Tooth substrate

Hotz, P., McLean, J. W., Seed, I. Wilson, A. D. (1977). The bonding of glass-ionomer cements to metal and tooth substrates. British Dental Journal, 142, 41-7. 

N. Nakabayashi, K. Kojima, E. Masuhara, The promotion of adhesion by the infiltration of monomers into tooth substrates, J. Biomed. Mater. Res. 16 (1982) 265-273. 

A.M. El Wakeel, D.W. Elkassas, M.M. Yousry, Bonding of contemporary glass ionomer cements to different tooth substrates microshear bond strength and scanning electron microscope study, Eur. J. Dent. 9 (2015) 176-182. 

Adhesion of restorative dental biomaterials to tooth substrates is primarily based on micromechanical interlocking of resin monomers to the components of the hard tissue. In addition to micromechanical retention, chemical bonding can be achieved via functional monomers, which are able to chemically and mechanically bond to the tooth [10, 11]. While commonly classified as generations by industry, the most appropriate way to classify the current adhesive systems is by the dentin surface treatment and application techniques. The application techniques recommended by manufacturers is greatly influenced by the composition of the adhesive polymer [12]. A summary of the current adhesive systems is shown in Table 9.1. 

Traditionally remineralization of tooth structures have relied on well established concepts of nucleation and crystal growth. Mineral ions interact with the tooth substrate and crystallization occurs at specific thermodyuamic conditions that are appropriate for formation of an stable apatite phase in register with the preserved tooth structures. Using these approaches, researchers have been able to demonstrate that in carious dentin, the intrafibrillar mineral that is not fully dissolved upon acidic attack may function as nucleation sites for subsequent deposition of calcium and phosphate within the intrafibrillar compartments of collagen fibrils [127]. This, in turn, has been shown to lead to significant increases in the mechanical properties of partially demineralized dentin. 

When freshly mixed, the carboxyHc acid groups convert to carboxjiates, which seems to signify chemical adhesion mainly via the calcium of the hydroxyapatite phase of tooth stmcture (32,34—39). The adhesion to dentin is reduced because there is less mineral available in this substrate, but bonding can be enhanced by the use of minerali2ing solutions (35—38). Polycarboxylate cement also adheres to stainless steel and clean alloys based on multivalent metals, but not to dental porcelain, resin-based materials, or gold alloys (28,40). It has been shown that basic calcium phosphate powders, eg, tetracalcium phosphate [1306-01-0], Ca4(P0 20, can be substituted for 2inc oxide to form strong, hydrolytically stable cements from aqueous solution of polyacids (41,42). 

Resins are also used for permanent tooth-colored veneers on fixed prostheses, ie, crown and bridges. Compositions for this application include acryflcs, vinyl—acryflcs, and dimethacrylates, as well as silica- or quartz-microfilled composites. The resins are placed on the metallic substrates of the prostheses and cured by heat or light. These resins are inexpensive, easy to fabricate, and can be matched to the color of tooth stmcture. Acrylic facings do not chemically adhere to the metals and are retained only by curing the resin into mechanical undercuts designed into the metal substrate. They have relatively low mechanical strength and color stability, and poor abrasion and strain resistance they also deform more under the stress of mastication than porcelain veneers or facings. 

There are many obstacles to permanent adhesion under oral conditions. The substrate is a biological tissue and subject to change, and the presence of moisture represents the worst kind of situation for adhesion. Water is the great barrier to adhesion. It competes for the polar surface of tooth material against any potential polymer adhesive. It also tends to hydrolyse any adhesive bond formed. These twin obstacles gave rise to considerable doubt as to whether materials adhesive to tooth material could be developed at all (Cornell, 1961). 

When a ferrous alloy is immersed in phosphoric acid, il initially forms a soluble phosphate. As the pH rises at the mclal/solutiun interface, the phosphate becomes insoluble and crystallizes epitaxially on Ihe substrate metal. The phosphate coating thus produced consists of a nonconduciivc layer nf crysinlx that insulates the metal from any subsequently applied film and provides a topography with enhanced tooth" for increased adhesion. The cry stals insulate microanode and microcathode centers caused by stress or imperfections in the metal surface. This greatly reduces Ihe severity of electrochemical corrosion. 

The Dylux 503 formulation contained a HABI, the leucodye TLA-454, a mixture of quinones, triethanolamine triacetate, several plasticizers, an organic acid, cellulose acetate butyrate binders, as well as antiblocking agents (fluorinated derivatives) as well as a silica derivative to provide tooth to the coating. The selection was made to provide maximum performance at minimum mill cost. The paper substrate required had high holdout, so as to permit two-sided coatings as well as to minimize the wicking of chemistry into the base. 

The formation of the chiton tooth takes place on a tongue-like process, the radula, which comprises more than a hundred rows of teeth and is around 3 cm long. Two of the teeth in each row are mineralized (Fig. 1.2). The chiton uses its teeth to scrape the rocky substrate for algae and sponges living on the surface or just below the surface [11, 12]. Teeth are worn out at a rate of about a row every 12-48 h, and are continuously replaced [13, 14]. Thus the radula is in essence a conveyor belt, and every tooth row represents the product of 12-48 h worth of assembly and mineralization activities. The chiton radula is thus an ideal object to study assembly and mineralization. Its major drawback is that the teeth are small 100 pm across [6]. 

Whilst the use of enamel and dentine as test substrates is widespread, they are complex materials to work with due to the natural variability both within and between specimens. A number of authors have examined alternative materials, which have similar mechanical properties to enamel and dentine, to use as test substrates. Acrylic [19, 20] and synthetic hydroxyapatite [21] have been proposed as suitable materials for abrasion testing, where mechanical effects dominate. These materials have several advantages since they are available as relatively large, smooth samples and exhibit better intra- and inter-sample reproducibility than their natural counterparts. This may, therefore, give better discrimination between test products for formulation development. However, the use of natural enamel and dentine is preferred, particularly for studies that aim to understand interactions between toothpaste products and tooth hard tissues. Other methods for assessing toothpaste abrasivity to hard tissues include gravimetry [22], scanning electron microscopy [23] and laser reflection [24]. 

H ow many times have you heard the lecture from parents or your dentist about brushing your teeth after a sugary snack Annoying as this lecture might be, it is based on sound scientific data that demonstrate that the cause of tooth decay is plaque and acid formed by the bacterium Streptococcus mutans using sucrose as its substrate. 

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