The root surface in human teeth: a microradiographic study.
In an attempt to clarify the nature of the human cemento-dentinal junction, ground sections of incompletely formed and fully formed extracted teeth were prepared and their histology compared with their microradiographic appearances. The results showed that incompletely formed teeth possess distinctive surface layers outside the granular layer of Tomes. The evidence indicates that these layers are of dentinal origin; their presence during development supports previous explanations by the author of the hyaline layer of Hopewell-Smith and of so-called intermediate cementum. The results also indicate that the granular layer of Tomes does not represent the outer limit of root dentine. The relationship of these surface layers to the definitive cementum which is present in fully formed teeth was studied in both young and older patients. From the results it was concluded that cementum formation begins in the more apical region of the teeth at a time when root formation is well advanced, and that it spreads towards the crown rather than in the generally accepted reverse direction. (+info)
Predicting protein decomposition: the case of aspartic-acid racemization kinetics.
The increase in proportion of the non-biological (D-) isomer of aspartic acid (Asp) relative to the L-isomer has been widely used in archaeology and geochemistry as a tool for dating. the method has proved controversial, particularly when used for bones. The non-linear kinetics of Asp racemization have prompted a number of suggestions as to the underlying mechanism(s) and have led to the use of mathematical transformations which linearize the increase in D-Asp with respect to time. Using one example, a suggestion that the initial rapid phase of Asp racemization is due to a contribution from asparagine (Asn), we demonstrate how a simple model of the degradation and racemization of Asn can be used to predict the observed kinetics. A more complex model of peptide bound Asx (Asn + Asp) racemization, which occurs via the formation of a cyclic succinimide (Asu), can be used to correctly predict Asx racemization kinetics in proteins at high temperatures (95-140 degrees C). The model fails to predict racemization kinetics in dentine collagen at 37 degrees C. The reason for this is that Asu formation is highly conformation dependent and is predicted to occur extremely slowly in triple helical collagen. As conformation strongly influences the rate of Asu formation and hence Asx racemization, the use of extrapolation from high temperatures to estimate racemization kinetics of Asx in proteins below their denaturation temperature is called into question. In the case of archaeological bone, we argue that the D:L ratio of Asx reflects the proportion of non-helical to helical collagen, overlain by the effects of leaching of more soluble (and conformationally unconstrained) peptides. Thus, racemization kinetics in bone are potentially unpredictable, and the proposed use of Asx racemization to estimate the extent of DNA depurination in archaeological bones is challenged. (+info)
Steric effects of N-acyl group in O-methacryloyl-N-acyl tyrosines on the adhesiveness of unetched human dentin.
We have prepared various O-methacryloyl-N-acyl tyrosines (MAATY) to reveal the relationship between molecular structure near carboxylic acid and adhesive strength of MAATY-HEMA type adhesive resin to unetched dentin. In this study, we attempted to change the steric hindrance effect without changing the HLB value, i.e., introducing an iso-acyl group instead of n-acyl group into MAATY. O-methacryloyl-N-ethylbutyryl tyrosine (MIHTY) showed significantly lower adhesive strength when compared with O-methacryloyl-N-hexanoyl tyrosine even though both MAATY have the same HLB value. The possible explanation of the significantly different adhesive strength was that the 2-ethylbutyryl group in MIHTY was bulky, resulting in inhibition of the hydrogen bonding of the carboxylic group. The HLB value is independent of the steric effect of molecular structure, and thus the steric factor should be taken into consideration for the explanation of different adhesive strengths within the adhesive monomers having the same HLB value but different molecular structures. (+info)
Dentinal tubule occlusion with lanthanum fluoride and powdered apatite glass ceramics in vitro.
To simulate hypersensitive dentin, the smear layer and dentinal plugs of bovine root dentin specimens were removed by immersion in 10% phosphoric acid, polishing with hydroxyapatite particles, and ultrasonic cleansing. The fluoride-tannic acid-lanthanum-apatite (FTLA) group was treated with acidulated phosphate fluoride (APF) containing tannic acid followed by rubbing with a paste of lanthanum chloride (LaCl3) and powdered apatite glass ceramics. The treated specimens were immersed in a remineralizing solution that mimics saliva for 6 weeks. The SEM observations revealed that the treated surfaces of the FTLA group were completely covered with fine spherical compounds and the dentinal tubules were occluded with plugs to a depth of about 3 microns. Fluoride and lanthanum were detected to a depth of over 20 microns by EPMA observation. After the remineralization, the surface of FTLA-treated specimen did not have any opened tubules and showed a remarkable increase in the number of fine spherical deposits in the dentinal tubules. These results suggest that the reaction products produced by sequential treatment with acidic fluoride and LaCl3 and powdered apatite glass ceramics are able to effectively occlude dentinal tubules. (+info)
Osteoclast differentiation factor acts as a multifunctional regulator in murine osteoclast differentiation and function.
