Self-Shielding of X-ray Emission from Ultrafast Laser Processing Due to Geometrical Changes of the Interaction Zone.

Materials processing with ultrashort laser pulses is one of the most important approaches when it comes to machining with very high accuracy. High pulse repetition rates and high average laser power can be used to attain high productivity. By tightly focusing the laser beam, the irradiances on the workpiece can exceed 1013 W/cm2, and thus cause usually unwanted X-ray emission. Pulsed laser processing of micro holes exhibits two typical features: a gradual increase in the irradiated surface within the hole and, with this, a decrease in the local irradiance. This and the shielding by the surrounding material diminishes the amount of ionizing radiation emitted from the process; therefore, both effects lead to a reduction in the potential X-ray exposure of an operator or any nearby person. The present study was performed to quantify this self-shielding of the X-ray emission from laser-drilled micro holes. Percussion drilling in standard air atmosphere was investigated using a laser with a wavelength of 800 nm a pulse duration of 1 ps, a repetition rate of 1 kHz, and with irradiances of up to 1.1·1014 W/cm. The X-ray emission was measured by means of a spectrometer. In addition to the experimental results, we present a model to predict the expected X-ray emission at different angles to the surface. These calculations are based on raytracing simulations to obtain the local irradiance, from which the local X-ray emission inside the holes can be calculated. It was found that the X-ray exposure measured in the surroundings strongly depends on the geometry of the hole and the measuring direction, as predicted by the theoretical model.

Microwave disinfection of facial silicone prostheses, Part 1: Color stability.

STATEMENT OF PROBLEM: The choice of cleaning method is an important consideration for lengthening the serviceable time of facial prostheses as microbial organisms and biofilms could degrade facial prostheses and cause skin irritation. Whether microwave disinfection is a suitable cleaning method without degradation of the properties of a prosthesis is unclear. PURPOSE: The purpose of this in vitro study was to measure the color stability of 6 commonly used facial silicone elastomers after microwave disinfection over a simulated 1.5-year period. MATERIAL AND METHODS: Six different facial silicone elastomers: MDX4-4210, MDX4-4210/Type A, M511, A-2186, VST-50, and A-2000 were mixed with intrinsic silicone white opacifier (except for the control group) and subsequently combined with 4 silicone intrinsic pigment color groups: red (R), yellow (Y), burnt sienna (B), and a mixture of R+Y+B (M). The control group was a silicone elastomer without opacifier or pigment. Each of the 30 experimental groups consisted of 5 specimens (N=150). Five specimens were placed in a 250-mL Erlenmeyer flask filled with 160 mL of tap water. Seven flasks were then placed in a 660-W microwave oven. An exposure of 6 minutes was used according to the antimicrobial efficacy of microwave disinfection protocol on facial silicone prostheses with a final water temperature of 60 °C for 18 times (simulating 1.5 years of microwave disinfection with one 6-minute exposure monthly). A spectrophotometer was used to measure reflectance color change values (∆E). Color differences were calculated following CIELab (∆E*ab) and CIEDE2000 (∆E00) formulae. ∆E*ab and ∆E00 were statistically analyzed by a linear mixed effects model with 3 factors (silicone type, color shade, and time) using the R Statistical software program (α=.05). RESULTS: Both ∆E*ab and ∆E00 of all silicone elastomers studied were less than the visual perceptibility thresholds (∆E*ab<1.1 and E00<0.7) and were considered clinically acceptable (∆E*ab<3.0 and E00<2.1) after the 1.5-year simulation of microwave disinfection. Yellow and blue pigments had more effect on MDX4-4210 and M511, while red pigment had more effect on MDX4-4210, MDX4-4210/Type A, and M511 (P<.05). Nevertheless, the values were still below the perceptibility threshold (∆E*ab≤1.0 and E00<0.6). CONCLUSIONS: All 6 facial silicone elastomers maintained clinically acceptable color after 18 months of exposure to microwave disinfection.

