The biocompatibility of hydroxyapatite implanted in the human periodontium

Titanium Implants Coated with Hydroxyapatite Used in Orbital Wall Reconstruction-A Literature Review

With the increasing incidences of orbital wall injuries, effective reconstruction materials and techniques are imperative for optimal clinical outcomes. In this literature review, we delve into the efficacy and potential advantages of using titanium implants coated with nanostructured hydroxyapatite for the reconstruction of the orbital wall. Titanium implants, recognized for their durability and mechanical strength, when combined with the osteoconductive properties of hydroxyapatite, present a potentially synergistic solution. The purpose of this review was to critically analyze the recent literature and present the state of the art in orbital wall reconstruction using titanium implants coated with nanostructured hydroxyapatite. This review offers clinicians detailed insight into the benefits and potential drawbacks of using titanium implants coated with nanostructured hydroxyapatite for orbital wall reconstruction. The highlighted results advocate for its benefits in terms of osseointegration and provide a novel strategy for orbital reconstruction, though further studies are essential to establish long-term efficacy and address concerns.

Porous biomaterials for tissue engineering: a review

The field of biomaterials has grown rapidly over the past decades. Within this field, porous biomaterials have played a remarkable role in: (i) enabling the manufacture of complex three-dimensional structures; (ii) recreating mechanical properties close to those of the host tissues; (iii) facilitating interconnected structures for the transport of macromolecules and cells; and (iv) behaving as biocompatible inserts, tailored to either interact or not with the host body. This review outlines a brief history of the development of biomaterials, before discussing current materials proposed for use as porous biomaterials and exploring the state-of-the-art in their manufacture. The wide clinical applications of these materials are extensively discussed, drawing on specific examples of how the porous features of such biomaterials impact their behaviours, as well as the advantages and challenges faced, for each class of the materials.

Role of Biomaterials Used for Periodontal Tissue Regeneration—A Concise Evidence-Based Review

Periodontal infections are noncommunicable chronic inflammatory diseases of multifactorial origin that can induce destruction of both soft and hard tissues of the periodontium. The standard remedial modalities for periodontal regeneration include nonsurgical followed by surgical therapy with the adjunctive use of various biomaterials to achieve restoration of the lost tissues. Lately, there has been substantial development in the field of biomaterial, which includes the sole or combined use of osseous grafts, barrier membranes, growth factors and autogenic substitutes to achieve tissue and bone regeneration. Of these, bone replacement grafts have been widely explored for their osteogenic potential with varied outcomes. Osseous grafts are derived from either human, bovine or synthetic sources. Though the biologic response from autogenic biomaterials may be better, the use of bone replacement synthetic substitutes could be practical for clinical practice. This comprehensive review focuses initially on bone graft replacement substitutes, namely ceramic-based (calcium phosphate derivatives, bioactive glass) and autologous platelet concentrates, which assist in alveolar bone regeneration. Further literature compilations emphasize the innovations of biomaterials used as bone substitutes, barrier membranes and complex scaffold fabrication techniques that can mimic the histologically vital tissues required for the regeneration of periodontal apparatus.

Biomaterials, Current Strategies, and Novel Nano-Technological Approaches for Periodontal Regeneration

Periodontal diseases involve injuries to the supporting structures of the tooth and, if left untreated, can lead to the loss of the tooth. Regenerative periodontal therapies aim, ideally, at healing all the damaged periodontal tissues and represent a significant clinical and societal challenge for the current ageing population. This review provides a picture of the currently-used biomaterials for periodontal regeneration, including natural and synthetic polymers, bioceramics (e.g., calcium phosphates and bioactive glasses), and composites. Bioactive materials aim at promoting the regeneration of new healthy tissue. Polymers are often used as barrier materials in guided tissue regeneration strategies and are suitable both to exclude epithelial down-growth and to allow periodontal ligament and alveolar bone cells to repopulate the defect. The problems related to the barrier postoperative collapse can be solved by using a combination of polymeric membranes and grafting materials. Advantages and drawbacks associated with the incorporation of growth factors and nanomaterials in periodontal scaffolds are also discussed, along with the development of multifunctional and multilayer implants. Tissue-engineering strategies based on functionally-graded scaffolds are expected to play an ever-increasing role in the management of periodontal defects.

Mechanism of Hydrogen-Bonded Complex Formation between Ibuprofen and Nanocrystalline Hydroxyapatite

