Growth and differentiation of human bone marrow osteoprogenitors on novel calcium phosphate cements

Materials that augment bone cell proliferation and osteogenic activity have important therapeutic implications for bone regeneration and for use in skeletal reconstruction and joint replacement. We have studied the growth and interactions of human bone marrow cells on a variety of new cement composites in vitro. These cement materials are composed of calcium-deficient hydroxyapatites, carbonated apatite and amorphous calcium phosphate. Cell proliferation was significantly reduced and cell differentiation increased in the presence of these cements compared with cells cultured on tissue culture plastic. Alkaline phosphatase, one of the markers of the osteoblast phenotype, was dramatically stimulated by 3 of the 4 cements examined between day 4 and day 10, above levels observed following culture of human osteoblasts on plastic alone. Photomicroscopic examination demonstrated growth and close integration of bone marrow cells and 3 of the composites. Longer term marrow cultures (15 day) on the cements confirmed the stimulation of cell differentiation over proliferation. From these studies, enhanced osteoblastic differentiation was observed on a 70% carbonated apatite, which has a composition similar to bone mineral, whereas, cell toxicity was observed on cells grown on amorphous calcium phosphate. This in vitro culture system demonstrates the use of human bone marrow cells for the potential evaluation of new biomaterials and the development of a novel carbonated apatite that may be of potential use in orthopaedic implants.     

Changes in skeletal metabolism in pubertal girls can be revealed by biochemical parameters of calcium metabolism and bone turnover

Biochemical changes related to skeletal turnover in puberty were investigated in a sample of 67 girls aged 8-14 years. The following biochemical parameters were measured in serum: total calcium, phosphate, magnesium, total alkaline phosphatase, osteocalcin, and calcium and hydroxyproline in the second morning urine. Thirty-five premenarchal girls (8-11 years) had significantly lower serum calcium, and higher alkaline phosphatase and phosphate than those menstruating regularly (N = 32, 12-14 years). A statistically significant negative correlation of serum parameters and age was found for phosphate and alkaline phosphatase in all subjects, and for calcium and magnesium only in the premenarchal girls. These results indicated the more intensive processes of skeletal metabolism occurring in prepubertal age and early puberty to reflect in basic biochemical parameters of calcium and bone metabolism. Analysis of correlation between biochemical parameters showed alkaline phosphatase and phosphate to correlate positively with hydroxyproline excretion and negatively with urinary calcium in all subjects. In the subjects after menarche, osteocalcin correlated with alkaline phosphatase and phosphate. Thus, biochemical parameters indirectly reflected physiologic changes occurring with bone turnover in puberty. Variations in bone turnover during puberty, including a more pronounced bone formation during prepubertal or early stages, can be indirectly observed through biochemical parameters related to calcium and bone metabolism. Investigations of skeletal growth and puberty would benefit from specific markers of bone remodeling and "basic" biochemical parameters, as it might disclose subtle metabolic relationships.     

Experimental bone replacement with resorbable calcium phosphate ceramic (author's transl)

Compact cylindrical implants (5 x 15.5 mm) of seven calcium phosphate ceramics of different formulations that had been implanted for 6 weeks without fixation in the tibia of dogs were examined histologically. The tissue compatibility of the implant turned out to be dependent on the mineralogical and chemical composition of the material: the ceramic material was biocompatible at a CaO/P2O5 ratio between 2:1 and 4:1, the optimum ratio being about 3:1 (tricalcium phosphate). In addition, cylindrical tetracalcium phosphate implatns with an entirely porous structure were implanted in the same manner. After 6 months, they were resorbed to a minor extent. Implants of different calcium phosphate mixtures, on the other hand, were resorbed to a large extend after the same time. The ceramic material was replaced by mineralised bone tissue which had formed directly on the ceramic implant as well as within the pores. There were no foreign body reactions. Investigations with segment-shaped implants which were implanted in the tibia of dogs and fixed with AO-plates or splints extra-cutaneously for about 8-10 weeks, provided information abouth the maximum stress that can be borne by the implants. While implants with a porosity of 75 percent did not sustain the stress after the fixation had been removed, those with a porosity of 45 percent could be subjected to physiological stress after removal of the splints.     

