Vickers Hardness (HV)

The results gained from the HV are illustrated in Figure  3-37. The means and standard deviation were expressed in MPa. A total of nine indents on three specimens were applied and the mean HV for each time point (1 hour and 1 month) was calculated as described in Materials and Methods in Chapter  2.2.5.

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Figure  3-37: Mean micro-HV and standard deviation of the experimental GIC (P1hour & 1month>

0.01).

The bar chart in Figure  3-37 illustrated the microhardness of the experimental GICs, depending on ageing time. The hardness increases throughout the 1 hour to 1 month ageing time for all three GIC compositions. Ca-Ba-GIC exhibits the highest hardness at 1 hour, followed by Ca-Sr-GIC and Ca-GIC. However, Ca-Sr-GIC exhibits the highest level of hardness after 30 days, followed by Ca-Ba-GIC and Ca-GIC. The microhardness values at 30 days are almost twice that of 1 hour.

The paired t-test was used to compare the HV of two experimental GIC compositions at different time intervals (1 hour and 1 month). Three comparisons (1. Ca-GIC to Ca- Sr-GIC, 2. Ca-GIC to Ca-Ba-GIC and 3. Ca-Sr-GIC to Ca-Ba-GIC) at two time points, 1 hour and 1 month, were performed via the t-test. Analysis by the paired two sample t-test for all experimental GIC compositions at 1 hour and 1 month showed no significant differences (P > 0.01).

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3.6 Nano-indentation

The results gained from the nano-indentation are illustrated in Figure  3-38 and the corresponding reduced modulus (Er) is presented in Figure  3-39. The means and standard deviation are expressed in GPa.

Figure  3-38: Mean nano-indentation and standard deviation of the three experimental GICs (P values are shown in Table  3-11).

The nano-indentation hardness, depending on the ageing time (Figure  3-38), slightly decreased from 1 hour to 1 month for all three GIC compositions. Ca-Ba-GIC decreased from 1 hour to 1 day but thereafter steadily increased up to 1 month. Sr substituted GIC decreased gradually up to 1 week followed by a slight increase from 1 week to 1 month. Ca-GIC fluctuated during the 1 month period. The hardness decreased from 1 hour to 1 day, followed by a minor increase from 1 day to 1 week and thereafter decreased from 1 week to 1 month. The three GIC compositions had exactly the same progress in their development for their reduced modulus (Figure

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The paired t-test was used to compare the nano-indentation and the reduced modulus of two experimental GIC compositions at different time intervals (1 hour, 1 day, 1 week and 1 month). Three comparisons (1. Ca-GIC to Ca-Sr-GIC, 2. Ca-GIC to Ca-Ba-GIC and 3. Ca-Sr-GIC to Ca-Ba-GIC) at each time point were performed via the t-test and P values are shown in Table  3-12. Analysis by the paired two sample t-test of the nano-indentation for all experimental GIC compositions showed no significant differences (P > 0.01), however, a significant difference was present at 1 day for Ca-Sr-GIC and Ca-Ba-GIC (P = 0.004).

Table  3-11: Analysis by the paired two sample t-test of the nan-indentation and reduced modulus of the three experimental GIC compositions.

Paired t-test of two

GIC compositions 1 hour 1 day Nano-indentation 1 week 1 month Ca-GIC to Ca-Sr-GIC P = 1 P = 0.06 P = 0.25 P = 0.08 Ca-GIC to Ca-Ba-GIC P = 0.71 P = 0.8 P = 1 P = 0.06 Ca-Sr-GIC to Ca-Ba-GIC P = 0.31 P = 0.004 P = 0.08 P = 0.09 Reduced modulus

1 hour 1 day 1 week 1 month Ca-GIC to Ca-Sr-GIC P = 0.02 P = 0.01 P = 0.85 P = 0.008 Ca-GIC to Ca-Ba-GIC P = 0.16 P = 0.49 P = 0.009 P = 0.002 Ca-Sr-GIC to Ca-Ba-GIC P = 0.42 P = 0.05 P = 0.07 P = 0.73

P > 0.01: no significant differences between the two GIC compositions present; P < 0.01: show significant differences between the two GIC compositions.

Analysis by the paired two sample t-test, for the reduced modulus for all experimental GIC compositions showed no significant differences (P > 0.01); however, a significant difference was present at 1 week for Ca-GIC to Ca-Ba-GIC (P = 0.009) and at 1 month for Ca-GIC to Ca-Sr-GIC (P < 0.008) and Ca-GIC to Ca-Ba-GIC (P < 0.002) (Table  3-12).

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Figure  3-39: Mean reduced modulus calculation from the nano-indentation and standard deviation of the three experimental GICs (P values are shown in Table  3-11).

Figure  3-40: Force-displacement curve of the three GIC compositions using a Berkovich indenter.

Figure  3-40 illustrates an example of the force/displacement curve, for the three GIC compositions at 1 hour. The force/displacement result of the three experimental GICs is typical for a C-GIC. Ca-Sr-GIC exhibited the highest hardness, followed by Ca-Ba- GIC and Ca-GIC.

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Figure  3-41 illustrates the creep response of the three experimental GICs. The results suggest that the mean displacement is after ca. 25 seconds for all three GIC compositions with ca. 5800 nm for Ca-Sr-GIC, ca. 6200 nm for Ca-Ba-GIC and ca. 8200 nm for Ca-GIC.

Figure  3-41: Creep response at a maximum load of 300 nm. 3.7 Wear behavior of glass ionomer cements

The wear result of all three GIC compositions after 24 hours is illustrated in Figure

3-42. Ca-Ba-GIC exhibited the least wear volume and Ca-Sr-GIC the highest wear volume. The highest wear depth caused by the alumina ball was in Ca-Sr-GIC, followed by Ca-Ba-GIC and the least wear depth was presented by Ca-GIC.

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Figure  3-42: Wear results of the three GICs compositions (P values are shown in Table  3-12).

The t-test was used to compare the wear behaviour (wear volume and wear depth) of two experimental GICs. Three comparisons (1. Ca-GIC to Ca-Sr-GIC, 2. Ca-GIC to Ca-Ba-GIC and 3. Ca-Sr-GIC to Ca-Ba-GIC) for the wear volume and wear depth were performed via the t-test and P values are shown in Table  3-12. Analysis by the t-test, for the wear volume for Ca-GIC to Ca-Ba-GIC and Ca-Sr-GIC to Ca-Ba-GIC, showed significant differences (P < 0.01).

Table  3-12: Analysis by the two sample t-test of the wear volume and wear depth of the three experimental GIC compositions.

Paired t-test of two GIC compositions

Wear behavior

Wear volume Wear depth

Ca-GIC to Ca-Sr-GIC P = 0.61 P = 0.006 Ca-GIC to Ca-Ba-GIC P < 0.001 P = 0.04 Ca-Sr-GIC to Ca-Ba-GIC P < 0.001 P = 0.04

P > 0.01: no significant differences between the two GIC compositions present; P < 0.01: show significant differences between the two GIC compositions.

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