Nanocrystalline hydroxyapatite (nanoHA) is the main hard component of bone and has the potential to be used to promote osseointegration of implants and to treat bone defects. Here, using active pharmaceutical ingredients (APIs) such as ibuprofen, we report on the prospects of combining nanoHA with biologically active compounds to improve the clinical performance of these treatments. In this study, we designed and investigated the possibility of API attachment to the surface of nanoHA crystals via the formation of a hydrogen-bonded complex. The mechanistic studies of an ibuprofen/nanoHA complex formation have been performed using a holistic approach encompassing spectroscopic (Fourier transform infrared (FTIR) and Raman) and X-ray diffraction techniques, as well as quantum chemistry calculations, while comparing the behavior of the ibuprofen/nanoHA complex with that of a physical mixture of the two components. Whereas ibuprofen exists in dimeric form both in solid and liquid state, our study showed that the formation of the ibuprofen/nanoHA complex most likely occurs via the dissociation of the ibuprofen dimer into monomeric species promoted by ethanol, with subsequent attachment of a monomer to the HA surface. An adsorption mode for this process is proposed; this includes hydrogen bonding of the hydroxyl group of ibuprofen to the hydroxyl group of the apatite, together with the interaction of the ibuprofen carbonyl group to an HA Ca center. Overall, this mechanistic study provides new insights into the molecular interactions between APIs and the surfaces of bioactive inorganic solids and sheds light on the relationship between the noncovalent bonding and drug release properties.

Processing and Properties of Strong and Non-rigid Calcium Phosphate Cement

A calcium phosphate cement (CPC) sets to form hydroxyapatite and has been used in dental and craniofacial applications. However, when CPC was used in periodontal repair, tooth mobility resulted in the fracture and exfoliation of the brittle implants. The aim of this study was to develop CPC-chitosan lactate composites with higher strength and increased strain before failure. It was hypothesized that the incorporation of chitosan lactate would render CPC non-rigid with improved properties. Two-way ANOVA showed significant effects of chitosan lactate and powder:liquid ratio (p < 0.001) on flexural strength, strain-at-peak-load, work-of-fracture, and elastic modulus. At powder:liquid = 2, the strength (mean ± SD; n = 6) at 20% chitosan lactate was 15.7 ± 1.3 MPa, higher than 4.9 ± 1.4 MPa of CPC without chitosan lactate. At powder:liquid = 1, the strain-at-peak-load was 0.2% for CPC without chitosan lactate; it increased to 15.8% for CPC containing 15% chitosan lactate. The work-of-fracture was increased by more than ten times. The novel strong and non-rigid CPC may provide compliance for tooth mobility without fracturing the implant, and may also extend the use of CPC into the repair of larger defects in stress-bearing locations.

Advances in surfaces and osseointegration in implantology. Biomimetic surfaces

The present work is a revision of the processes occurring in osseointegration of titanium dental implants according to different types of surfaces -namely, polished surfaces, rough surfaces obtained from subtraction methods, as well as the new hydroxyapatite biomimetic surfaces obtained from thermochemical processes. Hydroxyapatite’s high plasma-projection temperatures have proven to prevent the formation of crystalline apatite on the titanium dental implant, but lead to the formation of amorphous calcium phosphate (i.e., with no crystal structure) instead. This layer produce some osseointegration yet the calcium phosphate layer will eventually dissolve and leave a gap between the bone and the dental implant, thus leading to osseointegration failure due to bacterial colonization. A new surface -recently obtained by thermochemical processes- produces, by crystallization, a layer of apatite with the same mineral content as human bone that is chemically bonded to the titanium surface. Osseointegration speed was tested by means of minipigs, showing bone formation after 3 to 4 weeks, with the security that a dental implant can be loaded. This surface can be an excellent candidate for immediate or early loading procedures.

Key words:Dental implants, implants surfaces, osseointegration, biomimetics surfaces.

Biomaterials for periodontal regeneration: a review of ceramics and polymers

Periodontal disease is characterized by the destruction of periodontal tissues. Various methods of regenerative periodontal therapy, including the use of barrier membranes, bone replacement grafts, growth factors and the combination of these procedures have been investigated. The development of biomaterials for tissue engineering has considerably improved the available treatment options above. They fall into two broad classes: ceramics and polymers. The available ceramic-based materials include calcium phosphate (eg, tricalcium phosphate and hydroxyapatite), calcium sulfate and bioactive glass. The bioactive glass bonds to the bone with the formation of a layer of carbonated hydroxyapatite in situ. The natural polymers include modified polysaccharides (eg, chitosan,) and polypeptides (collagen and gelatin). Synthetic polymers [eg, poly(glycolic acid), poly(L-lactic acid)] provide a platform for exhibiting the biomechanical properties of scaffolds in tissue engineering. The materials usually work as osteogenic, osteoconductive and osteoinductive scaffolds. Polymers are more widely used as a barrier material in guided tissue regeneration (GTR). They are shown to exclude epithelial downgrowth and allow periodontal ligament and alveolar bone cells to repopulate the defect. An attempt to overcome the problems related to a collapse of the barrier membrane in GTR or epithelial downgrowth is the use of a combination of barrier membranes and grafting materials. This article reviews various biomaterials including scaffolds and membranes used for periodontal treatment and their impacts on the experimental or clinical management of periodontal defect.

