Biodegradation process of alpha-TCP particles and new bone formation in a rabbit cranial defect model

Induced Pluripotent Stem Cell-Derived Endothelial Networks Accelerate Vascularization But Not Bone Regeneration

Vascularization is critical for engineering mineralized tissues. It has been previously shown that biomaterials containing preformed endothelial networks anastomose to host vasculature following implantation. However, the networks alone may not increase regeneration. In addition, a clinically applicable source of cells for vascularization is needed. In this study, vascular networks were generated from endothelial cells (ECs) derived from human induced pluripotent stem cells (iPSCs). Network formation by iPSC-ECs within fibrin gels was investigated in a mesenchymal stem cells (MSCs) coculture spheroid model. Statistical design of experiments technique was evaluated for its predicting capability during the optimization of experimental parameters. The prevascularized units were combined with hydroxyapatite nanoparticles to develop a vascularized composite hydrogel that was implanted in a rodent critical-sized cranial defect model. Immunohistological staining for human-specific CD31 at week 1 indicated the presence and maintenance of the implanted vessels. At 8 weeks, the prevascularized systems resulted in higher vessel density over MSC-only scaffolds. The implanted vessels appeared to establish flow with host vasculature. While there was a slight increase in bone volume in the prevascularized bone construct compared to MSC-only bone constructs, there was not a profound increase in bone regeneration. These results show that scaffolds with network structures can be generated from ECs derived from iPSC and that the networks survive and inosculate with the host postimplantation in a bone model. Impact statement Vascularization is critical for engineering bone. Prevascularized scaffolds have been shown to improve postimplantation vascularization. Herein, vascularized networks were generated from induced pluripotent cells derived from endothelial cells. These vascularized units were combined with a fibrin/hydroxyapatite scaffold to develop a prevascularized construct for bone regeneration. Implantation of these scaffolds in a small animal cranial defect model resulted in network inosculation and increased vascularization, but exhibited only a limited effect on bone formation. This study provides insight into the challenges of generating vascularized bone.

Biofunctionalization of metallic implants by calcium phosphate coatings

Metallic materials have been extensively applied in clinical practice due to their unique mechanical properties and durability. Recent years have witnessed broad interests and advances on surface functionalization of metallic implants for high-performance biofunctions. Calcium phosphates (CaPs) are the major inorganic component of bone tissues, and thus owning inherent biocompatibility and osseointegration properties. As such, they have been widely used in clinical orthopedics and dentistry. The new emergence of surface functionalization on metallic implants with CaP coatings shows promise for a combination of mechanical properties from metals and various biofunctions from CaPs. This review provides a brief summary of state-of-art of surface biofunctionalization on implantable metals by CaP coatings. We first glance over different types of CaPs with their coating methods and in vitro and in vivo performances, and then give insight into the representative biofunctions, i.e. osteointegration, corrosion resistance and biodegradation control, and antibacterial property, provided by CaP coatings for metallic implant materials.

Nurse's A-Phase-Silicocarnotite Ceramic-Bone Tissue Interaction in a Rabbit Tibia Defect Model

Calcium phosphate materials are widely used as bone substitutes due to their bioactive and biodegradable properties. Also, the presence of silicon in their composition seems to improve the bioactivity of the implant and promote bone tissue repair. The aim of this study was to develop a novel ceramic scaffold by partial solid-state sintering method with a composition lying in the field of the Nurse’s A-phase–silicocarnotite, in the tricalcium phosphate–dicalcium silicate (TCP–C₂S) binary system. Also, we evaluated its osteogenic and osteoconductive properties after being implanted into tibia defects in New Zealand rabbits. X-ray, microcomputer tomography, and histomorphometry studies demonstrated that this porous ceramic is highly biocompatible and it has excellent osteointegration. The material was being progressively reabsorbed throughout the study and there was no unspecified local or systemic inflammatory response observed. These results suggest that ceramic imitates the physicochemical characteristics of bone substitutes used in bone reconstruction.

