Formation Of New Bone Tissue Research Articles

Improvement of in vitro physicochemical properties and osteogenic activity of calcium sulfate cement for bone repair by dicalcium silicate

Abstract An ideal bone graft substitute should have the same speed of degradation as formation of new bone tissue. To improve the properties of calcium sulfate hemihydrate (CSH) featured for its rapid resorption, a low degradation material of dicalcium silicate (DCS) was added to the CSH cement. This study examined the effect of DCS (20, 40, 60 and 80 wt%) on the in vitro physicochemical properties and osteogenic activities of the calcium-based composite cements. The diametral tensile strength, porosity and weight loss of the composite cements were evaluated before and after soaking in a simulated body fluid (SBF). The osteogenic activities, such as proliferation, differentiation and mineralization, of human mesenchymal stem cells (hMSCs) seeded on cement surfaces were also examined. As a result, the greater the DCS amount, the higher the setting time was in the cement. Before soaking in SBF, the diametral tensile strength of the composite cements was decreased due to the introduction of DCS. On 180-day soaking, the composite cements containing 20, 40, 60 and 80 wt% DCS lost 80%, 69%, 61% and 44% in strength, respectively. Regarding in vitro bioactivity, the DCS-rich cements were covered with clusters of apatite spherulites after soaking for 7 days, while there was no formation of apatite spherulites on the CSH-rich cement surfaces. The presence of DCS could reduce the degradation of the CSH cements, as evidenced in the results of weight loss and porosity. More importantly, DCS may promote effectively the cell proliferation, proliferation and mineralization. The combination of osteogenesis of DCS and degradation of CSH made the calcium-based composite cements an attractive choice for bone defect repair.

The combination of mesenchymal stem cells and a bone scaffold in the treatment of vertebral body defects

Vertebral body defects represent one of the most common orthopedic challenges. In order to advance the transfer of stem cell therapies into orthopedic clinical practice, we performed this study to evaluate the safety and efficacy of a composite bioartificial graft based on a hydroxyapatite bone scaffold (CEM-OSTETIC(®)) combined with human mesenchymal stem cells (MSCs) in a rat model of vertebral body defects. Under general isoflurane anesthesia, a defect in the body of the L2 vertebra was prepared and left to heal spontaneously (group 1), implanted with scaffold material alone (group 2), or implanted with a scaffold together with 0.5 million MSCs (group 3) or 5 million MSCs (group 4). The rats were killed 8 weeks after surgery. Histological and histomorphometrical evaluation of the implant as well as micro-CT imaging of the vertebrae were performed. We observed a significant effect on the formation of new bone tissue in the defect in group 4 when compared to the other groups and a reduced inflammatory reaction in both groups receiving a scaffold and MSCs. We did not detect any substantial pathological changes or tumor formation after graft implantation. MSCs in combination with a hydroxyapatite scaffold improved the repair of a model bone defect and might represent a safe and effective alternative in the treatment of vertebral bone defects.

Particulate bone matrix usage for alveolar bone conservation

Different filling materials have been used in an attempt to repair bone loss situations. Objective: The present study aimed to examine the effect of a bone matrix in post-extraction remodelling of the alveolar bone, and to perform a histomorphometric analysis of the residual alveolar ridges in Wistar rats.Material and Methods: Both rat first lower molars were extracted and the right alveoli were filled with particles of a bone matrix with mineral components (MO-UNC) (experimental group, EG). The left alveoli were used as a control group (CG). The animals were sacrificed at 0 hrs, 15, 30 and 60 days after extraction, and the samples were processed. Histological sections were made at the level of the mesial alveolus of the first lower molar.Repair of the alveoli was histologically evaluated and a histomorphometric study of total alveolar volume (TAV), height of the buccal plate (Bh), height of the lingual plate (Lh) and percentage of osseointegration (OI) of the particles was performed to compare the residual ridges of CG with those of the EG. Statistical analysis of the data was performed. Results: In the cases of the experimental group, newly-formed bone tissue was identified around the MO-UNC particles (osseointegration). Histomorphometric data indicate that, at 60 days post-extraction, TAV was significantly greater for EG when compared with CG (p<0.05) and the percentage of osseointegration of the particles increased as a function of time (57.6 %, 90.5% y 95.5%, for EG at 15, 30 y 60 days respectively). Conclusions: The bone matrix (MO-UNC) evaluated in this study is an osteoconductive material that prevents the collapse of post-extraction alveolar bone.

