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PubMed2004

Changes in macrophage function and morphology due to biomedical polyurethane surfaces undergoing biodegradation.

Monocytes are recruited to the material surface of an implanted biomedical device recognizing it as a foreign body. Differentiation into macrophages subsequently occurs followed by fusion to form foreign body giant cells (FBGCs). Consequently, implants can become degraded, cause chronic inflammation or become isolated by fibrous encapsulation. In this study, a relationship between material surface chemistry and the FBGC response was demonstrated by seeding mature monocyte-derived macrophages (MDMs) on polycarbonate-based polyurethanes that differed in their chemical structures (synthesized with poly(1,6-hexyl 1,2-ethyl carbonate) diol, and either (14)C-hexane diisocyanate and butanediol (BD) (referred to as HDI) or 4,4'-methylene bisphenyl diisocyanate and (14)C-BD (referred to as MDI)) and material degradation assessed. At 48 h of cell-material interaction, the FBGC attached to HDI were more multinucleated (73%) compared to MDI or the polystyrene (PS) control (21 and 36%, respectively). There was a fivefold increase in the synthesis and secretion of a protein with an approximate molecular weight of 48 kDa and a pI of 6.1 (determined by two-dimensional gel electrophoresis) only from cells seeded on HDI. Immunoprecipitation confirmed that MSE and CE were synthesized and secreted de novo. Immunoblotting also showed an increase in secreted monocyte-specific esterase (MSE) and cholesterol esterase (CE) from cells seeded on HDI relative to PS and MDI. Significantly more radiolabel ((14)C) release and esterase activity were elicited by MDMs on HDI than MDI (P < 0.05). The material that was more degradable (HDI), elicited greater protein synthesis and esterase secretion as well as more multinucleated MDMs than MDI, suggesting that the material surface chemistry modulates the function of MDM at the site of an inflammatory response to an implanted device.

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PubMed2005

The bone response of oxidized bioactive and non-bioactive titanium implants.

A number of experimental and clinical data on so-called oxidized implants have reported promising outcomes. However, little is investigated on the role of the surface oxide properties and osseointegration mechanism of the oxidized implant. Sul [On the Bone Response to Oxidized Titanium Implants: The role of microporous structure and chemical composition of the surface oxide in enhanced osseointegration (thesis). Göteborg: Department of Biomaterials/Handicap Research, University of Göteborg, Sweden; 2002; Biomaterials 2003; 24: 3893-3907] recently proposed two action mechanisms of osseointegration of oxidized implants, i.e. mechanical interlocking through bone growth in pores/other surface irregularities (1) and biochemical bonding (2). The aim of the present study is two-fold: (i) investigating the role of the implant surface chemistry on bone responses; (ii) investigating the validity of the biochemical bonding theory of the oxidized, bioactive bone implants with specific implant surface chemistry. Two groups of oxidized implants were prepared using micro arc oxidation process and were then inserted in rabbit bone. One group consisted of magnesium ion incorporated implants (MgTiO implant), the other consisted of TiO2 stoichiometry implants (TiO implant). Surface oxide properties of the implants were characterized with various surface analytic techniques. After 6 weeks of follow up, the mean peak values of removal torque of Mg implants dominated significantly over TiO implants (p < or = 0.0001). Bonding failure generally occurred in the bone away from the bone to implant interface for the MgTiO implant and mainly occurred at the bone to implant interface for the TiO implant that consisted mainly of TiO2 chemistry and significantly rougher surface as compared to the MgTiO implant. Between bone and the Mg- incorporated implant surface, ionic movements and ion concentrations gradient were detected. The current in vivo experimental data may provide positive evidence for the surface chemistry-mediated biochemical bonding theory of oxidized bioactive implants. However, the present study does not rule out potential synergy effects of the oxide thickness, micro-porous structure, crystal structure and surface roughness on improvements of bone responses to oxidized bioactive implants.

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PubMed2003

Microfabricated drug delivery systems: from particles to pores.

