A comparative study of fluoride-releasing adhesive resin materials.
(57/1113)
One of the most important and exciting properties of recently introduced dental restorative materials is their ability to release fluoride ions, as this has several advantageous effects on tooth structures. They have been extensively used as fluoride-releasing filling and luting materials. Recently, fluoride-releasing adhesive resins and fluoride-releasing adhesive resin cement have been developed and introduced for clinical use. The purpose of this study was to evaluate the fluoride release from these adhesive resins and the fluoride uptake by both enamel and dentin, as well as the acid-resistance of these tooth structures. Based on our results, we conclude that fluoride-releasing adhesive resins and luting cements are useful for the prevention of initial or secondary caries, especially along the margins of restorations. (+info)
Phospholipids in amelogenesis and dentinogenesis.
(58/1113)
Phospholipids have been identified in enamel and dentin. Before demineralization, a group of phospholipids extracted by lipid solvents was associated with cell membranes and is therefore closely related to cell growth and intracellular regulations. After demineralization, a second group of phospholipids, associated with the extracellular matrix, was extracted; this group is probably linked to the mineralized phase. Using imidazole-osmium tetroxide fixation of rat incisors, we stained cellular unsaturated fatty acids, so that we could visualize the membrane domains, coated pits, and endocytic inclusions. Filipin, a probe for cholesterol, varied in density along the plasma membrane of secretory ameloblasts, and allowed us to visualize membrane remnants inside the forming enamel. With respect to phospholipids located in the extracellular matrix, the malachite-green-glutaraldehyde (MGA) method or iodoplatinate (IP) reaction retains and visualizes enamel and dentin phospholipids. In predentin, aggregates appearing as granules and filaments, or liposome-like structures, were located in the spaces between collagen fibrils. In dentin, organic envelopes coating the crystals, also named "crystal-ghost" structures, outlined groups of collagen fibrils. Histochemical data provided evidence that phospholipids are co-distributed or interact with proteoglycans. Radioautography after IP reaction established that [3H] choline was detected in dentin as early as 30 min after the intravenous injection of the labeled precursor, before any labeling was seen in odontoblasts and predentin. This suggests that blood-serum-labeled phospholipids pass between odontoblasts, cross the distal permeable junctional complex, and diffuse in dentin prior to any cellular uptake and phospholipid synthesis. Pharmacologically and genetically induced pathology also supports the suggestion that phospholipids play an important role in the formation and mineralization of dental tissues. (+info)
Invasion of dentinal tubules by oral bacteria.
(59/1113)
Bacterial invasion of dentinal tubules commonly occurs when dentin is exposed following a breach in the integrity of the overlying enamel or cementum. Bacterial products diffuse through the dentinal tubule toward the pulp and evoke inflammatory changes in the pulpo-dentin complex. These may eliminate the bacterial insult and block the route of infection. Unchecked, invasion results in pulpitis and pulp necrosis, infection of the root canal system, and periapical disease. While several hundred bacterial species are known to inhabit the oral cavity, a relatively small and select group of bacteria is involved in the invasion of dentinal tubules and subsequent infection of the root canal space. Gram-positive organisms dominate the tubule microflora in both carious and non-carious dentin. The relatively high numbers of obligate anaerobes present-such as Eubacterium spp., Propionibacterium spp., Bifidobacterium spp., Peptostreptococcus micros, and Veillonella spp.-suggest that the environment favors growth of these bacteria. Gram-negative obligate anaerobic rods, e.g., Porphyromonas spp., are less frequently recovered. Streptococci are among the most commonly identified bacteria that invade dentin. Recent evidence suggests that streptococci may recognize components present within dentinal tubules, such as collagen type I, which stimulate bacterial adhesion and intra-tubular growth. Specific interactions of other oral bacteria with invading streptococci may then facilitate the invasion of dentin by select bacterial groupings. An understanding the mechanisms involved in dentinal tubule invasion by bacteria should allow for the development of new control strategies, such as inhibitory compounds incorporated into oral health care products or dental materials, which would assist in the practice of endodontics. (+info)
Morphology and thickness of the diffusion of resin through demineralized or unconditioned dentinal matrix.
(60/1113)
The formation of a hybrid layer is the main bonding mechanism of current dentin-bonding systems. This study evaluated the morphology and thickness of the resin-infiltrated dentinal layer after the application of adhesive systems. The dentin-bonding agents were evaluated on flat dentinal preparations confected on the occlusal surfaces of human teeth. The test specimens were prepared and inspected under scanning electron microscopy at a magnification of X 2,000. The adhesive systems were responsible for different hybrid layer thicknesses (p < 0.05), and the mean values were: for Scotchbond MP Plus (SM), 7.41 +/- 1.24 micrometer for Single Bond (SB), 5.55 +/- 0.82 micrometer for Etch & Prime 3.0 (EP), 3.86 +/- 1.17 micrometer and for Clearfil SE Bond (CB), 1.22 +/- 0.45 micrometer. The results suggest that the conventional three-step adhesive system (SM) was responsible for the thickest hybrid layer, followed by the one-bottle adhesive (SB). The self-etching adhesives, EP and CB, produced the formation of the thinnest hybrid layers. (+info)
The extent of odontoblast processes in the dentin is distinct between cusp and cervical regions during development and aging.
