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PubMed2002

Bioabsorbable ciprofloxacin-containing and plain self-reinforced polylactide-polyglycolide 80/20 screws: pullout strength properties in human cadaver parietal bones.

The aim of this study was to compare the pullout forces of recently developed bioabsorbable ciprofloxacin-containing and plain self-reinforced polylactide/polyglycolide (SR-PLGA) miniscrews in human cadaver parietal bones. Parietal bone pieces (approximately 6 x 20 cm) were collected from five human male cadavers (44-75 years of age). Fifty plain SR-PLGA 80/20 miniscrews (diameter = 1.5 mm, length = 4.0 mm) and 50 ciprofloxacin-containing SR-PLGA 80/20 miniscrews (diameter = 1.5 mm, length = 4.0 mm) were used in this study. The force needed to pull the screws from human parietal cadaver bones was measured using a tensile strength-testing machine. The screw pullout speed was 10 mm/min. Means and SDs were calculated and analyzed using the Student t test (SPSS version 10.0 for Windows). The pullout forces of the ciprofloxacin-containing and plain miniscrews were 66.8 +/- 4.9 N and 96.3 +/- 9.3 N (significant difference, P < 0.001), respectively. The most common cause of failure was screw-shaft breakage (60% in the case of ciprofloxacin-containing screws and 52% in the case of plain SR-PLGA screws). Scanning electron microscopy showed that the fibrillar strip-like microstructure of plain SR-PLGA miniscrews turns into a coarse, uniaxial, platelet-like morphology in antibiotic SR-PLGA miniscrews as a result of the addition of ciprofloxacin. Ciprofloxacin-containing SR-PLGA screws consequently have a lower pullout strength than corresponding plain conventional SR-PLGA screws. Nevertheless, it is evident that the ciprofloxacin-containing screws can be applied in craniomaxillofacial surgery in nonload-bearing or slightly load-bearing applications.

Absorbable Implants↗
PubMed2002

Comparison of the pull-out forces of bioabsorbable polylactide/glycolide screws (Biosorb and Lactosorb) and tacks: a study on the stability of fixation in human cadaver parietal bones.

The aim of this study was to compare the pull-out forces of bioabsorbable polylactide/glycolide (PLGA) tacks and screws in human cadaver parietal bones. Parietal bone pieces (c. 6 cm x 20 cm) were collected from five human male cadavers (age range: 47-75 years). Forty-nine BioSorbPDX (self-reinforced [SR] PLGA 80/20) tacks (1.5-mm diameter, 4.0-mm length), 47 BioSorbPDX (SR-PLGA 80/20) screws (1.5-mm diameter, 4.0-mm length), and 46 LactoSorb (PLGA 82/18) screws (1.5-mm diameter, 4.0-mm length) were applied. The tacks were applied to drill holes using a special applicator gun (no tapping or tightening). The screws were applied to drill holes in the traditional way using tapping and tightening with a screwdriver. A tensile testing machine was used. All the implants were tested thus: the head of the implant was held by an aluminum jig, and the jig was pulled with wire until implant failure. The testing pull speed was 10 mm/min. Means and SDs were calculated, and the data were analyzed using ANOVA. The pull-out force of the tacks was 115.9 +/- 8.3 N, that of Lactosorb screws was 112.9 +/- 12.1 N, and that of Biosorb screws was 110.4 +/- 8.9 N (statistically insignificant difference between the three groups). The most common reason for failure in the case of tacks was barb breakage (55.1%); it was thread breakage in the case of BioSorb screws (66%) and stem split in the case of Lactosorb screws (56%). Tacks seem to have a similar, perhaps even a little better, holding power to cranial bone as screws and can hence be recommended for clinical application, as the procedure saves time and, consequently, costs.

Absorbable Implants↗
PubMed2002

[Development of parietal bone based on ossification in the fetus].

