Biomedical subjects

P Pilet

Publications and source records attributed to P Pilet.

At least 19 recordsLinked to original sources

PubMed2006

Injectable bone substitute to preserve alveolar ridge resorption after tooth extraction: a study in dog.

The aim of the present study was to assess the efficacy of a ready-to-use injectable bone substitute on the prevention of alveolar ridge resorption after tooth extraction. Maxillary and mandibular premolars were extracted from 3 Beagle dogs with preservation of alveolar bone. Thereafter, distal sockets were filled with an injectable bone substitute (IBS), obtained by combining a polymer solution and granules of a biphasic calcium phosphate (BCP) ceramic. As a control, the mesial sockets were left unfilled. After a 3 months healing period, specimens were removed and prepared for histomorphometric evaluation with image analysis. Histomorphometric study allowed to measure the mean and the maximal heights of alveolar crest modifications. Results always showed an alveolar bone resorption in unfilled sockets. Resorption in filled maxillary sites was significantly lower than in control sites. Interestingly, an alveolar ridge augmentation was measured in mandibular filled sockets including 30% of newly-formed bone. It was concluded that an injectable bone substitute composed of a polymeric carrier and calcium phosphate can significantly increase alveolar ridge preservation after tooth extraction.

Alveolar Process↗

PubMed2006

[Experimental evaluation of microscan assessment of bone fusion].

PURPOSE OF THE STUDY: Certain confirmation of bone fusion remains difficult to obtain after arthrodesis despite progress in imaging techniques. Microscanning enables both qualitative and quantitative analysis of the bone microarchitecture. The purpose of this study was to evaluate this technique using a cervical arthrodesis with an intersomatic cage on an animal model and to validate results with histological analysis and electron scan microscopy (SEM). MATERIAL AND METHODS: C3-C4 discectomy was performed in 8 goats divided into two groups. In group 1 (3 animals), PEEK cages were inserted without bone graft. In group 2 (5 goats) the same cage was inserted and filled with an autologous iliac graft. The animals were sacrificed at six months. The instrumented levels were analyzed with a microscan. Histological slides were obtained and SEM performed. RESULTS: Nonunion was observed in the three animals with an empty cage (group 1) while only one animal in group 2 presented nonunion. Histology and SEM confirmed the diagnosis established with the microscan which also enabled a 3D analysis of the sample and study of the trabecular architecture of the intersomatic graft. DISCUSSION: The microscan enabled a micrometric analysis of the sample. This is the only technique enabling 3D analysis (slices can be obtained in the three planes for 3D reconstruction) for both qualitative and quantitative assessment. Analysis of the trabecular microstructure constitutes a major progress in evaluating the mechanical value of the fusion. The sample is not destroyed and can be studied further with other biomechanical techniques. CONCLUSION: Microscanning is an important technical advancement for the analysis of bone fusion. Future applications will undoubtedly be numerous (follow-up after arthrodesis, analysis of the mechanical quality of a graft). In vivo applications will probably be adapted soon.

Animals↗

PubMed2005

Small-animal models for testing macroporous ceramic bone substitutes.

The aim of this study was to compare the bone colonization of a macroporous biphasic calcium phosphate (MBCP) ceramic in different sites (femur, tibia, and calvaria) in two animal species (rats and rabbits). A critical size defect model was used in all cases with implantation for 21 days. Bone colonization in the empty and MBCP-filled defects was measured with the use of backscattered electron microscopy (BSEM). In the empty cavities, bone healing remained on the edges, and did not bridge the critical size defects. Bone growth was observed in all the implantation sites in rats (approximately 13.6-36.6% of the total defect area, with ceramic ranging from 46.1 to 51.9%). The bone colonization appeared statistically higher in the femur of rabbits (48.5%) than in the tibia (12.6%) and calvaria (22.9%) sites. This slightly higher degree of bone healing was related to differences in the bone architecture of the implantation sites. Concerning the comparison between animal species, bone colonization appeared greater in rabbits than in rats for the femoral site (48.5% vs. 29.6%). For the other two sites (the tibia and calvaria), there was no statistically significant difference. The increased bone ingrowth observed in rabbit femurs might be due to the large bone surface area in contact with the MBCP ceramics. The femoral epiphysis of rabbits is therefore a favorable model for testing the bone-bonding capacity of materials, but a comparison with other implantation sites is subject to bias. This study shows that well-conducted and fully validated models with the use of small animals are essential in the development of new bone substitutes.