Physico-chemical characterization and biocompatibility evaluation of hydroxyapatites

The aim of this study was to evaluate the physico-chemical and biocompatibility characteristics of two different hydroxyapatites. Physical and chemical properties were analyzed using granulometric analysis, scanning electron microscopy (SEM), X-ray energy-dispersion (EDX), X-ray fuorescence (XRF) and X-ray diffraction (XRD). Biomaterials were implanted into the subcutaneous tissue on the dorsum of 36 Wistar rats, divided into the following groups: Group 1 - Gen-Ox (natural); Group 2 - HA-U (synthetic) and Group 3 - Control (Sham). After 15 and 30 days, 6 animals/period were sacrificed and the subcutaneous tissue was taken for histological and histometric analysis, giving consideration to inflammatory reaction and granule area. The granulometric test results showed a mean granule diameter of 161.6 microm (min = 19.0 microm; max = 498.0 microm) and 48.7 microm (min = 7.0 microm; max = 256.0 microm) for groups 1 and 2 respectively. Analysis with SEM demonstrated irregular and sharp-edge particles in group 1 (3332.8 +/- 274.3 microm(2)) and irregular and rounded particles in group 2 (1320.8 +/- 83.0 microm(2)) (P < 0.0001; Student's t test). EDX and XRF revealed calcium, carbon, oxygen, sodium and phosphorus in both groups. XRD indicated that both biomaterials were pure and crystalline. There was a statistically significant difference in granule area between the two groups after 15 days (P = 0.022; Student's t-test). After 15 days, an increased inflammatory response was seen in group 2 (P < 0.0001; ANOVA and Tukey's post hoc test) whereas it was more pronounced in group 1 after 30 days (P < 0.0001; ANOVA and Tukey's post hoc test). It was concluded that these biomaterials have similar physical, chemical and biocompatibility characteristics.

Behaviour of an injectable calcium phosphate cement with added tetracycline

A calcium phosphate cement containing an antibiotic can be used for filling bone defects and to ensure local antibiotherapy. A calcium phosphate cement (already marketed under the name of Cementek can become injectable thanks to the addition of silicone. For dental applications, the behaviour of this injectable cement with added tetracycline was investigated. The tetracycline hydrochloride does not allow maturation of the cement: the tetracycline has to be treated with a calcium sulphate solution. The treated tetracycline (TTC) allowed maturation of the cement towards hydroxyapatite. But the setting time was longer and the mechanical properties decreased. Study in a continuous flow cell showed that the tetracycline is released in a continuous manner: thus, after 6 days, 60% of the antibiotic was released into the surrounding medium.

Tissue response to titanium implantation in the rat maxilla, with special reference to the effects of surface conditions on bone formation

Tissue responses to titanium implantation with two different surface conditions in our established implantation model in rat maxillae were investigated by light and transmission electron microscopy and by histochemistry for tartrate-resistant acid phosphatase (TRAPase) activity. Here we used two types of implants with different surface qualities: titanium implants sandblasted with Al2O3 (SA-group) and implants coated with hydroxyapatite (HA-group). In both groups, bone formation had begun by 5 days postimplantation when the inflammatory reaction had almost disappeared in the prepared bone cavity. In the SA-group, however, the bone formation process in the bone cavity was almost identical to that shown in our previous report using smooth surfaced implants (Futami et al. 2000): new bone formation, which occurred from the pre-existing bone toward the implant, was preceded by active bone resorption in the lateral area with a narrow gap, but not so in the base area with a wide gap. In the HA-group, direct bone formation from the implant toward the pre-existing bone was recognizable in both lateral and base areas. Many TRAPase-reactive cells were found near the implant surface. On the pre-existing bone, new bone formation occurred with bone resorption by typical osteoclasts. Osseointegration around the implants was achieved by postoperative day 28 in both SA- and HA-groups except for the lateral area, where the implant had been installed close to the cavity margin. These findings indicate that ossification around the titanium implants progresses in different patterns, probably dependent on surface properties and quality.

Chitosan-based gastrointestinal delivery systems

Chitosan, a natural polymer obtained by alkaline deacetylation of chitin, is non-toxic, biocompatible, and biodegradable. These properties make chitosan a good candidate for the development of conventional and novel gastrointestinal (GI) drug and gene delivery systems. The objective of this review is to summarize the recent applications of chitosan in oral and/or buccal delivery, stomach-specific drug delivery, intestinal delivery, and colon-specific drug delivery. The use of chitosan for targeting of drugs to each of these sites in the GI tract is illustrated by examples supported by in vivo studies. Chitosan appears to be a promising material for GI drug and gene delivery applications as many derivatives and formulations are being examined.

Bioabsorbable materials for guided bone regeneration prior to implant placement and 7-year follow-up: report of 14 cases

BACKGROUND

The purpose of the present study was to evaluate the efficacy of a guided bone regeneration (GBR) procedure prior to implant placement and the long-term outcome of the inserted implants.

METHODS

Prior to dental implant placement, GBR procedure was performed on 14 patients (mean age 48 years) using a synthetic hydroxyapatite (HA) spacer under a collagen membrane. After a mean healing period of 8 months, bone biopsies were obtained during the placement of 14 implants. The specimens were processed for histology without demineralization in order to assess bone quality and quantity of the regenerated bone.

RESULTS

Both the bone density and the resorption degree of HA particles were relatively varied between samples. The different phenotypes of osteoclasts and multinucleated giant cells and the individual host response could partially explain the unpredictable results in terms of bone remodeling and biomaterial resorption. However, the presence of HA particles in the regenerated bone had no influence on the osseointegration of implants presenting a success rate of 86% after a 7-year observation period.