Seventy-two parietal bones from human fetuses aged 15 to 29 weeks were studied. Three age groups were formed: I--15-19 weeks; II--19-24 weeks, III--25-29 weeks. The width and length of each parietal bone was determined. Microradiological studies were done with the Unipan 401 X-ray apparatus. Subsequently, pulverized bone for biochemical studies was prepared. Calcium, magnesium, zinc and iron content was determined using atomic spectrophotometry. Phosphates were measured with a colorimetric method and fluorine was assayed using an ion-selective electrode. The dimensions of fetal parietal bones changed almost linearly with age until the 20th week of life when a deceleration in the growth rate was noted (Tables 1, 2, 3, 4). This finding could be useful for estimation of fetal age when other methods are unavailable. The parietal bone is formed from one or two primary ossification centers lying in the same plane or one above the other (Figs. 1, 2, 3). Fusion of primary ossification centers was observed between 15 and 19 weeks of life (Fig. 3). Trabeculae radiate from the primary ossification center to the periphery of the parietal bone and take the form of a "coral reef" within the tuber (Figs. 2 and 5). Transverse ossification which was not coordinated with the growth of trabeculae from the primary ossification center was observed between week 15 and 19 of intrauterine life (Fig. 2). Fusion of peripheral trabeculae with those from the ossification center takes place at a later stage of osteogenesis (Fig. 4). Parietal bones of 29-week-old fetuses consisted of two layers of trabeculae and a distinct tuber, except for the sagittal and coronal sutures and the anterior fontanel, where a single layer of trabeculae was observed. Trabeculae were well developed and densely packed (Fig. 5). Analysis of the mineral composition of fetal parietal bones confirmed that the major elements are calcium and phosphorus and that their content increases with age (Figs. 6 and 7). Fluorine content differed widely and was unrelated to age (Fig. 9, Tab. 1). The importance of fluorine in the process of mineralization of parietal bones requires further study. Magnesium content increased with age (Fig. 8) and did not correlate with calcium or phosphorus. Apparently, these elements play different roles in the process of mineralization. The content of zinc and iron, two labile components of bone, decreased with age (Figs. 10 and 11). Some of these changes could have taken place during storage of the bones.

Calcium↗
PubMed1980

Areal growth in the human fetal parietal bone.

The areal growth of the human fetal parietal bone is described using 51 dissected right parietal bones of Japanese fetuses ranging from the fifth month to term. Their shadows were taken on printing paper and analyzed by a sonic digitizer. The absolute growth of the projected area of the fetal parietal bones progresses at a fairly constant rate during the latter half of the fetal period, despite some deceleration in the 9-10th month. By allometric analysis, the allometric coefficients against crown-rump length are 2.201 for males, 2.202 for females, and 2.204 for both sexes, respectively. The allometry is essentially monophasic, showing no inflection point, indicating a change in the slope of the regression line; that is, the growth of the human fetal parietal bone is continuous with a constant specific growth rate. These results are discussed in connection with growth in thickness of the bone.

Cephalometry↗
PubMed1989

[Ultrastructural studies of initial calcification of mouse fetal parietal bone in vitro].

The parietal bone fragment (1.5 mm square) extracted from murine fetal calvaria (periosteum was removed) in the latter stage of gestation was cultured in alpha-MEM containing 10% fetal bovine serum over 10-day period, and the initial calcification site was subsequently examined utilizing both electron microscopy and histochemical methods. At the initial calcification site, the so-called "matrix vesicle" (width 100 nm), derived from osteoblasts which induce matrix formation, and the larger vesicular structures (width 100-600 nm) which originated from degenerated or dead cells were observed. Additionally dead osteoblast-like cells phagocytosing bone crystals participated in bone nodul formation. In the border region between the degenerated or disrupted cells and the functioning cells, multilamellar structures (mainly composed of phospholipids) were frequently observed. Concurrently it was concluded that there is a possibility of partial deposition of calcium salts on the surface of the above mentioned cells under some circumstances. Through selective decalcification, it was determined that bone trabecule was formed by fusion of respective bone noduli and degraded collagen fibrils which filled the intervening spaces. From the above results, it was evident that both the matrix vesicles derived from functioning osteoblast, and the vesicular structures derived from the degenerated or dead cells concurrently phagocytosing spicules and collagen fibrils were involved in the initial calcification process of the membranous bone in vitro.

Animals↗
PubMed2000

Composite autogenous bone and demineralized bone matrices used to repair defects in the parietal bone of rabbits.

