Distinct subsets of Vδ1 effector and Vδ2 γδ T cells shift in frequency and are linked to plasma inflammatory markers during ART-suppressed HIV infection

BACKGROUND

Chronic inflammation is prevalent with ART-suppressed HIV-infection and one immune cell subset putatively driving this phenomenon is TIGIT + γδ T cells.

METHODS

To elucidate γδ T cell phenotypic diversity, spectral flow cytometry was performed on blood lymphocytes from individuals of an HIV and Aging cohort and data were analyzed using bioinformatic platforms. Plasma inflammatory markers were measured and correlated with γδ T cell subset frequencies.

RESULTS

39 distinct γδ T cell subsets were identified (22 Vδ1+, 14 Vδ2+, and three Vδ1-Vδ2-Vγ9+) and TIGIT was nearly exclusively found on the Vδ1+ CD45RA+ CD27- 'effector' populations. People living with ART-suppressed HIV-infection (PLWH) exhibited high frequencies of distinct clusters of Vδ1+ effectors distinguished via CD8, CD56, CD16, and CD38 expression. Among Vδ2+ cells, most Vγ9+ ('innate-effector') clusters were lower in PLWH, yet CD27+ subsets were similar in frequency between participants with and without HIV. Comparisons by age revealed lower 'naïve' Vδ1 + CD45RA+ CD27+ in older individuals, regardless of HIV status. Plasma inflammatory markers were selectively linked to subsets of Vδ1+ and Vδ2+ cells.

CONCLUSIONS

These results further elucidate γδ T cell subset complexity and reveal distinct alterations and connections with inflammatory pathways of Vδ1+ effector and Vδ2+ innate-effector subsets with ART-suppressed HIV infection.

Opioid use does not limit potent low-dose HIV-1 latency reversal agent boosting

The combined effects of the HIV-1 and opioid epidemics on virus reservoir dynamics are less well characterized. To assess the impact of opioid use on HIV-1 latency reversal, we studied forty-seven suppressed participants with HIV-1 and observed that lower concentrations of combination latency reversal agents (LRA) led to synergistic virus reactivation ex vivo, regardless of opioid use. The use of a Smac mimetic or low-dose protein kinase C agonist, compounds that did not reverse latency alone, in combination with low-dose histone deacetylase inhibitors generated significantly more HIV-1 transcription than phorbol 12-myristate 13-acetate (PMA) with ionomycin, the maximal known HIV-1 reactivator. This LRA boosting did not differ by sex or race and associated with greater histone acetylation in CD4+ T cells and modulation of T cell phenotype. Virion production and the frequency of multiply spliced HIV-1 transcripts did not increase, suggesting a post-transcriptional block still limits potent HIV-1 LRA boosting.

Integrase Inhibitor Use Associated with Weight Gain in Women and Incident Diabetes Mellitus

Excessive weight gain associated with integrase strand transfer inhibitor (InSTI) antiretrovirals is an emerging issue; however, the metabolic consequences of this effect have not been established. Our objective was to evaluate for InSTI-emergent weight gain and potential associated type 2 diabetes mellitus (T2DM) among a diverse HIV patient cohort. For this retrospective cohort study, we obtained clinical warehouse data for HIV+ patients between fiscal years 2007-17. We compared patients initiated on an InSTI with those started on an alternate regimen. Our primary outcome was percentage weight change from baseline to 24 months postinitiation using the linear mixed-effects model fit by restricted maximum likelihood. Our secondary outcome was incident T2DM as defined by a new prescription for antihyperglycemic medication within 18 months after antiretroviral therapy (ART) start. Diabetes-free survival was estimated using the Kaplan-Meier method, log-rank test, and Cox proportional-hazards model. The cohort included 1,235 individuals initiating ART, 136 (11.0%) with an InSTI. InSTI use in women was significantly associated with greater weight gain compared with non-InSTIs (11.0%, 95% confidence interval, CI: 5.22 to 16.8, p < .01), after adjusting for potential confounding variables. In a univariate analysis, InSTI use was associated with more incident T2DM diagnoses compared with non-InSTI regimens (unadjusted hazard ratio = 3.27, p = .01), although incident T2DM was not associated with weight gain. InSTIs were significantly associated with weight gain among females. We also observed an increased risk of incident diabetes mellitus among both sexes, however, unrelated to weight changes. Further prospective studies will be necessary to confirm this finding and investigate its mechanism.

Global COVID-19 vaccine inequity: The scope, the impact, and the challenges

Global vaccine inequity is prolonging the COVID-19 pandemic. Here, we outline the scope and impact of inequitable vaccine distribution and identify challenges in vaccine development, manufacturing, and distribution as well as potential solutions to address this crisis.

How Are Emerging Data Translated Into Clinical Practice? A Mixed Methods Investigation of Coronavirus Disease 2019 Institutional Treatment Protocols

Background

Early in the coronavirus disease 2019 (COVID-19) pandemic, there was minimal data to guide treatment, and we lacked understanding of how clinicians translated this limited evidence base for potential therapeutics to bedside care. Our objective was to systematically determine how emerging data about COVID-19 treatments was implemented by analyzing institutional treatment protocols.

Methods

Treatment protocols from North American healthcare facilities and recommendations from guideline-issuing bodies were collected. Qualitative data on treatment regimens and their applications were extracted using an adapted National Institutes of Health/US Food and Drug Administration experimental therapeutics framework. Structured data on risk factor and severity of illness scoring systems were extracted and analyzed using descriptive statistics.