One hundred years of orthopedics in the Netherlands. VII. biomaterials

The use of biomaterials in orthopaedics is becoming increasingly important. They are widely used in artificial joints, as bone replacement material and as resorbable material. Also (recombinant) bone morphogenetic proteins are used. Classification of biomaterials is based on composition (animal or human tissue, metals, polymers, ceramics or composites) or on biological reactions after implantation (bio-inert, bio-tolerant or bio-active). Depending on location and function biomaterials have to meet requirements with respect to durability (artificial joints), fixation (total hip prosthesis), flexibility (artificial ligaments), solubility (suture wire) and stiffness (plates and screws). The development of biomaterials is in full swing, focussing on the decrease of wear and the increase of durable fixation of artificial joints, and the induction of cells to form bone and cartilage tissue.     

Inter-relationships of carbonate, phosphate, monohydrogen phosphate, calcium, magnesium and sodium in uraemic bone: comparison of dialysed and non-dialysed patients

1. Chemical and morphological features of uraemic bone disease were studied by comparison of bone composition in 44 patients with uraemia (12 dialysed and 32 non-dialysed) and 36 control subjects. The significant changes included decreased bone mineral carbonate associated with calcium, a concomitant increase in phosphate, and an increase in magnesium. There was also an increase in osteoid and a reduction in the specific gravity of the compact bone. 2. The most marked changes in bone composition were observed in patients with uraemia of more than 1 year's duration, who had been dialysed. Bone mineral sodium concentrations were not significantly altered in any group. 3. The changes in bone mineral composition appeared to be the result of several simultaneous and/or successive mechanisms: (i) loss of fixed base, calcium carbonate; (ii) replacement of carbonate by phosphate; (iii) the addition of immature bone mineral, which contains high concentrations of phosphate and relatively low concentrations of carbonate. 4. These observations are consistent with earlier views of the bone salt as an indefinite calcium/phosphate/carbonate complex. Variations in bone composition may arise from a reciprocal relationship between phosphate and carbonate. The bone mineral analogue that best explains these variations in bone composition is octacalcium phosphate carbonate [Ca4 (PO4)2(HPO4)x(CO3)1-x,zH2O].     

In vivo osteogenesis assay: a rapid method for quantitative analysis

A quantitative in vivo osteogenesis assay is a useful tool for the analysis of cells and bioactive factors that affect the amount or rate of bone formation. There are currently two assays in general use for the in vivo assessment of osteogenesis by isolated cells: diffusion chambers and porous calcium phosphate ceramics. Due to the relative ease of specimen preparation and reproducibility of results, the porous ceramic assay was chosen for the development of a rapid method for quantitating in vivo bone formation. The ceramic cube implantation technique consists of combining osteogenic cells with 27-mm3 porous calcium phosphate ceramics, implanting the cell-ceramic composites subcutaneously into an immuno-tolerant host, and, after 2-6 weeks, harvesting and preparing the ceramic implants for histologic analysis. A drawback to the analysis of bone formation within these porous ceramics is that the entire cube must be examined to find small foci of bone present in some samples; a single cross-sectional area is not representative. For this reason, image analysis of serial sections from ceramics is often prohibitively time-consuming. Two alternative scoring methodologies were tested and compared to bone volume measurements obtained by image analysis. The two subjective scoring methods were: (1) Bone Scale: the amount of bone within pores of the ceramic implant is estimated on a scale of 0-4 based on the degree of bone fill (0=no bone, 1=up to 25%, 2=25 to 75%, 4=75 to 100% fill); and (2) Percentage Bone: the amount of bone is estimated by determining the percentage of ceramic pores which contain bone. Every tenth section of serially sectioned cubes was scored by each of these methods under double-blind conditions, and the Bone Scale and Percentage Bone results were directly compared to image analysis measurements from identical samples. Correlation coefficients indicate that the Percentage Bone method was more accurate than the Bone Scale scoring method. The Bone Scale scoring method gave an r2=0.767 while the Percentage Bone method gave a value of 0.902. These results indicate that scoring ceramic cubes by the percentage of pores containing bone gives a result that corresponds to image analysis measurements at nearly a 90% confidence level. Thus, the Percentage Bone method of scoring is an accurate and relatively quick scoring method for in vivo bone formation.     