We compared the amount of new bone produced by endochondral and intramembranous autogenous bone grafts in the presence of demineralized bone matrices (DBMs) prepared from intramembranous bone (DBM(IM)) or endochondral bone (DBM(EC)). Thirty-five bone defects were created in the parietal bone of 20 New Zealand White rabbits. In the experimental groups, 5 defects were grafted with endochondral bone, 5 with endochondral bone mixed with DBM(IM)) (EC-DBM(IM)), 5 with intramembranous bone mixed with DBM(IM)(IM-DBM(IM)) and 6 with endochondral bone mixed with DBM(EC)(EC-DBM(EC)). In the control groups, 10 defects were left alone (passive control) and 4 were grafted with rabbit skin collagen (active control). They were all killed on day 14 and the defects were prepared for histological study. Serial sections were cut across the whole defect. Quantitative analyses were made on 202 sections of the experimental groups by image analysis. A total of 414%, 708%, and 85% more new bone was formed in defects grafted with composite EC-DBM(IM), IM-DBM(IM)and EC-DBM(EC), respectively, than those grafted with endochondral bone alone (P<0.001). No bone was formed in either passive or active controls. In conclusion, demineralized bone matrices, particularly those derived from intramembranous bone, have extremely high osteoinductive properties and greatly improve the integration of autogenous bone grafts in the skull.

Analysis of Variance↗
PubMed1990

Simultaneous assessment of bone resorption and formation in cultures of 22-day fetal rat parietal bones: effects of parathyroid hormone and prostaglandin E2.

We have developed a method that allows us to measure bone resorption and formation simultaneously in the parietal bones from 22-day fetal rat calvaria. Parietal bones labeled with 45Ca, by injection of the mother, were cultured for 72 h with parathyroid hormone (PTH, bovine 1-34, 1.56 nM) or prostaglandin E2 (PGE2, 100 nM), in the presence or absence of indomethacin (Indo, 1 microM) or corticosterone (Cort, 1 microM). Two hours prior to the end of the culture, the bones were pulsed with [3H]-proline or [3H]-thymidine. Resorption was assessed as the percent of 45Ca released into the medium. Incorporation of [3H]-proline into collagenase digestible protein (CDP) and of [3H]-thymidine into DNA (TDR) were measured to assess collagen and DNA synthesis, respectively. Basal %45Ca release was 16 +/- 1% and was significantly decreased by Indo and Cort. Cort decreased TDR and CDP while Indo did not. PTH and PGE2 significantly increased %45Ca release, and this was not blocked by Indo. However, in the presence of Cort, only PTH increased %45Ca release while PGE2 did not. PGE2 increased TDR under all culture conditions while PTH increased TDR only in the presence of Cort. While PTH and PGE2 had the same effects on bone resorption, they had different effects on CDP. PGE2 increased CDP in the presence of Indo or Cort but PTH did not. Thus, this model allows us to study bone resorption, collagen synthesis, and DNA synthesis simultaneously. We have also shown that PTH and PGE2 differ in their sensitivity to inhibition of resorption by Cort and in their effects on bone formation.

Animals↗
PubMed1992

Parietal bone mobility in the anesthetized cat.

To quantify parietal bone motion in reference to the medial sagittal suture, a newly developed instrument was attached to the surgically exposed skull of anesthetized adult cats. The instrument differentiated between lateral and rotational parietal bone movements around the fulcrum of the suture. Bone movement was produced by external forces applied to the skull and by changes in intracranial pressure associated with induced hypercapnia, intravenous injections of norepinephrine, and controlled injections of artificial cerebrospinal fluid into the lateral cerebral ventricle. Responses varied considerably among test animals. Generally, lateral head compression caused sagittal suture closure, small inward rotation of the parietal bones, increased intraventricular pressure, transient apnea, and unstable systemic arterial blood pressure. Graded increases in intracranial volume produced stepped increases in pressure, lateral expansion at the sagittal suture, and outward rotation of the parietal bones. We attribute variations in animal response largely to differences in intracranial and suture compliance among them. Cranial suture compliance may be an important factor in defining total cranial compliance.

Animals↗
PubMed2006

Effects of bioactive glass on bone augmentation within a titanium cap in rabbit parietal bone.

