Treatment of peri-implant defects with combination growth factor cement

The Development of a Magnesium-Releasing and Long-Term Mechanically Stable Calcium Phosphate Bone Cement Possessing Osteogenic and Immunomodulation Effects for Promoting Bone Fracture Regeneration

Bone grafts are commonly used for the treatment of critical sized bone defects. Since the supply of autologous bone is insufficient, allogeneic bone grafts have been used most of the time. However, the poor osteogenic property of allogeneic bone grafts after pretreatment results in delayed union, non-union, or even occasional deformity. Calcium phosphate cement (CPC) is one of the most promising bone filling materials due to its good biocompatibility and similar chemical components as natural bone. However, clinical applications of CPC were hampered by limited osteogenic effects, undesired immune response which results in resorption, and poor mechanical stability in vivo. Magnesium (Mg) has been proven to trigger bone regeneration through modulating cell behaviors of mesenchymal stem cells and macrophages significantly. Unfortunately, the degradation raters of pure Mg and Mg oxide are extremely fast, resulting in early collapse of Mg contained CPC. In this study, we developed a novel magnesium contained calcium phosphate bone cement (Mg-CPC), possessing long-term mechanical stability and osteogenic effects through sustained release of Mg. Furthermore, in vitro studies showed that Mg-CPC had no cytotoxic effects on hBMMSCs and macrophage RAW 264.7, and could enhance the osteogenic differentiation as determined by alkaline phosphate (ALP) activity and calcium nodule staining, as well as suppress the inflammatory as determined by expression of anti-inflammatory cytokine IL-1RA. We also found that Mg-CPC promoted new bone formation and bone maturation in vivo. These results suggest that Mg-CPC should be a good substitute material for bone grafts in clinical use.

Molecular features and tissue engineering techniques applied to regenerative surgery: an overview of recent data

INTRODUCTION

Regenerative procedures have become common in the medical and dentistry rehabilitation fields. Often, tissue regeneration maneuvers are necessary to rehabilitate patients in a safe and predictable manner. The aim of this narrative review was to highlight the molecular implications during regenerative surgery.

EVIDENCE ACQUISITION

The analysis of the literature was conducted on the main scientific databases Pubmed, Scopus, MDPI.

EVIDENCE SYNTHESIS

After a screening of 66 results only 8 were included.

CONCLUSIONS

Knowing these molecular features, it is possible to highlight which are the biomaterials that offer greater potential and identify the best protocols according to the surgical needs.

Efficacy of growth factors for the treatment of peri-implant diseases: a systematic review and meta-analysis

OBJECTIVES

The aim of this study was to conduct a systematic review and meta-analysis on the efficacy of growth factors (GF) on clinical outcomes after treatment (surgical/non-surgical) of peri-implant diseases (peri-implant mucositis and peri-implantitis).

MATERIALS AND METHODS

A protocol was developed to answer the following focused question: Is there any difference for the use of GF for treatment of peri-implant diseases versus comparative GF treatment or without GF? Electronic database and manual searches were independently conducted to identify randomized controlled trials (RCTs). Publications were selected based on eligibility criteria and then assessed for risk-of-bias using the Cochrane Handbook. The primary outcome was probing depth (PD) and bleeding on probing (BOP) reduction along with changes in vertical defect depth (VDD). Changes in clinical attachment level, gingival recession, and plaque index, among others, were studied as secondary outcomes. Based on primary outcomes, random-effects meta-analysis was conducted.

RESULTS

A total of five RCTs were included. GF enhance the reduction of PD (standardized mean difference (SMD) = - 1.28; 95% confidence interval (CI) - 1.75, - 0.79; p = < 0.0001) and BOP (SMD = - 1.23; 95% CI - 1.70, - 0.76; p = < 0.0001) in the management of peri-implant mucositis. For the treatment of peri-implantitis, the use of GF yielded to significantly greater improvement in VDD (SMD = 0.68; 95% CI 0.22, 1.14; p = 0.004); however, there were no significant differences in terms of PD (SMD = 0.08; 95% CI - 1.08, 1.26; p = 0.887) and BOP (SMD = 0.211; 95% CI - 0.20, 0.63; p = 0.317). The overall risk of bias of the included studies was low to unclear.

CONCLUSION

The results of the present systematic review suggest that the addition of GF might enhance the outcomes in the treatment of peri-implant mucositis. However, there is a lack of evidence for supporting additional benefit of GF managing peri-implantitis.

CLINICAL RELEVANCE

Within the limitations of the current systematic review and based on the meta-analyses, (1) the addition of GF for the treatment peri-implant mucositis might be associated with better outcomes in terms of PD and BOP, and (2) an additional benefit of GF for the treatment peri-implantitis could not be determined on the basis of the selected evidence.

Role and influence of growth factors on early osseointegration in animal jaw bone: A meta-analysis

Aim:

Growth factors (GFs) are polypeptides, which are intricately involved in the regulation of bone formation, preservation, and regeneration through gene expression. However, the role of these bioactive agents in osseointegration of dental implants has not been substantially proven. The objective of this systematic review (SR) and meta-analysis was to explore the effect of GFs on early osseointegration of dental implants in animal jaws. An attempt to decipher an adjunctive role of GFs in modulating predictable bone growth in peri-implant areas was done.

Materials and Methods:

An electronic and manual search of different databases was performed. Only randomized controlled trials (RCTs) were included and reviewed. The risk of bias (ROB) of the selected studies was assessed using the SR Centre for Laboratory Animal Experimentation (Cochrane) tool. A meta-analysis was also performed to evaluate the different study characteristics quantitatively.