Animals↗

PubMed2005

Initial presentation of childhood-onset systemic lupus erythematosus: a French multicenter study.

OBJECTIVE: To describe the clinical and laboratory manifestations of childhood-onset systemic lupus erythematosus (SLE) at presentation. STUDY DESIGN: This retrospective French multicenter study involved 155 patients in whom SLE developed before the age of 16 years. Mean patient age at onset was 11.5 +/- 2.5 years (range, 1.5-16 years). The female to male ratio was 4.5. RESULTS: The most common initial manifestations were hematologic (72%), cutaneous (70%), musculoskeletal (64%), renal (50%), and fever (58%). Thirty-two percent of children had atypical symptoms, mainly including abdominal involvement in 26 patients, which lead to negative laparotomy results for presumed appendicitis. Severe renal, neurologic, hematologic, abdominal, cardiac, pulmonary, thrombotic, and/or cutaneous manifestations occurred within the first month after the diagnosis in 40% of patients. The mean erythrocyte sedimentation rate was 72 +/- 29 mm/h, and the mean C-reactive protein value 22 +/- 21 mg/L. Antinuclear antibodies an, anti-double stranded DNA antibodies, and low C3 or C4 level were retrieved in 97%, 93%, and 78 % of patients, respectively. CONCLUSION: Initial manifestations of childhood-onset SLE are diverse and often severe. The diagnosis of SLE should be promptly considered in any febrile adolescent with unexplained organ involvement, especially when associated with an increased erythrocyte sedimentation rate.

Child↗

PubMed2004

Calcium phosphate drug delivery system: influence of local zoledronate release on bone implant osteointegration.

Despite total hip replacement (THR) gives generally satisfactory results, the quality of outcome in young patients is markedly decreased compared to the average THR outcome. For this population, pharmacological treatment with bisphosphonate would be beneficial to decrease the peri-implant osteolysis. However, as this population does not necessarily suffer from osteoporosis, a nonsystemic treatment would be preferable. Zoledronate was then grafted to hydroxyapatite (HA) coating of titanium implants. The implants were inserted in rat condyles with various zoledronate concentrations. A positive concentration-dependent effect was observed on the peri-implant bone density and on different histomorphometric parameters. Importantly for the outcome of the implants, the mechanical fixation was increased by the local presence of zoledronate. The obtained results open the way of an easy transformation of currently existing HA-coated implants by grafting bisphosphonate onto the coating in order to increase their service life in the patients.

Animals↗

PubMed2004

Development of an odontoblast in vitro model to study dentin mineralization.

The aim of the present work was to characterize the odontoblastic proliferation, differentiation, and matrix mineralization in culture of the recently established M2H4 rat cell line. Proliferation was assessed by cell counts, differentiation by RT-PCR analysis, and mineralization by alizarin red staining, atomic absorption spectrometry, and FTIR microspectroscopy. The results showed that M2H4 cell behavior closely mimics in vivo odontoblast differentiation, with, in particular, temporally regulated expression of DMP-1 and DSPP. Moreover, the mineral phase formed by M2H4 cells was similar to that in dentin from rat incisors. Finally, because in mice, transforming growth factor (TGF)-beta1 over-expression in vivo leads to an hypomineralization similar to that observed in dentinogenesis imperfecta type II, effects of TGF-beta1 on mineralization in M2H4 cell culture were studied. Treatment with TGF-beta1 dramatically reduced mineralization, whereas positive control treatment with bone morphogenetic protein-4 enhanced it, suggesting that M2H4 cell line is a promising tool to explore the mineralization mechanisms in physiopathologic conditions.

Animals↗

PubMed2003

Phosphate is a specific signal for ATDC5 chondrocyte maturation and apoptosis-associated mineralization: possible implication of apoptosis in the regulation of endochondral ossification.

