Zorica Ajduković

Chitosan-PLGA polymer blends as coatings for hydroxyapatite nanoparticles and their effect on antimicrobial properties, osteoconductivity and regeneration of osseous tissues.

Composite biomaterials comprising nanostructured hydroxyapatite (HAp) have an enormous potential for natural bone tissue reparation, filling and augmentation. Chitosan (Ch) as a naturally derived polymer has many physicochemical and biological properties that make it an attractive material for use in bone tissue engineering. On the other hand, poly-D,L-lactide-co-glycolide (PLGA) is a synthetic polymer with a long history of use in sustained drug delivery and tissue engineering. However, while chitosan can disrupt the cell membrane integrity and may induce blood thrombosis, PLGA releases acidic byproducts that may cause tissue inflammation and interfere with the healing process. One of the strategies to improve the biocompatibility of Ch and PLGA is to combine them with compounds that exhibit complementary properties. In this study we present the synthesis and characterization, as well as in vitro and in vivo analyses of a nanoparticulate form of HAp coated with two different polymeric systems: (a) Ch and (b) a Ch-PLGA polymer blend. Solvent/non-solvent precipitation and freeze-drying were used for synthesis and processing, respectively, whereas thermogravimetry coupled with mass spectrometry was used for phase identification purposes in the coating process. HAp/Ch composite particles exhibited the highest antimicrobial activity against all four microbial strains tested in this work, but after the reconstruction of the bone defect they also caused inflammatory reactions in the newly formed tissue where the defect had lain. Coating HAp with a polymeric blend composed of Ch and PLGA led to a decrease in the reactivity and antimicrobial activity of the composite particles, but also to an increase in the quality of the newly formed bone tissue in the reconstructed defect area.

Substitution of Osteoporotic Alveolar Bone by Biphasic Calcium Phosphate/Poly-DL- lactide-co-glycolide Biomaterials

Lost bone tissue due to osteoporosis makes dentistry very difficult. The aim of thisstudy is to reconstruct the bone tissue with composite biomaterials and to estimate the optical density and alveolar ridge height of the mandible. Research is conducted on 30 postmenopausal women aged from 46 to 62 years, with diagnosed osteoporosis and defects in alveolar bones caused by extraction of paradontopathic teeth, enucleation of cysts and periapical changes, extraction of impacted teeth,or by trauma.Biphasic calcium phosphate/poly-DL-lactide-co-glycolide (BCP/PLGA) composite is implanted into the defects of alveolar bones. Six weeks after implantation of BCP/PLGA, the alveolar bone density in the region of premolars on the experimental side of the jaw is found to be lower than that on the untreated, control, side of the jaw. On thecontrary, 24 weeks after implantation, it is significantly higher compared with the density of the control side. A significant increase in optical density of alveolar bones in the region of premolars on the experimental side compared with the control one is noticed. These results indicate a high level of osteoregeneration and osteoblast activity. Synthetic BCP/PLGA composite belongs to the group of biomaterials, which facilitate formation of new bones and rehabilitation of alveolar bones weakened by osteoporosis. Because of its osteoconductive characteristics, BCP/PLGA composite is supposed to be the material of choice for replacement of bone tissue in the future.

Repair of bone tissue affected by osteoporosis with hydroxyapatite-poly-L-lactide (HAp-PLLA) with and without blood plasma

The aim of this study is to examine the reparatory ability of the synthetic biomaterial hydroxyapatite-poly-L-lactide (HAp-PLLA), the replacement of alveolar ridge, and rehabilitation of bone defects caused by osteoporosis, in an experimental group of animals. The experiments are performed on syngeneic Sprague Dawley rats. Osteoporosis is induced by glucocorticoids in rats during a 12-week period. After this, the experimental group of animals is divided into five subgroups. An artificial defect is made in the alveolar bone on the left side of the mandible. In one group of animals, the defect is left to heal by itself, while in other groups, pure HAp-PLLA or one mixed with plasma is implanted. The best results are achieved by the implantation of the HAp-PLLA composite biomaterial mixed with autologous plasma. Formation of a new mandibular bone is seen, growing intensely, leading to rapid osteogenesis.

