Surface Crack Monitoring by Rayleigh Waves with a Piezoelectric-Polymer-Film Ultrasonic Transducer Array.

This paper presents a method for measuring surface cracks based on the analysis of Rayleigh waves in the frequency domain. The Rayleigh waves were detected by a Rayleigh wave receiver array made of a piezoelectric polyvinylidene fluoride (PVDF) film and enhanced by a delay-and-sum algorithm. This method employs the determined reflection factors of Rayleigh waves scattered at a surface fatigue crack to calculate the crack depth. In the frequency domain, the inverse scattering problem is solved by comparing the reflection factor of the Rayleigh waves between the measured and the theoretical curves. The experimental measurement results quantitatively matched the simulated surface crack depths. The advantages of using the low-profile Rayleigh wave receiver array made of a PVDF film for detecting the incident and reflected Rayleigh waves were analyzed in contrast with those of a Rayleigh wave receiver using a laser vibrometer and a conventional lead zirconate titanate (PZT) array. It was found that the Rayleigh waves propagating across the Rayleigh wave receiver array made of the PVDF film had a lower attenuation rate of 0.15 dB/mm compared to that of 0.30 dB/mm of the PZT array. Multiple Rayleigh wave receiver arrays made of the PVDF film were applied for monitoring surface fatigue crack initiation and propagation at welded joints under cyclic mechanical loading. Cracks with a depth range of 0.36-0.94 mm were successfully monitored.

Hybrid versus distance learning environment for a paediatric dentistry course and its influence on students' satisfaction: a cross-sectional study.

BACKGROUND: During the novel COVID-19 pandemic, many universities adopted distance and hybrid learning as a modification to their teaching methods to ensure continuity of education, abiding by the worldwide recommendations of social distancing. AIM: To compare learning environments created through hybrid learning versus distance learning, to deliver paediatric dentistry course, and to assess the correlation between the created learning environment and students' satisfaction. METHOD: In this cross-sectional study, students enrolled in a hybrid paediatric dentistry course were asked to participate in an electronic survey. The learning environment was assessed using Distance Educational Learning Environment Survey (DELES), students' satisfaction was assessed using Satisfaction Scale (SS). Retrospective data for distance learning course was used for comparison. Ordinal data were compared using Mann-Whitney U test. Spearman's rank order correlation coefficient was used to correlate students' satisfaction with DELES. Multiple regression analysis was used to predict satisfaction. RESULTS: A total of 376 students' data were considered in the study. Hybrid learning had significantly higher scores than distance learning in 3 DELES scales. There was a statistically significant weak positive correlation between satisfaction and DELES. Multiple regression analysis model was statistically significant and accounted for (22.8%) of the variance in students' satisfaction. Only "Instructor support" (p = 0.001) and "Student autonomy" (p < 0.001) had a significant effect on satisfaction. CONCLUSION: This study supports the superiority of a hybrid learning environment over a complete distance learning environment, it also shows that satisfaction is correlated and can be predicted by the created learning environment. TRIAL REGISTRATION: This study has been registered on clinicaltrials.gov on 21 May 2020 with an identifier: NCT04401371 .

Validation of the Arabic translation of the caries impacts and experiences questionnaire for children.

BACKGROUND: The recently developed Caries Impacts and Experiences Questionnaire for Children (CARIES-QC) is originally an English questionnaire targeting the assessment of caries-related quality of life from a child's point of view. AIM: This study aimed to translate and adapt the CARIES-QC into the Arabic language and to test its reliability and validity on Arabic-speaking children. DESIGN: A total of 234 children aged 5-16 years answered the translated questionnaire. Internal consistency was measured using Cronbach's alpha; 62 children answered the questionnaire again to evaluate the test-retest reliability by calculating the intraclass correlation coefficient (ICC). Convergent validity was evaluated by correlating question scores with global question scores. Confirmatory factor analysis (CFA) was conducted to evaluate cross-cultural validity. RESULTS: Cronbach's alpha of the CARIES-QC/A was 0.905. The inter-item correlation coefficients of the CARIES-QC/A ranged from 0.240 to 0.850. The total ICC score was 0.960. CFA demonstrated acceptable fit to the data in the one-factor model. Convergent validity indicated moderate correlation with the global question (rs  = .740). CONCLUSION: The CARIES-QC/A is a valid and reliable tool that could be used to evaluate oral health-related quality of life in Arabic-speaking children.

