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Table of Contents   
ORIGINAL RESEARCH  
Year : 2015  |  Volume : 26  |  Issue : 2  |  Page : 163-166
Effect of denture cleansers on color stability and surface roughness of denture base acrylic resin


1 Department of Prosthodontics, Dental Research Center, Mashhad University of Medical Sciences, Mashhad, Iran
2 Department of Pediatrics, Faculty of Dentistry, Mashhad University of Medical Sciences, Mashhad, Iran

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Date of Submission27-Jul-2014
Date of Decision02-Sep-2014
Date of Acceptance07-Apr-2015
Date of Web Publication22-Jun-2015
 

   Abstract 

Background: Color stability of acrylic resin is one of the most important feature for denture wearers. Many patients use detergent solutions to remove denture stains. The purpose of this study was to evaluate color stability and surface roughness of two common acrylic resins in different detergent and tea solutions.
Materials and Methods: 112 acrylic resin blocks of Meliodent and Acropars (each 56 blocks) were divided into seven groups of different treatment: 1% sodium hypochlorite for 10 min a day for 1 month (H10m), 1% sodium hypochlorite for 8 hours a day for 1 week (H&h), Correga tabs solution for 8 hours a day for 1 month (C&H), tea bag for 2 hours a day for 1 month (T2 h), tea bag for 2 hours a day then 10 min in 1% sodium hypochlorite for 1 month (T-H), tea bag for 2 hours then 8 hours in the Correga tab solution a day for 1 month (T-C), and finally distilled water for 1 month as a control group (con). After specimen's treatment, color (CIE Lab) and surface roughness (Ra, µm) of samples were measured. The results were analyzed by analysis of variance (ANOVA), followed by Tukey's HSD and Dunnett T3.
Results: Group T2h exhibited a significant (P<0.05) color change and control specimens exhibited the lowest color change. Sodium hypochlorite caused a significant (P<0.05) color change in the Acropars group in comparison with the Meliodent group. In the Correga tab solution the difference was not significant (P=0.155). There was a significant (P<0.05) color change in the T-H treatment. The Acropars and Meliodent acrylic resin did not a show significant difference in surface roughness after different treatments.
Conclusion: Sodium hypochlorite 1% for 10 minutes a day in a month is the recommended hygiene protocol. The color stability of acryl is brand-type dependent but surface roughness is not.

Keywords: Denture cleanser, color stability, commission internationale de I′eclairage LAB, surface roughness

How to cite this article:
Haghi HR, Asadzadeh N, Sahebalam R, Nakhaei M, Amir JZ. Effect of denture cleansers on color stability and surface roughness of denture base acrylic resin. Indian J Dent Res 2015;26:163-6

How to cite this URL:
Haghi HR, Asadzadeh N, Sahebalam R, Nakhaei M, Amir JZ. Effect of denture cleansers on color stability and surface roughness of denture base acrylic resin. Indian J Dent Res [serial online] 2015 [cited 2020 Oct 30];26:163-6. Available from: https://www.ijdr.in/text.asp?2015/26/2/163/159149
Most dentures worldwide are fabricated from acrylic resins because of its low cost and ease of manipulation. Despite its advantages, acrylic resin is not an ideal material, with discoloration and surface roughness being two weaknesses. [1],[2]

Denture base acrylic resin should have a natural appearance, like oral tissues. [3] Color stability is one of the most important features of dental materials, [4] as discoloration is a sign of aging and damage. Many factors are associated with color change, such as stain accumulation, water sorption, degradation of ingredients, dissolving of intrinsic dyes, and surface roughness. It has been shown that colorful food and drinks can cause color change in dental polymers such as denture bases. [5]

The International Commission on Illumination (CIE) l * a * b * system is used commonly in dentistry to determine color change in dental materials. Colorimeter instruments measure three parameters of color; l* (lightness), a* (red/green), and b* (yellow/blue). ΔE is the color difference between two specimens, as calculated by the following formula. [6],[7],[8]



In clinical conditions when ΔE < 3.7, two specimens are assumed to be an acceptable match. However, color difference is perceptible by >50% of humans when ΔE ≈ 1. [9],[10],[11]

Applying a chemical solution in addition to mechanical cleaning for dentures is recommended in hygiene protocols for edentulous patients. [12] This is of particular importance in old patients who have dexterity or mental problems and who are not able to easily brush their dentures. [11]

Denture stomatitis is a common infectious disease in denture wearers with colonization of microorganisms in oral tissues and acrylic bases. [13] It is reported that 10-67% of denture wearers have this condition. [14]

