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To determine the sorption and solubility of heat-cured acrylic treated with a

Chapter 5: DISCUSSION

5.5 To determine the sorption and solubility of heat-cured acrylic treated with a

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of the polishing paste and that of artificial saliva affects the affinity between the specimens and the molecules in the solution, resulting in an increase in sorption.

The Tukey-Kramer Multiple Comparison Test deemed there to be no significant difference in sorption values between any of the sample groups in this study, with the exception of group A, which exhibited significantly higher sorption values than any other group. Because the differences in sorption values between the sample groups were so minute, it is difficult to make accurate assumptions as to why certain events occurred in the phenomenon of sorption.

In summary, mechanical polishing reduced the solubility levels of the material in both distilled water and artificial saliva when compared with the specimens that received no surface treatment. Although these reductions were not deemed statistically significant, it can be assumed that mechanical polishing will have a positive effect on the properties of Vertex

Rapid Simplified denture base material affected by solubility. The sorption values were only reduced in the sample group that received mechanical polishing soaked in distilled water.

Mechanical polishing was deemed to significantly reduce the sorption values of the specimens soaked in distilled water, but due to the minute differences in sorption values, it can be assumed that mechanical polishing will not have an effect that is clinically significant on the properties of Vertex™ Rapid Simplified denture base materials affected by sorption.

5.5 To determine the sorption and solubility of heat-cured acrylic treated with a

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light-cured varnish only recorded lower sorption values than the specimens which received no surface treatment soaked in distilled water. The Tukey-Kramer Multiple Comparison Test indicated that the lower sorption values recorded by the specimens that were treated with the light-cured varnish soaked in distilled water were statistically significant. Even though the light- cured varnish increased the solubility values observed in Vertex™ Rapid Simplified denture base material, this was deemed not to be of statistical significance (Table 4.9 and Table 4.10).

These findings indicate that the application of Optiglaze™ light-cured varnish increased the observed levels of solubility. The increase in solubility may perhaps be attributed to the composition of Optiglaze™ light-cured varnish. According to the safety data sheet, Optiglaze™

Glossy, Protective Agent consists of 25-50% methyl methacrylate (GC America, 2020). This additional methyl methacrylate present on the specimens may therefore be responsible for the elevated solubility levels, as suggested by published literature (Kedjarune et al., 1999:25–30;

Kostić et al., 2020:254–263; Tuna et al., 2008:191–197). The application of Optiglaze™ had a positive result on the sorption of Vertex™ Rapid Simplified denture base material soaked in distilled water. A possible explanation for this occurrence may be that the application Optiglaze™ alters the polarity of the specimen’s surface. As explained by Malacarne et al.

(2006:978), the resin’s polarity is one of the main factors governing the uptake of water into the structure of denture base acrylics, and a reduction in the concentration of polar sites may reduce the rate of sorption observed. A systematic review of the literature canvassed in Ferracane (2006:211–222), together with the product information supplied by GC America (2020), indicates that Optiglaze™ may act as a surface sealer, sealing microscopic cracks, pores and irregularities on the surface of the specimens. It has been suggested that water molecules are adsorbed to the surface of the material and are further absorbed into the body of the denture base through porosity and intermolecular spaces via diffusion (Ferracane, 2006:214; Sakaguchi & Powers, 2012:51–52). If the quantity of irregularities on the surface is reduced by the application of Optiglaze™, this may inhibit the uptake of water into the body of the material.

Objective six was established to determine the effect of a light-cured varnish on the sorption and solubility of Vertex™ Rapid Simplified denture base material soaked in artificial saliva. To accept or reject hypothesis six, it was necessary to compare sorption and solubility results for the specimens that were treated with Optiglaze light-cured varnish soaked in artificial saliva with those of the specimens that received no surface treatment soaked in artificial saliva. The specimens in sample group F obtained a mean sorption value of 21.6997 μg/mm3, and a mean solubility value of 0.1886 μg/mm3 (Table 4.6), which are both within the parameters set out by ISO 20795-1: 2013 (E) for a type-one polymer. The results indicated that the mean sorption value was lower and the mean solubility value was higher for heat-cured acrylic specimens

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that were treated with the light-cured varnish and soaked in artificial saliva, compared with the specimens that received no surface treatment soaked in artificial saliva. The null hypothesis relating to objective six was therefore partially accepted as the specimens that were treated with the light-cured varnish recorded only lower sorption values than the specimens that received no surface treatment soaked in artificial saliva. The Tukey-Kramer Multiple Comparison Test indicated that the higher solubility values recorded by the specimens that were treated with the light-cured varnish and soaked in artificial saliva were statistically significant. On the other hand, even though the light-cured varnish reduced the sorption values observed in Vertex™ Rapid Simplified denture base material, it was deemed not to be statistically significant (Table 4.9 and Table 4.10).

No similar studies investigating the interaction effect between artificial saliva and light-cured varnish on the sorption and solubility of denture base materials could be identified following a thorough review of the literature. This study found that the application of Optiglaze™ had the same positive effect on the sorption of the specimens soaked in artificial saliva as it had on the specimens soaked in distilled water. But unlike the case of distilled water, this effect was deemed not statistically significant by means of the ANOVA test. As with sample group E, it can again be proposed that this observed reduction in sorption levels may be due to a change in polarity and the sealing of irregularities on the surfaces of the specimens due to the application of Optiglaze™. The fact that the specimens in sample group F were submersed in artificial saliva means that the effect this may have had on sorption also needs to be considered. It is possible that both the diffusion coefficient and the concentration gradient between the specimen and the solution may impact the extent of diffusion taking place. As the artificial saliva solution has a higher viscosity than distilled water, as well as a different molecular composition, it is possible that the reduction in sorption that was observed may have been impacted by the diffusion coefficient and concentration gradient discrepancies between the specimens and the solution. As with sample group E, the application of Optiglaze™

resulted in an increase in the solubility levels recorded. This increase was deemed statistically significant and is again credited to the composition of Optiglaze™, which consists of 25–50%

methyl methacrylate.

In summary, the application of Optiglaze™ reduced the sorption levels of specimens in both distilled water and artificial saliva compared to specimens that received no surface treatment, but only the specimens that were soaked in distilled water were deemed to have a significant reduction. It can therefore be assumed that the application of Optiglaze™ will reduce the extent of sorption experienced by prostheses fabricated from Vertex™ Rapid Simplified denture base material soaked in artificial saliva or distilled water. The same positive effects that Optiglaze™

had on the sorption of Vertex™ Rapid Simplified denture base material was not, however,

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observed for solubility. The application of Optiglaze™ increased the solubility in both sample groups E and F, with the increase evinced by the specimens soaked in artificial saliva deemed to be statistically significant. It can therefore be assumed that the application of Optiglaze™ to prostheses fabricated from Vertex™ Rapid Simplified denture base material will result in an increase in solubility when the prostheses are soaked in distilled water or artificial saliva.

5.6 To determine which surface treatment results in the least sorption and