An economical in-class sticker microfluidic activity develops student expertise in microscale physics and device manufacturing

Educating new students in miniaturization science remains challenging due to the non-intuitive behavior of microscale objects and specialized layer-by-layer assembly approaches. In our analysis of the existing literature, we noted that it remains difficult to have low cost activities that elicit deep learning. Furthermore, few activities have stated learning goals and measurements of effectiveness. To that end, we created a new educational activity that enables students to build and test microfluidic mixers, valves, and bubble generators in the classroom setting with inexpensive, widely-available materials. Although undergraduate and graduate engineering students are able to successfully construct the devices, our activity is unique in that the focus is not on successfully building and operating each device. Instead, it is to gain understanding about miniaturization science, device design, and construction so as to be able to do so independently. Our data show that the activity is appropriate for developing the conceptual understanding of graduate and advanced undergraduate students (n = 57), as well as makes a lasting impression on the students. We also report on observations related to student patterns of misunderstanding and how miniaturization science provides a unique opportunity for educational researchers to elicit and study misconceptions. More broadly, since this activity teaches participants a viable approach to creating microsystems and can be implemented in nearly any global setting, our work democratizes the education of miniaturization science. Noting the broad potential of point-of-care technologies in the global setting, such an activity could empower local experts to address their needs.

Opportunities and considerations for studying liver disease with microphysiological systems on a chip

Advances in microsystem engineering have enabled the development of highly controlled models of the liver that better recapitulate the unique in vivo biological conditions. In just a few short years, substantial progress has been made in creating complex mono- and multi-cellular models that mimic key metabolic, structural, and oxygen gradients crucial for liver function. Here we review: 1) the state-of-the-art in liver-centric microphysiological systems and 2) the array of liver diseases and pressing biological and therapeutic challenges which could be investigated with these systems. The engineering community has unique opportunities to innovate with new liver-on-a-chip devices and partner with biomedical researchers to usher in a new era of understanding of the molecular and cellular contributors to liver diseases and identify and test rational therapeutic modalities.

Pathologically stiff erythrocytes impede contraction of blood clots

BACKGROUND

Blood clot contraction, volume shrinkage of the clot, is driven by platelet contraction and accompanied by compaction of the erythrocytes and their gradual shape change from biconcave to polyhedral, with the resulting cells named polyhedrocytes.

OBJECTIVES

Here, we examined the role of erythrocyte rigidity on clot contraction and erythrocyte shape transformation.

METHODS

We used an optical tracking methodology that allowed us to quantify changes in contracting clot size over time.

RESULTS AND CONCLUSIONS

Erythrocyte rigidity has been shown to be increased in sickle cell disease (SCD), and in our experiments erythrocytes from SCD patients were 4-fold stiffer than those from healthy subjects. On average, the final extent of clot contraction was reduced by 53% in the clots from the blood of patients with SCD compared to healthy individuals, and there was significantly less polyhedrocyte formation. To test if this reduction in clot contraction was due to the increase in erythrocyte rigidity, we used stiffening of erythrocytes via chemical cross-linking (glutaraldehyde), rigidifying Wrightb antibodies (Wrb ), and naturally more rigid llama ovalocytes. Results revealed that stiffening erythrocytes result in impaired clot contraction and fewer polyhedrocytes. These results demonstrate the role of erythrocyte rigidity in the contraction of blood clots and suggest that the impaired clot contraction/shrinkage in SCD is due to the reduced erythrocyte deformability, which may be an underappreciated mechanism that aggravates obstructiveness of erythrocyte-rich (micro)thrombi in SCD.

Vascularized Microfluidics and Their Untapped Potential for Discovery in Diseases of the Microvasculature

Microengineering advances have enabled the development of perfusable, endothelialized models of the microvasculature that recapitulate the unique biological and biophysical conditions of the microcirculation in vivo. Indeed, at that size scale (<100 μm)-where blood no longer behaves as a simple continuum fluid; blood cells approximate the size of the vessels themselves; and complex interactions among blood cells, plasma molecules, and the endothelium constantly ensue-vascularized microfluidics are ideal tools to investigate these microvascular phenomena. Moreover, perfusable, endothelialized microfluidics offer unique opportunities for investigating microvascular diseases by enabling systematic dissection of both the blood and vascular components of the pathophysiology at hand. We review (a) the state of the art in microvascular devices and (b) the myriad of microvascular diseases and pressing challenges. The engineering community has unique opportunities to innovate with new microvascular devices and to partner with biomedical researchers to usher in a new era of understanding and discovery of microvascular diseases.

