Characterization of the Protein Corona of Three Chairside Hemoderivatives on Melt Electrowritten Polycaprolactone Scaffolds

In tissue engineering, the relationship between a biomaterial surface and the host's immune response during wound healing is crucial for tissue regeneration. Despite hemoderivative functionalization of biomaterials becoming a common tissue-engineering strategy for enhanced regeneration, the characteristics of the protein-biomaterial interface have not been fully elucidated. This study characterized the interface formed by the adsorbed proteins from various hemoderivatives with pristine and calcium phosphate (CaP)-coated polycaprolactone (PCL) melt electrowritten scaffolds. PCL scaffolds were fabricated by using melt electrospinning writing (MEW). Three hemoderivatives (pure platelet-rich plasma (P-PRP), leucocyte platelet-rich plasma (L-PRP) and injectable platelet-rich fibrin (i-PRF)) and total blood PLASMA (control) were prepared from ovine blood. Hemoderivatives were characterized via SEM/EDX, cross-linking assay, weight loss, pH and protein quantification. The interface between PCL/CaP and hemoderivative was examined via FTIR, XPS and electrophoresis. i-PRF/PCL-CaP (1653 cm^-1), PLASMA/PCL-CaP (1652 cm^-1) and i-PRF/PCL (1651 cm^-1) demonstrated a strong signal at the Amide I region. PLASMA and i-PRF presented similar N1s spectra, with most of the nitrogen involved in N-C=O bonds (≈400 eV). i-PRF resulted in higher adsorption of low molecular weight (LMW) proteins at 60 min, while PLASMA exhibited the lowest adsorption. L-PRP and P-PRP had a similar pattern of protein adsorption. The characteristics of biomaterial interfaces can be customized, thus creating a specific hemoderivative-defined layer on the PCL surface. i-PRF demonstrated a predominant adsorption of LMW proteins. Further investigation of hemoderivative functionalized biomaterials is required to identify the differential protein corona composition, and the resultant immune response and regenerative capacity.

Oral health research funding in relation to disease burden in Australia

BACKGROUND

This study aims to investigate and compare the major Australian government research funding schemes for oral health science with other disciplines from the burden of disease perspective.

METHODS

Major government research funding scheme outcomes were identified. An innovative index of Fair Research Funding (FRF) was developed to examine the extent to which National Health and Medical Research Council funding is aligned with the disease burden. In addition to comparing different diseases, overall governmental research funding for different areas of oral health sciences was explored.

RESULTS

Oral disorders with $15 million NHMRC grant funds (2017-2021) and FRF of 10.7 has the lowest and most inequitable amount of Australian government support in relation to disease burden. The share of oral health science in the Australian Research Council and Medical Research Future Fund was very minimal, with $3.43 and $1.88 million respectively.

CONCLUSION

Governmental research funding for oral health sciences is inequitable according to the disease burden. More dedicated oral health sciences research funding schemes are essential. Funding for prevention-focused public oral health programmes is a vital requirement towards reducing the inequalities in population oral health.

Inner southern magnetosphere observation of Mercury via SERENA ion sensors in BepiColombo mission

Mercury's southern inner magnetosphere is an unexplored region as it was not observed by earlier space missions. In October 2021, BepiColombo mission has passed through this region during its first Mercury flyby. Here, we describe the observations of SERENA ion sensors nearby and inside Mercury's magnetosphere. An intermittent high-energy signal, possibly due to an interplanetary magnetic flux rope, has been observed downstream Mercury, together with low energy solar wind. Low energy ions, possibly due to satellite outgassing, were detected outside the magnetosphere. The dayside magnetopause and bow-shock crossing were much closer to the planet than expected, signature of a highly eroded magnetosphere. Different ion populations have been observed inside the magnetosphere, like low latitude boundary layer at magnetopause inbound and partial ring current at dawn close to the planet. These observations are important for understanding the weak magnetosphere behavior so close to the Sun, revealing details never reached before.

SERENA: Particle Instrument Suite for Determining the Sun-Mercury Interaction from BepiColombo

The ESA-JAXA BepiColombo mission to Mercury will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric particle dynamics at Mercury as well as their interactions with solar wind, solar radiation, and interplanetary dust. The particle instrument suite SERENA (Search for Exospheric Refilling and Emitted Natural Abundances) is flying in space on-board the BepiColombo Mercury Planetary Orbiter (MPO) and is the only instrument for ion and neutral particle detection aboard the MPO. It comprises four independent sensors: ELENA for neutral particle flow detection, Strofio for neutral gas detection, PICAM for planetary ions observations, and MIPA, mostly for solar wind ion measurements. SERENA is managed by a System Control Unit located inside the ELENA box. In the present paper the scientific goals of this suite are described, and then the four units are detailed, as well as their major features and calibration results. Finally, the SERENA operational activities are shown during the orbital path around Mercury, with also some reference to the activities planned during the long cruise phase.