Surface modification of porous alpha-tricalcium phosphate granules with heparin enhanced their early osteogenic capability in a rat calvarial defect model

Heparin binds to and modulates various growth factors, potentially augmenting the bone-forming capability of biomaterials. Here, α-tricalcium phosphate (α-TCP) granules were modified with peptide containing the marine mussel-derived adhesive sequence, which reacts with α-TCP surface, and cationic sequence, which binds to heparin (α-Ph). α-Ph retained the α-TCP phase and intergranule spaces after the surface modification. The existence of heparin on α-Ph granules was confirmed using X-ray photoelectron spectroscopy. Granules of α-TCP and α-Ph were implanted into critical-size defects in rat calvaria for 4 weeks. Micro-computed tomography, histological evaluation, and Alcian blue staining revealed that α-Ph induced superior bone formation compared with α-TCP. Newly formed bone on α-Ph was preferentially in contact with the Alcian blue-stained surfaces of granules. These results suggested that heparinization enhanced the early osteogenic capacity of α-TCP, possibly by modulating the secretion of Alcian blue-stained extracellular matrixes.

Current bone substitutes for implant dentistry

PURPOSE

Alveolar ridge augmentation is essential for success in implant therapy and depends on the biological performance of bone graft materials. This literature review aims to comprehensively explain the clinically relevant capabilities and limitations of currently available bone substitutes for bone augmentation in light of biomaterial science.

STUDY SELECTION

The biological performance of calcium phosphate-based bone substitutes was categorized according to space-making capability, biocompatibility, bioabsorption, and volume maintenance over time. Each category was reviewed based on clinical studies, preclinical animal studies, and in vitro studies.

RESULTS

Currently available bone substitutes provide only osteoconduction as a scaffold but not osteoinduction. Particle size, sensitivity to enzymatic or chemical dissolution, and mechanical properties affect the space-making capability of bone substitutes. The nature of collagen fibers, particulate size, and release of calcium ions influence the biocompatibility of bone substitutes. Bioabsorption of bone substitutes is determined by water solubility (chemical composition) and acid resistance (integrity of apatite structure). Bioabsorption of remnant bone substitute material and volume maintenance of the augmented bone are inversely related.

CONCLUSION

It is necessary to improve the biocompatibility of currently available bone substitutes and to strike an appropriate balance between bioabsorption and volume maintenance to achieve ideal bone remodeling.

Green Tea Extracts Epigallocatechin-3-gallate for Different Treatments

Epigallocatechin-3-gallate (EGCG), a component extracted from green tea, has been proved to have multiple effects on human pathological and physiological processes, and its mechanisms are discrepant in cancer, vascularity, bone regeneration, and nervous system. Although there are multiple benefits associated with EGCG, more and more challenges are still needed to get through. For example, EGCG shows low bioactivity via oral administration. This review focuses on effects of EGCG, including anti-cancer, antioxidant, anti-inflammatory, anticollagenase, and antifibrosis effects, to express the potential of EGCG and necessity of further studies in this field.

An innovative cell-laden α-TCP/collagen scaffold fabricated using a two-step printing process for potential application in regenerating hard tissues

Cell-laden scaffolds are widely investigated in tissue engineering because they can provide homogenous cell distribution after long culture periods, and deposit multiple types of cells into a designed region. However, producing a bioceramic 3D cell-laden scaffold is difficult because of the low processability of cell-loaded bioceramics. Therefore, designing a 3D bioceramic cell-laden scaffold is important for ceramic-based tissue regeneration. Here, we propose a new strategy to fabricate an alpha-tricalcium-phosphate (α-TCP)/collagen cell-laden scaffold, using preosteoblasts (MC3T3-E1), in which the volume fraction of the ceramic exceeded 70% and was fabricated using a two-step printing process. To fabricate a multi-layered cell-laden scaffold, we manipulated processing parameters, such as the diameter of the printing nozzle, pneumatic pressure, and volume fraction of α-TCP, to attain a stable processing region. A cell-laden pure collagen scaffold and an α-TCP/collagen scaffold loaded with cells via a simple dipping method were used as controls. Their pore geometry was similar to that of the experimental scaffold. Physical properties and bioactivities showed that the designed scaffold demonstrated significantly higher cellular activities, including metabolic activity and mineralization, compared with those of the controls. Our results indicate that the proposed cell-laden ceramic scaffold can potentially be used for bone regeneration.

