Staged implant placement after defect regeneration using biphasic calcium phosphate materials with different surface topographies in a minipig model

OBJECTIVE

To assess the influence of biphasic calcium phosphate materials with different surface topographies on bone formation and osseointegration of titanium implants in standardized alveolar ridge defects.

MATERIALS AND METHODS

Standardized alveolar ridge defects (6 × 6 mm) were created in the mandible of 8 minipigs and filled with three biphasic calcium phosphate materials (BCP1-3, 90% tricalcium phosphate/10% hydroxyapatite) with different surface properties (micro- and macroporosities) as well as a bovine-derived natural bone mineral (NBM) as a control. At 12 weeks, implants were placed into the augmented defects. After further 8 weeks of healing, dissected blocks were processed for histological analysis (e.g., mineralized (MT), residual bone graft material (BS), bone-to-implant contact (BIC)).

RESULTS

All four biomaterials showed well-integrated graft particles and new bone formation within the defect area. MT values were comparable in all groups. BS values were highest in the NBM group (21.25 ± 13.52%) and markedly reduced in the different BCP groups, reaching statistical significance at BCP1-treated sites (9.2 ± 3.28%). All test and control groups investigated revealed comparable and statistically not significant different BIC values, ranging from 73.38 ± 20.5% (BCP2) to 84.11 ± 7.84% (BCP1), respectively.

CONCLUSION

All bone graft materials facilitated new bone formation and osseointegration after 12 + 8 weeks of healing.

Clinical Evaluation of Three Types of CAD/CAM Inlay/ Onlay Materials After 1-Year Clinical Follow Up

OBJECTIVE

To evaluate the clinical performance and the marginal adaptation of inlay/ onlay restorations made of lithium of a new lithium disilicate strengthened, lithium alumino-silicate glass-ceramic (LAS) material compared with a conventional lithium-disilicate glass-ceramic (LDS) and new-generation polymer-based CAD/CAM resin composite (CS) materials over one year.

MATERIALS AND METHODS

Seventy-five inlay-onlay restorations were placed in 35 patients. The restorations were assigned and randomized to three groups as LDS, LAS, and CS. Clinical evaluations were performed after one week, six months, and one year after the cementation, according to the modified United States Public Health Services (USPHS) criteria. The marginal quality analyses of 21 samples (n=7) were assessed under a scanning electron microscope. The data were analyzed by using Friedman, Wilcoxon Signed Ranks, Chi-square and Paired t-tests (p⟨0.05).

RESULTS

No statistically significant difference (p⟩0.05) was found between groups in the modified USPHS, gingival index, and plaque index evaluations, and the total success rate was 100% for three groups after one year. Following SEM evaluations in all groups, continuous margin percentages were decreased, but these results were not statistically significant (p⟩0.05).

CONCLUSIONS

Lithium disilicate-strengthened lithium aluminosilicate glass-ceramics can be considered a reliable material for an option for posterior onlay/inlay restorations.

Tapered Implants in Dentistry: Revitalizing Concepts with Technology: A Review

The most common approach to lessen treatment times is by decreasing the healing period during which osseointegration is established. Implant design parameters such as implant surface, primary stability, thread configuration, body shape, and the type of bone have to be considered to obtain this objective. The relationship that exists between these components will define the initial stability of the implant. It is believed implant sites using a tapered design and surface modification can increase the primary stability in low-density bone. Furthermore, recent experimental preclinical work has shown the possibility of attaining primary stability of immediately loaded, tapered dental implants without compromising healing and rapid bone formation while minimizing the implant stability loss at compression sites. This may be of singular importance with immediate/early functional loading of single implants placed in poor-quality bone. The selection of an implant that will provide adequate stability in bone of poor quality is important. A tapered-screw implant design will provide adequate stability because it creates pressure on cortical bone in areas of reduced bone quality. Building on the success of traditional tapered implant therapy, newer tapered implant designs should aim to maximize the clinical outcome by implementing new technologies with adapted clinical workflows.

Effect of Osteotomy Preparation on Osseointegration of Immediately Loaded, Tapered Dental Implants

The aim of the present preclinical in vivo study was to evaluate whether a modified "drill-only" protocol, involving slight underpreparation of the implant site, may have an effect on aspects of osseointegration of a novel bone-level tapered implant, compared with the "standard drilling" protocol involving taping and profiling of the marginal aspect of the implant socket. In each side of the edentulated and completely healed mandible of 11 minipigs, 2 tapered implants (8 mm long × 4.1 mm Ø, BLT; Institut Straumann AG, Basel, Switzerland) were installed either with the drill-only or the standard drilling protocol. Significantly lower average insertion torque values were recorded for the standard drilling protocol group (52 ± 29 Ncm) compared with the drill-only group (70 ± 27 Ncm) (t test, P ≤ 0.05); no significant difference was observed between the 2 groups regarding implant stability, by means of resonance frequency analysis (75 ± 8 vs. 75 ± 6, respectively). Half of the implants were immediately loaded and the rest were submerged, providing observation times of 8 or 4 wk, respectively. Non-decalcified histological and histomorphometric analysis of the implants with surrounding tissues showed no significant differences between the 2 drilling protocols regarding the distance from the implant platform to the first coronal bone-to-implant contact (f-BIC), the total bone-to-implant contact (BIC) as a percentage of the total implant perimeter, and the bone density in an area extending 1 mm laterally from the implant (BATA) within 2 rectangular regions of interest (ROIs) 4 mm in height, representing the coronal (parallel-walled) and apical (tapered) aspect of the implant (ROI 1 and ROI 2, respectively) in non-submerged implants. In general, marginal peri-implant bone levels were at or slightly apical to the implant platform, and large amounts of bone-to-implant contact were observed. In contrast, immediately loaded implants placed with the drill-only protocol showed statistically significantly lower BIC values (66% ± 13.7%) compared with those installed with the standard drilling protocol (74.8% ± 11.2%) (P = 0.018). In addition, although marginal bone levels were in most of the immediately loaded implants at or slightly apical to the implant platform, some of the implants installed with the drill-only protocol showed marginal bone loss and crater formation. Thus, in this model system, even slight underpreparation of the implant socket appeared to compromise osseointegration of immediately loaded bone-level tapered implants.