Resorbable additively manufactured scaffold imparts dimensional stability to extraskeletally regenerated bone

Dimensionally stable vertical bone regeneration outside of the existing bony envelope is a major challenge in the field of orofacial surgery. In this study, we demonstrate that a highly porous, resorbable scaffold fabricated using additive manufacturing techniques enables reproducible extra-skeletal bone formation and prevents bone resorption. An additively manufactured medical grade polycaprolactone (mPCL) biphasic scaffold mimicking the architecture of the jaw bone, consisting of a 3D-printed outer shell overlying an inner highly porous melt electrowritten scaffold, was assessed for its ability to support dimensionally stable bone regeneration in an extraskeletal ovine calvarial model. To investigate bone formation capacity (stage 1), 7 different constructs placed under a protective dome were assessed 8 weeks post-implantation: Empty control, Biphasic scaffold with hydrogel (PCL-Gel), PCL-Gel with 75 or 150 μg of BMP-2 (PCL-BMP-75 and PCL-BMP-150), hydrogel only (Gel), Gel containing 75 or 150 μg of BMP-2 (Gel-BMP-75 and Gel-BMP-150). To assess dimensional stability (stage 2), in a separate cohort, 5 animals were similarly implanted with 2 samples of each of the Gel-BMP-150 and PCL-BMP-150 groups, and after 8 weeks of healing, the protective domes were removed and titanium implants were placed in the regenerated bone and allowed to heal for a further 8 weeks. Bone formation and osseointegration were assessed using micro-computed tomography, histology and histomorphometry. In stage 1, enhanced bone formation was found in the BMP-2 containing groups, especially the PCL-BMP constructs whereby regeneration of full bone height was achieved in a reproducible manner. There was no significant bone volume increase with the higher dose of BMP-2. In the dimensional stability assessment (stage 2), after the rtemoval of the protective dome, the biphasic scaffold prevented bone resorption whereas in the absence of the scaffold, the bone previously formed in the hydrogel underwent extensive resorption. This was attributed to the space maintenance properties and dimensional stability of the biphasic scaffold. Titanium implants osseointegrated into the newly formed bone within the biphasic scaffolds. In conclusion, additively manufactured biphasic scaffolds functionalized with BMP-2 facilitated dimensionally stable bone regeneration that supported dental implant osseointegration.

Developing a prototype for integrated dental and diabetes care: understanding needs and priorities

BACKGROUND

Periodontal treatment may be a useful adjunct to medical management of diabetes; however, oral health has not been integrated into multidisciplinary diabetes care in Australia. This study aimed to understand the needs of patients and staff at a diabetes clinic to inform a prototype of integrated dental and diabetes care.

METHODS

Quantitative and qualitative data were collected from patients and staff at West Moreton Diabetes Clinic (WMDC) between September-October 2019. Clinical information, survey responses and dental screening results were analysed for 41 patients. Semi-structured interviews were held with six patients and a focus group with seven staff.

RESULTS

Most patients (83%) had not seen a dentist in the previous year. Of the 37 patients with remaining natural teeth, 84% required periodontal assessment and 46% had multiple carious lesions. Unmet treatment needs and rates of access were similar for private and public dental patients. Staff and patients reported high levels of support for incorporation of dental care at WMDC.

CONCLUSIONS

Integrating oral health into diabetes management is well-supported by patients and staff to address significant unmet dental needs for both public and private dental patients. Incorporating dental screening/services within diabetes clinics may increase uptake and improve awareness of its importance in diabetes management.

An overview of decellularisation techniques of native tissues and tissue engineered products for bone, ligament and tendon regeneration

Decellularised tissues and organs have been successfully used in a variety of tissue engineering/regenerative medicine applications. Because of the complexity of each tissue (size, porosity, extracellular matrix (ECM) composition etc.), there is no standardised protocol and the decellularisation methods vary widely, thus leading to heterogeneous outcomes. Physical, chemical, and enzymatic methods have been developed and optimised for each specific application and this review describes the most common strategies utilised to achieve decellularisation of soft and hard tissues. While removal of the DNA is the primary goal of decellularisation, it is generally achieved at the expense of ECM preservation due to the harsh chemical or enzymatic processing conditions. As denaturation of the native ECM has been associated with undesired host responses, decellularisation conditions aimed at effectively achieving simultaneous DNA removal and minimal ECM damage will be highlighted. Additionally, the utilisation of decellularised matrices in regenerative medicine is explored, as are the most recent strategies implemented to circumvent challenges in this field. In summary, this review focusses on the latest advancements and future perspectives in the utilisation of natural ECM for the decoration of synthetic porous scaffolds.