Results

We extracted data from 105 independent protocols. Guideline-issuing organizations published recommendations after the initial peak of the pandemic in many regions and generally recommended clinical trial referral, with limited additional guidance. Facility-specific protocols favored offering some treatment (96.8%, N = 92 of 95), most commonly, hydroxychloroquine (90.5%), followed by remdesivir and interleukin-6 inhibitors. Recommendation for clinical trial enrollment was limited largely to academic medical centers (19 of 52 vs 9 of 43 community/Veterans Affairs [VA]), which were more likely to have access to research studies. Other themes identified included urgent protocol development, plans for rapid updates, contradictory statements, and entirely missing sections, with section headings but no content other than “in process.”

Conclusions

In the COVID-19 pandemic, emerging information was rapidly implemented by institutions into clinical practice and, unlike recommendations from guideline-issuing bodies, heavily favored administering some form of therapy. Understanding how and why evidence is translated into clinical care is critical to improve processes for other emerging diseases.

946. Risk factors and Metabolic Implications of Integrase Inhibitor Associated Weight Gain

Background

Excessive weight gain associated with integrase strand transfer inhibitor (InSTI) antiretrovirals is an emerging issue in the current antiretroviral treatment (ART) era. Despite the known association between excess weight and impaired glucose tolerance in the general population, the metabolic implications of InSTI-associated weight gain have not been established. The objective of this study was to evaluate the presence of InSTI-associated weight gain amongst a diverse, urban population and to investigate potential risk factors and metabolic implications.

Methods

We obtained demographic, pharmacy and laboratory data from the hospital clinical data warehouse for ART-naïve adult HIV+ patients at Boston Medical Center between fiscal year (FY) 2007-2017. We compared patients who initiated on an InSTI to those with an alternate regimen (i.e. PI, NNRTI) who remained on their initial regimen for at least 18 months. Individuals with diabetes mellitus (DM) prescription or ICD 9/10 code prior to ART initiation were excluded. Our primary outcome was percent weight change in the first 24 months of ART estimated by linear mixed effects model fit by restricted maximum likelihood. Our secondary outcome was incident DM diagnosis in the 18 months after ART using progression-free survival (PFS). PFS rates were estimated by the Kaplan-Meier method and log-rank test, and Cox proportional-hazards model were determined, all using R v3.6.2.

Results

Between FY 2007-2017, 139 patients were initiated on InSTIs and 1117 were initiated on alternative anchor regimens. Approximately, one third of the cohort was female and more than 75% were non-white. InSTI use in women was associated with increased weight gain in the first 24 months of ART compared to non-InSTIs (+9.57%, p = 0.002, Figure 1). InSTI use was associated with more incident DM diagnoses in the first 18 months of ART compared to non-InSTI regimens (HR = 3.27, p = 0.014).

Figure 1: Percentage weight change from baseline at ART initiation between InSTI and non-InSTI regimens

Conclusion

Females have higher InSTI-associated weight gain which suggests they may be more susceptible to adverse metabolic issues. InSTI use appears to be associated with an increased incidence of DM diagnoses following ART initiation. Further prospective and controlled studies will be necessary to describe the mechanism of this effect and refine HIV management strategies.

Disclosures

Archana Asundi, MD, Gilead (Scientific Research Study Investigator)Merck (Scientific Research Study Investigator)ViiV (Scientific Research Study Investigator) Nina H. Lin, MD, Gilead Sciences (Scientific Research Study Investigator)ViiV (Scientific Research Study Investigator)

153. pilot Study of a Novel Whole-genome Sequencing Based Rapid Bacterial Identification Assay in Patients with Bacteremia

Background

Blood stream infections (BSI) are among the leading cause of morbidity and mortality, yet gold standard culture-based diagnostics have limited ability to guide therapeutic intervention due to multi-day turnaround time and low sensitivity. Day Zero Diagnostics has developed Blood2Bac^™, a culture-free, species agnostic process to enrich bacteria direct from whole blood. Coupled with whole genome sequencing (WGS) and Day Zero Diagnostics’ Keynome^® algorithmic tools for species ID and antimicrobial resistance (AMR), we conducted the first proof-of-concept feasibility study in an inpatient clinical setting.

Methods

Study participants were enrolled and specimens collected from Boston Medical Center. Eligibility criteria included hospitalized adults with suspected and/or documented BSI, irrespective of empiric antibiotic therapy duration. Whole blood samples were processed with Blood2Bac, sequenced on a nanopore platform, and bacterial ID determined with Keynome ID. Keynome ID results were compared with blood culture results to measure concordance.

Results

Specimens from 21 participants were processed with Blood2Bac and nanopore sequencing. For 20/21 samples, Keynome ID calls were concordant with clinical blood culture, where 6 concordant positive and 14 were concordant negative. In 3 concordant samples, Keynome ID called positive while concurrent blood cultures were negative. However, all IDs corresponded with positive blood culture results from the day prior, suggesting potentially higher sensitivity for the Blood2Bac compared to blood culture. Two concordant positive IDs, resulted in >95% of the genome recovered and Keynome concomitantly resulted in AMR predictions with 100% accuracy compared to pathogen phenotype. In 1 discordant specimen, the Keynome ID result was negative while blood cultures 8 hours before were positive. In this case, the patient was on empiric therapy for 8 days prior to samples collection and cultures were negative 19-hours post specimen collection.

Conclusion

These results highlight the sensitivity of a real-time blood WGS approach to identify BSI and its utility as a diagnostic to minimize unnecessary antibiotic exposure contributing to the antibiotic resistance crisis.