CONCLUSIONS

These results confirm the possibility of regenerating bone by means of bioabsorbable materials, assuring at the same time the long-term success for implants inserted in regenerated sites.

Use of bovine-derived anorganic bone associated with guided tissue regeneration in intrabony defects. Six-month evaluation at re-entry

BACKGROUND

Different filling materials have been associated with guided tissue regeneration (GTR) in order to improve its regenerative potential and predictability. Anorganic bovine bone (ABB) has demonstrated biocompatibility and osteoconductive properties; however, there are limited data regarding its performance in the treatment of intrabony defects. This investigation aimed to evaluate the clinical outcome of the association of anorganic bovine bone with cellulose membranes in intrabony defects after 6 months.

METHODS

Twenty-six paired intrabony defects were selected from 11 non-smoking patients with no relevant medical history. The defects were similar regarding the number of bony walls and defect depth, and presented pocket depths > or = 6 mm. Four weeks after completion of basic therapy, probing depth (PD), clinical attachment level (CAL), and gingival margin position (GP) were recorded (baseline values). The defects were then surgically accessed and debrided, and the intrabony component measured to the nearest millimeter with periodontal probes and customized acrylic stents (distance from the stent to the base of the defect and from the stent to the alveolar crest). Each intrabony defect was randomly assigned to receive the membrane alone (control, C) or the membrane with anorganic bovine bone (test, T). The patients were re-evaluated after 6 months, and re-entry procedures were performed.

RESULTS

Significant (P <0.01) improvement in all variables was observed: mean pocket reduction of 4.61+/-1.60 mm (C) and 4.46+/-1.50 mm (T) and clinical attachment gain of 2.85+/-1.46 mm (C) and 3.15+/-1.40 mm (T); the difference between groups was not significant (P >0.05). Nevertheless, gingival recession in the control group (1.84+/-0.89 mm) was significantly (P <0.05) more pronounced than that observed in the test group (1.30+/-0.48 mm). Bone measurements indicated a significant resolution of the defects (P <0.01). A mean defect resolution of 2.76+/-0.72 mm (C) and 2.69+/-1.03 mm (T) and crestal resorption of 1.07+/-0.64 mm (C) and 1.30+/-0.85 mm (T) were detected (P >0.05). Stepwise multiple regression analysis indicated that for both groups, the baseline depth of the defects and the alveolar crest resorption accounted for 82% of the variability of bone fill observed in the control group (F = 23.65, P <0.001) and 89% in the test group (F = 41.32, P <0.001).

CONCLUSIONS

ABB may be used in conjunction with GTR in the treatment of intrabony defects. Its use, however, did not result in a better outcome than the use of membranes alone. Studies employing more patients would be of interest in order to determine the advantages and indications of the tested approaches on a more predictable basis.

Combined collagen membrane and hydroxyapatite/collagen chondroitin-sulfate spacer placement in the treatment of 2-wall intrabony defects in chronic adult and rapidly progressive periodontitis patients

This study, confined to non-smokers, evaluated guided-tissue regeneration in deep 2-wall intrabony defects using a diphenylphosphorylazide-cross-linked bovine type I collagen membrane supported by a hydroxyapatite/collagen/chondroitin-sulfate spacer in 43 adult periodontitis (AP) and 14 rapidly progressive periodontitis (RPP) patients, no more than 1 defect being randomly selected for each patient. Before surgery and 6 months after surgery, plaque (PI) and sulcus bleeding (SBI) indices, probing pocket depths (PPD), gingival margin locations (GML) and probing attachment levels (PAL) were recorded. During the post-surgical period, the biomaterials were well tolerated in all patients and PI and SBI were kept at a low level. Following therapy, there was a significant gain in PAL (4.2 mm for AP; 3 mm for RPP) and reduction in PPD (6.1 mm for AP; 4.7 mm for RPP) for both groups of patients (p < 0.05). A significantly greater gain in PAL and reduction in PPD were observed for AP compared to RPP patients (p < 0.05). The change in GML was not statistically different between groups (1.8 mm for AP; 1.6 mm for RPP). It is concluded that the combined use of a diphenylphosphorylazide-cross-linked bovine type-I collagen membrane, supported by a hydroxyapatite/collagen/chondroitin-sulfate spacer, is beneficial in improving PAL and reducing PPD in 2-wall intrabony defects in both AP and RPP patients during the quiescent phase of the disease, with statistically better results for the former group. However, longer observation periods are necessary to evaluate the stability of the improvements obtained by this combined treatment approach between and for each group of patients.