Evaluation of Injectable Constructs for Bone Repair with a Subperiosteal Cranial Model in the Rat

While testing regenerative medicine strategies, the use of animal models that match the research questions and that are related to clinical translation is crucial. During the initial stage of evaluating new strategies for bone repair, the main goal is to state whether the strategies efficiently induce the formation of new bone tissue at an orthotopic site. Here, we present a subperiosteal model in rat calvaria that allow the evaluation of a broad range of approaches including bone augmentation, replacement and regeneration. The model is a fast to perform, minimally invasive, and has clearly defined control groups. The procedure enables to evaluate the outcomes quantitatively using micro-computed tomography and qualitatively by histology and immunohistochemistry. We established this new model, using bone morphogenetic protein-2 as an osteoinductive factor and hyaluronic acid hydrogel as injectable biomaterial. We showed that this subperiosteal cranial model offers a minimally invasive and promising solution for a rapid initial evaluation of injectables for bone repair. We believe that this approach could be a powerful platform for orthopedic research and regenerative medicine.

Effect of autologous stem cells on regenerated bone during distraction osteogenesis by Ilizarov technique in the radius of dogs: histomorphometric analysis

To investigate by histomorphometry the distraction osteogenesis by Ilizarov technique in dog radius with the use of autologous stem cells in regenerated bone. Ten dogs (20 radiuses) underwent the osteotomy of 20% of extension of their radiuses, and osteogenic distraction using the Ilizarov technique after this procedure at rate of 1mm per day divided into 0.5mm every 12 hours. The elongation was performed until the regeneration reached 20% of the total length of the radius. The stem cells were isolated, concentrated and injected in the regenerated bone, when it reached 10% of the length of the entire radius. The regenerated bone was evaluated using histomorphometric analysis when the elongation was 20% the size of radius. The bone formation was evidenced by histomorphometric indices were significantly greater in the study group. In the histology evaluation the type of healing was mixed in 80% (intra membrane and endocondral) in both groups; the osteoblastic activity from moderate to intense was greater in the study group; and the space occupied by the newly-formed bone tissue was more evident in the study group. The histomorphometric indices in this study expressing the microarchitecture, trabecular thickness, trabecular spacing, number of trabecula and quantity of bone that was significant in the group study. These data suggest that the use of undifferentiated stem cells autologous bone marrow in the regenerate bone induces osteogenesis and bone quality.

Bone tissue formation under ideal conditions in a scaffold generated by a reaction-diffusion system.

The design of porous scaffolds for tissue engineering requires methods to generate geometries in order to control the stiffness and the permeability of the implant among others characteristics. This article studied the potential of the reaction-diffusion systems to design porous scaffolds for bone regeneration. We simulate the degradation of the scaffold material and the formation of new bone tissue over canal-like, spherical and ellipsoid structures obtained by this approach. The simulations show that the degradation and growth rates are affected by the form of porous structures. The results have indicated that the proposed method has potential as a tool to generate scaffolds with internal porosities and is comparable with other methodologies to obtain this type of structures.

Biological Evaluation of Polydimethylsiloxane Modified by Calcium Phosphate Nanoparticles for Potential Application in Spine Surgery

The biological properties of a composite made of polydimethylsiloxane matrix and two kinds of calcium phosphate nanoparticles (hydroxyapatite, beta tricalcium phosphate) were tested by means of in vitro and in vivo investigations. Chemical and phase analyses of the nanoparticles were performed. The effects of different volume fractions of nanoparticles were investigated. Human osteoblast-like cell cultures (MG 63) demonstrated that the addition of 5–15 vol.% of nanoparticles had a significantly positive effect on osteoblast viability, and that high concentration did not support cell proliferation. The highest rates of osteointegration in pig bone were attained for implants modified by 15 vol.% hydroxyapatite and more intensive formation of new bone tissue was observed. Our study indicates that hydroxyapatite probably better imitates the composition and structure of the mineral phase of real bone.

