dentin - Medical Dictionary

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dentin		The hard portion of the tooth surrounding the pulp, covered by enamel on the crown and cementum on the root, which is harder and denser than bone but softer than enamel, and is thus readily abraded when left unprotected. (From Jablonski, Dictionary of Dentistry, 1992) [ Articles \| Books \| Images \| Discussion groups ]

Additional comments : The structure of dentin is unusual in that the number and size of its tubules changes as one moves from the periphery toward the pulp chamber. Near the pulp, the tubules are very close together and the water content of this deep dentin is high. Near the enamel, the tubules are far apart, occupying less than 1% of the surface area. When enamel or dentin is cut, the surface becomes covered by an adherent layer of cutting debris called the smear layer. DH Pashley - Scanning Microsc, 1989 Dentin is the major mineralized extracellular matrix of the tooth. The organic components of dentin consist of type I collagen (90%) with 10% noncollagenous proteins, which are also components of bone. Two dentin proteins, dentin sialoprotein and dentin phosphoprotein, have been shown to be tooth-specific being expressed mostly by odontoblast cells. MacDougall M, Simmons D, Luan X, Nydegger J, Feng J, Gu TT. J Biol Chem. 1997 Jan 10;272(2):835-42. Dentin is permeable and allows the bidirectional movement of materials from the oral cavity, across dentin to the pulp and vice versa. The pupal irritation associated with microleakage is often dictated by the permeability of dentin. Thick dentin covered with a smear layer is a better barrier than thin dentin with the smear layer removed, while coronal dentin is more permeable than root dentin. Carious dentin is less permeable than normal dentin, but freshly cut dentin is more permeable than previously prepared dentin. Pashley DH, Pashley EL. Am J Dent. 1991 Feb;4(1):5-9. Dentin has a highly oriented tubule structure and thetubule number density and area fraction of intertubulardentin vary with distance from pulp. As is well-known,dentin is composed of about 50 vol% mineral, 30 vol% organic matter, and about 20 vol% liquid, and it consists of dentin tubules, peritubular dentin and intertubular dentin.The dentin tubule is surrounded by a highly mineralized peritubular dentin in a matrix of intertubular dentin consisting of collagen embedded with apatite crystals. N Konishi, LG Watanabe, JF Hilton, GW Marshall, SJ … - Dental Materials Free Full Text Efficacy of Gluma Desensitizer on dentin hypersensitivity in periodontally treated patients Pesqui Odontol Bras. 2006 Jul-Sep;20(3):252-6. The aim of this double-blind, controlled, split-mouth designed clinical trial was to assess the effect of a single application of Gluma Desensitizer on alleviating dentin hypersensitivity. Twelve subjects entered the study and ten completed the protocol. Each subject had two teeth treated: one with Gluma Desensitizer according to the manufacturer's instructions and one with water. The assessment of pain was performed with the VAS (Visual Analogue Scale), after tactile (probe), thermal (cold blast of water) and thermal/evaporative (cold blast of air) stimuli at baseline, immediately after treatment, after 1 week and after 4 weeks. The mean VAS values for the test and control teeth were compared by the paired t test (alpha = 0.05). Repeated measurements ANOVA was used to compare the different experimental times. The results showed that for test teeth, at baseline, mean VAS values were 1.76 (+/- 2.82), 7.10 (+/- 2.10) and 4.75 (+/- 2.65), and, after 4 weeks, the mean values were 1.70 (+/- 2.31), 5.50 (+/- 3.30) and 4.61 (+/- 3.14), respectively for probe, water and air stimuli. For the control teeth, at baseline, the mean VAS values were 1.86 (+/- 2.92), 6.61 (+/- 2.31) and 4.08 (+/- 2.91) and, after 4 weeks, 2.66 (+/- 3.07), 6.32 (+/- 2.94) e 4.76 (+/- 3.26). There were no statistically significant differences between test and control teeth at any time. No intra-group differences were demonstrated either. It was concluded that Gluma Desensitizer had no effect on hypersensitive teeth from periodontally treated patients for a period up to 4 weeks. Morphometric analysis of pulpal myelinated nerve fibers in human teeth with chronic periodontitis and root sensitivity Medicina (Kaunas). 2006;42(11):914-22. BACKGROUND: The reasons why root sensitivity occurs in some periodontally diseased teeth are still unknown. It is possible that root sensitivity may be related to changes of intradental myelinated nerve fibers, which are responsible for dentine sensitivity. OBJECTIVE: The aim of this study was to define the pattern of myelinated nerve fiber changes in the pulps of teeth with and without root sensitivity in the presence of chronic periodontitis. MATERIALS AND METHODS: A total of 33 cross-sectioned human dental pulp specimens were collected from noncarious, intact, permanent teeth sensitive to electric and thermal (cold) stimulus (10 hypersensitive teeth with chronic periodontitis (HTPP group), 15 nonsensitive teeth with chronic periodontitis (NTPP group), and 8 nonsensitive teeth with healthy periodontium (control group)). The morphometric parameters were estimated using light microscopy and image-analyzing computer program Image-Pro Plus. RESULTS: The means of myelinated nerve fiber density, fiber and axon diameter, area, perimeter, length, width, g ratio, index of circularity, and myelin sheath thickness in NTPP group significantly differed from HTPP group and the control group teeth (p<0.001). The great reduction in the density of myelinated nerve fibers in NTPP group was accompanied by unequal decrease in the number of very large-diameter myelinated nerve fibers. The mean values of morphometric parameters of all myelinated nerve fibers in HTPP group were almost the same as those in the control teeth, and no significant difference was observed. CONCLUSION: The findings of the present study suggest that the reason for enhanced root sensitivity has likely nothing to do with changes of the innervation of myelinated nerves in the dental pulp. While, decreased sensitivity of periodontally diseased teeth may be related to the degeneration of myelinated nerve