Electric-field assisted 3D-fibrous bioceramic-based scaffolds for bone tissue regeneration: Fabrication, characterization, and in vitro cellular activities

Nano/microfibrous structure can induce high cellular activities because of the topological similarity of the extracellular matrix, and thus, are widely used in various tissue regenerative materials. However, the fabrication of a bioceramic (high weight percent)-based 3D microfibrous structure is extremely difficult because of the low process-ability of bioceramics. In addition, three-dimensional (3D) microfibrous structure can induce more realistic cellular behavior when compared to that of 2D fibrous structure. Hence, the requirement of a 3D fibrous ceramic-based structure is an important issue in bioceramic scaffolds. In this study, a bioceramic (α-TCP)-based scaffold in which the weight fraction of the ceramic exceeded 70% was fabricated using an electrohydrodynamic printing (EHDP) process. The fabricated ceramic structure consisted of layer-by-layered struts entangled with polycaprolactone microfibers and the bioceramic phase. Various processing conditions (such as applied electric field, flow rate, nozzle size, and weight fraction of the bioceramic) were manipulated to obtain an optimal processing window. A 3D printed porous structure was used as a control, which had pore geometry similar to that of a structure fabricated using the EHDP process. Various physical and cellular activities using preosteoblasts (MC3T3-E1) helped confirm that the newly designed bioceramic scaffold demonstrated significantly high metabolic activity and mineralization.

Analysis of the Osteogenic Effects of Biomaterials Using Numerical Simulation

We describe the development of an optimization algorithm for determining the effects of different properties of implanted biomaterials on bone growth, based on the finite element method and bone self-optimization theory. The rate of osteogenesis and the bone density distribution of the implanted biomaterials were quantitatively analyzed. Using the proposed algorithm, a femur with implanted biodegradable biomaterials was simulated, and the osteogenic effects of different materials were measured. Simulation experiments mainly considered variations in the elastic modulus (20–3000 MPa) and degradation period (10, 20, and 30 days) for the implanted biodegradable biomaterials. Based on our algorithm, the osteogenic effects of the materials were optimal when the elastic modulus was 1000 MPa and the degradation period was 20 days. The simulation results for the metaphyseal bone of the left femur were compared with micro-CT images from rats with defective femurs, which demonstrated the effectiveness of the algorithm. The proposed method was effective for optimization of the bone structure and is expected to have applications in matching appropriate bones and biomaterials. These results provide important insights into the development of implanted biomaterials for both clinical medicine and materials science.

Bone regeneration with a collagen model polypeptides/α-tricalcium phosphate sponge in a canine tibia defect model

INTRODUCTION

We evaluated the effects of synthesized collagen model polypeptides consisting of a proline-hydroxyproline-glycine (poly(PHG)) sequence combined with porous alpha-tricalcium phosphate (α-TCP) particles on bone formation in a canine tibia defect model.

MATERIALS AND METHODS

The porous α-TCP particles were mixed with a poly(PHG) solution, and the obtained sponge was then cross-linked and characterized by x-ray diffraction and scanning electron microscopy. Tibia defects were analyzed in 12 healthy beagles using microcomputed tomography and histological evaluation.

RESULTS

At 2 and 4 weeks, the volume density of new bone was higher in the poly(PHG)/α-TCP group than in poly(PHG) alone group (P < 0.05); however, there was no difference at 8 weeks (P > 0.05). Histological evaluation at 4 weeks after implantation revealed that the poly(PHG) had degraded, and newly formed bone was present on the surface of the α-TCP particles. At 8 weeks, continuous cortical bone formation with a Haversian structure covered the top of the bone defects in both groups.

CONCLUSION

This study demonstrates that the composite created using porous α-TCP particles and poly(PHG) is sufficiently adaptable for treating bone defects.

Clinical experience of full custom-made artificial bones for the maxillofacial region

Introduction

Autologous, allogeneic, and artificial bones are clinically applied as graft materials for bone reconstruction, with each having their own advantages and disadvantages. Although artificial bones with various shapes are currently available, a product with a morphology that may be freely modified by operators has not yet been developed. In the present study, we developed a full custom-made artificial bone, and applied it to form the maxillofacial region. We herein report treatment outcomes.

Methods

An artificial bone was prepared on a 3-dimensional solid model, and data of its shape was collected on CT. A full custom-made artificial bone was prepared by laminating α-tricalcium phosphate powder using an aqueous polysaccharide curing solution and the ink-jet powder-laminating device, Z406 3D Printer (DICO, USA). Subjects comprised patients who underwent maxillofacial plasty using this artificial bone between March 2006 and September 2009.