A Workflow for Identifying Viable Crystal Structures with Partially Occupied Sites Applied to the Solid Electrolyte Cubic Li7La3Zr2O12.

To date, experimental and theoretical works have been unable to uncover the ground-state configuration of the solid electrolyte cubic Li7La3Zr2O12 (c-LLZO). Computational studies rely on an initial low-energy structure as a reference point. Here, we present a methodology for identifying energetically favorable configurations of c-LLZO for a crystallographically predicted structure. We begin by eliminating structures that involve overlapping Li atoms based on nearest neighbor counts. We further reduce the configuration space by eliminating symmetry images from all remaining structures. Then, we perform a machine learning-based energetic ordering of all remaining structures. By considering the geometrical constraints that emerge from this methodology, we determine that a large portion of previously reported structures may not be feasible or stable. The method developed here could be extended to other ion conductors. We provide a database containing all of the generated structures with the aim of improving accuracy and reproducibility in future c-LLZO research.

The impact of coronavirus disease 2019 pandemic on dental school assessments - Current status and future perspectives.

PURPOSE: To evaluate course directors' feedback on the assessment methods used during the coronavirus disease 2019 (COVID-19) pandemic and identify effective approaches for future assessments in dental education. METHODS: Course directors at the US dental schools were surveyed for changes in assessments implemented during the early stages of the pandemic (March-July 2020) using the Qualtrics platform. The survey questions addressed assessment methods utilized in didactic, preclinical, and clinical arenas pre-COVID-19 (before March 2020) and during the early phase of the pandemic (between March and July 2020) and identified any sustained changes in assessments post-COVID-19. Of the 295 responses for the type of courses directed, 48%, 22%, and 30% responses were for didactic, pre-clinical, and clinical assessments, respectively. Chi-square tests and 95% confidence intervals were used to assess quantitative differences. RESULTS: Computer-based un-proctored and remote- proctored assessments increased whereas paper-based in-person proctored assessments decreased during an early pandemic. For pre-clinical and clinical courses, objective-structured clinical exams and case-based assessments increased whereas, for didactic courses, the number of presentations, short-answer, and multiple-choice questions-based assessments increased. Specimen-based assessments and patient-based encounters decreased significantly in didactic and clinical courses, respectively. Manikin-based exams increased in clinical but not in pre-clinical courses. Survey respondents disagreed that alternative assessments helped students learn better, resulted in better course evaluations, or were an equivalent replacement for pre-COVID-19 assessments. Interestingly, 49% of respondents indicated a likelihood of continuing alternative assessments whereas 36% were unlikely and 15% were neutral. CONCLUSIONS: A combination of effective pre-pandemic and innovative alternative assessments developed during the pandemic may be the new normal in the dental education curriculum.

Comparative evaluation of intermediate solutions in prevention of brown precipitate formed from sodium hypochlorite and chlorhexidine gluconate.

OBJECTIVES: To evaluate intermediate treatments between sodium hypochlorite and chlorhexidine gluconate irrigations for the prevention of a toxic brown precipitate in root canal therapy. MATERIALS AND METHODS: Thirty-nine premolars were irrigated with 6% sodium hypochlorite and divided into either: No intermediate treatment; Dry paper points; three different irrigations with 17% ethylenediaminetetraacetic acid, deionized water, or 5% sodium thiosulfate. 2% chlorhexidine gluconate was the final irrigant in all groups. Sectioned teeth were analyzed for brown precipitate intensity and area using stereomicroscopy and components related to para-chloroaniline using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). RESULTS: Stereomicroscopy showed that 5% STS significantly reduced brown precipitate intensity and area as compared with no intermediate irrigation (p < .05, Chi-square, generalized linear model, and Tukey's multiple comparison tests). Utilizing ToF-SIMS, 5% sodium thiosulfate was most effective in reducing the components representing para-chloroaniline and chlorhexidine gluconate. CONCLUSION: The 5% sodium thiosulfate was most effective among other intermediate treatments, assessed by stereomicroscopy and ToF-SIMS.