UNLABELLED: Involvement of Pi and Ca in chondrocyte maturation was studied because their levels increase in cartilage growth plate. In vitro results showed that Pi increases type X collagen expression, and together with Ca, induces apoptosis-associated mineralization, which is similar to that analyzed in vivo, thus suggesting a role for both ions and apoptosis during endochondral ossification. INTRODUCTION: During endochondral ossification, regulation of chondrocyte maturation governs the growth of the cartilage plate. The role of inorganic phosphate (Pi), whose levels strongly increase in the hypertrophic zone of the growth plate both in intra- and extracellular compartments, on chondrocyte maturation and mineralization of the extracellular matrix has not yet been deciphered. MATERIALS AND METHODS: The murine chondrogenic cell line ATDC5 was used. Various Pi and calcium concentrations were obtained by adding NaH2PO4/Na2HPO4 and CaCl2, respectively. Mineralization was investigated by measuring calcium content in cell layer by atomic absorption spectroscopy and by analyzing crystals with transmission electron microscopy and Fourier transform infrared microspectroscopy. Cell differentiation was investigated at the mRNA level (reverse transcriptase-polymerase chain reaction [RT-PCR] analysis). Cell viability was assessed by methyl tetrazolium salt (MTS) assay and staining with cell tracker green (CTG) and ethidium homodimer-(EthD-1). Apoptosis was evidenced by DNA fragmentation and caspase activation observed in confocal microscopy, as well as Bcl-2/Bax mRNA ratio (RT-PCR analysis). RESULTS: We showed that Pi increases expression of the hypertrophic marker, type X collagen. When calcium concentration is slightly increased (like in cartilage growth plate), Pi also induces matrix mineralization that seems identical to that observed in murine growth plate cartilage and stimulates apoptosis of differentiated ATDC5 cells, with a decrease in Bcl-2/Bax mRNA ratio, DNA fragmentation, characteristic morphological features, and caspase-3 activation. In addition, the use of a competitive inhibitor of phosphate transport showed that these effects are likely dependent on Pi entry into cells through phosphate transporters. Finally, inhibition of apoptosis with ZVAD-fmk reduces pi-induced mineralization. CONCLUSIONS: These findings suggest that Pi regulates chondrocyte maturation and apoptosis-associated mineralization, highlighting a possible role for Pi in the control of skeletal development.

Animals↗

PubMed2002

Fourier transform infrared microspectroscopic investigation of the organic and mineral constituents of peritubular dentin: a horse study.

Peritubular dentin (PTD) is a relatively dense mineralized tissue surrounding tooth dentin tubules, whose composition and mode of formation are still unclear. Fourier transform infrared microspectroscopic studies of the organic and mineral components of the highly developed horse PTD indicate that the peritubular matrix is less abundant than the intertubular matrix but is also mainly composed of collagen, which is more hydrated. These data suggest that most of the crystals are located outside the collagen fibrils and probably not associated with protein components. The crystals in PTD have nearly the same crystallinity as those in intertubular spaces, showing comparable amounts of carbonate ions, although some PO4 groups have different nonapatitic environments. Horse PTD composition is very similar to that of ITD, with collagen as the main protein component and carbonated apatite as the mineral fraction but the different proportions of these constituents and the greater water content in PTD suggest a different organization.

Animals↗

PubMed2001

Filler effects of oil droplets on the rheology of heat-set emulsion gels prepared with egg yolk and egg yolk fractions.

Hen egg yolk is a traditional ingredient used in a wide variety of food emulsions, especially fluid sauces. Industrial processing of these sauces generally involves heat treatments in order to pasteurise or sterilise them. These heat treatments may cause undesired gelation of the emulsion, because egg yolk proteins are particularly thermosensitive. Heat gelation of oil-in-water emulsions prepared with egg yolk may differ from that of egg yolk solutions, because of the influence of oil droplets on network formation. In this study, we investigated the influence of oil droplets on the gelation of oil-in-water emulsions made with yolk. We studied three pH values: 3.0, 5.0 and 7.0 with a constant NaCl concentration: 0.55 M. Oil droplet size was controlled after emulsification, gelation of solutions and emulsions was monitored in situ by coupling heating with recording viscoelastic properties, and transmission electron microscopy was conducted in heat-set emulsion gels. In an attempt to target the proteins that impose the kinetic of gelation of egg yolk, we repeated the experiment with plasma and granules, the main fractions of yolk. In situ rheology showed that, in our experimental conditions [especially oil volume fraction (0.3) and oil droplet size (d3.2=1 &mgr;m)], emulsions made with yolk and plasma have a similar gelation process with oil droplets acting as inactive fillers. Furthermore, transmission electron microscopy showed similar network characteristics between heated emulsions made with yolk and plasma. Moreover, we demonstrated that acidic conditions provided the fastest gelation of yolk solutions and emulsions. On the other hand, in emulsions prepared with granules, oil droplets behaved as active filler particles and reinforced the gel strength.