Enamel Matrix Derivative Promotes Human Periodontal Ligament Cell Differentiation and Osteoprotegerin Production in vitro

Enamel matrix derivative (EMD) has been used successfully to aid periodontal repair. We sought to elucidate the mechanism of action of EMD and hypothesized that combined exposure to EMD and parathyroid hormone (PTH), which acts anabolicly when administered intermittently, would enhance periodontal ligament cell proliferation, differentiation, and local factor production. Confluent human periodontal ligament cells were exposed to EMD continuously or to PTH(1-34) intermittently, or a combination of both. Cell number, alkaline phosphatase activity, osteocalcin, and osteoprotegerin production were determined. Continuous challenge with EMD resulted in an increase of the differentiation parameters and osteoprotegerin production, while simultaneously inhibiting proliferation. Intermittent PTH(1-34) administration exerted opposite effects. Combined administration of EMD and PTH(1-34) weakened or even nullified the effects seen for the agents alone. These results suggest that EMD promotes periodontal ligament cell differentiation and osteoprotegerin production, potentially resulting in a microenvironment supporting periodontal repair, whereas combining EMD and PTH(1-34) failed to prove beneficial in this respect.

Integrative Performance Analysis of a Novel Bone Level Tapered Implant

Primary mechanical stability, as measured by maximum insertion torque and resonance frequency analysis, is generally considered to be positively associated with successful secondary stability and implant success. Primary implant stability can be affected by several factors, including the quality and quantity of available bone, the implant design, and the surgical procedure. The use of a tapered implant design, for instance, has been shown to result in good primary stability even in clinical scenarios where primary stability is otherwise difficult to achieve with traditional cylindrical implants—for example, in soft bone and for immediate placement in extraction sockets. In this study, bone-type specific drill procedures are presented for a novel Straumann bone level tapered implant that ensure maximum insertion torque values are kept within the range of 15 to 80 Ncm. The drill procedures are tested in vitro using polyurethane foam blocks of variable density, ex vivo on explanted porcine ribs (bone type 3), and finally in vivo on porcine mandibles (bone type 1). In each test site, adapted drill procedures are found to achieve a good primary stability. These results are further translated into a finite element analysis model capable of predicting primary stability of tapered implants. In conclusion, we have assessed the biomechanical behavior of a novel taper-walled implant in combination with a bone-type specific drill procedure in both synthetic and natural bone of various types, and we have developed an in silico model for predicting primary stability upon implantation.

Small-sized granules of biphasic bone substitutes support fast implant bed vascularization

The present study investigated the influence of granule size of 2 biphasic bone substitutes (BoneCeramic® 400–700 μm and 500–1000 μm) on the induction of multinucleated giant cells (MNGCs) and implant bed vascularization in a subcutaneous implantation model in rats. Furthermore, degradation mechanisms and particle phagocytosis of both materials were examined by transmission electron microscopy (TEM). Both granule types induced tissue reactions involving primarily mononuclear cells and only small numbers of MNGCs. Higher numbers of MNGCs were detected in the group with small granules starting on day 30, while higher vascularization was observed only at day 10 in this group. TEM analysis revealed that both mono- and multinucleated cells were involved in the phagocytosis of the materials. Additionally, the results allowed recognition of the MNGCs as the foreign body giant cell phenotype. Histomorphometrical analysis of the size of phagocytosed particles showed no differences between the 2 granule types. The results indicate that granule size seems to have impact on early implant bed vascularization and also on the induction of MNGCs in the late phase of the tissue reaction. Furthermore, the results revealed that a synthetic bone substitute material can induce tissue reactions similar to those of some xenogeneic materials, thus pointing to a need to elucidate their “ideal” physical characteristics. The results also show that granule size in the range studied did not alter phagocytosis by mononuclear cells. Finally, the investigation substantiates the differentiation of material-induced MNGCs, which are of the foreign body giant cell type.

Enamel matrix derivative, inflammation and soft tissue wound healing

Over 15 years have now passed since enamel matrix derivative (EMD) emerged as an agent capable of periodontal regeneration. Following thorough investigation, evidenced-based clinical application is now established for a multitude of clinical settings to promote regeneration of periodontal hard tissues. Despite the large number of studies and review articles written on this topic, no single review has compiled the influence of EMD on tissue inflammation, an area of research that merits substantial attention in periodontology. The aim of the present review was to gather all studies that deal with the effects of EMD on tissue inflammation with particular interest in the cellular mechanisms involved in inflammation and soft tissue wound healing/resolution. The effects of EMD on monocytes, macrophages, lymphocytes, neutrophils, fibroblasts and endothelial cells were investigated for changes in cell behavior as well as release of inflammatory markers, including interleukins, prostaglandins, tumor necrosis factor-α, matrix metalloproteinases and members of the OPG-RANKL pathway. In summary, studies listed in this review have reported that EMD is able to significantly decrease interleukin-1b and RANKL expression, increase prostaglandin E2 and OPG expression, increase proliferation and migration of T lymphocytes, induce monocyte differentiation, increase bacterial and tissue debris clearance, as well as increase fibroplasias and angiogenesis by inducing endothelial cell proliferation, migration and capillary-like sprout formation. The outcomes from the present review article indicate that EMD is able to affect substantially the inflammatory and healing responses and lay the groundwork for future investigation in the field.

