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Questions on Etching

  • The scope of orthodontics has expanded over the past two decades to include more adult patients, and it is expected that many of these people will have restorations placed on their teeth.  Although banding is always an alternative for the teeth that have restorations, bonding is desirable in aesthetic areas.
  • BONDING TO CERAMICS
  • Acid etching with phosphoric acid  is ineffective.
  • Alternative surface preparation techniques have been found to satisfactory results which includes;
  •        – Mechanical roughening with stones and diamonds
  •        – Sandblasting
  •        – Chemical roughening with hydrofluoric acid
  •        – Combination of sand blasting and chemical roughening with
  •          hydrofluoric acid and chemical coupling with the use of silanes.

 

  • This silane contains silanol groups that can bond with silanols on the ceramic surface, forming a siloxane (Si-O-Si) bond.  Additionally, this silane contains methacrylate groups that can form covalent bonds with the polymer matrix of the resin composite.
  • Etching of the ceramic surface with hydrofluoric acid (HF) was introduced in the early 1980s for bonding porcelain laminate veneers..  A commonly used hydrofluoric acid product has a concentration of 9.6% in gel form and is placed on the ceramic for two to four minutes.  Other available commercial products use 4% acidulated phosphate fluoride containing 1.43% hydrofluoric acid in gel form for two minutes. Acid etching of ceramic surface is recommended when maximum bond strength is required.

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