Material properties of the skull layers of the primate parietal bone: A single-subject study.

The outer cortical table of the parietal bone has been commonly used as a calvarial bone graft site for the craniofacial reconstruction. However, little is known about how removing the outer table may affect the function and structure of the inner table, and how the knowledge of the biomechanics and material properties of cortical bones will help the calvarial graft to better integrate into the biological and mechanical functions of its surrounding native tissues. In this study, it was hypothesized that there were significant differences in both density and material properties between inner and outer cortical plates in cranial bones. Twelve cylindrical specimens, including inner-outer layers, of cortical parietal bone of a female baboon were collected. Cortical thicknesses and densities were measured, and elastic properties were assessed using an ultrasonic technique. Results demonstrated remarkable difference in both thickness (t = 8.248, p ≤0.05) and density (t = 4.926, p≤0.05) between inner and outer cortical paired samples. Orthotropic characteristics of the cortical plates were detected as well, these findings suggest that there are differences in biomechanical properties between two surfaces of cranial bones at both tissue and organ levels. How these differences are linked to the stress environments of the inner and outer cranial cortical layers awaits further studies. Further study will greatly enhance our ability to address questions derived from both morphological and craniofacial medicine fields about the development and biomechanics of craniofacial skeletons.

Evaluation of the Biocompatibility of CS-Graphene Oxide Compounds In Vivo.

In the last few years, graphene oxide (GO) has gained considerable importance in scaffold preparation for tissue engineering due to the presence of functional groups that allow the interaction between the extracellular matrix and the components of the cellular membrane. The interaction between GO and chitosan (CS) can not only improve the biomechanical properties of the scaffold but also generate a synergistic effect, facilitating tissue recovery. In vivo studies on GO are scarce; therefore, biocompatibility tests on CS-GO scaffolds and bone regeneration experiments on critical size defects were carried out on Wistar rats. Scaffolds made of CS, CS-GO 0.5%, and CS-GO 1% were prepared and implanted on Wistar rats cranial bones for three months. Scaffold samples were analyzed through histochemistry and scanning electron microscopy. The analysis performed showed reabsorption of the material by phagocytic activity and new bone formation. The CS-GO 0.5% formulation gave the best performance in bone regeneration, with excellent biocompatibility. These results show the potential of this compound for tissue regeneration opening and medical applications.

Calcification during bone healing in a standardised rat calvarial defect assessed by micro-CT and SEM-EDX.

OBJECTIVE: The study was designed to investigate the process of calcification during bone healing in a standardized rat calvarial bone defect model, measured by bone mineral density and the concentrations and distributions of calcium, phosphorus and carbon in the bone matrix. MATERIALS AND METHODS: A standard defect was made on the parietal bone of 12-week-old rats under anaesthesia. The rats were fixed in weeks 1, 2, 4 and 8,and the calvaria were resected and examined with microcomputed tomography, then frozen and sectioned for histology and analysed with energy-dispersive X-ray spectroscopy (EDX). Parietal bone of 12-week-old control rats was processed similarly. RESULTS: The mineral density of healing bone increased with time. The healing bone became thicker and denser with time in histology. The distributions of Ca and P expanded over the bone matrix, whereas that of C became localised and complemented that of C and P. The Ca/P concentration ratio increased, whereas the C/Ca and C/P ratios decreased in the healing bone matrix. CONCLUSION: Healing bone is immaturely calcified initially and proceeds calcification gradually, that is, as the bone volume increases, mineral increases in density and matures in quality, while organic components decrease.

Cranial bone regeneration after cranioplasty using cryopreserved autogenous bone by a programmed freezer with a magnetic field in rats.

BACKGROUND: The purpose of this study was to develop a bone tissue bank using a programmed freezer with a magnetic field. Parietal bones were removed from rats and used for organ culture examination (non-cryopreserved, cryopreserved with a magnetic field (CAS) and cryopreserved without a magnetic field group). Next, other parietal bones were used for histological examination. The cryopreserved bones by a CAS freezer and dried bones were transplanted respectively. Control bones were replanted without cryopreservation. Animals were sacrificed at 4, 8, 12 and 24 weeks after surgery. After organ culture, the isolated osteoblasts from parietal bones which were cryopreserved by a CAS freezer can survive and proliferate as much as non-cryopreserved group. Histological examinations showed new bone formation in control and CAS group. These results suggest that bone tissue cryopreservation by CAS freezer can be successfully used for bone grafting which may be a novel option for regeneration medicine.