Microfabrication techniques which permit the creation of therapeutic delivery systems that possess a combination of structural, mechanical, and perhaps electronic features may surmount challenges associated with conventional delivery of therapy. In this review, delivery concepts are presented which capitalize on the strengths of microfabrication. Possible applications include micromachined silicon membranes to create implantable biocapsules for the immunoisolation of pancreatic islet cells-as a possible treatment for diabetes-and sustained release of injectable drugs needed over long time periods. Asymmetrical, drug-loaded microfabricated particles with specific ligands linked to the surface are proposed for improving oral bioavailability of peptide (and perhaps protein) drugs. In addition, microfabricated drug delivery systems ranging from transdermal microneedles to implantable microchips will be discussed.

Absorbable Implants↗
PubMed2001

Intraindividual comparative animal study of alpha- and beta-tricalcium phosphate degradation in conjunction with simultaneous insertion of dental implants.

An intraindividual comparative study of proximal tibial marrow defects in nine adult Goettinger miniature pigs (GMPs) was undertaken. The left side of the defect was filled with granular beta-tricalcium phosphate (TCP) ceramic ad modum Cerasorb, and the right side was filled with granular alpha-TCP ceramic ad modum Biobase alpha pore. Simultaneously, dental screw implants were inserted in each ceramic and fixed within the orthotopically replanted corticalis lids. Control defects were made in two other animals. The survival period ranged from 4 to 86 weeks (control study, 16 and 20 weeks). The reorganization and degree of bone regeneration, dynamics of ceramic degradation, and remodeling characteristics of the bone regenerate referring to osseo-integration of the dental implants were examined histomorphologically in nondecalcified specimens. The results reveal that both ceramic types were osteoconductive exclusively. Centripetally oriented angiogene bone regeneration occurred at the margins of the circular defects. Ceramic degradation was performed hydrolytically and within cells. Furthermore, it was demonstrated that decomposition of the intratrabecularly integrated ceramic residues underlies a dynamic process of degradation. Within 86 weeks, nearly 80% to 90% of the larger alpha-TCP granules, and nearly 90% to 95% of the beta-TCP granules were degraded. At this time, especially for the alpha-TCP modification, ceramic microparticles were found in the marrow, either unbound or within polynuclear macrophages. The predictable degradation of both ceramic types provides an early functional adaptation of bone regenerates and facilitates a biofunctional, anisotropic orientation of the neotrabeculae without delay. It is concluded that because of the initially pronounced accumulation of macrophages, dental implants should not be inserted simultaneously with ceramic, but after further progress of ceramic degradation (5 to 6 months after TCP implantation).

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PubMed1998

The use of a new allograft material for osseous reconstruction associated with dental implants.

This article introduces the use of a new bone graft material. The material is a human collagen allograft resorbable matrix impregnated with demineralized freeze-dried bone granules. This material is harvested from the same donor. A series of three cases of extractions with immediate implant placement accompanied by osseous defects were used to demonstrate the use of this material. Bone cores were harvested at Stage II uncovering of the implants. The histologic and clinical results are reviewed.

Absorbable Implants↗
PubMed2002

Significance of biodegradable implants in case of midfacial fractures.

The purpose of this prospective clinical study was to evaluate new resorbable implants for bone fixation. The plates and screws are made of poly (D, L)lactide (PDLLA). Bioresorbable osteosynthesis and fixation (ResorbX) has been applied in 22 patients. Indications for operations were craniofacial trauma (malar, orbital-floor or frontal bone fractures) or orthognathic procedures (Le Fort-I-osteotomies) as well as the surgical correction in case of craniofacial syndromes. In the initial follow up, the first patients showed clinically and radiologically uneventful fixation and healing of the bone. There were no implant material related complications. Overall, the advantages of PDLLA-implants appear to be their ease of use, radiolucency and resorption, although further experience is needed to determine the longterm benefits of biodegradable implants.

Absorbable Implants↗
PubMed2003

Plates, screws, and children: their relationship in craniomaxillofacial trauma.

The ideal modality for fixation of pediatric craniomaxillofacial fractures remains elusive for a number of reasons. Surgeons who manage these injuries have replaced wiring techniques with the introduction of some form of reconstructive implant. The most commonly used implants are either resorbable or semi-rigid titanium. This presentation is a synopsis of the past 30 years of the English-speaking scientific literature including plastic and reconstructive surgery, otolaryngology, head and neck surgery, oral and maxillofacial surgery, pediatric, trauma, craniofacial, materials, and biomaterials publications. While no consensus on ideal management was observed, various implant treatment options are discussed, including their indications, contraindications, considerations, and consequences after implant placement.