Statistical Analysis used:

The total Weighted mean difference was evaluated using the Rev-Manv5.3 algorithm. Chi-square test and I² test were done to assess the heterogeneity between the studies.

Results:

Seven RCTs were included in the study. These were associated with a high ROB. The total weighted mean difference (WMD) of the percentage of bone–implant contact was 3.25% (95% confidence interval [CI] = 1.49%–6.03%; P = 0.001; I² = 91%) between groups with and without exogenous application of GFs. The total WMD of the percentage of newly formed bone area was 4.48% (95% CI = 2.31%–5.90%; P < 0.00001, I² = 84%). A high level of heterogeneity (P < 0.001 for Chi-square test; I²>50 %) among comparable studies was observed.

Conclusion:

The ancillary application of external GFs exhibited evidence of early osseointegration, resulting in more predictable and faster results. However, a careful discernment of conclusions drawn from this SR is a must before conducting any human trials.

New approach for vertical bone regeneration using in situ gelling and sustained BMP-2 releasing poly(phosphazene) hydrogel system on peri-implant site with critical defect in a canine model

An injectable hydrogel system with sustained bone morphogenetic protein 2 (BMP-2) release ability was developed for vertical bone regeneration at peri-implant sites and enhanced osseointegration of dental implants. In three young male beagle dogs, a pair of defects was created on both sides of the mandibular bone. Next, two implants were transplanted into each defect. In situ gelling polymer solutions with or without BMP-2 were applied to cover the implants and mandibular defects. The effects of the in situ gelling and sustained BMP-2 releasing (IGSR) hydrogel system on peri-implant bone regeneration were evaluated by radiologic examination, micro-computed tomography, and histomorphometric analysis. Twelve weeks after the treatment, significant bone generation at the peri-implant site occurred following BMP-2/IGSR hydrogel treatment. Bone volume and mineral density were increased by 1.7- and 1.3-fold, respectively (p < 0.01 and 0.05 vs. control, respectively) for the BMP-2/IGSR hydrogel system. And, 0.57-0.31 mm vertical bone generation was observed at the peri-implant site for the BMP-2/IGSR hydrogel system, while rare vertical bone generation occurred in the control group. The BMP-2/IGSR hydrogel system significantly increased bone to implant contact % between induced bone and existing bone (p < 0.05 and 0.01 vs. control). These vertical bone regeneration and higher osseointegration levels demonstrated the effectiveness of the BMP-2/IGSR hydrogel system. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 751-759, 2018.

Self-setting calcium orthophosphate formulations

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are bioactive and biodegradable grafting bioceramics in the form of a powder and a liquid. After mixing, both phases form pastes, which set and harden forming either a non-stoichiometric calcium deficient hydroxyapatite or brushite. Since both of them are remarkably biocompartible, bioresorbable and osteoconductive, self-setting calcium orthophosphate formulations appear to be promising bioceramics for bone grafting. Furthermore, such formulations possess excellent molding capabilities, easy manipulation and nearly perfect adaptation to the complex shapes of bone defects, followed by gradual bioresorption and new bone formation. In addition, reinforced formulations have been introduced, which might be described as calcium orthophosphate concretes. The discovery of self-setting properties opened up a new era in the medical application of calcium orthophosphates and many commercial trademarks have been introduced as a result. Currently such formulations are widely used as synthetic bone grafts, with several advantages, such as pourability and injectability. Moreover, their low-temperature setting reactions and intrinsic porosity allow loading by drugs, biomolecules and even cells for tissue engineering purposes. In this review, an insight into the self-setting calcium orthophosphate formulations, as excellent bioceramics suitable for both dental and bone grafting applications, has been provided.

Modification of xenogenic bone substitute materials--effects on the early healing cascade in vitro

INTRODUCTION

Initial platelet activation with subsequent cytokine release at the defect site plays a crucial role in tissue integration. The aim of this study was to evaluate the influence of topographic and biomimetic collagen modifications of a xenogenic bone substitute material (BSM) on in vitro platelet activation and cytokine release.

MATERIAL AND METHODS

Three types of xenogenic BSM were used. Two BSM with different levels of granularity (large granule BSM [XBSM/L], small granule BSM [XBSM/S]) and a BSM with collagen (XBSM/C). All three samples were incubated with platelet concentrate of four healthy volunteers at room temperature for 15 min. For all groups, highly thrombogenic collagen type 1 served as a reference and an additional preparation with platelet concentrate only (without XBSM) served as control. Platelet count and cytokine release of VEGF, PDGF, TGF-β, and IGF into the supernatant were measured.

RESULTS

Compared with the control group, XBSM/C showed an increase in platelets consumption (mean 41,000 ± 26,000/ml vs. 471,000 ± 38,000/ml), cytokine release of VEGF (mean 46.8 ± 7.2 pg/ml vs. 18.8 ± 2.7 pg/ml), and PDGF (mean 18,350 ± 795 pg/ml vs. 2726 ± 410 pg/ml) but not IGF (194,728 ± 51,608 pg/ml vs. 1,333,911 ± 35,314 pg/ml). There was also an increase in cytokine release of TGF-ß in XBSM/C compared with XBSM/S (77,188 ± 27,413 pg/ml vs. 38,648 ± 13,191 pg/ml), but no such difference when compared with XBSM/L (77,188 ± 27,413 pg/ml vs. 53,309 ± 29,430 pg/ml). XBSM/L showed higher platelets consumption (301,000 ± 45,000 vs. 415,000 ± 98,000) and a higher cytokine release of PDGF (3511 ± 247 pg/ml vs. 3165 ± 78 pg/ml) compared with XBSM/S. There was no distinct difference in the levels of VEGF, TGF-ß, and IGF between XBSM/L and XBSM/S.