Femtosecond plasma mediated laser ablation has advantages over mechanical osteotomy of cranial bone.

BACKGROUND: Although mechanical osteotomies are frequently made on the craniofacial skeleton, collateral thermal, and mechanical trauma to adjacent bone tissue causes cell death and may delay healing. The present study evaluated the use of plasma-mediated laser ablation using a femtosecond laser to circumvent thermal damage and improve bone regeneration. METHODS: Critical-size circular calvarial defects were created with a trephine drill bit or with a Ti:Sapphire femtosecond pulsed laser. Healing was followed using micro-CT scans for 8 weeks. Calvaria were also harvested at various time points for histological analysis. Finally, scanning electron microscopy was used to analyze the microstructure of bone tissue treated with the Ti:Sapphire laser, and compared to that treated with the trephine bur. RESULTS: Laser-created defects healed significantly faster than those created mechanically at 2, 4, and 6 weeks post-surgery. However, at 8 weeks post-surgery, there was no significant difference. In the drill osteotomy treatment group, empty osteocyte lacunae were seen to extend 699 ± 27 µm away from the edge of the defect. In marked contrast, empty osteocyte lacunae were seen to extend only 182 ± 22 µm away from the edge of the laser-created craters. Significantly less ossification and formation of irregular woven bone was noted on histological analysis for drill defects. CONCLUSIONS: We demonstrate accelerated bone healing after femtosecond laser ablation in a calvarial defect model compared to traditional mechanical drilling techniques. Improved rates of early regeneration make plasma-mediated ablation of the craniofacial skeleton advantageous for applications to osteotomy.

Confocal laser scanning microscopic analysis of collagen scaffolding patterns in cranial sutures.

Although recent studies indicate that regional dura mater influences the fate of the overlying cranial suture, little is known about the assembly of extracellular matrix (ECM) molecules within the patent and fusing murine cranial suture complexes. Confocal laser scanning microscopy was used to study ECM assembly within patent and fusing cranial suture complexes. Coronal sections (20 microm thick) of patent sagittal (SAG) and fusing posterior frontal (PF) sutures from postnatal 8-, 14-, and 18-day-old Sprague-Dawley rats were scanned in 0.5-microm increments, and images were collected consecutively to create a z-series for three-dimensional reconstruction. Spatial and temporal collagen arrangements were compared between SAG and PF sutures by measuring interfiber distance, fiber thickness, and total collagen surface area at each time point. We demonstrate that on day 8 (before the onset of suture fusion), collagen bundles are randomly arranged in both the SAG and PF sutures. By day 14 (midfusion period), there was a statistically significant reduction in total collagen surface area (80.5% versus 67.4%; P < 0.05) as the collagen bundles were organized into orthogonal lattices along the anterior and endocranial margins of the PF suture. Furthermore, new bone matrix deposition was observed along the edges of these organized collagen bundles. In contrast, collagen within the SAG suture remained randomly arranged and unossified. By day 18 (late fusion period), the PF suture was completely fused except for the posterior-ectocranial portion. This patent section of the PF suture contained a highly organized mineralizing orthogonal collagen lattice. The total collagen surface area in the day-18 PF suture continued to decline compared with the day-8 PF suture (80.5% versus 55.6%; P < 0.05). In the day-18 SAG suture, the collagen bundles remained randomly arranged, and the total surface area did not change. The same analysis was performed in a human pathologic fusing and patent suture. Similar results were observed. The total collagen surface area significantly decreased in the pathologic fusing human suture compared with the patent suture (92.8% versus 60.6%; P < 0.05). Moreover, the pathologically fusing suture contained a highly organized mineralizing orthogonal collagen lattice. This is the first analysis of collagen patterns in patent and fusing cranial sutures.

Intraosseous infusion into the skull: potential application for the management of hydrocephalus.

