Objectives: 1) to measure the Linear Hygroscopic Expansion (LHE) of three RMGI cements: an experimental cement (EXP, Kerr), Rely X Luting (RXL, 3M), and Fuji Plus (FJP, GC America), along with a resin cement: Nexus 2 (NEX2, Kerr); and 2) to model the kinetics of LHE process. Methods: Specimens (n=3) were prepared using a ring mold (
f/h: 30/3mm). The distance between two known points was measured using a measuring microscope initially and then at pre-determined time intervals (up to 90 days) after the specimens were stored in de-ionized water at 37 ° C. Non-linear regression analyses were performed on LHE as a function of time. Results: ANOVA analysis revealed that NEX2 resin cement had significantly lower LHE (p < 0.05) than all RMGI's. Among RMGI's, EXP had significantly lower LHE (p < 0.05) than RXL and FJP. The LHE process can be best described by the sum of a short-term and long-term first order processes: Et=EI{1-exp(-KI* t)} + EII{1-exp(-KII* t)}; where E and K are the equilibrium LHE and rate constant for each process. The half-life for each process was calculated as T=ln2/K.|
Measured 90-day LHE, % |
Parameters From Model |
|||||
|
EI, % |
TI, days |
EII, % |
TII, days |
E ¥ (=E1+EII), % |
||
|
NEX2 |
0.36 ±0.05a |
0.09 |
1.56 |
0.31 |
30.9 |
0.40 |
|
EXP |
0.63 ±0.02b |
0.55 |
0.48 |
0.09 |
10.3 |
0.64 |
|
RXL |
1.12 ±0.02c |
0.65 |
0.46 |
0.49 |
16.7 |
1.14 |
|
FJP |
1.59 ±0.04d |
0.83 |
0.59 |
0.76 |
12.1 |
1.59 |
*
Means with the same letter are not statistically different at p < 0.05.Conclusions:. The kinetics of the LHE can be modeled by the sum of a short-term first order process with a half-life of 0.46-1.56 days and a long-term first order process with a half-life of 10.3-30.9 days. NEX2 resin cement had a half-life that is much longer than those for RMGI's due to its hydrophobic resin matrix that slows down water absorption process.