Stress dentin

The nature and type of initiation scheme plays an important role in the performance of the adhesive [194,202-204]. Stresses due to polymerization shrinkage lead to the creation of a gap between the adhesive and tooth material. In the case of bulk chemical initiation, shrinkage stresses tend to create gaps at all interfaces, drawing material inward isotropically. With a photoinitiation scheme, polymerization begins at the free surface and pulls the material away from the dentin towards the free surface [194]. Thus the gap is created at the... 

Dentin constitutes the bulk material of all vertebrate teeth. The outer working surface of a vertebrate tooth is composed of a much stiffer material called enamel, or in the case of fish, enameloid [6]. The two materials work together during mastication to provide the tooth with its functional properties [33]. In general the softer dentin functions in distributing and absorbing the compressive stress that is transmitted through the outer enamel layer [26],... 

Another unusual property of dentin is that its hardness properties vary continuously in three dimensions [33]. This is clearly under cellular control, and it was inferred that this design feature is part of the mechanism for distributing the applied compressive stress in such a way as to avoid cracks from developing. Unlike bone, teeth are generally not replaced (except once at puberty or... 

The FDA has made several modifications to the tests required by Part 1 of the ISO 10993 standard for the category of surface devices that permanently contact mucosal membranes. The ISO does not require acute, subchronic, or chronic implantation tests as does FDA. FDA requires irritation, systemic toxicity, acute, subchronic, and chronic tests for external communicating devices, tissue/bone/ dentin with prolonged and permanent contact. Device manufacturers are advised to consider tests to detect chemical components of device materials that may be pyrogenic. This matrix is a framework and not a checklist and it is stressed by the FDA that necessary safety testing will be decided on a case-by-case basis. 

Raman photoluminescence piezospectroscopy of bone, teeth and artificial joint materials has been reviewed by Pezzotti (2005) with emphasis placed on confocal microprobe techniques. Characteristic Raman spectra were presented and quantitative assessments of their phase structure and stress dependence shown. Vibrational spectroscopy was used to study the microscopic stress response of cortical bone to external stress (with or without internal damages), to define microscopic stresses across the dentine - enamel junction of teeth under increasing external compressive masticatory load and to characterise the interactions between prosthetic implants and biological environment. Confocal spectroscopy allows acquisition of spatially resolved spectra and stress imaging with high spatial resolution (Green etal., 2003 Pezzotti, 2005 Munisso etal., 2008). 

Abfraction is defined as the pathological loss of materials from the tooth caused by biomechanical loading forces [69], These loading forces cause flexure of the tooth that result in failure of the enamel and the dentine in a direction away from that of the loading. The concept of abfraction is primarily based on engineering considerations that assume stress concentration at the cervical region of the tooth. 

Although these contacts are transient, they do result in distinct forces on the tooth. The tooth is known to undergo tiny lateral displacements when loaded and this results in compressive stress on the side towards which the tooth bends and tensile stress on the other side [82,85], These stresses lead to miao-fractures in the enamel or dentine... 

Non-carious cervical lesions of the tooth are typically wedge-shaped and show loss of tooth tissue mainly on the buccal surfaces of the tooth close to the cemento-enamel junction. This is the case, regardless of the tooth affected [72]. When the tooth is loaded asymmetrically, there are typically flexing stresses, and these produce tension on one side of the tooth and compression on the other. Both types of force are located close to the cemento-enamel junction [86], The result is that tooth mineral fractures in this region, and falls away, causing a non-carious lesion to develop. These lesions typically involve exposure of the dentine [72]. 

In addition to providing a bridge between the hydrophilic dentine and hydrophobic composite, the DBA also has to accommodate the stresses resulting from polymerization contraction of the monomer. 

Fig. 7.72 Plots corresponding to cyclic fatigue data in Fig. 7.71 for sandblasted alumina and Y-TZP of thickness 1.5 mm, but in terms of critical loads instead of stress and for dentin-like substrate with intervening dental cement of thickness 100 pm, using Eqs. (7.17), (7.18), and (7.19) to convert the data. Ninety-five percent confidence bounds are used to evaluate uncertainties in sustainable loads at long lifetimes, tR = 10 years. Shaded band indicates nominal oral function range [35]. With kind permission of Elsevier...

C.L. Davidson, A.J. de Gee, A. Feilzer, The competition between the composite-dentin bond strength and the polymerization contraction stress, / Dent. Res., 63, 1396-1399,... 

A fracture of endodontically treated tooth is an important issue for restoration when brittle of the teeth is increased due to take the moisture out of the tooth. Hence, tooth fracture in larger occlusive force or files treatment can happen [1], Many posts have been developed in various shapes, diameters and materials to reinforce the tooth [2], An excellent post can reduce stress concentration and tooth damage, but good design for dental post is still unclear. Furthermore, stress distributions in the post and dentin were evidenced to be a factor of failure in post system [3]. 

The stress values at the core region of the traditional core crown post were two and three times greater than non split-shank and split-shank post respectively. Therefore, the structure of core crown post could induce stress concentration in the root around the end of the post. In addition, the Co-Cr crown base margin of buccal side of the traditional core crown post was demonstrated a stress concentration by pressing contact on the dentin margin of the root (Fig. 5). This also meant enlarged possibility of root fracture. 

Fig. 5 Stress concentration at the buccal side of dentin margin in the core...

Dentin stress at different sections was remarkably increased in all models from cervical margin towards apical area except the last section (apical area) which was sharply decreased (Fig. 7). The presence of a ferrule resulted in a marked declaim in the stress of dentin from cervical area till roughly middle of the root (Fig. 7) also increasing ferrule height results reducing dentin stress at the same area. 

There was significant correlation between ferrule height and dentin stress. By increasing ferrule length declined average stress in dentin (Fig. 7) consequently the fracture resistance is increased. These results observed by other researchers experimentally and clinically [9,10,30,31,32). 

The study suggests that a ferrule increases mechanical resistance of crown. Furthermore, a ferrule decreases stress in dentin and luting cement consequently, models with ferrule were benefited from low fracture and losing restoration risk. 

Ersoz E. (2000) Evaluation of stresses caused by dentin pin with finite element stress analysis method. J Oral Rehabil 27 769-773... 

Holmes DC, Diaz-Arnold AM, Leary JM. (1996) Influence of post dimension on stress distribution in dentin. J Prosthet Dent 75 140-147... 

Kishen, A. and Vedantam, S. (2007) Hydromechanics in dentine role of dentinal tubules and hydrostatic pressure on mechanical stress-strain distribution. Dent Mater, 23 (10), 1296-1306. 

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