Platelet heterogeneity enhances blood clot volumetric contraction: An example of asynchrono-mechanical amplification

Physiological processes such as blood clotting and wound healing as well as pathologies such as fibroses and musculoskeletal contractures, all involve biological materials composed of a contracting cellular population within a fibrous matrix, yet how the microscale interactions among the cells and the matrix lead to the resultant emergent behavior at the macroscale tissue level remains poorly understood. Platelets, the anucleate cell fragments that do not divide nor synthesize extracellular matrix, represent an ideal model to study such systems. During blood clot contraction, microscopic platelets actively pull fibers to shrink the macroscale clot to less than 10% of its initial volume. We discovered that platelets utilize a new emergent behavior, asynchrono-mechanical amplification, to enhanced volumetric material contraction and to magnify contractile forces. This behavior is triggered by the heterogeneity in the timing of a population of actuators. This result indicates that cell heterogeneity, often attributed to stochastic cell-to-cell variability, can carry an essential biophysical function, thereby highlighting the importance of considering 4 dimensions (space + time) in cell-matrix biomaterials. This concept of amplification via heterogeneity can be harnessed to increase mechanical efficiency in diverse systems including implantable biomaterials, swarm robotics, and active polymer composites.

Getting a good view: in vitro imaging of platelets under flow

As the anucleate cells responsible for hemostasis and thrombosis, platelets are exposed to a myriad of biophysical and biochemical stimuli within vasculature and heterogeneous blood clots. Highly controlled, reductionist in vitro imaging studies have been instrumental in providing a detailed and quantitative understanding of platelet biology and behavior, and have helped elucidate some surprising functions of platelets. In this review, we highlight the tools and approaches that enable visualization of platelets in conjunction with precise control over the local biofluidic and biochemical microenvironment. We also discuss next generation tools that add further control over microenvironment cell stiffness or enable visualization of the interactions between platelets and endothelial cells. Throughout the review, we include pragmatic knowledge on imaging systems, experimental conditions, and approaches that have proved to be useful to our in vitro imaging studies of platelets under flow.

The biophysics and mechanics of blood from a materials perspective

Cells actively interact with their microenvironment, constantly sensing and modulating biochemical and biophysical signals. Blood comprises a variety of non-adherent cells that interact with each other and with endothelial and vascular smooth muscle cells of the blood vessel walls. Blood cells are further experiencing a range of external forces by the hemodynamic environment and they also exert forces to remodel their local environment. Therefore, the biophysics and material properties of blood cells and blood play an important role in determining blood behaviour in health and disease. In this Review, we discuss blood cells and tissues from a materials perspective, considering the mechanical properties and biophysics of individual blood cells and endothelial cells as well as blood cell collectives. We highlight how blood vessels provide a mechanosensitive barrier between blood and tissues and how changes in vessel stiffness and flow shear stress can be correlated to plaque formation and exploited for the design of vascular grafts. We discuss the effect of the properties of fibrin on blood clotting, and investigate how forces exerted by platelets are correlated to disease. Finally, we hypothesize that blood and vascular cells are constantly establishing a mechanical homeostasis, which, when imbalanced, can lead to hematologic and vascular diseases.

Feeling the Force: Measurements of Platelet Contraction and Their Diagnostic Implications

In addition to the classical biological and biochemical framework, blood clots can also be considered as active biomaterials composed of dynamically contracting platelets, nascent polymeric fibrin that functions as a matrix scaffold, and entrapped blood cells. As platelets sense, rearrange, and apply forces to the surrounding microenvironment, they dramatically change the material properties of the nascent clot, increasing its stiffness by an order of magnitude. Hence, the mechanical properties of blood clots are intricately tied to the forces applied by individual platelets. Research has also shown that the pathophysiological changes in clot mechanical properties are associated with bleeding and clotting disorders, cancer, stroke, ischemic heart disease, and more. By approaching the study of hemostasis and thrombosis from a biophysical and mechanical perspective, important insights have been made into how the mechanics of clotting and the forces applied by platelets are linked to various diseases. This review will familiarize the reader with a mechanics framework that is contextualized with relevant biology. The review also includes a discussion of relevant tools used to study platelet forces either directly or indirectly, and finally, concludes with a summary of potential links between clotting forces and disease.

Towards remote assessment and screening of acute abdominal pain using only a smartphone with native accelerometers

Smartphone-based telehealth holds the promise of shifting healthcare from the clinic to the home, but the inability for clinicians to conduct remote palpation, or touching, a key component of the physical exam, remains a major limitation. This is exemplified in the assessment of acute abdominal pain, in which a physician's palpation determines if a patient's pain is life-threatening requiring emergency intervention/surgery or due to some less-urgent cause. In a step towards virtual physical examinations, we developed and report for the first time a "touch-capable" mHealth technology that enables a patient's own hands to serve as remote surrogates for the physician's in the screening of acute abdominal pain. Leveraging only a smartphone with its native accelerometers, our system guides a patient through an exact probing motion that precisely matches the palpation motion set by the physician. An integrated feedback algorithm, with 95% sensitivity and specificity, enabled 81% of tested patients to match a physician abdominal palpation curve with <20% error after 6 attempts. Overall, this work addresses a key issue in telehealth that will vastly improve its capabilities and adoption worldwide.