Disclosures

Archana Asundi, MD, Gilead (Scientific Research Study Investigator)Merck (Scientific Research Study Investigator)ViiV (Scientific Research Study Investigator) Nicole Billings, PhD, Day Zero Diagnostics (Employee) Zoe H. Rogers, MPH, Day Zero Diagnostics (Employee, Shareholder) Lisa S. Cunden, PhD, Day Zero Diagnostics (Shareholder) Imaly A. Nanayakkara, PhD, Day Zero Diagnostics (Employee, Shareholder) Chiahao Tsui, n/a, Day Zero Diagnostics (Employee, Shareholder) Paul Knysh, PhD, Day Zero Diagnostics (Employee) Cabell Maddux, n/a, Day Zero Diagnostics (Employee, Shareholder) Zachary Munro, n/a, Day Zero Diagnostics Inc. (Employee, Shareholder) Ian Herriott, BS, Day Zero Diagnostics (Employee, Shareholder) Miriam Huntley, PhD, Day Zero Diagnostics (Employee, Shareholder) Nina H. Lin, MD, Gilead Sciences (Scientific Research Study Investigator)ViiV (Scientific Research Study Investigator)

Prevalence of strongyloidiasis and schistosomiasis among migrants: a systematic review and meta-analysis

BACKGROUND

Global migration from regions where strongyloidiasis and schistosomiasis are endemic to non-endemic countries has increased the potential individual and public health effect of these parasitic diseases. We aimed to estimate the prevalence of these infections among migrants to establish which groups are at highest risk and who could benefit from screening.

METHODS

We did a systematic review and meta-analysis of strongyloidiasis and schistosomiasis prevalence among migrants born in endemic countries. Original studies that included data for the prevalence of Strongyloides or Schistosoma antibodies in serum or the prevalence of larvae or eggs in stool or urine samples among migrants originating from countries endemic for these parasites and arriving or living in host countries with low endemicity-specifically the USA, Canada, Australia, New Zealand, Israel, and 23 western European countries-were eligible for inclusion. Pooled estimates of the prevalence of strongyloidiasis and schistosomiasis by stool or urine microscopy for larvae or eggs or serum antibodies were calculated with a random-effects model. Heterogeneity was explored by stratification by age, region of origin, migrant class, period of study, and type of serological antigen used.

FINDINGS

88 studies were included. Pooled strongyloidiasis seroprevalence was 12·2% (95% CI 9·0-15·9%; I² 96%) and stool-based prevalence was 1·8% (1·2-2·6%; 98%). Migrants from east Asia and the Pacific (17·3% [95% CI 4·1-37·0]), sub-Saharan Africa (14·6% [7·1-24·2]), and Latin America and the Caribbean (11·4% [7·8-15·7]) had the highest seroprevalence. Pooled schistosomiasis seroprevalence was 18·4% (95% CI 13·1-24·5; I² 97%) and stool-based prevalence was 0·9% (0·2-1·9; 99%). Sub-Saharan African migrants had the highest seroprevalence (24·1·% [95% CI 16·4-32·7]).

INTERPRETATION

Strongyloidiasis affects migrants from all global regions, whereas schistosomiasis is focused in specific regions and most common among sub-Saharan African migrants. Serological prevalence estimates were several times higher than stool estimates for both parasites. These data can be used to inform screening decisions for migrants and support the use of serological screening, which is more sensitive and easier than stool testing.

FUNDING

None.

Novel methodology to measure pre-procedure antimicrobial prophylaxis: integrating text searches with structured data from the Veterans Health Administration's electronic medical record

Background

Antimicrobial prophylaxis is an evidence-proven strategy for reducing procedure-related infections; however, measuring this key quality metric typically requires manual review, due to the way antimicrobial prophylaxis is documented in the electronic medical record (EMR). Our objective was to electronically measure compliance with antimicrobial prophylaxis using both structured and unstructured data from the Veterans Health Administration (VA) EMR. We developed this methodology for cardiac device implantation procedures.

Methods

With clinician input and review of clinical guidelines, we developed a list of antimicrobial names recommended for the prevention of cardiac device infection. We trained the algorithm using existing fiscal year (FY) 2008–15 data from the VA Clinical Assessment Reporting and Tracking-Electrophysiology (CART-EP), which contains manually determined information about antimicrobial prophylaxis. We merged CART-EP data with EMR data and programmed statistical software to flag an antimicrobial orders or drug fills from structured data fields in the EMR and hits on text string searches of antimicrobial names documented in clinician’s notes. We iteratively tested combinations of these data elements to optimize an algorithm to accurately classify antimicrobial use. The final algorithm was validated in a national cohort of VA cardiac device procedures from FY2016–2017. Discordant cases underwent expert manual review to identify reasons for algorithm misclassification.

Results

The CART-EP dataset included 2102 procedures at 38 VA facilities with manually identified antimicrobial prophylaxis in 2056 cases (97.8%). The final algorithm combining structured EMR fields and text note search results correctly classified 2048 of the CART-EP cases (97.4%). In the validation sample, the algorithm measured compliance with antimicrobial prophylaxis in 16,606 of 18,903 cardiac device procedures (87.8%). Misclassification was due to EMR documentation issues, such as antimicrobial prophylaxis documented only in hand-written clinician notes in a format that cannot be electronically searched.

Conclusions

We developed a methodology with high accuracy to measure guideline concordant use of antimicrobial prophylaxis before cardiac device procedures using data fields present in modern EMRs. This method can replace manual review in quality measurement in the VA and other healthcare systems with EMRs; further, this method could be adapted to measure compliance in other procedural areas where antimicrobial prophylaxis is recommended.

