Three types of commercially available orthodontic bonding cements , a resin cement (SB) and two resin-modified glass ionomer (RMGI) cements classified as chemicalcured (FO) and light-cured (LC) types , were investigated to determine the setting time, amount of elements and mechanical properties . In addition, they were investigated to observe the powder particles and surface of the set cement. The setting time of cements differed for each cement , with a range of 4-6 min, and LC showed the

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... st setting time . The Al/Si ratio of FO (0.68) was higher than that of LC (0 .51) , which may affect the setting behavior of RMGI cements . Backscattered electron images of the surface of the set RMGI cements demonstrated that smaller particles were filled heavily around the larger particles (10-20 pm) . Resin structure separated from the matrix phase in the cement was observed in the surface of FO. The mechanical properties of RMGI cement regarding tensile and bending characteristics were significantly lower than those of SB . Lower elastic deformation revealed that RMGI cements were more brittle than SB . These properties may also affect the fracture type on the surface when brackets are debonded , and the removal property for residual cement from the surface.