) were compared using the Kruskal-Wallis and post-hoc Mann-Whitney pairwise U test. The total scores of the GRS were also analysed in the same manner. A correlation test (Correlation Matrices Test) was carried out for the entire sample between the specific checklist and the GRS (on total score). The intraclass correlation coefficient was used to measure the degree of agreement between the two evaluators. The statistical analysis was performed with XLSTAT® and Statistica® (significance p = .05). RESULTS: The partial pulpotomy specific checklist graded from one to five demonstrated good internal consistency (0.86) and a good interrater reliability (0.91), a correct construct validity (p generally < .05) and a good positive correlation with the validated GRS (r = .92). CONCLUSIONS: To address the need to develop education in vital pulp treatment, and more specifically the technical skills assessment of partial pulpotomy, an OSATS-specific checklist was developed and preliminary validated. The checklist will need to be validated in larger cohorts.

Meta-analyses of the associations of mentalization and proxy variables with anxiety and internalizing problems.

Mentalization, the high-order function of detecting and interpreting one's own and others' mental states, has gained interest in the fields of clinical and developmental psychopathology. However, little is known about mentalization's associations with anxiety and broader internalizing problems. Using the framework of the multidimensional model of mentalization, the aim of this meta-analysis was to quantify the strength of the association between mentalization and anxiety/internalizing problems and to identify potential moderators of this association. A systematic review of the literature led to the inclusion of 105 studies (N = 19,529) covering all age groups. The global effect analysis showed a small negative association between mentalization and the overall anxious and internalizing symptomatology (r = -0.095, p = .000). Various effect sizes were found for associations between mentalization and specific outcomes (unspecified anxiety, social anxiety, generalized anxiety, and internalizing problems). The methods of assessment of mentalization and anxiety moderated their association. Findings support the presence of modest impairments in the mentalizing capacities of anxious individuals, likely influenced by their vulnerability to stress and the context in which they mentalize. Further studies are needed to draw a clear profile of mentalizing capacities with regard to specific anxious and internalizing symptomatologies.

Comparison of the cyclic fatigue resistance of One Curve, F6 Skytaper, Protaper Next, and Hyflex CM endodontic files.

Objectives: This study compared the cyclic fatigue resistance of One Curve (C wire) and F6 Skytaper (conventional austenite nickel-titanium [NiTi]), and 2 instruments with thermo-mechanically treated NiTi: Protaper Next X2 (M wire) and Hyflex CM (CM wire). Materials and Methods: Ten new instruments of each group (size: 0.25 mm, 6% taper in the 3 mm tip region) were tested using a rotary bending machine with a 60° curvature angle and a 5 mm curvature radius, at room temperature. The number of cycles until fracture was recorded. The length of the fractured instruments was measured. The fracture surface of each fragment was examined with a scanning electron microscope (SEM). The data were analyzed using one-way analysis of variance and the post hoc Tukey test. The significance level was set at 0.05. Results: At 60°, One Curve, F6 Skytaper and Hyflex CM had significantly longer fatigue lives than Protaper Next X2 (p < 0.05). No statistically significant differences were found in the cyclic fatigue lives of One Curve, F6 Skytaper, and Hyflex CM (p > 0.05). SEM images of the fracture surfaces of the different instruments showed typical features of fatigue failure. Conclusions: Within the conditions of this study, at 60° and with a 5 mm curvature radius, the cyclic fatigue life of One Curve was not significantly different from those of F6 Skytaper and Hyflex CM. The cyclic fatigue lives of these 3 instruments were statistically significantly longer than that of Protaper Next.

Preclinical 3D-printed laboratory simulation of deep caries and the exposed pulp reduced student anxiety and stress, while increasing confidence and knowledge in vital pulp treatment.