Effect of screw position on bone tissue differentiation within a fixed femoral fracture

Plate and screw constructs are routinely used in the treatment of long bone fractures. Despite considerable advancements in technology and techniques, there can still be complications in the healing of long bone fractures. Non-unions, delayed unions, and hardware failures are common complications observed in clinical practice following open reduction and internal fixation of fractures [1]. Potential causes of these adverse clinical effects may be disruptive to the periosteal and endosteal blood supply, stress shielding effects, and inadequate mechanical stability. The goal of the present study was to explore the effect of screw position on the fracture healing and formation of new bone tissue with mechanoregulatory algorithms in a computational model. An idealized poroelastic 3D finite element (FE) model of a femur with a 5 mm fracture gap, including a plate-screw construct was developed. Nineteen different plate-screw combinations, created by varying the number and position of screws within the plate, were created to identify a construct with the most favourable attributes for fracture healing. The first phase of the study evaluated constructs through mechanical stress analyses to identify those constructs with high loadsupport capability. The second phase of the study evaluated healing and bone formation with a biphasic mechanoregulatory algorithm to simulate tissue differentiation for fixation within selected constructs. The results of our analysis demonstrated a 4-screw symmetrical construct with the largest distance between screws to provide the most favourable balance of stability and optimized conditions to promote fracture healing.

Coupling systems biology with multiscale mechanics, for computer simulations of bone remodeling

Bone remodeling is a process involving removal of mature bone tissue and subsequent formation of new bone tissue. This process is driven by complex actions of biological cells and biochemical factors, and it is sensitive to the loads applied onto the skeleton. Herein, we develop a mathematical framework describing this process at the (macroscopic) level of cortical bone, by combining, for the first time, bone cell population kinetics with multiscale bone mechanics. Key variables are concentrations of biological cells (osteoclasts, osteoblasts and their progenitors) and biochemical factors (RANK, RANKL, OPG, PTH, and TGF-β), as well as mechanical strains, both at the (“macroscopic”) level of cortical bone and at the (“microscopic”) level of the extravascular bone matrix. Multiscale bone mechanics delivers, as a function of the vascular porosity, the relation between the macroscopic strains resulting from the loads, and the microscopic strains, which are known to modulate, either directly, or via poromechanical couplings such as hydrostatic pressure or fluid flow, the expression or proliferation behavior of the biological cells residing in, or attached to the extravascular bone matrix. Hence, these microscopic strains enter the biochemical kinetics laws governing cell expression, proliferation, differentiation, and apoptosis. Without any additional phenomenologically motivated paradigm, this novel approach is able to explain the experimentally observed evolutions of bone mass in postmenopausal osteoporosis and under microgravity conditions: namely, a decrease of bone loss over time.

Platelet-rich plasma in periodontal defect treatment after extraction of impacted mandibular third molars.

Purpose:The extraction of mesioangular impacted third molars may cause multiple periodontal defects at the distal root of the second molar. Platelet-rich plasma (PRP) is a material containing many autologous growth factors that may be used in repairing and preventing periodontal complications at the distal root of the second molar adjacent to the extracted third molar.Materials and Methods:We analyzed the effects of autologous PRP on periodontal tissues after extraction of the third molar in 18 young patients (age, 20–30 years). Inclusion criteria were the presence of a pocket distal to the mandibular second molar with a probing depth [3] of 7.5 mm and a probing attachment level [3] of 6 mm.Results:We observed, at 12 weeks after surgery, a notable reduction in the probing depth and an improvement in the probing attachment level in those cases treated with PRP compared with the controls, as well as formation of new bone tissue in the bone defect.Conclusion:We showed that PRP is effective in inducing and accelerating bone regeneration for the treatment of periodontal defects at the distal root of the mandibular second molar after surgical extraction of a mesioangular, deeply impacted mandibular third molar.