Differential effects of prostaglandin E(2) and enamel matrix derivative on the proliferation of human gingival and dermal fibroblasts and gingival keratinocytes

BACKGROUND AND OBJECTIVE

Elevated levels of prostaglandins contribute to periodontal destruction but can impair gingival healing by affecting local fibroblasts. Enamel matrix derivative (EMD) has beneficial effects on supporting and gingival tissues. We showed that prostaglandin E(2) (PGE(2) ) inhibits the proliferation of human gingival fibroblasts (hGFs) and that EMD stimulates it. Prostaglandins and EMD may also affect skin healing by targeting dermal fibroblasts (DFs). Thus, we compared the effects of these two agents on the proliferation of hGFs, human gingival keratinocytes (hGKs) and hDFs.

MATERIAL AND METHODS

Cells from healthy human gingiva or skin were treated with PGE(2) and/or EMD, and proliferation was assessed by measuring cell number and DNA synthesis.

RESULTS

In hGFs, PGE(2) (1 μm) inhibited proliferation while EMD stimulated it. When present together, EMD abolished the PGE(2) -induced inhibition. Serum increased (by a factor of 10) the amount of phosphorylated extracellular signal-regulated kinase (p-ERK), PGE(2) reduced it (by 70-80%) and EMD restored it when present with PGE(2). Prostaglandin E(2) stimulated cAMP production in hGFs while serum or EMD did not. Enamel matrix derivative stimulated hDF proliferation, but the inhibitory effect of PGE(2) was milder than with hGFs. When present together, EMD abolished the PGE(2) -induced inhibition. Enamel matrix derivative inhibited the proliferation of primary hGKs, but PGE(2) had no effect. Finally, we found that hDFs contained about five times less prostaglandin EP(2) receptor mRNA than hGFs, while hGKs contained none.

CONCLUSION

Prostaglandin E(2) inhibits and EMD stimulates hGF proliferation via distinct pathways. The different sensitivities of hDFs and hGKs to PGE(2) can be explained by the levels of EP(2) expression.

Nanocrystalline Apatites for Bone Reconstruction

Poorly crystalline apatites (PCA) are characterized by a non-stoichiometric composition, a high specific surface area and the existence of labile, non-apatitic environments detected by spectroscopic techniques. These environments have been shown to belong mainly to an hydrated layer at the surface of the crystals and determine their surface and bulk reactivity. PCA can be easily synthesized in aqueous media and the amount of labile, non-apatitic environments can be modulated by using apatites at different maturation stage. PCA can adsorb many active proteins or drugs, Growth factors (FGF-2, for example), were strongly bound and remained mostly attached to the surface. Several mineral ions which have been shown to have a biological activity such as strontium, can also be trapped at the surface or into the lattice of poorly crystalline apatites. Due to their reactivity, PCA cannot be shaped easily into materials, however, they have the ability to agglomerate irreversibly into solid body at low temperature. These low temperature ceramics show a variable amount of pores (30 to 60 %) and pore size (5 to 25 nm) in which organic components can be trapped and are released only by the dissolution of the ceramic.

Cyclo-DfKRG peptide modulates in vitro and in vivo behavior of human osteoprogenitor cells on titanium alloys

The first aim of the present study was to investigate the capacity of a cyclo-DfKRG-coated hydroxyapatite-titanium alloy (Ti-HA-RGD) to activate in vitro human osteoprogenitor cells adhesion and differentiation. The second purpose was to examine in vivo the role of a autologous cell seeding on cyclo-DfKRG-functionalized materials to provide bone repair after implantation in femoral condyle of rabbits. Our in vitro results have demonstrated that both titanium alloy functionalized with hydroxyapatite (Ti-HA-RGD and Ti-HA) contributed to higher cell adhesion than titanium alloy alone respectively 85 and 55% vs 15% compared to tissue culture polystyrene after one hour of cell seeding. As for differentiation, after 3 days of culture, Ti-HA presented the highest increase of ALP mRNA of all surfaces studied. Ti-HA-RGD showed an intermediate value about half as high as Ti-HA. Moreover after 3 days, both Ti-HA and Ti-HA-RGD surfaces showed the highest increase of cbfa1 mRNA expression. Two weeks following implantation, in vivo findings revealed that percentage of lacunae contact observed with pre-cellularized Ti-HA-RGD samples remains significantly lower than with Ti-HA group (10.5+/-9.6 % vs 33.7+/-11.5 %, P<0.03). Meanwhile, RGD peptide coating had no significant additional effect on the bone implant contact and area. Moreover, histomorphometry analysis revealed that implantation of pre-cellularized RGD coated materials with ROP cells increased significantly peri-implant fibrous area (24+/-11.6% vs 3+/-1.7% for Ti-HA-RGD, P<0.02). RGD coatings demonstrated osteoblastic adhesion, differentiation and in vivo bone regeneration at most equivalent to HA coatings.