OBJECT: Hydrocephalus results from abnormal cerebrospinal fluid (CSF) volumes or flow patterns. The absorption of CSF is determined largely by pressures within veins and venous sinuses in the head and adjacent to the spine. Most surgical solutions for hydrocephalus involve diversion of excess CSF into alternative absorption sites, and most of these solutions are still suboptimal. The focus of this work has been to recreate more normal CSF absorption into the dural venous sinuses without having to directly access the superior sagittal sinus (SSS). METHODS: Intraosseous skull infusion for the purpose of accessing the SSS and the systemic venous system was tested by experimental skull infusions of tracer fluids into living large animals (14 adult pigs). Compared with control injections into an ear vein, infusions into the skull through specially designed infusion devices had similar systemic absorption characteristics. This suggested that intraosseous skull infusion in a living large animal was successful in gaining access to the SSS and systemic venous system. CONCLUSIONS: This study constitutes the first demonstration of the success of intraosseous skull infusion in gaining rapid access to the systemic venous system and it thus opens the possibility of using this strategy for diversion of CSF back into the intracranial venous system for the treatment of hydrocephalus.

Nanostructural and nanomechanical properties of synostosed postnatal human cranial sutures.

Craniosynostosis represents a heterogeneous cluster of congenital disorders and manifests as premature ossification of one or more cranial sutures. Cranial sutures serve to enable calvarial growth and function as joints between skull bones. The mechanical properties of synostosed cranial sutures are of vital importance to their function and yet are poorly understood. The present study was designed to characterize the nanostructural and nanomechanical properties of synostosed postnatal sagittal and metopic sutures. Synostosed postnatal sagittal sutures (n = 5) and metopic sutures (n = 5) were obtained from craniosynostosis patients (aged 9.1 +/- 2.8 months). The synostosed sutural samples were prepared for imaging and indentation on both the endocranial and ectocranial surfaces with the cantilever probe of an atomic force microscopy. Analysis of the nanotopographic images indicated robust variations in sutural surface characteristics with localized peaks and valleys. In 5 x 5 mum scan sizes, the surface roughness of the synostosed metopic suture was significantly greater (223.6 +/- 93.3 nm) than the synostosed sagittal suture (142.9 +/- 80.3 nm) (P < 0.01). The Young's modulus of the synostosed sagittal suture at 0.7 +/- 0.2 MPa was significantly higher than the synostosed metopic suture at 0.5 +/- 0.1 MPa (P < 0.01). These data suggest that various synostosed cranial sutures may have different structural and mechanical characteristics.

Two types of bone resorption lacunae in the mouse parietal bones as revealed by scanning electron microscopy and histochemistry.

To understand the bone resorption process on the basis of the morphology of bone resorption lacunae, the inner surface of parietal bones in juvenile mice was exposed with a treatment of ultrasonic waves or NaOCl treatment and examined by scanning electron microscopy (SEM). The bone resorption lacunae were divided into two types (I and II) according to differences in morphological features of their walls; the wall of type I lacunae was covered with loose collagen fibrils, while that of type II lacunae was smooth with almost no fibrillar structures. Collagen fibrils in type I lacunae treated with ultrasonic waves differed in appearance from those treated with NaOCl; the collagen fibrils were thin and displayed a smooth surface in type I lacunae treated with ultrasonic waves, while they were thick and showed a rough surface in those treated with NaOCl-probably because superficial uncalcified collagen fibrils were digested with the chemical. The results indicated that type I lacunae occupied 77% of all of the bone resorption lacunae treated with ultrasonic waves, but 51% of those treated with NaOCl. This finding led to the idea that type I lacunae can be subdivided into two: lacunae (Ia), covered with partially calcified fibrils as well as superficial uncalcified fibrils; and lacunae (Ib), covered only with uncalcified fibrils. The presence of uncalcified fibrils in the bone resorption lacunae was further confirmed by backscattered electron (BSE) imaging of SEM. Histochemistry for acid phosphatase or immuno-histochemistry for cathepsin B or carbonic anhydrase in combination with SEM revealed that type I lacunae were located under osteoclasts but type II lacunae were not. These findings indicate that type I lacunae are in the process of bone resorption by osteoclasts, while type II lacunae are in the final stage of bone resorption and free from osteoclasts. Bone resorption may thus proceed in the order of Ia, Ib, and II.

Histological and TEM examination of early stages of bone healing after Er:YAG laser irradiation.