HRTEM study of biological crystal growth mechanisms in the vicinity of implanted synthetic hydroxyapatite crystals

Calcium phosphates are widely used as biomaterials. Ultrastructural assessments are of the utmost importance in our understanding of interfacial phenomena. The aim of this study was to learn more about the newly formed crystal growth mechanisms. The interfaces between implanted synthetic hydroxyapatite crystals (HAS) and newly formed crystallites were thoroughly examined on a molecular level. The bone-grafting material (HAS) was implanted into two adult patients, and small biopsies were recovered 6 months after implantation. The raw biomaterial was analyzed by x-ray diffraction and high-resolution transmission electron microscopy (HRTEM). Six months after their implantation, the HAS aggregates were surrounded by a mineralized bone matrix. Tiny crystallites also filled the spaces between the HAS crystals within the aggregates. These newly formed crystallites growing at the surfaces of the implanted HAS crystals appeared to be apatitic. The crystallographic investigations of the nucleation and growing mechanisms of the newly formed crystallites were performed by HRTEM in association with computer simulation and mathematical processing of digitized images. A relationship was noted between the orientation axes of crystallites growing nearby and the zone axes of the implanted HAS, thus strongly suggesting a guiding or substratum role of the HAS particles.

Net-shaped hydroxyapatite implants for release of agents modulating periodontal-like tissues

Periodontal-like tissues and, in particular, alveolar bone- and root cementum-like material can theoretically be modulated by release of biochemical agents such as bisphosphonate (PCP), growth hormone (GH) and alkaline phosphatase (ALP) from the implant surface. The present research focused on porous ceramic hydroxyapatite (PCHA) implants. In the past the PCHA implants were machined on a lathe out of simple blocks of PCHA ceramic. This was a tedious and cumbersome method, often resulting in implants with undesirable characteristics: different porosities, cracks and fractures. Therefore a moulding technique was developed to sinter near-net-shaped PCHA implants at 2 different sintering temperatures: 1170 degrees C and 1280 degrees C, resulting in PCHA implants with porosities of 62.06% (PCHA type 1) and 40.74% (PCHA type 2), respectively. After 1 h incubation in a 10(-2) M solution of PCP, the total amounts adsorbed onto PCHA type 1 and type 2 were 114.9 +/- 2.1 micrograms and 46.1 +/- 1.5 micrograms, respectively. This was approximately 5 times higher than after incubation for 1 wk in a 10(-4) M solution of PCP. The total amounts of PCP released after the observation period of 75 d from PCHA type 1 and type 2 after incubation in the 10(-2) M solution were 103.1 +/- 1.8 micrograms and 42.8 +/- 1.5 micrograms, respectively. The total amounts released from type 1 and 2 after incubation in the 10(-4) M solution were 7.4 +/- 0.4 micrograms and 4.1 +/- 0.1 micrograms, respectively. After 2 wk of incubation in a liver/bone/kidney ALP solution the total amount of ALP adsorbed onto PCHA type 1 implants was 5039 +/- 412 mU/ml. The total amounts of ALP released were 4674 +/- 438 mU/ml and 53 +/- 20 mU/ml after 1 and 2 wk, respectively. The release of ALP was high at the beginning but slowed down thereafter. It was evident that despite the well-known high bonding affinity of PCP to HA the release of PCP occurred steadily, over a long period of time in vitro.

Ultrastructural aspects of the intact titanium implant-bone interface from undecalcified ultrathin sections

An osseointegrated oral implant with surrounding bone was used for electron microscopical analyses of the implant-bone interface. The bulk metal was removed by sawing and grinding techniques, leaving only the plasma-sprayed titanium coating anchored in mineralized bone. Ultrathin sections were realized from these reduced interface areas and underwent ultrastructural and crystallographic assessments. The microscopical observations showed that ultramicrotomy was suitable for producing such interface sections. Two different, concomitant, interfacial structures were noticed. On the one hand it was possible to observe bone crystals directly apposed on the implant surface; on the other, a granular electron-dense substance was interposed between the plasma-sprayed coating and the bone. The applied technical approach allows one to study the osseointegration process, at high resolution levels, of intact interfaces from complete osseointegrated implants.

Osteoclastic resorption of calcium phosphates is potentiated in postosteogenic culture conditions

Cell-mediated resorption of densely sintered hydroxyapatite (HA1250), tricalcium phosphate (TCP), and 600 degrees or 900 degrees C calcined hydroxyapatite (HA600 and HA900, respectively), was investigated by using two culture systems. The first was an osteoclastic cell culture, and the second was a two-stage culture that was composed of a bonelike tissue formation on the substrata in the first stage and its subsequent resorption by osteoclasts in the second stage. Neither of the materials showed resorption or surface alterations in the osteoclastic cell culture, except for some limited phagocytotic activity on HA600 and HA900. In the two-stage culture, production of mineralized extracellular matrix was only observed on HA1250 and TCP, and its subsequent resorption by osteoclastlike cells was evident. Small and occasionally larger tartrate-resistant acid phosphatase positive cells produced 20-150 microns diameter resorption pits in both the mineralized extracellular matrix on HA1250 and TCP and the surfaces of HA600 and HA900. Resorption of the mineralized extracellular matrix on TCP also resulted in degradation of the underlying ceramic surface, mainly initiating from intergrain boundaries, whereas the surface of HA1250 remained unaltered. The results of this study clearly demonstrate that osteoclastic resorption of calcium phosphates is potentiated in postosteogenic culture conditions. A possible role for bone matrix constituents in cell-mediated resorption is hypothesized, whereas the occurrence of resorption seems to be mainly governed by the combined effects of material characteristics such as grain size and crystal structure.