Periodontal Tissue Engineering with a Multiphasic Construct and Cell Sheets

This study reports on scaffold-based periodontal tissue engineering in a large preclinical animal model. A biphasic scaffold consisting of bone and periodontal ligament compartments manufactured by melt and solution electrospinning, respectively, was used for the delivery of in vitro matured cell sheets from 3 sources: gingival cells (GCs), bone marrow-derived mesenchymal stromal cells (Bm-MSCs), and periodontal ligament cells (PDLCs). The construct featured a 3-dimensional fibrous bone compartment with macroscopic pore size, while the periodontal compartment consisted of a flexible porous membrane for cell sheet delivery. The regenerative performance of the constructs was radiographically and histologically assessed in surgically created periodontal defects in sheep following 5 and 10 wk of healing. Histologic observation demonstrated that the constructs maintained their shape and volume throughout the entirety of the in vivo study and were well integrated with the surrounding tissue. There was also excellent tissue integration between the bone and periodontal ligament compartments as well as the tooth root interface, enabling the attachment of periodontal ligament fibers into newly formed cementum and bone. Bone coverage along the root surface increased between weeks 5 and 10 in the Bm-MSC and PDLC groups. At week 10, the micro-computed tomography results showed that the PDLC group had greater bone fill as compared with the empty scaffold, while the GC group had less bone than the 3 other groups (control, Bm-MSC, and PDLC). Periodontal regeneration, as measured by histologically verified new bone and cementum formation with obliquely inserted periodontal ligament fibers, increased between 5 and 10 wk for the empty, Bm-MSC, and PDLC groups, while the GC group was inferior to the Bm-MSC and PDLC groups at 10 wk. This study demonstrates that periodontal regeneration can be achieved via the utilization of a multiphasic construct, with Bm-MSCs and PDLCs obtaining superior results as compared with GC-derived cell sheets.

Osteonecrosis of the jaws: a 14-year retrospective survey of hospital admissions

BACKGROUND

Osteonecrosis of the jaw (ONJ) is a serious complication of both radiation and antiresorptive therapies. This study aimed to determine how many patients have been treated for medication-related osteonecrosis of the jaws (MRONJ) and osteoradionecrosis (ORN), and whether the number of diagnoses has decreased over time with improved awareness and preventative measures.

METHODS

Medical records at the Royal Brisbane and Women's Hospital, Gold Coast University Hospital and Robina Hospital were reviewed to identify patients diagnosed with MRONJ and ORN between January 2003 and May 2017. Data on patient demographics, year of admission and primary disease were analysed.

RESULTS

Two hundred and thirty-eight patients were diagnosed with ONJ, of which 74.4% were ORN and 25.6% were MRONJ. Tongue (24.6%), floor of mouth (17.3%) and tonsillar (15.1%) squamous cell carcinomas were the most common primary diseases associated with ORN, with a strong male predominance (80%). Of patients diagnosed with MRONJ, 52.5% were taking low-dose antiresorptives for osteoporosis (44.2%), rheumatoid arthritis (4.6%) or Paget's disease (3.3%), while 47.5% were oncology patients receiving high-dose antiresorptives.

CONCLUSIONS

The number of patients diagnosed with MRONJ and ORN has trended upwards since 2003. ORN affected three times more patients than MRONJ, and patients on low-dose antiresorptives accounted for over half of the MRONJ cases.

Induced Pluripotent Stem Cells: A New Frontier for Stem Cells in Dentistry

Induced pluripotent stem cells (iPSCs) are the newest member of a growing list of stem cell populations that hold great potential for use in cell-based treatment approaches in the dental field. This review summarizes the dental tissues that have successfully been utilized to generate iPSC lines, as well as the potential uses of iPSCs for tissue regeneration in different dental applications. While iPSCs display great promise in a number of dental applications, there are safety concerns with these cells that need to be addressed before they can be used in clinical settings. This review outlines some of the apprehensions to the use of iPSCs clinically, and it details approaches that are being employed to ensure the safety and efficacy of these cells. One of the major approaches being investigated is the differentiation of iPSCs prior to use in patients. iPSCs have successfully been differentiated into a wide range of cells and tissue types. This review focuses on 2 differentiation approaches-the differentiation of iPSCs into mesenchymal stem cells and the differentiation of iPSCs into osteoprogenitor cells. Both these resulting populations of cells are particularly relevant to the dental field.

Three-Dimensional Bioprinting for Regenerative Dentistry and Craniofacial Tissue Engineering

Craniofacial tissues are organized with complex 3-dimensional (3D) architectures. Mimicking such 3D complexity and the multicellular interactions naturally occurring in craniofacial structures represents one of the greatest challenges in regenerative dentistry. Three-dimensional bioprinting of tissues and biological structures has been proposed as a promising alternative to address some of these key challenges. It enables precise manufacture of various biomaterials with complex 3D architectures, while being compatible with multiple cell sources and being customizable to patient-specific needs. This review describes different 3D bioprinting methods and summarizes how different classes of biomaterials (polymer hydrogels, ceramics, composites, and cell aggregates) may be used for 3D biomanufacturing of scaffolds, as well as craniofacial tissue analogs. While the fabrication of scaffolds upon which cells attach, migrate, and proliferate is already in use, printing of all the components that form a tissue (living cells and matrix materials together) to produce tissue constructs is still in its early stages. In summary, this review seeks to highlight some of the key advantages of 3D bioprinting technology for the regeneration of craniofacial structures. Additionally, it stimulates progress on the development of strategies that will promote the translation of craniofacial tissue engineering from the laboratory bench to the chair side.