Results

Maxillofacial plasty using the full custom-made artificial bone was applied to 23 regions in 20 patients (14 females and 6 males). The recipient region was the maxilla in 3, mandibular ramus in 13, mental region in 7, and frontal bone in 1. Postoperative courses were favorable in 18 out of the 23 regions; however, the fit was insufficient in 2 regions and the recipient regions were exposed within 1 year after surgery. Three regions were exposed 1 year or more after surgery.

Conclusion

We developed a novel reconstruction method using a full custom-made artificial bone. Its fit with the recipient bone was considered to be important, since an ill fit between the recipient and artificial bones potentially resulting in the artificial bone being detached. Therefore, fixation is important in order to prevent the detachment, and careful course observations are required when an ill fit is concerned during the follow-up period.

Synchronization of calcium sulphate cement degradation and new bone formation is improved by external mechanical regulation

A major challenge faced in the bone materials of weight-bearing without internal fixture support is the mismatch of material degradation and new bone formation, leading to weakening or even failure of the overall bony structure. This study demonstrated in the rat femur model that calcium sulphate cement degradation and new bone formation could be better synchronized by external mechanical force. An ascending force in line with calcium sulphate cement degradation could achieve bone healing in 37 days with ultimate load to failure of 87.00 ± 7.30 N, similar to that of intact femur (80.46 ± 2.79 N, p = 0.369). In contrast, the healing process under either a constant force or no force illustrated significant residual defect volumes of 1.47 ± 0.44 and 4.08 ± 0.89 mm(3) (p < 0.001), and weaker ultimate loads to failure of 69.56 ± 4.74 and 59.17 ± 7.48 N, respectively (p < 0.001). Our results suggest that the mechanical regulation approach deserves further investigation and may potentially offer a clinical strategy to improve synchronization.

Capability of new bone formation with a mixture of hydroxyapatite and beta-tricalcium phosphate granules

OBJECTIVES

The aim of this experimental study was to test a mixture of hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP) granules inserted in cranial defects in rabbits, by the evaluation of the hard tissues volume, new bone formation, and residual graft after 4 and 8 weeks.

MATERIAL AND METHODS

Two defects of 8 mm diameter were created at the calvarial bone of 24 Japanese white rabbits for a total of 48 defects. Four groups were created: defects filled with a mixture of HA and beta-TCP granules (test A), defects filled with HA alone (test B), defects filled with beta-TCP (test C), and empty defects (control). Hard tissues volume (remaining graft + new bone) was evaluated by μ-CT and new bone (NB) and remaining graft (RG) percentages were evaluated by histomorphometry. The animals were sacrificed at 4 or 8 weeks postoperatively.

RESULTS

The test groups A, B, and C showed a significant higher total volume compared with controls at 4 and 8 weeks (P < 0.05). Regarding the percentages of NB and RG at 4 and 8 weeks, no significant differences were detected (P > 0.05). When comparing 4 and 8 weeks, test group A showed a significant increase in new bone formation. At both 4 and 8 weeks, no group showed significant differences in NB (P > 0.05). At 8 weeks, test group B had more RG than test group A.

CONCLUSIONS

The novel mixture could maintain the volume of the grafted area compared with that with intervention, and in a similar way compared with HA.

Biodegradation process of α-tricalcium phosphate and α-tricalcium phosphate solid solution bioceramics in vivo: a comparative study

This article reports the structure and morphology of the in vivo interface between implants composed of either a tricalcium phosphate (αTCP) or αTCP doped with 3.0 wt% dicalcium silicate (αTCP(ss)) ceramic, and natural bone of rabbit tibias. Both interfaces developed a new bone layer in direct contact with the implants after 4 and 8 weeks of implantation. The specimens were examined using analytical scanning and transmission electron microscopy, up to the lattice plane resolution level. Degradation processes of the implants developed at the interfaces encouraged osseous tissue ingrowth into the periphery of the material, changing the microstructure of the implants. The ionic exchange initiated at the implant interface with the environment was essential in the integration process of the implant, through a dissolution–precipitation–transformation mechanism. The interfaces developed normal biological and chemical activities and remained reactive over the 8-week period. Organized collagen fibrils were found at the αTCP(ss)/bone interface after 4 weeks, whereas a collagen-free layer was present around the Si-free αTCP implants. These findings suggest that the incorporation of silicate ions into αTCP ceramic promotes processes of the bone remodeling at the bone/αTCP(ss) interface, hence the solubility rate of the aTCP(ss) material decreased.

