Impact of early clinical exposure on the learning experience of undergraduate dental students.

AIMS: The aim of this research was to evaluate the impact of early clinical exposure on the learning experiences of undergraduate dental students. METHODS: This study was based on mixed methods. The first phase involved administering a purposely designed questionnaire consisting of 16 items, grouped into three subscales. The second phase of the research was conducted using qualitative semi-structured interviews to explore the perceptions and experiences of stakeholders regarding early clinical exposure. RESULTS: In total, 134 undergraduate dental students and eight clinical supervisors responded to the questionnaire and reported positive perceptions regarding the learning experiences, professional relationship and learning environment. Qualitative interviews were conducted with 12 participants, and early clinical exposure was perceived to be useful in providing a context to theoretical learning and development of interpersonal skills. Curriculum overload and further need for consolidation were highlighted as the main challenges. CONCLUSIONS: This study provided insights into the clinical training model in an undergraduate dental programme and highlights the benefits and challenges of early clinical exposure in the study population. The study served as a vehicle for engagement with a range of stakeholders using a mixed methods approach to inform further development of the training model.

A surprisingly poor correlation between in vitro and in vivo testing of biomaterials for bone regeneration: results of a multicentre analysis.

New regenerative materials and approaches need to be assessed through reliable and comparable methods for rapid translation to the clinic. There is a considerable need for proven in vitro assays that are able to reduce the burden on animal testing, by allowing assessment of biomaterial utility predictive of the results currently obtained through in vivo studies. The purpose of this multicentre review was to investigate the correlation between existing in vitro results with in vivo outcomes observed for a range of biomaterials. Members from the European consortium BioDesign, comprising 8 universities in a European multicentre study, provided data from 36 in vivo studies and 47 in vitro assays testing 93 different biomaterials. The outcomes of the in vitro and in vivo experiments were scored according to commonly recognised measures of success relevant to each experiment. The correlation of in vitro with in vivo scores for each assay alone and in combination was assessed. A surprisingly poor correlation between in vitro and in vivo assessments of biomaterials was revealed indicating a clear need for further development of relevant in vitro assays. There was no significant overall correlation between in vitro and in vivo outcome. The mean in vitro scores revealed a trend of covariance to in vivo score with 58 %. The inadequacies of the current in vitro assessments highlighted here further stress the need for the development of novel approaches to in vitro biomaterial testing and validated pre-clinical pipelines.

Strontium oxide doped quaternary glasses: effect on structure, degradation and cytocompatibility.

This preliminary study focuses on the effect of adding SrO to a Ti-containing quaternary phosphate glass system denoted by P(2)O(5)-Na(2)O-CaO-TiO(2). The following four different glass compositions were manufactured: 0.5P(2)O(5)-0.17Na(2)O-0.03TiO(2)-(0.3-x)CaO-xSrO where x = 0, 0.01, 0.03 and 0.05. Structural characterisation revealed glass transition temperatures in the range 427-437 degrees C and the presence of sodium calcium phosphate as the dominant phase in all the glasses. Degradation and ion release studies conducted over a 15-day period revealed that the Sr-containing glasses showed significantly higher degradation and ion release rates than the Sr-free glass. Cytocompatibility studies performed over a 7-day period using MG63 cells showed that the addition of 5 mol% SrO yielded glasses with cell viability nearly equivalent to that observed for quaternary TiO(2) glasses.

Fluorescence spectroscopy combined with 5-aminolevulinic acid-induced protoporphyrin IX fluorescence in detecting oral premalignancy.