Microfluidic Transduction Harnesses Mass Transport Principles to Enhance Gene Transfer Efficiency

Ex vivo gene therapy using lentiviral vectors (LVs) is a proven approach to treat and potentially cure many hematologic disorders and malignancies but remains stymied by cumbersome, cost-prohibitive, and scale-limited production processes that cannot meet the demands of current clinical protocols for widespread clinical utilization. However, limitations in LV manufacture coupled with inefficient transduction protocols requiring significant excess amounts of vector currently limit widespread implementation. Herein, we describe a microfluidic, mass transport-based approach that overcomes the diffusion limitations of current transduction platforms to enhance LV gene transfer kinetics and efficiency. This novel ex vivo LV transduction platform is flexible in design, easy to use, scalable, and compatible with standard cell transduction reagents and LV preparations. Using hematopoietic cell lines, primary human T cells, primary hematopoietic stem and progenitor cells (HSPCs) of both murine (Sca-1⁺) and human (CD34⁺) origin, microfluidic transduction using clinically processed LVs occurs up to 5-fold faster and requires as little as one-twentieth of LV. As an in vivo validation of the microfluidic-based transduction technology, HSPC gene therapy was performed in hemophilia A mice using limiting amounts of LV. Compared to the standard static well-based transduction protocols, only animals transplanted with microfluidic-transduced cells displayed clotting levels restored to normal.

Platelet-Microcapsule Hybrids Leverage Contractile Force for Targeted Delivery of Hemostatic Agents

We report a cell-mediated, targeted drug delivery system utilizing polyelectrolyte multilayer capsules that hybridize with the patient's own platelets upon intravenous administration. The hybridized platelets function as the sensor and actuator for targeted drug delivery and controlled release in our system. These capsules are biochemically and mechanically tuned to enable platelet adhesion and capsule rupture upon platelet activation and contraction, enabling the targeted and controlled "burst" release of an encapsulated biotherapeutic. As platelets are the "first responders" in the blood clot formation process, this platelet-hybridized system is ideal for the targeted delivery of clot-augmenting biotherapeutics wherein immediate therapeutic efficacy is required. As proof-of-concept, we tailored this system to deliver the pro-clotting biotherapeutic factor VIII for hemophilia A patients that have developed inhibitory antifactor VIII antibodies. The polyelectrolyte multilayer capsules physically shield the encapsulated factor VIII from the patient's inhibitors during circulation, preserving its bioactivity until it is delivered at the target site via platelet contractile force. Using an in vitro microfluidic vascular injury model with factor VIII-inhibited blood, we demonstrate a 3.8× increase in induced fibrin formation using capsules loaded with factor VIII at a concentration an order of magnitude lower than that used in systemic delivery. We further demonstrate that clot formation occurs 18 min faster when factor VIII loaded capsules are used compared to systemic delivery at the same concentration. Because platelets are integral in the pathophysiology of thrombotic disorders, cancer, and innate immunity, this paradigm-shifting smart drug delivery system can be similarly applied to these diseases.

Magnetic forces enable controlled drug delivery by disrupting endothelial cell-cell junctions

The vascular endothelium presents a major transport barrier to drug delivery by only allowing selective extravasation of solutes and small molecules. Therefore, enhancing drug transport across the endothelial barrier has to rely on leaky vessels arising from disease states such as pathological angiogenesis and inflammatory response. Here we show that the permeability of vascular endothelium can be increased using an external magnetic field to temporarily disrupt endothelial adherens junctions through internalized iron oxide nanoparticles, activating the paracellular transport pathway and facilitating the local extravasation of circulating substances. This approach provides a physically controlled drug delivery method harnessing the biology of endothelial adherens junction and opens a new avenue for drug delivery in a broad range of biomedical research and therapeutic applications.

The transportation of large molecules through the vascular endothelium presents a major challenge for in vivo drug delivery. Here, the authors demonstrate the potential of using external magnetic fields and magnetic nanoparticles to enhance the local extravasation of circulating large molecules.

Single-platelet nanomechanics measured by high-throughput cytometry

Haemostasis occurs at sites of vascular injury, where flowing blood forms a clot, a dynamic and heterogeneous fibrin-based biomaterial. Paramount in the clot's capability to stem haemorrhage are its changing mechanical properties, the major drivers of which are the contractile forces exerted by platelets against the fibrin scaffold. However, how platelets transduce microenvironmental cues to mediate contraction and alter clot mechanics is unknown. This is clinically relevant, as overly softened and stiffened clots are associated with bleeding and thrombotic disorders. Here, we report a high-throughput hydrogel-based platelet-contraction cytometer that quantifies single-platelet contraction forces in different clot microenvironments. We also show that platelets, via the Rho/ROCK pathway, synergistically couple mechanical and biochemical inputs to mediate contraction. Moreover, highly contractile platelet subpopulations present in healthy controls are conspicuously absent in a subset of patients with undiagnosed bleeding disorders, and therefore may function as a clinical diagnostic biophysical biomarker.