Biphasic Calcium Phosphate/Poly-(DL-Lactide-co-Glycolide) Biocomposite as Filler and Blocks for Reparation of Bone Tissue

Composite biomaterials, like calciumphosphate/bioresorbable polymer, offer excellent potential for reconstruction and reparation of bone tissue defects induced by different sources. In this paper synthesis of calciumphosphate/poly-DL-lactide-co-glycolide (BCP/DLPLG) composite biomaterial formed as filler and blocks was studied. BCP/DLPLG composite biomaterial was produced in the form of spherical granules of BCP covered by a DLPLG layer, average diameter of 150-250 µm. By cold and hot pressing of granules at up to 10000 kg/cm2, blocks with fine distribution of phases and porosity up to 3% were obtained. Characterization was performed by wide-angle X-ray structural analysis (WAXS), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), infrared spectroscopy (IR), and mechanical properties by defining the compressive strength. In vitro citotoxicity research was carried out on cellular cultures of fibroblasts of human (MRC5) and mouse (L929). In vivo research was performed in two steps. Reparatory ability of BCP/DLPLG in mice was examined in the first step, and then bone tissue reconstruction possibilities on 10 patients in the next step. In vitro tests showed very good fibroblast adhesion and non-citotoxicity of the composite. A material is considered non-cytotoxic if the cell survival is above 50 %, and in our case it was 90%. In vivo research on mice indicated high level of reparatory ability of this composite with formation of new bone and vascular tissue six weeks after reparation. Application of this composite for healing infrabone defects of patients showed a high level of osseous regeneration.

Size effect of calcium phosphate coated with poly-DL-lactide- co-glycolide on healing processes in bone reconstruction

In this article, synthesis and application of calcium phosphate/poly-DL-lactide-co-glycolide (CP/PLGA) composite biomaterial in particulate form, in which each CP granule/particle is coated with PLGA, are described. Two types of the particulate material having different particle sizes were synthesized: one with an average particle diameter between 150 and 250 mum (micron-sized particles, MPs) and the other with an average particle diameter smaller than 50 nm (nanoparticles, NPs). A comparative in vivo analysis was done by reconstructing defects in osteoporotic alveolar bones using both composites. The material, CP granules/particles covered with polymer, was characterized using X-ray structural analysis, scanning electron microscopy, and atomic force microscopy. Changes in reparatory functions of tissues affected by osteoporosis were examined in mice in vivo, using these two kinds of composite materials, with and without autologous plasma. Having defined the target segment, histomorphometric parameters-bone area fraction, area, and mean density-were determined. The best results in the regeneration and recuperation of alveolar bone damaged by osteoporosis were achieved with the implantation of a mixture of nanoparticulate CP/PLGA composite and autologous plasma. After the implantation of microparticulate CP/PLGA, in the form of granules, mixed with autologous plasma, into an artificial defect in alveolar bone, new bone formation was also observed, although its formation rate was slower.

Enhanced Osteogenesis of Nanosized Cobalt-substituted Hydroxyapatite

Hydroxyapatite (HAp) is an extensively studied material with known biocompatible and osteoconductive properties in bone tissue reconstruction. The improvement of the osteogenetic potential of HAp has been tested through modification of its structure, by replacing Ca2+ ions with Co2+ ions. In our study, we comparatively analyze the osteogenetic potential of the synthesized HAp and Co2+-substituted HAp (HAp/Co) designed on the nano-scale with the aim of specifically stimulating osteogenesis in vivo. We present a quantitative study of the microscopic organization and structure of the newly formed tissue in a bone defect after 12 weeks and 24 weeks. A quantitative analysis of the calcium, magnesium and phosphorus content in the defect and its close environment was used to determine the deposition of minerals after bone reconstruction. The defect reconstructed with HAp/Co nanoparticles (Co2+ content 12 wt%) was filled with a new tissue matrix composed of dense collagen fibers containing centers of mineralization after 24 weeks. The mineral deposition rate was also higher when the defect was reconstructed with HAp/Co than when it was filled with pure HAp. A histological analysis confirmed that the alveolar bone, in which osteoporosis-induced defects were repaired using HAp/Co nanoparticles, was recuperated.