BACKGROUND: Early detection of premalignant/malignant lesions in the oral cavity can certainly improve the patient's prognosis. This study presents fluorescence imaging with the topical application of 5-aminolevulinic as a way to improve detection of various oral tissue pathologies. This procedure depends mainly on comparing the intensity of red and green fluorescence emitted from tissues during examination. MATERIALS AND METHODS: Seventy-one patients who presented with clinically suspicious oral leukoplakia were recruited for this study. Each of the patients was required to have 5-aminolevulinic acid in the form of mouth rinse prior to fluorescence imaging. Following this a surgical biopsy was acquired from the exact examination site. The results of the fluorescence spectroscopy have been compared with histopathology. RESULTS: A Student's t-test was applied to test the viability of the ratio between red and green fluorescence. The red-to-green ratio was found to increase significantly when the lesion was identified as dysplastic or carcinoma in situ. By applying a threshold line to discriminate between normal and dysplastic lesions; a sensitivity of 83-90% and specificity of 79-89% were obtained. CONCLUSION: Fluorescence spectroscopy combined with 5-aminolevulinic acid-induced protoporphyrin IX was found as a valuable tool in the diagnosis of oral premalignancy. This technique offers the potential to be advantageous over other non-optical techniques in terms of providing real-time diagnosis, in situ monitoring, cost effectiveness and more tolerated by patient compared to surgical biopsy.

Roughness response genes in osteoblasts.

Titanium (Ti) and Ti alloys are widely used as dental and orthopedic implants, but the effects of the surface characteristics of these materials, including roughness, on the response of target tissues in vivo are not well understood. The present study has therefore examined the effects of a moderately rough (sand-blasted, acid-etched; SLA) Ti surface, a highly rough (plasma-sprayed; TPS) surface, and a smooth surface (SMO) on bone cells in vitro. X-ray photoelectron spectroscopy showed that these surfaces had similar surface chemistry, while scanning electron microscopy suggested that the SLA provided a transiently less biocompatible surface, with initially less well-attached cells. SLA also delayed bone cell growth compared with SMO, whereas the TPS surface elicited the greatest increase in cell numbers. In addition, expression profiling using the ATLAS gene array showed marked differences in gene responses after 3 h of incubation; this increased further after 24 h, with TPS generating the largest number of up- and down-regulated genes compared with SLA and SMO. A number of osteoblast genes were also identified as 'roughness' genes on the basis of their similar response on SLA and TPS, compared with SMO. These findings show, for the first time, that the surface roughness of Ti has a profound effect on the profile of genes expressed by bone cells and suggest that improvements in the biological activity and possibly the clinical efficacy of these materials could be achieved by selective regulation of gene expression mediated via modification of surface roughness.

Glass reinforced hydroxyapatite for hard tissue surgery--part II: in vitro evaluation of bone cell growth and function.

Hydroxyapatite (HA)-based materials are considered to be potentially useful as bone implant materials, particularly those reinforced with glass to improve mechanical strength. However, the precise effects of glass-reinforced HA on the growth and functions of bone cells are still unclear. The present study has therefore examined the response of human osteoblast-like cells to HA and HA reinforced with two different proportions of glass, namely 2.5% and 5%. All materials enabled the cells to attach and proliferate during 7 days in culture and, although the growth was less than on control plastic surfaces, there was no deleterious effect of the 5% glass composite compared with HA alone. Flow cytometry analysis showed that there was no effect on cell size and granularity, but there were marked and highly selective changes in the expression of certain connective tissue proteins. Thus, while bone sialoprotein and osteonectin were down-regulated on HA alone, the expression of these antigens was relatively enhanced on the composite materials, and collagen type I was also up-regulated on the glass-reinforced HA. Thus, modulation of the glass composition of HA materials could be used to produce not only improved mechanical strength, but also enhanced biocompatibility.

Neo-intimal development on textured biomaterial surfaces during clinical use of an implantable left ventricular assist device.

Implantable left ventricular assist systems are being developed for long term clinical use. Prototype devices are currently used as extended mechanical bridges to cardiac transplantation. The Thermo Cardiosystems Inc. (TCI) pneumatic pusher plate left ventricular assist device (LVAD) features textured blood contacting surfaces to encourage the formation of an adherent fibrin-cellular coagulum. This serves as the foundation for the development of a neo-intimal lining. The TCI LVAD was implanted in 6 male patients (age range 22-53 years) between 1986 and 1988. The duration of implantation ranged from 1-41 days. No clinical thromboembolic events or pump-related thromboembolism occurred and none was evident at necropsy. The six device linings have been fully evaluated. Explanted devices were free of thrombus and calcification. Lining samples for light and electron microscopy were collected from areas of the diaphragm identical for flex and blood shear conditions and from high and low shear areas on the static housing. Islands of collagenous tissue were deposited on the static housing amongst compact fibrin. By day 13, cells populated the surface of the developing neo-intima overlying the diaphragm. By 41 days, the surface cell density increased and the cells became spindle shaped and relatively orientated in the high shear/flex area. Immunohistochemical techniques suggest that these cells are of mesenchymal origin. Textured blood contacting surfaces appear satisfactory in the preliminary clinical use of this device.

