The Effect of Different Denture Cleansers on Different Color Properties of Permanent Soft Liner

AIMS: To determine the effect of different denture cleansers on hue, value, and chroma of permanent silicone soft liner at different immersion periods. MATERIALS AND METHODS: Soft liner specimens were immersed in four denture cleansers (“citric acid + soda”, salt, “apple vinegar + soda”, and alum) for periods of 1, 3, 7, and 14 days. A digital spectrophotometer was used to access color differences of soft liner before and after each storage period in each solution. RESULTS: The citric acid and salt cleansers decrease the value, chroma, and hue. The apple vinegar cleanser does not affect significantly any color property. The alum cleanser decrease value and chroma, but does not affect hue of soft liner. CONCLUSIONS: The effects of different denture cleansers tested on different color properties of soft liner were different. The effect of the immersion period on the different color properties tested was different for each denture cleanser.


INTRODUCTION
The use of soft denture liners has become increasingly popular for providing comfort for denture wearers. Soft denture liners are often used for patients who cannot tolerate a conventional denture base. (1) The denture cleanliness is an essential component of oral health to prevent malodor, poor esthetic and accumulation of plaque and calculus with its deleterious effect on oral mucosal tissue. (2) A chemical soaking technique is primarily the method of choice for geriatric patients and for those with poor motor capacity. (3,4) Denture cleaners can cause significant deterioration of soft liners because they can cause loss of soluble components and plasticizers, or absorption of water or saliva by the soft liners. Thus the selection of denture cleanser should be considered to avoid or minimize changes in the properties of soft liners. (3,4) There is some knowledge about the changes in color stability of soft denture lining materials caused by denture cleansers. (5,6) Many researchers attempt to use natural, locally available materials as denture cleansers. Of the important materials used are citric acid, sodium chloride, vinegar, and alum. (2,(7)(8)(9) The color stability criteria may provide an important information on the serviceability of the dental materials. (10) Color is a three-dimensional phenomenon. The three dimensions are hue, value, and chroma. Hue is the quality that distinguishes one family of colors from another. It is specified as the dominant range of wavelengths in the visible spectrum that yields the perceived color, even though the exact wavelength of the perceived color may not be present because in fact hue is an interpretation of a sum of wavelengths. Value, or brightness, is the amount of light returned from an object. Munsell described value as a white toblack gray scale. Bright objects have lower amounts of gray, and low-value objects have larger amounts of gray and will appear darker. Lowering value means diminished light returns from the object illuminated; more light is being absorbed, scattered elsewhere, or transmitted through. Chroma is the saturation, intensity, or strength of the color. (11) The aim of this research is to determine the effect of four denture cleansers (which are "citric acid + soda", salt, "apple vinegar + soda", and alum) on the three dimensions of color (which are hue, value, and chroma) of permanent silicone soft liner at different immersion periods.
For each denture cleanser, ten specimens were prepared to be evaluated.
The specimens were immersed in distilled water for 7 days for conditioning. During the storage of specimens in water and subsequently during their immersion in the denture cleansers, the specimens were suspended in the solutions by a stainless steel dental wire passing through the center. This will hold the specimens in a vertical position and prevent the contact between the specimens during their immersion in the tested solutions, so each specimen was in contact only with the immersing solutions. (10,2) After the specimens were taken out, initial color measurements were taken. (12) A digital spectrophotometer (Easyshade, Vita, Germany) was used to measure the color properties of soft liner specimens including the value, chroma, and hue which displayed digitally on the device ( Figure 1). Easyshade spectrophotometer contain a color analyzer with its own light source that has accompanying software for the downloading, evaluation, and transmission of the relevant color data recorded. It standardize the measurements of hue, value, and chroma.
The color distribution of Easyshade was more ordered (in the value, chroma, and hue scale) than previously reported color distributions of other, traditional shade guides. (13) The Easyshade spectrophotometer was the most reliable instrument in both in vitro and in vivo circumstances. (14) The individual white color index of the instrument was used as a color control. (12,15) The specimens were immersed in denture cleanser solutions for 1, 3, 7, and 14 days. (16) Specimens placed in water served as controls. Color differences before and after each storage period in each solution were assessed. (16,12) Mean values for the effect of type of denture cleanser on three properties of the color tested at each immersion period were compared using ANOVA followed by Duncan multiple range test to determine the significant difference at P<0.05 level.

