Sandblasting
Air-abrasion (sandblasting) techniques have long been employed in restorative dentistry to enhance the mechanical adhesion between metals and adhesive resins. Sandblasting uses a high-speed stream of aluminum oxide particles propelled by compressed air to remove unfavorable oxides and contaminants, increase surface energy, bonding surface area, and surface roughness. Sandblasting in orthodontics has been implemented to improve the bond strength of new brackets/bands or to remove adhesive remnants from debonded brackets prior to rebonding.71 However, in vivo data from a randomized trial indicate that no significant difference exists in the bond failure rates of sandblasted and non-sandblasted brackets or in the ARI of debonded brackets.72 Finally, sandblaster has also been implemented directly on the tooth enamel surface as an alternative or adjunct to conventional acid-etching techniques, but as no randomized trial exists on this subject, the efficacy cannot be assessed in an evidence-based way at the present time.
Grit-blasting or sandblasting, if available, may also be used. A specially-trained operator is needed to produce uniformity within pieces by sand blasting tank. A clean, uniform-size grit is essential for proper surface preparation with sandblasting. This may be a problem when treating GPR surfaces, and for that reason this technique is rarely used.
After sanding or sandblasting, the surface is sometimes wiped with solvent such as MEK, acetone, toluene, trichloroethylene, Freon® TF, or Freon® TMC, depending on the known mold lubricants. In some cases, a solvent is used before and after abrading the surface. If water-break-free surfaces are not obtained, the procedure should be repeated.
Glass-reinforced plastic laminates prepared for bonding by hand- and machine-sanding can be stored to 30 days at 23°C and 50% RH with no adverse effect on bond strength. Machine sanding gave slightly better results than hand sanding. Tear ply and sanding gave about the same results, but the tear-ply method has less risk of surface contamination. Variations in bond strength are more likely to occur as a result of changes in sanding techniques than by the difference in methods.
In general, bond quality diminished with increased surface exposure time (SET). The best overall adhesive evaluated was epoxy film adhesive, which was found to be the least sensitive to the method of surface preparation. In general, the best result was obtained when GPR laminates were bonded within four hours after sanding. If absolutely necessary, bonding can be carried out after periods of time up to 14 days SET with only moderate strength loss. Brass is an alloy of copper and zinc. Sandblasting or other mechanical means of surface preparation may be used.
Shot peening (which is a similar process to sandblasting, but has more controlled peening power, intensity, and direction) is a cold working process in which the surface of a part is bombarded with small spherical media called shot. Each piece of shot striking the material acts as a tiny hammer, imparting to the surface small indentations or dimples. In order for a dimple to be created, the surface fibers of the material must be yielded in tension. Below the surface, the fibers try to restore the surface to its original shape, thereby producing below the dimple a hemisphere of cold-worked material highly stressed in compression.