Objective: Common methods for measurement of acid-erosion are often confounded by other physical parameters. This study investigates the role of water-expansion on measured acid-erosion of different luting cements. The cements used were five commercial materials RelyX Luting (RLC, 3M ESPE), Ketac Cem (KC, 3M ESPE), Fuji Plus (FP, GC), FujiCEM (FC, GC), Zinc Cement (ZPh, Fleck) and two experimental resin-modified glass-ionomer (RMGI) cements (EXPC-1&EXPC-2, 3M ESPE). RLC, KC, FP, ZPh are powder/liquid systems while FC and EXPCs are paste/paste. Method: The acid-erosion depths were measured per ISO-9917 following McCabe’s methodology that calls for 24h cure at 37C/95%RH before immersion in 37C acidic medium. In an attempt to separate the expansion effects from those of erosion, cements were also cured at 37C/95%RH for 2h and immersed in 37C water before being transferred to acidic solution. For water-expansion measurements, cements were cured at 37C/95%RH for 24h prior to immersion in 37C water. Five specimens of each category were made and the changes were monitored over a three-day immersion period. The depths/protrusions were measured using Mitutoyo profiler. Results: Mean values including standard deviations are summarized below:
|
Luting Cement |
Type |
Water-Expansion (3-day), % |
Acid-Erosion Depth (1-day), mm |
|
RLC |
RMGI |
1.1(0.3) |
0.008(0.003) |
|
KC |
GI |
0.1(0.1) |
0.042(0.004) |
|
FC |
RMGI |
2.0(0.2) |
0.010(0.005) |
|
FP |
RMGI |
1.8(0.4) |
0.008(0.002) |
|
ZPh |
zinc phosphate |
0.0(0.2) |
0.154(0.010) |
|
ExpC-1 |
RMGI |
1.1(0.2) |
0.001(0.002) |
|
ExpC-2 |
RMGI |
1.3(0.2) |
0.004(0.004) |
Conclusions: The proposed sample preparation methodology effectively removes the water-expansion effects commonly seen in acid-erosion measurements of RMGI cements. Water-expansion of RMGI cements was seen to slow down appreciably within the first two days of immersion. ANOVA analysis was performed at p < 0.05. There were significant differences between RMGI cements and other cements (GI and zinc phosphate) in water-expansion and acid-erosion depth. Among RMGI cements, RLC and experimental cements had significantly lower water-expansion than FC and FP.