Characteristics of Experimental Resin-modified Glass Ionomer for Filling

Objectives: This study examined the compressive and shear strengths and disintegration of experimental resin-modified glass ionomer for filling in an effort to develop a new glass ionomer without HEMA.

Methods: An experimental resin-modified glass ionomer for filling [Shofu] containing polyacid monomer was tested. The cements were mixed at three different powder-liquid ratios(manufacturer’s recommended ratio(MRR,4.5) and MRR±20%). An hour after the start of mixing, the specimens prepared for each testing were immersed in deionized water at 37°C for 23 hours. Then, the compressive strength and disintegration were determined according to the materials specification(JIST6607).The shear strength was determined using a punch tool(ASTMD732:1990). The results were analyzed using ANOVA/Scheffe’s test among different mixing ratios and t test for comparison with the specification requirement values at p=0.05.

Results: The table shows mean compressive or shear strength values(MPa,  n=5) and disintegration values(mass%, n=5). Compressive strength values decreased in order of MRR, MRR+20% and MRR-20%(p<0.05). No significant differences were found in the shear strength values among the mixing ratios(p>0.05). The disintegration value was greater at MRR+20% than the others(p<0.05). All compressive strength values and disintegration values were found(p<0.05) to satisfy the specification requirement values(>50MPa for compressive strength and <0.7% for disintegration, JIST6607). The shear strength values appeared to be lower than those published data for  the resin-modified glass ionomers(Yamazaki, 2007),  probably due to brittle nature of  the experimental cement.

Mixing ratio	MRR-20%	MRR	MRR+20%
Compressive strength(MPa)	163(5)	191(5)	178(9)
Shear strength(MPa)	19.4(3.2)	17.0(2.4)	22.6(6.3)
Disintegration(mass%)	0.509(0.043)	0.522(0.042)	0.602(0.030)
[Data represent Mean(SD)]

Conclusions: Our previous study(Hibino, Transactions IDMC2011) reported that the mean flexural strength of the present experimental cement showed the values more than 26 MPa at 24 hours, which indicated to be above the minimum requirement  strength value(20 MPa) specified in JIST6609-2.  In addition to the previous study, the present study suggested that the experimental cement examined revealed to be a possible new resin-modified glass ionomer.