Dentin Alteration of Deciduous Teeth in Human Hypophosphatemic Rickets

Familial hypophosphatemic rickets is in most cases transmitted as an X-linked dominant trait and results from mutation of the PHEX gene, predominantly expressed in osteoblast and odontoblast. Patients have been reported to display important dentin defects, and therefore, we explored the dentin structure, composition, and distribution of extracellular matrix (ECM) molecules in hypophosphatemic human deciduous teeth. Compared to age-matched controls, the dentin from hypophosphatemic patients exhibited major differences: presence of large interglobular spaces resulting from the lack of fusion of calcospherites in the circumpulpal dentin; defective mineralization in the interglobular spaces contrasting with normal Ca-P levels in the calcospherites on X-ray microanalysis; abnormal presence of low-molecular weight protein complexes recognized on Western blots by antibodies against matrix extracellular phosphoglycoprotein (MEPE), dentin sialoprotein, osteopontin, and reduced osteocalcin (OC) level; and accumulation in the interglobular spaces of immunolabeling with antibodies against DSP, dentin matrix protein, bone sialoprotein, MEPE and OC, while chondroitin/dermatan sulfate glycosaminoglycans were exclusively located inside calcospherites. Alterations of the post-translational processing or partial degradation of some ECM appear as key factors in the formation of the defective hypophosphatemic dentin.     

The role of estrogen in pubertal skeletal physiology: epiphyseal maturation and mineralization of the skeleton

The year 1994 is likely to be remembered by many endocrinologists as the year in which dramatic new light was shed on the role played by estrogen in human skeletal physiology. It was in 1994 that two new syndromes were described, each representing a human model in which estrogen action was lacking. The first case was a female with an aromatase defect and a resultant inability to synthesize estrogen, and the second case was a man with an estrogen receptor gene defect that resulted in a non-functioning estrogen receptor and complete estrogen resistance. By examining the phenotypes of these two individuals, we were able, for the first time, to see what pubertal skeletal changes occur in the absence of estrogen action and directly extrapolate the role of estrogen in skeletal physiology. What has become abundantly clear is that it is estrogen and not androgen that is responsible for pubertal epiphyseal maturation and skeletal mineralization     

A comparative study of the transition between predentin and dentin, using various preparative procedures in the rat

The appearance of the junction between predentin and dentin of rat incisors was investigated after chemical fixation (aldehyde), physical fixation (high pressure freezing and freeze substitution) and by histochemistry. Physical fixation revealed a 1–2 urn wide intermediary zone, in which only the collagen fibers were mineralized. In dentin, which looked denser and more homogeneous, both collagen fibers and intercollagen-ous spaces were mineralized. The intermediary layer could not be seen after aldehyde fixation. When cationic dyes were used during fixation in order to retain proteoglycans, a 0.5–5 μm border zone located at the junction between predentin and dentin was densely stained on the dentin side, whereas in dentin only the interglobular network displayed electron density. The periodic acid-thiocarbohydrazide-silver proteinate reaction, visualizing glycoproteins, and the phosphotungstic acid/chromic acid mixture, which reveals glycoproteins and phosphorylated proteins, produced extensive staining of the transitional zone located at the dentin edge, whereas staining was weaker in dentin. These morphological and histochemical investigations support the existence of an intermediary zone in which mineralization occurs. This transitional zone between predentin and dentin has specific properties; therefore we propose it be termed metadentin.     

Ultrastructural features of the epithelial-mesenchymal interface in an ameloblastic fibro-odontoma

The ultrastructural features of the epithelial-mesenchymal interface in a case of an ameloblastic fibro-odontoma was studied with special reference to possible signs of “inductive” processes. In most parts of the tumor, the odontogenic epithelium was separated from the connective tissue by a thick rim of a finely filamentous mesh work in which a basal lamina was occasionally observed. Mesenchymal cells were seen to touch the filamentous mesh work but no membrane bound matrix vesicles were recorded. Small areas of dentin-like tissue were found in the juxtaepithelial connective tissue while enamel-like areas and spherical calcified masses were encountered in epithelial islands. The organic matrix in relation to the enamel-like tissue consisted of either tubular fibers or a fine-granular material. It was assumed that the tubular matrix component directed the formation of long enamel-like crystals, and that the fine-granular matrix was degraded tubular fibers in which spherical calcified masses might arise. Spherical calcified masses could be found in separate follicles also where they were related to a fine-fibrillar matrix or collagenous material. The cell layers forming the wall of the islands had a great resemblance to those of an enamel organ, but the findings of dentin-free, enamel-like areas are not compatible with the inductive theory of normal odontogenesis.     