Denture cleansers are recommended to prevent Candida colonization and plaque formation. [15]

Oxygen releasing agents and hypochlorite solutions are two examples of types of immersion cleanser. Effervescent tablets contain alkaline peroxide, which releases oxygen bubbles in water, resulting in both a chemical and mechanical cleaning action. [16],[17]

Sodium hypochlorite (NaOCl) solutions are more effective on Candida albicans in denture stomatitis than other denture cleansers. [18],[19]

The physical and mechanical properties of acrylic dentures can be influenced by different methods of hygiene. [20] Davi et al. showed that sodium hypochlorite 1% causes a color change and reduces flexural strength within 180 days. [21] Little information is available concerning the effect of sodium hypochlorite and effervescent tablets on the color and surface roughness in relation to time, tea discoloration, and acrylic type.

The aim of this study was to investigate the effect of cleansing agents on the surface roughness and discoloration of two heat-polymerizing denture base acrylic resins with respect to tea consumption. The hypothesis was that both cleansing agents have an adverse effect on color and roughness.


   Materials and Methods Top


Two heat-polymerizing acrylic resins were tested. The names and details of the acrylic resins are presented in [Table 1].
Table 1: Characteristics of the acrylic resins


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Specimen preparation

Fifty-six specimens of each acrylic resin were prepared by positioning stainless steel disks (23 mm × 3 mm) within flasks in silicone rubber supported by dental stone. The powder and liquid were mixed according to ratios specified in the manufacturers' instructions [Table 1]. The mixture was allowed to reach a doughy stage and then packed into the molds. Acrylic specimens were polymerized in a controlled water bath [Table 1]. After deflasking, any acryl was removed and polished using silicon carbide paper (600, 1200). Specimens were checked visually, and removed from analysis if any void was identified.

Specimens were divided into seven groups of eight specimens each. Specimens treatments were performed using 1% sodium hypochlorite (Behdad Ind., Tehran, Iran) for 10 min a day for 1-month (H10 m), 1% sodium hypochlorite for 8 h a day for 1-week (H and h), Correga tabs (Block Drug Company, Inc, USA) solution for 8 h a day for 1-month (C and H), tea bag (Ahmad tea) for 2 h a day for 1-month (T2 h), tea bag (Ahmad tea) for 2 h a day then 10 min in 1% sodium hypochlorite for 1-month (T-H), tea bag (Ahmad tea) for 2 h then 8 h in the Correga tab solution a day for 1-month (T-C), and finally distilled water for 1-month as a control group (con).

After disinfection or tea immersion, specimens were washed and kept in distilled water.

To make the tea solution, one bag of Ahmad tea was left for 2 min in 800 ml distilled boiling water. The solution was then allowed to cool. Fresh tea was made for each specimen. A tea-immersion time of 2 h was calculated from the average length of time in a day that people are exposed to colored drinks such as tea.

For the Correga tabs solution, one tablet was dissolved in 250 ml of water at 40°C ± 2°C. Correga tabs are predominantly alkaline peroxide.

We included the H8 h group in an effort to identify any possible effect of long-term use of sodium hypochlorite on the color and roughness of acrylic resin. The T-H and T-C groups were included to simulate the cumulative effect of colored drinks and cleansing agents on the color and roughness of acrylic denture bases.

Roughness test

The surface roughness (Ra, μm) was measured using a profilometer (Surtronic T+, Taylor Hodson Co; London, England), with a diamond stylus which is moved across the surface, connected to a system that analyses the information. The analyzer tip moved 4.8 mm on the surface from the center of the disk in four different radii, and the final Ra average was calculated.

Colorimetery

Color measurements were made using a colorimeter (Minolta Konica Japan). Three readings were recorded, and the mean was accepted as the color of the specimens in the CIE lab color scale. The magnitude of the color difference is formulated by ΔE, which is designed to provide numerical data for colors.

The colorimeter was calibrated according the manufacturer's instructions using a white plate.

Statistical analysis

The results obtained were ANOVA, followed by Tukey's honest significant difference and Dunnett T3.

Statistical analyses were performed at the 95% level of confidence to determine the effect of acryl type and cleansing protocol on surface roughness and color change in an acrylic resin base. Before analyses, data homogeneity of variance was tested using the Kolmogorov-Smirnov test.


   Results Top


Color change

Group T2 h exhibited a significant (P < 0.05) color change and the greatest mean color change (ΔE). Control specimens exhibited the lowest color change. However, Acropars acrylic resin exhibited a greater color change in group H8 h. Meliodent acrylic resin showed a greater color change in the T2 h group.

