Porosity in manually and machine mixed resin-modified glass ionomer cements

The powder and liquid components of resin-modified glass ionomer cements ar e available in manual and machine mixed forms. This study quantified the ef fect mixing methods have on the porosity and shear strength of a resin-modi fied glass ionomer cement (RMGIC). A RMGIC (Fuji II LC) was manually or machined mixed according to manufactur er's instructions. Thin, disc-shaped specimens (n=5) were made by compressi ng the cement between glass platens to a thickness of approximately 76 mum. The specimens were light cured for 120 seconds. Digital images of the spec imens were recorded using a measuring microscope and slide film scanner. Di gital imaging software was used to determine the number and volume of the c ement's pores. Shear test specimens of manual and machine mixed cements (n= 10) of each group (similar to 800 mum thickness) were made as previously de scribed. Shear punch tests were conducted using a 3.75 mm diameter punch mo unted on a universal testing machine. The mean number and total volume of pores in the manually mixed specimens w as considerably greater than that of the machine mixed group (p <0.05). The shear punch test results of the machine mixed group was significantly high er than the manual mixed group, (p <0.05).