Osteoclastic resorption of Ca-P biomaterials implanted in rabbit bone

The nature of the multinucleated cells involved in the resorption processes occurring inside macroporous calcium-phosphate biomaterials grafted into rabbit bone was studied using light microscopy, histomorphometric analysis, enzymatic detection of tartrate-resistant acid phosphatase (TRAP) activity, scanning, and electron microscopy. Samples were taken at days 7, 14, and 21 after implantation. As early as day 7, osteogenesis and resorption were observed at the surface of the biomaterials, inside the macropores. Resorption of both newly formed bone and calcium-phosphate biomaterials was associated with two types of multinucleated cells. Giant multinucleated cells were found only at the surface of the biomaterials; they showed a large number of nuclei, were TRAP negative, developed no ruffled border, and contained numerous vacuoles with large accumulation of mineral crystals from the biomaterials. Osteoclasts exhibited TRAP positivity and well-defined ruffled border. They were observed at the surface of both newly formed bone and biomaterials, around the implant, and inside the macropores. In contract with the biomaterials, infoldings of their ruffled border were observed between the mineral crystals, deeply inside the microporosity. The microporosity of the biomaterials (i.e., the noncrystalline spaces inside the biomaterials) increased underneath this type of cell as compared with underneath giant cells or to the depth of the biomaterials. These observations demonstrate that macroporous calcium-phosphate biomaterials implanted in bone elicit osteogenesis and the recruitment of a double multinucleated cell population having resorbing activity: giant multinucleated cells that resorb biomaterials and osteoclasts that resorb newly formed bone and biomaterials.

Biodegradation and bioresorption of calcium phosphate ceramics

The use of several calcium phosphate (Ca-P) materials for bone repair, augmentation, substitution and as coatings on metal implants has gained clinical acceptance in many dental and medical applications. These Ca-P materials may be of synthetic or natural origin, available in different physical forms (dense or macroporous, particles or blocks) and are used in bulk as coatings for metallic and non-metallic substrates or as components in composites, cements and bioactive glasses. Biodegradation or bioresorption of calcium phosphate materials implies cell-mediated degradation in vitro or in vivo. Cellular activity during biodegradation or bioresorption occurs in acid media; thus the factors affecting the solubility or the extent of dissolution (which in turn depends on the physico-chemical properties) of the Ca-P materials are important. Enrichment of the microenvironment due to the release of calcium and phosphate ions from the dissolving Ca-P materials affects the proliferation and activities of the cells. The increase in the concentrations of the calcium and phosphate ions promotes the formation of carbonate apatite which are similar to the bone apatite. The purpose of this invited paper is to discuss the processes of biodegradation or bioresorption of Ca-P materials in terms of the physico-chemical properties of these materials and the phenomena involved including the formation of carbonate apatite on the surfaces and in the vicinity of these materials. This phenomenon appears to be related to the bioactivity of the material and the ability of such materials to directly attach to bone and to form a uniquely strong material-bone interface.

Human gingival tissue response to HTR polymer

Biopsies secured during reentry surgical evaluation of previously treated periodontal osseous defects were examined for gingival tissue response to HTR polymer. Eleven patients provided biopsies of HTR grafted sites 6-7 months after initial implantation. Minimal inflammation and infrequent foreign body giant cells were found. Bone was present in about half of the samples and osteogenesis associated with the HTR graft material was seen in about 20% of the biopsies. Serendipitously, biopsies of other graft materials or debridement only sites from 6-30 months post-treatment were also available for analysis and comparison, and showed similar tissue response. The results of this study suggest that HTR polymer (and other graft materials) is very biocompatible and elicits no untoward gingival tissue responses when placed in periodontal osseous defects.

Ultrastructural and ultracytochemical characteristics of multinucleated cells after hydroxyapatite implantation into rat periodontal tissue

Multinucleated cells (MNCs) that appeared after hydroxyapatite (HAP) implantation into experimentally-produced bone defects in rat periodontal tissues were investigated both ultrastructurally and ultracytochemically. At day 5 after implantation, MNCs first appeared along the HAP surface. They had no features of typical osteoclasts such as ruffled border and clear zone. By d 14, these cells acquired features similar to osteoclasts, including ruffled border and clear zone. With the appearance of ruffled borders in MNCs, new bone deposited around the implanted HAP. MNCs appeared to excavate both newly-formed bone and implanted HAP simultaneously. Ingested HAP particles were observed not only in MNCs but also in macrophages. MNCs contained both tartrate-resistant acid phosphatase (ACPase) and carbonic anhydrase (CAase). ACPase activity was detected along all the biosynthesizing pathways in MNCs. Extracellular ACPase activity around the ruffled border region was also demonstrable. CAase activity could be detected only in the cytosol, vesicles and mitochondrial cristae of the MNCs. These cytochemical characteristics were almost the same regardless of the time elapsed after implantation.