Evaluating dental students' perspectives on the concurrent teaching of didactic and case-based courses.

PURPOSE: To evaluate student perception of integrating biomedical and clinical sciences based on survey of dental students on the concurrent teaching of a didactic systems-based course and a case-based course. METHODS: First-year to fourth-year students (DS1-DS4) students were surveyed for their experiences in concurrent teaching. Student response rate for the survey was 55% (229/420). Pearson's Chi-squared tests and Kruskal-Wallis rank sum tests were used to assess statistical significance (p < 0.05). RESULTS: Of the students surveyed, 83% strongly agreed or agreed that concurrent teaching of the didactic and case-based courses helped them better understand the biomedical science background and the clinical ramifications (p < 0.001). On average, 75% percent strongly agreed or agreed that concurrent teaching kept them engaged, motivated, think critically, apply the course content and prepare for clinical practice (p < 0.001). Of the students surveyed, 69% support expanding concurrent teaching to all four years (p < 0.001). Mean responses from DS1 and DS4 students differed for questions relating to understanding of biomedical sciences, critical thinking and application to clinic (p < 0.01). Qualitative data showed that students enjoyed the reinforcement of concepts and application to clinical scenarios. CONCLUSIONS: Concurrent teaching of didactic and case-based learning courses, thus showing clinical relevance of biomedical sciences in the first year of dental curriculum, is perceived by students as an effective method of educating dental students. Such integrative learning process with horizontal and vertical integration and concurrent curriculum is even more relevant with the implementation of the integrated national board dental examination.

Influence of Pulse Duration on X-ray Emission during Industrial Ultrafast Laser Processing.

Soft X-ray emissions during the processing of industrial materials with ultrafast lasers are of major interest, especially against the background of legal regulations. Potentially hazardous soft X-rays, with photon energies of >5 keV, originate from the fraction of hot electrons in plasma, the temperature of which depends on laser irradiance. The interaction of a laser with the plasma intensifies with growing plasma expansion during the laser pulse, and the fraction of hot electrons is therefore enhanced with increasing pulse duration. Hence, pulse duration is one of the dominant laser parameters that determines the soft X-ray emission. An existing analytical model, in which the fraction of hot electrons was treated as a constant, was therefore extended to include the influence of the duration of laser pulses on the fraction of hot electrons in the generated plasma. This extended model was validated with measurements of H (0.07) dose rates as a function of the pulse duration for a constant irradiance of about 3.5 × 1014 W/cm2, a laser wavelength of 800 nm, and a pulse repetition rate of 1 kHz, as well as for varying irradiance at the laser wavelength of 1030 nm and pulse repetition rates of 50 kHz and 200 kHz. The experimental data clearly verified the predictions of the model and confirmed that significantly decreased dose rates are generated with a decreasing pulse duration when the irradiance is kept constant.

Assessment of the cytotoxic effects and chemical composition of the insoluble precipitate formed from sodium hypochlorite and chlorhexidine gluconate.