OBJECTIVE: The aim of this study was to analyze the early healing process of bone tissue irradiated by Er:YAG laser and compare it with that treated by mechanical drilling and CO(2) laser. BACKGROUND DATA: Er:YAG laser has a great potential for cutting hard tissues as it is capable of ablation with less thermal damage. METHODS: Twenty-four male Wistar rats were used for this study. The calvarial bone of rats was exposed and straight grooves were prepared by Er:YAG laser, mechanical bur and continuous wave CO(2) laser. Four rats each were sacrificed at six time points: 10 min, 6 and 24 h and 3, 7, and 14 days post-surgery. Sections were prepared for light and transmission electron microscopic (TEM) observations. RESULTS: Compared to mechanical bur and CO(2) groups, the inflammatory cell infiltration adjacent to the irradiated bone surface, fibroblastic reaction, and revascularization were more pronounced in the Er:YAG laser-irradiated tissues. A cell-rich granulation tissue with fibroblasts and osteoblasts was predominant in 7-day specimens of Er:YAG laser group. Histopathological analysis of 14-day specimens in the Er:YAG group also revealed significantly greater new bone formation, compared with the mechanical bur and CO(2) laser groups. CONCLUSIONS: Initial bone healing following Er:YAG laser irradiation occurred faster than that after mechanical bur and CO(2) laser. Er:YAG laser treatment may be advantageous for wound healing of bone tissue, presumably by providing a favorable surface for cell attachment.

Calcitonin-induced change in serum calcium levels and its relationship to osteoclast morphology and number of calcitonin receptors.

It has been shown that, in live subjects, the ability of calcitonin (CT) to decrease serum calcium (Ca) levels can be lost in response to its continued or repeated administration. The present study investigated the relationship between such changes of in vivo serum Ca levels and the response of osteoclasts to CT administration, including the downregulation of their CT receptors (CTRs). Rats were either given a single injection of CT or repeated injections at either 6- or 24-h intervals, after which their serum Ca levels were evaluated. Their parietal bones were dissected, and the amount of 125I-labeled elcatonin (125I-eCT) binding to their osteoclasts measured using autoradiography. Ultrastructural changes in the osteoclasts were also examined. Twenty-four hours after a single CT administration, serum Ca levels had dropped, and there was an absence of ruffled borders on the osteoclasts. Less 125I-eCT binding to the osteoclast was found than in the control group. Forty-eight and 72 h after CT administration, serum Ca levels had almost returned to control levels, and the osteoclasts showed ruffled borders once again. The amount of 125I-eCT binding to the osteoclast also recovered to control levels. When these osteoclasts were then incubated in CT, their ruffled borders once again disappeared. In the 6-h interval multiple CT administration schedule subjects, upon inspection 72 h after their first administration (6 h following the final one), serum Ca levels were found to have almost returned to control levels with the presence of osteoclast ruffled borders. The amount of 125I-eCT binding to these osteoclasts was remarkably limited, and no disappearance of the ruffled borders occurred in response to additional CT incubation. In the 24-h interval multiple administration schedule subjects, upon inspection 72 h after their first CT administration (24 h following the final one), there was less 125I-eCT binding than in the single-dose subjects tested 24 h after their injection, and the ability of CT to lower their serum Ca levels was reduced. The ability of CT to lower serum Ca levels was therefore related to the response of osteoclasts to the CT (the disappearance of the ruffled borders), and this response was related to the amount of CTRs available for binding with CT on the osteoclast surface. Furthermore, the reduced effectiveness of CT in response to repeated CT administration was found to be related to the downregulation of the CTRs on the osteoclast surface.

Morphology of the development of the sagittal suture of mice.