CONCLUSIONS

Topographic as well as biomimetic modifications of the xenogenic BSM showed an increased platelet activation and cytokine release in vitro. This effect on the intrinsic healing cascade could result in comparable enhanced soft- and hard-tissue regeneration in vivo.

Systematic review of pre-clinical models assessing implant integration in locally compromised sites and/or systemically compromised animals

OBJECTIVE

The aim was to systematically search the dental literature for pre-clinical models assessing implant integration in locally compromised sites (part 1) and systemically compromised animals (part 2), and to evaluate the quality of reporting of included publications.

METHODS

A Medline search (1966-2011) was performed, complimented by additional hand searching. The quality of reporting of the included publications was evaluated using the 20 items of the ARRIVE (Animals in Research In Vivo Experiments) guidelines.

RESULTS

One-hundred and seventy-six (part 1; mean ARRIVE score = 15.6 ± 2.4) and 104 (part 2; 16.2 ± 1.9) studies met the inclusion criteria. The overall mean score for all included studies amounted to 15.8 ± 2.2. Housing (38.3%), allocation of animals (37.9%), numbers analysed (50%) and adverse events (51.4%) of the ARRIVE guidelines were the least reported. Statistically significant differences in mean ARRIVE scores were found depending on the publication date (p < 0.05), with the highest score of 16.7 ± 1.6 for studies published within the last 2 years.

CONCLUSIONS

A large number of studies met the inclusion criteria. The ARRIVE scores revealed heterogeneity and missing information for selected items in more than 50% of the publications. The quality of reporting shifted towards better-reported pre-clinical trials within recent years.

Bone morphogenic protein-2 induces apoptosis and cytotoxicity in periodontal ligament cells

BACKGROUND

Periodontal ligament (PDL) expresses endogenous growth factors, such as bone morphogenic proteins (BMPs), which facilitate maintenance of tissue homeostasis. Inflammatory conditions, such as chronic periodontitis, could disrupt this homeostasis, and physiologic levels of growth factors may be insufficient to maintain tissue homeostasis. BMPs facilitate periodontal bone regeneration but also are implicated in causing tooth ankylosis and root resorption. The underlying mechanism of tooth ankylosis is unclear. However, there is evidence that BMPs induce apoptosis in progenitor cells. Little is known about BMP-induced cytotoxicity in PDL cells, which contain a population of progenitor cells. The aim of this study is to determine BMP2-induced osteogenic mediators and cytotoxic effects in PDL cells and compare these cells to osteoblasts.

METHODS

Human PDL cells and primary osteoblasts were stimulated with doses of 1 to 200 ng/mL BMP2. Expression of alkaline phosphatase (ALP), in vitro mineralization along with osteonectin expression, induction of apoptosis, and cytotoxicity assays were performed.

RESULTS

PDL cells and osteoblasts upregulated ALP and in vitro mineralization in a dose-dependent manner with BMP2 stimulation. However, at BMP2 concentrations >10 ng/mL, ALP, in vitro mineralization, and osteonectin were downregulated in PDL cells. Relative to osteoblasts, PDL cells were susceptible to apoptosis and cytotoxicity with 10 times lower concentration of BMP2.

CONCLUSIONS

Relative to osteoblasts, PDL cells are susceptible to BMP2-induced cytotoxicity. BMP-induced tooth ankylosis is controversial and is poorly understood. Disruption of PDL homeostasis by BMP-induced apoptosis could play a role in tooth ankylosis.

Doxycycline counteracts bone morphogenic protein 2-induced osteogenic mediators

BACKGROUND

Microbial colonization during wound healing may exaggerate the inflammatory response and could adversely affect the outcome of periodontal regeneration. Bone morphogenic proteins (BMPs) directly augment bone regeneration. Interestingly, inhibitors of tissue collagenases, such as sub-antimicrobial-dose doxycycline, also indirectly promote hard-tissue regeneration. In this study, it is hypothesized that BMP2-mediated bone regeneration would be positively affected by simultaneous treatment of sub-antimicrobial-dose doxycycline.

METHODS

Human periodontal ligament (PDL) cells were stimulated with: 1) 10 ng/mL BMP2; 2) 1 μg/mL doxycycline; or 3) a combination of the two. The expressions of alkaline phosphatase, osteocalcin, osteonectin, and osteopontin were analyzed along with in vitro mineralized nodule formation and calcium accumulation.

RESULTS

BMP2 was a potent inducer of osteocalcin/osteopontin (statistically significant at P <0.01) and osteonectin in PDL cells relative to stimulation with doxycycline. However, doxycycline relative to BMP2 (statistically significant at P <0.001) upregulated the expression of alkaline phosphatase and in vitro mineralized nodule formation. Contrary to expected results, combined BMP2 and doxycycline induced a statistically significant (P <0.001) downregulation of alkaline phosphatase, osteocalcin, osteonectin/osteopontin, and in vitro mineralized nodule formation compared to stimulation with either BMP2 or doxycycline alone.

CONCLUSIONS

Combined treatment of BMP2 and doxycycline in PDL cells counteracts the osteogenic mediators. Molecular interaction of growth factors should be explored before using a combination of these biologic molecules. It is important and clinically relevant to determine whether tetracycline and its other derivatives also counteract BMP functions. Animal models should be used to confirm these in vitro results.