Stratified scaffolds for osteochondral tissue engineering applications: electrospun PDLLA nanofibre coated Bioglass®-derived foams.

This work focuses on designing bilayered constructs by combining electrospun poly-DL-Lactide (PDLLA) fibers and Bioglass®-derived scaffolds for development of osteochondral tissue replacement materials. Electrospinning was carried out using a solution of 5 wt/v% PDLLA in dimethyl carbonate. The PDLLA layer thickness increased from 2 to 150 µm with varying electrospinning time. Bioactivity studies in simulated body fluid showed that HA mineralization decreased as the thickness of the PDLLA layer increased. A preliminary in vitro study using chondrocyte cells (ATDC5) showed that cells attached, proliferated and migrated into the fibrous network, confirming the potential applicability of the bilayered scaffolds in osteochondral defect regeneration.

Single-step electrochemical deposition of antimicrobial orthopaedic coatings based on a bioactive glass/chitosan/nano-silver composite system.

Composite orthopaedic coatings with antibacterial capability containing chitosan, Bioglass® particles (9.8µm) and silver nanoparticles (Ag-np) were fabricated using a single-step electrophoretic deposition (EPD) technique, and their structural and preliminary in vitro bactericidal and cellular properties were investigated. Stainless steel 316 was used as a standard metallic orthopaedic substrate. The coatings were compared with EPD coatings of chitosan and chitosan/Bioglass®. The ability of chitosan as both a complexing and stabilizing agent was utilized to form uniformly deposited Ag-np. Due to the presence of Bioglass® particles, the coatings were bioactive in terms of forming carbonated hydroxyapatite in simulated body fluid (SBF). Less than 7wt.% of the incorporated silver was released over the course of 28days in SBF and the possibility of manipulating the release rate by varying the deposition order of coating layers was shown. The low released concentration of Ag ions (<2.5ppm) was efficiently antibacterial against Staphyloccocus aureus up to 10days. Although chitosan and chitosan/Bioglass® coating supported proliferation of MG-63 osteoblast-like cells up to 7days of culture, chitosan/Bioglass®/Ag-np coatings containing 342 µg of Ag-np showed cytotoxic effects. This was attributed to the relatively high concentration of Ag-np incorporated in the coatings.

Titanium-containing bioactive phosphate glasses.

The use of biomaterials has revolutionized the biomedical field and has received substantial attention in the last two decades. Among the various types of biomaterials, phosphate glasses have generated great interest on account of their remarkable bioactivity and favourable physical properties for various biomedical applications relating to both hard and soft tissue regeneration. This review paper focuses mainly on the development of titanium-containing phosphate-based glasses and presents an overview of the structural and physical properties. The effect of titanium incorporation on the glassy network is to introduce favourable properties. The biocompatibility of these glasses is described along with recent developments in processing methodologies, and the potential of Ti-containing phosphate-based glasses as a bone substitute material is explored.

Effect of deposition parameters and post-deposition annealing on the morphology and cellular response of electrosprayed TiO2 films.

