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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.Shot-peening (which is a similar process to sand blasting cabinet, 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 the 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. Any successful rehabilitation measure demands proper preparation of the structural element. This includes surface preparation, such as dry sand blasting tank, of the concrete to a desired degree, storage of fiber and resin constituent materials, as well as mixing of the resin system. On-site processing, if performed incorrectly, contains a high potential for flaw introduction. It further necessitates assessments with regards to the integrity and bond capability of the concrete substrate. In some cases, cracked or split concrete sections may contain wide cracks that must be injected with resin prior to application of the composite-strengthening system. Defects induced by preparation and site processing are listed below.Concrete is a porous material and hence absorbs liquids. Moreover, due to abrasion of cement paste during sand blasting room, a large number of small to medium diameter voids become exposed on the concrete surface. Prior to application of the composite overlay, regardless of type, a compatible primer coat should be applied. The role of this primer is to fill voids and quench the absorption so that the surface is prepared for the subsequently applied composite material. If primer coatings are omitted, the saturating resin would be to an extent absorbed. In addition, the primer presents a ‘bondable’ surface. To ensure an intimate bond between composite and concrete, the thickness of the coating should be kept as thin as possible. If excessive amounts of primer are used, low stress transfer capabilities and resin dripping can result.