Journal Article↗

PubMed2001

Fourier transform infrared microspectroscopic investigation of the maturation of nonstoichiometric apatites in mineralized tissues: a horse dentin study.

Fourier transform infrared microspectroscopy (FTIRM) was used to study carbonated apatite/collagen interactions and maturation in horse secondary dentin. Unlike human dentin, this model contains no peritubular material around the odontoblastic processes and is thus quite similar to bone in composition, but not subject to tissue turnover. Crystals close to the mineralization front were very immature, showing high HPO(4) and very low CO(3) levels. Carbonate ions were located essentially in very labile, reactive environments, probably on the crystal surface. Removal of some of the HPO(4) ions from crystals during maturation was linked to an increase in total carbonate content. The CO(3) ions in labile environments decreased, probably after incorporation into more organized regions of the lattice. However, this increase of total carbonate content was associated with greater mineral crystallinity, confirming findings in other studies of synthetic apatite maturation in vitro. The good correlation between these results and those of in vitro experiments suggests that crystal maturation is essentially due to physicochemical processes and that the organic matrix controls only crystal size, multiplication, and/or organization.

Animals↗

PubMed2001

Macroporous biphasic calcium phosphate ceramics versus injectable bone substitute: a comparative study 3 and 8 weeks after implantation in rabbit bone.

Macroporous biphasic calcium phosphate ceramics (MBCP) and a calcium phosphate injectable bone substitute (IBS), obtained by the association of biphasic calcium phosphate (BCP) ceramic granules and an aqueous solution of a cellulosic polymer, were compared in the same animal model. The two tested biomaterials were implanted in distal femoral osseous defects in rabbits. Qualitative and quantitative histological evaluation was performed three and eight weeks after implantation to investigate bone colonization and ceramic biodegradation associated with the two bone substitutes. Both biomaterials expressed osteoconduction properties and supported the apposition of a well-mineralized lamellar newly-formed bone. Bone colonization occurred much earlier and faster for IBS than for MBCP implants, although the respective rates of newly-formed bone after eight weeks of implantation did not differ significantly. For both biomaterials, ceramic resorption occurred regularly throughout the implantation period, though to a greater extent with IBS than with MBCP implants. The associated polymer in IBS produced intergranular spaces allowing body fluids to reach each BCP ceramic granule immediately after implantation, which may have favored osteoblastic activity, new bone formation and ceramic resorption. This completely interconnected open macroporosity could account for the earlier and more satisfactory bone substitution achieved with IBS.

Journal Article↗

PubMed2001

Scanning electron microscopic description of cellular activity and mineral changes in feline odontoclastic resorptive lesions.

The cellular activity and changes in mineral composition of dental tissues involved in feline odontoclastic resorptive lesions were investigated. Teeth with at least 1 lesion (n = 10) were extracted from 10 different cats that were presented primarily for chronic gingivostomatitis and/or severe periodontal disease. Scanning electron microscopic methods were used to determine the presence of resorptive cells in 8 teeth while 2 teeth were evaluated for pathologic changes in dental mineral composition. Observations were complicated by the presence of organic wear on the dental surfaces, however resorptive cells could be clearly identified in feline odontoclastic resorptive lesions. Resorptive cells had morphologic features indicative of "osteoclast-like" cells or odontoclasts. Resorptive cell activity created a resorption area of darker dentin continuous with physiologic dentin. The darker dentin area seemed poorly mineralized and showed a significantly lower calcium/phosphorous ratio compared with adjacent physiologic denting in 1 tooth. A significantly higher level of magnesium combined with available carbonate ions may have increased the solubility in areas of darker dentin.

Animals↗

PubMed2000

Ultrastructural properties of bone mineral of control and tiludronate-treated osteoporotic rat.