Ultrastructural demonstration of the importance of crystal size of bioceramic powders implanted into human periodontal lesions

Stages in bone formation were studied ultrastructurally after the implantation of the following 3 bioceramic powders into human periodontal lesions: (1) beta-tricalcium phosphate whitlockite (Synthograft) consisting of particles with a mean length of 229 +/- 87 microns in SEM and appearing in TEM as crystals with a mean diameter 488 +/- 192 nm; (2) an hydroxyapatite (Bioapatite) which consisted of particles with a mean length of 283 +/- 87 microns in SEM and of crystals with a mean diameter of 146 +/- 47 nm in TEM; and finally (3), a microsized hydroxyapatite consisting of elongated platelets with a mean length of 32 +/- 4 microns in SEM, composed of small crystals with a mean diameter of 38 +/- 16 nm in TEM. In a preliminary experiment in rats, it appeared that the microsized hydroxyapatite implanted into the alveolar region after first molar extraction exhibited biocompatibility. In 6- and 12-month biopsies, it appeared that bone formation in association with the 3 bioceramics tested in human periodontal lesions occurred through similar mechanisms at the ultrastructural level. After the appearance of peripheral fibroblast-like or osteoblast-like cells with an interposed layer reminiscent of an osteoid tissue, collagen fibrils were observed in the intercrystalline spaces. These spaces subsequently underwent mineralization, with deposition of bone apatite crystals followed by the peripheral deposition of a thin inner bone layer with a granular appearance and an outer normal bone layer of either woven bone, lamellar bone or bone with parallel calcified collagen fibrils. These bone nodules, however, formed around the bioceramic particles at highly variable time intervals. Bone formation was observed around Synthograft and Bioapatite implants only in 12-month biopsies, and thicker layers of peripheral bone were observed with the latter hydroxyapatite implant. With microsized hydroxyapatite, a significant amount of peripheral bone formation had already occurred by 6 months, strongly suggesting an important effect of crystal size on bone formation.

In vitro properties of a chitosan-bonded hydroxyapatite bone-filling paste

A possible bone substitute material for dental treatment was developed and tested. The material is composed of powdered hydroxyapatite (HA), ZnO and CaO, kneaded into a chitosan sol to make a quick-hardening paste. A composition was found which showed neutral pH, short setting time, and relatively high compressive strength. The use of such a paste for the treatment of periodontal defects or the augmentation of edentulous alveolar ridges may alleviate problems now associated with the implantation of particulate HA, such as early migration of particles and recontouring of the implant.

Mechanical behavior of mandibular continuity defects reconstructed using combinations of hydroxylapatite and autogenous bone

The purpose of this investigation was to determine the mechanical behavior of primate (Macaca mulatta) mandibles with continuity defects reconstructed using varying ratios of an alloplastic hydroxylapatite (HA) implant material mixed with autogenous bone (AB). The defects were allowed to heal for 6 and 18 months before killing the animals and mechanical testing. Each animal had one side of the mandible restored with 100% AB as control. The fracture strength and section modulus of the opposite side of the mandible, containing the test ratio of HA-AB, were directly compared with the mechanical behavior of the control side. The fracture strength and section modulus were evaluated by a cantilever type of mechanical test that took into account the anisotropic, viscoelastic, and geometric nature of the mandible. The type of bone and tissue at the fracture site was examined by scanning electron microscopy and a direct correlation between the amount of bone and/or fibrous tissue growth around the HA implant material and the fracture strength and section modulus values was established. The average fracture strength of the AB graft sites at 18 months was 9,975 +/- 4,300 psi, with ratios of 25:75 and 50:50 HA-AB giving test results approaching those of the AB graft sites.

The diagnostic value of subtraction radiography in the assessment of granular hydroxylapatite implants

Although histologic analysis of osseous changes around hydroxylapatite (HA) implants can be highly accurate, it is of limited use in human beings. Digital subtraction radiography may provide a noninvasive alternative. Ten patients with bony lesions were operated on and nine of the iatrogenic defects were filled with granulated HA. In one patient, the defect was left unfilled for reference. Customized film holders provided standardized radiography. Follow-up images after 4 to 6 months were subtracted from immediately obtained postoperative images, and changes around the implants were noted. From ten pairs of radiographs, eight could be successfully subtracted, whereas two pairs required corrective image transformation before subtraction. Although no bone loss was observed in any of the patients, the implants did not appear to enhance physiologic bone regeneration either. Hence, subtraction radiography holds the potential of clinical utility for the follow-up of HA implants. However, technical improvements are necessary to yield quantitative data.