AIM: To investigate (1) the cytotoxic potential of the brown precipitate (BP) formed with sodium hypochlorite (NaOCl) and chlorhexidine gluconate (CHX), using both a small animal model of Caenorhabditis elegans (C. elegans) and cultured human gingival fibroblasts; and (2) the chemical composition of BP using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). METHODOLOGY: Brown precipitate was obtained by mixing equal volumes of 6% NaOCl and 2% CHX and separating the BP from clear supernatant by centrifugation. The brown precipitate was weighed and solubilized in dimethyl sulfoxide for cytotoxicity experiments. The cytotoxic effect of BP was assessed using C. elegans larvae and primary immortalized human gingival fibroblasts-hTERT (hTERT-hNOF) cells. Various dilutions of BP (25 ng/µL-150 ng/µL), supernatant (0.15% v/v), NaOCl (1:100-1:1000 dilutions of 6% NaOCl) or CHX (1:500-1:1000 dilutions of 2% CHX) along with vehicle control (0.5% v/v ethanol and 0.15% v/v DMSO) or untreated control (growth medium) were tested on C. elegans larvae and hTERT-hNOF cells. Viability was assessed in C. elegans larvae using stereomicroscopy and in hTERT-hNOF cells using dehydrogenase-based colorimetric assay. ToF-SIMS was used to assess the chemical composition of BP in comparison with CHX and para-chloroaniline (PCA). The C. elegans and cell line data were analysed using Log-Rank test and Student's t-test, respectively (p < .05). RESULTS: BP-75 ng/µL and BP-150 ng/µL were significantly more toxic to C. elegans larvae than the untreated, vehicle, supernatant or CHX treatment groups (p < .0001). Similarly, in hTERT-hNOF cells, BP-50 ng/µL, BP-75 ng/µL and BP-150 ng/µL induced significant cytotoxicity within 2 h compared with untreated, vehicle, supernatant and CHX treatments (p < .05). ToF-SIMS analysis of BP revealed ion composition characteristic of both CHX and the carcinogen PCA. CONCLUSIONS: Brown precipitate was toxic in both C. elegans larvae and hTERT-hNOF cells. The ToF-SIMS analysis of BP revealed ions characteristic of CHX and PCA that could account for the toxicities observed in C. elegans larvae and human gingival fibroblasts. Because of the insoluble and toxic nature of BP, consecutive use of CHX and NaOCl irrigants should be avoided in root canal treatment.

When should sleep bruxism be considered in the diagnosis of temporomandibular disorders?

OBJECTIVE: Both temporomandibular disorders (TMDs) and sleep bruxism (SB) are known to be destructive to the masticatory system. However, the association between the 2 conditions is poorly understood. The aim of our study was to assess the relationship between TMD and SB through the signs and symptoms in 2 patient groups: TMD only and TMD with SB. STUDY DESIGN: A retrospective chart review was conducted from November 1, 2015, to April 1, 2018, on patients with completed International Network for Orofacial Pain and Related Disorders Methodology history questionnaires and Diagnostic Criteria for Temporomandibular Disorder clinical examinations. Fifty-two patients, including 12 with TMD only and 40 with TMD with SB, met the study criteria. Subjective descriptions and objective measurements of patient symptoms were investigated. The χ2 test and Fisher's exact test were used for statistical analysis. RESULTS: The TMD with SB group exhibited increased oral behaviors compared with the TMD-only group (P = .0004). The TMD with SB group also experienced more headaches compared with the TMD-only group (P = .045). CONCLUSIONS: Our results revealed that patients with jaw pain who self-report increased oral behaviors and/or exhibit temporal headaches should be evaluated for sleep bruxism.

Methods and timing of curricular integration in U.S. dental education in preparation for the Integrated National Board Dental Examination.

PURPOSE: To characterize methods, timing, faculty training, and barriers pertaining to curricular integration in preparation for the Integrated National Board Dental Examination (INBDE) at U.S. dental schools METHODS: Academic deans at 67 U.S. dental schools were emailed an online survey consisting of questions on the time frame and methods of curricular integration, faculty training, and barriers to curricular integration RESULTS: Approximately 86% of schools have implemented (∼39%) or will implement (∼61%) changes in curriculum in preparation for the INBDE. Curricular integration was completed in 3-4 years in most schools, with those schools with larger class sizes taking longer. While 56% of respondents reported avoiding a complete curricular overhaul, 79% reported course sequencing changes, adding, subtracting, or combining courses, and making some changes in existing courses. Curriculum committees had the most input in curricular changes, while individual instructors had the least influence. Sixty seven percent of respondents reported faculty being trained to teach in an integrated curriculum. Problem/case-based learning and clinical case presentations are being used more for incorporation of biomedical sciences in clinical curriculum; use of clinical examples was the most used mechanism to integrate clinical information in biomedical sciences curriculum. Eighty two percent of respondents indicated that lack of faculty time to prepare courses as the primary barrier for implementing an integrated curriculum. CONCLUSIONS: Our results show that most U.S. dental schools are implementing integrated teaching models to prepare their students for the INBDE. However, lack of faculty time and training need to be addressed for more successful curricular integration.