AIM: To evaluate the impact of a preclinical laboratory session using 3D printed teeth on dental student stress, anxiety, confidence and knowledge when treating deep caries and pulp exposure. METHODOLOGY: This was a two-centre controlled study, with randomized distribution of students into two groups: a vital pulp treatment (VPT) lecture-only (control) group and a VPT-lecture combined with a VPT-laboratory (experimental) group. In both universities, preclinical students with endodontic or operative dentistry laboratory sessions could participate. All students were invited to the lecture. Two weeks later (timepoint-T1), both groups completed validated and bespoke questionnaires and scales to evaluate their stress (Stress-VAS), anxiety (STAI Trait [T] and State [S]), self-confidence and knowledge. Thereafter, only the experimental group attended the hands-on laboratory session demonstrating the techniques of selective caries removal and partial pulpotomy on a commercial 3D-printed tooth. Two weeks later (timepoint-T2), the participants from both groups repopulated the same questionnaires and VAS. The control group had the laboratory session after the completion of the study. The statistical analysis was performed with Statistica® (significance p = .05). The homogeneity between the two samples was checked by Khi2 and Student tests. Stress-VAS, STAI-S, confidence and knowledge scores were compared within each group, and between the two groups, at T1 and T2, with a repeated measures anova test (+/-Tukey post-hoc test). RESULTS: The groups comprised 54 students each, with no statistical difference between the groups regarding demographic, academic data and STAI-T score. The two groups had no significant difference of Stress-VAS, STAI-S, confidence and knowledge scores at T1 while they presented a significant difference in stress, anxiety and confidence scores at T2, but with no significant difference in knowledge score. However, knowledge score, as other parameters, improved significantly between T1 and T2 in the experimental group. CONCLUSIONS: The addition of a laboratory session using 3D-printed teeth that simulated deep caries and pulp exposure management, significantly reduced the stress and anxiety of students and increased their confidence. Within the limitations of this study, the benefit of introducing new technology in increasing student confidence and reducing stress offers opportunity for educational improvement in the VPT and cariology areas.

Knowledge and Opinions of French Dental Students in Operative Dentistry - Management of Deep Carious Lesions.

PURPOSE: A questionnaire survey was recently undertaken among French dental students (FDSs) to investigate their practices, knowledge and opinions in various domains of minimal intervention (MI) in cariology. The present work focuses on management of deep carious lesions (DCLs). MATERIALS AND METHODS: The questionnaire was administered (Spring 2018) to all the fifth-year students of the 16 French dental schools. Descriptive analyses were performed. RESULTS: Among 1370 FDSs (response rate: 84.5%), hardness was the most commonly reported criterion for assessing the endpoint of carious tissue removal (53.9%), followed by firm dentin (40.0%). Regarding FDSs' opinion of leaving carious dentine under a restoration, 41.9% of the respondents agreed that carious tissues should always be removed completely. For an asymptomatic tooth with DCLs and exposed pulp, direct pulp capping was mainly chosen (93.9%). In a clinical case correctly diagnosed as a reversible pulpitis by 79.7% of respondents, nearly half of FDSs chose a one-step complete excavation (48.3%) followed by selective excavation (25.1%), then two-step complete excavation (20.9%) and a minority (5.7%) opted for pulpal therapy (biopulpotomy or endodontic treatment). CONCLUSION: The present results suggest an inadequate dissemination of MI concepts among FDSs towards DCL management. The present results show the need for a harmonisation and a reinforcement of teaching evidence-based MI according to the latest European recommendations.

Reflective Functioning in Children and Adolescents With and Without an Anxiety Disorder.

Reflective functioning (RF), meaning the capacity to interpret mental states (intentions, emotions, thoughts, desires, and beliefs) underlying one's own and others' behaviors, may help understand the dysfunctional self-regulation associated with anxiety disorders. However, research on anxiety and RF in clinical samples is scarce. This study aimed to assess whether mothers' and youths' RF was associated with youths' (a) anxiety disorders and symptoms and (b) internalizing symptoms. Another goal was to explore whether RF predicted anxiety and internalizing symptoms beyond the more commonly established effect of attachment. Canadian children and adolescents aged between 8 and 16years, and their mothers were recruited in an outpatient psychiatric clinic (clinical group with a diagnosed anxiety disorder, n=30, mean age=11.5±2.8years) and in the general population (non-clinical group, n=23, mean age=11.5±2.1years). The Child Attachment Interview was used to assess youths' attachment along with three dimensions of RF (global, regarding self, regarding others). Mothers' attachment and RF were assessed with the Adult Attachment Interview. Children's and adolescents' anxiety and internalizing symptoms were measured with the Behavior Assessment Scale for Children, second version. The clinical and non-clinical groups did not differ in mothers' or youths' RF. However, in the overall sample, youths' RF regarding themselves and maternal attachment preoccupation were associated with internalizing symptoms. Sequential regression analyses revealed that higher RF regarding self predicted a higher level of self-reported internalizing symptoms, beyond the effect of maternal attachment (ß=0.43, p<0.05). This study's finding suggests that clinically anxious children and adolescents have adequate RF. We propose that the sustained hypervigilance and apprehension associated with anxiety make anxious youths sensitive to their own and others' mental states. Our findings suggest that psychotherapeutic treatments for anxiety should make use of patients' RF abilities to help them make sense of their symptoms and thus reduce them.