Tissue engineered periodontal products

Attainment of periodontal regeneration is a significant clinical goal in the management of advanced periodontal defects arising from periodontitis. Over the past 30 years numerous techniques and materials have been introduced and evaluated clinically and have included guided tissue regeneration, bone grafting materials, growth and other biological factors and gene therapy. With the exception of gene therapy, all have undergone evaluation in humans. All of the products have shown efficacy in promoting periodontal regeneration in animal models but the results in humans remain variable and equivocal concerning attaining complete biological regeneration of damaged periodontal structures. In the early 2000s, the concept of tissue engineering was proposed as a new paradigm for periodontal regeneration based on molecular and cell biology. At this time, tissue engineering was a new and emerging field. Now, 14 years later we revisit the concept of tissue engineering for the periodontium and assess how far we have come, where we are currently situated and what needs to be done in the future to make this concept a reality. In this review, we cover some of the precursor products, which led to our current position in periodontal tissue engineering. The basic concepts of tissue engineering with special emphasis on periodontal tissue engineering products is discussed including the use of mesenchymal stem cells in bioscaffolds and the emerging field of cell sheet technology. Finally, we look into the future to consider what CAD/CAM technology and nanotechnology will have to offer.

Decellularized periodontal ligament cell sheets with recellularization potential

The periodontal ligament is the key tissue facilitating periodontal regeneration. This study aimed to fabricate decellularized human periodontal ligament cell sheets for subsequent periodontal tissue engineering applications. The decellularization protocol involved the transfer of intact human periodontal ligament cell sheets onto melt electrospun polycaprolactone membranes and subsequent bi-directional perfusion with NH4OH/Triton X-100 and DNase solutions. The protocol was shown to remove 92% of DNA content. The structural integrity of the decellularized cell sheets was confirmed by a collagen quantification assay, immunostaining of human collagen type I and fibronectin, and scanning electron microscopy. ELISA was used to demonstrate the presence of residual basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), and hepatocyte growth factor (HGF) in the decellularized cell sheet constructs. The decellularized cell sheets were shown to have the ability to support recellularization by allogenic human periodontal ligament cells. This study describes the fabrication of decellularized periodontal ligament cell sheets that retain an intact extracellular matrix and resident growth factors and can support repopulation by allogenic cells. The decellularized hPDL cell sheet concept has the potential to be utilized in future "off-the-shelf" periodontal tissue engineering strategies.

Multiphasic scaffolds for periodontal tissue engineering

For a successful clinical outcome, periodontal regeneration requires the coordinated response of multiple soft and hard tissues (periodontal ligament, gingiva, cementum, and bone) during the wound-healing process. Tissue-engineered constructs for regeneration of the periodontium must be of a complex 3-dimensional shape and adequate size and demonstrate biomechanical stability over time. A critical requirement is the ability to promote the formation of functional periodontal attachment between regenerated alveolar bone, and newly formed cementum on the root surface. This review outlines the current advances in multiphasic scaffold fabrication and how these scaffolds can be combined with cell- and growth factor-based approaches to form tissue-engineered constructs capable of recapitulating the complex temporal and spatial wound-healing events that will lead to predictable periodontal regeneration. This can be achieved through a variety of approaches, with promising strategies characterized by the use of scaffolds that can deliver and stabilize cells capable of cementogenesis onto the root surface, provide biomechanical cues that encourage perpendicular alignment of periodontal fibers to the root surface, and provide osteogenic cues and appropriate space to facilitate bone regeneration. Progress on the development of multiphasic constructs for periodontal tissue engineering is in the early stages of development, and these constructs need to be tested in large animal models and, ultimately, human clinical trials.

Animal models for bisphosphonate-related osteonecrosis of the jaws--an appraisal

The prolonged use of bisphosphonates has been shown to cause a condition termed 'bisphosphonate related osteonecrosis of the jaws' (BRONJ). BRONJ is a disease entity which has only been described relatively recently, and its multi-factorial aetiology is yet to be fully elucidated. Therefore, the treatment of BRONJ lesions remains a challenge, and animal models are necessary to assist researchers in better understanding the disease. This has led to the recent publication of a number of studies utilising a variety of animal models of BRONJ. This review outlines the factors to be considered when selecting an animal model for BRONJ and discusses the current literature in this rapidly progressing field of research. It is important to consider the applicability of a given model to the clinical condition presenting in humans, and to this end, thorough characterisation of the clinical, histological, radiographic and systemic features is necessary. The development of a clinical lesion is an important consideration in terms of choosing a relevant model, and it appears clear that surgical manipulation, generally involving tooth extraction, is necessary for successful induction of the classic 'clinical' lesion of BRONJ.

Periodontal regeneration

The ultimate goal of periodontal therapy is the regeneration of the tissues destroyed as a result of periodontal disease. Currently, two clinical techniques, based on the principles of "guided tissue regeneration" (GTR) or utilization of the biologically active agent "enamel matrix derivative" (EMD), can be used for the regeneration of intrabony and Class II mandibular furcation periodontal defects. In cases where additional support and space-making requirements are necessary, both of these procedures can be combined with a bone replacement graft. There is no evidence that the combined use of GTR and EMD results in superior clinical results compared to the use of each material in isolation. Great variability in clinical outcomes has been reported in relation to the use of both EMD and GTR, and these procedures can be generally considered to be unpredictable. Careful case selection and treatment planning, including consideration of patient, tooth, site and surgical factors, is required in order to optimize the outcomes of treatment. There are limited data available for the clinical effectiveness of other biologically active molecules, such as growth factors and platelet concentrates, and although promising results have been reported, further clinical trials are required in order to confirm their effectiveness. Current active areas of research are centred on tissue engineering and gene therapy strategies which may result in more predictable regenerative outcomes in the future.