Making Emergency Use of Experimental Vaccines Safer

Ethical and logistical challenges of deploying experimental vaccines in humanitarian emergencies are exacerbated by a paucity of safety and efficacy data. For outbreaks caused by pathogens with high mortality rates and few treatments, such as Ebola virus disease, not offering access to experimental vaccines with some evidence of efficacy can also be ethically suspect. This article recommends (1) gathering more preclinical data about experimental vaccines' safety and (2) improving research infrastructure to enable participation of a wide range of subjects in affected communities over long trial periods. Motivating these goals would facilitate clearer definitions of population vulnerability and risk acceptability.

Infectious Myelitis

Myelitis refers to inflammation of the spinal cord which can result in a spectrum of neurologic impairment. Infectious pathogens are an important etiologic category, and can result in myelitis through direct pathogenic effect or through immune-mediated parainfection; this review focuses on the former category. The spectrum of clinical manifestations is summarized and a diagnostic workup provided to aid clinicians in developing an approach to patients presenting with symptoms suggestive of infectious myelitis. This is followed by an overview of the important viral, bacterial, parasitic, and fungal causes of infectious myelitis. The typical presentations, diagnostic modalities, and treatment approaches are outlined for key pathogens culprit in infectious myelitis to allow clinicians to promptly recognize and diagnose specific infectious etiologies of myelitis.

340. Clinical Use of a Multiplex PCR Meningitis/Encephalitis Panel at an Urban Tertiary Care Center

Background

The FilmArray® Meningitis/Encephalitis (ME) Panel (BioFire Diagnostics, Salt Lake City, Utah) is the first multiplex polymerase chain reaction (PCR) test for detection of 14 pathogens in cerebrospinal fluid (CSF) that are commonly associated with meningitis and encephalitis. Its impact on clinical management has not been well evaluated. Our aim was to describe the experience using the ME panel since its implementation at an urban tertiary care center.

Methods

We conducted a retrospective chart review of all patients aged >21 who had CSF samples analyzed by the ME panel from January 1 to July 31, 2017. We abstracted demographic, clinical, laboratory, and imaging data to assess ME panel results and their influence on clinical management.

Results

We reviewed the charts of 93 patients aged 21 to 85 who had the ME panel performed. Forty-nine (53%) were males and eight (9%) were immunosuppressed. Eight (9%) patients had a positive test for at least one target pathogen: four for a bacterial target (S. pneumoniae, N. meningitidis, or H. influenza), three for a viral target (HSV-2 or VZV), and one for both a bacterial and a viral target (S. pneumoniae and HSV-2). CSF cultures were negative for all five cases with bacteria detected. Confirmatory uniplex PCR was not performed for the positive viral results. Four of the five patients with positive results for a bacterial pathogen had received broad-spectrum antibiotics prior to lumbar puncture. In all five, antibiotics were modified (either started or de-escalated) based on the pathogen identified on the ME panel. All four patients with a positive result for a viral target received anti-viral therapy—in one case this was started empirically, while in the remaining three treatment was started only after the ME panel had resulted. Antibiotic management in the 85 patients with a negative ME panel varied widely based on clinical suspicion and other laboratory data. Three (3%) of the 93 patients had positive cultures for pathogens that are not ME panel targets (S. aureus and S. hominis).

Conclusion

The ME panel yielded positive results in cases where conventional tests did not, including when antibiotics had been initiated prior to CSF sampling. While a positive ME panel prompted changes in therapy, negative results, in the majority of cases, did not supersede clinical suspicion.

Disclosures

N. Miller, BioFire Diagnostics: Paid speaker, single day event (1 time only): 4/6/2017, BioFire Diagnostics, Syndromic Testing Symposium, Burlington, MA, Speaker honorarium.

163. Development of an Electronic Flagging Tool for Identifying Cardiac Device Infections: Insights from the VA CART Program

Background

Surveillance is an essential aspect of infection prevention. Despite the high morbidity and mortality associated with procedure-related Cardiac Implantable Electronic Device (CIED) infections, methods for identifying them are limited. The objective of this study was to develop an algorithm with electronic flags to facilitate detection of CIED infections in a large, multi-center cohort.

Methods

A sample of patients who underwent CIED procedures entered into the VA Clinical Assessment Reporting and Tracking Electrophysiology (CART-EP) program from FY 2007 to 2015 were included in the nested case–control study. After cohort creation, data from this review process were combined with electronic variables (e.g., microbiology orders, ICD 9/10 codes) to develop a preliminary algorithm that categorized patients as high, intermediate, or low risk of CIED infection.

Results

A total of 1,014 unique patients out of a cohort of 5,955 procedures underwent manual review. Among these cases, 59 CIED infections and 955 controls were identified. Electronic variables predictive of CIED infection included ICD 9/10 infection codes and microbiology orders (table). ICD 9/10 codes had excellent PPV for flagging infections but sensitivity was limited (47.5%, see figure). Adding microbiology order flags increased sensitivity but lowered specificity. Specificity in patients without either flag was outstanding (99%).

Conclusion

Absence of ICD 9/10 and microbiology orders is highly specific for ruling out CIED infections. The discriminatory abilities of the algorithm for intermediate probability flags (+microbiology/−ICD9/10) need improvement. In patients without ICD codes, at least microbiology orders should be used as a flag to streamline review of possible device infections. Refinement of this tool using other clinical flags may improve operating characteristics and clinical utility.

Disclosures

W. Branch-Elliman, Veterans’ Integrated Service Network Career Development Award: Investigator, Research grant. American Heart Association: Investigator, Research grant.

Further investigation on the phase stitching and system errors in digital holography

In this work, an improved phase stitching algorithm is proposed in digital holography (DH) based on a deduced phase errors model and a global optimization algorithm. In addition, to correct the relative rotation error between the coordinate systems of a CCD and xy-motion stages, we presented a simple and reliable image-based correction method. The experimental results obtained from our proposed method are compared with those calculated from the existing phase stitching method to verify the performance of the presented method. It is shown that our new proposed methods are robust and valid for measurement of a large microstructure element. As far as we know, the improved phase stitching algorithm and image-base correction method have not been discussed in DH, as we presented in this paper.