Titania films (TiO(2)) were deposited on Ti alloy substrates by electrohydrodynamic atomization (EHDA), also called electrospraying, and the morphology and phase composition of the coatings were evaluated. A range of TiO(2) sols (2-8 wt%) were prepared via the hydrolysis of polymeric precursors using isopropanol (prOH) as a solvent carrier. Stable cone-jet formation during the EHDA process was greatly influenced by varying the liquid physical properties. Deposition parameters such as sol concentration, needle-to-substrate distance and spray time were found to affect film morphology. Dense and continuous films were obtained under optimized conditions whereby a 2 wt% TiO(2) sol was atomized at a flow rate of 5 µl min(-1) by a needle of 300 µm inner diameter, kept at a distance of 20 mm from the grounded substrate and operating at an applied voltage of 3.5-4.2 kV. The films were then crystallized by heating to 300-600 °C. Annealing increased the hydrophilicity of the films but did not significantly affect the surface roughness of the films. In vitro cellular response was determined by studying the interaction between MG63 cells and the films annealed at the various temperatures. MG63 cells were able to grow and proliferate on all the TiO(2) films, while the highest proliferation rate was found on the TiO(2) films annealed at 600 °C. Our results indicate that electrosprayed TiO(2) films possess great potential for biomedical applications.

In vitro antibacterial efficacy of tetracycline hydrochloride adsorbed onto Bio-Oss bone graft.

Local delivery of antibiotics may provide the advantage of reducing the potential side effects associated with their systemic administration. This study assessed, in vitro, the antimicrobial efficacy of tetracycline hydrochloride (TCH) adsorbed onto Bio-Oss bone grafts against a range of pathogenic bacteria. Various levels of TCH were adsorbed onto Bio-Oss granules by immersing in TCH aqueous solutions of different initial concentrations for 48 h at room temperature. TCH release was assessed in phosphate buffered saline at 37 degrees C, and its antimicrobial efficacy, up to 96 h, was tested against two Gram-negative bacteria associated with periodontal diseases: Aggregatibacter (formerly Actinobacillus) actinomycetemcomitans, and Porphyromonas gingivalis, and one Gram-positive bacterium associated with soft-tissue and bone infections: Staphylococcus aureus. The range of TCH concentrations studied was also assessed for cytotoxicity against osteoblast-like human osteosarcoma cell lines. The amount of TCH adsorbed and released from Bio-Oss was concentration dependent. All TCH adsorbed Bio-Oss resulted in a reduction of A. actinomycetemcomitans, P. gingivalis, and S. aureus and higher concentrations were generally more effective in reducing or eliminating bacterial growth. The proliferation of HOS cells was not substantially reduced except for the maximum concentration of TCH. In addition to its osteoconductive role, TCH adsorbed Bio-Oss could also be functional in negating systemically antibiotic prophylactic treatment in the prevention of implant or biomaterial related infections.

Chemical, modulus and cell attachment studies of reactive calcium phosphate filler-containing fast photo-curing, surface-degrading, polymeric bone adhesives.

The initial structure, setting and degradation processes of a poly(lactide-co-propylene glycol-co-lactide) dimethacrylate adhesive filled with 50, 60 or 70 wt.% reactive calcium phosphates (monocalcium phosphate monohydrate (MCPM)/beta-tricalcium phosphate (beta-TCP)) have been assessed using nuclear magnetic resonance, Fourier transform infrared spectroscopy, Raman, X-ray powder diffraction and gravimetric studies. Filler incorporation reduced the rapid light-activated monomer polymerization rates slightly, but not the final levels. Upon immersion in water for 24h, the set composite mass and volume increased due to water sorption. This promoted initial soluble MCPM loss from the composite surfaces, but also its reaction and monetite precipitation within the specimen bulk. After 48 h, composite gravimetric and chemical studies were consistent with surface erosion of polymer with reacted/remaining filler. The filled formulations exhibited more rapid early water sorption and subsequent surface erosion than the unfilled polymer. Calcium and phosphate release profiles and solution pH measurements confirmed early loss of surface MCPM with protons from polymer degradation products. At later times, the slower release of monetite/beta-TCP buffered composite storage solutions at approximately 5 instead of 3.2 for the unfilled polymer. Incorporation of filler increased both the early and later time material modulus. At intermediate times this effect was lost, presumably as a result of enhanced water sorption. The early modulus values obtained fell within the range reported for cancellous bone. Despite surface degradation, initial human mesenchymal cell attachment to both composites and polymer could be comparable with a non-degrading positive Thermanox control. These studies indicate that the filled formulations may be good candidates for bone repair. Release of calcium and phosphate ions provides components essential for such repair.

