Method: Composite (Filtek™ Supreme Ultra, 3M) 4mm width x 7mm depth samples were made by curing (Demi, Kerr) for 20s with a Mylar strip (n=79; Matrix Mylar Strips, Benco Dental) against the superficial surface or without a Mylar strip (n=97). Additionally the deep sides of samples were cured for 20s, labeled by treatment, and further divided into 5 duration groups for distilled water storage: 5min, 30min, 1hr, 24hrs, or 72hrs . Adhesive (ExciTE®F, Ivoclar Vivadent) was added, cured for 10s and 4mm3composite was added and cured for 20s. The samples were tested for SBS at a crosshead speed of 1mm/min (Instron™ 5566A, Norwood, MA).
After testing for normality using a Shapiro-Wilk test, an independent samples t-test was performed to test difference between the means. Data was analyzed using SAS 9.2. A Non-parametric test, Wilcoxon-Mann-Whitney U test was used to test the hypothesis (p<0.05).
Result: SBS values from each group indicated normality (except for the 5min untreated values). Statistical analysis failed to reject the null hypothesis for all time points except for at 30min (p=.002, statistically significant) where median values were 6.02MPa (Mylar-treated), 14.82MPa (untreated) (Table 1).
Table 1
Sample Treatment |
Time |
N |
Mean Shear-bond strength (MPa)
|
Standard Deviation |
Median Shear-bond strength (MPa) |
Shapiro-Wilk p-value |
Wilcoxon-Mann-Whitney U p-value |
None |
5min. |
23 |
9.06 |
5.77 |
6.70 |
0.020 |
0.8126 |
Mylar |
5min. |
15 |
8.11 |
4.37 |
7.06 |
0.391 |
|
None |
30min. |
16 |
6.98 |
4.33 |
6.02 |
0.048 |
0.002 |
Mylar |
30min. |
15 |
15.13 |
6.27 |
14.82 |
0.7628 |
|
None |
1hr. |
18 |
13.72 |
6.54 |
14.48 |
0.8552 |
0.707 |
Mylar |
1hr. |
15 |
15.17 |
7.47 |
13.97 |
0.346 |
|
None |
24hrs. |
20 |
9.45 |
5.54 |
7.97 |
0.136 |
0.139 |
Mylar |
24hrs. |
15 |
12.06 |
4.47 |
11.83 |
0.924 |
|
None |
72hrs. |
20 |
9.99 |
5.95 |
9.78 |
0.401 |
0.727 |
Mylar |
72hrs. |
19 |
10.70 |
4.72 |
10.63 |
0.206 |
Conclusion: In all groups but the 30min time, there were no statistically significant differences between the presence of and absence of the Mylar-treatment, suggesting that Mylar-treatment does not affect SBS. Larger sample sizes and focused time points may help explore the difference at the 30min time. Larger sample sizes would provide greater power and statistical support.