Bisphosphonates have been widely used in the treatment of human bone pathologies including osteoporosis. In this case, bisphosphonates have been shown to reduce bone resorption, thereby increasing the mass and mechanical resistance of bone. Determining the effects of these molecules on the properties of the bone apatite crystals could provide a better insight into the mechanism of bisphosphonate/bone interaction. The aim of this study was to determine the ultrastructural effects of a third generation bisphosphonate (tiludronate) on the morphology, size, distribution, chemical composition, and structure of apatite crystals in bone (trabecular) in a rat osteoporotic model. Four groups of rats were studied: (1) sham operated, (2) untreated ovariectomized (OVX), (3) OVX rats which received 35 mg/kg of tiludronate, (4) OVX rats which received 160 mg/kg of tiludronate. The rats of groups 3 and 4 received tiludronate orally in 2 consecutive days every week for 1 year. Scanning electron microscopy (SEM), high and low resolution transmission electron microscopy (TEM), and electron microprobe analysis (EDX) were used for the ultrastructural characterization of the bone mineral. This study demonstrated that tiludronate slightly increased the width of bone apatite crystals without changing any other crystal characteristics.

Animals↗

PubMed2000

[In vitro effects of growth hormone on osteoclastic activity: clinical applications].

PURPOSE OF THE STUDY: This study was designed to investigate the in vitro effects of human growth hormone (hGH) on osteoclastic resorption in a nonfractionated rabbit bone cell model. MATERIAL AND METHODS: Rabbit bone cells were cultured on dentine slices in the presence of parathyroid hormone and vitamin D3. The percentage of dentine slice surface resorbed, number of lacunae per surface unit and mean area of lacunae were compared between cell cultures grown in the presence of graded concentrations of hGH and human insulin-like growth factor-1 (hIGF-1) and controls. RESULTS: After 4 days of culture, rabbit bone cells cultured on dentine slices in the presence of hGH and hIGF-1 showed significantly stimulated osteoclastic resorption activity. When neutralizing anti-hIGF-1 anti-serum (4 microg/l) was added to the starting culture, the stimulatory effects of hIGF-1 and hGH on osteoclastic resorption activity were totally abolished. DISCUSSION: These findings indicate that the effects of hGH stimulation on osteoclastic resorption in vitro are mediated via local hIGF-1 secretion by stromal cells such as osteoblasts. Proteases appear to play a role in the degradation of the organic matrix. Our experiments show that hIGF-1 and hGH stimulate the production of matrix metalloproteinases MMP-9 and MMP-2. Similar to the resorption activity, hGH stimulates protease activity via stromal cell production of hIGF-1. CONCLUSION: This study suggests that natural or synthetic MMP inhibitor modulation of protease activity could reduce the degradation of the organic matrix and then prevent, for example, inflammatory reactions subsequent to prosthetic loosening.

Animals↗

PubMed1999

Influence of biphasic calcium phosphate granulometry on bone ingrowth, ceramic resorption, and inflammatory reactions: preliminary in vitro and in vivo study.

Calcium-phosphate ceramics used in surgery, as bone-bonding materials, are currently available in different forms (blocks, granules, etc.). However, progress in noninvasive surgery has favored the development of injectable composite materials associating a polymeric and a dusty mineral phase. The purpose of this study was the in vivo evaluation of biphasic calcium phosphate of various grains sizes, to elucidate the role of granulometries in ceramic degradation/resorption, bone ingrowth, and inflammatory reactions. Three particle sizes were compared: 10-20, 80-100, and 200-400 microm. The 10-20-microm powders provided the best bone ingrowth, with a higher resorption/degradation rate in conjunction with stronger early inflammatory reactions. The 200-400-microm powders showed higher bone ingrowth than 80-100-microm ones, indicating that properties of cell recruitment for osseous apposition and mechanical support for bone bonding may both play a role in both ingrowth mechanisms. Our results suggest that the strong inflammatory reaction in 10-20-microm granulated powders was due to a faster reversal of the resorption/apposition sequence in bone. This may have resulted from massive release of bone ingrowth factors, which implies that the brief inflammatory process observed in the early stages of implantation was favorable to the osteoconduction process.

Bone Development↗

PubMed1999

Biological activities of sustained polymyxin B release from calcium phosphate biomaterial prepared by dynamic compaction: an in vitro study.