EGFR in Enamel Matrix Derivative-induced Gingival Fibroblast Mitogenesis

We previously reported that EMD (Enamel Matrix Derivative) induces proliferation of human gingival fibroblasts via activation of Extracellular Regulated Kinase (ERK), and this study assessed the possible mediatory role of EGFR (Epidermal Growth Factor Receptor) in this effect. Treatment of gingival fibroblasts with EMD resulted in tyrosine phosphorylation of the EGFR, as assessed by immunoblotting and ELISA, while EMD-induced ERK activation and thymidine incorporation were markedly inhibited (~ 40–50%) by a specific EGFR tyrosine kinase inhibitor. Using appropriate inhibitors, we established that EMD-induced EGFR activation is largely due to shedding of HB-EGF (Heparin-binding EGF) from the cell membrane via a metalloproteinase-mediated process. Finally, the addition of PP1, a Src family inhibitor, abrogated both EGFR phosphorylation and ERK activation. Taken together, these results indicate that, at least in human gingival fibroblasts, EMD-induced ERK activation and proliferation are partially due to a Src-dependent, metalloproteinase-mediated transactivation of EGFR.

Enamel matrix derivative protects human gingival fibroblasts from TNF-induced apoptosis by inhibiting caspase activation

Emdogain, a formulation of enamel matrix derivative (EMD), is used clinically for regeneration of the periodontium (tooth supporting tissues), but the molecular mechanisms of its action have not been elucidated. Several clinical studies suggested that EMD may also improve gingival healing after periodontal surgery and thus affect the fate of gingival fibroblasts (GFs). Since these cells are targets for local inflammatory mediators such as TNF, a pro-apoptotic cytokine, during the course of periodontal disease, we tested whether EMD protects human GFs (hGFs) from TNF-induced cytotoxicity. Quiescent primary hGFs were challenged with TNF (10-100 ng/ml) with or without EMD (100 microg/ml) pretreatment. Cell viability was assessed by neutral red staining, cell death by LDH release and apoptosis by caspase activity. Signaling pathways were evaluated by Western blotting and pharmacological inhibitors. TNF induced classical signs of apoptosis in hGFs, including typical cellular morphology and increased caspase activity. TNF-induced cytotoxicity was entirely caspase-dependent. Pretreatment (4-24 h) with EMD dramatically inhibited the activation of initiator and executioner caspases and enhanced hGF survival. Although TNF induced the activation of p38 MAPK, JNK, ERK and PI-3K signaling, these pathways were not crucial for EMD protection of hGFs. However, EMD increased the levels of c-FLIP(L), an anti-apoptotic protein located upstream of caspase activation. These data demonstrate, for the first time, that EMD protects hGFs from inflammatory cytokines and, together with our recent reports that EMD stimulates rat and human GF proliferation, could help explain the mechanisms whereby in vivo use of EMD promotes gingival healing.

Functionalization of dental implant surfaces using adhesion molecules

The aim of the present study was to test the hypothesis that organic coating of titanium screw implants that provides binding sites for integrin receptors can enhance periimplant bone formation. Ten adult female foxhounds received experimental titanium screw implants in the mandible 3 months after removal of all premolar teeth. Four types of implants were evaluated in each animal: (1) implants with machined titanium surface, (2) implants coated with collagen I, (3) implants with collagen I and cyclic RGD peptide coating (Arg-Gly-Asp) with low RGD concentrations (100 micromol/mL), and (4) implants with collagen I and RGD coating with high RGD concentrations (1000 micromol/mL). Periimplant bone regeneration was assessed histomorphometrically after 1 and 3 months in five dogs each by measuring bone implant contact (BIC) and the volume density of the newly formed periimplant bone (BVD). After 1 month, BIC was significantly enhanced only in the group of implants coated with the higher concentration of RGD peptides (p = 0.026). Volume density of the newly formed periimplant bone was significantly higher in all implants with organic coating. No significant difference was found between collagen coating and RGD coatings. After 3 months, BIC was significantly higher in all implants with organic coating than in implants with machined surfaces. Periimplant BVD was significantly increased in all coated implants in comparison to machined surfaces also. It was concluded that organic coating of machined screw implant surfaces providing binding sites for integrin receptors can enhance bone implant contact and periimplant bone formation.

Cyclo-(DfKRG) peptide grafting onto Ti–6Al–4V: physical characterization and interest towards human osteoprogenitor cells adhesion

In the present paper, specific interest has been devoted to the design of new hybrid materials associating Ti-6Al-4V alloy and osteoprogenitor cells through the grafting of two RGD containing peptides displaying a different conformation (linear RGD and cyclo-DfKRG) onto titanium surface. Biomimetic modification was performed by means of a three-step reaction procedure: silanization with APTES, cross-linking with SMP and finally immobilization of peptides thanks to thiol bonding. The whole process was performed in anhydrous conditions to ensure homogeneous biomolecules layout as well as to guarantee a sufficient amount of biomolecules grafted onto surfaces. The efficiency of this new route for biomimetic modification of titanium surface was demonstrated by measuring the adhesion between 1 and 24 h of osteoprogenitor cells isolated from HBMSC. Benefits of the as-proposed method were related to the high concentration of peptides grafted onto the surface (around 20 pmol/mm(2)) as well as to the capacity of cyclo-DfKRG peptide to interact with integrin receptors. Moreover, High Resolution beta-imager (using [(35)S]-Cys) has exhibited the stability of peptides grafted onto the surface when treated in harsh conditions.

