Answer is A
In dentistry a widely used mechanism for attachment of polymerizable resin materials is the so-called acid etch technique. In this procedure, the tooth enamel surface is treated for about one minute with an acid solution or gel, usually 30 to 50% phosphoric acid.
- This treatment results in dissolution of the outer layer of the enamel to a depth of around 20 micrometers and the production of a clean etched porous surface.
- When a fluid polymerizable resin composition is placed on the etched surface, capillary action draws the monomers into the surface porosity to a depth of as much as 100 micrometers.
- After setting of the resin composition by chemical activation or radiation-induced polymerization, a strong bond of the resin to the tooth is induced by virtue of the extensive micromechanical interlocking created through penetration of the resin into the many pores in the etched surface of the enamel.
- Such a bond is as strong as the weaker of the resin and the enamel surface.
- This acid-etch technique has been used to attach resin coatings to teeth to seal the fissures in the biting surfaces to prevent decay and to provide facings which improve the aesthetic appearance of the teeth.
- Another preventive dentistry application of the acid-etch technique is to bond orthodontic attachments directly to the tooth in order to move teeth within the jaws.
- For restorative purposes, acid-etching is used to improve the bond of restorative resins to fractured teeth and to minimize leakage around composite resin fillings.
- Still other applications include the splinting of loose teeth and temporary tooth replacement.
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