الفهرس 
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Abstract
Summary and conclusions
The aim of this study was to evaluate the effect of enamel sandblasting before acid etching and wire sandblasting on retention of two different lingual fixed retainers.
A total number of 112 primary bovine teeth were collected. Each two teeth were embedded in acrylic block contacting each other and forming 56 blocks. Half of the blocks were used for testing 0.016x0.022 in multistranded st.st dead soft wire and the other half for testing twisted 0.032 in coaxial wire. Blocks were divided were equally divided into 2 main groups according to type of wire used; Each group was subdivided into 4 subgroups of 7 blocks to test the effect of sandblasting to either the wire or enamel on shear bond strength of rectangular and round wire.
Wires were sandblasted using 50μm aluminum oxide particles at 90 Psi for 15 seconds till becoming dull at 3 mm distance while enamel was sandblasted at 70 Psi for 3 seconds at 5 mm distance. Enamel acid etching was done using 37% phosphoric acid for 30 seconds.
Wires were bonded on lingual surfaces using Reliance LCR adhesive.
Shear bond strength was tested using Instron testing machine.
Lingual enamel of three teeth were evaluated under scanning Electron microscope representing intact enamel, acid etched enamel and sandblasted enamel before acid etching. Two sections of each wire type were evaluated under SEM before and after sandblasting.
It was found that there was statistically significant difference between sandblasted wire bonded to non-sandblasted enamel (Groups IB
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and IIB) and non-sandblasted wire bonded to sandblasted enamel (Groups IC and IIC) for both type of wires. This showed that enamel sandblasting before acid etching didn’t increase bond strength of non- sandblasted wires.
Enamel acid etching had showed better homogenous uniform surface roughening than enamel sandblasting before acid etching. The 0.016x0.022 wire showed uniform dull roughening along wire section while 0.032 wire showed frost surface with areas that weren’t affected by sandblasting.
Based on the results of the current study, the following conclusions were conducted:
1- Sandblasted wires bonded to non- sandblasted enamel showed highest mean shear bond strength values over other groups.
2- There was no significant difference in shear bond strength between both wires.
3- Sandblasted 0.016x0.022 wire showed better roughening pattern than sandblasted 0.032 wire under SEM.
4- Sandblasting enamel before acid etching didn’t increase shear bond strength of the wires.
5- Etching enamel caused uniform homogenous roughening pattern rather than sandblasting enamel before acid etching.