Biochemical markers of calcium and bone metabolism during 18 months of lactation in Gambian women accustomed to a low calcium intake and in those consuming a calcium supplement

The effect of 18 months of lactation on indexes of calcium and bone metabolism was studied in 60 Gambian women accustomed to a very low calcium intake. Half the women consumed a calcium supplement from 10 days postpartum for 52 weeks (supplement, 714 mg Ca/day; total Ca intake, 992 +/- 114 mg/day), and half consumed placebo (total Ca intake, 288 +/- 128 mg/day). Fasting blood and 24-h urine samples were collected at 1.5, 13, 52, and 78 weeks of lactation and analyzed for calciotropic hormones (intact PTH, 1,25-dihydroxyvitamin D, and calcitonin), bone turnover markers (osteocalcin, bone alkaline phosphatase, and urinary deoxypyridinoline), and plasma minerals (calcium and phosphate). The first months of lactation were associated with increased bone turnover and plasma phosphate, and decreased PTH and 1,25-dihydroxyvitamin D. These effects diminished by 52 weeks, although breast milk volumes remained high. The Gambians had higher PTH, 1,25-dihydroxyvitamin D, and bone formation than British women with a greater customary calcium intake. None of the biochemical indexes was affected by calcium supplementation, with the possible exception of bone alkaline phosphatase (-29% at 52 weeks; P = 0.015). These data demonstrate that lactation-associated changes in calcium and bone metabolism are physiological and are independent of dietary calcium supply in women with very low calcium intakes.     

Restoration of pedicle screw fixation with an in situ setting calcium phosphate cement

STUDY DESIGN: Pedicle screws were pulled out of human cadaveric vertebrae before and after augmentation with polymethylmethacrylate or in situ-setting calcium phosphate cement. The fixation strength of screws augmented with calcium phosphate cement was compared with that of screws augmented with polymethylmethacrylate. OBJECTIVES: To determine whether a new in situ-setting calcium phosphate cement might be suitable for augmenting the fixation of pedicle screws. The principle objective was to compare the pull-out resistance of screws augmented with calcium phosphate cement with the pull-out behavior of screws augmented with polymethylmethacrylate. Polymethylmethacrylate augmentation was chosen as the standard because of its current clinical use. Five types of screws were tested to determine whether screw design had an effect on the efficacy of augmentation. SUMMARY OF BACKGROUND DATA: Although many factors affect the pull-out resistance of pedicle screws, a key determinant of their performance is the strength of their attachment to the spine. In elderly, osteopenic patients, the screw-bone interface is especially at risk for stripping during insertion or pull-out after surgery. In these patients, polymethylmethacrylate has been used to augment pedicle screw fixation, although its use is not without risk. In situ-setting calcium phosphate cements may provide an alternative to polymethylmethacrylate in this application. Like polymethylmethacrylate, calcium phosphate cements can be injected into the prepared screw hole. They have the added advantage of being resorbed and replaced during healing and normal bone remodeling. METHODS: Thirty human lower lumbar vertebrae (L3-L5) were implanted bilaterally with one of five types of pedicle screws (n = 6 for each screw type). The screws were pulled out 3.0 mm at 0.25 mm/sec with a servohydraulic materials testing machine. The 3.0-mm pull-out distance, which was slightly longer than one thread pitch, was designed to strip the screw-bone interface but to leave the pedicle otherwise intact. After the initial testing, the screws in each vertebrae were removed, and the screw tracks were filled with 2.0 cc of polymethylmethacrylate (one side) or calcium phosphate cement (contralateral side). After augmentation, the screws were reinserted, and the cements were allowed to harden for 24 hours. Postaugmentation testing followed the protocols for preaugmentation testing, and the pull-out resistance of screws augmented with calcium phosphate cement was compared with the pull-out resistance of screws augmented with polymethylmethacrylate. RESULTS: Mechanically, calcium phosphate cement compared favorably with polymethylmethacrylate for augmenting pedicle screws. Both restored the strength of the screw-bone interface: across all screw types, the average increase in pull-out strength was 147% with polymethylmethacrylate augmentation and 102% with calcium phosphate cement. There were no significant differences because of screw type with either type of augmentation. CONCLUSIONS: The in situ-setting calcium phosphate cement investigated in this study compared favorably with polymethylmethacrylate in a single-cycle, pull-out test of augmented pedicle screws in senile trabecular bone. With further evaluation, this cement may offer an alternative to polymethylmethacrylate for the enhancement of pedicle screw fixation clinically.     