Platelet mechanosensing of collagen matrices

During vascular injury, platelets adhere to exposed subendothelial proteins, such as collagen, on the blood vessel walls to trigger clot formation. Although the biochemical signalings of platelet-collagen interactions have been well characterized, little is known about the role microenvironmental biomechanical properties, such as vascular wall stiffness, may have on clot formation. To that end, we investigated how substrates of varying stiffness conjugated with the same concentration of Type I collagen affect platelet adhesion, spreading, and activation. Using collagen-conjugated polyacrylamide (PA) gels of different stiffnesses, we observed that platelets do in fact mechanotransduce the stiffness cues of collagen substrates, manifesting in increased platelet spreading on stiffer substrates. In addition, increasing substrate stiffness also increases phosphatidylserine exposure, a key aspect of platelet activation that initiates coagulation on the platelet surface. Mechanistically, these collagen substrate stiffness effects are mediated by extracellular calcium levels and actomyosin pathways driven by myosin light chain kinase but not Rho-associated protein kinase. Overall, our results improve our understanding of how the mechanics of different tissues and stroma affect clot formation, what role the increased vessel wall stiffness in atherosclerosis may directly have on thrombosis leading to heart attacks and strokes, and how age-related increased vessel wall stiffness affects hemostasis and thrombosis.

Simplified prototyping of perfusable polystyrene microfluidics

Cell culture in microfluidic systems has primarily been conducted in devices comprised of polydimethylsiloxane (PDMS) or other elastomers. As polystyrene (PS) is the most characterized and commonly used substrate material for cell culture, microfluidic cell culture would ideally be conducted in PS-based microsystems that also enable tight control of perfusion and hydrodynamic conditions, which are especially important for culture of vascular cell types. Here, we report a simple method to prototype perfusable PS microfluidics for endothelial cell culture under flow that can be fabricated using standard lithography and wet laboratory equipment to enable stable perfusion at shear stresses up to 300 dyn/cm(2) and pumping pressures up to 26 kPa for at least 100 h. This technique can also be extended to fabricate perfusable hybrid PS-PDMS microfluidics of which one application is for increased efficiency of viral transduction in non-adherent suspension cells by leveraging the high surface area to volume ratio of microfluidics and adhesion molecules that are optimized for PS substrates. These biologically compatible microfluidic devices can be made more accessible to biological-based laboratories through the outsourcing of lithography to various available microfluidic foundries.

Mitochondrially mediated integrin αIIbβ3 protein inactivation limits thrombus growth

When platelets are strongly stimulated, a procoagulant platelet subpopulation is formed that is characterized by phosphatidylserine (PS) exposure and epitope modulation of integrin αIIbβ3 or a loss of binding of activation-dependent antibodies. Mitochondrial permeability transition pore (mPTP) formation, which is essential for the formation of procoagulant platelets, is impaired in the absence of cyclophilin D (CypD). Here we investigate the mechanisms responsible for these procoagulant platelet-associated changes in integrin αIIbβ3 and the physiologic role of procoagulant platelet formation in the regulation of platelet aggregation. Among strongly stimulated adherent platelets, integrin αIIbβ3 epitope changes, mPTP formation, PS exposure, and platelet rounding were closely associated. Furthermore, platelet mPTP formation resulted in a decreased ability to recruit additional platelets. In the absence of CypD, integrin αIIbβ3 function was accentuated in both static and flow conditions, and, in vivo, a prothrombotic phenotype occurred in mice with a platelet-specific deficiency of CypD. CypD-dependent proteolytic events, including cleavage of the integrin β3 cytoplasmic domain, coincided closely with integrin αIIbβ3 inactivation. Calpain inhibition blocked integrin β3 cleavage and inactivation but not mPTP formation or PS exposure, indicating that integrin inactivation and PS exposure are mediated by distinct pathways subsequent to mPTP formation. mPTP-dependent alkalinization occurred in procoagulant platelets, suggesting a possible alternative mechanism for enhancement of calpain activity in procoagulant platelets. Together, these results indicate that, in strongly stimulated platelets, mPTP formation initiates the calpain-dependent cleavage of integrin β3 and associated regulatory proteins, resulting in integrin αIIbβ3 inactivation, and demonstrate a novel CypD-dependent negative feedback mechanism that limits platelet aggregation and thrombotic occlusion.

Biomechanics of haemostasis and thrombosis in health and disease: from the macro- to molecular scale

Although the processes of haemostasis and thrombosis have been studied extensively in the past several decades, much of the effort has been spent characterizing the biological and biochemical aspects of clotting. More recently, researchers have discovered that the function and physiology of blood cells and plasma proteins relevant in haematologic processes are mechanically, as well as biologically, regulated. This is not entirely surprising considering the extremely dynamic fluidic environment that these blood components exist in. Other cells in the body such as fibroblasts and endothelial cells have been found to biologically respond to their physical and mechanical environments, affecting aspects of cellular physiology as diverse as cytoskeletal architecture to gene expression to alterations of vital signalling pathways. In the circulation, blood cells and plasma proteins are constantly exposed to forces while they, in turn, also exert forces to regulate clot formation. These mechanical factors lead to biochemical and biomechanical changes on the macro- to molecular scale. Likewise, biochemical and biomechanical alterations in the microenvironment can ultimately impact the mechanical regulation of clot formation. The ways in which these factors all balance each other can be the difference between haemostasis and thrombosis. Here, we review how the biomechanics of blood cells intimately interact with the cellular and molecular biology to regulate haemostasis and thrombosis in the context of health and disease from the macro- to molecular scale. We will also show how these biomechanical forces in the context of haemostasis and thrombosis have been replicated or measured in vitro.