Grafting RGD containing peptides onto hydroxyapatite to promote osteoblastic cells adhesion

Ceramics possess osteoconductive properties but exhibit no intrinsic osteoinductive capacity. Consequently, they are unable to induce new bone formation in extra osseous sites. In order to develop bone substitutes with osteogenic properties, one promising approach consists of creating hybrid materials by associating in vitro biomaterials with osteoprogenitor cells. With this aim, we have developed a novel strategy of biomimetic modification to enhance osseointegration of hydroxyapatite (HA) implants. RGD-containing peptides displaying different conformations (linear GRGDSPC and cyclo-DfKRG) were grafted onto HA surface by means of a three-step reaction procedure: silanisation with APTES, cross-linking with N-succinimidyl-3-maleimidopropionate and finally immobilisation of peptides thanks to thiol bonding. Whole process was performed in anhydrous conditions to ensure the reproducibility of the chemical functionalisation. The three-step reaction procedure was characterised by high resolution X-ray photoelectron spectroscopy. Efficiency of this biomimetic modification was finally demonstrated by measuring the adhesion of osteoprogenitor cells isolated from HBMSC onto HA surface.

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.

A cyclo peptide activates signaling events and promotes growth and the production of the bone matrix

The interaction of bone cells and their underlying extracellular matrix impacts biological processes such as maintenance of tissue integrity. The biological recognition of the extracellular matrix by attached cells is mediated by the activity of integrins that recognize adhesive-specific domains. The most widely recognized adhesive motif is the RGD sequence, common to many of the adhesive matrix molecules. Here, we show that cyclo DFKRG which was previously selected to increase cell adhesion of human bone marrow stromal cells (HBMSC), increases both cell differentiation and mineralization through activation of tyrosine kinases, focal adhesion kinase (p(125)FAK) and Mitogen Activated Protein (MAP) kinases.

Electrochemically assisted deposition of thin calcium phosphate coatings at near-physiological pH and temperature

An electrochemical method for the deposition of calcium phosphate phases on titanium surfaces using the galvanostatic mode is presented. Deposition was performed in a (Ca(2+) / H(x)PO(4) ((3-x)-))-containing electrolyte near physiological conditions with regard to pH (6.4) and temperature (36 degrees C). Cathodic alkalization leads first to the formation of a thin homogeneous layer that shows a nanoscale surface topography of alternating wall-like elevations and channels. It is thought that these channels in the calcium phosphate prelayer are formed as pathways for hydroxyl ions and hydrogen. Upon this layer, spheres of amorphous calcium phosphate (ACP) are formed as indicated by Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy. According to transmission electron microscopy images, these spheres consist of small clusters of calcium phosphate (approximately 30 nm) and can grow up to 300 nm in diameter. Characteristic for this ACP is a high water content as seen by FTIR. As a function of current density, the ACP is then transformed into crystalline hydroxyapatite (HAP), which was identified using FTIR and X-ray diffraction. The morphology of the HAP crystals can be described as needles with dimensions of <500-nm length and <60-nm width. By choice of different electrochemical parameters, a homogeneous coating of either ACP, HAP, or the intermediate phase can be achieved, as shown in a kinetic phase diagram, thus allowing the formation of coatings with different properties in solubility and morphology.

Biological performance of biomimetic calcium phosphate coating of titanium implants in the dog mandible

The aim of the present study was to analyze the in vivo effect of biomimetic calcium phosphate coating of titanium implants on periimplant bone formation and bone-/implant contact. Five types of implants were used: 1) Ti6Al4V implants with a polished surface; 2) Ti6Al4V implants with collagen coating; 3) Ti6Al4V implants with a mineralized collagen layer; 4) Ti6Al4V implants with sequential coating of hydroxyapatite (HA) and collagen; and 5) Ti6Al4V implants with HA coating only. All implants had square cross sections with an oblique diameter of 4.6 mm and were inserted press fit into trephine burr holes of 4.6 mm in the mandibles of ten beagle dogs. The implants of five animals each were evaluated after a healing period of 1 month and 3 months, respectively, during which time sequential fluorochrome labeling of bone formation had been performed. Bone formation was evaluated by morphometric measurement of the newly formed bone around the implants and the percentage of implant bone contact. After 1 month, there was a significantly higher percentage of mean bone/implant contact in the HA-coated implants compared to those with polished surface and those with the collagen-coated surface. After 3 months, these differences were not present anymore. Bone apposition was significantly higher next to implants with sequential HA/collagen coating compared to polished surfaces and mineralized collagen layer. It is concluded that biomimetic coating of titanium implants with HA has shown the clearest trend to increase bone-implant contact in the early ingrowth period. The addition of collagen to an HA coating layer may hold some promise when used as sequential HA/collagen coating with mineralized collagen as the surface layer.

Function of linear and cyclic RGD-containing peptides in osteoprogenitor cells adhesion process

Cell adhesion directly influences cell growth, differentiation and migration as well as morphogenesis, integrity and repair. The extracellular matrix (ECM) elaborated by osteoblast cells constitutes a regulator of the cell adhesion process and then of the related phenomenon. These regulatory effects of ECM are mediated through integrins and some of them are able to bind RGD sequences. The aim of this study was to determine the role of the sequence and the structure of RGD-containing peptides (linear and cyclic) as well as their role in the cell adhesion process. Cell adhesion assays onto ECM proteins coated surfaces were performed using a range of linear and cyclic RGD-containing peptides. We showed a different human osteoprogenitor cell adhesion according to the coating for ECM proteins and for RGD-peptides. Inhibition assays using peptides showed different responses depending on the coated protein. Depending on the amino-acid sequence and the structure of the peptides (cyclic linear), we observed 100% inhibition of cell adhesion onto vitronectin. These results suggest the importance of sequence, structure and conformation of the peptide, which may play a crucial function in the ligand/receptor interaction and/or in the stability of the interaction.

