Permeability dentin

The relationship between the degradation of organic matrix and dentin lesion formation has been studied both in vitro and in situ. Several authors employed matrix destruction to assess the role of the matrix in de-and remineralization. For example, Apostolopoulos and Buonocore (1966) reported facilitated demineralization of dentin at pFl<5.5 after treatment with ethylene diamine. Inaba and coworkers (1996) found that removal of matrix from dentin lesions by hypochlorite promotes remineralization, consistent with a larger crystal surface available for mineral deposition after ashing (McCann and Fath, 1958). Flypochlorite-mediat-ed destruction also increases the permeability of mineralized dentin (Barbosa et ah, 1994). 

Barbosa SV, Safavi KE and Spangberg LSW (1994) Influence of sodium hypochlorite on the permeability and structure of cervical human dentine. Int Endod J 27, 309-312. 

The constructions of the teeth of an adult human and herbivorous animals are illustrated in Fig. 14.1. Both types of teeth consist of an enamel portion, a dentine portion, and a cementum portion [4]. The enamel portion consists of 97% hydroxyapatite, 2% protein, and a small amount of carbonate the dentine consists of 30% hydroxyapatite, and 70% protein and water and the cementum contains an inorganic part below 30%, around 10-20%. The enamel is compact and hard, and assists in the cutting and grinding of food, whereas the dentine and cement portions are softer, are more permeable, and support the enamel region. The propor-... 

The reason to extend the experiments to tooth material was the idea that the matrix would have a less porous structure compared to human haversian bone and be less exposed to diagenetic alteration. While the porosity in human bone is mainly determined by a complicated network between the Haversian system and the Volk-mann canals that are perpendicular to it, especially enamel is a far denser material than human bone and its organic content is significantly less (2% of organic material only). But in contrast to the enamel, dentine has a similar composition of the organic and the inorganic matrix compared to bone, and it has a high microporosity due to nerve canals that start from the pulpa and stop close to the enamel-dentine junction (edj). However, these nerve canals have a smaller diameter than a haversian pore (70 pm) and the canals are orientated parallel and are not connected with each other. So a fluorine ion cannot percolate from one pore to another, as it is the case in a human bone, but it has to overcome the distance from one canal to the next one by diffusion. So the permeability is low and this results in a smaller diffusion rate D. 

Bouillaguet S, Virgillito M, Wataha J, Ciucchi B, Holz J. The influence of dentine permeability on cytotoxicity of four dentine bonding systems, in vitro. J Oral Rehabil 1998 25(1) 45-51. 

Beneath the layer of enamel is a structure craUed dentine. It is a permeable pale yellow material that consists of approximately 70% hydroxyapatite, 20% organic matter (mainly collagen) and 10% water by mass. 

D. Pashley, R.M. Carvalho, Dentine permeability and dentine adhesive, J. Dent. 25 (1997)... 

J. Tagami, L. Tao, D.H. Pashley, Correlation among dentin depth, permeability, and bond strength of adhesive resins. Dent. Mater. 6 (1990) 45-50. 

D.H. Pashley, H.J. Andringa, G.D. Derkson, M.E. Derkson, S.R. Kalathoor, Regional variability in the permeability of human dentine. Arch. Oral Biol, 32, 519-523,1987. 

D.H. Pashley, E.L. Pashley, Dentin permeability and restorative dentistry A status report for the American Journal of Dentistry, Am. /. Dent., 4, 5-9,1991. 

D.H. Pashley, V. Michelich, T. Kehl, Dentin permeability Effects of smear layer removal, /. Prosthet. Dent., 46, 531-527,1981. 

As a major component of the bonded interface, the dental tissue components have a dramatic effect of the stability of resin-tooth interface. While there is still much to learn about the composition and role of organic components in different forms of dentin and enamel, there is a consensus that the stability of the dentin matrix remains key to the long-term strength and permeability of the interface. 

Sauro, S., Thompson, I., and Watson, T.E (2011) Effects of common dental materials used in preventive or operative dentistry on dentin permeability and remineralization. Open Dent, 36 (2), 222-230. 

An important feature controlling the biocompatibility of bonding agents is the permeability of the dentin and also its thickness. This will determine whether or not monomers diffuse all the way through to the pulp and whether they arrive at sufficiently high concentrations to cause damage. 

Of particular concern in these studies has been the presence of 2 hydroxethyl methacrylate (HEMA). This has been shown experimentally to be able to diffuse through the pulp chamber when released from a bonding agent placed beneath a composite resin (Hamid and Hume 1997). Thickness made a difference to the rate of diffusion, but even relatively thick layers of dentin (i.e., in the range 3.4—3.6 mm) were not sufficient to eliminate it completely. Another finding of significance was that diffusion of HEMA was much more rapid in teeth that had been severely affected by caries. In other words, the reason that tooth repair is needed clinically, caries, turns out to be responsible for affecting dentine permeability adversely, and opens the way for potentially harmful monomers to reach the pulp. 

---