The effect of platelet-rich plasma on osteoblast and periodontal ligament cell migration, proliferation and differentiation

BACKGROUND AND OBJECTIVE

Platelet-rich plasma is used to deliver growth factors, in a safe and convenient manner, for enhancing bone and periodontal regeneration. However, conflicting reports regarding its effectiveness suggest that further study of the relevant cellular mechanisms is required. The aim of this study was to investigate the in vitro effect of platelet-rich plasma on osteoblasts and periodontal ligament cell function.

MATERIAL AND METHODS

Various concentrations of platelet-rich plasma (100, 50, 20 and 10%) and platelet-poor plasma, obtained from human donors, were applied to primary cultures of human osteoblasts and periodontal ligament cells. [(3)H]-Thymidine incorporation, crystal violet staining and MTT assays were utilized to assess DNA synthesis and proliferation. Migration was determined by assessing the cell response to a concentration gradient, while differentiation was assessed using Alazarin Red staining.

RESULTS

Platelet-rich plasma and platelet-poor plasma had stimulatory effects on the migration of both human osteoblasts and periodontal ligament cells. At 24 h, DNA synthesis was suppressed by the application of the various concentrations of platelet-rich plasma, but over a 5-d period, a beneficial effect on proliferation was observed, especially in response to 50% platelet-rich plasma. Platelet-poor plasma resulted in the greatest enhancement of cellular proliferation for both cell types. At a concentration of 50%, platelet-rich plasma and platelet-poor plasma facilitated differentiation of both cell types.

CONCLUSION

Platelet-rich plasma can exert a positive effect on osteoblast and periodontal ligament cell function, but this effect is concentration specific with maximal concentrations not necessarily resulting in optimal outcomes. Platelet-poor plasma also appears to have the ability to promote wound healing-associated cell function.

The role of cytokines in a Porphyromonas gingivalis-induced murine abscess model

INTRODUCTION

Porphyromonas gingivalis is an important periodontopathic bacterium that is strongly associated with periodontal disease and is part of human dental plaque. Periodontal disease results from the interaction of the host with bacterial products, and T-cell-derived cytokines remain critical in the immunoregulation of periodontal disease.

METHODS

The aim of this study was to examine the role of T helper type 1 [interleukin-12p40 (IL-12p40), interferon-gamma, tumour necrosis factor (TNF)] and type 2 (IL-4, IL-10) cytokines in the immune response to a subcutaneous challenge with P. gingivalis using a well-established murine abscess model, in genetically modified cytokine-specific knockout mice.

RESULTS

IL-12p40(-/-) mice exhibited more advanced tissue destruction and a reduced inflammatory cell infiltrate after subcutaneous P. gingivalis challenge. Deficiency of IL-4 or IL-10 did not result in increased susceptibility to P. gingivalis-mediated tissue destruction. Furthermore, TNF deficiency appeared to reduce local tissue destruction. Interestingly, serum-specific antibodies suggested a strong T helper type 2 response.

CONCLUSION

The results of our study indicate an important role for IL-12 in a primary P. gingivalis subcutaneous challenge.

Gene expression profiling of cells involved in periodontal regeneration

Understanding the molecular mechanisms involved in periodontal regeneration is important for the development of more predictable clinical techniques. This study aimed to identify these mechanisms by comparing the gene expression profiles of cells derived from regenerating defects with patient-matched periodontal ligament cells. Gene profiling was carried out via Affymetrix U133A arrays containing probes for 22,000 genes. Robust differences in gene expression were obtained by identifying genes that consistently changed by a minimum of 2-fold. Analysis of molecular function as designated by gene ontology (GO) identified differentially regulated mechanisms including protein metabolism, tyrosine kinase activity, and skeletal development. The differentially expressed genes could be broadly divided into the categories of protein biosynthesis and turnover, structural constituents of the cytoskeleton and extracellular matrix, and signal transduction. The differential expression of 4 genes (EGR-1, elastin, osteoprotegerin, and IGFBP3) was confirmed via real-time polymerase chain reaction (PCR). Further, the expression of another 2 differentially expressed transcripts, decorin and biglycan, was immunohistochemically confirmed in a periodontal wound healing model and the protein expression was consistent with the pattern of gene expression. This study gives insight into the molecular processes involved in periodontal regeneration and identifies cell markers that are characteristic of regenerating periodontal tissues.

Alveolar bone loss in T helper 1/T helper 2 cytokine-deficient mice

BACKGROUND AND OBJECTIVES

The role of cytokines in bone loss is important in the context of periodontitis, where inflammation-induced bone destruction is a major manifestation. Numerous cytokines have been implicated as mediators of bone resorption. The purpose of this study was to observe the impact of targeted gene deletion of T helper 1 (Th1) and T helper 2 (Th2) cytokines on naturally occurring alveolar bone loss in genetically modified mice.

