Sara Ricci

Decellularization and Delipidation Protocols of Bovine Bone and Pericardium for Bone Grafting and Guided Bone Regeneration Procedures

The combination of bone grafting materials with guided bone regeneration (GBR) membranes seems to provide promising results to restore bone defects in dental clinical practice. In the first part of this work, a novel protocol for decellularization and delipidation of bovine bone, based on multiple steps of thermal shock, washes with detergent and dehydration with alcohol, is described. This protocol is more effective in removal of cellular materials, and shows superior biocompatibility compared to other three methods tested in this study. Furthermore, histological and morphological analyses confirm the maintenance of an intact bone extracellular matrix (ECM). In vitro and in vivo experiments evidence osteoinductive and osteoconductive properties of the produced scaffold, respectively. In the second part of this study, two methods of bovine pericardium decellularization are compared. The osmotic shock-based protocol gives better results in terms of removal of cell components, biocompatibility, maintenance of native ECM structure, and host tissue reaction, in respect to the freeze/thaw method. Overall, the results of this study demonstrate the characterization of a novel protocol for the decellularization of bovine bone to be used as bone graft, and the acquisition of a method to produce a pericardium membrane suitable for GBR applications.

Influence of immediate loading on healing of implants installed with different insertion torques – an experimental study in dogs

OBJECTIVE To evaluate the influence of different insertion torques on healing of implants loaded immediately or left unloaded. MATERIAL AND METHODS In six Labrador dogs, all mandibular premolars and molars were extracted. After 4 months of healing, flaps were elevated, and two implant sites were prepared at each side of the mandible. The distal sites were prepared conventionally while the mesial sites were underprepared by 0.3 mm. As a consequence, different final insertion torques of about 30 Ncm at the distal and >70 Ncm at the mesial sites were recorded. Healing abutments were applied to the left and transmucosal abutments to the right side. Flaps were sutured, crown preparation of the upper right second and third premolars was performed, and impressions were taken. Within 24 h, crowns were cemented both to implants and teeth in the right side of the mouth. After 4 months, the animals were sacrificed and ground sections obtained for histological evaluation. RESULTS A higher buccal bony crestal resorption and a more apical position of the coronal level of osseointegration were found at the loaded compared with the unloaded sites. MBIC% and percentages of peri-implant mineralized tissue (MB%) were higher at the loaded compared with the unloaded sites. Moreover, a higher MBIC% was found at the lower compared with the higher final insertion torque. CONCLUSIONS Immediate loading does not seem to have a negative effect on osseointegration. High torque values for the immediate loading procedures were not necessary. Probably, low torque values, were sufficient to obtain primary stability and hence may provide better osseointegration than high torque value.

Healing of implants installed in over- or under-prepared sites--an experimental study in dogs.

OBJECTIVE To study bone healing at implants installed with different insertion torques. MATERIAL AND METHODS In six Labrador dogs, all mandibular premolars and first molars were extracted. After 4 months of healing, flaps were elevated, and two implant sites were prepared at each side of the mandible. In the right side of the mandible, the distal sites were prepared conventionally, while the mesial sites were over-prepared by 0.2 mm. As a consequence, a final insertion torque of ~30 Ncm at the distal and a minimal insertion torque close to 0 Ncm at the mesial sites were obtained. In the left sides of the mandible, however, the recipient sites were underprepared by 0.3 mm resulting in an insertion torque of ≥ 70 Ncm at both implants. Cover screws were applied, and flaps sutured to fully submerge the experimental sites. After 4 months, the animals were sacrificed and ground sections obtained for histological evaluation. RESULTS The mineralized bone-to-implant contact was in the range of 55.2-62.1%, displaying the highest value at implants with ~30 Ncm insertion torque and the lowest value at the implant sites with close to 0 Ncm insertion torque. No statistically significant differences were revealed. Bone density was in the range of 43.4-54.9%, yielding the highest value at implants with ≥ 70 Ncm insertion torque and the lowest at the implant sites with close to 0 Ncm insertion torque. The difference between the sites of ~30 Ncm and the corresponding ≥ 70 Ncm insertion torque reached statistical significance. CONCLUSIONS Similar amounts of osseointegration were obtained irrespective of the insertion torque applied. Moreover, implants installed in sites with close to 0 Ncm insertion torque may properly osseointegrate as well.

