Quayle dental resin and Major The Effect of Thickness of Heat Cured Acrylic Resin with Additives on Water Sorption and Solubility

Aims : The aims of this study were to determine the effect of thickness and additives (Nigella Stavia oil and Thymol oil) on water sorption and solubility of heat cured acrylic resin denture base. Materials and Methods: Two types of heat cured acrylic resin Quayle dental resin and Major base2 were used. Two additive materials (0.5%) have been added to major base 2 which are(Nigella Stavia oil and Thymol oil) . Water sorption and solubility of specimens were measured by mean of mass change in material after water saturation and dehydration. The specimens were prepared in three thicknesses (1mm, 2mm and 3mm). The effect of thickness on water sorption and solubility also has been measured. The data were analyzed using analysis of variance and Duncan's multiple range tests. Results: Increase thickness causes decrease in water sorption and solubility; Q.D has more water sorption and solubility than major acrylic resin. The two additives caused an increase in the water sorption and solubility of major acrylic resin denture base. Conclusions: The thickness and type of manufacturing materials added into acrylic resin played an important role in determining its water sorption and solubility.


INTRODUCTION
Acrylic was introduced to dentistry in 1937 (1) and to date, no other material has been found that matches the appearance of the oral tissues with as great as fidelity as acrylic resin. It is overall performance is regarded as satisfactory and it is widely used for the construction of complete denture (2)(3)(4)(5) . The basic material and technique have remained as the denture base material of choice since that time. Although, various polymers have been developed(modification of polymethylmethacrylate by the addition of chemical materials) for the use in dentistry to overcome the strength deficiencies of polymethylmethacrylate (6) .
Acrylic resin polymer absorbs water over a period of time. This due to primarily to the polar properties of resin (7) . Sorption of material represents the amount of water absorbed on the surface and absorbed into the body of the material during fabrication or while the restoration is in service (8) . The absorbed water stays in gaps among the interpolymeric chains that form acrylic resin structure. The magnitude of these interpolymeric gaps determines the amount of water to be absorbed (9) .

ISSN: 1812-1217
The Effect of Thickness of Heat Cured Acrylic Resin with Additives on Water Sorption and Solubility www.rafidaindentj.net Within the establish limit water sorption can be considered a desirable property because it compensates resin polymerization shrinkage, beyond these limits water sorption value can lead to undesirable dimensional alteration (9) .
Acrylic resin polymer is not soluble in water, the solubility represents the mass of soluble material that leaches out from polymers. The only soluble materials are initiators,plasticizer and free monomer (10) .
Water sorption and solubility were measured by mean of mass change in the material after water saturation and dehydration (11,12) .
The aim of this study was evaluating water sorption and solubility of acrylic resin before and after the addition of chemical material(which has been added as a disincentive agents ) (13) and compared it with that off acrylic visible light cure(V.L.C). The effect of thickness on water sorption and solubility of new type of acrylic resin also has been evaluated.

MATERIALS AND METHODS
Two types of heat cured acrylic resin Quayle dental resin and Major base2 were used. The additive materials (Nigella Stavia Oil and Thymol Oil) have been added to the monomer of major base 2 at a percentage of 0.5% (13) . The water sorption and solubility of heat cured (major base 2) acrylic resin have been measured and compared with that after the addition of chemical material and with that of acrylic visible light cure(Megatray,Germaby 2A628D,Pink) ; also the effect of thickness (with and without additive materials) on water sorption and solubility has been evaluated.
The specimens were prepared as disk like with dimension 50mm in diameter and with 3 thicknesses (1mm, 2mm and 3mm, ±0.5mm). A stainless steel matrix with a diameter of 50 mm has been used to prepare the specimens (11) . Five specimens of each material were prepared.
For heat cured resin, the specimens cured in water path with the conventional curing cycle. The specimens processed at 74c° for 1.5 hours , then the temperature of water bath increased the boiling (100°C) for additional 3 hours . (14) .
For Visible light cure acrylic resin specimens(V.L.C) the past packed in mold and kept under hydraulic press for 5 minutes and then the specimens deflasked and transferred to curing in Visible light curing machine(MegalightSt,Megadent,GmbltD0145 4Germany) .
After completing the polymerization all acrylic resin specimens were deflasked and finished using tungsten drill and aluminum oxide sand papers(180#,220#,400#) at low speed (4) .
The specimens were dried over silica gel in a desicator at 37°C and weighted to an accuracy of 0.0001 gm using an electronic balance device(Mettler PM 460, Germany). This was considered to be initial weight of specimens (W1). The specimens then immersed in distilled water ,each specimens being in separated containers . The specimens were removed from their container after 1 week. Excess water was removed by blotting with filter paper and the weight of the specimens was recorded (W2). This represented the weight of the specimen after absorption of distilled water. The specimens were dried by placing in the Disicator. It placed in a recipient containing dry and fresh silica gel which was stored at 37±1c° during 24 hours. Afterward, the recipient was left bench-cooling for 1 hour until reaching room temperature.
The specimens were weighted in an analytical balance accurate to 0.001 gm . This condition cycle was repeated every 24 hours until all specimen(W3) reaches final weight .
The absorption and solubility values were determined as follows (15)(16)(17)(18)(19) : The mean and standard deviation were calculated . One way analysis of variance and Duncan's multiple rang test were used to analyze the data and to determine the level of significant difference among the test groups at P ≤ 0.05% level of significant.

