12-Month Bottom/Top Knoop Hardness Ratios of Resin-Modified Glass-Ionomer Restorative Materials

Bottom/Top Knoop Hardness Ratios of Resin-Modified Glass-Ionomer Restorative Materials over Twelve Months

HW Roberts*, DW Berzins, DG Charlton

Objective: To investigate the 12-month dark-cure behavior of RMGI restorative materials using bottom/top Knoop Hardness (KH) ratios as a function of material thickness and storage time. Methods: RMGI materials were prepared per manufacturer directions, placed into 2-, 3-, 4-, and 5-mm-thick Delrin molds (n=5), photopolymerized, and stored at 37°C/100% humidity. At established intervals, bottom/top KH ratios were determined for each specimen using a microhardness tester (Leco) and a mean group ratio calculated. Two-way ANOVA (thickness, time)/Scheffé (a=.05) were used to analyze the data. Results: For both materials, KH ratios at all time periods were statistically lower for thicker specimens. Statistically significant increase in KH ratios was noted with 4 and 5 mm Fuji II LC specimens at 12 months, but not for Vitremer. Conclusions: The dark-cure capability of RMGI materials appears limited.

Product	Thickness	Storage Time
Fuji II LC (GC America)		24 hours	1 Mo	3 Mo	6 Mo	12 Mo
	2 mm	88.3(1.9) Aa	91.1(2.7) Aa	91.3(4.2) Aa	94.4(1.1) Aa	91.8(5.2) Aa
	3 mm	74.7(1.4) Ba	82.8(3.8) Bb	93.9(1.7) Ac	92.9(1.6) Ac	87.3(1.8) Abc
	4 mm	55.8(6.1) Ca	62.5(5.8) Ca	62.2(6.2) Ba	65.8(2.7) Ba	77.2(3.5) Bb
	5 mm	47.6(1.5) Da	52.9(5.7) Da	51.4(3.8) Ca	56.3(7.6) Ca	69.3(1.8) Cb
Vitremer (3M/ESPE)	2 mm	93.0(4.1) Aa	89.8(1.1) Aa	93.4(6.4) Aa	85.3(3.4) Aa	91.6(1.1) Aa
	3 mm	90.5(1.7) Aa	89.5(2.3) Aa	86.4(3.5) ABa	80.7(2.1) Ab	90.4(1.1) Aa
	4 mm	84.7(5.8) Aa	77.2(1.8) Ba	80.1(9.8) BCa	80.1(5.3) Aa	80.1(3.8) Ba
	5 mm	71.5(9.9) Ba	66.3(1.3) Ca	66.9(5.5) Ca	69.8(4.5) Ba	68.0(4.7) Ca

For each material, the same capital letters indicate non-sig diff within a column; lower-case letters indicate non-sig diff within a row.