Acid-etching of enamel

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. 

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

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 corrosive effects of sulfuric acid on teeth with chronic exposure are well established." The damage, etching of dental enamel followed by erosion of enamel and dentine with loss of tooth substance, is limited to tbe parts of the teeth that are exposed to direct impingement of acid mist upon the surface. Although etching typically occurs after years of occupational exposure, in one case exposure to an average of 0.23mg/m for 4 months was sufficient to initiate erosion. ... 

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]. 

Therapeutically, dilute phosphoric acid has been used well-diluted in preparations used in the treatment of nausea and vomiting. Phosphoric acid 35% gel has also been used in dentistry to etch tooth enamel. 

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. 

Fluoride mouthwashes are examples of preparations for dental use. Dental solutions in general have the advantage that mouthwashes are easy to use by the patient. Semisolid dental gels can be applied to specific places on the teeth. Normally this is done by the dentist or dental hygienist. An example is a hydrogel with phosphoric acid, used in etching teeth enamel to facilitate composite restoration. 

---