Introduction
The escalating population of elderly individuals relying on dentures underscores the imperative need to emphasize preventive measures and protective strategies against denture staining, coupled with a decreased occurrence of defects (1). Inadequate denture hygiene poses a substantial risk for both oral infections and systemic dissemination, as noted in previous research. Sumi et al. (2) highlighted that denture bases may serve as reservoirs for bacteria, contributing to the development of aspiration pneumonia, opportunistic infections, and endocarditis. The porous nature of most denture materials, particularly acrylic resins, renders them susceptible to bacterial adherence, especially when the denture surface is scratched due to improper cleaning methods (3, 4). Maintaining optimal denture cleanliness, achieved through appropriate cleaning methods, becomes pivotal for patients with compromised resistance to infections (5).
Denture hygiene can be achieved through either mechanical or chemical procedures (6, 7). The chemical approach involves using an alkaline peroxide solution with active ingredients, inducing the release of oxygen bubbles that detach biofilm from the denture surface (8). This method, while effective, also possesses antibacterial properties and aids in stain removal (9–13). Mechanical methods, such as brushing, sonic vibrators, and ultrasonic devices, offer alternatives for denture cleaning (14). Brushing, which is the most commonly employed method (15–17), has been extensively reported, although concerns about potential wear and superficial damage to denture base resin persist (18–22). Ultrasonic devices, introduced as mechanical aids for denture cleaning, utilize sound waves to induce liquid movement (vibration) and the collapse of bubbles formed during the vibration process (23, 24). While combining chemical and mechanical cleaning methods seems advantageous, its effectiveness remains untested. Despite the American Dental Association (ADA) protocol recommending denture immersion in a cleanser once a week followed by brushing, the longevity and stain resistance of dentures are often compromised within months after delivery (18). Consequently, a pertinent question arises regarding the need for an efficient denture cleaning method that minimizes defects and effectively removes stains.
This study endeavors to compare the physical properties of denture base resin after staining by beverages, evaluate the impact of four distinct cleaning methods, and identify the optimal cleaning approach.
Materials and methods
A total of 200 specimens were crafted in square dimensions (20 × 20 × 2 mm). Lucitone Fas-Por + Self-curing dental base resin (Dentsply India, USA) was manipulated, packed into a lab-made metal matrix, and polymerized as per the manufacturer’s instructions in a pressure pot (Ivomat, Dentek, Inc., Buffalo, USA). The excess polymerized resin was trimmed using a tungsten carbide drill (Buffalo Dental, NY, USA) employing a low-speed micromotor (Henry Schein Inc., UK). Subsequently, both flat sides of each specimen underwent polishing in the horizontal lathe spindle (AutoMet 250, Buehler, Lake Bluff, IL, USA) using 70, 45, and 15 μm diamond grinding discs. One of the flat faces of each specimen was polished with a polishing cloth and 1 μm Buehler supreme polycrystalline diamond suspension at a low speed of 200 rpm in the horizontal lathe spindle. Post-polishing, the final thicknesses of the specimens were verified using a CD-6 CSX-B digital caliper (Mitutoyo, Tokyo, Japan). The samples were marked with three carvings using a diamond drill on the lateral side. Following the markings, the specimens were stored in distilled water at 37 °C for 50 ± 2 h to eliminate residual monomer (25).
The denture cleanser subjected to testing was Polident Overnight denture cleanser (Gaxo Smith Kline Consumer Healthcare, L.P. Moon Township, PA, USA), containing principal ingredients such as sodium bicarbonate, citric acid, potassium monopersulfate, sodium carbonate, sodium percarbonate, TAED, sodium benzoate, PEG-180, sodium lauryl sulfoacetate, Aroma, VP/VA copolymer, Blue 1 aluminum lake, and Blue 2. The staining solutions utilized in this study comprised filtered coffee (100% Colombian coffee, Kirkland, Seattle, WA, USA), red wine (Central Valley Frontera Chile, Vina Conchay Toro, SA, Chile), and tea (Lipton, Unilever, Englewood Cliffs, NJ, USA), with all solutions prepared following the manufacturers’ instructions. The coffee solution was created by dissolving 50 g of coffee in 500 mL of boiled water, stirring for 10 minutes, and filtering. The tea solution was prepared by immersing five teabags (10 g) in 500 mL of boiled water, stirring for 10 minutes, and filtering (26).
Immersion and cleaning procedures
The denture samples were randomly assigned to 20 groups, each with a sample size of 10 (n = 10). The primary groups were as follows: Cleanser + Brush (Group A), involving immersion in denture cleanser and brushing with distilled water; Cleanser + Ultrasound (Group B), consisting of immersion in denture cleanser and cleaning in an ultrasonic cleaner; Brush Only (Group C), entailing immersion in distilled water and brushing with distilled water; Ultrasound Only (Group D), involving immersion in distilled water and cleaning in an ultrasonic cleaner; and Control (Group E), with immersion in distilled water. Within each main group, the specimens were further divided into subgroups (n = 10) as follows: control (Subgroup I), immersion in distilled water; coffee (Subgroup II), immersion in coffee; tea (Subgroup III), immersion in tea; red wine (Subgroup IV), immersion in red wine after staining. The specimens were thus distributed across a total of 20 groups, as detailed in Table 1.