Feasibility of alpha tricalcium phosphate for vertical bone augmentation

AIM

Inadequate vertical bone compromises dental implant positioning and subsequent restoration. This study was carried out to investigate the feasibility of alpha tricalcium phosphate (α-TCP) for vertical bone augmentation.

METHODS

Nine cortical perforations were made on each side of the parietal bone of rat calvaria under continuous saline coolant. Polytetrafluoroethylene cylinders were placed under the periosteum and α-TCP particles were applied in the cylinders in the TCP group while the cylinders were left empty in the control group. The animals were sacrificed at 4 and 8 weeks after surgery and analyzed radiologically and histologically.

RESULTS

The augmented bone volumes in the control and TCP groups were 91.5 ± 25.6% and 76.5 ± 49.8% (mean ± SD) of the original bone at 4 weeks, and 136.3 ± 59.7% and 139 ± 62.4% at 8 weeks respectively. There was no significant difference between control and test groups. At 4 weeks the bone height was augmented by 168.8 ± 26.7% and 128.8 ± 62% in the control and TCP groups respectively (not significant), whereas significantly higher vertical bone was achieved in the TCP group than in the control group at 8 weeks (251 ± 32% vs 179.2 ± 30.3%, P < 0.05).

CONCLUSION

After 8 weeks α-TCP is effective in maintaining space under periosteum and potentially would be applicable in vertical bone augmentation.

COMPARATIVE STUDY ON USE OF PLATELET-RICH PLASMA ALONE AND IN COMBINATION WITH ALPHA-TRICALCIUM PHOSPHATE CEMENT FOR BONE REPAIR IN RATS

Objectives: To evaluate the effect of alpha-tricalcium phosphate (α-TCP) cement combined with platelet-rich plasma (PRP) on osteogenesis, and to compare the results with use of PRP alone. Methods: A bilateral defect was produced in rat femurs and was filled with one of two types of treatments (PRP or α-TCP + PRP). The outcomes were evaluated after four and eight weeks. Radiographic images provided values for the lesion area, and histology (picrosirius staining) indicated the area of new bone formation. Results: The means relating to the lesion area of the α-TCP + PRP group (2.64 ± 2.07 and 1.91 ± 0.93 mm², after four and eight weeks, respectively) showed numerically better but non-significant results (p > 0.05) than those seen in the PRP group (5.59 mm 2 ± 2.69 and 3.23 ± 1.46 mm 2, after four and eight weeks, respectively). The mean new bone formation rates were 62.7% ± 12.1 and 79.01% ± 6.25 in the PRP group, and 73.3% ± 12.7 and 85.86% ± 10.45 in α-TCP + PRP group, after four and eight weeks, respectively (p > 0.05). Conclusion: The data from this study suggest that treatment with α-TCP cement combined with PRP does not show any significant difference in comparison with PRP alone. However, there is a possible early effect on bone regeneration when the two biomaterials are applied together.

Effects on bone regeneration when collagen model polypeptides are combined with various sizes of alpha-tricalcium phosphate particles

We evaluated the effects on bone formation of combining synthesized collagen model polypeptides consisting of a Pro-Hyp-Gly [poly(PHG)] sequence and alpha-tricalcium phosphate (α-TCP) particles with various median sizes (large: 580.8 μm; small: 136.2 μm; or large and small mixed: 499.3 μm) in a skull defect model in mini-pigs. Quantitative image analyses for the volume density (VD) of new bone revealed that the VD in each α-TCP group was significantly higher than that in the poly(PHG) control group, with the mixed group showing the highest VD among all the groups at 4 weeks after implantation. Histological assessments revealed that the small α-TCP particles were almost completely degraded at 8 weeks. At 12 weeks, all sizes of α-TCP particles were completely degraded and remodeling of the lamellar bone was observed. The present findings suggest that particle size may influence the success of bone formation in defects.