Syndesmotic sutures of the skull are formed by dense connective tissue and called "open"; they are "closed" by formation of a synostosis between adjacent bones. Open sutures are considered as areas of growth and as hinges. The importance of open sutures during the period of skull growth is reflected by pathological situations in which premature closure of the sutures occurs. As alterations of the FGF receptor have been reported in genetical disorders accompanied by premature suture closure (Bellus et al. 1996), the role of fibroblasts and connective tissue in the development of the sagittal suture of mice has been investigated by light and electron microscopy. Morphological changes of the sagittal suture at the following stages are reported: at embryonic day 18, days 1, 5, 9, 14, 20, 26, 28 after birth and in adult mice. Two skulls per stage were investigated. Early osteogenesis appeared in a thin plate, followed by a second plate underneath the first one. Both were separated by blood vessels. In general, vascularization preceded desmoid mineralization; the space around blood vessels was occupied by non-bone-forming cells leaving cavities for the presumptive bone marrow. Mineralization of the collagen-rich osteoid at the mineralizing rim of the bone plates was accompanied by apoptoses and cell disintegration. Newly formed bone was immediately covered by osteoblasts forming a sheet of bone-lining cells. At day 9, the double-layered bone plates of both sides reached the median area of the skull but were separated by non-mineralizing, collagen-rich connective tissue. From day 14 onwards, the bone plates thickened. Bone apposition, recognizable by the formation of collagen-rich osteoid and proceeding from day 14 pp onwards, occurred mainly at the outer and inner surfaces of the calvariae, but neither at bone marrow surfaces nor at the medial edges of the parietal bones. These opposite bone faces showed fewer osteoblasts and bone-lining cells, but an increased number of fibroblasts. Tendon-like collagen bundles connected both bone plates of the open suture of day 26 pp as well as in the adult mice, whereby synostotically closed areas alternated. Formation of an open, syndesmotic suture can, therefore, be described as a transition of bone-forming tissue into a bone-tendon junction. The results indicate the importance of the replacement of osteoblasts by fibroblasts at the sutural front of the bone plates in order to prevent a premature suture closure.

Effect of metabolic acidosis on the potassium content of bone.

Metabolic acidosis induces resorption of cultured bone, resulting in a net efflux of calcium (Ca) from the bone and an apparent loss of mineral potassium (K). However, in these organ cultures, there is diffusion of K between the medium and the crystal lattice, causing difficulty in interpretation of the acid-induced changes in mineral ion composition. To determine the effects of acidosis on bone mineral K, we injected 4-day-old neonatal mice with pure stable isotope 41K, equal to approximately 5% of their total body K. Calvariae were dissected 24 h later and then cultured for 24 h in medium without added 41K, either at pH approximately 7.4 (Ctl) or at pH approximately 7.1 (Ac), with or without the osteoclastic inhibitor calcitonin (3 x 10(-9) M, CT). The bone isotopic ion content was determined with a high-resolution scanning ion microprobe utilizing secondary ion mass spectrometry. 41K is present in nature at 6.7% of total K. The injected 41K raised the ratio of bone 41K/(39K+41K) to 9.8+/-0.5% on the surface (ratios of counts per second of detected secondary ions, mean+/-95% confidence interval) but did not alter the ratio in the interior (6.9+/-0.4%), indicating biological incorporation of the 41K into the mineral surface. The ratios of 41K/40Ca on the surface of Ctl calvariae was 14.4+/-1.2, indicating that bone mineral surface is rich in K compared with Ca. Compared with Ctl, Ac caused a marked increase in the net Ca efflux from bone that was blocked by CT. Ac also induced a marked fall in the ratio of 41K/40Ca on the surface of the calvariae (43+/-0.5, p < 0.01 vs. Ctl), which was partially blocked by CT (8.2+/-0.9, p < 0.01 vs. Ctl and vs. Ac), indicating that Ac causes a greater release of bone mineral K than Ca which is partially blocked by CT. Thus, bone mineral surface is rich in K relative to Ca, acidosis induces a greater release of surface mineral K than Ca, and osteoclastic function is necessary to support the enriched levels of surface mineral K in the presence of acidosis.

Detection of mineral density on the surface of mouse parietal bones: backscattered electron imaging of low accelerating voltage scanning electron microscopy.

Backscattered electron (BSE) imaging of scanning electron microscopy (SEM) was applied to a study on the mineral density of the bone surface. The neonatal and adult mouse parietal bones freed of the periosteum and covering cells were examined in a field emission scanning electron microscope equipped with a high sensitivity BSE detector at 1-30 kV accelerating voltages. The mineral density of the bone surface was observable in BSE images at 5 kV accelerating voltage while only the topographic structures of the surface were obtained under an accelerating voltage less than 5 kV. As the accelerating voltages increased from 5 kV, the bright areas were extended, probably due to the imaging of the calcified bone matrix under the uncalcified osteoid. The bone surface is usually divided into smooth and rough areas according to its irregularities. BSE images at 5 kV clearly showed that the smooth areas were further divided into dark and bright areas which apparently corresponded to the uncalcified osteoid and calcified bone matrix, respectively. Bright granules, about 1.0-3.0 microns in diameter, were sometimes observed at the border between the osteoid and calcified bone matrix; these granular calcified areas were regarded as the calcifying front forming the calcified bone matrix from the osteoid. The present study demonstrated that the distribution of the osteoid on the mouse parietal bone surface changes depending on age: the osteoid occupied a large area in the parietal bone surface in neonatal mice, but was small in adult mice. Thus, low accelerating voltage SEM using BSE provides new information on the distribution of the osteoid and the bone matrix calcification under both normal and pathological conditions.