Direct deposited porous scaffolds of calcium phosphate cement with alginate for drug delivery and bone tissue engineering

This study reports the preparation of novel porous scaffolds of calcium phosphate cement (CPC) combined with alginate, and their potential usefulness as a three-dimensional (3-D) matrix for drug delivery and tissue engineering of bone. An α-tricalcium phosphate-based powder was mixed with sodium alginate solution and then directly injected into a fibrous structure in a Ca-containing bath. A rapid hardening reaction of the alginate with Ca2+ helps to shape the composite into a fibrous form with diameters of hundreds of micrometers, and subsequent pressing in a mold allows the formation of 3-D porous scaffolds with different porosity levels. After transformation of the CPC into a calcium-deficient hydroxyapatite phase in simulated biological fluid the scaffold was shown to retain its mechanical stability. During the process biological proteins, such as bovine serum albumin and lysozyme, used as model proteins, were observed to be effectively loaded onto and released from the scaffolds for up to more than a month, proving the efficacy of the scaffolds as a drug delivering matrix. Mesenchymal stem cells (MSCs) were isolated from rat bone marrow and then cultured on the CPC–alginate porous scaffolds to investigate the ability to support proliferation of cells and their subsequent differentiation along the osteogenic lineage. It was shown that MSCs increasingly actively populated and also permeated into the porous network with time of culture. In particular, cells cultured within a scaffold with a relatively high porosity level showed favorable proliferation and osteogenic differentiation. An in vivo pilot study of the CPC–alginate porous scaffolds after implantation into the rat calvarium for 6weeks revealed the formation of new bone tissue within the scaffold, closing the defect almost completely. Based on these results, the newly developed CPC–alginate porous scaffolds could be potentially useful as a 3-D matrix for drug delivery and tissue engineering of bone.

Osteogenic differentiation of two distinct subpopulations of human adipose-derived stem cells: an in vitro and in vivo study

The first stem cells considered for the reconstruction of bone were bone marrow mesenchymal stem cells (BMSCs). Subsequently, cells with similar marker expression panel and differentiation potential were found in new sources of cells, such as adipose tissue. This source of stem cells has a promising future in tissue-engineering applications, considering the abundance of this tissue in the human body, the easy harvesting and the high number of stem cells that are available from such a small amount of tissue. The isolation of the adipose stem cells is generally performed by means of enzymatic digestion of the tissues, followed by a natural selection of the stem cells based on their capacity to adhere to the culture flasks, leading to a quite heterogeneous population. This constitutes a major drawback for the use of these cells, since the heterogeneity of the cell culture obtained can compromise their proliferation and differentiation potential. In the present study we have analysed the in vitro and in vivo behaviour of two selected subpopulations with high osteogenic potential. For this purpose, ASCs(CD29+) and ASCs (STRO-1+)subpopulations were isolated and in vitro cultured onto a biodegradable polymeric scaffold, using osteogenic medium, before implantation in a nude mice model. The biodegradable polymeric scaffold used is a fibre-mesh structure based on a blend of starch and polycaprolatone (SPCL) that has been successfully used in several bone tissue-engineering studies. The implanted ASCs-scaffold constructs promoted the formation of new bone tissue in nude mice. However, the results obtained show differences in the behaviour of the two ASCs subpopulations under study, particularly regarding their potential to differentiate into the osteogenic lineage, and allowed the indentification of ASCs (STRO-1+) as the best subpopulation for bone tissue-engineering applications.