MATERIAL AND METHODS

Alveolar bone loss was measured histomorphometrically in interleukin-4, interleukin-10, interleukin-12p40, interferon-gamma (IFN-gamma) and tumor necrosis factor (TNF) knockout mice at 6, 16 and 30 wk of age.

RESULTS

Both Th1 (interleukin-12p40, IFN-gamma, TNF) and Th2 (interleukin-10, interleukin-4) knockout mice exhibited significantly more alveolar bone loss than their respective wild-type control mice (p<0.001). Interleukin-10-/- and interleukin-12p40-/- mice exhibited a three-fold increase in alveolar bone loss at 30 wk of age, whereas bone loss in IFN-gamma-/-, TNF-/- and interleukin-4-/- mice was 1.5- to two-fold higher compared with wild-type control mice.

CONCLUSION

The results of the present study indicate that both Th1 and Th2 cytokines play an important role in maintaining alveolar bone homeostasis. The kinetics of alveolar bone loss seen in cytokine gene knockout mice indicates that bone loss is age dependent and late in onset.

Deficiency of iNOS contributes to Porphyromonas gingivalis-induced tissue damage

Periodontitis is a chronic inflammatory disease that results in extensive soft and hard tissue destruction of the periodontium. Porphyromonas gingivalis possesses an array of virulence factors and has been shown to induce expression of inducible nitric oxide synthase (iNOS) in inflammatory cells. The aim of this study was to investigate the effect of eliminating iNOS in a murine model of P. gingivalis infection. This was achieved by utilizing a P. gingivalis-induced skin abscess model, and an alveolar bone loss model employing an oral infection of P. gingivalis in iNOS knockout mice. The results indicated that iNOS knockout mice exhibit more extensive soft tissue damage and alveolar bone loss in response to P. gingivalis infection compared to wild-type mice. The local immune response to P. gingivalis in iNOS knockout mice was characterized by increased numbers of polymorphonuclear monocytes, while the systemic immune response was characterized by high levels of interleukin-12. The iNOS is required for an appropriate response to P. gingivalis infection.

Stem cells in the periodontal ligament

The ability to identify and manipulate stem cells has been a significant advancement in regenerative medicine and has contributed to the development of tissue engineering-based clinical therapies. Difficulties associated with achieving predictable periodontal regeneration, means that novel techniques such as tissue engineering need to be developed in order to regenerate the extensive soft and hard tissue destruction that results from periodontitis. One of the critical requirements for a tissue engineering approach is the delivery of ex vivo expanded progenitor populations or the mobilization of endogenous progenitor cells capable of proliferating and differentiating into the required tissues. By definition, stem cells fulfill these requirements and the recent identification of stem cells within the periodontal ligament represents a significant development in the progress toward predictable periodontal regeneration. In order to explore the importance of stem cells in periodontal wound healing and regeneration, this review will examine contemporary concepts in stem cell biology, the role of periodontal ligament progenitor cells in the regenerative process, recent developments in identifying periodontal stem cells and the clinical implications of these findings.

Growth hormone regulates osteogenic marker mRNA expression in human periodontal fibroblasts and alveolar bone-derived cells

BACKGROUND

Growth hormone (GH) is a potent regulator of bone formation. The proposed mechanism of GH action is through the stimulation of osteogenic precursor cell proliferation and, following clonal expansion of these cells, promotion of differentiation along the osteogenic lineage.

OBJECTIVES

We tested this hypothesis by studying the effects of GH on primary cell populations of human periodontal ligament cells (PLC) and alveolar bone cells (ABC), which contain a spectrum of osteogenic precursors.

METHODS

The cell populations were assessed for mineralization potential after long-term culture in media containing beta-glycerophosphate and ascorbic acid, by the demonstration of mineral deposition by Von Kossa staining. The proliferative response of the cells to GH was determined over a 48-h period using a crystal violet dye-binding assay. The profile of the cells in terms of osteogenic marker expression was established using quantitative reverse transcriptase polymerase chain reaction (RT-PCR) for alkaline phosphatase (ALP), osteopontin, osteocalcin, bone sialoprotein (BSP), as well as the bone morphogenetic proteins BMP-2, BMP-4 and BMP-7.

RESULTS

As expected, a variety of responses were observed ranging from no mineralization in the PLC populations to dense mineralized deposition observed in one GH-treated ABC population. Over a 48-h period GH was found to be non-mitogenic for all cell populations. Quantitative reverse transcriptase polymerase chain reaction (RT-PCR) BSP mRNA expression correlated well with mineralizing potential of the cells. The change in the mRNA expression of the osteogenic markers was determined following GH treatment of the cells over a 48-h period. GH caused an increase in ALP in most cell populations, and also in BMP expression in some cell populations. However a decrease in BSP, osteocalcin and osteopontin expression in the more highly differentiated cell populations was observed in response to GH.

CONCLUSION

The response of the cells indicates that while long-term treatment with GH may promote mineralization, short-term treatment does not promote proliferation of osteoblast precursors nor induce expression of late osteogenic markers.