Osmosis is not driven by water dilution

There is a misconception among plant scientists that osmosis is driven by the tendency of solutes to dilute water. In this opinion article, we discuss the quantitative and qualitative failures of this view, and go on to review the correct kinetic picture of osmosis as it appears in physics textbooks.

Endothelialized microfluidics for studying microvascular interactions in hematologic diseases

Advances in microfabrication techniques have enabled the production of inexpensive and reproducible microfluidic systems for conducting biological and biochemical experiments at the micro- and nanoscales (1,2). In addition, microfluidics have also been specifically used to quantitatively analyze hematologic and microvascular processes, because of their ability to easily control the dynamic fluidic environment and biological conditions(3-6). As such, researchers have more recently used microfluidic systems to study blood cell deformability, blood cell aggregation, microvascular blood flow, and blood cell-endothelial cell interactions(6-13).However, these microfluidic systems either did not include cultured endothelial cells or were larger than the sizescale relevant to microvascular pathologic processes. A microfluidic platform with cultured endothelial cells that accurately recapitulates the cellular, physical, and hemodynamic environment of the microcirculation is needed to further our understanding of the underlying biophysical pathophysiology of hematologic diseases that involve the microvasculature. Here, we report a method to create an "endothelialized" in vitro model of the microvasculature, using a simple, single mask microfabrication process in conjunction with standard endothelial cell culture techniques, to study pathologic biophysical microvascular interactions that occur in hematologic disease. This "microvasculature-on-a-chip" provides the researcher with a robust assay that tightly controls biological as well as biophysical conditions and is operated using a standard syringe pump and brightfield/fluorescence microscopy. Parameters such as microcirculatory hemodynamic conditions, endothelial cell type, blood cell type(s) and concentration(s), drug/inhibitory concentration etc., can all be easily controlled. As such, our microsystem provides a method to quantitatively investigate disease processes in which microvascular flow is impaired due to alterations in cell adhesion, aggregation, and deformability, a capability unavailable with existing assays.

Microenvironmental geometry guides platelet adhesion and spreading: a quantitative analysis at the single cell level

To activate clot formation and maintain hemostasis, platelets adhere and spread onto sites of vascular injury. Although this process is well-characterized biochemically, how the physical and spatial cues in the microenvironment affect platelet adhesion and spreading remain unclear. In this study, we applied deep UV photolithography and protein micro/nanostamping to quantitatively investigate and characterize the spatial guidance of platelet spreading at the single cell level and with nanoscale resolution. Platelets adhered to and spread only onto micropatterned collagen or fibrinogen surfaces and followed the microenvironmental geometry with high fidelity and with single micron precision. Using micropatterned lines of different widths, we determined that platelets are able to conform to micropatterned stripes as thin as 0.6 µm and adopt a maximum aspect ratio of 19 on those protein patterns. Interestingly, platelets were also able to span and spread over non-patterned regions of up to 5 µm, a length consistent with that of maximally extended filopodia. This process appears to be mediated by platelet filopodia that are sensitive to spatial cues. Finally, we observed that microenvironmental geometry directly affects platelet biology, such as the spatial organization and distribution of the platelet actin cytoskeleton. Our data demonstrate that platelet spreading is a finely-tuned and spatially-guided process in which spatial cues directly influence the biological aspects of how clot formation is regulated.

Cementoblastoma associated with a primary tooth: a rare pediatric lesion

An intraosseous, slightly painful swelling was noted upon clinical examination of an eight-year-old girl. The swelling was of an unspecified duration and slow growing in nature. A radiopaque mass with a radiolucent periphery attached to the roots of the mandibular right second primary molar was noted on a periapical radiograph. The diagnosis of cementoblastoma was verified by the histologic assessment.

Performance of sealants applied to first permanent molars in a dental school setting

PURPOSE

The purpose of this study was to assess the performance of sealants placed by senior dental students as part of a comprehensive dental care program that included periodic patient recall.

METHODS

The dental records of 100 patients ranging in age from 6 to 13 years were selected for review to determine the treatments provided for first permanent molars over time. Criteria for inclusion were: 1) at least five documented recall examinations and 2) all four first permanent molars had to have been treated with an occlusal pit and fissure sealant. The data collected included: 1) the age of the patient at the time of initial sealant placement; 2) the subsequent treatment provided to the first permanent molars, including retreatment with sealant or restoration and the date the services were provided; 3) the last date of follow-up examination in the pediatric dental program.

