Effect of denture cleanser on the color stabil- ity of artificial denture teeth

Aims: To evaluate the effect of three different cleanser on the color stability of three different types of artificial teeth. Materials and methods: sixty samples of artificial anterior teeth were prepared which are Acry-Rock, RMH teeth and Porcelain teeth and immersed in three types of denture cleanser(Bony plus, Protefix and soda+ vinegar) for 8 hours and the color of the teeth was measured by Easyshade's spectrophotometer at 3 intervals(1,2and4weeks). Results: Showed that the a'b values of ceramic teeth and L value of RHM teeth were significantly differencent after 2 week of immersion in three type of denture cleanser. Analysis of variance demonstrated that L'a'b value for ceramic teeth and RHN teeth were statistically significant after 4 week immersion in three type of denture cleanser, The result of color change (∆E) for three denture cleansers of three periods of immersion were clinically accepted. Conclusion: Long period of immersion of artificial teeth in denture cleanser cause significant color change for L*a*b* values but they were clinically accepted. Key wards: Artificial teeth ,Denture cleanser, Spectrophotometer. Sadoon MM, Jaffer NT, Al-Saraj AN. Effect of denture cleanser on the color stability of artificial denture teeth. Al–Rafidain Dent J. 2011; 11(1):202-210. Received:7/4/2011 Sent to Referees: 7/4/2011 Accepted for Publication: 3/5/201


INTRODUCTION
Acrylic resins and porcelains have been used for the fabrication of artificial teeth; however, neither type completely accomplishes the requirements of an ideal prosthetic tooth. For this reason, acrylic resin teeth have been modified to overcome the disadvantages of acrylic resin by using interpenetrating cross-linking agents, different monomers, and the addition of nanofillers (1)(2)(3) Color stability is one of the most important physical properties that affect the aesthetic of restorative and prosthetic dental materials (4,5) .
Color change is an indicator of aging or damage to dental materials and can be assessed by colorimetry, which is based on the digital expression of the color perceived from the object (6) .
In dentistry, the HSB (Hue, Saturation or Chroma, Brightness or Value) system is Effect of denture cleanser on the color stability of artificial denture teeth most commonly used for color communication (7,8) .
Chroma is the purity of color, hue is referred as the basic color, value the quality by which a light color is distinguished from a dark color (9) .
The rate at which the deposits accumulate on the denture may vary between individual (10) .
It is well established that the use of denture cleansers helps to control or reduce the amount of plaque residing on denture surface (11) .
Denture cleanliness is essential to prevent malodor, poor esthetic and accumulation of plaque and important for long-term success of prosthodontic treatment. The most common commercial denture cleansers use immersion technique which is the suitable method for many elderly patients in long-term care hospital because of disease and poor dexterity (12) .
There are large number of solutions, tablets and powders available for cleaning dentures. An ideal denture cleanser should be non toxic, bactericidal, fungicidal and compatible with denture base (11) .
Denture cleanser must clean effectively without adversely affecting denture base material properties especially roughness because rough surface is unfavorable and may affect plaque formation or inhibit its removal (15,16) .
Khalil (17) prepared anew formulas of compound as a denture cleanser and concluded that the safest prepared solutions is sodium bicarbonate +clear commercial vinegar.
The aims of this study is to evaluate the effect of three different cleanser on the color stability of there different types of artificial teeth.

MATERIALS AND METHODS
Three types of artificial anterior teeth of shade (A 2 ) were used in this study: Acry-Rock (acrylic resin teeth, Italy), RMH teeth (cross-linked, China) and Porcelain teeth (Alloy pin porcelain, China). For each type, twenty models were made by positioning the tooth in the centre of a polyvinyl chloride tube (20X20mm) pre-viously filled with autopolymerizing acrylic resin (Respal, Italy). The lingual surface of the tooth was embedded within the autopolymerizing resin ,until the polymerization reaction was completed, while the labial surface of the tooth was exposed.
Denture cleansers that were used in this study are of three types: two commercial:Bony plus tablet (Switzerland) and Protefix tablet (Germany) and one cleanser solution was prepared by mixing sodium bicarbonate (China) 9.52 gm and clear commercial vinegar (UAE) 16 ml in 100 ml of distilled water (17) , the control group was distilled water. Twenty samples were prepared for each type of artificial teeth, those were divided in such away that each cleanser had five samples and five samples inside distilled water as a control. All the artificial teeth were underwent color measurement technique by using Easyshade's spectrophotometer before their immersion in the disinfectant solutions. The samples were immersed in their cleansers in plastic containers at room temperature for one month simulating one month usage by a patient, the immersion time was eight hours /day in which the cleansers were changed daily throughout one month, while distilled water was changed every twenty four hours (17) . The color of the samples were measured after 1 week, 2weeks and 4 weeks of immersion by using Easyshade's spectrophotometer to obtain delta information about color represented by parameters individually (hue/ chroma/ value) (18) .
The data convert from (H C V system ) to L*a*b system by using commercial graphic software program (Adobe Photoshop 9.0).
Where L is measurement of lightness, a* value represent poisons on red-green axis, the b* value represent poison on yellow -blue. (19,20) Data of the study were analyzed statistically by Analysis of Variance (ANOVA) followed by Duncan's multiple range test to determine the significance level.

