Enamel acid-etching

When the direct-on process is utilized, surface preparation requirements are more critical to ensure effective enamel adhesion. The acid etch is often deeper and the nickel deposition is always thicker. Typically, the nickel coating is 0.01 to 0.02 g/m2 for direct-on coating as compared to 0.002 to 0.007 g/m2 for two-coat applications. A few porcelain enamelers prefer to omit the nickel deposition step. Although the nickel enhances enamel bonding, product quality requirements may not require nickel deposition. The omission of the nickel step necessitates the utilization of a heavy acid etch to ensure a clean, properly conditioned surface for enamel bonding.3-6... 

The demand for aesthetic dental restorative materials continues to increase and may be the most important criterion for the promising future of the aesthetic polymeric composite resins. As the physical, mechanical, and wear properties of these materials improve, their use in dentistry will expand. The acid-etching of dental enamel [20] and dentin bonding procedures [21] will allow for conservative cavity preparation and the preservation of healthy tooth structure. 

The system for bonding to enamel was developed by Buonocore in the 1950s [260]. This acid etch procedure requires the preparation of the enamel surface with an acidic solution, usually about 37 % phosphoric acid. The surface then has altered surface tension and altered topography with enamel prismatic tags approximately 25 microns long and 5 microns apart [258,261]. An unfilled, low viscosity resin can be allowed to flow between these tags and then polymerize to form a tight junction with the tooth enamel [262]. 

Kuroiwa M, Kodaka T, Kuroiwa M, Abe M Brushing induced effects with or without a non-fluo-ride abrasive dentifrice on remineralization of enamel surfaces etched with phosphoric acid. Caries Res 1994 28 309-314. 

Acid etching pretreatment of enamel, such as the use of buffered 50% phosphoric acid solutions, has found clinical applications to bond enamel to restorative materials, sealants and orthodontic brackets (4, ). The etching creates an increased enamel surface area and opens pores into which the resin can flow. Greater porosity of the substrate allows an easier ingress of un-... 

Acid etching pretreatment of dentin prior to application of a resin restorative leaves the collagenous component of this substrate substantially untouched. The collagen at the dentin surface interferes with the mechanical adhesion of the hydroxyapatite, (the inorganic constituent of dentin) to the adhesive. Thus, in contrast to its successful use with enamel, etching pretreatment produces a bond between dentin and restorative resin that is too weak to withstand the forces encountered at the interface under clinical conditions. 

A combination of modified features of the last-named two bonding systems is realized in an adhesive applieation known as the Kanca technique, in which dentin and enamel pre-treatment by phosphorie acid etching is followed by the consecutive layering of NTG-GMA, PMDM, and HEMA-bis-GMA adhesive resins, onto which the restorative is placed by conventional manipulation. Low microleakage, and composite shear bond strengths to enamel/dentin at the 18-MPa level, have been reported [54]. 

The success of acid-etching is due in part to the structure and composition of enamel [4]. As can be seen in Table 5.1, enamel contains almost no protein phase or water. Hence a fraction of the mineral phase can be removed without causing the enamel structnre to collapse. This procedure produces a chalky appearance in the enamel, and once this develops, the etching process is considered to be complete and the enamel is ready to receive the liquid resin component. A scanning electron miCTo-scope (SEM) image of etched human dentine is shown in Fig. 5.1. 

The enamel is etched with 37% ortho-phosphoric acid (often in the form of a gel) to prodnce a rongh snrface. The composite flows into this etch pattern and can be retained... 

Tensile strength for phosphoric acid-etched bovine enamel after standing for 2 weeks at 37°C in water. 

Glass-ionomer cements have taken a major place in dental treatments as restorative filling materials and also in a range of more adhesive applications due to their ability to bond to both dentine and composite fillers. Acid-etching techniques are well established for the bonding of resins to enamel. 

Phosphoric acid has traditionally been used as a conditioner of enamel and dentin for adhesive restorative treatments, as desalbed in section Polymers in Dental Adhesion . 37 % phosphoric acid has been shown to decalcify enamel and dentin in a desirable pattern, thus facilitating impregnation of adhesive monomers required for placement of composite resin restorations in the tissue matrix. Despite the known efficiency of 37 % phosphoric add gels in acid-etching enamel and dentin, it has been shown that its effects in increasing the surface porosity of the pseudo-intact surface layer of enamel lesions was not sufficient [117]. To overcome this limitation, 15 % hydrochloric acid (generally for 2 min) has been tested and shown to remove about 30 pm of surface enamel, thus allowing for much improved penetration of viscous resins in white spot lesions [116]. 

J. (2009) Effect of fluoride on the morphology of calcium phosphate crystals grown on acid-etched human enamel. Caries Res., 43 (2), 132-136. 

Acid etching owes part of its success to the nature of the enamel. Enamel contains very little protein or water and can therefore be dried without causing the structure to collapse. Clinically, the procedure leads to the observation of a chalky appearance to the enamel, which can be taken as an indication of the success of the etching process and the readiness of the enamel to receive the bonding layer. 

Kidd EAM (1976) Microleakage a review. J Dent 4 199 Kitayama S, Nikaido T, Ikeda M, Foxton RM, Tagami J (2007) Enamel bonding of self-etch and phosphoric acid-etch orthodontic adhesive systems. Dent Mater 126 135... 

The interfacial adhesion between nanocomposites, and between nanocomposites and virgin materials, is determined by the surface and interfacial free energies of each respective material. Modification of the surface to create greater surface area, in addition to imparting free radical surface effects to create new surface bonds with introduced chemical functionalities, are primary approaches for maximizing interfacial adhesions. Surface roughening by mechanical or chemical means has been successful for low volume processes. Acid-etch and lasers, for example, have been used as distinct methods for promoting adhesion of nanocomposite materials to enamel. 

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