Isolation and characterization of fibroblasts derived from regenerating human periodontal defects

In an attempt to understand better the cells responsible for periodontal regeneration, cells from human gingiva, periodontal ligament and regenerating periodontal defects treated with expanded polytetrafluorethylene membranes were isolated, cultured and characterized. Guided tissue regeneration procedures were carried out on three human volunteers around molar teeth destined for extraction. After a 6-week 'healing phase', fibroblast cell cultures were established from explants of the regenerating soft connective tissue (RTF), as well as from the associated periodontal ligament (PLF) and gingiva (GF). Following stimulation with platelet-derived growth factor-beta (PDGF) and insulin-like growth factor-1 (IGF-1), [3H]thymidine-uptake and dye-binding assays were used to assess the rate of DNA synthesis and cell proliferation, respectively. Northern blotting was used to measure the expression of mRNA for the extracellular matrix proteoglycans decorin, biglycan and versican. The results show that the GF and RTF proliferated more quickly than the PLF. PDGF and IGF-1 were mitogenic for all three cell types. Decorin mRNA expression was stronger in the GF than the RTF and PLF, whereas versican mRNA expression was stronger in the GF and PLF than the RTF. Biglycan mRNA expression was strong in the PLF, moderate in the GF and weak in the RTF. The growth factors did not affect the mRNA expression for biglycan, but they upregulated versican and downregulated decorin mRNA. It can be concluded that RTF exhibits properties characteristic of a reparative phenotype. More specifically, it proliferates faster than PLF, from which it is derived, while exhibiting a unique pattern of proteoglycan mRNA expression. Therefore, this study demonstrates that fibroblasts obtained from the regenerating periodontal defects exhibit characteristics consistent with their ability to facilitate periodontal regeneration.

Expression of bone matrix protein mRNAs by primary and cloned cultures of the regenerative phenotype of human periodontal fibroblasts

The successful regeneration of periodontal tissues is dependent, in part, on the ability of cells to reconstitute the mineralized tissues of cementum and bone. The aim of the present study was to characterize regeneration-associated cells in terms of their ability to express mineralized tissue macromolecules. Following guided tissue regeneration, cell cultures were established from regenerating tissue, periodontal ligament, and gingiva. Additionally, these cells were transfected, and single-cell-derived clones were established. Following treatment with platelet-derived growth factor-BB and insulin-derived growth factor-1, the presence of mRNA for alkaline phosphatase, osteocalcin, bone sialoprotein, osteopontin, and bone morphogenetic proteins-2 and -4 was assessed. The three cell types expressed similar mRNA levels for alkaline phosphatase, bone morphogenetic protein-2, and bone morphogenetic protein-4, whereas the expression of osteopontin, osteocalcin, and bone sialoprotein was greater in the periodontal ligament and regenerating tissue fibroblasts compared with the gingival fibroblasts. The two growth factors did not affect the expression of any of the genes. This study has identified markers that correlate with the known ability of periodontal ligament and regenerating tissue-derived fibroblasts to facilitate regeneration of the mineralized tissues of the periodontium.

Expression of bone associated macromolecules by gingival and periodontal ligament fibroblasts

The expression of hard tissue associated proteins may be used to identify periodontal fibroblasts with the capability to facilitate periodontal regeneration. The aim of this study was to describe, by immunohistochemistry, the distribution of osteocalcin, osteopontin, bone sialoprotein and bone morphogenic proteins-2 and -4 (BMP-2 and BMP-4) within the human periodontium. Furthermore, the expression of mRNA for the above proteins and alkaline phosphatase by gingival and periodontal ligament fibroblasts in vitro was also assessed by reverse transcriptase polymerase chain reaction (RT-PCR). Localization of osteopontin, osteocalcin, BMP-2 and BM P-4 within sections of human periodontal structures was stronger in the periodontal ligament compared to the gingiva. Bone sialoprotein was not detected in either of the soft tissues but, along with osteopontin and osteocalcin, it was localized in the cementum and bone. In vitro, both the gingival and periodontal ligament fibroblasts expressed mRNA for alkaline phosphatase, BMP-2, BMP-4 and osteopontin. Although there were no differences in the expression of alkaline phosphatase and BMP-4 mRNA between the two cell types, we noted significantly higher mRNA levels of osteopontin in the periodontal ligament and BM P-2 in the gingival fibroblasts. Osteocalcin and bone sialoprotein mRNA expression was only noted in the cultured periodontal ligament fibroblasts. From these results, it can be concluded that distinct differences exist between the two fibroblast populations in terms of the localization and mRNA expression of the majority of the hard tissue associated proteins. Furthermore, the elevated in vitro mRNA expression for osteocalcin, osteopontin and bone sialoprotein may be used to identify cells with the potential to facilitate hard tissue formation and hence periodontal regeneration.

