The influence of resin coating time on GI shear strength

Objectives: High strength, auto-cure glass ionomer (GI) restorative cement (Fuji 9© GC) is supplied with resin coating (G-Coat Plus© GC) to protect the restoration from early exposure to water. However water might be needed for maturation. The aims of this study were: to examine the effect of coating, coating for predetermined time only and no coating on the shear punch strength (SPS) of the material exposed to artificial saliva Methods: 270 cylindrical specimens (6x1.5mm) of Fuji 9© – GC were prepared in individual washers and allowed to set for 7 min between polyester strips. Following removal of the strips, they were divided into three equal groups: No Coating (NC), With Coating (WC), and With Coating for predetermined time (PC). Each group was then divided into 6 subgroups: storage in 37°C artificial saliva for 2h, 24h, 1W, 1M, 2M, 3M. SPS of the specimens in the NC and WC groups was measured at the end of each time interval in a Universal testing machine (0.5mm/min.). Specimens in the PC group were uncoated at the end of the initial storage time and returned to the incubation medium till 3M and then tested. Results: In the PC group the highest SPS (MPa) was when specimens were coated for 2h and then uncoated (71.73±5.2) while the lowest SPS was after coating for 24h and then uncoating (61.74±9.0) (P<0.05). In the NC and WC groups: after 2h the SPS was the lowest (NC=11.61±0.38, WC=11.36±0.41 p=0.092) and the highest was after 3M (NC=59.14±7.3, WC=63.24±4.3 p=0.072). Conclusions: There was no benefit of coating the specimens. The significant SPS improvement was from 2h to 24h.