Knowledge and Opinions of French Dental Students Toward Occlusal and Proximal Restorative Thresholds.

PURPOSE: To investigate the practices, knowledge and opinions of French dental students (FDSs) in various domains of minimal intervention (MI) in cariology. MATERIALS AND METHODS: A cross-sectional, questionnaire-based study was conducted in spring 2018 among all fifth-year French dental students (FDSs) from the 16 French dental schools. The present article focuses on restorative management. Statistical analyses (descriptive, chi-squared) were performed. RESULTS: The response rate was 84.5%. Overall, 97.4% of respondents would have operatively intervened for proximal and 83% for occlusal carious lesions, respectively, while non-or micro-invasive intervention would have been possible. Interestingly, 15% would completely open the occlusal fissures. For both occlusal and proximal lesions requiring a restoration, composite resin was indicated by over 95% of the respondents. In a clinical case, 51.6% of FDSs who rightly diagnosed an enamel carious lesion would operatively intervene. When FDSs could not diagnose the type of carious lesions, a high proportion of invasive actions were also reported (40%). FDSs who read scientific articles were more likely to consider the high importance of not filling sound teeth unnecessarily (p = 0.033). CONCLUSION: FDSs do not have sufficient awareness of MI guidelines regarding occlusal and proximal restorative thresholds. Efforts are required in dental schools to teach FDSs to postpone invasive/restorative strategies to later stages of carious progression. There is a need to strengthen prevention techniques and non-invasive options in the teaching of MI in cariology.

Knowledge and opinions of French dental students related to caries risk assessment and dental sealants (preventive and therapeutic).

OBJECTIVES: A national questionnaire study was performed to document knowledge and opinions of French dental students (FDSs) about minimal intervention (MI) in dentistry especially caries risk assessment (CRA) and dental sealants (DSs). MATERIALS AND METHODS: A questionnaire was administered to the fifth-year dental FDSs (n = 1370) from the 16 French dental schools. Descriptive and statistical analyses were performed. RESULTS: The response rate was 84.5%. A large majority of respondents (87.8%) linked MI with minimally invasive dentistry and 77.4% considered MI as a concept based on prevention. About 80% stated they use CRA in clinical practice, mostly without any specific form. If 80.4% of the respondents would base their treatment plans on CRA, only 55.1% would regularly plan preventive regimens according to individual risk level. However, while 96.6% declared they perform preventive DSs, only 44.3% considered therapeutic sealants as a routine treatment. Although 75.1% of FDSs stated that they had sufficient learning and training related to CRA, 55.9% thought that they need further education about preventive and therapeutic DSs. CONCLUSION: Although FDSs seem to be aware of the importance of CRA and preventive strategies, this study shows the need to harmonize the teaching in cariology according to the latest European recommendations. CLINICAL RELEVANCE: A national questionnaire study showed variability towards knowledge and opinions of FDSs related to MI in cariology. This may impact care provisions in their future professional life showing the urgent need to harmonize the teaching of MI in cariology in France.

Dental emergencies at sea: A study in the French maritime TeleMedical Assistance Service.

INTRODUCTION: The aim of the study was to assess the frequency, features and management of dental emergencies at sea in France. METHODS: A descriptive study was carried out by retrospectively examining medical records of patients who were assisted by the French maritime TeleMedical Assistance Service (TMAS) from 2012 to 2016. Data were ranked in different categories: socio-demographic data, diagnosis, prescription, and monitoring or treatment prescribed. RESULTS: The TMAS recorded 9122 medical files for all medical emergencies. Among these medical records 135 concerned oral diseases. The main causes for dental emergencies are dental abscess (51.8%), tooth decay (33.3%), and dental fracture (8.9%). Even where teledentistry is validated for remote screening and oral lesion diagnosis, management of dental emergencies mostly requires a dental procedure. On board, without special equipment and/or specifically trained healthcare workers, this management often results in the prescription of medication. DISCUSSION: The International Medical Guide for Ships published by the World Health Organization could be updated to suit the latest recommendations of dental emergency management. This could facilitate the addition of a medical act to dental management, resulting in more effective treatment. Furthermore, simple and specific equipment could be added to the medical supplies.