Review paper: DNA delivery strategies to promote periodontal regeneration

Periodontal diseases are caused by bacteria with an inflammatory component that result in the loss of bone and soft tissue around the neck of the teeth. Recent therapies allow clinicians to regenerate some of the lost structures of the periodontium. Regeneration of these lost supporting structures is a highly orchestrated process, involving various cellular and molecular players, leading to the complete restoration of the periodontium (the tooth-supporting apparatus). The introduction of growth factors has positively influenced the clinical outcome of the existing regenerative procedures but the supra-physiological doses and the high cost associated with these growth factors can be drawbacks. Gene therapy may offer some interesting advantages to current therapies. In the field of periodontology, several studies have been conducted to explore the efficacy of delivering the DNA of key growth factors using viral vectors in both periodontal and peri-implant bone regeneration. Relatively few studies have explored the application of nonviral gene therapy in periodontal regeneration. This article is aimed at reviewing the studies conducted so far using viral and nonviral gene delivery approaches to achieve periodontal and peri-implant bone regeneration.

Platelet-poor plasma stimulates the proliferation but inhibits the differentiation of rat osteoblastic cells in vitro

INTRODUCTION

Recent studies have shown that the use of platelet preparations in bone and implant surgery might stimulate bone formation. However, the biological mechanisms are not well understood. Moreover, few studies have attempted to evaluate the effect of platelet-poor plasma (PPP), which is a product of the platelet-rich plasma preparation process.

OBJECTIVE

Thus, this study investigated the behavior of osteoblasts isolated from fetal rat calvaria cultivated in the presence of homologous PPP.

MATERIAL AND METHODS

PPP was obtained by centrifugation of the rat mother's blood and used in replacement of fetal calf serum, which is classically used in primary culture procedures. Proliferation was measured by an MTT assay at 24, 48, and 72 h. Real-time PCR was performed to study the expression of Runx2, Dlx5, and osteocalcin (OC) on days 0 (4 h), 1, 3, 7, and 12.

RESULTS

Alkaline phosphatase (ALP) biochemical activity was evaluated on days 0 (4 h), 1, 3, 7, and 12. Observations by phase-contrast microscopy showed that osteoblasts were able to differentiate until the mineralization of the matrix in the presence of PPP. PPP enhanced the proliferation significantly compared with the control group (P< or =0.001). PCR results showed that Runx2, Dlx5, and OC were expressed by cells in the experimental group at lower levels compared with the control group. Biochemical assay of ALP showed a lower activity in the experimental group compared with the control group (P<0.001).

CONCLUSION

These results suggest that, in the presence of homologous PPP, rat osteoblastic cells are able to maintain their phenotype, with a higher rate of proliferation. However, PPP seems to inhibit osteoblastic differentiation.

Calcium Orthophosphate Cements and Concretes

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are a bioactive and biodegradable grafting material in the form of a powder and a liquid. Both phases form after mixing a viscous paste that after being implanted, sets and hardens within the body as either a non-stoichiometric calcium deficient hydroxyapatite (CDHA) or brushite, sometimes blended with unreacted particles and other phases. As both CDHA and brushite are remarkably biocompartible and bioresorbable (therefore, in vivo they can be replaced with newly forming bone), calcium orthophosphate cements represent a good correction technique for non-weight-bearing bone fractures or defects and appear to be very promising materials for bone grafting applications. Besides, these cements possess an excellent osteoconductivity, molding capabilities and easy manipulation. Furthermore, reinforced cement formulations are available, which in a certain sense might be described as calcium orthophosphate concretes. The concepts established by calcium orthophosphate cement pioneers in the early 1980s were used as a platform to initiate a new generation of bone substitute materials for commercialization. Since then, advances have been made in the composition, performance and manufacturing; several beneficial formulations have already been introduced as a result. Many other compositions are in experimental stages. In this review, an insight into calcium orthophosphate cements and concretes, as excellent biomaterials suitable for both dental and bone grafting application, has been provided.

Assessment of the potential of growth factors for localized alveolar ridge augmentation: a systematic review

OBJECTIVE

To systematically assess the literature regarding the clinical, histological, and radiographic outcome of bone morphogenetic proteins (BMP-2, BMP-7), growth/differentiation factor-5 (GDF-5), platelet-derived growth factor (PDGF), and parathyroid hormone (PTH) for localized alveolar ridge augmentation.

MATERIAL AND METHODS

Five separate Medline searches were performed in duplicate for human and animal studies, respectively. The primary outcome of the included studies was bone regeneration of localized alveolar ridge defects or craniofacial defects.

RESULTS

In six human studies, BMP-2 affected local bone augmentation with increasing volume for higher doses. A majority (43 of 45) of animal studies using BMP-2 showed a positive effect in favour of the growth factor (GF). In six of eight studies, a positive effect was associated with the use of BMP-7. Only one animal study was included for GDF-5 revealing statistically significantly higher bone volume. Regarding PDGF, statistically significantly higher bone volume was observed in five of 10 included studies. Four animal studies using PTH revealed statistically significantly more bone regeneration compared with controls.

CONCLUSIONS

Differing levels and quantity of evidence were noted to be available for the GFs evaluated, revealing that BMP-2, BMP-7, GDF-5, PDGF, and PTH may stimulate local bone augmentation to various degrees. Human data for the potential of rhBMP-2 are supportive.

Next generation calcium phosphate-based biomaterials

It has been close to a century since calcium phosphate materials were first used as bone graft substitutes. Numerous studies conducted in the last two decades have produced a wealth of information on the chemistry, in vitro properties, and biological characteristics of granular calcium phosphates and calcium phosphate cement biomaterials. An in depth analysis of several key areas of calcium phosphate cement properties is presented with the aim of developing strategies that could lead to break-through improvements in the functional efficacies of these materials.