表面修饰煅烧骨的制备及其理化性质的研究

探讨一种新的仿生骨材料表面修饰煅烧牛松质骨的制备方法,以提高煅烧牛松质骨作为组织工程骨的活性。将制备好的大小一致的煅烧牛松质骨随机分成两组,分别浸泡在配制好的单倍模拟体液(SBF)和1.5倍SBF中。每组材料的浸泡时间均为7、14和21d共3个时间点。浸泡结束干燥后用扫描电镜(SEM)观察材料表面形态并分析材料表面矿化成分。通过比较筛选出效果最理想的表面修饰煅烧牛松质骨材料,研究其孔径、孔隙率、抗压和抗折强度等理化性质,并与未经表面修饰的煅烧骨材料进行比较。研究表明,煅烧骨材料在1.5倍SBF中浸泡14d可以获得最佳表面修饰效果,同时保留了原有煅烧骨材料的基本理化特性。     

LIM矿化蛋白-1与LIM矿化蛋白-3共转染骨髓间充质干细胞的基因表达

目的探讨LIM矿化蛋白（LIMmineralizationprotein,LMP）-1和LMP-3双基因共转染骨髓间充质干细胞（bonemesenchymalstemcells,BMSC）的表达情况。方法采用人工设计合成人LMP-1和LMP-3基因片段,分别与质粒pEGFP-N2连接,经酶切、测序鉴定后。分离培养新西兰兔BMSC,用脂质体包裹转染BMSC,按转染情况分为5组：未转染组（A组）、转染空载体组（B组）、转染LMP-1基因组（C组）、转染LMP-3基因组（D组）、LMP-1与LMP-3双基因共转染组（E组）。采用实时聚合酶链反应（real-timepolymerasechainreaction,RT-PcR）和蛋白质印迹法检测LMP-1和LMP-3的表达。结果酶切及测序表明真核表达质粒pEGFP-N2-LMP-1和pEGFP-N2-LMP-3构建成功。E组可同时较高水平表达LMP-1和LMP-3分子。对RT-PcR及蛋白质印迹法检测结果行灰度值测量并行统计学分析显示：LMP-1mRNA及蛋白水平的表达,5组间差异有统计学意义（P〈O．05）,但E组与C组的差异无统计学意义（P〉O．05）;LMP-3mRNA及蛋白水平的表达,5组间差异有统计学意义（P〈O．05）,且E组与D组差异也有统计学意义（P〈O．05）。结论双基因共转染的BMSC能在体外同时表达LMP-1与LMP-3,为基因修复骨缺损带来新思路。     

Hutchinson‐gilford progeria is a skeletal dysplasia

Hutchinson‐Gilford progeria syndrome (HGPS) is a rare segmental premature aging disorder that affects bone and body composition, among other tissues. We sought to determine whether bone density and structural geometry are altered in children with HGPS and whether relationships exist among these parameters and measures of skeletal anthropometry, body composition, and nutrition. We prospectively enrolled 26 children with HGPS (ages 3.1 to 16.2 years). Outcomes included anthropometric data; bone age; areal bone mineral density (aBMD) and body composition by dual‐energy X‐ray absorptiometry (DXA); volumetric bone mineral density (vBMD), strength‐strain index (SSI), and bone structural rigidity calculated from radial transaxial peripheral quantitative computed tomographic (pQCT) images; serum bone biomarkers and hormonal measures; and nutrition assessments. Children with HGPS had low axial aBMD Z‐scores by DXA, which improved after adjustment for height age, whereas differences in radial vBMD by pQCT were less striking. However, pQCT revealed distinct abnormalities in both novel measures of bone structural geometry and skeletal strength at the radius compared with healthy controls. Dietary intake was adequate, confirming that HGPS does not represent a model of malnutrition‐induced bone loss. Taken together, these findings suggest that the phenotype of HGPS represents a unique skeletal dysplasia. © 2011 American Society for Bone and Mineral Research.     