RESULTS
The results of the mean values of the water sorption Table(l) showed a decrease in water sorption of acrylic specimens by increasing their thickness. There was a slight mean differences between water sorption of Major and Q.D acrylic resin denture base at (1mm,2mm and 3mm:0.003, 0.101 and 0.000 respectively). The results of this study showed that the greatest decrease in the water solubility of acrylic specimens Table(2) was with 3mm thickness. V.L.C demonstrated less water sorption and solubility than that of both Major and Q.D acrylic resin specimens.  Tables (3and 4) revealed that this statistically significant decrease in water sorption and solubility of both acrylic resins(Major and Q.D) and visible light cure, except that there is no statistic al significant decrease in solubility of V.L.C with increasing the thickness of acrylic resin specimens and that for Q.D acrylic resin specimens at 2mm and 3mm at (P ≤ 0.05%).  represented that there is an increase in water sorption and solubility of Major acrylic resin after the addition of both nigella stavia oil and thymol oil. This increase in water solubility and sorption was statistically significant increase at (P ≤ 0.05%) Table (9).   Duncan's multiple range test Figures  (1and 2) revealed that there is a statistically significant increase in water sorption and solubility of major acrylic resin before and after the addition of Nigella Stavia oil and Thymol oil, also there is statistically significant decrease in water sorption and solubility with increasing the thickness of prepared specimens at(P ≤ 0.05%).The percentage of increase of water solubility of major base 2 acrylic resin specimens with the addition of Nigella stavia oil was higher than that with the addition of Thymol oil.

DISCUSSION
All types of acrylic resin used in this study demonstrated water sorption and solubility Table(1 and 2) after storage in water. Sorption can be related to the polarity of acrylic resin(due to unsaturated bond) (7) . While, solubility can be related to the leach of soluble material that present in an acrylic resin (initiator, plasticizer, residual monomer) ( 20 ) . The result of this study revealed that there is a decreasing in water sorption and solubility of all acrylic specimens with increasing the thickness of specimens Table(1and 2) . This can be related to the decrease in the surface area of specimens that exposed to the action of water and also to the fact that monomer content of resin specimens depends on the thickness of specimens . Thin acrylic specimens had a higher level of residual monomer than thick one (12,21) . During polymerization process . Thick acrylic specimens reached a higher temperature(heat evolved during polymerization) resulting in greater degree of polymerization and corresponding reduction in the amount of residual monomer (22) .While, for VLC as it is monomer free (18) so that there is no statistically significant decrease in water solubility of the specimens with increasing the thickness of acrylic specimens .
Statistical analysis Table (5) revealed that there is no statistically difference between water sorption and solubility of major base2 and Q.D acrylic resin. This was in agreement with Ammar et al (19) .While a statistically significant difference in water sorption and solubility of major base 2 and VLC Table (6). This can be related to the proper polymerization technique and monomer free content of VLC (18,22,(23)(24)(25) .
The addition of chemical materials (Nigella Stavia Oil and Thymol Oil) into major base 2 acrylic resin specimens produced a statistically significant increase of its water sorption and solubility Table (7  and 8). The addition of chemical materials caused alteration in molecular resin chain ( modify the magnitude of the polymeric gaps) and consequently alter water sorption and solubility (26) . Water sorption and solubility depended on homogeneity of the material (27) .

CONCLUSIONS
Different types of acrylic resin significantly demonstrated varying degree of water sorption and solubility . Increasing the thickness of acrylic specimens produce a statistically significant decreasing in the water sorption and solubility of acrylic specimens. The addition of chemical materials to the Major acrylic resin produce a statistically significant increase in its water sorption and solubility . VLC has low water sorption and solubility than major base