An immunohistochemical study of matrix molecules associated with barrier membrane-mediated periodontal wound healing

Guided tissue regeneration (GTR) is a clinical procedure developed to facilitate periodontal regeneration by using barrier membranes to selectively promote the repopulation of a periodontal defect by periodontal ligament and bone cells at the expense of epithelial and gingival connective tissue cells. The aim of this study was to gain insight into the biological events occurring during membrane mediated periodontal wound healing by examining the immunohistochemical expression of a number of extracellular matrix components in tissues treated via the GTR technique. Experimental periodontal defects were created around the second premolar tooth in 4 dogs and wound closure was achieved by application of expanded polytetrafluoroethylene membranes around each tooth and flap positioning coronal to the cementoenamel junction. The dogs were sacrificed after a 4-wk healing period, block dissections of the part of the mandible containing the experimental tooth were obtained and paraffin sections were prepared. Using standard immunohistochemical techniques, the sections were stained with a monoclonal antibody against bone morphogenetic proteins 2 and 4 (BMP-2 and -4) and polyclonal antibodies against collagen I, collagen II, decorin, biglycan, bone sialoprotein, osteopontin and osteocalcin. Collagen I was predominantly localized within the regenerating bone, whereas collagen III staining was more abundant in the soft connective tissues of the defect. Decorin and biglycan staining was faint within the extracellular matrix of the regenerating defect, although both proteoglycans exhibited intense intracellular localization within some of the cells inhabiting the defect. The staining for BMP-2 and -4 was weak within the bone but strong within the extracellular matrix of the regenerating soft tissue. Osteopontin and bone sialoprotein were strongly localized in the regenerating bone and cementum found within the defect. Osteocalcin staining was present in both the regenerating and mature cementum and associated cementoblasts, and it was relatively weaker in the regenerating bone compared to the mature bone. The observed pattern of immunolocalization of the extracellular matrix macromolecules suggests that the heterogeneous cell population filling the GTR wound had created an environment that was conducive to periodontal regeneration.

Periodontal-derived cells attach to cementum attachment protein via alpha 5 beta 1 integrin

A specific collagenous cementum attachment protein (CAP) has been identified in human cementum which promotes selective cell migration towards and attachment of various periodontal derived cell populations to root surfaces in vitro. The CAP is known to support attachment of periodontal-derived cell via an RGD motif, which suggests an integrin-mediated mode of attachment. The purpose of the present study was to ascertain which integrin(s) are involved in the attachment of periodontal-derived cells to CAP. The integrins examined comprised subunits of the major receptors for fibronectin (alpha 5) and collagen (alpha 2, alpha 3), as well as the common beta 1 subunit which is present in many extracellular matrix receptors. The wells of 48-well non-tissue culture treated plates were coated with CAP (2 micrograms/ml). For negative and positive controls the wells were coated with bovine serum albumin and fibronectin (5 micrograms/ml), respectively. Human gingival fibroblasts and periodontal ligament fibroblasts were labeled with [3H]-proline, incubated with anti-integrin antibodies and added to the precoated wells. Attachment was assessed after incubating the cells for 1 h at 37 degrees C in the presence of the antibodies. Antibodies to alpha 5 and beta 1 inhibited the attachment of both human gingival fibroblasts and human periodontal ligament fibroblasts to CAP, while anti alpha 2 and alpha 3 antibodies did not affect the attachment. The binding of the fibroblasts to fibronectin was also inhibited by anti-alpha 5 and beta 1 antibodies, both of which are components of the "classical" fibronectin receptor and remained unaffected by the addition of anti-alpha 2 and alpha 3 antibodies. Proteins migrating in SDS-polyacrylamide gels in positions similar to the alpha 5 and beta 1 integrin subunits were present in fractions bound to a column of CAP coupled to Sepharose CL-4B. These results indicate that the attachment to CAP of the periodontal-derived cells, human gingival fibroblasts and human periodontal ligament fibroblasts, is mediated primarily via the integrin alpha 5 beta 1.

Disinfection of dental stone casts: antimicrobial effects and physical property alterations

OBJECTIVES

The purpose of this study was to evaluate the effectiveness of disinfecting solutions incorporated into dental stone casts against a standard and representative group of microorganisms and to note changes in the physical properties of the casts.

METHODS

Irreversible hydrocolloid impressions were contaminated individually with Escherichia coli, Staphylococcus aureus, Enterobacter cloacae, Pseudomonas aeruginosa, Klebsiella pneumoniae, Actinobacter calcoaceticus, Bacillus subtilis, Mycobacterium phlei and Candida albicans. Four readily available disinfecting solutions (glutaraldehyde, povidone-iodine, chlorhexidine and sodium hypochlorite) were added to the die stone mix used to pour up the impressions. The set cast surfaces were swabbed at 1 h and 24 h, the samples plated on agar and incubated at 37 degrees C for 24 h and 3 d for M. phlei. Subsequently, colony forming units were counted. The physical properties assessed were setting time, setting expansion, compressive strength, detail reproduction and delayed expansion of the stone.

RESULTS

Only glutaraldehyde and povidone-iodine killed all contaminating microorganisms within 1 h, while the 1:5 dilution of sodium hypochlorite solution was equally effective after 24 h. Two percent glutaraldehyde was the most effective disinfectant with the least adverse effects on the physical properties of the set cast. Although povidone-iodine caused a decrease in the compressive strength of the set cast, it can be considered to be a sound alternative.

SIGNIFICANCE

This study supports the concept of incorporating disinfectants into model stone as a standard operating procedure for impressions of unknown history and, most sensibly, all dental impressions.