α-Tricalcium phosphate: synthesis, properties and biomedical applications

Nowadays, α-tricalcium phosphate (α-TCP, α-Ca(3)(PO(4))(2)) is receiving growing attention as a raw material for several injectable hydraulic bone cements, biodegradable bioceramics and composites for bone repair. In the phase equilibrium diagram of the CaO-P(2)O(5) system, three polymorphs corresponding to the composition Ca(3)(PO(4))(2) are recognized: β-TCP, α-TCP and α'-TCP. α-TCP is formed by heating the low-temperature polymorph β-TCP or by thermal crystallization of amorphous precursors with the proper composition above the transformation temperature. The α-TCP phase may be retained at room temperature in a metastable state, and its range of stability is strongly influenced by ionic substitutions. It is as biocompatible as β-TCP, but more soluble, and hydrolyses rapidly to calcium-deficient hydroxyapatite, which makes α-TCP a useful component for preparing self-setting osteotransductive bone cements and biodegradable bioceramics and composites for bone repairing. The literature published on the synthesis and properties of α-TCP is sometimes contradictory, and therefore this article focuses on reviewing and critically discussing the synthetic methods and physicochemical and biological properties of α-TCP-based biomaterials (excluding α-TCP-based bone cements).

Evaluation of the osteoconductivity of α-tricalcium phosphate, β-tricalcium phosphate, and hydroxyapatite combined with or without simvastatin in rat calvarial defect

The purpose of this study is to evaluate the osteoconductivity of three different bone substitute materials: α-tricalcium phosphate (α-TCP), (β-TCP), and hydroxyapatite (HA), combined with or without simvastatin, which is a cholesterol synthesis inhibitor stimulating BMP-2 expression in osteoblasts. We used 72 Wistar rats and prepared two calvarial bone defects of 5 mm diameter in each rat. Defects were filled with the particles of 500-750 μm diameter combined with or without simvastatin at 0.1 mg dose for each defect. In the control group, defects were left empty. Animals were divided into seven groups: α-TCP, β-TCP, HA, α-TCP with simvastatin, β-TCP with simvastatin, HA with simvastatin, and control. The animals were sacrificed at 6 and 8 weeks. The calvariae were dissected out and analyzed with micro CT. The specimens were evaluated histologically and histomorphometrically. In α-TCP group, the amount of newly formed bone was significantly more than both HA and control groups but not significantly yet more than β-TCP group. Degradation of α-TCP was prominent and β-TCP showed slower rate while HA showed the least degradation. Combining the materials with Simvastatin led to increasing in the amount of newly formed bone. These results confirmed that α-TCP, β-TCP, and HA are osteoconductive materials acting as space maintainer for bone formation and that combining these materials with simvastatin stimulates bone regeneration and it also affects degradability of α-TCP and β-TCP. Conclusively, α-TCP has the advantage of higher rate of degradation allowing the more bone formation and combining α-TCP with simvastatin enhances this property.

Implantation of green tea catechin α-tricalcium phosphate combination enhances bone repair in rat skull defects

The purpose of the present study is to investigate effects of the combination of epigallocatechin-3-gallate (EGCG) and α-tricalcium phosphate (α-TCP) on bone regenerative capacity in a bilateral rat calvarial bone defect model.

MATERIALS AND METHODS

Bilateral 5-mm-diameter calvarial defects were created in adult male Wistar rats and filled with preparations of EGCG (0, 0.1, 0.2, 0.4 mg) combined with α-TCP particles. This was done by dissolving EGCG in 100% ethanol (50 μL/14 mg) and dropping under sterile condition. The control group was left unfilled (n = 8). The animals were sacrificed at 2 and 4 weeks. Radiological images were taken, and histological analysis was done. Six animals from control (0 mg EGCG + α-TCP) group and (0.2 mg EGCG+ α-TCP) group were labeled with fluorescent dyes and histomorphometrically analyzed (n = 6) at 2 and 4 weeks.

RESULTS

Histomorphometric analysis revealed that the combination of EGCG and α-TCP at doses of 0.1 and 0.2 mg yielded significantly more new bone formation than untreated control group at 2 and 4 weeks (p > 0.05). Mineral apposition rate at 0.2-TCP group was enhanced compared with the one of the positive control α-TCP group at 4 weeks (p > 0.05).

CONCLUSION

The combination of α-TCP particles and 0.2 mg EGCG stimulates maximum bone regeneration in rat calvarial defects, and this combination would be potentially effective as bone graft material.

Surface characteristics of biomaterials used for space maintenance in a mandibular defect: a pilot animal study

PURPOSE

The purpose of the present study was to evaluate the effect of implant porosity on wound healing between solid and porous implants placed within a bony mandibular defect with intraoral exposure.