Absorbable Implants↗
PubMed2002

Comparative study of buccal dehiscence defects in immediate, delayed, and late maxillary implant placement with collagen membranes: clinical healing between placement and second-stage surgery.

BACKGROUND: Implants can be placed at the time of tooth extraction (immediate), after several weeks (delayed), or after complete healing (late). The purpose of this study was to evaluate clinical bone healing of buccal dehiscence-type defects around maxillary implants placed together with bioabsorbable collagen barrier membranes and bone graft at the 3 time points. METHODS: Three implant placement protocols were compared: immediate procedures primarily closed by a rotated split palatal flap (19 patients, 23 implants; group 1); delayed sites closed by a rotated (full-thickness) palatal flap at the time of tooth extraction (25 patients, 39 implants; group 2); and late implantation (22 patients, 40 implants; group 3). One to 3 proximal implants were simultaneously placed. Defect height and width were measured at the time of implant placement and at second-stage surgery. Surface area was calculated as half ellipses. RESULTS: The best results were obtained with delayed implantation. The mean percentage of the reduced defect height for groups 1, 2, and 3 was 77.4%+/-16.92%, 88.8%+/-15.29%, and 75.2%+/-17.99%, respectively, and the mean percentage area of the reduced defect was 90.2%+/-9.15%, 95.6%+/-8.73%, and 87.6%+/-11.48%, respectively. Differences between groups were statistically significant. The mean percentage of the reduced defect height and area was significantly smaller when there was spontaneous implant cover screw exposure. Single rather than multiple implant placement led to significantly better results. CONCLUSIONS: Timing of placement, number of simultaneously placed implants, and spontaneous implant exposure significantly influence clinical bone healing around maxillary implants placed together with augmentation procedures.

Absorbable Implants↗
PubMedDate not supplied

Regeneration procedures in immediate transmucosal implants: an animal study.

The aim of the present study was to evaluate bone regeneration around nonsubmerged implants placed immediately in extraction sites in the canine mandible using a combination of synthetic hydroxyapatite (HA) and collagen membranes. Ten beagle dogs were used in this study. After the second and third mandibular premolars were extracted, hollow-screw implants were placed in the distal extraction sockets. In each animal, one site received no treatment (control site), while other defects received randomly 1 of the following treatments: grafting with porous HA in the peri-implant region, collagen membrane adapted to the implant cervical collar covering the peri-implant defects, or a combination of the 2 treatments, i.e., HA grafting and membrane placement. After 4 months of healing, block biopsies were obtained and prepared for histologic analysis using the cutting-grinding technique. The histometric evaluation took into account the number of integrated screw threads, the extent of bone-to-implant contact, and the density of peri-implant bone. At sites covered by membrane alone or by membrane and HA, the number of integrated threads was statistically higher than sites treated only with HA. The extent of bone-to-implant contact was significantly different between treatments. However, the use of bioabsorbable materials did not significantly enhance peri-implant bone regeneration in immediate implantation.

Absorbable Implants↗
PubMed2001

[Assembly and evaluation of tissue engineered human cellular alveolar bony implanting materials in vitro].

OBJECTIVE: To assembly human cellular alveolar bony implanting materials in vitro and evaluate their osteogenic activities. METHODS: Human alveolar bone cells were separated from alveolar bone around the third impacted teeth of 3 patients by enzyme digestion and cultured in alpha-MEM containing beta-glycerophosphate and Dexamethasone at 5% CO2, 37 degrees C for 21-28 days. Confirmed osteoblasts-like cells were then seeded onto 3 kinds of degradable biomaterials of polyglycolic acid scaffold, collagen sponge, and L-lactic acid/epsilon-caprolactone to form the cell-scaffold complexes. The 3 types of complexes were continued to culture for 21-28 days at the same conditions. The cell proliferation, morphological changes, ALPase activity and mineral nodule formation on scaffolds were measured and observed at 3 days intervals. RESULTS: The results indicated that the cultured human alveolar bone origin cells from 3 patients could successfully express the osteoblasts phenotype in single layered culturing after stimulated by beta-glycerophosphate and Dexamethasone. The cultured osteoblast-like cells seeded on PGAS matrix had the highest attachment, proliferative and osteogenic activities, suggesting a good bio-affinity between the human alveolar osteoblast-like cells and the PGAS matrix. The statistical analysis (ANOVA) showed that there were significant differences between PGAS- osteoblasts complex and CLGS or LACT complexes on osteogenic activities (P < 0.05). CONCLUSION: PGAS-osteoblast complex is worth to be further developed into a tissue-engineered cellular artificial bony implant for reconstructing the oral-maxillofacial bony defects.