Biomimetic coatings functionalized with adhesion peptides for dental implants

A complete biological integration into the surrounding tissues (bone, gingiva) is a critical step for clinical success of a dental implant. In this work biomimetic coatings consisting either of collagen type I (for the gingiva region) and hydroxyapatite (HAP) or mineralized collagen (for the bone interface) have been developed as suitable surfaces regarding the interfaces. Additionally, using these biomimetic coatings as a matrix, adhesion peptides were bound to further increase the specificity of titanium implant surfaces. To enhance cell attachment in the gingiva region, a linear adhesion peptide developed from a laminin sequence (TWYKIAFQRNRK) was bound to collagen, whereas for the bone interface, a cyclic RGD peptide was bound to HAP and mineralized collagen using adequate anchor systems. The biological potential of these coatings deduced from cell attachment experiments with HaCaT human keratinocytes and MC3T3-E1 mouse osteoblasts showed the best results for collagen and laminin sequence coating for the gingiva region and mineralized collagen and RGD peptide coatings for regions with bone contact. Our concept opens promising approaches to improve the biological integration of dental implants.

Adsorption of vascular endothelial growth factor to two different apatitic materials and its release

The aim of our study was to assess the ability of calcium phosphate powders to serve as growth factor carriers. Vascular endothelial growth factor (VEGF), in particular, is locally involved in the bone formation process throughout osteoblast differentiation. Two different apatitic substrates were tested: hydroxyapatite (HA), widely used as biomaterial, and nanocrystalline carbonated apatite (CA), which has a composition similar to bone mineral crystals. These materials have been compared for their VEGF adsorption and release properties. The adsorption of the growth factor was higher on CA than on HA probably due to differences of both the proteins and the powders involved. The specific activity of the VEGF released was also tested to determine the available activity for cells in contact with these materials. Interestingly, the bioactivity of the VEGF released from CA quantified on fetal bovine aortic endothelial cells (FBAE) by evaluating the proliferation activity, exhibited no marked difference compared to native VEGF. Qualitatively, VEGF adsorbed on CA material induced well-defined collagen type I immunostaining on osteoblast cells compared to the staining obtained after VEGF adsorption on HA.

Evaluation of the effect of three calcium phosphate powders on osteoblast cells

The aim of the present study was to assess the effect of three calcium phosphate powders entering in the composition of bone substitute materials on osteoblast-cells activity. These powders were hydroxyapatite (HA) widely used as a biomaterial, nanocrystalline carbonate apatite (C A) very close to bone mineral crystals, and an experimental one: calcium phosphate cement-1 (CPC-1) composed of an amorphous Ca-P phase and brushite. The powders were physico-chemically characterized. The very reactive CPC-1 powder became transformed in cell culture medium: recrystallization of amorphous precursors and hydrolysis of brushite into poorly crystalline apatite occurred. Osteoblast-cells activity was evaluated: for low level of calcium phosphates (>100 microg/ml) CPC-1 enhanced proliferation and, to a lesser degree, differentiation on alkaline phosphatase activity. For 100 microg/ml of powders we observed a great alteration of biological activity of the osteoblasts: evaluation of proliferation indicated an inhibition for all samples, and a decrease of two differentiation markers: alkaline phosphatase activity and osteocalcin release were noticed, suggesting a down regulation due to the presence of large amount of mineral powder.

[Pilot study of controlled liberation of growth factors from polylactide implants]

The aim of the present study was to test polylactic acid material as a controlled release carrier for polypeptide growth factors. Basic fibroblast growth factor (bFGF) was incorporated into DL polylactic acid (PLA) pellets under hyperbaric CO2 pressure in two different ways. (1) Lyophilized bFGF was crushed and mixed with PLA granules, filled into cylindric moulds of 5 x 3 mm, and submitted to hyperbaric CO2 pressure. (2) Lyophilized bFGF was reconstituted in phosphate buffer, mixed with PLA granules, and relyophilized. In vitro assessment of bFGF release from the PLA implants by immunoassay showed that loading of PLA with crushed lyophilized bFGF resulted in a rapid and high release, while loading by solubilized bFGF and relyophilization led to a low and more regular release of the polypeptide growth factor.

Various evaluation techniques of newly formed bone in porous hydroxyapatite loaded with human bone marrow cells implanted in an extra-osseous site

The purpose of this work was to develop qualitative methods for in situ analysis of bone formation in an osteoconductive hydroxyapatite matrix (ENDOBON), loaded with human bone marrow cells (HBMSC) implanted subcutaneously in athymic mice. Samples were taken before implantation (T0), 1, 2, 4 and 6 weeks after implantation. Bone-biomaterial interaction were investigated on undecalcified sections by histological, cytochemical, immunological and molecular biology methodologies. Histological observations were performed in order to observe inflammatory cells, vessels, newly formed bone, woven and lamellar bone. Enzymohistochemistry was carried out to detect positive tartrate resistant acid phosphatase activity (TRAP+). Immunohistochemistry using antibodies against type I collagen and osteocalcin permitted us to characterize the content of the matrix elaborated within the implant. Moreover, in situ hybridization was carried out to discriminate, the implanted human cells from the murine cells, and to evaluate the function of these human cells in osteogenesis. Results demonstrated an early formation of lamellar bone only in the pores of the studied HAP loaded with HBMSC. This bone contained a matrix showing positive reaction for type I collagen and osteocalcin. In situ hybridization identified some of these cells as human cells. At 6 weeks, examination of histological results showed persistance of lamellar bone in the implants. We only found TRAP+ activity in the materials loaded with human bone marrow cells. Molecular hybridization no longer revealed positive cells for the human DNA probe. All these results indicate that the various evaluation techniques performed on undecalcified sections, permit us to evaluate the response of human bone marrow cells in HAP implanted into mice.