RESULTS

A total of 400 molars were followed for an average of 54 months. Fifty-two percent of all molars received no further treatment after initial placement of sealant. Approximately 35% received retreatment with sealant only. The total number of molars receiving sealant material only was 343 (86%). The total number of teeth that were judged to require restoration was 57 (14%). No relationship was noted between the patient's age at placement of the occlusal sealant and sealant performance.

CONCLUSION

In a dental school clinic, occlusal sealants were effective at preventing caries in a comprehensive care program that included periodic recall.

An outcomes assessment of 15 years of patient care experiences in predoctoral pediatric dentistry

The purpose of this study was to examine the trends in numbers, demographic characteristics, and treatment history of pediatric dental patients under the care of dental students over the period 1980 through 1994. Data were collected for: exams, sealants, surfaces of amalgam, composite resin surfaces, pulpotomies, stainless steel crowns, and extractions. Correlations were done across the 15-year period to determine significant trends over time. During the 15-year period, the average number of patient visits required for each student to complete the requisite number of patients, declined from 45 appointments to complete 10 patients in 1980, to 35 visits to complete 13 patients in 1994. Over time, the numbers of amalgam surfaces, pulpotomies, extractions and stainless steel crowns decreased significantly, while the number of composite resin surfaces increased (P < 0.05). Based on a previous outcome assessment that indicated declining numbers of procedures performed between 1980 and 1985, the required number of patients treated per student was raised from 10 to 13, beginning with the 1986 class.

Dentists' perceptions of selected characteristics of their child patients

The purpose of this project was to examine the perceptions of both general and pediatric dentists regarding selected characteristics of the children they treat. A survey including questions on patients' ages, caries activity estimates, and types of patients treated was mailed once to a national random sample of 2,000 general and 1,000 pediatric dentists. The respondents provided a reasonable distribution by age and location, with the majority (69%) in practice more than 10 years. The pediatric dentists who responded perceive that they treat a younger population of child patients with more caries activity (P < 0.001), except in those patients older than 12 years. They also perceive that their patients pools include a larger percentage of patients with handicapping conditions (P < 0.01), behavior problems (P < 0.001) and patients who require treatment with general anesthesia (P < 0.001) than do the general dentists.

Dentists' perceptions of the variety of dental services provided for children

The purpose of this project was to describe the variety of dental services provided to child patients by general dentists and pediatric dentists. A survey was mailed to a random sample of 2000 general dentists and 1000 pediatric dentists requesting information about the dental services provided to children. Six hundred sixty-two general dentists (33 percent) and 492 pediatric dentists (49 percent) responded. Pediatric dentists reported more frequently obtaining informed consent (p < .0001), placing strip crowns (p < .0001), steel crowns (p < .0001) and pulp treatment procedures (p < .0001). Sealant use in both groups was high but the general dentists reported more frequently sealing occlusal surfaces with incipient caries (p < .001). There were differences in the reported provision of orthodontic services. The general dentists were more likely to refer children for treatment while the pediatric dentists reported they performed limited or comprehensive orthodontic treatment (p < .0001). The results of the survey demonstrate that pediatric dentists perceive that they provide a broader scope of restorative and orthodontic services.

The use of behavior management techniques by dentists across practitioner type, age, and geographic region

The purpose of this project was to describe the behavior management procedures employed for child dental patients based on practitioner type (general dentist vs. pediatric dentist), age, and geographic location. A survey of practice characteristics, which included questions relating to child behavior management, was mailed once to a national random sample of 3000 dentists--2000 general dentists and 1000 pediatric dentists. The pediatric dentists who responded employed a broader spectrum of management techniques than did the general dentists. Significant regional and practitioner age differences were reported in the use of behavior management techniques. The use of sedation and general anesthesia was reported more frequently in the western regions. Of the five age groups, the 40- to 49-year-old age group reported using the broadest spectrum of behavior management techniques. The survey revealed practitioner type, age, and regional differences in the child behavior management procedures employed by dentists.

Gender differences in the characteristics of dental services provided for children

The purpose of this project was to describe the differences and similarities in the practice of dentistry for children by male and female dentists. A once-mailed survey with a series of questions regarding the characteristics of their dental practices was sent to a random sample of 3,000 dentists. There were 1,154 useable responses (39 percent). Approximately 8 percent of the respondents were women, which is representative of the percentage of female dentists practicing in the United States. Chi square analysis was employed. There were differences in the practice characteristics of the male and female dentists responding to this survey. The female respondents were: significantly younger; had been in practice for a shorter period of time; more likely to be employees rather than solo practitioners; more likely to treat younger patients; less likely to do comprehensive orthodontic treatment and more likely to use physical restraints than their male counterparts.

