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

The powder and liquid components of resin-modified glass ionomer cements are available in manual and machine mixed forms. This study quantified the effect mixing methods have on the porosity and shear strength of a resin-modified glass ionomer cement (RMGIC). A RMGIC (Fuji II LC) was manually or machined mixed according to manufacturer's instructions. Thin, disc-shaped specimens (n = 5) were made by compressing the cement between glass platens to a thickness of approximately 76 microns. The specimens were light cured for 120 seconds. Digital images of the specimens were recorded using a measuring microscope and slide film scanner. Digital imaging software was used to determine the number and volume of the cement's pores. Shear test specimens of manual and machine mixed cements (n = 10) of each group (approximately 800 microns thickness) were made as previously described. Shear punch tests were conducted using a 3.75 mm diameter punch mounted on a universal testing machine. The mean number and total volume of pores in the manually mixed specimens was considerably greater than that of the machine mixed group (p < 0.05). The shear punch test results of the machine mixed group was significantly higher than the manual mixed group, (p < 0.05).