SEM corrosion-casts study of the microcirculation of the flat bones in the rat.

BACKGROUND: Little is known about the organization of microcirculation in flat bones in comparison with long bones. This study, therefore, helps us to determine the design of this vascular system in flat bones in relation to their structure and function. METHODS: The organization of microvasculature in parietal, scapula, and ileum bones of 15 young sexually mature rats, aged 6-7 weeks, was studied by light and scanning electron microscopy (SEM) from vascular corrosion cast (vcc), a resin-cast obtained material. RESULTS: Our observations show that the pattern of the microcirculation in flat bones is different in the thick and thin parts of such bones. Where the bone is thinner than 0.4 mm, only periosteal and dural network exist. Larger vessels which do not form a real network connect the two tables of the bones in these regions. In thicker areas, the organization of the microvasculature is similar to that in long bones, with distinct periosteal, cortical and bone marrow networks. Moreover, in different bones, outer networks show slightly different characteristics according to the different adjacent structures (dura mater, muscles etc.). Different types of vessels were recognized by comparing their different diameter, course and endothelial imprints. CONCLUSIONS: The microvascular patterns of the flat bones are strongly influenced by the bone thickness. The different microvascular systems can interact both with the bone modelling and remodeling and with the variable metabolic needs, modifying the microvascular pattern and the blood flow. This is even more important in view of the reciprocal influence of the different networks within the same bone.

Junctions between early developing osteoblasts of rat calvaria as revealed by freeze-fracture and ultrathin section electron microscopy.

Although intercellular junctions have been described between mature lamellar bone cells, little has been known about junctions between osteoblasts in early developing bone. We therefore conducted a freeze-fracture and ultrathin section study on developing calvaria of rat embryos aged 17-19 days to determine what types of intercellular junctions appear between osteoblasts in early osteogenesis. We observed that three main types of junctional structures, i.e., adherens of the macular type, gap, and focal tight junctions, coexist between osteoblasts in early developing bone. Their possible involvement in early morphogenetic events is discussed. Tight junctions are considered to be involved in compartmentalization of the early matrix and final polarization of osteoblasts.

Solitary infantile myofibromatosis of bone. An immunohistochemical and ultrastructural study.

A rare case of solitary infantile myofibromatosis of bone in an 11-month-old boy is reported. Radiographically the lesion of parietal bone was round, well-circumscribed, and osteolytic with a sclerotic rim. Histologically the tumor was made up of nodules that were hyalinized or cellular and containing plump, spindle-shaped cells that were intermediate in appearance between fibroblasts and smooth-muscle cells, arranged in short bundles or whorls. Another typical feature was the presence of distended, cleft-shaped vascular spaces around the nodules. The microscopic features of this tumor were consistent with those of infantile myofibromatosis of other sites, such as the skin and deep soft tissue. The tumor cells showed immunoreactivities for vimentin and alpha-smooth muscle actin. Microfilaments with dense bodies were observed in the fibroblast-like tumor cells. In addition, many tumor cells stained for collagen type IV and were covered by incomplete external laminae, indicating infantile myofibromatosis has more advanced smooth-muscle differentiation than conventional fibromatosis.

[Scanning electronic microscope (SCM) examination of the hydroxylapatite (HA) combined with bone morphogenetic protein (BMP) implanted on the bone surface].

HA combined with BMP was implanted on the surface of rabbit's parietal bone and examined with SCM. The results indicate that there are a large amount of new bone formation within the combined material and the amount is increasing as the time lapsed. The new bone is directly connected with the HA particles, forming a bony interface between the host bone and the implants to integrate them. In contrast, there are a lot of fibrous tissues with a little new bone formed on the interface if HA is implanted alone. The result implies that the BMP plays a very important role in new bone formation and the combined material is ideal for alveolar ridge augmentation.