Tools for tissue engineering of mineralized oral structures

This paper presents a short review of three groups of tools which can be or are used for the tissue engineering of mineralized oral structures: growth factor delivery systems (GFDS) and surface bioactivation with covalent bound peptides or with nanomechanically linked proteins. According to the reported personal experience of the authors, GFDS have to face the following challenging issue before being used routinely in dentistry, e.g., as a tool for reparative dentinogenesis or bone healing: adaptation of the GFDS design to the tissue where it will be implanted in order to deliver the right dose of growth factor (GF) at the right time. The bioactivation of surfaces, for example of dental implants, with covalent bound peptides or nanomechanically linked proteins represents a second innovative way to improve dental health in the future. Here we report on the experimental use of cyclic RGD peptides grafted on polymethylmethacrylate to improve osteoblast adhesion. Furthermore, we show the potential advantage of immobilizing and incorporating collagen I on titanium implant surfaces. These techniques or a combination of them will help to create improvements, for example, of dental implants in the near future. They will also help to promote bone and dentin regeneration.

Guided bone regeneration around endosseous implants using a resorbable membrane vs a PTFE membrane

The aim of the present experimental pilot study was to assess bone regeneration underneath resorbable barrier membranes vs non-resorbable extended polytetrafluoroethylene (ePTFE) membranes in peri-implant defects. Two implants were inserted into surgically created defects on each side of the mandibles of 6 adult beagle dogs 3 months after extraction of all premolar teeth. One implant on each side was covered with a porous polylactic acid membrane or a ePTFE membrane, respectively, while the second implant served as control. Fluorochrome labelling was administered during the 1st, 5th, 12th and the 18th week. Three animals each were evaluated after 3 and 6 months. Bone regeneration was assessed by measuring the distance from the first fluorochrome label to the level of the regenerated bone immediately adjacent to the implant surface and to the top of the newly formed alveolar contour both on the lingual and buccal side. The increase in bone height was significantly higher compared to the controls under both barrier membranes after 3 months at the top of the alveolar crest but not immediately adjacent to the implant surface. After 6 months, bone height was significantly increased only at the top of the alveolar contour underneath the ePTFE membranes, while bone underneath the polylactic acid membranes showed signs of superficial resorption. It is concluded that guided bone regeneration underneath barrier membranes can restore alveolar bone contour but is not necessarily associated with a higher bone/implant contact. The use of resorbable membranes may be associated with untoward biological effects at later stages, when membrane degradation starts due to degradation products of the polymer material or decreasing membrane stability. Future efforts have to refine the relation between degradation kinetics, membrane porosity and mechanical properties of degradable barrier membranes to improve membrane performance.

Alveolar ridge repair using resorbable membranes and autogenous bone particles with simultaneous placement of implants: an experimental pilot study in dogs

The aim of this experimental study was to evaluate the use of autogenous bone harvested during preparation of implant sites in combination with resorbable membranes for vertical ridge augmentation under 2 different defect site conditions. Combined vertical/horizontal alveolar bone defects were created by experimentally induced periodontal infections around all premolar teeth in the mandibles of 3 dogs (group 1). In another 3 dogs, fresh surgical defects were created after extraction of all premolar teeth in the mandibles (group 2). In all dogs, 2 implants were placed on each side of the mandible into the defect areas. One implant on each side of the mandible received augmentation with autogenous bone particles, and both implants on one side of the mandible were covered with polylactic acid membranes. After 5 months, the material was evaluated histologically. There was a small but significant increase in bone regeneration in the defects augmented with bone particles with and without membrane coverage in group 1. In group 2, no significant difference was seen between the controls and the augmented sites. The major limiting effect for bone regeneration appeared to be insufficient stability of the bone material to withstand the overlying soft tissue pressure. It was concluded that the placement of autogenous bone particles, either with or without membrane coverage, had little effect on the regeneration of peri-implant bone defects.

Induced tissue integration of bone implants by coating with bone selective RGD-peptides in vitro and in vivo studies

The optimal function of medical implant materials used in tissue substitution is often limited due to its healing properties. This effect is linked to reduced interactions of the implants with the surrounding tissue. Implant surfaces biologically functionalized with arginine-glycine-aspartic acid (RGD) peptides, a class of cellular adhesion factors, are described in this paper. The RGD-peptides are either bound via bovine serum albumin linking on culture plastic dishes as a model surface or via acrylic acid coupling on PMMA surface as a potential implant material. Resulting functionalized surfaces aquire the capability to bind cultured osteoblasts in high levels and show high proliferation rates in vitro. These results are observed for osteoblast cultures as well as from different species with different preparation procedures. A critical minimum distance between the bioactive portion of the RGD-peptides and the implant surface of 3.0-3.5 nm is crucial for the induction of an optimum cell binding process. In vivo animal studies in the rabbit show that newly formed bone tissue generated a direct contact with the RGD-peptide coated implants. In contrast uncoated implants are separated from newly formed bone tissue by a fibrous tissue layer thereby preventing the formation of a direct implant-bone bonding.