Characterization and Antimicrobial Susceptibility of Lactococcus lactis Isolated from Endodontic Infections in Ouagadougou, Burkina Faso.

BACKGROUND: This study aimed to characterize and test the antimicrobial susceptibility of Lactococcus lactis isolated in endodontic infections in Burkina Faso. MATERIAL AND METHODS: This was a prospective study conducted at the Municipal Oral Health Center of Ouagadougou, Burkina Faso, from June to October 2014. Clinical data were collected using a questionnaire form. The method of streaking on selective medium was used to isolate bacteria. Identification was made using the API 20 Strep gallery. Antibiotic susceptibility was performed by the diffusion method on solid medium. RESULTS: One hundred and twenty-five (125) patients were received with a significant proportion from the age group of 19 to 40 years (55.2%). Apical periodontitis accounted for 50.4% and cellulitis for 49.6% of cases. Lactococcus lactis ssp. lactis was identified in five exudate samples. Isolates were 100% resistant to cefixime and metronidazole, 80% to ceftriaxone, cefuroxime, cefotaxime, chloramphenicol and 60% to penicillin G, amoxicillin, amoxicillin clavulanic acid. A multidrug resistance of more than three families of antibiotics was noticed. No strains produced extended spectrum ß-lactamases. CONCLUSION: Lactococcus lactis is part of endodontic biofilm. The reported strong antibiotic resistance involving endodontic therapy will focus on the effect of the disinfectant solution and the mechanical action of the canal instruments.

A Survey of Endodontic Practices among Dentists in Burkina Faso.

AIM: Dental surgeons must be aware of the most appropriate endodontic treatments and how to properly conduct them. The aim of this study was to evaluate the knowledge of dental surgeons in Burkina Faso in terms of endodontic treatment procedures. MATERIALS AND METHODS: This descriptive, cross-sectional study was performed during the regular annual conference of the National Board of Dental Surgeons of Burkina Faso, held on February 27 and 28, 2015 in Ouagadougou, through a questionnaire. RESULTS: A total of 33 practitioners took part (52.4% of the dental surgeons of Burkina Faso) in the study. The majority of them (90.9%) used sodium hypochlorite as their preferred irrigation solution. Nearly half of the dental surgeons (48.5%) did not know how to use a permeabilization file, and most did not make use of nickel-titanium (NiTi) mechanized instruments (78.8%) or rubber dams (93.9%). Approximately two-thirds of participants did not perform file-in-place radiography (66.7%) or control radiography of the canal obturation (63.6%). The adjusted single-cone technique was the most commonly used (87.9%). CONCLUSION: This study highlights that the majority of dental surgeons in Burkina Faso are not using the currently recommended endodontic procedures to perform obturations. CLINICAL SIGNIFICANCE: Dental surgeons in Burkina Faso must commit to regularly upgrading their knowledge and techniques. Key words: Burkina faso, Cross-sectional study, Dental surgeons, Endodontic treatments, Protocol adherence.

Sleep and attachment in early childhood: a series of meta-analyses.

Empirical findings regarding the association between child attachment and sleep have been inconsistent. The objectives of this series of meta-analyses were to assess the size of the association between child sleep and attachment and to examine whether study methodology (attachment measure, sleep measure) and age moderate this association. Sixteen studies (2783 children aged from 6 to 38 months) were included. Significant associations were found between attachment security and sleep efficiency (r = .18) and attachment resistance and sleep problems (r = .18). There were significant moderator effects of sleep measure and age of the child, with the size of the association between sleep and attachment security increasing with age (R2 analog = .67). Inconsistent findings are likely due to inter-study variabilities in methodology and to a developmental effect on the sleep-attachment association.

Dental pain induced by an ambient thermal differential: pathophysiological hypothesis.

Dental pain triggered by temperature differential is a misrecognized condition and a form of dental allodynia. Dental allodynia is characterized by recurrent episodes of diffuse, dull and throbbing tooth pain that develops when returning to an indoor room temperature after being exposed for a long period to cold weather. The pain episode may last up to few hours before subsiding. Effective treatment is to properly shield the pulpal tissue of the offending tooth by increasing the protective layer of the dentin/enamel complex. This review underscores the difference in dentin hypersensitivity and offers a mechanistic hypothesis based on the following processes. Repeated exposure to significant positive temperature gradients (from cold to warm) generates phenotypic changes of dental primary afferents on selected teeth with subsequent development of a "low-grade" neurogenic inflammation. As a result, nociceptive C-fibers become sensitized and responsive to innocuous temperature gradients because the activation threshold of specific TRP ion channels is lowered and central sensitization takes place. Comprehensive overviews that cover dental innervation and sensory modalities, thermodynamics of tooth structure, mechanisms of dental nociception and the thermal pain are also provided.