Least-squares calibration method for fringe projection profilometry considering camera lens distortion

By using the least-squares fitting approach, the calibration procedure for fringe projection profilometry becomes more flexible and easier, since neither the measurement of system geometric parameters nor precise control of plane moving is required. With consideration of camera lens distortion, we propose a modified least-squares calibration method for fringe projection profilometry. In this method, camera lens distortion is involved in the mathematical description of the system for least-squares fitting to reduce its influence. Both simulation and experimental results are shown to verify the validity and ease of use of this modified calibration method.

Digital moiré interferometric investigations on the deformation gradients of enamel and dentine: an insight into non-carious cervical lesions

OBJECTIVES

The objective of this study was to evaluate the biomechanical basis of non-carious cervical lesions by examining the patterns of deformation (strain) in the enamel and dentine.

METHODS

The digital moiré interferometry is optics based non-destructive, whole-field experimental technique that provides whole-field strain information. Diffraction gratings (with a frequency of 1200 lines/mm) were transferred onto sagittal sections of human teeth, which were subsequently loaded compressively for loads ranging from 10 to 200 N at the incisal edge of the tooth. The acquired digital moiré fringe patterns were used to determine the in-plane deformation pattern in the enamel and the dentine in the direction parallel to the long axis (axial direction) and in the direction perpendicular to the long axis (lateral direction) of the tooth.

RESULTS

It is observed that the enamel displayed marked strain gradients in the lateral direction, while the coronal dentine experienced marked strain gradients in the axial directions during compression. With the increase in applied loads, the strains in the enamel increased at the cervical edge (above the cemento-enamel junction) on the facial side, while the strains in the dentine increased below the cemento-enamel junction on the facial side.

CONCLUSION

The enamel and dentine displayed unique in-plane deformation patterns in the axial and the lateral directions of the tooth. These experiments support the hypothesis that occlusal loading will contribute to cervical loss of dental hard tissues.

Experimental investigation on the role of water in the mechanical behavior of structural dentine

Dentine is a porous hydrated composite structure that forms the major bulk of the human tooth. The aim of this study was to investigate the role of free water on the in-plane, mechanical strain response in dentine structure. A digital moire interferometry was used for this purpose. It was observed from this experiment that structural dentine demonstrated distinct strain gradients in the axial (perpendicular to the dentinal tubules) and lateral (parallel to the dentinal tubules) directions. The hydrated dentine displayed significant increase in strain with stress in the direction perpendicular to the dentinal tubules, and this response was characteristic of a tough material. On the contrary, the dehydrated dentine, which was dehydrated at 24 degrees C, 55% relative humidity for 72 h showed a strain response characteristic of a brittle material. The strains formed in the direction parallel to the dentinal tubules for hydrated dentine were consistent and did not vary much with increase in applied loads. Upon dehydration, the outer dentine experienced higher strains, and the difference between the outer and inner dentine became more conspicuous with increase in loads. This experiment highlights hydration-induced, distinct in-plane strain gradients in the directions perpendicular and parallel to the dentinal tubules in the dentine structure.

Photomechanical investigations on the stress-strain relationship in dentine macrostructure

In this study photomechanical experiments were carried out to examine the relationship between macroscopic mechanical stress and strain gradients within the root dentine structure. Three-dimensional digital photoelasticity was used to study the stress distribution patterns in tooth models, while digital moire interferometry was used to study the strain gradients within the natural teeth. The stress analysis showed a distinct bending stress distribution, along faciolingual plane in the coronal and cervical regions of the tooth. There was a reduction in bending towards the apical third of the tooth model. The strain analysis displayed strain gradients in the axial (along the long axis of the tooth) and lateral (perpendicular to the long axis of the tooth) directions in dentine. There was a conspicuous reduction in strains from the cervical to the apical third of the root dentine. The root dentine displayed uniform distribution of normal strains. Although there was a steep increase in stresses from the inner core region to the outer surface of an isotropic tooth model, there were more uniform strain gradients in the natural dentine structure. It is apparent from these observations that complex organization of material properties facilitated distinct strain gradients in dentine structure during mechanical functions.

Chairside sensor for rapid monitoring of Enterococcus faecalis activity

In this study, optical spectroscopy was used to monitor a chromogenic, enzyme-substrate reaction for the rapid identification of Enterococcus faecalis. The detection system, comprising a miniature spectrophotometer and an accompanying data acquisition system, was placed in an incubator. During testing, a 3-ml test sample was placed in a cuvette within the spectrophotometer. This permitted online, real-time, and remote analysis of spectral signature needed to monitor the bacteria. It was observed that the absorption peak intensity increased conspicuously 3.5 h after inoculation and through the entire period of testing. A linear-regression analysis demonstrated a significant correlation between the increase in absorption peak intensity at 610 nm (r = 0.9389) and 653 nm (r = 0.9387) with the formation of colony-forming units. Optical spectroscopy-based sensing systems can pave the way for rapid, nonlaboratory-based approaches to monitor microbial status quantitatively and qualitatively from clinical samples.

