THE EFFECT OF OLIVE OIL AND GLYCERIN OIL AS SEPARATING MEDIA ON THE POROSITY

OF ACRYLIC RESINS DENTURE BASE (A COMPARATIVE STUDY)

Assistant Teacher: Saja Ali Muhsin ((M. Tech.)) Assistant Teacher: Ekhlas Zaid Abboud ((M. Tech.)) College of Health and Medical Techniques Department of Dental Technology The Foundation of Technical Education

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ABSTRACT: This study aims at establishing the effect of olive oil and glycerin oil as separating media on the porosity of both (heat and cold) cured acrylic resins denture base, and compares these effects with those obtained when other types of separating materials such as tin foil and tin foil substitute (cold-mould seal) were used. Samples were made from semi square acrylic specimens for porosity analysis. There were 4 experimental groups, each group sub-divided into heat and cold (n = 10 per sub-group): G1) olive oil G2) glycerin oil; G3) tin foil; G4) cold-mould seal. Porosity was assessed after specimens were immersed in black ink and the pores counted in a microscope. The results revealed that the cold cure acrylic specimens in general showed more porosity than heat-cure acrylic specimens, and the tin-foil is the best separating medium concerning porosity in heat and cold-cure acrylic specimens, while the porosity are comparable in both olive oil and cold mould seal lined specimens of heat and cold-cure acrylic. The suggestions that recommended for further studies are to estimate the effect of these separating medium on the mechanical properties of acrylic denture base materials such as transverse, tensile, and impact strength Introduction: Separating media is a coating applied to a surface and serving to prevent a second surface from adhering to the first. When polymers were first used for the construction of denture, it is necessary to apply some of the separating medium to the plaster surface before packing to prevent the absorption of monomer into the plaster (16, 27). It is used on the master model, in order to reproduce the detail on the model; this medium should seal all the pores in the stone model without adding any additional bulk, the use of

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separating medium which adds bulk results in a distortion of the denture (13). The separating media are either sheets, such as tin foil, rubber dam and cellophane; and this type was laid over the surface of the mould to provide the required protection, or liquids such as the alginates which are painted on to the empty mould to seal the pores of the investment (15). The different dimensional behavior of resin processed in tin-foil and tin-foil substitute was caused by adsorption of water through the substitute film during processing (22). The acrylic resin specimens that processed against the tin-foil substitute showed blanching and fogging and in some cases adherence of plaster particles (8). While the heat-cured resin materials that processed against the tin-foil were substantially dry at the end of the curing cycle (23). Many authors classified the separating medium as alcoholic, ethereal or aqueous solutions and oils, but the most popular separating agent are water soluble alginates which produce a very fine film on the applied surface. However, oils such as vaseline was used as a separating medium for acrylic work (9, 17, 2), and glycerin oil was also used as a separating medium in 2005 (5, 7).The presence of surface and sub surface voids may compromise the physical and, aesthetic and hygienic properties of a processed denture base, porosity is likely to develop in thicker portions of a denture base (6). The porosity may not be noticed until grinding or polishing exposes the deeper layer (13). Recently some authors stated that the soaking of the gypsum dies or casts in glycerin or different oils make their surfaces smoother (11). Based on the existing literature, the aim of this study was to estimate the necessary effect of olive oil (14, 24) and glycerin oil (7) as a separating medium on the porosity of both (heat and cold) cured acrylic resins denture base. Materials and Methods Metal pattern Semi square stainless steel plate with dimensions of (65 x 62 x 64 x 61 mm), with (3 mm) thickness according to (ADA specification No.12) were constructed for porosity analysis to save time and effort. The pattern was included in metal flask, the lower half of each flask was completely filled with type III dental stone (Elite model, Italy) whose surface was flattened with 320 and 400m silicon carbide paper discs (Germany) after the setting reaction. Separating medium application When using the separating medium such as tin-foil (Dent aurum, Pforzheim) it was adapted to the stone surface in each half of the flask, with fingers, while, in case of using olive oil (AL-Kassuon Co. Iraq), glycerin oil (Trihydroxy alcohol, Malaysia); and cold-mould seal (11b, Switzerland), separating medium (2cc) was measured by using a disposable syringe and applied onto the stone surface in the flask, with a fine brush (no.0) (5). Mould preparation The metal pattern was included in metal flask, the lower half of each flask was completely filled with type III dental stone (Elite model, Italy) whose surface was flattened with 320 and 400m silicon carbide paper discs (Germany) after the setting reaction. The patterns were positioned on the stone surface, additional dental stone filled the upper half of the flask which was opened after complete setting under compression (0.5 ton), and the metal mould removed, inspecting the cavities for integrity. The mold was washed with water and neutral detergent, and coated with a separating medium.