MATERIALS AND METHODS

Solid poly(methyl methacrylate) (PMMA) implants similar to those used currently in clinical space maintenance applications in maxillofacial surgery were compared with poly(propylene fumarate) implants that contained a porous outer surface surrounding a solid core. A 10-mm diameter nonhealing bicortical defect with open communication into the oral cavity was created in the molar mandibular region of 12 adult male New Zealand white rabbits. Of the 12 rabbits, 6 received the hybrid poly(propylene fumarate) implants and 6 received the solid PMMA implants. At 12 weeks, the rabbit mandibles were harvested and sent for histologic staining and sectioning.

RESULTS

Gross inspection and histologic examination showed all 6 poly(propylene fumarate) implants to be intact within the defect site at the termination of the study period, with 3 of the 6 specimens exhibiting a continuous circumferential soft tissue margin. In contrast, 5 of the 6 PMMA-implanted specimens were exposed intraorally with an incomplete cuff of soft tissue around the implant. One of the PMMA-implanted specimens exhibited complete extrusion and subsequent loss of the implant. Fisher's exact test was used to compare the occurrence of oral cavity wound healing between the 2 groups (P = .09).

CONCLUSIONS

Although statistically significant differences between the 2 groups were not seen, our results have indicated that advantages might exist to using porous implants for space maintenance. Additional study is needed to evaluate these findings.

Effects of the combination with alpha-tricalcium phosphate and simvastatin on bone regeneration

BACKGROUND

Although local application of statins stimulates bone formation, high dose of simvastatin induces inflammation.

OBJECTIVE

A study was conducted to test the hypothesis that maximum bone regeneration with less inflammation would be achieved by combining an optimal dose of simvastatin with alpha-tricalcium phosphate (alpha-TCP), which is an osteoconductive biomaterial capable of releasing the drug gradually.

MATERIAL AND METHODS

Bilateral 5-mm-diameter calvarial defects were created in adult Wistar rats and filled with preparations of different doses of simvastatin (0, 0.01, 0.1, 0.25 and 0.5 mg) combined with alpha-TCP particles or left empty. The animals were sacrificed at 2, 4 and 8 weeks and analyzed radiologically and histologically. Half of the animals of 4 and 8 weeks were labeled with fluorescence dyes and histomorphometrically analyzed.

RESULTS

Simvastatin doses of 0.25 and 0.5 mg caused inflammation of the soft tissue at the graft site whereas control and other doses did not. The micro-CT analysis revealed that the alpha-TCP with 0.1 mg simvastatin (TCP-0.1) group yielded significantly higher bone volumes than untreated control group at all three time points (249%, 227% and 266% at 2, 4 and 8 weeks, respectively). The percentage of defect closure, bone mineral content and bone mineral density were also higher in the TCP-0.1 group than in the other groups.

CONCLUSION

When combined with alpha-TCP particles, 0.1 mg simvastatin is the optimal dose for stimulation of the maximum bone regeneration in rat calvarial defects without inducing inflammation and it could be applied as an effective bone graft material.

Bone augmentation ability of autogenous bone graft particles with different sizes: a histological and micro-computed tomography study

OBJECTIVES

The purpose of this study was to investigate the augmentation process and ability of autogenous bone graft particles of two different sizes in a vertical augmentation chamber.

MATERIAL AND METHODS

The cranial bones of 24 rabbits were used. Two polytetrafluoroethylene chambers were filled with harvested bone from tibia with small bone (SB; 150-400 microm) and large bone (LB; 1.0-2.0 mm) of the same weight. Animals were sacrificed after 1, 2, 4 and 8 weeks. The samples were analyzed by micro-computed tomography (micro-CT) for quantitative analysis, and embedded in polyester resin as non-decalcified specimens for histological analysis. Total bone volume (TBV), bone height (BH) and distribution of bone structure were calculated by micro-CT.

RESULTS

Micro-CT evaluation and histology revealed a significant difference between the investigated specimens. TBV and BH of SB decreased to about 50% of the initial situation, and there was a statistically significant difference between 1 and 8 weeks. In contrast, TBV and BH of LB were almost retained at all experimental time points. Significant differences in TBV and BH were also observed between LB and SB at 8 weeks. Bone volume of SB decreased predominantly in the upper half of the chamber at 4 and 8 weeks. In the histological observations, SB showed favorable new bone formation and rapid bone resorption in a time-dependent manner during the entire experimental period. However, LB exhibited favorable morphological stability and continued new bone formation.

CONCLUSION

SB follows a smooth osteogenic process, whereas it is not effective in volume augmentation. LB is superior to SB in augmentation ability.