Osteoclast differentiation factor (ODF), a novel member of the TNF ligand family, is expressed as a membrane-associated protein by osteoblasts/stromal cells. The soluble form of ODF (sODF) induces the differentiation of osteoclast precursors into osteoclasts in the presence of M-CSF. Here, the effects of sODF on the survival, multinucleation, and pit-forming activity of murine osteoclasts were examined in comparison with those of M-CSF and IL-1. Osteoclast-like cells (OCLs) formed in cocultures of murine osteoblasts and bone marrow cells expressed mRNA of RANK (receptor activator of NF-kappaB), a receptor of ODF. The survival of OCLs was enhanced by the addition of each of sODF, M-CSF, and IL-1. sODF, as well as IL-1, activated NF-kappaB and c-Jun N-terminal protein kinase (JNK) in OCLs. Like M-CSF and IL-1, sODF stimulated the survival and multinucleation of prefusion osteoclasts (pOCs) isolated from the coculture. When pOCs were cultured on dentine slices, resorption pits were formed on the slices in the presence of either sODF or IL-1 but not in that of M-CSF. A soluble form of RANK as well as osteoprotegerin/osteoclastogenesis inhibitory factor, a decoy receptor of ODF, blocked OCL formation and prevented the survival, multinucleation, and pit-forming activity of pOCs induced by sODF. These results suggest that ODF regulates not only osteoclast differentiation but also osteoclast function in mice through the receptor RANK. (+info)
Deficiency of SHP-1 protein-tyrosine phosphatase activity results in heightened osteoclast function and decreased bone density.
Mice homozygous for the motheaten (Hcphme) or viable motheaten (Hcphme-v) mutations are deficient in functional SHP-1 protein-tyrosine phosphatase and show severe defects in hematopoiesis. Comparison of femurs from mev/mev mice revealed significant decreases in bone mineral density (0.33 +/- 0.03 mg/mm3 for mev/mevversus 0.41 +/- 0.01 mg/mm3 for controls) and mineral content (1.97 +/- 0.36 mg for mev/mevversus 10.64 +/- 0.67 for controls) compared with littermate controls. Viable motheaten mice also showed reduced amounts of trabecular bone and decreased cortical thickness. These bone abnormalities were associated with a 14% increase in numbers of multinucleated osteoclasts and an increase in osteoclast resorption activity. In co-cultures of normal osteoblasts with mutant or control bone marrow cells, numbers of osteoclasts developing from mutant mice were increased compared with littermate control mice. Although mev/mev osteoclasts develop in the absence of colony-stimulating factor (CSF)-1, nevertheless cultured osteoclasts show increased size in the presence of CSF-1. CSF-1-deficient osteopetrosis (op/op) mutant mice develop severe osteosclerosis. However, doubly homozygous mev/mevop/op mice show an expansion of bone marrow cavities and reduced trabecular bone mass compared with op/op mice. Western blot analysis showed that several proteins that were markedly hyperphosphorylated on tyrosine residues were detected in the motheaten osteoclasts, including a novel 126-kd phosphotyrosine protein. The marked hyperphosphorylation of a 126-kd protein in motheaten osteoclasts suggests that this protein depends on SHP-1 for dephosphorylation. These findings demonstrate that the decreased SHP-1 catalytic activity in me/me and mev/mev mice results in an increased population of activated osteoclasts and consequent reduction in bone density. (+info)
Intermittent inhibition of dentin mineralization of rat incisors under continual infusion of 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP) using a subcutaneous mini osmotic pump.
The inhibitory effect of the continual administration of 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP) (8 mgP/kg/day) through a mini osmotic pump on dentin mineralization was examined in relation to the diurnal rhythm of the rat and compared with that of daily injections of same amounts of HEBP known to inhibit dentin mineralization. After daily injections of HEBP, a series of alternating rows of mineralized and non-mineralized dentin islands appeared in the newly formed portion of the crown-analogue of rat incisors. A similar phenomenon occurred under the continual administration of HEBP in rats raised either under regular environmental photofraction or constant lighting conditions. The average distance between the adjacent mineralized dentin islands was 521.0 +/- 51.3 microns in the injected rats. After continual HEBP administration, this was 426.0 +/- 13.2 microns and 416.5 +/- 19.4 microns under ordinary photofraction and constant light, respectively. Although the pattern of individual mineralized dentin islands tended to become irregular in nocturnal rats, no statistical difference was noted between the two values. Rows of mineralized and non-mineralized dentin islands also appeared in the root analogue dentin. No sign of the intermittent inhibition of mineralization was recognized in mesodermal hard tissues other than dentin in the HEBP-affected animals. These data implicate the presence of intrinsic cycles in dentin mineralization at the growing end of rat incisors independent of environmental photofraction as well as the ameloblast function. (+info)
Interaction between vacuolar H(+)-ATPase and microfilaments during osteoclast activation.
Vacuolar H(+)-ATPases (V-ATPases) are multisubunit enzymes that acidify compartments of the vacuolar system of all eukaryotic cells. In osteoclasts, the cells that degrade bone, V-ATPases, are recruited from intracellular membrane compartments to the ruffled membrane, a specialized domain of the plasma membrane, where they are maintained at high densities, serving to acidify the resorption bay at the osteoclast attachment site on bone (Blair, H. C., Teitelbaum, S. L., Ghiselli, R., and Gluck, S. L. (1989) Science 249, 855-857). Here, we describe a new mechanism involved in controlling the activity of the bone-resorptive cell. V-ATPase in osteoclasts cultured in vitro was found to form a detergent-insoluble complex with actin and myosin II through direct binding of V-ATPase to actin filaments. Plating bone marrow cells onto dentine slices, a physiologic stimulus that activates osteoclast resorption, produced a profound change in the association of the V-ATPase with actin, assayed by coimmunoprecipitation and immunocytochemical colocalization of actin filaments and V-ATPase in osteoclasts. Mouse marrow and bovine kidney V-ATPase bound rabbit muscle F-actin directly with a maximum stoichiometry of 1 mol of V-ATPase per 8 mol of F-actin and an apparent affinity of 0.05 microM. Electron microscopy of negatively stained samples confirmed the binding interaction. These findings link transport of V-ATPase to reorganization of the actin cytoskeleton during osteoclast activation. (+info)