A fiber optic biosensor (FOBS) to monitor mutans streptococci in human saliva

A fiber optic biosensor (FOBS) to monitor mutans streptococci activity in human saliva is developed. The biosensor utilizes e fiber optic evanescent wave spectroscopy to monitor a bacterial mediated biochemical reaction. To achieve this, a short length of the cladding is removed; the fiber core surface is treated and coated with a thin film of porous glass medium using sol-gel technique. The mutans streptococci mediated reaction with sucrose is monitored using a photosensitive indicator, which is immobilized within the porous glass coating. Spectroscopic analysis shows that the transmitted intensity at 597 nm increases conspicuously when monitored for 120 min. Two distinct phases are observed, one from 0 to 60 min and the other from 60 to 120 min. A negative correlation coefficient between the rate of increase in absorption peak intensity recorded by the FOBS and the decrease in pH measured using the pH meter, was calculated to be rho=-0.994. This investigation highlights the potential benefits of this sensor to monitor mutans streptococci activity in saliva.

Total protein measurement using a fiber-optic evanescent wave-based biosensor

A novel method and instrumental system to determine the total protein concentration in a liquid sample is described. It uses a fiber optic total protein sensor (FOPS) based on the principles of fiber optic evanescent wave spectroscopy. The FOPS applies a dye-immobilized porous glass coating on a multi-mode optical fiber. The evanescent waves at the fiber optic core-cladding interface are used to monitor the protein-induced changes in the sensor element. The FOPS offers a single-step method for quantifying protein concentrations without destroying the sample. The response time and reusability of the FOPS are evaluated. This unique sensing method presents a sensitive and accurate platform for the quantification of protein.

Photomechanical investigations on post endodontically rehabilitated teeth

An investigation of the stress distribution patterns in post-core restored teeth and the behavior of dentin material to fracture propagation was conducted using experimental techniques such as digital photoelasticity (on photoelastic models), mechanical testing and scanning electron microscopy (SEM) (on extracted teeth). Digital photoelastic experiments showed that endodontic post-core restoration resulted in regions of high tensile stress and of stress concentrations in the remaining dentin structure. It was observed from mechanical testing that the fracture resistance in post-core restored teeth is significantly lower (p<0.0001) than that in intact tooth. There was a significant correspondence between the plane of stress concentrations identified in the photoelastic models and in those of the plane of fracture exhibited by the rehabilitated tooth specimens. While the fracture of post-core rehabilitated teeth was consistent, that of control teeth was not as distinct. The SEM highlighted varying dentin response to fracture propagation at the inner core and the outer regions. The fractographs showed brittle and ductile response to fracture propagation in the outer and inner core dentin, respectively. These photomechanical studies highlighted that the stress concentrations, high tensile stress and loss of inner ductile dentin associated with post endodontic rehabilitation diminished their resistance to fracture.

Approaching biomimetics in dental restorations via photonics

It is established that a natural system balances functional requirements with the anatomical optimizations it has achieved. Though such process of functional adaptation is recognized in bone tissue, any mode of functional adaptation in dental tissue is yet to be understood. In this study a three-dimensional digital photoelasticity is conducted to evaluate the nature of stress distribution in the sagittal aspect and the cross-sections of the dentine structure. Later, a fluoroscopic X-ray microscopic analysis and a microindentation experiments, are performed on different sections obtained from the sagittal and cross-sections of the dentine. These experiments aided in correlating the multi-plane pattern of mineralization and the spatial gradients in elastic modulus in the original dentine structure with the three-dimensional stress distribution in photoelastic models. This study highlights dentine structure as a biologically graded structure to functional loads.

Phase-shifting moireí method with an atomic force microscope

Using a phase-shifting technique with an atomic force microscope (AFM), we propose a phase-shifting AFM scanning moiré method. The phase shifting is realized in four steps from 0 to 2pi by a piezoscanner in the AFM. The measurement method and experimental techniques are described in detail. For demonstration this method is applied to determine the phase distribution in the AFM moiré of a 1200-line/mm holographic grating used to measure the thermal deformation in a Quad FlatPack electronic package.

Analysis on the nature of thermally induced deformation in human dentine by electronic speckle pattern interferometry (ESPI)

OBJECTIVE

To examine the in-plane and out-of-plane response of human dentine to thermal loads in real time.

METHODS

An Electronic Speckle Pattern Interferometry (ESPI) system sensitive to both the in-plane and out-of-plane displacements was configured and used in conjunction with an advanced fringe processing technique. Specimens were prepared from freshly extracted lower central incisor teeth and were separately mounted on a thermal block to apply thermal loads from room temperature (25 degrees C) to 60 degrees C. The real time speckle patterns were acquired using a digital camera. These digital fringe patterns were subjected to further image processing to enhance the quality of fringes. The resultant images were later analyzed to study the out-of-plane and in-plane displacement gradients in the facio-lingual plane of the dentine.

RESULTS

The out-of-plane deformations were observed in the plane perpendicular to the long axis of the tooth, while the in-plane deformations occurred in the plane parallel to the long axis of the tooth.

CONCLUSION

The ESPI analysis revealed whole-field and distinct thermal response in human dentine in-plane and out-of-plane. The cervical dentine experienced distinct and conspicuous displacement to the temperature changes.

Dynamic phase-shifting photoelasticity

The application of phase-shifting photoelasticity to a real-time dynamic event involves simultaneous recording of the four phase-shifted images. Here an instrument, believed to be novel, is developed and described for this purpose. Use of a Multispec Imager is introduced into digital photoelasticity for the first time to our knowledge. This device enables splitting the optical energy of an object into four identical paths, thus permitting recording of the required four phase-shifted images. Experimental demonstration is provided for validation.

Investigations of thermal property gradients in the human dentine

An investigation of the adaptation of dentine to temperature variation was conducted with the aid of digital moiré interferometry and thermomechanical analysis. The moiré interferometric patterns provided direct evidence of two major phases of thermally involved deformation in dentine. An initial phase of expansion was followed by contraction at higher temperatures. Significant gradients in thermal strain and the coefficient of thermal expansion were identified. Close agreement was found between the response of dentine to thermal changes as observed by moiré interferometry and that detected by thermomechanical analysis. This study highlights the biological adaptation of dentine to thermal variations.