Regeneration of Skull Bones in Adult Rabbits after Implantation of Commercial Osteoinductive Materials and Transplantation of a Tissue-Engineering Construct

We performed a comparative study of reparative osteogenesis in rabbits with experimental critical defects of the parietal bones after implantation of commercial osteoinductive materials "Biomatrix", "Osteomatrix", "BioOss" in combination with platelet-rich plasma and transplantation of a tissue-engineering construct on the basis of autogenic multipotent stromal cells from the adipose tissue predifferentiated in osteogenic direction. It was found that experimental reparative osteogenesis is insufficiently stimulated by implantation materials and full-thickness trepanation holes were not completely closed. After transplantation of the studied tissue-engineering construct, the defect was filled with full-length bone regenerate (in the center of the regenerate and from the maternal bone) in contrast to control and reference groups, where the bone tissue was formed only on the side of the maternal bone. On day 120 after transplantation of the tissue-engineering construct, the percent of newly-formed bone tissue in the regenerate was 24% (the total percent of bone tissue in the regenerate was 39%), which attested to active incomplete regenerative process in contrast to control and reference groups. Thus, the study demonstrated effective regeneration of the critical defects of the parietal bones in rabbits 120 days after transplantation of the tissue-engineering construct in contrast to commercial osteoplastic materials for directed bone regeneration.

Recruitment of a Host's Osteoprogenitor Cells Using Exogenous Mesenchymal Stem Cells Seeded on Porous Ceramic

The contribution of the host's circulating progenitor cells after implantation of mesenchymal stem cells (MSC)/bioscaffold combinations for repairing bone defects has not been elucidated, although this issue affects the clinical application of the tissue engineering approach. We implanted blocks of hydroxyapatite loaded with murine MSCs into syngenic, allogenic, and immunocompromised recipients. After 8 weeks, we found that bone tissue was formed in syngenic and immunocompromised animals. The implanted cells appeared pivotal in the early stages of tissue development, but cells of the recipient's origin finally made bone. In this system, osteoprogenitors migrated from the recipient to the implant, whereas the implanted cells left the scaffold and entered the circulatory flow. We observed rapid destruction of implanted cells when allogenic MSC/bioscaffold combinations were grafted onto immunocompetent recipients without immunosuppressant therapy. This destruction blocked the recruitment process and did not allow the formation of new bone tissue. The possibility that the implanted exogenous MSCs could engage the host's osteoprogenitor cells to form new bone tissue could open new perspectives for the tissue engineering approach to bone repair, including the opportunity of using allogenic cells combined with a temporary immunosuppressant therapy, stimulating the replacement of the exogenous cells with autologous cells.

A new approach to osteomyelitis treatment

A high incidence of suppurative inflammation, difficulty of its treatment, consistent clinical manifestations, severity of the pathology, and frequent complications shows the importance of this problem. Its comprehensive analysis leads to main theoretical conclusion that alteration, exudation, and tissue proliferation and regeneration in different forms of the inflammation are stages of the same process. They follow a consistent pattern and are essentially general, defensive and adaptive reactions aimed at eliminating the inflammatory substrate from, and restoration of, the focus [1‐7, 9‐ 11]. Osteomyelitis is one of such serious problems. The percentage of unsatisfactory results of its treatment remains about 30% or even higher. Here, we suggest a new conceptual scheme of pathogenesis that will help to develop an algorithm of treatment for a specific form and any stage of the disease. This approach is expected to considerably increase the probability of successful treatment. Current views on osteomyelitis are widely publicized [2‐4, 8, 12, 13]. In the acute inflammation phase of osteomyelitis, the state of the bone focus is qualitatively changed. The prevailing processes are microcirculation disturbances, progressive intraosseous hypertension, and pyesis destroying bone structures, which is observable in X-ray examination beginning from about the third week of the disease (foci of bone dystrophy and disappearance of trabeculae). Inflammation accelerates bone destruction. As defensive mechanisms are involved into the inflammatory reaction, signs of the restoration of the bone tissue based on proliferation appear. In X-ray examination, this is seen as a periost reaction consisting in cell proliferation in the bone structures responsible for the production of new bone tissue. The periost plays the main role in this process. The destruction and restoration of the bone tissue are not isolated: destruction of bone structures is prevailing in the acute phase, and their regeneration, in the chronic phase. The balance between them becomes and remains disturbed during inflammation. The longer the conditions favoring destruction in a bone segment are retained, the more irreversible they are. The situation remains the same upon the transition to the chronic stage. The body, activating all mechanisms of local and general homeostasis, seeks to localize the infection focus. Bone structures regenerate; therefore, bone restoration zones appear along with destruction foci. A bone segment looks motley in X-rays. It contains sequestral boxes, pathological fractures, bone tissue defects, periostal layers of immature bone tissue, external fenestration of the bone segment, sequestra, foci of osteosclerosis, etc. Together with the associated microbial infection, this favors recurrent progress of osteomyelitis. Since the bone destroyed and formed simultaneously and in parallel, regenerative mechanisms of the body general and local defense lead to the formation of imperfect bone structure. Pathological foci appear near the zone of normal bone structure; therefore, the formation of new bone tissue is stimulated, but its normal structure is not ensured. The less efficient the treatment (including surgery), the worse the results. Surgery aimed at sanitation of the inflammation focus and effective artificial drainage remains the main treatment. If osteomyelitis treatment is ineffective at the acute stage, and inflammation becomes chronic, this is usually accounted for by the presence of a cavity containing a sequestrum or the formation of a persistent, unhealing fistula. The fistula and sequestrum cavity ensure drainage, even if partial and inefficient. The intraosseous hypertension as a pathogenetic stage, continuing regeneration of the bone, and the formation of imperfect bone structure are mainly maintained by the inefficient drainage. The general and local changes in the body accompanying osteomyelitis depend on the intensity of the reaction to inflammation and determine the form and stages of the pathological process. In osteomyelitis caused by mechanical damage (especially open injuries), exudate may be partly drained from the focus at early stages; therefore, the disease progress is more favorable: regeneration mechanisms leading to local