Markers of bone turnover in patients with nephrolithiasis

A total of 19 patients with active nephrolithiasis, 14 patients with non-active nephrolithiasis and 17 healthy subjects were examined under standardized intake of calcium, phosphorus, purine and protein. In patients with both active and non-active renal stone disease the following abnormalities were found: elevated plasma levels of PTH and osteocalcin, increased activity of the bone isozyme of alkaline phosphatase, low plasma levels of phosphate and increased urinary excretion of calcium and oxalic acid. These abnormalities were more marked in patients with active than non-active nephrolithiasis. No correlation was found between plasma PTH levels and parameters of bone turnover as well as calciuria and oxaluria. Results presented in this paper suggest that (a) Smith's criteria of active renal stone disease are of minor pathogenetic and therapeutic value and (b) patients with active nephrolithiasis differ from non-active renal stone formers by more elevated oxaluria and markers of bone turnover and more marked abnormalities in calcium-phosphate metabolism related parameters.     

Tamoxifen and bone metabolism in postmenopausal low-risk breast cancer patients: a randomized study

PURPOSE: This trial was undertaken to evaluate the effect of adjuvant tamoxifen on bone metabolism in postmenopausal women undergoing surgery for low-risk breast cancer. PATIENTS AND METHODS: In an open trial, 25 women were randomized to receive tamoxifen 30 mg/d for 2 years, and 25 women constituted the control group. Twenty women treated with tamoxifen and 23 women in the control group provided data for the analysis. Inclusion criteria were operation for low-risk breast cancer and cessation of menstruations for more than 1 year. Exclusion criteria were presence of metastases, disorders of bone metabolism, contraindications against tamoxifen, use of drugs with influence on bone metabolism, ailments that made bone mineral measurements impossible, and age greater than 65 years. Repeated measurements of bone mineral density and content at the lumbar spine and forearms, serum alkaline phosphatase, phosphate, and ionized calcium were performed in all patients. RESULTS: Lumbar spine bone mineral density increased during the first year in women treated with tamoxifen and then stabilized, compared with decreased bone mineral density in the control group (P = .00074). Bone mineral content at the forearms remained almost stable in tamoxifen-treated women compared with a decrease in the control group (P = .024). Serum alkaline phosphatase, phosphate, and ionized calcium decreased in the tamoxifen group (P < .00001, P = .002, and P = .002, respectively). CONCLUSION: Tamoxifen has estrogen-like effects on bone metabolism that result in an increase and stabilization of bone mineral density in the axial skeleton and a stabilization of bone mineral content in the appendicular skeleton.     

Mechanical strength of calcium phosphate cement in vivo and in vitro

Two different kinds of calcium phosphate cement were developed for implant fixation: cement A comprised of alpha-tricalcium phosphate (alpha-TCP) 95% and dicalcium phosphate dihydrate (DCPD) 5%, and cement B comprised of alpha-tricalcium phosphate 90% and dicalcium phosphate dihydrate 10%. The compression strength and pullout force of the new materials were tested both in vitro and in vivo. Microscopic observations were performed on the interface between bone and cement. Cement A showed a greater mechanical strength than cement B. The results suggest the clinical possibility of this calcium phosphate cement, which could be used as a material for enhancing implant fixation.     

A case series of ocular disease as the primary manifestation in sarcoidosis

Calcium phosphate ceramics recently have been used for administering therapeutic agents in bone. The present work investigated the efficacy of macroporous biphasic calcium phosphate (MBCP) implants as a matrix for local delivery of human growth hormone (hGH). An initial study showed that the release of 5 microg of hGH loaded onto MBCP cylinders was rapid during the first 48 h and sustained for a total of 11 days. The biological integrity of hGH (88.2%) was checked using a specific bioassay (cellular proliferation of hGH-sensitive Nb2 cells) in comparison with a radioimmunoassay to calculate the proportion of bioactive hGH released. MBCP cylinders then were loaded with 1, 10, and 100 microg of hGH and implanted into rabbit femurs (n = 16) to determine hGH effects on bone ingrowth and ceramic resorption, as evaluated by scanning electron microscopy and image analysis. Results indicated that hGH increased bone ingrowth and ceramic resorption significantly in comparison with contralateral and control implants. Biochemical parameters monitored in rabbit plasma showed that hGH did not produce detectable systemic effects. Thus the use of MBCP appears to be effective for local delivery of hGH and for increasing bone ingrowth.     