BACKGROUND: The condition of alveolar bone influences the success and subsequent esthetics of implant treatment. This study investigated the early effects of bioactive glass (BG) on bone augmentation within a hemispherical titanium cap in rabbit parietal bone. METHODS: Twelve adult male Japanese white rabbits were used. One titanium cap (test site) was packed with BG in a collagen gel, and the other (control site) was packed with the collagen gel alone. After 1 and 3 months, animals were euthanized, and the experimental area was examined using fluorescence and light microscopy. RESULTS: Newly generated bone was observed at 1 and 3 months of healing. Although bone was also generated without BG, newly mineralized bone was generated sooner with BG present for guided bone augmentation than without BG. At 1 and 3 months, the BG was not bioabsorbed completely, and some particles remained. CONCLUSION: New bone is generated at an early stage of bone formation using BG for bone augmentation.

Animals↗
PubMed1996

17 beta-estradiol increases calcium content in fetal mouse parietal bones cultured in serum-free medium only at physiological concentrations.

Using a bone organ culture system that shows mineralization in vitro, we investigated whether 17 beta-estradiol dose-dependently increases calcium content in cultured calvarial bones in serum-free medium. Fetal mouse parietal bones (3 x 3 mm) were cultured in phenol red-free BGJ medium containing phosphate (3-4 mmol/L), calcium (1-1.25 mmol/L), insulin (6 micrograms/ML), and transferrin (6 micrograms/mL) for 4-5 days. Under these culture conditions, the calcium content of the cultured bones (at dissection 34.0 +/- 4.6 micrograms/bone [mean +/- SD], n = 50) increased by 15-20 micrograms during 4-5 days of culture. 17 beta-Estradiol increased the calcium content significantly at 10(-12) to 10(-11) mol/L, but not at lower (10(113) mol/L) or higher (10(-10) to 10(-9) mol/L) concentrations. 17 alpha-Estradiol had no effect. The stimulatory effect of 17 beta-estradiol was completely inhibited by the antiestrogen agent ICI-182,780. The anabolic effect of 17 beta-estradiol was elicited not only in bones from females but also in those from males. 17 beta-Estradiol had no significant effect on 45Ca release from prelabeled parietal bones. Furthermore, light- and electron-microscopic examinations revealed that bone mineralization proceeded through formation of matrix vesicles, without any metastatic or dystrophic calcification. These in vitro findings suggest that 17 beta-estradiol elicits small, but reproducible, direct effects on calcium content in the parietal bones not only in female but also in male fetal mice at physiological-free E2 concentrations (10(-12)-10(-11) mol/L), which is attainable in serum of normal human subjects. In contrast to in vivo studies, pharmacological doses of 17 beta-estradiol had no anabolic effect on parietal bones. The mechanism of such a biphasic effect of estrogens remains to be elucidated.

Analysis of Variance↗
PubMed1997

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.

Aging↗
PubMed1991

Cortisol modulates the actions of interleukin-1 alpha on bone formation, resorption, and prostaglandin production in cultured mouse parietal bones.

Previous studies have shown that both interleukin-1 (IL-1) and glucocorticoids inhibit collagen synthesis in bone organ and cell cultures. In this study we examined their interactions in cultured neonatal mouse parietal bones. IL-1 alpha stimulated [3H]thymidine incorporation. Cortisol decreased thymidine incorporation, but did not block the effect of IL-1. Both cortisol and IL-1 alpha decreased the incorporation of [3H]proline into collagenase-digestible protein (CDP) and reduced alpha 1(I)procollagen mRNA levels at 72 h. Noncollagen protein (NCP) labeling was increased by IL-1 and decreased by cortisol. In the presence of cortisol, IL-1 alpha (6 pM) increased CDP as well as NCP labeling. The increase in CDP labeling was paralleled by an increase in alpha 1(I)procollagen mRNA, suggesting a pretranslational site for the cortisol-IL-1 alpha interaction. In the same bones, cortisol consistently blocked IL-1 alpha-stimulated 45Ca release and prostaglandin E2 (PGE2) production. The ability of IL-1 alpha to increase CDP in the presence of cortisol was the same in the presence or absence of indomethacin, an inhibitor of PGE2 synthesis, or aphidicholin (30 microM), an inhibitor of DNA synthesis, indicating that the reversal was neither PG mediated nor dependent on cell proliferation. In conclusion, our results demonstrate that IL-1 inhibits collagen, but not NCP or DNA, synthesis and that cortisol inhibits IL-1 alpha-induced bone resorption and PGE2 production and reverses its inhibitory effect on collagen synthesis in cultured neonatal mouse calvariae.