Calcium phosphate ceramics (CaP) have recently been proposed as a potential matrix for a bioactive drug delivery system (DDS) in which the effect in situ of a released therapeutic agent is favored by the biocompatibility, osteoconductivity, and bioresorption of the ceramic material. Polymyxin B (PMB) is a polypeptidic antibiotic which undergoes thermodamage above 60 degrees C. The dynamic compaction method was developed to consolidate the drug load on CaP powder without external heating. Two projectile velocities (50 and 25 m/s) were used here to achieve powder consolidation. Among the different techniques used to associate therapeutic agents with CaP, wet adsorption was performed before the dynamic compaction process. The PMB release profile was measured by a capillary electrophoresis technique, CaP crystallography was studied by x-ray diffraction, and CaP physicochemical analysis was performed by infrared spectroscopy. The biological activities of PMB-loaded compacted CaP were determined by the effect of the antibiotic and monocyte/macrophage degradation on compact surfaces. PMB release began after 2-3 days of incubation for blocks compacted at 25 m/s velocity and on day 5 for those compacted at 50 m/s velocity. A discrepancy was noted between the amounts of PMB released (0.5-2.1 mg) and the amounts initially compacted (2-8 mg) with CaP powder. The biological activities (antibacterial activity and inhibited lipopolysaccharide effects on monocyte/macrophage CaP degradation) of PMB released from compacted calcium-deficient apatite were unaltered. Thus, dynamic compaction allows PMB to be used with CaP ceramics without any loss in its integrity and biological effects.

Anti-Bacterial Agents↗

PubMed1999

Role of fibronectin during biological apatite crystal nucleation: ultrastructural characterization.

The role of adhesion molecules like osteopontin and bone sialoprotein, both containing the Arg-Gly-Asp sequence have been shown to have a role in mineral formation, whereas fibronectin (FN), another adhesive protein, was never studied during the mineralization processes. The formation and maturation of biological apatite crystals are under matrix control, and one of the roles of specific crystal proteins is to control the nucleation and growth of biological apatite during the mineralization process (promotion or inhibition). In the case of calcium phosphate ceramic used as a bone substitute, a dissolution-precipitation process occurs after implantation before the bone ingrowth and bone mineralization. The early precipitation consists of common biological apatite crystals. These crystals are the result of secondary nucleation and a heteroepitaxic growth process on synthetic residual crystals. In in vivo studies, hydroxyapatite crystals were implanted subcutaneously into mice for 1 or 2 weeks. Fibronectin immunogold labeling of the newly formed crystals on surfaces of high-resolution transmission electron microscopy sections of retrieved implants revealed the close association of these precipitated crystals with FN. In in vitro experiments using a solution of human FN incubated in the presence of calcium phosphate crystals, we obtained apatite crystal precipitation. The fibronectin network observed in high-resolution transmission electron microscopy showed numerous clusters of very small particles (1 nm in diameter and 2 nm in length), whereas the same experiment realized as control on albumin revealed no crystal precipitation. These results demonstrate for the first time the role of FN in early biological crystal nucleation. This process could have important biological significance in accounting for ectopic calcification, primary nucleation in calcified tissue, and bone ingrowth on calcium phosphate ceramics.

Animals↗

PubMed1999

Elaboration conditions influence physicochemical properties and in vivo bioactivity of macroporous biphasic calcium phosphate ceramics.

Two different preparations of biphasic calcium phosphate (BCP) were characterized in vitro: BCP1 from a mechanical mixture of hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP) powders, and BCP2 from calcination of a calcium-deficient apatite (CDA). The structural, physicochemical and mechanical parameters of these two preparations were investigated, and two different macroporous BCP1 (MBCP1) and BCP2 MBCP2) implants were manufactured and implanted in rabbit bone for in vivo bioactivity studies. Scanning electron microscopy observations showed that MBCP1 implants had a significantly higher degradation rate (P<0.0001) than MBCP2 implants. This was probably caused by the presence of calcium oxide impurities in BCP1 and the more intimate mixture and stable ultrastructure of BCP2. No significant difference about the newly formed bone rate in these two BCP preparations was observed. Very slight variations in sintering conditions appeared to influence the biodegradation behavior of the two MBCP implants despite their identical HA/-TCP ratios and similar porosity. Precise and complete in vitro characterization enabled us to understand and predict in vivo degradation behavior.

Journal Article↗