Transmission FT-IR microspectroscopy of mineral phases in calcified tissues

Fourier-transform infrared microspectroscopy (FT-IRM) was used to study bone mineralization processes in an in vivo model and in enamel in osteogenesis imperfecta. Finally, the ability of FT-IRM to map new bone formed in implanted macroporous calcium phosphate biomaterial from sections was reported for the first time. FT-IRM allowed the correlation of the microstructure of bone formation in the in vivo model with modifications in carbonate and phosphate environments of the mineral phases during maturation. FR-IRM analysis on enamel sections revealed changes in the mineral environment of carbonate and phosphate ions and probably in the size of enamel crystals. These modifications contributed to the fragility of enamel in osteogenesis imperfecta. The infrared functional group imaging of a part of implanted biomaterial and the bone ingrowth provided the visualization of chemical modifications occurring in biomaterial implants at 20 microns spatial resolution. The use of FT-IRM, in conjunction with appropriate sampling methods and data analysis should provide further insight into the molecular structure of mineral phases of calcified tissues and help to elucidate mineralization processes, skeletal disorders and properties of the biomaterials used as bone substitute.     

Effects of lithium therapy on bone mineral metabolism: a two-year prospective longitudinal study

Many studies showed an increased occurrence of primary hyperparathyroidism during lithium therapy. We studied 53 patients receiving lithium therapy prospectively for 2 yr. Serum PTH levels were unequivocally elevated. The baseline PTH level was 2.8 +/- 1.2 pmol/L and increased progressively to 3.9 +/- 1.5 pmol/L after 2 yr (P < 0.0005). There was no change in serum calcium, alkaline phosphatase, inorganic phosphate concentrations or tubular reabsorption of phosphate in relation to glomerular filtration rate. Fasting urinary reabsorption of calcium increased significantly (P < 0.0005), which was concordant with the PTH change. Fasting and 24-h urinary excretion of calcium decreased significantly (P < 0.0005), suggesting reduced, rather than enhanced, bone resorption as in primary hyperparathyroidism. This may be the main mechanism in maintaining normocalcemia, despite PTH elevation, during lithium therapy.     

Morphological evaluation of osteoblasts cultured on different calcium phosphate ceramics

The objective of these investigations was to develop an in vitro test system for evaluating novel rapidly resorbable calcium phosphate ceramics of varying composition. Rat bone marrow cells were cultured on the disc-shaped test substrates for 14 days. Five calcium phosphates were examined: R1 CaNaPO4; R1/M2, composed of CaNaPO4 and MgNaPO4; R1/2, composed of CaNaPO4 and Mg2SiO4; R1 + 9% SiO2 consisting of CaNaPO4 and 9% SiO2 (wt%) and R17, Ca2KNa(PO4)2. Two studies were performed. In study I cultures were re-fed every two to three days. In study II the medium was changed daily, and calcium and phosphate concentrations of the medium were determined daily. Specimens were prepared for light microscopy and morphometric evaluation of the cell-covered substrate area, scanning electron microscopy and energy-dispersive X-ray analysis. With all materials tested except for R1/2, an increase of cellular growth was observed after changing the medium daily. Of the different calcium phosphate ceramics tested, R17 and R1/M2 facilitated osteoblast growth and elaboration of extracellular matrix to the highest degree. The inhibition of cell growth encountered with R1 in study I and R1/2 in both studies seemed to be related to a high phosphate-ion release from these materials.     

Influence of magnesium substitution on a collagen-apatite biomaterial on the production of a calcifying matrix by human osteoblasts

The induction of a calcifying matrix is of great interest in the restoration of bone defects. In a previous in vitro study we demonstrated that a collagen sponge constituted of type I collagen fibrils, chondroitin sulfates, and hydroxyapatite crystals induces an earlier and a more abundant synthesis of a new extracellular calcifying matrix than do other biomaterials such as collagen or hydroxyapatite alone. Bone mineral contains various amounts of magnesium ions, either adsorbed at the surface of apatite crystals or incorporated inside the crystal structure. Magnesium is known to reduce the degradation rate of tricalcium phosphate ceramics and to influence the crystallization of mineral substance. Thus we evaluated two sponges modified with different substituted apatites. The substituted low magnesium-containing apatite sample decreased the osteoinductive properties of the sponge whereas the substituted high magnesium-containing apatite sample had a toxic effect on bone cells and prevented the formation of any extracellular matrix. Such a toxic effect can be explained by the presence of large numbers of magnesium ions released into the culture medium even though at physiological level magnesium is able to promote bone mineralization and to control the growth of hydroxyapatite crystals. Thus collagen sponges containing hydroxyapatite remain one of the most appropriately evaluated biomaterials used for the restoration of periodontal pockets and bone defects.     

