Changes in bone mineral and matrix in response to a soft diet.

Alterations in the magnitude of habitual mechanical loads upon the skeleton may not only affect bone architecture, but also influence the nature of the bone matrix. We tested the hypothesis that changing the mechanical consistency of the diet affects both the mineral and non-mineralized moieties of bone matrix. Female rats were fed a soft diet (powdered chow as a paste), while control animals were fed the standard chow. After 8 or 20 wks, animals were killed. Cranial (mandible, maxilla, parietal, and frontal) bones and ulnae were analyzed for mineralization density by quantitative backscattered electron microscopy, and sulphated glycosaminoglycan levels with alcian blue staining were measured by microdensitometry. The soft diet group showed a significant increase in mineralization density distribution at almost all cranial sites and a reduction in alcian blue staining in alveolar bone. Altering the consistency of the diet significantly affects mineral concentration and glycosaminoglycan content of alveolar bone.

Ovariectomy vs. hypofunction: their effects on rat mandibular bone.

Previous studies have suggested that the mandible may be more influenced by mechanical loading than by circulating hormone levels. We tested the hypothesis that hypofunction has a greater influence than ovariectomy on mandibular bone. Two-month-old rats were ovariectomized (OVX) or had maxillary molars removed from one side to induce unilateral mandibular hypofunction. Control animals remained untreated. After 5 months, animals were killed, and bones were assessed by micro-tomography (muCT), quantitative back-scattered electron analysis in an SEM (qBSE-SEM), and light microscopy. Mineralization density was reduced in calvarial, maxillary, and mandibular alveolar bone following OVX, yet was increased in lingual mandibular alveolar bone of the hypo-function animals compared with controls. OVX caused a reduction in osteocyte density in alveolar bone, while hypofunction showed an increase compared with controls. Hypofunction led to alveolar bone becoming more highly mineralized and more cellular, while ovariectomy caused a reduction in both mineralization density and osteocyte numbers.

Cortical vascular canals in human mandible and other bones.

The human mandible is highly mineralized. We hypothesized that this is related to the local vascularity of the bone. This could not be examined directly, but, as a surrogate, intracortical vascular canal spaces of the human mandible were studied so that we could determine possible relationships with age, gender, location, dental status, and tissue mineralization. Canal numbers, area, and volume fraction were calculated from quantitative backscattered electron images of human mandibles aged 16-96 years. Data were compared with calvaria, maxilla, lumbar vertebra, femoral neck, and iliac crest. In the mandible, the buccal aspect of the midline was the most porous, the canals being larger and more numerous. The cortical porosity in the posterior of partially dentate mandibles was significantly greater than that of either dentate or edentate mandibles, and there was a significant increase in the size of canals in the mandible with increasing age. Female mandibles had more porous cortices. No relationship was found between cortical porosity and the degree of bone mineralization.

An immunohistochemical analysis of human Merkel cell density in gingival epithelium from dentate and edentulous subjects.

OBJECTIVE: To investigate whether there is a difference in the density of Merkel cells between the gingiva of dentate and edentate subjects. METHODS: One hundred and two blocks of human mandibular (n=55) and maxillary (n=47) gingiva from 69 white skinned individuals (44 males, 25 females, mean age 70.1 years, range 42--92 years) were analysed. Twenty-six individuals had teeth remaining in at least one jaw (mean age of dentate 64.5 years, edentate 72.1 years), of which 15 were dentate in both jaws. Overall, 24/55 mandibles and 17/47 maxillae were dentate. Five micrometer sections were stained with a monoclonal antibody to cytokeratin 20 (CK 20) using standard immunoperoxidase or immunoalkaline phosphatase methods. Positive cells were counted in 20 consecutive high power fields using the x 40 objective in three sections from each biopsy, and the results analysed for differences related to age, sex, site and presence of teeth. RESULTS: CK 20-positive Merkel cells were present either singly or in clusters in the basal epithelial layers, particularly at the tips of rete ridges. Numbers of gingival Merkel cells were significantly higher (p<0.005, Mann-Whitney) in edentate (cells per field mean, median, standard deviation, respectively: 1.39, 0.64, and 1.85) when compared to dentate (0.67, 0.20, and 1.21) specimens. The differences were not statistically significant for any other variable. CONCLUSION: The data raise the possibility that reduced perception following loss of teeth may be compensated for by an increase in the local Merkel cell population.