Electromechanically Active As-Electrospun Polystyrene Fiber Mat: Significantly High Quasistatic/Dynamic Electromechanical Response and Theoretical Modeling.

Flexible and lightweight pressure sensors have attracted tremendous attention as a promising component of wearable biological motion sensors and artificial electronic skins. Here, the electromechanical response of as-electrospun fiber mats composed of a commodity polymer, atactic polystyrene, which can be applied in low-cost/large-area, flexible, and lightweight pressure sensors is demonstrated. The fiber mat demonstrates a significantly high apparent converse piezoelectric constant of >30 000 pm V-1 under static measurement and ≈13 000 pm V-1 even at a high frequency of 1 kHz. The first theoretical model to explain the unique electromechanical response is constructed, which reveals that the softness and moderate charge of the fiber mat are the reasons for the significantly high electromechanical response. Further, apparent piezoelectric constants obtained by direct measurement are lower than those obtained by the converse measurement, which is attributed to the densification and hardening of the fiber mat due to prepressure applied in direct measurement. These findings are likely to serve as a milestone for the development of large-area, flexible, and lightweight pressure sensors at low cost, as well as highly movable actuators like optical modulators without a substantial mechanical load.

Effectiveness of buccal infiltration anaesthesia compared to inferior alveolar nerve block anaesthesia in primary mandibular molar extractions: a randomised controlled study.

Aim The current study assessed the efficiency of buccal infiltration (BI) and inferior alveolar nerve block (IANB) during the extraction of deciduous mandibular molars.Subjects and method A total of 112 children aged between 5-8 years with mandibular molar indicated for extraction were divided into two groups at random. The BI group was injected with 4% articaine using BI, while the IANB group was injected with 2% lidocaine using IANB. The effectiveness of both techniques was examined using the Wong-Baker FACES Pain Rating Scale (W-BFPRS); Faces, Legs, Activity, Cry, and Consolability (FLACC) scale; and pulse oximetry.Results Using the W-BFPRS scale, success rates were 83.9% and 75.0% for the BI group and 82.1% and 71.4% for the IANB group during the injection and extraction, respectively, while using the FLACC scale, success rates were 83.9% and 92.9% for the BI group and 78.6% and 89.3% for the IANB group. In terms of pulse rate and oxygen saturation, there was no significant difference between the two groups.Conclusions BI with articaine is as efficient as IANB with lidocaine in the extraction of deciduous mandibular molars.

Inhibitory effect of silver nanoparticles synthesized using the chamomile extract against Streptococcus mutans cariogenic pathogen.

BACKGROUND: With the recent use and development of nanomaterials, silver nanoparticles (AgNPs) are gaining much attention as a promising antibacterial agent for use in caries prevention. OBJECTIVES: This study aimed to biosynthesize AgNPs using chamomile extract as a reducing agent and to investigate its inhibitory effect against Streptococcus mutans (S. mutans) dental bacteria. MATERIAL AND METHODS: Chamomile extract was prepared by sonication and added dropwise to silver nitrate (1mM) solution to synthesize AgNPs. Its formation was confirmed spectrophotometrically, and its size was determined. The disc diffusion method was used to test the antibacterial activity of the biosynthesized AgNPs against S. mutans. Also, its minimum inhibitory concentration (MIC) was assessed. RESULTS: The spectrum of biosynthesized AgNPs showed a maximum peak at 454 nm, and the peak area increased with increasing time. The mean AgNP size was 41 nm. The inhibition zone diameter recorded for AgNPs against S. mutans was 10 mm, while the MIC was 280 µg/ml. CONCLUSIONS: AgNPs biosynthesized using chamomile extract were proven to exert good antibacterial activity against cariogenic S. mutans. Using chamomile extract as a reducing agent can provide a rapid, affordable, and eco-friendly approach for AgNP production, which could be incorporated into various dental vehicles for dental caries prevention.

Enabling Distributed Intelligence with Ferroelectric Multifunctionalities.