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Mixing and packing of acrylic Pink heat and cold cured acrylic resin (Triplex hot Ivoclar vivadent, Liechtenstein) was used to fabricate the samples in this study, following the manufacturers instructions of powder/ liquid ratio by volume. Heat-cured acrylics were mixed (3:1), while the cold-cured acrylic was (2.5:1) by volume, and then left to reach the dough phase at room temperature (approximately 23C). After filling the mold with the dough, the flasks were fitted and pressed together in a hydraulic bench press for (5) minutes before polymerization process.

Curing of acrylic Curing was carried out by placing the clamped flask in a water bath and processed by heating at 74C for about (1.30) hr, the temperature was then increased to 100C for (30) minutes (1), and then the flask was allowed to cool slowly at room temperature for (30) minutes followed by complete cooling of the flask with tap water for (15) minutes before deflasking, While in case of cold cure acrylic resin, flasks containing the acrylic resin dough were left in a bench press for (2 hrs) at 23C 5C (26). The acrylic patterns were then removed from the mould, as shown in figure (1).

FIGURE 1 - Acrylic sample Porosity test In order to prepare a specimen for optical microscopy, the specimens were reduced in thickness from both sides by grinding using carbide bur (Germany) with continuous water-cooling (25), then the surface were smoothed using silicone carbide grit paper 240 fallowed by grade 400 and 600 until a very thin section (0.4- 0.5)mm was obtained, then polished using pumice (England) with rag wheel to be examined clearly under optical microscope (12), after that 4 equal fields of (5)mm from each specimen were made (3) of them at the periphery of the specimen and the last one at the center, then the specimens were immersed in a solution of black ink (china)for 30 minutes, washed for 10 seconds, and dried with absorbent paper (19, 20). The fields were observed under 100 X magnification in a microscope (Olympus, Japan); the mean of pores for each specimen was calculated by dividing the total number of pores in all of the four fields by the number of those fields (10, 3, 4, 20).

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Statistical analysis Porosity data were analyzed by analysis of variance (ANOVA) and less significant deference (LSD). Tests were performed at a confidence level of 95% (21). Porosity test Porosity test results are shown in table 1, 2 and figure (2): Table (1), there were a significant porosity difference (P

Figure (2)

Table (2): Multi- comparison for porosity test among studied groups.

Studied groups Comparison of Significant (LSD)P-value Sig.

Olive Oil Heat cure

Glycerin OIL-Heat cure 0.034 Sig.(P0.05) Glycerin OIL Heat cure

Tin Foil- Heat cure 0.000 Sig.(P

Discussion Cold cure acrylic specimens in general showed more increase in porosity than heat-cure acrylic specimens including those prepared in tin-foil lined mould which appear to be the best lining material for the stone mould and provided a perfect scaling. This appears to be due to the using of tin-foil as a separating medium which make a good scaling and prevent the monomer of acrylic from evaporation or transmission which lead to porous specimens, also due to the fact that heat-cured acrylic is less porous than cold-cured acrylic, this evidence is also approved by Wozniak et al in 1981 as they attributed easer staining of cold-cure acrylic to greater porosity, and Phillips in 1984 who stated that surface porosity in cold-cure acrylic is more than that associated with heat-cure acrylic. The type of denture base material specimens prepared with olive oil lining showed statistically not significant increase in porosity in heat and cold-cure acrylic with tin-foil and cold mould seal, in another hand the glycerin oil showed statistically higher porosity than the tin-foil, this appear to agree with Al- Musawi (2005), while the glycerin oil showed higher porosity value than cold mould seal separating medium, and this results disagree with Al- Musawi (2005) who stated that the porosity value are comparable in both glycerin oil and cold mould seal lined specimens of heat and cold-cure acrylic.

Conclusion The study suggests that the cold cure acrylic specimens in general showed more porosity than heat-cure acrylic specimens, and the tin-foil is the best separating medium concerning porosity in heat and cold-cure acrylic specimens. while the porosity are comparable in both olive oil and cold mould seal lined specimens of heat and cold-cure acrylic; also it can be concluded from this study that the olive oil can be safely used as a separating medium for processing acrylic denture base resins.

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