Collagen fiber orientation affects osteoclastic resorption.

The bone surrounding the teeth is constantly remodeled throughout life, particularly during tooth movement and following tooth loss. Alveolar bone proper contains many highly oriented extrinsic fibers, but whether their orientation affects resorption is unknown. To determine if it does, we selected sperm whale cementum to provide large anisotropic substrates resembling extrinsic fiber bone. Slices cut either perpendicular or parallel to the extrinsic fiber axis were cultured for 24 hours with pre-hatched chick osteoclasts. Resorption pit areas and volumes were measured by video-rate reflection confocal microscopic mapping. Pits in the perpendicular group were smaller in area and were deeper than those in the parallel group (median values, 402 micron2 and 572 micron2, n > 950, p < 0.0001; volume/area 5.37 microm and 4.58 microm); volume differences only just reached significance (2,137 micron3 and 2,554 micron3, p < 0.05). These results show that the fiber orientation within a substrate can profoundly influence the shape of resorption lacunae. This pattern of resorption may help in the maintenance of an optimally functioning attachment of periodontal ligament fibers to alveolar bone.

Osteoclastic resorption of equine cranial and postcranial bone in vitro.

To address possible differences in the resorbability of cranial and postcranial bone, slices of equine frontal bone and leg (first phalanx or third metacarpus) were seeded with embryonic chick bone cells and cultured for 20-24h. After removing the cells and drying the specimens, the areas and volumes of more than 800 resorption pits in each set were measured using a video-rate reflection confocal microscope system. Relative mineralization densities were determined by quantitative electron backscattering analysis. The mean mineralization density was greater in the leg bone, but the mean depths for resorption pits in frontal bone were smaller (median volume/area ratios, experiment 1 and experiment 2: 1.98 microm frontal and 3.79 microm leg versus 2.70 microm and 4.20 microm, respectively; P < 0.0001, Mann-Whitney), even though the areas were greater in the frontal (medians, 286 microm2 and 324 microm2, versus 242 microm2 and 201 microm2; P < 0.0001). This study has shown a difference between cranial and postcranial equine bone in the shape and size of resorption pits formed in vitro. Overall, it has shown that cranial bone may be resorbed at least as readily as postcranial bone. This result is counter to the clinical impression that cranial bone has a greater staying power than postcranial bone when used as a grafting material.

Mineralization density and apparent density of bone in cranial and postcranial sites in the aging human.

This study addressed the question whether bone density of the mandible reflects bone density at other sites. Samples of cranial bone (mandible and parietal bone) and postcranial bone (fourth lumbar vertebral body, iliac crest and femoral neck) from 14 individuals aged 69-96 years were compared. One slice from each bone was used for apparent density determination by weighing it and dividing by a volume calculated as the product of section thickness and the mean area of the two sides of the section. Another slice was embedded in poly(methylmethacrylate) and micromilled to study the mineralization density by quantitative backscattered electron (QBSE) analysis in a scanning electron microscope, rescaling image histograms to the signal range from a monobrominated (0) to a monoiodinated (255) dimethacrylate resin standard. Mandibular QBSE values (e.g., at the mental foramen region 178.0) were much higher (p < 0.0001, paired t-test) than at other sites (parietal, 170.1; fourth lumbar vertebra (L4), 155.4; iliac crest (IC), 155.2; femoral neck (FN), 160.7 units), and correlated only with parietal bone (r = 0.70). Mean QBSE values for the postcranial sites were correlated (L4 with IC, r = 0.63; L4 with FN, r = 0.88; IC with FN, r = 0.59) as were the apparent density values (L4 with IC, r = 0.87; L4 with FN, r = 0.75; IC with FN, r = 0.80). Neither the apparent density nor the mineralization density of the mandible showed a correlation with values for the postcranial sites. The condition of bone in the elderly mandible should not be used to infer status at postcranial sites.