Interaction of bone morphogenetic proteins with cells of the osteoclast lineage: review of the existing evidence

The present review evaluates the existing scientific proofs of this supplementary role of the BMPs and summarises its clinical implications. Bone regeneration is a process consisting of bone formation and bone resorption, two different but closely coupling pathways, which in most circumstances proceed simultaneously. Plenty of evidence has also characterised the bone morphogenetic proteins (BMPs) as inducing factors of bone formation. However, there is also evidence that these multifunctioning proteins affect bone resorption and the osteoclast homeostasis utilising various pathways. The present review evaluates the existing scientific evidence of this supplementary role of the BMPs, and summarises its clinical implications.

Bone increase in rat tibiae by local administration of amino-terminally truncated rhFGF-4(73-206)

Fibroblast growth factor 4 (FGF-4) plays important roles in bone development during embryogenesis. Human FGF-4 consists of 206 amino acid residues. We produced amino-terminally truncated rhFGF-4, named rhFGF-4(73-206), that increases bone mineral density when systemically administered to mice. In the present study, we examined the effects of rhFGF-4(73-206) in bone after local administration. We injected 1 microg of rhFGF-4(73-206) into tibiae of 10-week-old Sprague-Dawley rats. At days 4 and 7, sets of animals were subjected for tibial bone marrow cell culture in an osteogenic medium. The bone marrow cells from FGF-4-injected tibiae produced more alkaline phosphatase-positive cells and mineralized nodules than those from control tibiae, indicating that local injection of rhFGF-4(73-206) increased the osteoblastic population in the bone marrow. The remaining sets of animals were killed on days 7 and 10. The tibiae were then analyzed with soft X-ray, dual energy X-ray absorptiometry, peripheral quantitative computed tomography, and histomorphometry. The radiographic analyses revealed increases in trabecular bone in the tibiae but no difference in the cortical bone between the rhFGF-4(73-206) group and the control group. High bone turnover and a derived increase of trabecular bone mineral density were demonstrated by histomorphometry in the rhFGF-4(73-206) group. The present results indicate that local injection with rhFGF-4(73-206) elicited an increase in the osteogenic cell population in the tibial bone marrow, which resulted in more trabecular bone.

In vivo release of rhBMP-2 loaded porous calcium phosphate cement pretreated with albumin

In this study, the release of rhBMP-2 loaded porous Ca-P cement was studied in vitro and in vivo. We hypothesized that adsorption sites of Ca-P ceramic with high affinity for rhBMP-2 can be blocked by pretreatment of the ceramic with albumin prior to rhBMP-2 loading, which would result in weaker rhBMP-2 binding and enhanced release of rhBMP-2. Preset porous Ca-P cement discs with a diameter of 6.35 mm (volume: 75 mm3) were pretreated by incubation in a solution of 10% rat serum albumin for 24 h or in ddH2O (control group) prior to administration of 5 mug radiolabeled 131I-rhBMP-2. Release was assessed in vitro in phosphate buffered saline (PBS) and fetal calf serum and in vivo by longitudinal scintigraphic imaging of radiolabeled 131I-rhBMP-2 and gamma counting of dissected implants. In vitro release from pretreated discs was higher during the first day. For both formulations, release in PBS was limited compared to release in serum. In vivo release considerably exceeded in vitro release. In vivo release kinetics showed no significant difference of half-lives between pretreated and control discs. Both formulations showed sustained release during at least 4 weeks. Ex vivo gamma counting of retrieved samples confirmed scintigraphic results and showed that the capsule and surrounding tissues only contained a minor fraction rhBMP-2. We conclude that 1. scintigraphy of 131I-labeled rhBMP-2 provides a reliable method for longitudinal measurement of rhBMP-2 release kinetics in vivo. 2. albumin pretreatment of porous Ca-P cement does not results in relevant increase of initial release of rhBMP-2 in vivo, and 3. preset rhBMP-2 loaded porous Ca-P cement discs exhibit one phase exponential release kinetics in the rat ectopic model, characterized by a retention of 20-30% after 4 weeks.

Gene therapeutics for periodontal regenerative medicine

There has been significant advancement in the field of periodontal tissue engineering over the past decade for the repair of tooth-supporting structures. Although encouraging results for periodontal tissue regeneration have been found in numerous clinical investigations using recombinant growth factors, limitations exist with topical protein delivery. Newer approaches seek to develop methodologies that optimize growth factor targeting to maximize the therapeutic outcome of periodontal regenerative procedures. Genetic approaches in periodontal tissue engineering show early progress in achieving delivery of growth factor genes, such as platelet-derived growth factor or bone morphogenetic protein, to periodontal lesions. Ongoing investigations in ex vivo and in vivo gene transfer to periodontia seek to examine the extent of the potential effects in stimulating periodontal tissue engineering.

The Effect of Combination of Recombinant Human Bone Morphogenetic Protein-2 and Basic Fibroblast Growth Factor or Insulin-Like Growth Factor-I on Dental Implant Osseointegration by Confocal Laser Scanning Microscopy

BACKGROUND

The healing period of bone-implant osseointegration usually varies from 3 to 6 months or even longer. Failure may occur during this time. This study aimed to investigate whether osseointegration of dental implants can be enhanced by the combination of growth factors.

METHODS

Sixty-four implants were coated with polylactic acid and divided into four groups. Group I was applied with 1.0 mg recombinant human bone morphogenetic protein-2 (rhBMP-2) and 200 microg recombinant human basic fibroblast growth factor (rhbFGF), group II with 1.0 mg rhBMP-2 and 250 mug recombinant human insulin-like growth factor-I (rhIGF-I), group III with 1.0 mg rhBMP-2, and group IV without growth factors as control. In total, 16 rabbits were used, and two osteotomies were drilled on each side of the femur, in which four different groups were randomly placed. Four weeks after implanting, 20 mg calcein green/kg body weight was administered intravenously, and 8 weeks after implanting, 20 mg alizarin/kg body weight was administered intravenously. Twelve weeks after implanting, the animals were sacrificed. The block of bone with implants was embedded in methylmethacrylate and sectioned, and the percentage of new bone surrounding the implant was analyzed by confocal laser scanning microscopy.

