Normal osteoconduction and repair in and around submerged highly bisphosphonate-complexed hydroxyapatite implants in rat tibiae.

BACKGROUND: Ceramic hydroxyapatite implants have been used in dentistry for their unique compatibility with alveolar bone. Recently it was reported that bisphosphonates may be beneficial in preventing alveolar bone destruction associated with natural and experimental periodontal disease. Furthermore, bisphosphonate does prevent resorption of alveolar bone following mucoperiosteal flap surgery. We undertook a preliminary study evaluating the effects of highly bisphosphonate-complexed hydroxyapatite implants on osteoconduction and repair in rat tibiae. METHODS: Porous hydroxyapatite implants were pre-incubated in 10(-2)M bisphosphonate solutions at pH 3.49 and pH 7.32. The implants had a diameter of 2.1 mm and a height of 2 mm and adsorbed 115 microg bisphosphonate in vitro. Bisphosphonate/hydroxyapatite implants and plain hydroxyapatite implants were inserted in opposite tibial metaphyses of 35 rats. The measurement errors for the mineral density (MD) of the implants and the proximal trabecular mineral bone density (TD) were estimated by peripheral computed tomography and the bone mineral density (BMD) measurement error by dual x-ray absorptiometry. RESULTS: The measurement errors for the MD of the implants and the TD by peripheral computed tomography were 0.81% and 1.96%, respectively ex vivo. The BMD measurement error estimated by dual x-ray absorptiometry was 0.51% ex vivo. TD and BMD for bisphosphonate/hydroxyapatite implants were insignificantly higher compared to plain hydroxyapatite implants. Bisphosphonate/hydroxyapatite pre-incubated at pH 7.32 were found to be nondegradable implants, while bisphosphonate/hydroxyapatite (pH 3.49) implants were slowly degradable and lost a significant 5% of their density. Histologically, all bisphosphonate/hydroxyapatite implants appeared to be fully integrated and effective as bone replacement material in rat tibial bone. They exhibited vascularization and osteoconduction of tibial bone growth along and inside their porous structure. CONCLUSIONS: Our study suggests that normal osteoconduction and repair occurred in and around the highly bisphosphonate-complexed hydroxyapatite implants in rat tibiae.

Alveolar bone response to submerged bisphosphonate-complexed hydroxyapatite implants.

BACKGROUND: In most studies using submerged hydroxyapatite implants, maintenance of alveolar bone after tooth extraction was attempted with plain hydroxyapatite materials. However, clinical results have shown that hydroxyapatite may require biological modification with a bone resorption-inhibiting agent which may be beneficial for maintenance of alveolar bone. We conducted experimental and clinical studies to evaluate the effect of highly bisphosphonate-complexed hydroxyapatite implants on osteoconduction and repair in alveolar bone. METHODS: Porous hydroxyapatite implants were pre-incubated in 10(-2)M bisphosphonate solutions at pH 3.49. The implants had a diameter of 2.1 mm and a height of 2 mm and adsorbed 115 microg bisphosphonate. Five goats were implanted with 4 plain hydroxyapatite implants on each side of the mandible in root extraction sockets for the precision analysis of dual x-ray absorptiometry (DEXA) measurements. Ten goats were implanted with 4 bisphosphonate/hydroxyapatite implants on one side of the mandible and 4 plain hydroxyapatite implants on the opposite mandible. In a clinical study, 23 bisphosphonate/hydroxyapatite implants were placed in periodontally destroyed tooth root sockets and followed up during one year. RESULTS: The range for the bone mineral density (BMD) measurement errors for goat histologic sections was 0.48% to 1.03%. There were large differences in peri-implant BMDs in the left and right mandible of the same goat, irrespective as to whether hydroxyapatite or bisphosphonate/hydroxyapatite implants were present. This was due to local anatomical differences typical of alveolar bone. These differences were not significant. Histologically, all bisphosphonate/hydroxyapatite as well as hydroxyapatite controls appeared to be fully integrated and effective as bone replacement material in goat alveolar bone. They exhibited vascularization and osteoconduction of alveolar bone growth along and inside their porous structure. In patients peri-implant healing was clinically and radiographically comparable to plain hydroxyapatite implants. All implants were retained and no dehiscences developed. Radiographically, peri-implant radiolucencies disappeared and alveolar bone was deposited in close proximity to the implants. CONCLUSIONS: This study contributes to the understanding of the biological properties of hydroxyapatite implants as carriers for the bone-modulating agent bisphosphonate. Our study suggests that normal osteoconduction and repair occurred in alveolar bone around the highly bisphosphonate-complexed hydroxyapatite implants.

Degradable bisphosphonate-alkaline phosphatase-complexed hydroxyapatite implants in vitro.