RESULTS
The effect of the immersion period on the different color properties tested was different for each denture cleanser.
At the first day, the effects of different denture cleansers on the value of permanent soft liner were significant(P=0.000)( Table 1); with the citric acid cleanser significantly decrease value, and the effects of other cleansers are shown on (Figure 2).The effects on chroma were also significant(P=0.000)( Table 1); with the salt and alum cleansers significantly decrease chroma, while the citric acid and vinegar cleansers do not ( Figure  3).The effects on hue were not significant when compared with the control group(Table 1, Figure 4). At the third day, the effects of denture cleansers on value were significant (P=0.008) ( Table 2); with the citric acid, salt, and alum cleansers significantly decrease value; the results are more illustrated in( Figure 5). The effects on chroma were significant(P=0.002)( Table 2); with the citric acid, salt, and alum cleansers significantly decrease chroma while vinegar cleanser does not( Figure 6). The effects on hue were significant(P=0.002) ( Table 2); with the citric acid and salt cleansers significantly decrease hue while the vinegar and alum cleansers do not(Figure7).  At the seventh day, the effects on value were significant(P=0.010)( Table 3); with the citric acid, salt, and alum cleansers significantly decrease value. The results are more specified in (Figure 8). The effects on chroma were significant (P=0.000) ( Table 3); with the citric acid, salt, and alum cleansers significantly decrease chroma while the vinegar cleanser does not (Figure 9).The effects on hue were significant(P=0.041)( Table 3); with the citric acid cleanser decrease hue and the other results are shown on (Figure 10).  At the fourteenth day, the effects on value were significant(P=0.000) ( Table 4); with the citric acid, salt, and alum cleansers significantly decrease value and the vinegar cleanser does not( Figure 11). The effects on chroma were significant (P=0.000)( Table 4); with the citric acid, salt, and alum cleansers significantly decrease chroma while the vinegar cleanser does not ( Figure 12). The effect on hue were significant (P=0.001)( Table 4); with the citric acid and salt cleansers significantly decrease hue while the vinegar and alum cleansers do not( Figure 13).

DISCUSSION
It has been reported that denture cleansers can cause loss of soluble components and plasticizers, or absorption of water or saliva by the soft lining materials. (17) The mechanism of color change cannot be known exactly, but it can be estimated. (18) The color change of the denture base polymer may be also caused by penetration of the colored substance through the process of sorption. Therefore, if the contacting solutions are pigmented, discoloration will be possible. (10) The color changes of soft denture liners are attributed to changes in the colorants used, a change in color of the elastomer, or both. Some colorants or elastomers may be affected by high humidity. (19) "Citric acid+ soda" produced a significant decrease in the value, chroma, and hue of the soft liner specimens and this decrease may be due to the chelating property of the sodium citrate that is produced from the reaction between the citric acid and soda(sodium bicarbonate). This can be illustrated as sodium citrate solution has pH value close to the neutral which makes it more effective in chelation (removal of the organic and inorganic components of the deposit). The chelating process will involve removal of colorant substances of material. (20,8) These findings are in agreement with Al-Aubadi. (2) "Apple vinegar+ soda"(Acidic denture cleanser) was shown to affect insignificantly the value, chroma, and hue of the soft liner specimens. These findings are in agreement with Al-Abbas and Asmussen who found that the reduction of the pH of the storage water had only little effect on the color of acrylic resin materials. (10,21) Alum (potassium Aluminum sulphate) produced a significant decrease in the value and chroma of the soft liner specimens. This may be due to the fact that when the non-aqueous solution of the The very high acidity of the solution (pH=3.27) leads to an increase in water sorption. (2)

CONCLUSIONS
The effects of different denture cleansers tested on different color properties of permanent soft liner tested were different. The effect of the immersion period on the different color properties tested was different for each denture cleanser. The citric acid solution cleanser decrease value, chroma, and hue. The salt solution cleanser decrease value, chroma, and hue. The citric acid and salt solution cleansers differ in their effect in relation to the amount of decrease in all color properties tested and the time required for such change. The apple vinegar solution cleanser does not affect significantly any of the color properties tested. The alum solution cleanser decrease value and chroma, but does not affect hue.