Influence of saliva medium on freeing heavy metal ion from fixed dentures

In dental-prosthetic practice, various kinds of fixed dentures, crowns and bridges, have very often been used in order to replace natural teeth and to respond to all health and esthetic needs. This study investigated the effect of saliva medium on migration of ions of heavy metals from fixed dentures that were fixed with various cements. Also, the influence of saliva medium on natural human teeth was observed. Potentiometric stripping analysis was used in order to determine the content of toxic heavy metals in the examined samples. The study confirmed that synthetic saliva had no significant influence on heavy metal ion migration from the natural teeth, whereas slight migration of some observed toxic heavy metal ions from the fixed dentures was present. This, however, indicates that these contents, although very low, must be taken seriously, because the above mentioned metals have cumulative effect which after some period of time may lead to functional disorders of some organs, and even to some very serious diseases.

Aspects of Orthodontic-Prosthetic Rehabilitation of Dentofacial Anomalies

Skeletal class III malocclusion is one of the most difficult dentofacial anomalies, characterized by deviation in the development of the mandible and maxilla in the sagittal plane, where the mandible is dominant in relation to the maxilla. In patients with class III malocclusion, anomalies in the dentoalveolar level and esthetic discrepancies are also frequent. The etiology of class III malocclusion is multifactorial due to the interaction of hereditary and environmental factors. Rehabilitation and treatment of malocclusion is one of the major goals of modern dentistry. This article presents the orthodontic-prosthetic therapy and rehabilitation of a 45-year-old patient with an abnormal occlusal vertical dimension and a skeletal class III malocclusion. The patient came to the clinic complaining about degraded esthetics and disordered functions of the orofacial region (functions of eating, swallowing, speech) and also pain in the temporomandibular joint. After the diagnosis was made, the patient was first referred to orthodontic treatment with fixed orthodontic appliances (self-ligating brackets system Rot 0.22). Upon completion of the orthodontic treatment, the patient was sent for further prosthetic treatment. Fixed prosthetic restorations were made in the upper and lower jaw, thus achieving a satisfactory result in terms of esthetics and function of the stomatognathic system.

Histopathological Analysis of Bone Tissue Reaction on Implanted Biomaterials

In implantology, several techniques such as light and polarizing microscopy and histomorphometry are available for evaluation of the bone reactions. Descriptive histology and histomorphometry are the two main types of histological methods. At the microscopic level, bone consists of two forms: woven (an immature disorganized form of bone) and lamellar. During replacement of biomaterial, the remodeling of woven bone is first. Lamellar bone actively replaces woven bone over time and is found in a several structural and functional units with greater organization. Bone remodeling is characterized by the spatial and temporal coupling of bone formation by osteoblasts and bone resorption by osteoclasts. Histomorphometry can be very valuable in measuring the changes in the tissues that surround an implant. The parameters used in the evaluation procedure must be as simple as possible. However, analysis requires considerable expertise and remains time-consuming, despite the reduction in variables. To overcome the limitations presented by the 2D histological section reconstruction from serial sections is an option.

Scanning electron microscopy analysis of dental cements

The aim of this study was to compare in vitro the characteristics of different types of luting cements (zinc phosphate, glass-ionomer and resin based composite cement) using scanning electron microscopy (SEM) analysis and microleakage for the quality range of materials. Dental cements were mixed in accordance with the manufacturers instructions and formed with posts in dental root canals of extracted teeth. The quality of cement was determined by SEM observation on horizontal sectioned roots with fixed posts according to specific pore and marginal gap diameter. The microleakage was measured on specimens immersed in Lofler (methylene blue) solution. The mean values of the maximal diameter of pores, marginal gaps and microleakage of conventional cements are remarkably larger in comparison with composite luting agents. In conclusion, the quality and efficiency of composite luting agents in comparison with conventional cements are more successful in protecting the interior of tooth from penetration of oral fluids, bacteria and bacterial toxins into unprotected dentine.