Comparative analysis of canal transportation and centring ability of three Ni-Ti rotary endodontic systems: Protaper®, MTwo® and Revo-S™, assessed by micro-computed tomography.

The aim of this study was to use high-resolution micro-CT to evaluate the effects of three Ni-Ti rotary endodontic instruments, Mtwo® (VDW, München, Germany), ProTaper® (Dentsply-Maillefer, Ballaigues, Switzerland) and Revo-S™ (MicroMega, Besançon, France), on canal transportation and centring ratio. Fifty-four mesial roots of extracted mandibular molars with an angle of curvature of 25-35° were randomly divided into three groups of eighteen. Each group was instrumented with a previously unused Ni-Ti rotary system. The final instruments used were #30/0.05 taper (Mtwo®), F3 #30/0.09 apical taper (ProTaper®) and AS30 #30/0.06 taper (Revo-S™). Teeth were scanned before and after instrumentation using micro-computed tomography with a spatial resolution of 20 µm to measure volume and shaping changes. All images were filtered to improve signal-to-noise ratio. To determine the perimeter of roots and canals exactly, images were segmented in each slice with an edge detection process. Canal transportation and centring ratio were evaluated at 1, 3, 5 and 7 mm from the end of each root. The method developed by Gambill et al. was chosen. ANOVA was conducted with the significance threshold set at p < 0.05. No statistically significant differences were found among the three groups in terms of canal transportation or centring ratio at any level. These systems give similar results with regard to the tested shaping parameters. Under the tested conditions and within the limitations of this study, these systems were able to produce centred preparations of curved canals with minimal transportation.

Cell types and coincident synapses in the ellipsoid body of Drosophila.

Cellular ultrastructures for signal integration are unknown in any nervous system. The ellipsoid body (EB) of the Drosophila brain is thought to control locomotion upon integration of various modalities of sensory signals with the animal internal status. However, the expected excitatory and inhibitory input convergence that virtually all brain centres exhibit is not yet described in the EB. Based on the EB expression domains of genetic constructs from the choline acetyl transferase (Cha), glutamic acid decarboxylase (GAD) and tyrosine hydroxylase (TH) genes, we identified a new set of neurons with the characteristic ring-shaped morphology (R neurons) which are presumably cholinergic, in addition to the existing GABA-expressing neurons. The R1 morphological subtype is represented in the Cha- and TH-expressing classes. In addition, using transmission electron microscopy, we identified a novel type of synapse in the EB, which exhibits the precise array of two independent active zones over the same postsynaptic dendritic domain, that we named 'agora'. This array is compatible with a coincidence detector role, and represents ~8% of all EB synapses in Drosophila. Presumably excitatory R neurons contribute to coincident synapses. Functional silencing of EB neurons by driving genetically tetanus toxin expression either reduces walking speed or alters movement orientation depending on the targeted R neuron subset, thus revealing functional specialisations in the EB for locomotion control.

How does pea architecture influence light sharing in virtual wheat-pea mixtures? A simulation study based on pea genotypes with contrasting architectures.

BACKGROUND AND AIMS: Light interception is a key factor driving the functioning of wheat-pea intercrops. The sharing of light is related to the canopy structure, which results from the architectural parameters of the mixed species. In the present study, we characterized six contrasting pea genotypes and identified architectural parameters whose range of variability leads to various levels of light sharing within virtual wheat-pea mixtures. METHODOLOGY: Virtual plants were derived from magnetic digitizations performed during the growing cycle in a greenhouse experiment. Plant mock-ups were used as inputs of a radiative transfer model in order to estimate light interception in virtual wheat-pea mixtures. The turbid medium approach, extended to well-mixed canopies, was used as a framework for assessing the effects of leaf area index (LAI) and mean leaf inclination on light sharing. PRINCIPAL RESULTS: THREE GROUPS OF PEA GENOTYPES WERE DISTINGUISHED: (i) early and leafy cultivars, (ii) late semi-leafless cultivars and (iii) low-development semi-leafless cultivars. Within open canopies, light sharing was well described by the turbid medium approach and was therefore determined by the architectural parameters that composed LAI and foliage inclination. When canopy closure started, the turbid medium approach was unable to properly infer light partitioning because of the vertical structure of the canopy. This was related to the architectural parameters that determine the height of pea genotypes. Light capture was therefore affected by the development of leaflets, number of branches and phytomers, as well as internode length. CONCLUSIONS: This study provides information on pea architecture and identifies parameters whose variability can be used to drive light sharing within wheat-pea mixtures. These results could be used to build up the architecture of pea ideotypes adapted to multi-specific stands towards light competition.

