Enamel, bonding

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... 

Industrially, enameling is currently mainly carried out on steel (and steel alloys). The applied layers in steel-enameling adhere very firmly to the substrate as a result of chemical reactions which take place between the glowing metal and the molten frits, leading to a composite material. The sheet steel-enamel bond can withstand a tensile. stress of 1000 kp/cm. In addition to steel (ca. 90%) ca.st iron (ca. 6%) and aluminum (ca. 4%) are also enameled. Annually ca. 450 10 t/a of enamel is applied to a total surface of ca. 750 10 m. Ca. 30% is used in Europe and 20% in the USA. In the Federal Republic of Germany there are ca. 50 enameling plants with an annual enamel consumption of ca. 13 lO- t. 

Vitreous enamels bonded to glass surfaces are used to produce translucent colours for functional or decorative purposes. Such enamels have a low melting point and are applied by spraying, silk screening or decalcomania and are fired in a decorative lehr [1]. 

M. Brannstrom, K.J. NordenvaU, Bacterial penetration, pulpal reaction and the inner surface of Concise Enamel Bond. Composite fillings in etched and unetched cavities, J. Dent. Res. 57 (1978) 3-10. 

The forces are transmitted to the tooth by a wire that is coupled to a bracket bonded to the tooth surface. The most common brackets are made of stainless steel and have either a groove cast into the base or a metal mesh brazed onto the bracket base to increase the available surface area for bonding. The challenge of orthodontic bonding is that the bracket/enamel bond must be sufficient to withstand the forces applied by the wire and the fatigue conditions produced by thermal and occlusal load cycling in the mouth, yet must be easily debonded without damaging the enamel surface at the end of treatment (typically two years). 

Surface conditioning before applying adhesives effectively increases the surface bonding area and enhances the strength of the bonding agent. The enamel is commonly etched with an aqueous solution of phosphoric acid or other acids. Most current enamel bonding systems employ phosphoric acid in various concentrations and viscosities as an etchant (169,170). 

M. Hannig, K.-J. Reinhardt, B. Bott, Self-etching primer vs phosphoric acid An alternative concept for composite-to-enamel bonding, Open Dent., 24,172-180,1999. 

M. Miyazaki, M. Sato, H. Onose, Durability of enamel bond strength of simplified bonding systems, Open Dent, 25,75-80,2000. 

Kanehira, M. et al. (2006) Relationship between degree of polymerization and enamel bonding strength with selfetching adhesives. / Adhes. Dent, 8 (4), 211-216. 

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... 

---