Materials and methods

The composite inlay materials used are described in Table 6.1 and in Appendix A.2. Five discs of each system were prepared using 15mm diameter split stainless steel rings, to give a total of 25 specimens. Specimen preparation was completed using the methods described in section 6.2. Normally the moulds in all systems were packed with small amounts of composite material, but in this study an additional group of specimens were prepared where a single measured quantity of material (Charisma) was used to reduce the possibility of air inclusions into the test specimens (Charisma Chairside 2). These specimens were cured as normal for Charisma as a surgery chairside system. As previously any samples with porosity or observable faults were discarded. The remainding samples were conditioned by being placed in a desiccator at 37+/-l°C until a constant weight had been achieved. All weighings were made using a 5 figure balance (Oertling London), and a constant weight was determined when the last three readings were within +/- 0.0001 gram.

After conditioning the specimens were then immersed in water at a temperature of 37+/-l°C. At predetermined time intervals after immersion the discs were removed, waved in air for 10 seconds and carefully blot dried using paper tissues to remove excess water. Weighing was completed within 30 seconds for removal from the water and specimens replaced into the storage solution within 45 seconds. Weighing was continued at regular time intervals until equilibrium was achieved. This was when three or more weight readings became constant to within +/- 0.0001 gram.

Once equilibrium was reached, the specimens were removed from the water and placed in a desiccator at 37+/-l°C. The weight of the specimens was monitored at regular intervals throughout this desorption phase until a constant weight was again achieved.

These procedures were repeated until each specimen had been subjected to three sorption/desorption cycles and no further loss in weight was noted on redesiccation.

The water sorptions and solubility for each system were calculated using the following formulae;

£q.6.6 The true water sorption in the last cycle as a percentage;

= Equilibrium wt. in HiOHast cvcleVDesiccated wt. at start of last cycle xlOO Initial desiccated wt. at the start of the last cycle

Eq.6.7 The overall solubility as a percentage;

= Original wt. after conditioning - Desiccated wt. at the end of last cycle xlOO Original wt. after conditioning

Eq.6.8 Water sorption if the resin component is assumed to be responsible for the total water uptake (the resin component is derived from the manufacturers data sheet);

= Equilibium wt. in H^O last cvcle - Desiccated wt. at start of last cvcle xlOO Wt. o f resin component in desiccated sample at the start of the cycle

Eq.6.9 The solubility o f inlay assuming products are only lost from the resin fraction;

= Original wt. of conditioned sample - Desiccated wt at end of last cvcle xlOO Wt. of resin in original sample after conditioning

Eq.6.10 Water sorption as an increase in weight per unit surface area in the last cycle;

= Increase in wt. in sorption phase of last cycle Imgl Total surface area of sample (cm )

Eq.6.11 Solubility as a loss in weight after 3 sorption/desorption cycles per unit surface area;

= Original wt. after conditioning-Desiccated wt. at the end of last cvcle (mg) Total surface area of sample (cm^)

When surface area of each sample;

= % Dh + 2 nr^

Statistical analysis was carried out using comparison of values for water sorption and solubility o f these materials after 3 sorption/desorption cycles, using non parametric statistics (Mann-Whitney U test).

6.4.2 Results

The mean water sorption and solubility values for the five groups after three sorption/desorption cycles are shown in Table 6.4 and Figure 6.4.

Statistical analysis showed that there was a significantly smaller water sorption at the 95% confidence level, for Brilliant when compared with all the other inlay systems (Table 6.4 and Appendix B2). Likewise the solubility of Isosit was significantly greater than Charisma (lab) and Charisma (chair.2), the latter of which was significantly less than Brilliant and Charisma (lab) inlay systems.

The differences in the water sorption and solubilities were more marked when the effect of the filler was excluded. It was then possible to estimate the water uptake attributable to the resin component (Table 6.4 and Figure 6.5).

During the sorption phase it was initially noted that there was a reduction in weight of the samples over the first few hours. Then there was a rapid increase in weight. This rate of increase diminished after about 10 days to reach a more constant weight in 10-20 days for each cycle. In the third cycle the sorption phase reached a lower maximum weight before stabilising. This is demonstrated for Brilliant in Figure 6.6. Similar patterns of water sorption were found in all materials.

A more rapid loss in weight was noted over the first 5 days of the desorption cycle compared to the increase in weight over a similar period during the sorption of water. The third desorption phase shows a lower mean minimum weight after 20 days than the previous 2 desorption phases.

Figure 6.7 demonstrates the linear nature of the relationship between increasing weight and time over the first 36 days in all the samples. Trendlines have been drawn from the mean values to show the increase in weight during water sorption for all materials under test, although the sorption of water falls after 10 days and is more variable after 30 days.

6.4.3 Discussion