Restoration of mandibular continuity defects using combinations of hydroxylapatite and autogenous bone: microscopic observations

The purpose of this investigation was to assess by light, transmission, and scanning electron microscopy the healing of mandibular continuity defects reconstructed with varying ratios of an alloplastic hydroxylapatite implant material (HA) mixed with autogenous bone (AB). This study reports the microscopic observations of implant and control sites at 6 and 18 months postsurgery. The results confirm the biocompatibility of dense HA granules. Specimens exhibited differing degrees of osseous regeneration that appeared related to the percent composition of HA. At 18 months, 86% and 91% of the HA granules were completely surrounded by bone in those specimens reconstructed with implants consisting of 25% and 50% HA, respectively. In contrast, specimens receiving implants consisting of 75% and 100% HA features osseous encapsulation of 75% and 66% of the granules, respectively. The results of this limited study indicate that dense HA granules mixed with AB in ratios ranging from 3:1 to 1:1 (AB:HA) may be successfully used as a bone extender during reconstructive surgery.

Histological investigation of the tissue response to hydroxyapatite used as an implant material in periodontal treatment

Patients with severe periodontitis and who had one or more teeth with infrabony pockets were treated by periodontal surgery with implantation of hydroxyapatite particles into the bone defects at the time of surgery. Subsequently, in three patients it was found necessary to extract a tooth for reasons not related to the previous periodontal treatment. Specimens that included the local soft tissues and crestal bone attached to the teeth were obtained at 22, 40 and 80 weeks after placement of the implant. They were decalcified and stained with haematoxylin and eosin and examined under light microscopy. The healing response was found to vary between specimens, and between sites within the same specimen. The early stage of healing showed the implant particles surrounded by collagen. Subsequently, varying degrees of resorption of the periphery of the particles was seen, and at some sites bone deposition was observed. These different healing responses were found to be progressing concurrently at sites in close proximity. Further work is needed to confirm the histological findings described in the paper.

Differential diagnosis of severe periodontal lesions

In current clinical practice, a differential diagnosis of severe localized periodontal lesions is rarely made; such lesions are considered to be manifestations of periodontitis caused by specific microbes from the commensal oral flora. However, deep seated lesions of the periodontium which are in communication with the alveolar crest, are well documented periodontal consequences of pulpal pathoses and can mimic the signs and symptoms of 'periodontitis'. The very low incidence of tooth-threatening periodontal disease in ancient and modern man is revealed when differential diagnoses are used in the examination of alveolar defects in anthropological materials and when epidemiological studies use more appropriate indices. However, no periodontal index to date has incorporated a differential diagnosis between gingival and pulpal causes of alveolar bone loss. The gingival and periodontal signs of severe localized periodontal lesions are reviewed and the imprecise nature of current clinical diagnostic tests (radiography, 'pulp testing', darkfield microscopy, bleeding on probing, periodontal probing) is discussed. None of these tests is able to detect disease activity and cannot be used to predict future patterns of disease behaviour. However, the commonly held belief that the tests are accurate has resulted in most severe periodontal lesions being falsely labelled as periodontitis. Failure to carry out differential diagnosis of severe periodontal lesions has resulted in the instigation of periodontal therapy for many lesions of non-gingival origin. Whenever severe localized lesions of the periodontium are detected, the differential diagnosis between pulpal and periodontal origins should be made. The results of diagnostic tests in current use should be interpreted with extreme caution; clinicians are left to exercise their judgment based on consideration of all the available evidence.

Ultrastructural and histochemical study of beta-tricalcium phosphate resorbing cells in periodontium of dogs

beta-TCP was implanted in surgically prepared alveolar bone defects on the mesial side of the upper canine. The dogs that we used were sacrificed after 5 weeks, fixed by perfusion, and the beta-TCP resorbing cells were examined ultrastructurally and histochemically, with the following results: (1) beta-TCP was resorbed by macrophages and multinucleated giant cells. (2) Mitochondria, vacuoles and Golgi apparatus were abundant in beta-TCP-resorbing multinucleated giant cells that possessed neither ruffled borders nor clear zones. (3) The addition of tartric acid inhibited acid phosphatase activity in the cytoplasm of the multinucleated giant cells and macrophages.

A clinical, radiographic, and histological evaluation of permucosal dental implants of dense hydroxylapatite in dogs

A clinical, histological, and radiographic examination was performed on 77 permucosal dental implants, made of dense sintered hydroxylapatite: 34 solid cylinders and 43 hollow cylinders. The hollow cylinders were pre-compressed between two titanium caps. The implants were placed in partly edentulous mandibles of dogs, and were physiologically loaded. Healing was clinically and radiographically evaluated during a six-month to five-year period. At various times, implants with their surrounding tissues were removed and prepared for light and electron microscopy. All implants showed a good initial fit and were maintained in place without undercut or mechanical stabilization. After 18 months, 76% of the solid cylinders had fractured at the implant/bone junction due to fatigue. However, the submerged portions of the solid cylinders were preserved without clinical problems, and became entirely embedded in bone. The pre-stressed implants did not fracture, and 91% were functioning 24 months after placement. The average scores of pocket depths and gingival bleeding showed no significant differences between implants and surrounding natural teeth. Bone deposition occurred on the entire surface of the implant below the crest of the alveolar bone, and intimate bone contact was confirmed by electron microscopy. It was also observed that a layer of bone tissue was deposited on the implant surface in the permucosal area just above the alveolar bone level. Embedding of gingival fibers in this layer resulted in gingival attachment to the implant, comparable with that of natural teeth.