增材制造技术制备生物植入材料的研究进展

增材制造技术突破了传统模具加工工艺的限制,可用于高效个性化定制生物医用材料。近年来,医学上对骨骼修复和移植的个性化需求显著增加,增材制造可满足该定制化的需求,促使增材制造技术在生物医用材料领域占据重要地位。随着材料科学技术和计算机辅助技术（CAD/CAM）的发展,可用于增材制造的生物植入材料不再局限于钛系、钽系、钴铬钼等合金,聚醚醚酮、磷酸钙盐等非金属类材料因良好的生物相容性也得到了广泛应用,增材制造技术制备仿生人造骨植入体成为新的研究热点。本文介绍了增材制造技术的原理,对激光、电子束、光固化等增材制造技术进行了比较,并阐述了增材制造在生物植入体和医疗器械方面的应用现状,对增材制造技术在医疗领域的应用及发展做了展望。     

Nucleation of hydroxyapatite by bone sialoprotein

Bone sialoprotein (BSP) and osteopontin, the major phosphorylated proteins of mammalian bone, have been proposed to function in the initiation of mineralization. To test this hypothesis, the effects of BSP and osteopontin on hydroxyapatite crystal formation were determined by using a steady-state agarose gel system. At low calcium phosphate concentrations, no accumulation of calcium and phosphate occurred in control gels or gels containing osteopontin. Gels containing BSP at 1-5 micrograms/ml, however, exhibited a visible precipitation band and significantly elevated Ca + PO4 contents. By powder x-ray diffraction, the precipitate formed in the presence of BSP was shown to be hydroxyapatite. These findings suggest that bone sialoprotein may be involved in the nucleation of hydroxyapatite at the mineralization front of bone.     

Calcium metabolism and bone calcium content in normal and oophorectomized rats consuming various levels of saline for 12 months

The effect of different intakes of salt for 12 mo on bone calcium content and urinary excretion of calcium and hydroxyproline were examined in sham operated and oophorectomized (OX) rats to determine the long term effects of high sodium intake and its interaction with estrogen deficiency. Sham operated (n = 24) and OX (n = 24) rats were divided into groups of six rats in a 2 x 4 design. One group of sham and one of OX rats were given 0, 2, 6 or 18 g/L sodium chloride to drink. Urine samples were collected at 0, 2, 4, 6, 10 and 12 mo for the measurement of sodium, calcium, creatinine and hydroxyproline. At the end of 12 mo, blood was taken for measurement of calcium, albumin, alkaline phosphatase and creatinine and the left femur was removed and analyzed for calcium and phosphate. Body weights of the OX rats were higher than the sham operated controls. At the start of the experiment (10 d after OX) urinary excretions of calcium and hydroxyproline were significantly higher in OX rats. However, after 4-6 mo, they were significantly lower in OX rats. Calcium excretion and hydroxyproline excretion were increased by high salt intake, and there was a significant correlation between sodium and calcium excretion (r = 0.962). Bone calcium content of OX rats was lower than their corresponding sham-operated controls. Sodium intake also had a significant effect on bone calcium content. Multiple regression analysis showed that OX and sodium intake explained 7.6% and 1.5% of the variation in bone calcium content. We conclude that high sodium intake causes increased loss of calcium and reduces bone calcium content in sham-operated as well as OX rats.     

Clinical and histologic observation of replacement of biphasic calcium phosphate by bone tissue in monkeys

Biphasic calcium phosphate, consisting of beta-tricalcium phosphate and hydroxyapatite, was implanted in wide and deep periodontal osseous defects of monkeys in combination with the guided tissue regeneration technique. After 12 weeks, sites treated with a combination of biphasic calcium phosphate and guided tissue regeneration maintained the shape of the ridge, but both guided tissue regeneration and control sites (untreated) showed extreme resorption. A histopathologic investigation revealed that numerous macrophages contained small particles of ceramic within their vesicles and the active bone replacement occurred from the surrounding bone. Biphasic calcium phosphate has osteoconductive potential and this potential may be related to degradation by macrophage phagocytosis.