RESULTS

There was a statistical difference in bone formation between rhBMP-2-applied groups and the non-applied group at 4 or 8 weeks, and no significant difference between groups I and II (although bone formation in group II was greater than that in group I at 4 weeks). The bone formation in group II was greater than that in group III at 4 or 8 weeks. The formed bone in group I was also greater than the one in group III at 8 weeks, but there was no difference at 4 weeks.

CONCLUSIONS

rhBMP-2 could increase new bone formation, and it acted synergistically with rhbFGF and rhIGF-I to improve bone-implant osseointegration. The combination of rhBMP-2 and rhbFGF (group 1) showed faster growth of new bone than other groups at 8 months.

The effect of platelet-rich plasma on the cellular response of rat bone marrow cells in vitro

The aim of this study was to investigate the effect of platelet-rich plasma (PRP) on the proliferation and the differentiation of rat bone marrow cells (RBMCs). PRP, platelet-poor plasma (PPP), and bone marrow cells were derived from the rats (hearts and tibia) and the cells were cultured with or without PRP or PPP (0 [control]), 0.2 approximately 10 microL/mL). The proliferation of RBMCs was measured on days 2 and 4, and alkaline phosphatase (ALP) staining and activity measurement were evaluated to determine the effect of PRP on the differentiation on days 4 and 8. PRP enhanced the proliferation significantly compared to the control group (P < .05). These enhancements were greater than ones induced by the addition of PPP. ALP staining appeared to show that PRP decreased the number of ALP positive cells and ALP activity significantly (P < .05). Our results demonstrate that PRP stimulates the proliferation but suppresses the differentiation of RBMCs.

The contribution of platelet-derived growth factor, transforming growth factor-beta1, and insulin-like growth factor-I in platelet-rich plasma to the proliferation of osteoblast-like cells

The aim of this study was to investigate the effect of platelet-rich plasma (PRP) on the proliferation of osteoblast-like cells in vitro. PRP was prepared using a centrifuge; the number of platelets (n = 32) and the levels of platelet-derived growth factor-AB (PDGF-AB), transforming growth factor-beta1 (TGF-beta1), and insulin-like growth factor-I (IGF-I) were measured (n = 16). For the proliferation assay, SaOS-2 was cultured in the presence of platelet-poor plasma (PPP), whole blood, or PRP. The cell number was counted after 36 and 72 hours. To investigate the effect of each growth factor, the cells were cultured with PRP in the absence or presence of neutralizing antibodies, and counted as described. The mean platelet count of PRP was 1546.36 +/- 382.25 x 10(3)/microL, and the mean levels of PDGF-AB, TGF-beta1 and IGF-I were 0.271 +/- 0.043, 0.190 +/- 0.039, and 0.110 +/- 0.039 ng/1500 x 10(3) platelets, respectively. Cell proliferation was enhanced in all PRP groups in a dose-dependent manner, and all neutralizing antibodies significantly suppressed proliferation compared with the PRP group, lacking antibody, at 36 hours. However, at 72 hours, the neutralizing antibodies of PDGF and TGF-beta1, but not IGF-I, significantly suppressed proliferation. These results show the beneficial abilities of PRP in the proliferation of osteoblast-like cells from the standpoint of growth factors, including the contribution of each factor.

Effects of calcium and thrombin on growth factor release from platelet concentrates: kinetics and regulation of endothelial cell proliferation

Platelet concentrates (PCs) constitute new biological mediators used in osseous reconstructive surgery. In this study, we assessed (i) the effects of various concentrations of calcium and thrombin on the kinetics of platelet-derived growth factor (PDGF-BB), transforming growth factor-beta1(TGF-beta 1), basic fibroblast growth factor (bFGF), and vascular endothelial growth factor (VEGF) release by PCs and (ii) the contribution of PC supernatants to endothelial cell proliferation. Our results indicate that high concentrations of calcium (Ca) and thrombin (Thr) trigger an immediate and significant increase in bFGF, TGF-beta 1 and PDGF-BB concentrations. Thereafter, PDGF-BB, VEGF and TGF-beta 1 levels remained generally constant over a 6-day period while a decrease in bFGF concentrations was noted after 24h. Lower Ca and Thr concentrations tended to reduce and delay growth factors release from PCs. Endothelial cell proliferation was greatly enhanced with PC supernatants (mean: 20-fold increase). This was especially evident when endothelial cells were treated with supernatants harvested early after PC treatment with high concentrations of Ca and Thr or later after PC treatment with low Ca and Thr concentrations. Additional research aiming to measure the effects of Ca and Thr on bone formation in vivo is needed.