fibers in the pulp. Reduced antigenicity of type I collagen and proteoglycans in sclerotic dentin J Dent Res. 2006 Feb;85(2):133-7. Antigenic alterations to the dentin organic matrix may be detected by an immunohistochemical approach. We hypothesized that alterations in the antigenicity of type I collagen and proteoglycans occur in sclerotic dentin under caries lesions. Transverse sections were prepared from carious teeth in the sclerotic zone and normal hard dentin. A double-immunolabeling technique was performed on these sections, with anti-type I collagen and anti-chondroitin 4/6 sulfate monoclonal primary antibodies. We used gold-conjugated secondary antibodies to visualize the distribution of intact collagen fibrils and proteoglycans by high-resolution SEM. For sclerotic dentin, labeling densities were 19.57 +/- 3.01/microm2 for collagen and 9.84 +/- 2.62/microm2 for proteoglycans. For normal hard dentin, values were 35.20 +/- 2.73/microm2 and 17.03 +/- 1.98/microm2, respectively. Distribution of intact collagen fibrils and proteoglycans in sclerotic dentin was significantly lower than in normal hard dentin. Reductions in antigenicity from the organic matrix of sclerotic dentin under caries lesions raise concern about the potential of intrafibrillar remineralization. Relationship between large tubules and dentin caries in human deciduous tooth Bull Tokyo Dent Coll. 2005 May;46(1-2):7-15. The purpose of this study was to elucidate the relationship between large tubules and dentin caries by using human deciduous incisors that showed various levels of attrition but no macroscopical lesions resulting from caries. The teeth were cut longitudinally in the mesio-distal direction and the exposed surfaces observed with a high-resolution field emission scanning electron microscope. The inside of each large tubule showed dense collagen fibers running parallel to its long axis and small spherical bodies of aggregated crystals, but no marked attrition. In teeth where attrition had exposed dentin at the incisal edge, oral bacteria had infiltrated the large tubules. Furthermore, in teeth with advanced attrition, it was difficult to distinguish between the large tubules and the surrounding dentin matrix, and numerous bacteria were observed in both areas. These findings support the hypothesis that large tubules play a role in the pathway of caries formation in coronal dentin when incisal dentin is exposed by attrition. This suggests that early treatment of exposed dentin surfaces might be effective in preventing dental caries. Cementum and dentin in hypophosphatasia J Dent Res. 2005 Nov;84(11):1021-5. Hypophosphatasia (HPP) often leads to premature loss of deciduous teeth, due to disturbed cementum formation. We addressed the question to what extent cementum and dentin are similarly affected. To this end, we compared teeth from children with HPP with those from matched controls and analyzed them microscopically and chemically. It was observed that both acellular and cellular cementum formation was affected. For dentin, however, no differences in mineral content were recorded. To explain the dissimilar effects on cementum and dentin in HPP, we assessed pyrophosphate (an inhibitor of mineralization) and the expression/activity of enzymes related to pyrophosphate metabolism in both the periodontal ligament and the pulp of normal teeth. Expression of nucleotide pyrophosphatase phosphodiesterase 1 (NPP1) in pulp proved to be significantly lower than in the periodontal ligament. Also, the activity of NPP1 was less in pulp, as was the concentration of pyrophosphate. Our findings suggest that mineralization of dentin is less likely to be under the influence of the inhibitory action of pyrophosphate than mineralization of cementum. How does fluoride affect dentin microhardness and mineralization? J Dent Res. 2005 Oct;84(10):951-7. Fluoride (F) has been a useful instrument in caries prevention. However, only limited data exist on the effect of its long-term use on dentin mineralization patterns and microhardness. The objective of this study was to evaluate the influence of tooth F concentration ([F]) and dental fluorosis (DF) severity on dentin microhardness and mineralization. We collected 137 teeth in Montreal and Toronto, Canada, and Fortaleza, Brazil, where optimum or suboptimum levels of water F were 0.2 ppm, 1 ppm, and 0.7 ppm, respectively. Teeth were analyzed for DF severity, dentin [F], enamel [F], dentin microhardness, and dentin mineralization. Dentin [F] correlated with DF severity; enamel [F] correlated with dentin microhardness and dentin mineralization; DF severity correlated with dentin microhardness. Genetic factors (e.g., DF severity) and environmental factors (e.g., tooth [F]) influenced the mechanical properties (microhardness) of the teeth, while only the environmental factors influenced their material properties (e.g., mineralization). Fortaleza teeth were harder and less mineralized and presented higher dentin [F] values. Montreal teeth presented lower levels of DF when compared with both Toronto and Fortaleza teeth. Dentine hypersensitivity - an enigma? A review of terminology, mechanisms, aetiology and management Br Dent J. 1999 Dec 11;187(11):606-11; discussion 603 Dentine hypersensitivity is a relatively common problem experienced in clinical dental practice. This condition may disturb the patient during eating, drinking, brushing and sometimes even breathing. Therapeutic intervention by desensitising agents may provide only partial pain relief and recurrence is common. Much remains unknown about dentine hypersensitivity, even the terminology can be questioned. Most of the literature over decades has been concerned with reporting clinical trials proving the efficacy of numerous treatments for dentine hypersensitivity. Indeed, besides haemorrhoids, there can be few other diseases or conditions known to man that can apparently be successfully treated by so many and extremely varied agents and formulations applied topically. This paper will discuss the epidemiology, mechanisms of pain production and aetiological factors for the condition in the hope of developing ideas for more realistic prevention and management strategies.

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