Synapse loss in olfactory local interneurons modifies perception.

Synapse loss correlates with cognitive decline in aging and most neurological pathologies. Sensory perception changes often represent subtle dysfunctions that precede the onset of a neurodegenerative disease. However, a cause-effect relationship between synapse loss and sensory perception deficits is difficult to prove and quantify due to functional and structural adaptation of neural systems. Here we modified a PI3K/AKT/GSK3 signaling pathway to reduce the number of synapses--without affecting the number of cells--in five subsets of local interneurons of the Drosophila olfactory glomeruli and measured the behavioral effects on olfactory perception. The neuron subsets were chosen under the criteria of GABA or ChAT expression. The reduction of one subset of synapses, mostly inhibitory, converted the responses to all odorants and concentrations tested as repulsive, while the reduction of another subset, mostly excitatory, led to a shift toward attraction. However, the simultaneous reduction of both synapse subsets restored normal perception. One group of local interneurons proved unaffected by the induced synapse loss in the perception of some odorants, indicating a functional specialization of these cells. Using genetic tools for space and temporal control of synapse number decrease, we show that the perception effects are specific to the local interneurons, rather than the mushroom bodies, and are not based on major structural changes elicited during development. These findings demonstrate that synapse loss cause sensory perception changes and suggest that normal perception is based on a balance between excitation and inhibition.

Comparative analysis of torsional and bending behavior through finite-element models of 5 Ni-Ti endodontic instruments.

OBJECTIVES: The objectives of this study were to compare numerically the bending and torsional mechanical behavior of 5 endodontic rotary Ni-Ti instruments with equivalent size and various designs for tapers, pitch, and cutting blades.First, the geometries of Hero (20/0.06), HeroShaper (20/0.06), ProFile (20/0.06), Mtwo (20/0.06), and ProTaper F1 were generated by finite element code. Then, the 2 most representative clinical loadings, i.e., bending and torsion, were studied with an ad hoc model for the superelasticity of Ni-Ti. Bending was generated by tip deflection and torsion by a constant twist-angle of the tip. RESULTS: Mechanical behavior of these 5 endodontic rotary Ni-Ti instruments could be evaluated and compared. Protaper F1 presented the greatest level of bending stress and torque. Hero and HeroShaper were more rigid than ProFile and Mtwo. CONCLUSIONS: This numerical comparison evaluated the effects of the geometrical parameters on the instrumental mechanical behavior. The 5 endodontic instruments, investigated in the present study, do not have the same bending and torsional mechanical behavior. Each clinician must be aware of these behavior differences so as to use the adequate file according to the clinical situation and to the manufacturer's recommendations.

An improved model of 3-dimensional finite element analysis of mechanical behavior of endodontic instruments.

OBJECTIVES: The aim of this study was to develop a numeric method to study the mechanical behavior of an endodontic instrument during different loading paths and to demonstrate the importance of the behavior model in the finite element results. STUDY DESIGN: A numeric study of an endodontic instrument was carried out. At first, the geometry was meshed with a finite element code. Then, 3 among the most representative loadings in clinical use, i.e., bending, torsion, and nonproportional bending-torsion, were studied. Each of them was simulated by setting 3 different behaviors: elasticity, elastoplasticity, and an ad hoc model for the superelasticity. RESULTS: The simulations with nonproportional bending-torsion loading showed that the mechanical behavior of Ni-Ti shape memory alloy was strongly affected by change in the loading direction. Elastic and elastoplastic models were unable to consider this feature of Ni-Ti behavior. Only a superelastic model taking into account the effects of nonproportional loading proved to respect this crucial point. CONCLUSION: To realize valid simulations of the mechanical behavior of Ni-Ti instruments during different mechanical loading paths, it is necessary to use an ad hoc mechanical behavior model.