Bioactive composite ceramics in the hydroxyapatite-tricalcium phosphate system

Synthetic materials based on hydroxyapatite (HA), an analogue of the mineral component of the bone tissue, are used in medicine for the repair of damaged bone tissue [1‐3]. A new repair technology is based on implanting porous ceramic scaffolds containing cultivated cells and proteins into the bone tissue [4]. The formation of new bone tissue is a complex process that includes protein adsorption as an important stage [5, 6]. Scaffolds should be resorbable with time in the human body with gradual replacement by newly formed bone tissue and should ensure a high protein-adsorption capacity. Hydroxyapatite is stable against dissolution by body fluids, whereas tricalcium phosphate (TCP) has a much higher resorption rate compared to that of HA. By varying the component ratio in an HA/TCP composite, one can control the resorption rate. The problems of design of such composite materials have been considered in reviews [7, 8]. Two-phase composites (TCMs) are produced by thermal decomposition of calcium-deficient HA followed by sintering [8]. Using this method, it is difficult to control the component ratio in the material. Some aspects of the influence of the phase composition on the biological behavior of TCMs remain obscure. This study is devoted to the production of TCMs with specified composition and porosity and elucidation of the question of which factor, porosity or phase composition, is more important for protein adsorption.

Experimental studies on the effect of osteotomy technique on the bone regeneration in distraction osteogenesis

The objective of the experiment was to study the effect of osteotomy technique on the course of bone regeneration in distraction osteogenesis in sheep. Thirty five merino sheep were divided into 5 groups of 7 sheep each, depending on the osteotomy technique: subcutaneous corticotomy, open corticotomy, Cattaneo corticotomy, open osteotomy and osteoclasia. Formation of regenerate and its remodeling was assessed, based on roentgenograms and morphological examination (bone sections, histological evaluation, SEM, superficial X-ray analysis). Irrespective from the osteotomy technique applied, in all experimental groups, regenerates filling the distraction gap were obtained. Analysis of bone sections and histological slides indicated the most advanced osteogenesis processes in the osteoclasia group. SEM examination and X-ray microanalysis confirmed not only the presence of mature bone tissue structures in this group, but also showed a mineralization close to that of a healthy bone. Osteogenesis was the slowest in the group of subcutaneous corticotomy. The observed histological picture and analysis of elemental composition indicate a normal course of distraction osteogenesis in this group, but its consecutive phases proceed with a certain delay, compared to the remaining groups. With a good deal of caution, it can be assumed that the delay of osteogenesis in the group of subcutaneous corticotomy in the 14th post-operative week was ca. 3 weeks compared to the osteoclasia group. In all experimental groups, few cartilaginous nodules were observed in regenerates 5 weeks and, in few cases, 9 weeks old. Ossification in such places was indirect, cartilage-based. In the remaining regions direct, membrane-based ossification prevailed. Direct apposition bone lamellae on islands of fibrous bone tissue was observed in regenerates aged 9 and 14 weeks, especially in periosteal regions. The intensity and rate of formation of new bone tissue varied between the experimental groups, based on roentgenological analysis and histological evaluation. Complex morphological studies on the course of regeneration in sheep showed the most advanced remodeling and mineralization of bone tissue in animals subject to osteoclasia.

