Alessandra Trirè

Collagen Structure of Tendon Relates to Function

A tendon is a tough band of fibrous connective tissue that connects muscle to bone, designed to transmit forces and withstand tension during muscle contraction. Tendon may be surrounded by different structures: 1) fibrous sheaths or retinaculae; 2) reflection pulleys; 3) synovial sheaths; 4) peritendon sheaths; 5) tendon bursae. Tendons contain a) few cells, mostly represented by tenoblasts along with endothelial cells and some chondrocytes; b) proteoglycans (PGs), mainly decorin and hyaluronan, and c) collagen, mostly type I. Tendon is a good example of a high ordered extracellular matrix in which collagen molecules assemble into filamentous collagen fibrils (formed by microfibrils) which aggregate to form collagen fibers, the main structural components. It represents a multihierarchical structure as it contains collagen molecules arranged in fibrils then grouped in fibril bundles, fascicles and fiber bundles that are almost parallel to the long axis of the tendon, named as primary, secondary and tertiary bundles. Collagen fibrils in tendons show prevalently large diameter, a D-period of about 67 nm and appear built of collagen molecules lying at a slight angle (< 5). Under polarized light microscopy the collagen fiber bundles appear crimped with alternative dark and light transverse bands. In recent studies tendon crimps observed via SEM and TEM show that the single collagen fibrils suddenly changing their direction contain knots. These knots of collagen fibrils inside each tendon crimp have been termed “fibrillar crimps”, and even if they show different aspects they all may fulfil the same functional role. As integral component of musculoskeletal system, the tendon acts to transmit muscle forces to the skeletal system. There is no complete understanding of the mechanisms in transmitting/absorbing tensional forces within the tendon; however it seems likely that a flattening of tendon crimps may occur at a first stage of tendon stretching. Increasing stretching, other transmission mechanisms such as an interfibrillar coupling via PGs linkages and a molecular gliding within the fibrils structure may be involved.

Influence of a zirconia sandblasting treated surface on peri-implant bone healing: An experimental study in sheep.

A sandblasting process with round zirconia (ZrO(2)) particles might be an alternative surface treatment to enhance the osseointegration of titanium dental implants. Our previous study on sheep compared smooth surface titanium implants (control) with implant surfaces sandblasted with two different granulations of ZrO(2). As the sandblasted surfaces proved superior, the present study further compared the ZrO(2) surface implant with other surface treatments currently employed: machined titanium (control), titanium oxide plasma sprayed (TPS) and alumina sandblasted (Al-SL) at different times after insertion (2, 4 and 12weeks). Twelve sheep were divided into three groups of four animals each and underwent implant insertion in tibia cortical bone under general anaesthesia. The implants with surrounding tissues were subjected to histology, histomorphometry, scanning electron microscopy and microhardness tests. The experimentation indicated that at 2weeks Zr-SL implants had the highest significant bone ingrowth (p<0.05) compared to the other implant surfaces, and a microhardness of newly formed bone inside the threads significantly higher than that of Ti. The present work shows that the ZrO(2) treatment produces better results in peri-implant newly formed bone than Ti and TPS processing, whereas its performance is similar to the Al-SL surface treatment.

Osteogenesis and Morphology of the Peri-Implant Bone Facing Dental Implants

This study investigated the influence of different implant surfaces on peri-implant osteogenesis and implant face morphology of peri-implant tissues during the early (2 weeks) and complete healing period (3 months). Thirty endosseous titanium implants (conic screws) with differently treated surfaces (smooth titanium = SS, titanium plasma sprayed = TPS, sand-blasted zirconium oxide = Zr-SLA) were implanted in femur and tibiae diaphyses of two mongrel sheep. Histological sections of the implants and surrounding tissues obtained by sawing and grinding techniques were observed under light microscopy (LM). The peri-implant tissues of other samples were mechanically detached from the corresponding implants to be processed for SEM observation. Two weeks after implantation, we observed osteogenesis (new bone trabeculae) around all implant surfaces only where a gap was present at the host bone-metal interface. No evident bone deposition was detectable where threads of the screws were in direct contact with the compact host bone. Distance osteogenesis predominated in SS implants, while around rough surfaces (TPS and Zr-SLA), both distance and contact osteogenesis were present. At SEM analysis 2 weeks after implantation, the implant face of SS peri-implant tissue showed few, thin, newly formed, bone trabeculae immersed in large, loose, marrow tissue with blood vessels. Around the TPS screws, the implant face of the peri-implant tissue was rather irregular because of the rougher metal surface. Zr-SLA screws showed more numerous, newly formed bone trabeculae crossing marrow spaces and also needle-like crystals in bone nodules indicating an active mineralising process. After 3 months, all the screws appeared osseointegrated, being almost completely covered by a compact, mature, newly formed bone. However, some marrow spaces rich in blood vessels and undifferentiated cells were in contact with the metal surface. By SEM analysis, the implant face of the peri-implant tissue showed different results. Around the SS screws, the compact bone with areas of different mineralisation rate appeared very smooth, while around the rougher TPS screws, the bone still showed an irregular surface corresponding to the implant macro/microroughness. Around the Zr-SLA screws, a more regular implant-bone surface and sparse, calcified marrow spaces were detectable.Results from this research suggest that 2 weeks after implantation, trabecular bone represents the calcified healing tissue, which supports the early biological fixation of the implants. The peri-implant marrow spaces, rich in undifferentiated cells and blood vasculature, observed both 2 weeks and 3 months after surgery, favour the biological turnover of both early and mature peri-implant bone. The implant surface morphology strongly influences the rate and the modality of peri-implant osteogenesis, as do the morphology and arrangement of the implant face in peri-implant bone both during early healing (after 2 weeks) and when the implant is just osseointegrated; rough surfaces, and in particular Zr-SLA, seem to better favour bone deposition on the metal surface.