The resorption of vital and devitalized bone in vitro: significance for bone grafts.

Several studies have suggested that devitalized bone is less satisfactory than live tissue for surgical grafting purposes because an initial resorption step, prior to new formation, is lacking. We have compared the osteoclastic resorption of cultured bone containing living osteocytes with that of similar bone in which the osteocytes were dead. In experiment I, transverse slices cut from freshly harvested adult rabbit femora were either placed in phosphate buffered saline (Set 1) or subjected to freezing and thawing (Set 2). In experiment II, a heated set (Set 3) was prepared in addition. All slices were cultured with osteoclasts for 24 hours, eight slices per set being seeded with bone cells in experiment I and three per set in experiment II. The areas and volumes of resorption pits formed during the culture period were measured using reflection confocal microscopy. In both experiments, the mean values for the areas of the pits were smaller in the bone containing live osteocytes (P < 0.03, Mann Whitney test), and in experiment II the volumes of the pits in Set 1 were smaller than those in Set 3 (P < 0. 0001, Mann Whitney test). However, in neither experiment was there a significant difference between the Sets in the volume:area ratios (mean depths) of the pits. The findings show that devitalized bone is resorbed by osteoclasts at least as readily as bone containing vital osteocytes in vitro, and indicate that if grafted devitalized bone resorbs less well in vivo it is not because the bone tissue is intrinsically resistant to osteoclastic resorption.

Post-extraction remodeling of the adult mandible.

Following tooth loss, the mandible shows an extensive loss of bone in some individuals. This may pose a significant problem in the prosthodontic restoration of function and esthetics. The many factors which have been proposed as being responsible for the inter-individual variation in post-extraction remodeling mean that a perfunctory analysis of the literature, in which well-controlled, relevant studies are scarce, may not provide the whole story. This article reviews the local and systemic factors which may play a role in the post-extraction remodeling of the mandible. Since severe residual ridge resorption may occur even when the bone status in the rest of the skeleton is good and vice versa, it is concluded that local functional factors are of paramount significance. It is now essential to determine how they can be modified and applied to help maintain ridge height and quality in our aging, edentulous population.

The frequency of fungal infection in biopsies of oral mucosal lesions.

OBJECTIVE: To determine the frequency of fungal infection in biopsies of oral mucosal lesions. MATERIALS AND METHODS: Histopathology reports issued between 1991-1995 inclusive were reviewed. During this period, a single section of each mucosal biopsy had been stained using the periodic acid-Schiff (PAS) technique. RESULTS: A total of 223 (4.7%) biopsies contained PAS-positive fungi: 191 individuals were affected, 124 (64.9%) of whom were male. There was a significant (P < 0.01) positive association of fungal infection with moderate and severe epithelial dysplasia, median rhomboid glossitis and squamous papillomas. Where a subsequent biopsy was available, 21.9% dysplasias which were infected with fungi worsened in histological severity, as compared with 7.6% of dysplasias which were not infected at any stage. There was a significant negative association of fungal infection with benign fibrous overgrowths (P < 0.01), benign hyperkeratoses, lichenoid reactions and pyogenic granulomas (P < 0.05). The difference in frequency of infection between the tongue and other sites was also significantly higher (P < 0.01). CONCLUSIONS: There is a statistically significant association between histologically-determined fungal infection and epithelial dysplasia, and we recommend that a PAS stain be performed whenever oral epithelial dysplasia is diagnosed, especially in male patients. On histological confirmation of dysplasia, anti-fungal therapy should be considered in the management of these lesions.

Variation in the apparent density of human mandibular bone with age and dental status.