Bioglass-derived glass-ceramic scaffolds: study of cell proliferation and scaffold degradation in vitro.

Cell support function as well as cell proliferation on highly porous Bioglass(R)-derived glass-ceramic scaffolds (designed for bone tissue engineering) have been assessed in vitro using osteoblast-like cells (MG 63) cultured for up to 6 days. The biodegradation and mechanical stability of the scaffolds in the cell-culture medium have also been investigated. It was found that the scaffolds had excellent cell supporting ability, with cells effectively infiltrating into and surviving at the center of the scaffolds. A quantitative study using the AlamarBlue assay revealed that the proliferation of cells on the glass-ceramic materials was comparable to that on the noncrystallized Bioglass. While the crystalline phase in the glass-ceramic scaffolds transformed into a biodegradable amorphous calcium phosphate phase during cell culture, the mechanical strength of the scaffolds was maintained when compared with that of scaffolds incubated in simulated body fluid or immersed in cell-free culture medium. It is believed that the attached cells and collagen secreted by cells could fill the micropores and microcracks on the surface of the foam struts, thus contributing to the mechanical stability of the degrading scaffolds. In summary, the developed glass-ceramic scaffolds possess the most essential features of a scaffold for bone tissue engineering: they are capable to support and foster relevant cells, able to provide temporary mechanical function, and biodegradable.

Zinc-containing phosphate-based glasses for tissue engineering.

It has been shown that the addition of zinc to hydroxyapatite promotes osteoblast cell adhesion (Ishaug et al 1994 J. Biomed. Mater. Res. A 28 1445-53). Therefore, this study presents a series of phosphate-based glass compositions that contain varying amounts of zinc in order to promote osteoblast cell adhesion. The compositions investigated were P(50)Ca((40-x))Na(10) where x = 0, 1, 2, 3, 4 and 5 mol%. The dissolution rate and effect on pH of glass discs were investigated and ion release from the glass discs was examined in distilled water at 37 degrees C after 1, 2, 3, 4 and 7 days. The attachment of osteoblast-like cells (HOB) was observed by SEM on the glass discs. A linear decrease in the %mass of the glass discs was observed for all compositions for the duration of the study. The dissolution rates were similar for all the compositions. After 7 days, a mass loss of 3-6% was observed for all the compositions. The pH of distilled water decreased to a range of pH 4.5-5.5 from pH 7 after 1 day, and remained in this range for the duration of the study. The composition containing 0 mol% Zn reduced the pH to a lesser extent than the composition containing the highest amount of Zn. Furthermore, Zn(2+) ion release was observed from all the Zn-containing compositions. These glass compositions may therefore be suitable for tissue engineering applications.

Development of soluble glasses for biomedical use Part II: the biological response of human osteoblast cell lines to phosphate-based soluble glasses.

Soluble glasses are considered to be of potential clinical value in orthopaedic and dental surgery. However, the biological response to these materials is not well understood. To determine the effects of these glasses, two human osteoblast cell lines, MG63 and HOS (TE85), were incubated in vitro in the presence of increasing concentrations of extracts of the glasses. The effects of the extracts on cell growth was measured using the MTT assay and an ELISA assay was used to measure the expression of bone sialoprotein (BSP), osteonectin (ON) and fibronectin (FN), antigens which play a fundamental part in the integrity and function of hard connective tissue. The results showed that the proliferation of the cells was adversely affected only by the more soluble glasses, which also down-regulated the expression of the bone-associated proteins. In contrast, the extract of the glass with the lowest dissolution rate, which contains relatively elevated levels of Ca2+, was found to enhance bone cell growth and antigen expression. These findings suggest that the compositions of these glasses at least partly determine the response of cells and thus, that the glasses could be modified to elicit a more optimal biological response and clinical efficacy.

Retroviral transduction of alveolar bone cells with a temperature-sensitive SV40 large T antigen.

