Dentinal tubules

There are several reasons why these cements are bland. Acid irritation is probably minimal. Poly(acrylic acid) is a weak add and, in addition, because of its high molecular weight will not readily diffuse along dentinal tubules and is also immobilized by phosphatic material in these tubules. Moreover, once set these cements rapidly become neutral. 

Which sentence best describes dentinal tubules ... 

Cavity varnishes are used to seal the exposed dentinal tubules and protect the pulp from the irritation of chemicals in the filling materials. They are generally largely NR or a synthetic polymeric resin such as 2-hydroxyethyl methacrylate (HEMA). 

Dentine is composed of a mixture of about 70% hydroxlyapatite (Ca5(P04)3(0H)), 20% collagenous proteins and about 10% water. The microscopic structure of dentine consists of microscopic canals called dentinal tubules that radiate out from the pulp cavity to the cementum border. The diameter of these canals varies among different animals, and ranges... 

Figure 1.5. Transverse section through a mouse incisor tooth. E, enamel D, dentin P, pulp cavity. Note the dentin tubules, radiating out from the pulp cavity to the...

Dentine is the first calcified tissue to be deposited during tooth embryogenesis by the odontoblasts lining the inner pulp chamber. Odontoblasts lay down the dentinal organic matrix, and the dentine formation proceeds inwards. The mineralization begins when an organic layer of about 10-20 pm thick was deposited, and only cells process encased in the dentinal tubules are present in dentine. 

Several theories have been advanced to explain the mechanism of dentinal hypersensitivity innervation of the dentinal tubules, permitting transmission of impulses to the pulp, or the presence of lymph fluid in the dentinal tubules. In the latter case, exposure of dentin results in increased colloidal pressure on the tubules (thereby increasing pressure on the odontoblastic cells). Also proposed is a hydrodynamic... 

The primary mechanisms postulated for these dentifrices are that they occlude dentinal tubules, preventing stimuli from the oral cavity from irritating the dental nerve via these tubules. Also, those containing potassium may depolarize nerve fibers resulting in decreased impulse conduction and an associated decrease in pain. 

This is especially true for enamel where details of the prepared surface are masked by debris. A smear layer often covers the dentin surface. Complete drying of the surface cannot be accomplished under in vivo conditions, since fluid seeps rapidly from the dentinal tubules. Thus the tooth surface is highly heterogeneous and bonding is only accomplished at localized active sites. 

The tip response in SECM is strongly dependent on local mass transport, and this may in fact be utilized to image local mass transport. Examples include the transport of oxygen and electroactive ions in cartilage (80), convective (81) and diffusional (34) transport in dentinal tubules, and ionic fluxes through skin (82), which are described in Chapters 9 and 12. In this section we discuss briefly experiments by Pohl, Antonenko and coworkers which, though not SECM, employ microelectrode techniques in a similar manner. 

JV Macpherson, MA Beeston, PR Unwin, NP Hughes, D Littlewood. Scanning electrochemical microscopy as a probe of local fluid-flow through porous solids—application to the measurement of convective rates through a single dentinal tubule. J Chem Soc Faraday Trans 91 1407-1410, 1995. 

Another important feature of the pre-treatment of the dentine surface is that the smear layer is removed and so also are the smear plugs. The latter is especially important as it opens to dentinal tubules, which means that liquid bonding agent can flow into the tubules (see Fig. 5.2). When polymerization occurs, this results in the formation of... 

The essential mechanism of action of self-etch adhesives is that they simultaneously etch and prime the freshly cut tooth surface, and in doing so, incorporate the components of the smear layer [58,60]. Because of the presence of the smear layer, and also because of smear plugs blocking the dentinal tubules, self-etch adhesives have been claimed to provoke less post-operative sensitivity in patients than the etch-and-rinse approach [61,62]. However, this has not been confirmed by scientific studies [63,64], but rather any reduction in patient discomfort has been attributed to operator technique [15]. 

Compared to the SEM photomicrographs of an untreated dentin surface, photomicrographs of the AA treated dentin cross sections for times of 15, 30, 45, 60, and 120 s all showed significant surface changes(Figures 3-8). Optimal smear layer removal and opening of dentinal tubules occurred after 30-60 s of AA etching. 

II Applied load approximately parallel to either the long axis of the enamel rods or dentinal tubules. 

Fracture or applied load approximately perpendicular to the long axis of the enamel rods, t Applied load with respect to either the long axis of the enamel rods or dentinal tubules was variable. 

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