Distributed intelligence involving a large number of smart sensors and edge computing are highly demanded under the backdrop of increasing cyber-physical interactive applications including internet of things. Here, the progresses on ferroelectric materials and their enabled devices promising energy autonomous sensors and smart systems are reviewed, starting with an analysis on the basic characteristics of ferroelectrics, including high dielectric permittivity, switchable spontaneous polarization, piezoelectric, pyroelectric, and bulk photovoltaic effects. As sensors, ferroelectrics can directly convert the stimuli to signals without requiring external power supply in principle. As energy transducers, ferroelectrics can harvest multiple forms of energy with high reliability and durability. As capacitors, ferroelectrics can directly store electrical charges with high power and ability of pulse-mode signal generation. Nonvolatile memories derived from ferroelectrics are able to realize digital processors and systems with ultralow power consumption, sustainable operation with intermittent power supply, and neuromorphic computing. An emphasis is made on the utilization of the multiple extraordinary functionalities of ferroelectrics to enable material-critical device innovations. The ferroelectric characteristics and synergistic functionality combinations are invaluable for realizing distributed sensors and smart systems with energy autonomy.

Sound Absorption Improvement in Porous Ferroelectret Polyethylene with Effective Piezoelectric Mechanism.

Airborne sound absorption in porous materials involves complex mechanisms of converting mechanical acoustic energy into heat. In this work, the effective piezoelectric properties of polyethylene ferroelectret foams on sound absorption were investigated by comparable samples with and without the piezoelectric response. Corona poling and thermal annealing treatments were applied to the samples in order to enable and remove the piezoelectric property, respectively, while the microstructure and the mechanical properties remained substantially unchanged. The effective piezoelectric properties and airborne sound absorption coefficients of the polyethylene foam samples before and after material treatments were measured and analyzed. Our experimental results and theoretical analysis showed that the open-cell ferroelectret polymer foam with an effective piezoelectric property provides an additional electromechanical energy conversion mechanism to enhance the airborne acoustic absorption performance.

Intercalation-driven ferroelectric-to-ferroelastic conversion in a layered hybrid perovskite crystal.

Two-dimensional (2D) organic-inorganic hybrid perovskites have attracted intense interests due to their quantum well structure and tunable excitonic properties. As an alternative to the well-studied divalent metal hybrid perovskite based on Pb2+, Sn2+ and Cu2+, the trivalent metal-based (eg. Sb3+ with ns2 outer-shell electronic configuration) hybrid perovskite with the A3M2X9 formula (A = monovalent cations, M = trivalent metal, X = halide) offer intriguing possibilities for engineering ferroic properties. Here, we synthesized 2D ferroelectric hybrid perovskite (TMA)3Sb2Cl9 with measurable in-plane and out-of-plane polarization. Interestingly, (TMA)3Sb2Cl9 can be intercalated with FeCl4 ions to form a ferroelastic and piezoelectric single crystal, (TMA)4-Fe(iii)Cl4-Sb2Cl9. Density functional theory calculations were carried out to investigate the unusual mechanism of ferroelectric-ferroelastic crossover in these crystals.

Structure and High Performance of Lead-Free (K0.5Na0.5)NbO3 Piezoelectric Nanofibers with Surface-Induced Crystallization at Lowered Temperature.

Lead-free potassium and sodium niobate (KNN) nanofiber webs with random and aligned configurations were prepared by the electrospinning process from polymer-modified chemical solution. The crystallization process, structure, composition, dielectric, ferroelectric, and piezoelectric properties of the nanofibers and nanofiber webs were investigated. Theoretical analysis and experimental results showed that the surface-induced heterogeneous nucleation resulted in the remarkable lower crystallization temperature for the KNN nanofibers with the {100} orientation of the perovskite phase in contrast to the bulk KNN gel and thus well-controlled chemical stoichiometry. Low dielectric loss, large electric polarization, and high piezoelectric performance were obtained in the nanofiber webs. In particular, the aligned nanofiber web exhibited further improved piezoelectric strain and voltage coefficients and higher FOM than their thin film counterparts and is promising for high-performance electromechanical sensor and transducer applications.

Case Report: Clinical manifestation and dental management of Papillon-Lefèvre syndrome.

Background: Papillon-Lefèvre syndrome (PLS) is considered a rare syndrome, which is characterized by the presence of palmar-plantar hyperkeratosis and aggressively progressing periodontitis that finally leads to premature loss of both deciduous and permanent teeth. Case report: A four-year-old Egyptian boy presented with a maternal complaint that her child suffers from early loss of many teeth, presence of loose teeth along with an asymptomatic swelling related to the upper anterior area. The patient was diagnosed with PLS. A symptomatic management and prevention program was followed and the swelling was excised; afterwards diagnosed as peripheral ossifying fibroma. Conclusion: Early recognition and intervention for patients with PLS is essential to avoid the threat of being edentulous if left unmanaged.