Method of payment for children's dental services by practice type and geographic location

The purpose of this project was to evaluate practice type and geographical differences in methods of payment accepted for children's dental services. A survey was mailed to 2000 general dentists and 1000 pediatric dentists randomly selected to provide representation from the 50 United States. Dentists were asked to specify the type of practice and the state in which they primarily practice. The survey included Medicaid, dental insurance, preferred provider organizations (PPO), and self-payment as payment options. Dentists were asked to indicate whether they never, occasionally, or frequently accepted each option of payment for children's dental services. Responses were received from 1245 (42%) dentists, including 723 general dentists and 522 pediatric dentists. Chi-square statistical analysis revealed significant practice type and regional differences in the acceptance of Medicaid for payment. Pediatric dentists accept Medicaid more frequently than general dentists (P < 0.001). Most dentists accept dental insurance and self-payment, while few indicate involvement with a PPO. The study revealed significant practice type differences only in the acceptance of Medicaid as payment for children's dental services. On a geographic basis, there were significant differences in the acceptance of Medicaid and dental insurance.

Analyzing dental procedures performed by an HIV-positive dental student

No evidence of HIV transmission was found between an HIV-positive dental student and 163 treated patients.

The influence of practice type, region, and age on treatment recommendations for primary teeth

The purpose of this study was to investigate dentists' treatment recommendations for interproximal surfaces of primary molars based on the type of practitioner (general dentist or pediatric dentist), geographic location, and age of practitioner. Simulated cases, which included histories and pictures of bite-wing radiographs, were mailed to a random sample of 2000 general dentists and 1000 pediatric dentists. Dentists were asked to select their treatment recommendations for eight cases involving the interproximal surface of a specified primary molar. The return rate was 42% (1245) overall, with 36% (723) from general dentists and 52% (522) from pediatric dentists. An amalgam restoration was recommended most often for these eight cases. Dentists in the age 60+ category and pediatric dentists were more likely to recommend treatment for smaller interproximal lesions. Composite resins were recommended infrequently; however, dentists in the 60+ age category and dentists in the Northeast and Southwest were somewhat more likely to recommend composite resin than younger dentists, or dentists in other geographic locations. Dentists in the 40-49 age range, pediatric dentists, and dentists in the Southwest were the most likely to recommend stainless steel crowns. These simulated cases demonstrate differences and similarities in the treatment recommendations for interproximal lesions on primary molars based on age, practice type, and region.

A comparison of general dentists' and pediatric dentists' treatment recommendations for primary teeth

A survey which included a series of demographic questions, a brief clinical history, and pictures of eight radiographs was mailed to 2000 general dentists and 1000 pediatric dentists. Usable responses were received from 1369 (45%) dentists--765 (38%) general dentists, and 604 (60%) pediatric dentists. The dentists were asked to select the optimal treatment for a specified tooth in each radiograph. The results of this survey indicate that there were differences in the treatment recommendations of general and pediatric dentists. Whether or not pulp therapy was recommended, general dentists frequently recommended restoring teeth with amalgam. Pediatric dentists more frequently recommended restoring primary teeth with stainless steel crowns. There were differences in treatment recommendations within each group of practitioners, as well as between the two groups.

Management considerations for an HIV positive dental student

Health care workers who are HIV positive or who have AIDS are faced with unique and perplexing problems. Likewise dental students who are HIV positive present a special circumstance that demands review of ethical, legal, managerial, and medical considerations. The purpose of this paper is to describe the management considerations at the Medical College of Georgia following a recent report of an HIV positive dental student. The administration assembled a diverse team of experts for advice in the situation. This group assumed that the circumstance was a potential crisis with possible serious long-term implications. Therefore detailed planning, appropriate announcements, and careful management have been the administration's principle goal for several weeks. The key management strategies and actions are described from the time of notification of the student's HIV antibody test results through the initial testing of the patient population subgroup.

The role of race and ethnic status on the psychosocial correlates of smokeless tobacco use in adolescent males

From a stratified, random sampling of non-urban high schools in the Southeast, survey data were obtained from 5374 adolescent males. Over half reported trying smokeless tobacco, and approximately one third of these reported a regular, substantial level of use. The average age at initial use was 12.2 yr. and was negatively correlated with the level of use. Factor analysis of the psychosocial items resulted in four factors: substance use/deviant style, modeling, perceived negative consequences, and health behavior. Discriminant analysis of initial use indicated that substance use and modeling influences were the strongest predictors of trying smokeless tobacco. Regression analysis of level of smokeless tobacco use indicated that substance use, modeling, and perceived negative consequences were equivalent in their contribution. Separate analyses were performed for American Indian, Black, and White males. Although predictors of initial use were similar, level of smokeless tobacco use was most associated with the use of other substances in Blacks and with modeling influences in Whites.

Radiographic recommendations for the transitional dentition: comparison of general dentists and pediatric dentists

A survey which included brief case histories and intraoral photos of four transitional dentitions, including examples of ectopic and delayed eruption, as well as carious lesions, was mailed to a random sample of 2000 general dentists and 1000 pediatric dentists. Radiographic options were listed, from which each dentist was to indicate all films needed for each child's examination. Surveys were returned by 1273 (43%) dentists, including 713 (36%) general dentists and 560 (56%) pediatric dentists. The pediatric dentists took significantly more diagnostic radiographs than did the general dentists for each of the four transitional dentition cases. Pediatric dentists were more likely than the general dentists to take panoramic films and combinations which included panoramic films, bite-wing radiographs and periapical films. The most frequently ordered combinations were bite-wing radiographs plus panoramic films and bite-wing radiographs plus anterior periapical films. General dentists recommended bite-wing radiographs films only more frequently than did pediatric dentists. In view of the results of this study and the USDHHS guidelines for radiographic examinations, (1987) education must be provided for both general dentists and pediatric dentists regarding appropriate radiographic examinations for transitional dentition patients.