Biochemical Markers of Bone Tissue Metabolism in Cosmonauts after a Prolonged Spaceflight

Parameters of calcium homeostasis and its hormonal regulation, including biochemical markers of bone metabolism, were measured in the blood serum of Russian cosmonauts after prolonged flights on the International Space Station during the period from 2000 to 2003. The duration of the spaceflights was 129–196 days. Flight factors had an impact on calcium and bone tissue metabolism after a flight. Increased levels of osteogenesis and resorption markers were detected in the blood of the cosmonauts in the early rehabilitation period after a spaceflight. The prevalence of resorption over the formation of new bone tissue was observed in the early rehabilitation period, when the hormonal system maintaining calcium homeostasis was activated.

Use of Autologous Platelet-Rich Plasma (PRP) in Periodontal Defect Treatment After Extraction of Impacted Mandibular Third Molars

The extraction of mesioangular impacted third molars may cause multiple periodontal defects at the distal root of the second molar. Platelet-rich plasma (PRP) is a material containing many autologous growth factors that may be used in repairing and preventing periodontal complications at the distal root of the second molar adjacent to the extracted third molar. We analyzed the effects of autologous PRP on periodontal tissues after extraction of the third molar in 18 young patients (age, 21-26 years). Inclusion criteria were the presence of a pocket distal to the mandibular second molar with a probing depth>or=7.5 mm and a probing attachment level>or=6 mm. We observed, at 12 weeks after surgery, a notable reduction in the probing depth and an improvement in the probing attachment level in those cases treated with PRP compared with the controls, as well as formation of new bone tissue in the bone defect. We showed that PRP is effective in inducing and accelerating bone regeneration for the treatment of periodontal defects at the distal root of the mandibular second molar after surgical extraction of a mesioangular, deeply impacted mandibular third molar.

Controlling rigidity and degradation of alginate hydrogels via molecular weight distribution.

The mechanical rigidity and degradation rate of hydrogels utilized as cell transplantation vehicles have been regarded as critical factors in new tissue formation. However, conventional approaches to accelerate the degradation rate of gels deteriorate their function as a mechanical support in parallel. We hypothesized that adjusting the molecular weight distribution of polymers that are hydrolytically labile but capable of forming gels would allow one to alter the degradation rate of the gels over a broad range, while limiting the range of their elastic moduli (E). We investigated this hypothesis with binary alginate hydrogels formed from both ionically and covalently cross-linked partially oxidized (1% uronic acid residues), low [molecular weight (MW) approximately 60,000 g/mol] and high MW alginates (MW approximately 120,000 g/mol) in order to examine the utility of this approach with various cross-linking strategies. Increasing the fraction of low MW alginates to 0.50 maintained a value of E similar to that for the high MW alginate gels but led to faster degradation, irrespective of the cross-linking mode. This result was attributed to a faster separation between cross-linked domains upon chain breakages for the low MW alginates, coupled with their faster chain scission than the high MW alginates. The more rapidly degrading oxidized binary hydrogels facilitated the formation of new bone tissues from transplanted bone marrow stromal cells, as compared with the nonoxidized high MW hydrogels. The results of these studies will be useful for controlling the physical properties of a broad array of hydrogel-forming polymers.