Animals↗
PubMed1983

The preosteoclast and its cytodifferentiation into the osteoclast: ultrastructural and histochemical studies of rat fetal parietal bone.

In order to elucidate the cytological features of preosteoclasts and the process of their differentiation into osteoclasts, fetal rat parietal bone was examined using light microscopy, organ culture, electron microscopy and histochemical methods. Parietal bones of rat fetuses from 15 to 21 days of gestational age were examined light microscopically. A solid bone plate was found in 19 day old fetuses, but not multinucleated giant cells were observed in either the ecto- or endocranial periosteal surfaces. They were first observed at the endocranial periosteal surface in 20 day old fetuses, and increased in number in 21 day old fetuses. Parietal bones of fetuses from 15 to 19 days of age were cultured and the possible occurrence of preosteoclasts prior to the appearance of osteoclasts was examined. During organ culture, eosinophilic multinucleated cells appeared in the parietal bones from 17, 18 and 19 day old fetuses, and increased in those from 19 day old fetuses. Electron microscope observation of the parietal bones in 19 day old fetuses revealed moderate numbers of mononuclear cells identified as preosteoclasts (Scott, 1967) principally among the osteoblasts and preosteoblasts at the endocranial periosteal surface. Preosteoclasts with ill-developed cell organelles tended to be located between blood vessels and active osteoblasts, and sometimes located close to the bone surface with only the thin cytoplasmic processes of adjacent osteoblasts intervening. On the other hand, well-developed preosteoclasts tended to be located close to flattened osteoblasts and came into direct contact with the exposed mineralized bone between them. Preosteoclasts were not clustered together but were usually found in contact with adjacent osteoblasts and/or preosteoblasts. Membrane fusion between a preosteoclast and a flattened osteoblastic cell was observed. Multinucleated cells were principally preosteoclastic in appearance but some were both osteoclastic and osteoblastic. The multinucleated cells with ruffled borders identified as active osteoclasts increased in number over a particular time span. The cytochemical localizations of ALPase, ACPase and peroxidase activities in the preosteoclasts resembled those in the osteoclasts but differed from the osteoblasts and preosteoblasts with respect to the ALPase activity. An intense peroxidase activity was detected only in monocytes and neither in preosteoclasts nor in osteoclasts. These results suggest that the cytodifferentiation of preosteoclasts into osteoclasts may be induced by their direct contact to the mineralized bone surface exposed by detachment of osteoblasts, and that the detached osteoblasts may also serve as either an inducer or a constituent of the forming osteoclasts.

Acid Phosphatase↗
PubMedDate not supplied

Normal prenatal development of the human parietal bone and interparietal suture.

This study describes the prenatal human parietal bone development and interparietal suture morphology under normal conditions. The human fetal material consisted of 15 normal specimens, derived from spontaneous and therapeutically induced abortions. The study was based upon a radiographic analysis of the calvariae. Special attention was paid to the parietal tuber area, the interparietal (sagittal) suture and the frontal-parietal bone edge. The osseous morphology of these regions showed a well-defined primary ossification center at the tuber region from where bone trabeculae of uniform size and radiopacity radiated. The uniform trabeculae radiate at nearly right angles to the long axis of the sagittal suture. The bony trabeculae radiate uniformly towards the anterior fontanelle where at the peripheral border of the parietal bone radiopaque, transverse ossification corpora were observed. In the small fetuses, these corpora were located anterior to the trabeculae and in the larger fetuses close to the trabeculae. Insight into the morphological pattern in normal suture formation is essential for the further description of pathological suture morphology and for understanding normal and pathological suture development.

Cranial Sutures↗
PubMed2002

A new technique for cranial bone osteofixation: use of bioabsorbable tacks and plates to fix parietal bone split grafts used for reconstruction of a posttraumatic frontal bone defect.