Basic fibroblast growth factor adsorption and release properties of calcium phosphate

Basic fibroblast growth factor (bFGF) is well known as a potent angiogenic factor playing a crucial role in wound-healing processes. Apatitic substrates such as hydroxyapatite and carbonated apatite (CA) could be potential carriers of growth factors because of their physicochemical similarities to bone mineral. These materials have been compared for their bFGF adsorption and release properties. The adsorption of the growth factor was higher on carbonated apatite than on hydroxyapatite, probably owing to environments with labile nonapatitic CO3(2-) and HPO4(2-) groups, along with a higher specific surface area which gives the CA a higher surface reactivity. These environments can be exchanged very rapidly, leading to the release of bFGF. The controlled release of adsorbed growth factor from carbonated apatite could provide means of improving bone healing in the future.

In vitro growth of human adult bone-derived cells on hydroxyapatite plasma-sprayed coatings

The growth of adult human bone-derived cells on hydroxyapatite (HA) plasma-sprayed coatings was investigated. Such cells were difficult to grow on original plasma-sprayed coatings, even following rinsing and rubbing down. We obtained cell growth only on samples previously immersed 15 or 22 days in complete culture medium. We describe a dissolution/precipitation phenomenon on the HA coating surface assessed by modifications of Ca and P concentrations in the culture medium, by the transformation of the HA coating into carbonated HA (X-ray diffraction and infrared spectrometry and by the presence demonstrated by scanning electron microscopy of spherocrystallites on the HA after 15 days of immersion. Our results show that adult human bone-derived cells are apparently particularly sensitive to the changes in the coating surface induced by liquid immersion. We raise the question of the limits of in vitro investigations on bioactive ceramics such as HA plasma-sprayed coatings susceptible to modification by simple immersion in aqueous solutions such as cell culture medium or physiologic saline.

Histology of alveolar bone and primary tooth roots in a case of cleidocranial dysplasia

Cleidocranial dysplasia is commonly reported as an autosomal dominant inherited condition with defective formation of clavicles, malformation of the craniofacial bones, very slow exfoliation of the primary teeth and failure of the eruption of the permanent dentition. Lack of clinical resorption of the roots of the deciduous teeth and/or surrounding bone, lead to eruption failure of permanent teeth. Histopathological study (light and scanning electron microscopy), in a case of cleidocranial dysplasia, gives prominence to the hypothesis of abnormal remodelling of bone and cementum.

Effects of synthetic calcium phosphates on the 3H-thymidine incorporation and alkaline phosphatase activity of human fibroblasts in culture

Gingival fibroblasts were cultured with four different calcium phosphate minerals (hydroxyapatite, whitlockite, beta-tricalcium phosphate, and octocalcium phosphate). 3H-thymidine incorporation into DNA and alkaline phosphatase specific activity were determined after different incubation periods. As a consequence of the phagocytosis of calcium phosphates crystals, we pointed out, compared to control, a stimulation of the rate of 3H-thymidine incorporation and sharp decreases in alkaline phosphatase activity. The magnitude of the alkaline phosphatase activity inhibition was observed to be increased with the solubility of the materials. We propose that the effects of calcium phosphates on alkaline phosphatase and 3H-thymidine incorporation could be calcium-mediated events, resulting from intracellular dissolution of phagocytized materials. We suggest that in vitro determination of 3H-thymidine incorporation and alkaline phosphatase activity, which are highly sensitive tests, could be involved in evaluation procedures of calcium phosphates biomaterials.

Cytoskeleton and calcium. A review

The aim of the present paper was to summarize the main features about cytoskeleton in order to understand the possible interactions between this system of filamentous, microfilaments structures (including microtubules, intermediate filaments, microfilaments) and calcium in mesenchymal cells of the oral cavity.

A transmission electron microscope study of fibroblast changes in human deciduous tooth pulp

The coronal pulps of four primary canines, free from radicular resorption, and of three primary teeth, with roots entirely resorbed, were prepared for electron microscopy. Mature fibroblasts, similar to those reported in the pulps of permanent teeth, were present in the pulps of the clinically mature teeth. Regression of fibroblasts, evident in the pulps of deciduous teeth at the root resorption stage, was characterized by cytoplasmic changes, modifications in the cytoskeleton and dissociation of cells and fibrils. Deciduous teeth might provide a model for studying pulp fibroblast ageing.

Transmission electron microscopy of the morphological relationship between fibroblasts and pulp calcifications in temporary teeth

Calcifications found in the coronal pulps of primary teeth extracted in an 8-year-old child were studied by TEM. Different types of relationship were observed between fibroblasts and pulp calcifications: extension of cell processes towards calcifications, modelling of the cells upon calcifications, internalizing process of calcifications. Fibroblasts proved to be able to enclose small pulp calcifications within intracytoplasmic vesicles. There was no evidence of any active role played by fibroblasts in the genesis of pulp calcifications. It was shown that collagen fibres could be involved or not in the mineralizing process. It is suggested that mitochondria might provide an adequate environment for initial mineralization. It is likely that the role played by the cytoskeleton in the internalizing process of calcifications is important.

[Dental enamel pearls: histopathological study]

Enamel pearls are small rounded or egg-shaped nodules which most frequently develop in the furcation area of molars. They may consist of enamel only or enamel containing a small core of tubular dentin. They often sit upon strands of cementum or Tomes granular layer. Histologically, the enamel surface of enamel pearls resembles immature enamel and may be covered with cementum. Small calcoglobules presenting varying degrees of organization are often found related to enamel pearls. Some of them, which have the same radiodensity as the enamel of the pearl and of the affected tooth, may be considered as an enamel-type of calcifications. Others, which present a concentric structure revealed by a polarization cross when viewed between cross polars, may be similar to cementicles. All calcifications located in contact with enamel pearls or at a distance, from them are dystrophic calcifications.