Sodium hypochlorite caused a significant (P < 0.05) color change in the Acropars group in comparison with the Meliodent group. In the Correga tab solution, the Acropars group exhibited higher values for color change than the Meliodent group, but the difference was not significant (P = 0.155). For the T-h and T-C groups, the Acropars acrylic resin exhibited a greater color change than the Meliodent acrylic resin, but there was a significant (P < 0.05) color change in the T-h treatment only [Table 2].
Table 2: Color changes following cleaning with different solutions


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Roughness

Irrespective of the acrylic resin type, the T-C group exhibited greater roughness (Ra, μm) and T 10 M exhibited lower roughness after treatment. However, the difference was not significant in comparison with the control group (P > 0.05). The Acropars and Meliodent acrylic resin did not show a significant difference in surface roughness after different treatments [Table 3].
Table 3: Roughness following cleaning with different solutions


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   Discussion Top


In this study, two denture base acrylic resins were investigated with respect to their color and surface roughness after immersion in two cleansing solutions and tea. Chemical solutions are necessary among denture wearers for disinfection, treatment of stomatitis, and stain removal. Therefore, the effect of repeated exposure to and immersion in cleansing solutions on the mechanical and physical properties of denture resin is important. It was demonstrated that tea solution has a significant effect on color, irrespective of the acrylic type. [5] It is possible that depositing a layer on the surface of the acrylic resins causes the color change. Rough surfaces and porosities have a greater tendency for staining.

This study shows that sodium hypochlorite has a greater effect on the color of acrylic resin than Correga tabs. Chloride ions have a possible effect on color change. As with our findings, Davi et al. [21] also demonstrated that sodium hypochlorite for 8 h a day for 180 days causes a significant color change in acrylic resin bases. Jagger et al. [4] showed that hypochlorite solutions were more effective on stain removal from acrylic resin.

However, some studies showed no significant clinical color change after immersion in cleansing solution. [22],[23] These findings may be related to the time of exposure to the cleansing agent or to the effect of the colorimetery method used. [20],[24] In color change, the hypothesis is accepted.

In a comparison of two brands of acryl, we observed that Meliodent specimens had a more stable color. This observation may be explained by the instability of intrinsic colors in Acropars.

The results of this study showed no significant change (P > 0.05) in surface roughness. Therefore, the hypothesis is rejected. Azevedo et al. studied the effect of sodium hypochlorite 1%, chlorhexidine gluconate 4%, and water for different exposure times on surface roughness, and demonstrated that the changes were not significant. [25] Shen demonstrated no clear surface change when alkaline solution was used. [26]

In our study, the mean surface roughness after treatment for both Meliodent acrylic specimens (1.04-1.27) and Acropars specimens (0.88-1.44) was lower than would be expected for the increase in bacterial colonization (Ra: 2.2 μm); [27] however, a surface roughness >0.7 μm indicated the possibility of plaque accumulation. [28]

In the present investigation, the T-C group (2 h in tea solution and 8 h in Correga tabs for 1-month) demonstrated greater surface roughness than the other groups; although the difference was not significant (P > 0.5). In addition, the tea-immersion specimens demonstrated less surface roughness than the other groups. One possible explanation is that the tea staining layer causes a change in surface topography. Therefore further studies must be performed on the surface roughness of acrylic resins over greater periods of time with variations in the colored drinks used in order to reach a definitive conclusion.


   Conclusions Top


Within the limitations of the present in vitro study, the following conclusions are reached:

  • Meliodent acryls have a stable color
  • The color stability of acryls is brand-type dependent
  • The exposure time is relevant when using a sodium hypochlorite cleansing agent, but has no significant effect on color change when using effervescent tablets
  • Irrespective of the type of acryl, sodium hypochlorite is the strongest stain cleaner
  • Type of acryl and cleansing technique had no significant effect on the surface roughness
  • Sodium hypochlorite 1% for 10 min a day in a month is the optimal hygiene protocol.


 
   References Top

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Correspondence Address:
Dr. Hamidreza Rajati Haghi
Department of Prosthodontics, Dental Research Center, Mashhad University of Medical Sciences, Mashhad
Iran
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Source of Support: Research Grant from the chancellor of research at Mashhad University of Medical Sciences, Iran., Conflict of Interest: None


DOI: 10.4103/0970-9290.159149

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    Tables

  [Table 1], [Table 2], [Table 3]

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