Repair of calvarial defects in rats by prefabricated hydroxyapatite cement implants

The aim of the present study was to test the hypothesis that calvarial defects can be repaired by using preformed implants of calcium phosphate bone cement (CPBC) in rats. Sixty adult female Sprague-Dawley rats received full-thickness calvarial nonhealing defects with a diameter of 8 mm. Three different CPBCs were used: group 1: tetracalcium phosphate-based powder; group 2: a blend of amorphous and crystalline calcium phosphate precursors; and group 3: an alpha-tricalcium phosphate (alpha-TCP)-based powder. Implants were left to cure for 25-40 min at room temperature in a silicon mold of 7.9 mm and inserted press fit into the defects. Fifteen animals served as unfilled controls. After 13, 26, and 52 weeks, the material was analyzed qualitatively by using surface-stained undecalcified thick-section specimens and quantitatively by using semiautomated histometry. Kruskal-Wallis tests were applied to compare mean values of periimplant bone formation at a significance level of p < 0.05. Three implants of group 1 fractured during insertion. Resorption of CPBC without complementary bone formation was noticed in these implants. Unfractured implants were resorbed with simultaneous apposition of bone on the implant surface. After 52 weeks, the resorption rate varied between 23.1 and 39.3%. Periimplant bone formation increased continuously on average around all implant types, but it reached statistical significance only in group 2. The results showed that repair of calvarial defects can be achieved by preformed CPBC implants. The rate of resorption of preformed implants is, however, much lower than that reported for in vivo cured CPBC.

Platelet Concentrates: Effects of Calcium and Thrombin on Endothelial Cell Proliferation and Growth Factor Release

BACKGROUND

Clinical evidence suggests that platelet concentrate (PC) could have beneficial therapeutic effects on hard and soft tissue healing, due to the contents of growth factors (GFs) stored in the platelets. The objectives of this study were: 1) to determine the concentrations of platelet-derived growth factor-BB (PDGF-BB), transforming growth factor-beta1 (TGF-beta1), vascular endothelial growth factor (VEGF), and basic fibroblast growth factor (bFGF) released from PCs and whole blood (WB), before and after the addition of various concentrations of calcium and thrombin, and 2) to assess the physiological importance of the released GFs on angiogenesis.

METHODS

WB and PCs were harvested and prepared from three healthy volunteers. Enzyme-linked immunosorbent assay tests, specific for PDGF-BB, TGF-beta1, VEGF, and bFGF, were performed on WB and PC supernatants, collected before and 30 minutes after the addition of various concentrations of calcium and thrombin. The supernatants were also added to human umbilical vein endothelial cell (HUVEC) cultures in order to measure their effects on endothelial cell proliferation.

RESULTS

Growth factor concentrations detected in PC supernatants were significantly greater (280% to 800% increase) than concentrations present in WB supernatants. Calcium and thrombin induced immediate GF release from PCs in a dose-dependent fashion. Furthermore, PC supernatants led to greater HUVEC proliferation rates than WB supernatants. However, there was no correlation between the concentrations of specific GFs and HUVEC proliferation rates.

CONCLUSION

These results suggest that PCs could stimulate blood vessel formation. They also reinforce the relevance for using PCs in regenerative therapies.

A resorbable porous ceramic composite bone graft substitute in a rabbit metaphyseal defect model

The success of converted corals as a bone graft substitute relies on a complex sequence of events of vascular ingrowth, differentiation of osteoprogenitor cells, bone remodeling and graft resorption occurring together with host bone ingrowth into and onto the porous coralline microstructure or voids left behind during resorption. This study examined the resorption rates and bone infiltration into a family of resorbable porous ceramic placed bilaterally in critical sized defects in the tibial metaphyseal-diaphyseal of rabbits. The ceramics are made resorbable by partially converting the calcium carbonate of corals to form a hydroxyapatite (HA) layer on all surfaces. Attempts have been made to control the resorption rate of the implant by varying the HA thickness. New bone was observed at the periosteal and endosteal cortices, which flowed into the centre of the defect supporting the osteoconductive nature of partially converted corals. The combination of an HA layer and calcium carbonate core provides a composite bone graft substitute for new tissue integration. The HA-calcium carbonate composite demonstrated an initial resorption of the inner calcium carbonate phase but the overall implant resorption and bone ingrowth behaviour did not differ with HA thickness.

FGF-4 and titanium implants: a pilot study in rabbit bone

AIM

To evaluate the effect of a local single injection of amino-terminally truncated recombinant human fibroblast growth factor-4 (rhFGF-4s) on titanium implant incorporation in a rabbit bone.

MATERIAL AND METHODS

Thirty-six threaded titanium implants were inserted into the femur and tibia of six rabbits. Three weeks prior to implant insertion 10 microg of FGF-4 in an altelocollagen carrier or the carrier alone was injected into the intended implant sites. Biomechanical evaluation by (i) resonance frequency analysis and (ii) peak removal torque measurements was performed after 6 weeks. The implants with surrounding tissue were processed to undecalcified ground sections followed by light-microscopic quantifications of the bone in threaded area and the apical parts of the implants.

RESULTS

A general trend, however not statistically significant, with higher mean values obtained in the above-mentioned tests was found. The FGF-4-treated implants revealed a significantly increased bone area in the apical part of the implants compared to the corresponding control implants.

CONCLUSION

A local single injection of rhFGF-4 may stimulate bone formation around titanium implants in bone. However, further research is required to confirm these results, understand the mechanisms of FGF, and establish optimal dose and delivery methods.