Recent advances in bioabsorbable devices have introduced tacks that do not require tapping. This may help to reduce operative time and, consequently, costs. The goal of this study was to demonstrate the feasibility of a new method of cranial bone osteofixation using novel bioabsorbable tacks and plates instead of screws. A 36-year-old man presented for elective cranioplasty to reconstruct a large frontal cranial bone defect that followed a decompression operation performed because of a head injury sustained 6 months previously. Cranioplasty was performed using split parietal bone grafts to reconstruct the defect. Bone grafts were fixed together and to the skull using self-reinforced (SR) poly(L/DL)lactide [SR-poly(L/DL)lactide] (70/30) (Biosorb FX) plates (n = 10) and tacks (n = 98). The plates were 0.6 mm thick, 102 mm long, and 12 mm wide. The tacks had a maximum thread diameter of 2 mm and a length of 6 mm. The tacks used did not require any tapping procedure, and they were applied using a special applicator gun. Stable and secure fixation was obtained during surgery. The postoperative period was uneventful, except for delayed epithelialization of a small area (1 x 0.5 cm) over the frontal skin that healed later. One year after surgery, the cosmetic result was excellent, and no complications were detected. Stabilization of large cranial bone pieces can be achieved using bioabsorbable SR-poly(L/DL)lactide plates and tacks, with excellent cosmetic results. The method is thought to be reliable and may help to reduce operative time.

Absorbable Implants↗
PubMed2005

Parietal bone as graft material for maxillary sinus floor elevation: structure and remodeling of the donor and of recipient sites.

Particulate parietal bone is used for maxillary sinus floor elevation procedure prior to dental implant placement. However, data on internal structure of the parietal bone and on graft remodeling and incorporation in the host bone are limited. We determined the structure and remodeling activities of 24 parietal bone specimens sampled at time of sinus grafting (T1 samples), and the amount and turnover of bone formed at the recipient site at time of implant placement (T2 samples, obtained 10 months after T1 samples, on average). In T1 samples, the outer cortex was 1.16+/-0.45 mm thick, had a typical haversian structure, and showed a low level of remodeling. In the cancellous portion of the samples, trabecular bone volume represented 52.8+/-10.3%. Bone remodeling was more active in the cancellous portion than in the cortical portion, but few osteoblasts and osteoclasts were seen. T2 samples consisted solely of trabecular bone, which occupied 49.4+/-18.4% of total sample volume. The boundary between new bone and the recipient bed was not discernible. Remnants of the graft particles were embedded within new bone, and showed signs of intense resorption. Bone remodeling was highly active, as shown by the presence of numerous osteoclasts resorbing new bone, together with thick osteoid seams and large osteoblasts. A loose cotton-like mineralized material was frequently observed in the marrow spaces; this acellular and non-collagenous material was strongly stained by toluidine blue, suggesting a glycoprotein nature. This study offers insights into cortical and trabecular bone structure and shows the low-level remodeling activity of parietal bone. About 10 months after grafting, the grafted chips were incorporated in new bone and almost completely resorbed. This high turnover may be beneficial for implant placement.

Adult↗
PubMed1983

Surface structures and osteoclasts of mouse parietal bones: a light and scanning electron microscopic study.

The resorption surface caused by osteoclasts are identified by scanning electron microscopy (SEM), but the morphological interrelation between these resorption surfaces and Howship's lacunae observed by light microscopy remains obscure, and little evidence showing that the distribution and structures of the resorption surface change according to the function of osteoclasts is available. To understand the relationship between the function of osteoclasts and the morphological evidence of bone resorption, surface structures of the parietal bones in mice, newborn to adult, were studied by SEM. The osteoclasts on the inner surface of the calvaria are considered to be involved in the growth of the skull. The outer surface of the parietal bone was smooth, whereas the inner surface consisted of both smooth and rough areas. The rough areas were usually much larger than Howship's lacunae, which are generally thought to be of osteoclast size. These areas were composed of small and shallow concavities with oval or polygonal outlines. The borders between adjacent concavities appeared as ridges. The rough areas were very wide in the growing skull and osteoclasts were scattered on these wide rough areas. The osteoclasts were much larger than the concavities in the rough areas. During the growth of the skull, the proportion of rough areas occupying the inner surface changed parallel to the number of osteoclasts, which varied in correspondence with the growth rate of the skull. The maximum value of the proportion was ab out 60% at 1 week of age. The findings suggest that the osteoclasts resorb the bone by moving along its surface, forming small concavities and leaving rough areas larger than Howship's lacunae of osteoclast size. Furthermore, they suggest that the size and distribution of the rough areas and the morphological features of the concavities in the rough areas vary depending upon the activities of the osteoclasts.

Animals↗