Degradable hydroxyapatite (HA) implants complexed with the resorption inhibiting agent bisphosphonate (PCP) and the mineralizing agent alkaline phosphatase (ALP) can theoretically maintain alveolar bone mass directly after extraction of teeth. The present in vitro study investigated the surface properties of PCP-ALP-complexed HA implants in relation to the requirements of implant behavior and action. Adsorbed PCP (pH 3.49) resulted in a flattening and broadening of the phosphate peaks and the formation of carbonate peaks in the HA pattern of the implant indicating a chemical alteration of the HA surface. Adsorption of ALP onto PCP-altered HA surfaces was 26% lower than onto HA implant blank surfaces. PCP-ALP-complexed HA implants released the PCP and ALP steadily and continuously over observation periods of, respectively, 75 and 14 days. During these observation periods, the ceramic grains of the HA implant became smaller and intergrain boundaries became broader. These morphologic characteristics suggested preconditioning of the HA implant surface for future bonding and degradation in vivo. Individual grains were no longer bonded to other grains and detached from the implant which had become rounded in shape. From in vitro mice experiments we found that PCP concentrations between 10(-4) and 10(-3) M resulted in 45Ca-release from the bone HA. Our calculations showed, however, that only a total concentration of 1.4 x 10(-4) M PCP was gradually released over the whole observation period. In another experiment, it appeared that a PCP concentration in solution < 10(-3) M did not reduce ALP activity. It is concluded that release of PCP by the PCP-ALP-complexed implants is maintained at levels in the range to impair osteoclast bone resorption but not high enough to block osteoblast activity. The amount of ALP released can lead to induction of bone formation onto implant surfaces. pH-induced alterations in the microstructure and chemistry of the HA surface allow for controlled degradation of the HA implants in vitro. A PCP-ALP-complexed HA implant acting as temporary scaffolding for alveolar bone growth enhancement, mineralization, and maintenance seems to be a reasonable concept for preservation of the edentulous alveolus.

Behavior of calcium phosphate coatings with different chemistries in bone.

Calcium phosphate ceramic coatings with a hydroxyapatite chemistry applied on the surface of dental implants eliminate the need for initial mechanical retention and decrease the time necessary for bonding the implants to the bone. Hydroxyapatite-coated implants retrieved from patients were found to be compatible and to have bonded strongly to the bone, but the coatings showed thinning because of partial or total loss of coating material. This study compared the behavior in bone of newly developed fluorapatite and heat-treated hydroxyapatite coatings, with the clinically used hydroxyapatite coatings used as controls in experimental studies in dogs. The biologic responses to fluorapatite and heat-treated hydroxyapatite coatings were the same as those to hydroxyapatite coatings, and bone condensation around all coatings was histologically evident. However, the coating thickness of the fluorapatite and heat-treated hydroxyapatite coatings remained stable with only minor changes during the observation period of 24 months.

Ceramic hydroxyapatite implants for the release of bisphosphonate.

Maintaining bone mass after extraction of teeth is a major problem in the prevention of oral disease. Maintenance theoretically could be enhanced by immediate implantation of submerged ceramic hydroxyapatite (HA) implants releasing the bone resorption-inhibiting agent bisphosphonate (P-C-P). Four different types of ceramic HA implants were designed as release systems for an in vitro study and assayed in saline at a temperature of 37 degrees C during 3 months. The implants were either rod- or tube-shaped, with densities of 3.104 g/cm3 and 1.408 g/cm3 (microporous) or 2.369 g/cm3 (macro/microporous). Loading of the implants with the P-C-P was done by adsorption into the ceramic (rod-shaped implants) or by filling the reservoir of the implant (tube-shaped implants). Despite the fact that P-C-P has a high bonding affinity to HA it appeared that the release of adsorbed P-C-P from the ceramic HA occurred steady, controlled and over a long period of time. The rod-shaped implants had much better release properties than the tube-shaped implants. Microporous ceramic HA rods sintered at 800 degrees C and macro/microporous rods sintered at 1300 degrees C are considered to be promising release systems for P-C-Ps.

Histological evaluation of biocompatible orthopaedic polymer.

The biocompatibility of biocompatible orthopaedic polymer implant materials was studied in subcutaneous and bony tissue of rats and rabbits. The tissue response was evaluated by histological techniques. No bone induction capacity of biocompatible orthopaedic polymer could be observed. In rabbits, the presence of plasma cells was significantly higher than in rats. The biomaterial showed some signs of biodegradation and was not very biocompatible.

[Implants with plasma spray coatings of hydroxyapatite: an experimental study in alveolar bone]. / Implantaten met plasmaspray-coatings van hydroxylapatiet: Eerste experimentele ervaringen in alveolair bot.

Sintered hydroxyapatite ceramic can be coated to a titanium core by means of a high temperature plasma spray procedure. The biological response of alveolar bone to an implant with such a coating of hydroxyapatite was evaluated in an animal experimental study. The results indicated that the plasma spray coating gave a very strong and direct bonding to cortical alveolar bone. The shear strength between bone and ceramic was greater than the shear strength between ceramic and titanium. From a radiological, macroscopic and microscopic point of view the conclusion could be drawn that the biological properties of a plasma spray coating of hydroxyapatite are the same as the properties of bulk hydroxyapatite ceramic. The outermost layer of the hydroxyapatite coating appeared to be unstable under the experimental conditions.

Eleven-year study of hydroxyapatite implants.