Comparing treatment options for occlusal surfaces utilizing an invasive index

The purpose of this project was to develop an invasive index to: 1) compare the treatments recommended by dentists for the occlusal surfaces of molars; 2) compare the invasive index score of each tooth with the extent of the carious lesion as determined by electrical resistance and histological examination; and 3) compare the relative extent of the total crown destruction resulting from the carious lesion and the cavity preparation. Twenty dentists examined 19 extracted permanent molar teeth using a #23 explorer and selected the most appropriate treatment from the following options: no treatment (score 0), occlusal sealant (score 1), preventive resin (score 2), occlusal amalgam (score 3). The invasive index scores determined for each dentist and each tooth were compared using an analysis of variance. The electrical conductivity of each tooth was measured with an electronic caries detector (Vanguard). Electrical resistance scores were compared to the invasive index scores and to a histological examination. The results demonstrate that the invasive index is a useful means to compare treatments recommended by different dentists. The invasive index suggests there is considerable variation among dentists in the treatment they recommend for occlusal surfaces. Electrical resistance testing did not provide helpful information for treatment planning of questionably carious occlusal surfaces.

Radiographic recommendations for the primary dentition: comparison of general dentists and pediatric dentists

A survey which included brief case histories and intraoral photos of four primary dentitions ranging from healthy to severely carious was mailed to a random sample of 2000 general dentists and 1000 pediatric dentists. Radiographic options were listed, from which the dentist was to indicate all films needed for each child's examination. Surveys were received from 1273 (43%) dentists, including 713 (36%) general dentists and 560 (56%) pediatric dentists. The pediatric dentists recommended significantly more diagnostic radiographs than did the general dentists across all four primary dentition cases. This trend was apparent in the absence of clinically visible caries. When radiographs were recommended, bite-wing radiographs were the most frequently ordered films. The most frequently ordered combination among all respondents was bite-wing radiographs plus anterior periapical films. The results suggest that, frequently, neither general dentists nor pediatric dentists prescribe radiographs for the primary dentition patient that conform to the USDHHS guidelines for radiographic examination (1987).

Smokeless tobacco use in adolescent females: prevalence and psychosocial factors among racial/ethnic groups

From a stratified, random sampling of Southeastern, nonurban high schools, survey data on smokeless tobacco use and potential psychosocial risk factors were obtained from 5683 adolescent females. Of the 15.3% who reported trying smokeless tobacco, most (75%) reported only experimental use. Factor analysis of the psychosocial items resulted in four factors: perceived negative consequences, substance use, modeling, and active lifestyle. Discriminant analysis on use indicated that modeling influences and use of other substances were the strongest predictors of initial smokeless tobacco use. Level of use, however, was most strongly associated with lower perceived negative consequences for use and the use of other substances. Separate analyses on American Indian, Black, and White subgroups suggested that factors associated with initial use were similar but that substantial differences exist between subgroups on risk factors for level of smokeless tobacco use.

Typology and correlates of smokeless tobacco use

The incidence, use patterns, and correlates of smokeless tobacco have become increasingly important as usage rates rise and harmful health effects become established. The present study assessed the incidence of smokeless tobacco use in a Southeastern U.S. sample and selected correlates of use. From the responses of 3725 high school students, 19.9% reported trying smokeless tobacco products (35.5% for males, 5.8% for females). Most agreed that tobacco use has harmful health consequences. Those disagreeing with these health beliefs were more likely to use smokeless tobacco. Cigarette smoking was strongly associated with initial use. Of those reporting any use of smokeless tobacco, most used it for less than an hour per day, but 18% reported 3 or more hours of use per day. Forty-four percent reported a first use of smokeless tobacco before 13 years of age. Early initial use was associated with greater frequency and duration of use. Early initial users also reported greater influence from family and advertisements. Encouragement from friends, however, appeared to be the major factor regardless of age at initial use. Of particular concern is that 8.4% of those having any experience with smokeless tobacco felt they were addicted to the substance. Finally, 27.9% reported swallowing the substance or spittle, suggesting the need for further research on the potential health implications of this behavior.

Localized prepubertal periodontitis: literature review and report of case

This case describes a young, healthy, white female who demonstrated anterior alveolar bone loss along with premature loss of her primary incisors. The alveolar bone loss remains unexplained. The root surfaces of most of the primary anterior teeth exhibited one or more eroded areas devoid of cementum with some evidence in two teeth of cellular resorptive activity. These findings suggest that premature root resorption was occurring concurrently with unexplained extensive alveolar bone loss. The child will be examined periodically to determine whether this process of bone loss with subsequent tooth loss will involve additional primary or permanent teeth.