(61/1113)
The question of whether odontoblast processes extend to the dentinal surface has been widely debated in previous studies. In this study odontoblast processes were investigated in the developing and aging dentin of rats and monkeys (Japanese macaques). For this purpose, F-actin of microfilaments and cellular membranes were stained with phalloidin and DiI, respectively. This dual staining demonstrated that positive signals for odontoblast processes were present in the dentinal surface in both the cusp and cervical regions of the dentin at 2 weeks of age. The tips of doubly positive processes were detectable in the dentinal surface in the cusp region even at 100 weeks of age, whereas in the cervical region they were retracted from the dentinal surface towards the pulp during the period of 3-6 weeks of age. During these stages, phalloidin-positive signals showing retracted odontoblast processes in the cervical region were closely associated with the interglobular dentin that was stained with sWGA-lectin. After 6 weeks of age, no association was observed between the processes and the interglobular dentin, since they were retracted approximately to the inner third portion of the dentinal tubules. This staining pattern can be detected until 100 weeks of age. Moreover, different distribution patterns of odontoblast processes between the two dentinal regions were also confirmed in dentin of monkey teeth. These results suggest that the existence of the regional differences in the extent of the odontoblast processes in the dentin, i.e., the persistence of the processes in the dentinal surface in the cusp region and their retraction from the dentinal surface in the cervical region. (+info)
A RANK/TRAF6-dependent signal transduction pathway is essential for osteoclast cytoskeletal organization and resorptive function.
(62/1113)
Signaling through receptor activator of nuclear factor-kappaB (RANK) is essential for the differentiation and activation of osteoclasts, the cell principally responsible for bone resorption. Animals genetically deficient in RANK or the cognate RANK ligand are profoundly osteopetrotic because of the lack of bone resorption and remodeling. RANK provokes biochemical signaling via the recruitment of intracellular tumor necrosis factor receptor-associated factors (TRAFs) after ligand binding and receptor oligomerization. To understand the RANK-mediated signal transduction mechanism in osteoclastogenesis, we have designed a system to recapitulate osteoclast differentiation and activation in vitro by transfer of the RANK cDNA into hematopoietic precursors genetically deficient in RANK. Gene transfer of RANK constructs that are selectively incapable of binding different TRAF proteins revealed that TRAF pathways downstream of RANK that affect osteoclast differentiation are functionally redundant. In contrast, the interaction of RANK with TRAF6 is absolutely required for the proper formation of cytoskeletal structures and functional resorptive activity of osteoclasts. Moreover, signaling via the interleukin-1 receptor, which also utilizes TRAF6, rescues the osteoclast activation defects observed in the absence of RANK/TRAF6 interactions. These studies are the first to define the functional domains of the RANK cytoplasmic tail that control specific differentiation and activation pathways in osteoclasts. (+info)
Effect of tubule orientation and dentin location on the microtensile strength of bovine root dentin.
(63/1113)
To investigate the mechanical properties of root dentin and to further clarify the cause of vertical root fracture (VRF), this study evaluated the effect of tubule orientation (parallel, perpendicular and oblique to the cross-section of dumbbell specimens in microtensile tests) and dentin location (cervical, middle, and apical location of the root) on the microtensile strength of bovine root dentin. Each specimen was stressed in tension at a crosshead speed of 1.0 mm/min. The results of the microtensile strength measurements were statistically analyzed with one-way ANOVA and the Fisher PLSD. The oblique group (95.18+/-23.80 MPa) was significantly (p<0.01) higher than the parallel group (38.93+/-5.28 MPa) or the perpendicular group (32.64+/-4.69 MPa). There were no significant differences among the different dentin locations within the parallel group (p>0.05). It was clarified that the VRF occurs frequently in practical situations due to the tubule orientation of root dentin. (+info)
Mutation of the signal peptide region of the bicistronic gene DSPP affects translocation to the endoplasmic reticulum and results in defective dentine biomineralization.
(64/1113)
Dentine dysplasia type II is an autosomal dominant disorder in which mineralization of the dentine of the primary teeth is abnormal. On the basis of the phenotypic overlap between, and shared chromosomal location with, dentinogenesis imperfecta type II, a second disorder of dentine mineralization, it has been proposed that the two conditions are allelic. As recent studies have shown that dentinogenesis imperfecta type II results from mutation of the bicistronic dentine sialophosphoprotein gene (DSPP ), we have tested this hypothesis by sequencing DSPP in a family with a history of dentine dysplasia type II. Our results have shown that a missense change, which causes the substitution of a tyrosine for an aspartic acid in the hydrophobic signal peptide domain of the protein, underlies the phenotype in this family. Biochemical analysis has further demonstrated that this mutation causes a failure of translocation of the encoded proteins into the endoplasmic reticulum, and is therefore likely to lead to a loss of function of both dentine sialoprotein and dentine phosphoprotein. (+info)