An 11-year clinical research study was conducted with both unloaded bulk hydroxyapatite implants and loaded hydroxyapatite-coated titanium implants. A total of 102 submerged bulk hydroxyapatite implants were placed after extraction of teeth to maintain the volume of the residual alveolar ridge by their physical presence. All 21 implants under fixed partial dentures and 51 of 81 implants under lower complete dentures remained submucosal. A total of 71 hydroxyapatite-coated titanium implants were connected with permucosal superstructures by use of a two-stage method. Modifications in design and in implantation technique were required. This long-term research indicates that cylindrical hydroxyapatite implants are reliable devices as natural tooth root substitutes that bond directly to bone instead of simply being osseointegrated.

Effects of experimental defects of the articular disc of the temporomandibular joint in rats.

Triangular defects were made in different locations of the disc in rat temporomandibular joints. After 3 months the following effects were observed. Central defects had become rounded without gross changes in the mandibular head. Peripheral defects were enlarged towards the centre, occasionally accompanied by condylar hyperplasia. Microscopically the cartilagenous covering of the mandibular head in all operated cases was characterized by thickening, dispersion of cells normally closely packed in the intermediate zone, and the constant appearance of a tear parallel to the surface.

The healing of biologic and synthetic bone implants. An experimental study.

The aim of the present study was to investigate the osteogenic properties of different types of cancellous bone grafts inserted in large osseous defects in dogs and to compare these with those of sintered hydroxyapatite implants. Fresh cancellous autografts were rapidly revascularized and invariably induced a complete healing of the defect. Frozen and fresh cancellous allografts were largely resorbed, the latter evoking a strong antigenic response in two of the five cases. Sintered hydroxyapatite granules were largely encapsulated in fibrous tissue, neither stimulating nor inhibiting osseous ingrowth. Degradation of the hydroxyapatite implant was not observed.

Boiled and unboiled detached autogenous bone fragments--an experimental study.

Boiled and unboiled standardized detached bone fragments were compared in a canine model. The fragments were either left detached or fixed with a lag-screw. Additionally, various replacements were combined with transverse osteotomy followed by reduction and fixation with a six-hole neutralization plate based on the AO-principle. Follow-up was at 0-6 weeks, 6-12 weeks and 12-24 weeks. Examination of the specimens comprised radiology, histology, microradiography, fluorescence-microscopy and microangiography. Qualitative assessment indicated that boiled bone showed some delay in resorption and new bone formation when compared with unboiled bone after six weeks, but this difference was no longer discernible after 12 weeks. Semi-quantitative assessment revealed hardly any difference after six weeks. During the first few weeks, however, boiled fragments showed a clear delay of 10-14 days in resorption and new bone formation when compared with unboiled fragments. The clinical relevance is that detached bone fragments contaminated with street-refuse can be sterilized by boiling without harmful effects. Replacement of the boiled bone fragments shows a somewhat delayed, but otherwise normal resorption and new bone formation.

Bacterially contaminated detached autogenous bone fragments--an experimental study.

Bacterially contaminated and uncontaminated standardized autogenous bone fragments were compared in an experimental canine model. Bacterial contamination was effected by immersing in a Staphylococcus aureus suspension of 6 X 10(8)/ml for 15 minutes. The fragments were replaced and either left detached or fixed with a lag screw. In a number of cases bone replacement was combined with transverse osteotomy followed by reduction and fixation with a six-hole neutralization plate based on the AO-principle. Follow-up carried out after six and 12 weeks, comprised radiological, histological, microradiographic, fluorescence microscopic and micro-angiographic investigation. Non-quantitative assessment indicated that the rate of resorption and new bone formation in the bacterially contaminated fragments definitely exceeded that of the uncontaminated fragments. Semi-quantitative findings seemed to confirm these conclusions. After 12 weeks this difference had virtually disappeared, except in loosely replaced infected fragments, which still showed more resorption and new bone formation. Integration of all fragments was good, there was no encapsulation with sequestration.

Connective tissue as an active participant in the process of malignant growth.

This review deals with the different ways connective tissue stroma is involved both in carcinogenesis and cancer growth. Changes may be regressive or productive, of a quantitative or a qualitative nature. Both cells and extracellular matrix exhibit profound alterations. To explain the diversity of involvement it is argued that tumour cells and stroma form an integrated system that also in malignancy reacts as an entity by virtue of its many functional interrelationships.

The possible role of stromal influences in tumor cell heterogeneity. Histology and fibronectin pattern of the Yoshida sarcoma of the rat.

Yoshida tumors implanted subcutaneously in the rat are conspicuously heterogeneous. A definite zoning can be discerned. Cell nuclei range from uniform epitheloid (type I) via pleomorphic (type II) to compact (type III). Type III is seen to detach at the rim of the tumor and to infiltrate the dermis. Type I is characterized by positive pericellular fibronectin staining, type II and III are fibronectin-negative. A marked spatial relationship was seen between types II and III on one hand and the presence of collagenous stroma on the other. It is conjectured that stromal components play a role in tumor promotion or progression.