Advanced digital photoelastic investigations on the tooth-bone interface

The purpose of this study was to investigate the behavior of the tooth-bone interface on the nature of stress distribution in the tooth and its supporting alveolar bone for various occlusal loads using an advanced digital photoelastic technique. A digital image processing system coupled with a circular polariscope was used for the stress analysis. The phase shift technique and a phase unwrapping algorithm was utilized for fringe processing. This aids in obtaining qualitative and quantitative information on the nature of stress distribution within the dento-osseous structures. The experiments revealed bending stresses within dento-osseous structures. However, the compressive stress magnitude was larger than the tensile stress. Zero stress regions were also identified within the dento-osseous structures. The results suggest that the geometry of the dento-osseous structures and the structural gradients at the tooth-bone interface play a significant role in the distribution of stresses without stress concentrations. Further, the application of an advanced image-processing system with the circular polariscope showed notable advantages and could be applied in other biomechanical investigations.

Study of the mechanical properties of Nd:YVO4 crystal by use of laser interferometry and finite-element analysis

A hybrid method that combines experimental and numerical approaches for determining the material properties of Nd:YVO4 is reported. In the experimental investigations a laser interferometer is proposed for measuring the physical deformation of lasing materials at the end-pump surface. By matching with the measured end bulging, we have implemented a numerical solution with finite-element analyses to determine the Poisson ratio and Young's modulus of the crystal. The accuracy interval of the evaluated Poisson ratio of 0.33 and Young's modulus of 133 GPa is discussed numerically. Based on the mechanical properties obtained, the end effect is separated from thermal effects, and it shows that the end effect results in an approximate equal thermal lensing effect compared with the index parts for end-pumped Nd:YVO4 lasers.

Stress distribution in the dento-alveolar system using digital photoelasticity

Past research has confirmed that the governing factors in cellular modelling and remodelling adhere to sound principles of engineering mechanics. Hence studies of stress distributions would provide better understanding of the functional adaptation of dental supporting structures. Photoelasticity is an established experimental tool to study whole-field stress distribution in structures subjected to forces. However, it has certain limitations that make its application in biological specimens tedious. In this investigation an advanced digital photoelastic system is used to visualize and study the nature of the stress distribution in dental supporting structures. These digital fringe patterns are analysed using a phase-shift technique. The present biomechanical study shows that dental supporting structures exhibit a characteristic stress distribution, promoting structural adaptation based on needs. Furthermore, the advantage of using a digital image processing system along with the circular polariscope is discussed.

Intracore fiber bragg gratings for strain measurement in embedded composite structures

An intracore Bragg grating written on a photosensitive fiber core is used for strain measurement in composite specimens under load. The strain information is directly related to the absolute change in the Bragg-reflected wavelength. Fiber Bragg grating (FBG) sensors (fibers with intracore gratings) are thus sensitive to strain that is caused by changes in temperature as well as to load-induced changes. Thus these sensors can be made to be independent of source intensity variations and losses. FBG sensors used for load-induced strain sensing in composite structures and the effects of temperature on them are discussed. A detailed account of the use of such embedded structures as self-monitoring nondestructive testing devices is given.

Experimental studies on the nature of property gradients in the human dentine

We conducted an investigation into the nature of dentine mineralization and mechanical property gradients with the aid of experimental techniques such as the fluoroscopic X-ray microanalysis and instrumented microindentation, respectively. It was found that the tooth adapts to a complex structure with significant gradients in properties. We observed a significant correlation between the degree of mineralization within the dentine and the mechanical properties. The natural gradation in mechanical properties is explained by the stress analysis within anatomical-sized tooth specimens done using digital photoelasticity. These results are explained within the context of the functional requirements that are imposed on the tooth. This study highlights tooth structure as a biologically adapted, functionally graded material.

A strain gauge and photoelastic analysis of in vivo strain and in vitro stress distribution in human dental supporting structures

Strain gauge and photoelastic experiments have been workhorses of experimental stress analysis for over 50 years. In this study, both were used to analyse the nature of stress distribution from the tooth root surface to the supporting alveolar bone. Such studies help in understanding the behaviour of dental supporting structures under physiological function. In the strain gauge experiment, the mechanical strains were measured on the supporting bone surface and the root surface of the tooth under applied bite force. It was found that higher strains were distributed along the cervical region of the supporting bone and the root surface. The photoelastic study was also done to evaluate the stress distribution pattern from the root surface to the supporting bone under clinical conditions. The stress patterns were found to decrease from the cervical to the apical region of the root surface. These studies highlight the role of the periodontium in stress distribution and bone remodelling.

Sampled-speckle photography for measurement of deformation

Speckles usually are of two kinds: laser speckle and white-light speckle. An additional kind, termed a sampled speckle, is proposed. Whereas laser speckles arise from multiple interference of light scattered from an object illuminated by a coherent laser beam and white-light speckles are a physically generated speckle pattern on the surface of the object, sampled speckles are generated as a result of the sampling of a digital image. The generation of these speckles and their application to displacement measurement are demonstrated.