Assessment of Critical Thinking in a First-Year Dental Curriculum.

We studied how students in a Doctor of Dental Surgery (DDS) program perceived the importance of critical thinking and the extent to which critical thinking was perceived to be included in each of 25 courses of the first-year curriculum at The University of Texas School of Dentistry at Houston (UTSD). Sixty-nine of the 102 second-year students who were invited participated in an online survey. The survey had three parts, with all statements of each part evaluated on a five-point Likert scale ranging from strongly agree to strongly disagree. The first two parts assessed the importance of critical thinking in dental education and the criteria by which critical thinking in didactic curriculum can be measured. In the third part of the survey, students evaluated how well each course of the first-year curriculum achieved critical thinking. More than 90% of the respondents strongly agreed/agreed that critical thinking is essential to making clinical decisions. Students strongly agreed/agreed that 19 of 25 of the courses incorporated critical thinking. However, when students were asked to rank the top five of the 25 courses, only two courses (Human Biology, Neuroscience) emerged above all others in their weighted ranks, with another seven courses standing out, leaving 16 courses with low weighted rankings for their inclusion of critical thinking. In summary, students agreed on the importance of critical thinking in dental education, and on the criteria by which the incorporation of critical thinking should be measured in didactic and pre-clinical courses.

Bell's palsy.

INTRODUCTION: Bell's palsy is characterised by an acute, unilateral, partial, or complete paralysis of the face (i.e., lower motor neurone pattern). The weakness may be partial (paresis) or complete (paralysis), and may be associated with mild pain, numbness, increased sensitivity to sound, and altered taste. Bell's palsy remains idiopathic, but a proportion of cases may be caused by reactivation of herpes viruses from the geniculate ganglion of the facial nerve. Bell's palsy is most common in people aged 15 to 40 years, with a 1 in 60 lifetime risk. Most make a spontaneous recovery within 1 month, but up to 30% show delayed or incomplete recovery. METHODS AND OUTCOMES: We conducted a systematic review to answer the following clinical question: What are the effects of treatments in adults and children? We searched: Medline, Embase, The Cochrane Library, and other important databases up to June 2010 (Clinical Evidence reviews are updated periodically. Please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA). RESULTS: We found 14 systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions. CONCLUSIONS: In this systematic review we present information relating to the effectiveness and safety of the following interventions: antiviral treatment, corticosteroids (alone or plus antiviral treatment), hyperbaric oxygen therapy, facial nerve decompression surgery, and facial retraining.

Bell's palsy.

INTRODUCTION: Bell's palsy is characterised by an acute, unilateral, partial or complete paralysis of the face, which may occur with mild pain, numbness, increased sensitivity to sound, and altered taste. Bell's palsy remains idiopathic, but a proportion may be caused by reactivation of herpes viruses from cranial nerve ganglia. Bell's palsy is most common in people aged 15-40 years, affecting 1 in 60 in their lifetime. Most make a spontaneous recovery within 1 month, but up to 30% have delayed or incomplete recovery. METHODS AND OUTCOMES: We conducted a systematic review and aimed to answer the following clinical question: What are the effects of treatments in adults and children? We searched: Medline, Embase, The Cochrane Library and other important databases up to February 2006 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA). RESULTS: We found eight systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions. CONCLUSIONS: In this systematic review we present information relating to the effectiveness and safety of the following interventions: antiviral treatment, corticosteroids (alone or plus antiviral treatment), facial nerve decompression surgery, and mime therapy.