Dentin matrix protein 1 and dentin sialophosphoprotein in human sound and carious teeth: an immunohistochemical and colorimetric assay

Dentin matrix protein 1 (DMP1) and dentin sialophosphoprotein (DSPP) are extracellular matrix proteins produced by odontoblasts involved in the dentin mineralization. The aim this study was to compare the distribution of DMP1 and DSPP in human sound dentin vs human sclerotic dentin. Sixteen sound and sixteen carious human molars were selected, fixed in paraformaldehyde and processed for immunohistochemical detection of DMP1 and DSPP by means of light microscopy, transmission electron microscopy (TEM) and high-resolution field emission in-lens scanning electron microscopy (FEI-SEM). Specimens were submitted to a pre-embedding or a post-embedding immunolabeling technique using primary antibodies anti DMP1 and anti-DSPP and gold-conjugated secondary antibodies. Other samples were processed for the detection of DMP1 and DSPP levels. Dentin from these samples was mechanically fractured to powder, then a protein extraction and a protein level detection assay were performed. DMP1 and DSPP were more abundant in carious than in sound samples. Immunohistochemical analyses in sclerotic dentin disclosed a high expression of DMP1 and DSPP inside the tubules, suggesting an active biomineralization of dentin by odontoblasts. Furthermore, the detection of small amounts of these proteins inside the tubules far from the carious lesion, as shown in the present study, is consistent with the hypothesis of a preventive defense of all dentin after a noxious stimulus has undermined the tooth.

Correlative Microscopy of Bone in Implant Osteointegration Studies

Routine morphological analyses usually include investigations by light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Each of these techniques provides specific information on tissue morphology and all the obtained results are then combined to give an in-depth morphological overview of the examined sample. The limitations of this traditional comparative microscopy lie in the fact that each technique requires a different experimental sample, so that many specimens are necessary and the combined results come from different samples. The present study describes a technical procedure of correlative microscopy, which allows us to examine the same bone section first by LM and then, after appropriate processing, by SEM or TEM. Thanks to the possibility of analyzing the same undecalcified bone sections both by LM and SEM, the approach described in the present study allows us to make very accurate evaluations of old/new bone morphology at the bone-implant interface.

Ultrastructural and biochemical analysis of in vitro odontoblast differentiation

The purpose of this study was to develop an in vitro model of odontoblast differentiation and dentin formation which allows to deeply and better study the process of odontoblast differentiation and protein matrix deposition and mineralization. Human dental pulp cells were obtained from extracted molar teeth of donors under informed consent. Cells were induced to odontoblast differentiation for 7, 14, 21 and 28 days by adding in the cell medium dexamethasone, β-glicerophosphate, ascorbic acid and TGF-β1. Alizarin red staining, electron microscopy, western blotting were carried out to demonstrate the odontoblast differentiation process, extracellular matrix deposition and mineralization. Alizarin red staining results showed a gradual calcium deposition during the treatment, reaching the highest signal at 28 days of stimulation. Electron microscopy demonstrated the deposition of fibrillar structures in the extracellular matrix, connected with extracellular matrix proteins. Western blotting analysis showed the expression of collagen type I and dentin matrix protein 1, markers for the odontoblast phenotype. The in vitro odontoblast differentiation model described if an highly repetitive model and it represents a potential and promising tool to explore the extracellular matrix deposition and mineralization process in physiological and pathological conditions.

Evaluation of thread pitch as a design key factor in dental implant osseointegration

Long term success and predictability of endosseous dental implants in tooth replacement treatment have became a well documented outcome and are strictly related to initial mechanical stability as a crucial prerequisite in achieving osseointegration. Various factors (original bone density, implant surface topography, implant design) influence this stability and in the present research we investigated implant design because of its critical role, particularly in low density bone. The leading hypothesis is that selecting implant design features that maximize surface area available for contact may improve mechanical anchorage and primary stability in cancellous bone. We aimed to evaluate the role of implant thread pitch as a design key parameter on osseointegration process in poor bone density and limited availability of height by comparing two different implant profiles in an animal model. ”Narrow pitch” implants (NP) with a 0.5 mm pitch and “wide pitch” implant (WP) with a 1.5 mm pitch were tested for osseointegration after 0 days, 4 and 8 weeks in a sheep iliac crest model. Biological investigations (histology and histomorphometry) as well as biomechanical tests (insertion/ removal torque test) have been performed. The data showed that initial mechanical anchorage and subsequent early endosseous integration in low density bone can be improved with a reduction of thread pitch. The greater surface area gained by decreasing thread pitch shows to increase bone to implant contact and primary stability since the implant placement. This better performance of NP profile can be appreciated even at early healing time when the subsequent biological integration results enhanced. In conclusion, these results confirm that, when primary stability is a concern, as in cancellous bone, increasing the implant surface area by using implants with smaller pitch may be beneficial.

An investigation of 19th century pertrochanteric fracture and its probable relation to osteoporotic disorders

1 Department of Human Anatomical Sciences and Pathophysiology of Locomotor Apparatus, Human Anatomy Section, University of Bologna, Italy 2 Laboratory of Bioarchaeology and Forensic Osteology, Department of Experimental Evolutionary Biology, Alma Mater Studiorum University of Bologna, Italy 3 Division of Palaeopathology, History of Medicine and Bioethics, Department of Oncology, Transplants and Advanced Technologies in Medicine, University of Pisa, Italy 4 Department of Radiology, Rizzoli Orthopaedic Institute, Bologna, Italy 5 Department of Chemistry “G. Ciamician”, Alma Mater Studiorum University of Bologna, Italy