Experimental and computational investigation of Morse taper conometric system reliability for the definition of fixed connections between dental implants and prostheses

Nowadays, dental implantology is a reliable technique for treatment of partially and completely edentulous patients. The achievement of stable dentition is ensured by implant-supported fixed dental prostheses. Morse taper conometric system may provide fixed retention between implants and dental prostheses. The aim of this study was to investigate retentive performance and mechanical strength of a Morse taper conometric system used as implant-supported fixed dental prostheses retention. Experimental and finite element investigations were performed. Experimental tests were achieved on a specific abutment–coping system, accounting for both cemented and non-cemented situations. The results from the experimental activities were processed to identify the mechanical behavior of the coping–abutment interface. Finally, the achieved information was applied to develop reliable finite element models of different abutment–coping systems. The analyses were developed accounting for different geometrical conformations of the abutment–coping system, such as different taper angle. The results showed that activation process, occurred through a suitable insertion force, could provide retentive performances equal to a cemented system without compromising the mechanical functionality of the system. These findings suggest that Morse taper conometrical system can provide a fixed connection between implants and dental prostheses if proper insertion force is applied. Activation process does not compromise the mechanical functionality of the system.

Neuronal Properties of Dental Stem Cells

The neurodegenerative disorders are characterized by loss of nerve structure or function. The prevalent disorders are Alzheimer’s disease, frontotemporal dementia, amyotrophic lateral sclerosis, Parkinson’s disease, Huntington’s disease, and multiple sclerosis. These neurodegenerative diseases are increasing worldwide, not only due to increased incidences of direct or indirect injury to the central nervous system (CNS) but also due to the increase in the percentage of the aging population [1]. Despite great progress in understanding the etiology of these disorders, the underlying mechanisms are still indistinct. Furthermore, no means of treating the underlying cause have been devised. For the past decade, researchers have been interested in stem cells and the prospect of using them for understanding the pathogenesis of disease and for facilitating the development of novel therapeutics [2]. In model organisms, both endogenous and exogenous neural stem cells (NSCs) have been investigated for their capacity to regenerate a damaged nervous system [3]. Due to the low incidence of human adult NSCs and problems with accessibility, the use of exogenous sources of stem cells with neural potential has been suggested as a plausible approach to stem cell therapy. Although embryonic stem cells (ESCs) and bone marrow stem cells (BMSCs) have been assessed as potential candidates for neuronal therapy, adult stem cell populations derived from cranial neural crest cells may possess a greater propensity for neuronal differentiation and repair [4]. Interestingly, the dental pulp tissue, termed “ectomesenchyme”, derives from ectodermal cells growing on the periphery of the neural tube during embryonic development, migrating into the oral region, and transdifferentiating into a mesenchymal phenotype [5]. Consequently, Dental Stem Cells (DSCs) have been proposed as a promising source of stem cells to treat nerve regeneration due to their close embryonic origin and easy accessibility. Indeed, DSCs can be obtained from extracted teeth and their surrounding tissue that are usually discarded during dental procedures without invasive methods and additional injury.

Dental Stem Cells (DSCs): Classification and Properties

Dental stem cells (DSCs) are a promising source of mesenchymal stem cells for use in cell therapy and regenerative medicine. To date, seven types of DSCs have been described in the literature: Dental Pulp Stem Cells (DPSCs), Stem cells from Human Exfoliated Deciduous teeth (SHED), Periodontal Ligament Stem Cells (PDLSCs), Dental Follicle Progenitor Cells (DFPCs), Stem Cells from Apical Papilla (SCAP), Gingival Mesenchymal Stem Cells (GMSCs), and human Natal Dental Pulp Stem Cells (NDP-SCs). All these easily-accessible stem cells can be derived from dental tissues obtained from young or adult patients.