Evidence that Treatment with Risedronate in Women with Postmenopausal Osteoporosis Affects Bone Mineralization and Bone Volume

Risedronate is used in osteoporosis treatment. Postmenopausal women enrolled in the Vertebral Efficacy with Risedronate Therapy trial received either risedronate (5 mg/day) or placebo for 3 years. Subjects received calcium and vitamin D supplementation if deficient at baseline. Lumbar spine bone mineral density (BMD) was measured at baseline and at 3 years. Quantitative back-scattered electron imaging (qBEI) was performed on paired iliac crest biopsies (risedronate, n = 18; placebo, n = 13) before and after treatment, and the mineral volume fraction in the trabecular bone was calculated. Combining dual-energy X-ray absorptiometric values with the mineral volume fraction for the same patients allowed us to calculate the relative change in trabecular bone volume with treatment. This showed that the effect on BMD was likely to be due partly to changes in matrix mineralization and partly due to changes in bone volume. After treatment, trabecular bone volume in the lumbar spine tended to increase in the risedronate group (+2.4%, nonsignificant) but there was a significant decrease (−3.7%, P < 0.05) in the placebo group. Calcium supplementation with adequate levels of vitamin D led to an ∼3.3% increase in mineral content in the bone material independently of risedronate treatment. This increase was larger in patients with lower matrix mineralization at baseline and likely resulted from correction of calcium/vitamin D deficiency as well as from reduced bone remodeling. Combining BMD and bone mineralization density distribution data show that in postmenopausal osteoporosis 3-year treatment with risedronate preserves or may increase trabecular bone volume, unlike placebo. This analysis also allows, for the first time, separation of the contributions of bone volume and matrix mineralization to the increase in BMD.     

Substitution of bovine dentine sialoprotein with chondroitin sulfate glycosaminoglycan chains

Dentine sialoprotein (DSP) represents 5-8% of all non-collagenous proteins present in the tooth, but, together with dentine phosphoprotein, has been shown to be vital for correct tooth formation. Recently, the existence of a highly glycosylated form of porcine DSP has been reported and it was shown to possess glycosaminoglycan (GAG) chains. The current investigation confirms that this is also the case for bovine DSP and has further characterized these carbohydrates. Dentine sialoprotein was purified from bovine dentine extracts by anion exchange chromatography and identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), western blotting, and mass spectroscopy. An increase in molecular mass was observed, from 120 kDa to greater than 250 kDa, with a corresponding rise in anionic strength. Cellulose acetate electrophoresis and western blotting indicated the presence of chondroitin sulfate GAG chains within these dentine fractions. Further examination using sequential digestion with chondroitinase AC and N-glycosidase cleaved the samples first to 95 kDa and then to 80 kDa, respectively, confirming a high level of glycosylation. These results support the classification of bovine DSP as a proteoglycan, and that the carbohydrate substitutions may contribute to the functional properties of DSP.     

Effect of low intensity laser irradiation on surgically created bony defects in rats

Low intensity lasers have been used by clinicians to improve healing and reduce pain in humans. Lasing also results in new bone formation around hydroxyapatite implants and a significant increase in the total bone area. However, the exact mechanism of cell biostimulation by laser is still unclear. This study biochemically assessed the effects of low intensity laser (Gallium-Arsenide) using 4 and 22.4 mW cm(-2) power density on the bone healing process after surgically creating bony cavities in rat mandibles. Rats (n = 24) were divided into two groups each treated with specific energy, 4 or 22.4 mW cm(-2), for 3 min each day post-surgery. Surgical cavities were created on both sides of the mandible: the left served as an untreated control, the right was treated with laser. All rats were sacrificed after 1, 2 and 4 weeks of treatment. In the newly formed callus, accumulation of radiocalcium and alkaline phosphatase activity was measured to indicate osteogenic activity. One-way anova with repeated measures showed that the low intensity laser using 4 mW cm(-2) power density significantly increased radiocalcium accumulation from 2 weeks post-surgery, whereas 22.4 mW cm(-2) had no effect. No changes were noted in the activity of alkaline phosphatase with the laser treatment. These results suggest that laser therapy of low power density is effective on the bone healing process in artificially created osseous cavities by affecting calcium transport during new bone formation.