Porous titanium-nickel for intervertebral fusion in a sheep model: part 1. Histomorphometric and radiological analysis

Porous titanium-nickel (PTN) implants represent an alternative to traditional intervertebral fusion cages. Indeed, PTN materials possess interconnecting pores with cell capillarity properties that may promote bone ingrowth and intervertebral fusion without the need for bone grafting. In this study, a PTN intervertebral fusion device was compared to a conventional TiAlV cage packed with autologous bone in a sheep model. The two devices were implanted at two noncontiguous intervertebral lumbar sites for 3, 6, and 12 months. PTN osseointegration showed a time-dependent trend increasing from 21.4% to 37.6% (3-12 months), whereas TiAlV cages remained at the same level of bone ingrowth (22.7%-25.4%; 3-12 months). Furthermore, PTN bone apposition (10.9%-24.2%; 3-12 months) was significantly higher than that of TiAlV implants (1.1%-5.1%; 3-12 months; p < 0.001, ANOVA). Radiological fusion scores increased with postsurgery time regardless of material type, but were consistently superior for PTN (12.5-18.5; 3-12 months) than for TiAlV cages (2.0-15.0; 3-12 months; p < 0.001, ANOVA). Implant materials were not significantly different according to the radiological interbody index based on preoperative disc height: Interbody index began at 132.6% (PTN) and 123.5% (TiAlV) immediately after surgery, then declined to 80.8% (PTN) and 91.0% (TiAlV) after 12 months. Nevertheless, ungrafted PTN constituted an excellent substrate for osteogenic cell integration and represents a new osteoconductive biomaterial with improved fusion characteristics in comparison to conventional TiAlV cages.

Bone growth factors in maxillofacial skeletal reconstruction

A literature review was performed to survey the available information on the potential of bone growth factors in skeletal reconstruction in the maxillofacial area. The aim of this review was to characterize the biological and developmental nature of the growth factors considered, their molecular level of activity and their osteogenic potential in craniofacial bone repair and reconstruction. A total of 231 references were selected for evaluation by the content of the abstracts. All growth factors considered have a fundamental role in growth and development. In postnatal skeletal regeneration, PDGF plays an important role in inducing proliferation of undifferentiated mesenchymal cells. It is an important mediator for bone healing and remodelling during trauma and infection. It can enhance bone regeneration in conjunction with other growth factors but is unlikely to provide entirely osteogenic properties itself. IGFs have an important role in general growth and maintenance of the body skeleton. The effect of local application of IGFs alone in craniofacial skeletal defects has not yet shown a clear potential for enhancement of bone regeneration in the reported dosages. The combination of IGF-I with PDGF has been effective in promoting bone regeneration in dentoalveolar defects around implants or after periodontal bone loss. TGFbeta alone in skeletal reconstruction appears to be associated with uncertain results. The presence of committed cells is required for enhancement of bone formation by TGFbeta. It has a biphasic effect, which suppresses proliferation and osteoblastic differentiation at high concentrations. BMPs, BMP2, BMP4 and BMP7 in particular, appear to be the most effective growth factors in terms of osteogenesis and osseous defect repair. Efficacy of BMPs for defect repair is strongly dependent on the type of carrier and has been subject to unknown factors in clinical feasibility trials resulting in ambiguous results. The current lack of clinical data may prolong the period until this factor is introduced into routine clinical application. PRP is supposed to increase proliferation of undifferentiated mesenchymal cells and to enhance angiogenesis. There is little scientific evidence about the benefit of PRP in skeletal reconstructive and preprosthetic surgery yet and it is unlikely that peri-implant bone healing or regeneration of local bone into alloplastic material by the application of PRP alone will be significantly enhanced.

Injectable calcium phosphate cement as a filler for bone defects around oral implants: an experimental study in goats

The aim of this study was to evaluate the clinical applicability and biological behavior of a newly developed injectable calcium phosphate (Ca-P) cement as bone filler for gaps around oral implants. Twenty-four step-like implants, creating gaps of 1 and 2 mm, were inserted into the trabecular bone of the medial femoral condyles of six goats. Four different situations were tested: (1) implant + gaps; (2) implant + gaps, but covered with a polylactic acid membrane; (3) implant + gaps that were filled with Ca-P cement; and (4) implant + gaps that were filled with Ca-P cement and covered with a membrane. All implants were left in place for 12 weeks. Histological and quantitative histomorphometrical measurements demonstrated that implants + gaps had generally poor bone contact at the implant base. Furthermore, fibrous encapsulation was observed in the gap part. In contrast, the presence of a membrane promoted bone ingrowth into the gap and also the bone contact at the implant base. Injection of Ca-P cement resulted in an almost complete filling of the gaps around the implant. The cement surface was completely covered by bone. Active resorption and remodeling of cement particles was observed, suggesting a pattern of slow resorption associated with full replacement with newly formed bone. Additional use of a membrane did not result in adjunctive benefits. Bone-to-implant contact at the implant base was comparable with the implants provided only with a membrane. In conclusion, the Ca-P cement used here showed excellent clinical handling properties combined with a superior bone behavior. On the other hand, the degradation rate of the material was still very slow. This current characteristic can hamper the final clinical applicability of the material as gap filler for periimplant or periodontal defects.

Effect of four acrylic bone cements on transforming growth factor-beta1 expression by osteoblast-like cells MG63

Based on the hypothesis that bone cements cause changes in the production of transforming growth factor-beta 1 (TGF-beta1) by bone cells, the effects of four acrylic bone cements (Sulfix-60, CMW 1, CMW 2 and CMW 3) were examined using the osteoblast-like cell line MG63. The extracts in MEM of the cements were tested, following 1 h- and 7 day-curing. MG63 cells seldom expressed mRNA specific for TGF-beta1 in basal conditions. The cultures expressed mRNA constantly after incubation with the extract of CMW 1 cured for 1 h. TGF-beta1 specific mRNA was seldom expressed after incubation with the other cement extracts. The release of TGF-beta1 into the conditioned medium was increased significantly by CMW 1 extract at 1 h-curing, but was not changed significantly by CMW 1 extract at 7 day-curing and by the extracts of the other cements, at both curing times. The stimulating effect of CMW 1 on the secretion of TGF-beta1, even with all the restrictions of an in vitro study of continuous cell lines, if confirmed in vivo, might favor the development of the synovial-like membrane around the implant, and therefore impair the chance of success of the prosthesis.