Absorbable Implants↗
PubMedDate not supplied

Repair of the perforated sinus membrane with a resorbable collagen membrane: a human study.

PURPOSE: The purpose of this study was to evaluate the results of the repair of perforated sinus membranes with resorbable collagen membrane. MATERIALS AND METHODS: A split-mouth design was followed. Twelve subjects requiring bilateral sinus grafting were included in the study; one site had been accidentally perforated during sinus augmentation and the other site had not been perforated. The perforated sites were repaired with a resorbable collagen membrane. Dental implants were placed during a second surgery, and biopsy samples were harvested from both sinuses during implant placement. New bone formation was measured for all sites. Implant survival was recorded at second-stage surgery. Panoramic radiographs were taken before and after sinus grafting and after implant placement. RESULTS: Nonperforated sites demonstrated significantly more bone formation (33.58% +/- 7.45%) than perforated sites (14.17% +/- 7.06%) (P < .0001). Perforated sites demonstrated significantly more soft tissue formation (63.58% +/- 12.96%) than nonperforated sites (48.5% +/- 12.57%) (P = .006). In nonperforated sites, residual graft particles had more of their surface in contact with bone (40.17% +/- 14.92%) than perforated sites (14.5% +/- 12.03%) (P < .0001). The implant survival rate at second-stage surgery was superior for nonperforated sites (100%) in comparison to perforated sites (69.56%) (P = .0028). DISCUSSION: This study suggested that repairing the perforated site of the sinus membrane with a resorbable collagen membrane may result in reduced bone formation and implant survival rate. A different technique and/or materials than those used in the current study may offer better results for the repair of the perforated sinus membrane. CONCLUSION: The study demonstrated that perforation and repair of the sinus membrane may compromise new bone formation and implant survival.

Absorbable Implants↗
PubMed2002

A novel polyethylene depot device for the study of PLGA and P(FASA) microspheres in vitro and in vivo.

Polymer microspheres (0.5-5.0 microm) are difficult to characterize in vivo because they degrade, migrate, and are endocytosed. A novel polyethylene mesh pouch containing microspheres allowed for retrieval of degraded polymeric products from rats without affecting the rate of degradation. Pouches containing poly(lactic-co-glycolic acid) (PLGA) or poly(fumaric-co-sebacic acid) (P(FASA)) microspheres were implanted intramuscularly, subcutaneously, and intraperitoneally and analyzed after 3, 7, 14, and 28 days. In vivo, subcutaneous or intraperitoneal implants experienced an immediate mass loss and a delayed decrease in molecular weight (Mw). Intramuscular implants behaved similarly to in vitro samples, decreasing in Mw immediately and lagging in mass loss. These results suggest that mass loss, which is usually dependent on Mw loss in vitro, may be directly due to enzymatic, rather than hydrolytic, degradation subcutaneously and intraperitoneally, while intramuscular implants appear to be mostly dependent on hydrolytic cleavage. This observation is further supported by histology. Additional experiments on pouches loaded with PLGA microspheres encapsulating osteoprotegerin, a protein drug used to prevent bone resorption, revealed that use of the device prevented the artifactual polymer compression inherent to microsphere centrifugation during release studies and allowed for the extraction of active protein from microspheres implanted for 3 days in vivo.

Absorbable Implants↗
PubMed2002

Peri-implant bone regeneration using recombinant human bone morphogenetic protein-2 in a canine model: a dose-response study.