Optical grating diffraction method: from strain microscope to strain gauge

The grating diffraction method for direct strain measurement is reviewed. Two systems which use this method are presented. The first system is a compact strain microscope. A Leitz optical transmitting microscope with white light source is reconstructed by developing a loading and recording system. Gratings with median density of between 40 and 200 lines/mm are used. With the help of a Bertrand lens, the Fourier spectrum of the grating is formed with high image quality on the CCD sensor plane. Software is developed to precisely, quickly and automatically determine the diffraction spot centroids. The second system is a new strain sensor based on a high-frequency grating and two Position Sensor Detectors (PSDs). The grating, attached to the surface of the specimen, is illuminated by a focused laser beam, generally with a frequency of 1,200 lines/mm. The centroids of diffracted beam spots from the grating are automatically determined using two PSD sensors connected to a personal computer. The shift of diffracted beam spots due to specimen deformation is detected. Strain sensitivity of one micro-strain can be obtained, as can a 0.4 mm spatial resolution for strain measurement. The system can be used for both static and dynamic tests.

Phase-shifting method with a normal polariscope

In many laboratories of universities and industrial organizations, commercial polariscopes have the feature that the relative position of the two quarter-wave plates is fixed. This is due to the requirement of transforming a plane polariscope to a circular polariscope with greater precision and ease. Unfortunately, these polariscopes cannot implement Patterson and Wang's [Strain 27, 49-56 (1991)] phase-shifting algorithm because this algorithm requires that the second quarter-wave plate and the analyzer of the circular polariscope be capable of independent rotation. A new phase-shifting method that can be applied under these constraints is proposed. A comparative study with Patterson and Wang's [Strain 27, 49-56 (1991)] algorithm shows very good agreement. Furthermore, it is shown that four phase steps are sufficient to determine both the isoclinic and the isochromatic parameters.

Unified calibration technique and its applications in optical triangular profilometry

A unified calibration technique based on ray tracing for optical triangular profilometry is presented. The proposed technique based on the inherent geometric relation between depth and a distorted signal is capable of speedy and accurate measurement without the determination of geometric parameters. The technique can also reduce calibration error caused by the lens distortion of the projector and the camera owing to the reasonable assumption that mapping in a small local area is a linear transformation and the coefficients of the linear transformation may be varied in different local areas. Three classical systems of triangular profilometry, spot inspection, a single-line system, and a projection-grating system, are discussed and demonstrated by experiment.

Biomechanics of endodontic endosseous implants--a comparative photoelastic evaluation

Dental biomechanics is an interdisciplinary study wherein engineering principles are used for the better understanding of clinical dentistry. The present biomechanical study was done to understand the mechanism by which an endodontic implant transmits occlusal forces to the surrounding bone. In this experimental study, photoelastic techniques were utilized to compare stress distribution patterns in the supporting bone of an intact tooth, a tooth with supporting bone loss, and a tooth stabilized using an endodontic endosseous implant. It was concluded that there were distinct variations in the biomechanics underlying various dental clinical conditions. Further, the implant did not appear to improve the stress distribution.

Fast phase-unwrapping algorithm based on a gray-scale mask and flood fill

Phase-unwrapping algorithms, an active and interesting subject in recent years, are important in a great number of measurement applications. Active research is being undertaken to develop reliable and high-speed procedures. The current process uses a gray-scale mask and the flood-fill concept from image processing for phase unwrapping. The algorithm unwraps phase from an area with higher reliability to one with lower reliability. In addition to robustness, the speed of the algorithm proposed is much faster than conventional routines. The experimental results of different algorithms are compared by analysis of a tooth plaster and a photoelastic specimen.

Scanning moiré and phase shifting with time delay and integration imaging

Scanning moiré is generated by undersampling of a phase-modulated grating pattern. In projection profilometry the scanning moiré pattern represents equal height and depth contours on a test object. By use of time delay and integration (TDI) imaging, it is possible to generate an on-line scanning moiré pattern from the complete periphery of a rotating cylindrical object. For automated phase and profile unwrapping from scanning moiré fringes, phase-shifting interferometry techniques are most desirable. However, lack of spatial information in the undersampled scanning moiré fringes introduces serious errors in phase unwrapping. We report a method that uses oversupply of data to balance the effect of undersampling. This oversupply is achieved with a TDI feature that permits programmable image magnification in the scanning direction.

Photoelastic illumination by using cathode-ray-tube displays

The need to perform computer-aided fringe-analysis schemes in photoelasticity for automated stress analysis has necessitated further developments in specimen illumination. Commonly available cathode-ray-tube color displays are investigated for such a purpose.

Dynamic Photoelasticity Using LED and Polaroid Film

Dynamic photoelasticity relies on high-speed photographic systems to record the fringes in motion. Several systems are being used, but the delayed microflash is widely popular in non-destructive studies due to the high-contrast recording and low cost. Flash lamps and lasers are routinely employed as the light source in these setups. The use of LED as a microflash in such systems is presented. Capability of the system is demonstrated by recording fringe patterns from a photoelastic model under dynamic loading. A high-speed Polaroid film is used for recording the dynamic fringe patterns. Low cost, low power, and simplicity in the experimental setup make it possible to adapt the system to undergraduate laboratories.

Multiple LED camera for dynamic photoelasticity

Dynamic photoelasticity involves the high-speed recording of rapidly moving fringe patterns in synchronization with loading. Cranz Schardin cameras are routinely utilized in the recording of dynamic photoelastic patterns. There are no moving components in these cameras, making the setup simple and attractive. Amultiple LED camera based on the Cranz Schardin format is presented. Highspeed instant polaroid film is used for recording the photoelastic fringes. Low cost, simplicity in the experimental setup, and rapid repeatability are the advantages of the camera.

Dynamic Recording Using a TDI Camera

Dynamic recording of physical events is an interesting andchallenging problem for scientists and artists. Applicationof a digital camera for dynamic recording and analysis ispresented. Some experiments are described demonstratingthe working modes, advantages, and limitations of the device.