We have transduced adult human alveolar bone (AB) cells with a gene construct encoding a temperature-sensitive mutation of the SV40 large T antigen (tsT). Such cells divided rapidly, for more than 50 passages thus far, at a permissive low temperature (34.5 degrees C), comparable to the non-transduced parental cells at 37 degrees C. However, the tsT-transduced AB cells failed to grow at a non-permissive high temperature (39 degrees C) at which the T antigen is inactivated. Nevertheless, the cells formed mineralised nodules in vitro at both the low and high temperatures. Flow cytometry analysis showed that the transduced cells cultured at 34.5 degrees C, like the parental cells at 37 degrees C, were smaller and less granular than the transduced cells incubated at 39 degrees C. Moreover, the transduced cells grown at 34.5 degrees C were also found to express bone sialoprotein, osteopontin and type I collagen at levels similar to those of the parental cells at 37 degrees C, although osteonectin and fibronectin were down-regulated. When the transduced cells were incubated at 39 degrees C, the expression of all antigens was up-regulated, particularly osteonectin. Thus, we have obtained long-term cultures of tsT-transduced AB cells whose growth is temperature-dependent and which express certain features characteristic of bone-derived cells.

Gene expression profiling of bone cells on smooth and rough titanium surfaces.

Titanium (Ti) and Ti alloys are widely used as dental and orthopaedic implants, but the effects of the surface characteristics of these materials on the response of cells and target tissues is not well understood. The present study has therefore examined the effects of a rough Ti (RT) and a smooth Ti (ST) surface on human bone cells in vitro. Scanning electron microscopy showed attachment and spreading of cells on both surfaces. Expression profiling using ATLAS gene arrays showed marked differences in gene responses after 3 h of culture. A number of osteoblast genes were identified as "roughness response" genes on the basis of changes in expression on the RT compared with the ST surfaces. The surface roughness of Ti was thus found to have a profound effect on the profile of genes expressed by the bone cells, and suggests that improvements in the biological activity and possibly the clinical efficacy of these materials could be achieved by selective regulation of gene expression mediated by controlled modification of Ti surface.

Pathological sequelae of implantation of intracorporeal left ventricular assist devices in the calf.

Thromboembolic complications have previously been a major pathological complication of left ventricular assist device (LVAD) insertion and appear to be a consequence of the use of smooth polyurethane linings. Textured biomaterial surfaces are designed to attract a stable coagulum which becomes organized to form a neointima. We describe the pathological changes following experimental implantation of textured-surface LVADs in calves. The incidence of systemic embolization from such linings appears to be low. Surface modifications with cell seeding offer the possibility of further reduction in incidence of this problem. However, degradation of prosthetic valves may be a potential source of emboli and infection. With these complications minimized, the most significant pathological changes observed appear to relate to the device haemodynamics. At present renovascular changes associated with systemic hypertension appear to be the greatest potential problem for the long-term use of these devices.

The lining of textured surfaces in implantable left ventricular assist devices. An immunocytochemical and electronmicroscopic study.

OBJECTIVE: The aim was to examine and identify some components of biological linings developed upon the textured surfaces of a circulatory assist device. The development of biological linings upon a textured surface circulatory assist device was evaluated in patients implanted for periods ranging from 84 to 132 days. METHODS: Explanted devices were examined macroscopically. Light microscopy, transmission electron microscopy and immunocytochemistry techniques were employed to evaluate the histogenesis of the tissue deposits upon the device surfaces. Visible material was essentially limited to focal areas upon the static housing and the periphery of the pusher-plate diaphragm (Biomer). RESULTS: Microscopy of the linings showed fibrin-rich areas with platelets, monocytes and few spindle-shaped surface cells. Central areas were composed of multiple layers of spindle-shaped cells separated, mainly, by collagen. Giant-cell foreign-body reaction to Biomer fibrils was seen. CONCLUSION: Transmission electron microscopy and immunocytochemistry indicated the presence of at least two cell populations: fibroblasts and smooth muscle-like cells, or 'myofibroblasts'. There was no evidence of endothelial cell presence.