The objective of this study was to evaluate the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) dose on alveolar ridge augmentation and dental implant osseointegration. Bilateral, 5 mm supraalveolar, peri-implant defects were surgically created in 6 beagle dogs. rhBMP-2 (0.05, 0.1 or 0.2 mg/ml) in an absorbable collagen sponge (ACS) carrier was molded around the fixtures and wounds were closed. Treatment variations were alternated between animals (incomplete block design). Animals were sacrificed at week 8 postsurgery. Nine of twelve jaw quadrants healed uneventfully. Two jaw quadrants exhibited wound failure by week 4 and one by week 8 postsurgery. Radiographic bone regeneration was observed in defects without wound failure from week 4 postsurgery. Radiolucent voids of variable size and shape were observed and regressed over time. In weeks 6 through 8, there was an apparent increase in bone density and trabecular structure, while bone height and volume decreased. Histometric analysis revealed limited differences in bone regeneration between experimental conditions. Bone regeneration area averaged (+/- SD) 1.0 +/- 0.5, 3.5 +/- 1.4 and 2.3 +/- 0.4 mm2 for the 0.05, 0.1 and 0.2 mg/ml dose, respectively. There were no significant differences in osseointegration. Osseointegration in newly formed bone averaged 19 +/- 4%, 18 +/- 10% and 21 +/- 6% for the 0.05, 0.1 and 0.2 mg/ml rhBMP-2 sites, respectively. Collectively, the data suggest that there are no dramatic differences in bone induction and osseointegration within the selected dose and observation interval.

Absorbable Implants↗
PubMed2004

Guided bone regeneration at immediate implant insertion and loading: a case report.

A tapered-end, SLA- (sandblasted and acid-etched) surfaced ITI implant was placed in a compromised ridge at the time of tooth removal. After placement of nonautogenous regenerative materials, the implant was immediately loaded with a provisional restoration within 2 hours of implant insertion. Six-month reentry demonstrated regeneration of lostalveolar bone surrounding the implant and clinical implant immobility. Clinical ramifications of these findings are discussed.

Absorbable Implants↗
PubMed2004

Resolution of bone defects of varying dimension and configuration in the marginal portion of the peri-implant bone. An experimental study in the dog.

BACKGROUND: It was demonstrated that a marginal defect of about 1 mm between the bone wall and the metal surface after implant installation can heal with a high degree of bone fill and osseointegration. OBJECTIVE: The aim of the present animal experiment was to study bone healing at implant sites with hard tissue defects of varying dimensions and configuration. MATERIAL AND METHODS: Four Labrador dogs were used. All mandibular premolars and first molars were extracted. After 3 months of healing, five experimental sites, two control (C1, C2) and three test (T1, T2, T3) sites, were identified. In all five sites, custom-made implants with a sand-blasted, large-grit, acid-etched (SLA) surface and with an outer dimension of 3.3x10 mm, were used. In site C1, traditional implant installation was performed. In site C2, the marginal 5 mm of the canal, prepared for the implant, was widened to 5.3 mm using a step-drill. Thus, following the installation of the implant, a circumferential gap occurred between the bone tissue and the metal rod that was 5 mm deep and between 1 and 1.25 mm wide. In test site T1, the canal was widened to establish a marginal gap of 2-2.25 mm. In test sites T2 and T3, the marginal 5 mm of the canal was first widened to 5.3 mm (T2) or 7.3 mm (T3). The buccal bone wall opposite the defect was subsequently removed. Following the placement of a cover screw in sites C2, T1, T2, and T3, a resorbable membrane was placed over the defect. All implants were submerged. After 4 months of healing, block biopsies of each implant site were dissected and processed for ground sectioning. RESULTS: The observations disclosed that four-wall defects of different dimensions (1-2.25 mm wide) that occurred in the marginal portion of the recipient sites following implant installation were resolved during healing. Further, at sites where the buccal bone wall during defect preparation was intentionally removed, healing resulted in defect resolution at the mesial, distal, and lingual aspects. At the buccal aspects, healing was incomplete but the dimension of the defect was reduced by the limited amounts of new bone formation extending from the lateral and apical borders of the defect. CONCLUSION: Wide marginal defects may during healing be filled with bone. In such defects a high degree of osseointegration may occur to implants designed with an SLA surface.

Absorbable Implants↗
PubMed2002

Third-generation biomedical materials.

Whereas second-generation biomaterials were designed to be either resorbable or bioactive, the next generation of biomaterials is combining these two properties, with the aim of developing materials that, once implanted, will help the body heal itself.

Absorbable Implants↗