RESULT
The result showed that there was no significant differences of L'a'b* values of ceramic teeth , and RHM teeth and a' val-ue for Acry-rock teeth after 1 week of denture cleanser immersion, while there was a significant difference for L'b* value of Acry-rock teeth types (Table 1). Table (2) showed that the a'b values of ceramic teeth and L value of RHM teeth were significantly differencent (p≤ 0.05) after 2 week of immersion in three type of denture cleanser.
Analysis of variance (Table 3) demonstrated that L'a'b value for ceramic teeth and RHN teeth were statistically significant after 4 week immersion in the three types of denture cleanser.
Duncan's multiple range test showed that L value of Acry-rock teeth after 1 week immersion of Soda + vinegar had significant differences than that for control and the other two denture cleansers.
While there was a significant differences of L value of RHM teeth immersed for 2 week in soda + vinegar, and Bony plus denture cleanser than other cleanser. Whereas after 4week immersion the L value of ceramic and RHN teeth were statistically significant after immersion in the three types of denture cleanser (Figure 1). Figure (2) revealed that a' value of ceramic teeth which immersed in Bony plus for 2 week was significantly different from that immersed in protifex and soda + vinegar.
2weeks 4weeks Figure (3) demonstrated than soda + vinegar was affecting significantly the b' value of Acry-rock teeth after 1 week of immersion, while bony plus significantly affect the b' value of ceramic teeth after 2 week of immersion. The three denture cleanser significantly affected the color of ceramic teeth after immersion for 4 week compared to the control . At the same time the color of RHM teeth immersed in protifex, and soda + vinegar was significantly differed from the control.   (19,20) DISCUSSION Factors that may contribute to the change in the color of materials include stain accumulation, dehydration and oxidation of the reacted carbon-carbon double bonds that produces colored peroxide compounds, and continuing formation of the colored degradation products (21) . Table (1) and Figures (1,  2 and3) the lightness value (L*) and hue (b*) value of Acry-rock artificial teeth was significantly increased after 1 week immersion in soda+ vinegar cleanser which had acidic pH (73.8 and 19.2 respectively) in respect to distilled water immersion (70.8 and 16.2) this result may be due to the fact that a denture cleansing composition for dissolution in water to form a cleansing bath with a initial acidic pH (22) this decrease in pH of solution lead to increase in water sorption of acrylic denture teeth which lead to penetration of colorants constituents of solution (21,23) .  While after 2 week of artificial teeth immersion in denture cleanser Table(2) and Figures(1,2 and 3) the L*value of RHM teeth were decreased by the effect of Bony plus and soda+ vinegar cleansers (75.8, 77) in respect to distilled water (80.2). For a* (15.6) and b* (21.6)value was significantly increased for ceramic teeth immersed in Bony plus denture cleanser in contrast to control group. This result may be due to the fact that after two weeks of immersion in soda+ vinegar PH effect was increase on RHM teeth and the active oxidation effect of bony plus was increased which effect the ceramic teeth. (24) After 4 week of immersion ceramic teeth and RHM teeth show significantly decrease in L*a*b values in contrast to Acry-rock teeth and control teeth. This result may be due to accumulating whitening effect (dehydration and oxidation) in ceramic teeth and RHM teeth after 30 days of simulated use of denture cleansers (24) .

CONCLUSION
Soda+ vinegar and Bony plus denture cleanser cause color change of artificial teeth rather than protifex , cross linked teeth with nano fillers (Acry-rock) had color stability rather than ceramic teeth and RHM cross linked teeth. Long period of immersion of artificial teeth in denture cleanser cause significant color change for L*a*b* values but they were clinically accepted.