This study examines the variability in the anatomy of mandibles of differing ages and different stages of tooth loss. Mandibles from individuals between 19 and 96 y were sectioned into 2 mm thick vertical plane-parallel slices and cleaned of marrow and periosteum. The apparent density (mass per unit volume in g/ml) from midline (MID) and mental foramen region (MF) sites was determined by weighing the slices and dividing by a volume calculated as the product of section thickness and the mean area of the 2 sides of the section. The cortical thickness of the inferior border and the basal and alveolar bone heights were measured in radiographs of the slices. Mandibular apparent density was negatively correlated with the cross sectional area (midline r=-0.48, mental foramen r=-0.45), and at the midline was significantly greater in edentulous than in dentate individuals (means (+/-S.E.M.) edentulous n=13: 1.43 (+/-0.07) g/ml; dentate n=17: 1.27 (+/-0.04) g/ml, P < 0.05). Where a large enough age range was available, mandibular apparent bone density showed a significant increase with age (midline males: r=0.53, n=18) especially for dentate individuals (r=0.91, n=8). There was a correlation between the apparent densities at the two sites in the same mandible (r=0.64), with the values obtained for the midline being significantly greater than for the mental foramen region (midline 1.34 (+/-0.04) g/ml; mental foramen 1.19 (+/-0.04) g/ml, P < 0.001, paired t test). The mandible shows great interindividual variability, but there may be a considerable reduction in cross sectional girth of the mandible following tooth loss, and, unlike postcranial sites, an increase in apparent density with age.

Mineralisation density of human mandibular bone: quantitative backscattered electron image analysis.

This study examined the tissue level mineralisation density distribution in mandibles from 88 adult humans. Mandibles (19-96 y) were sectioned vertically in midline (MID), mental foramen (MF), and third molar (M3) regions. Surgical fragments from M3 were obtained from individuals aged 16-38 y. All specimens were cleaned, embedded in PMMA, micromilled and examined by digital 20 kV backscattered electron (BSE) stereology. Quantitation was based on rescaling image histograms to the signal range between a monobrominated (0) and a monoiodinated (255) dimethacrylate resin standard. Mineralisation density increased with age (r=0.70; P < 0.0001): the mean for 39 individuals aged between 16 and 50 y was significantly lower (P < 0.0001) than for 35 individuals over 51 y (mean (+/-S.E.M.): 158.20 (1.63) and 174.71 (1.27) normalised grey level units respectively). There was good correlation in mean mineralisation density between different sites in the same mandible, but MID was significantly less highly mineralised than the other sites: MID 173.90, MF 177.34, M3 177.11 (P < 0.002 and 0.01 for MF and M3 respectively; paired t test), as was the alveolar bone density when compared with the bone of the inferior cortex (e.g. MID: 171.13 (1.53) and 174.46 (1.14) P < 0.0001). No sex difference was found. Partially dentate mandibles generally had regions of higher mineralisation than fully dentate and edentulous mandibles. The lowest density bone occurred at the alveolar crest anteriorly and superolingually at M3, matching sites of net resorption following tooth loss. Highest densities were found inferolingually at MID, inferiorly at MF and buccally at M3, matching the sites thought to experience the highest functional strains. This stresses the importance that local factors may have in the remodelling of the edentulous mandible. Morphology showed that there is a preponderance of highly mineralised cement lines, and of packets containing dead, mineralised, osteocytes.

Age changes in bone.

Changes in bone structure as a function of age have been studied by simple inspection, x-ray imaging, stereo-photography, deep field optical microscopy, circularly polarised light microscopy, and scanning electron microscopy (SEM), including both topographic and compositional backscattered electron (BSE) imaging modes. The study of bone as a three-dimensional object, rather than in thin sections, enables us to envisage modelling and remodelling processes in context. The study of ultra-flat block surfaces permits the acquisition of data from an effectively very thin layer in the block face, and to examine bone as a spectrum of tissue types varying in the degree of mineralisation. Particular attention has been paid in our earlier studies to the iliac crest, lumbar vertebral bodies, femoral mid-shaft, neck and head and parietal and frontal skull bones. Recently, we have compared findings from these sites with observations on the mandible. We conclude, from our new imaging data, that common generalisations about the changes in bone in ageing and osteoporosis are too simplified, and that the mandible differs sufficiently from post-cranial skeletal sites that it would be unwise to extrapolate from findings in the jaw to the circumstances elsewhere.