Table 1. Groups and treatment timeline for each cycle.
For the brushing test, a custom-made toothbrush machine was utilized, allowing simultaneous brushing of four sets of specimens at a frequency of 70 rpm. The brush covered a course of 3 cm, and the load was standardized at 200 gf, following ISO/DTS 145692 guidelines. The toothbrushes used in the study were Oral-B Indicator soft regular 40, with rounded ends, uniform length, flexibility, and 38 tufts (40 sticks per tuft) of smooth bristles, each with a diameter of 0.25 mm and a height of 10 mm. The specimens underwent evaluation through tests measuring weight, thickness, surface roughness, surface hardness, and color. Baseline data for the specimens were recorded before immersion.
During the experiment, the specimens were immersed in staining solutions or distilled water (control group) for 14 hours to simulate weekly exposure (2 h per day for 7 days) to beverages. After staining, the specimens were rinsed in tap water for 10 seconds and air-dried. Cleaning procedures were then applied based on the assigned groups: Cleanser + Brush (Group A), involving immersion in denture cleanser for 8 hours and brushing with distilled water in a brushing machine for 3 minutes (70 cycles/min for 210 cycles); Cleanser + Ultrasound (Group B), with 8 hours of immersion in denture cleanser and 15 minutes of cleaning in an ultrasonic cleaner (Quantrex 140, L&R, New Jersey, USA); Brush Only (Group C), including 8 hours of immersion in distilled water and 3 minutes of brushing with distilled water; Ultrasound Only (Group D), with 8 hours of immersion in distilled water and 15 minutes of cleaning in an ultrasonic cleaner; Control (Group E), involving 8 hours of immersion in distilled water (overnight). The specimens were then rinsed and air-dried, and subsequent tests were conducted. This weekly procedure was repeated, totaling 48 cycles to simulate 12 months of denture usage. All tests were repeated at baseline, and at the 12th, 24th, 36th, and 48th cycles.
Test series
The surface roughness (Ra) of the test samples was assessed utilizing a profilometer (SJ-201P, Mitutoyo Corp., Kawasaki, Japan) with a 0.4-gf load. A stylus featuring a 5 μm tip radius traversed the surface, recording data at a resolution of 0.01 μm. The specimens were affixed to the profilometer measuring table using a double-sided tape. Each sample underwent three readings over a 4.0 mm length, with a cutoff value of 0.8 mm, at a speed of 0.1 mm/s in regions corresponding to specimen marks. The roughness for each sample was determined as the arithmetic mean of three measurements (μm). The alteration in surface roughness (ΔRa) was computed as the difference between post-immersion and baseline values. Surface roughness was standardized for all resins before immersion, with standardization within each group. The Ra value represented the arithmetic average of all profile samples across the mean sample length. A single operator conducted all measurements.
The mass of each specimen was measured using an electronic balance (AB204-SRS, Mettler Toledo, Switzerland) before and after brushing or ultrasonic cleaning. Mass loss was calculated based on the initial mass and differences after brushing or ultrasonic cleaning, with the balance offering a resolution of 0.0001 g.
Specimen thickness was measured with a CD-6 CSX-B digital micrometer (Mitutoyo, Tokyo, Japan) before and after brushing or ultrasonic cleaning. Thickness loss was determined by the initial thickness and differences after cleaning, with the micrometer’s precision being 0.005 mm.
Color and color differences for each specimen were gauged using a spectrophotometer (Color i5, X rite GretagMacbeth, Mochenwangen, Germany) against a gray background. The spectrophotometer, calibrated per manufacturer instructions, recorded values in the CIE LAB color system, encompassing L* (lightness), a* (red-green), and b* (yellow-blue) coordinates. ΔL*, Δa*, and Δb* denoted differences between baseline and post-immersion values, while total color alteration (ΔE*) was calculated as ΔE* = [(ΔL*)2+ (Δa*)2 + (Δb*)2]½.
The Vickers hardness (VHN) of the test samples was determined with a Microhardness Tester (Micromet 2003, Buehler, Illinois, USA) using a 100-gf load for 30 seconds. Diagonals of the pyramid impressed on the specimen by the Vickers diamond indenter were measured under a microscope at 600×, with the VHN value being the arithmetic mean of three measurements for each sample. A single operator recorded all measurements, and the mean Vickers hardness number was then calculated for each sample. After immersion in cleaning solutions, the average value was used to represent an overall mean indicative of the materials.
Data were analyzed with SPSS on the repeated-measures general linear model. A significant level of 0.05 was used to determine the presence of significance between groups.
Result
Compare the effects of cleaning methods on the physical properties of denture resin
Figure 1 shows the surface roughness changes of different cleaning methods. It is the test results in the control subgroups immersed in water. It is reversed that surface roughness increased in all treatment groups, and significantly higher values were detected at 36th and 48th cycles in brush-only groups. Meanwhile, the surface roughness significantly increased for the cleanser and brushed combined groups compared to other groups.
Figure 1. Surface roughness changes of different cleaning methods in water.
Similar changes were found in weight and thickness measurements, in which cleanser and brush combined methods caused defection on the specimens (Figures 2 and 3). In the surface hardness changes, all groups showed a trend of increase. However, no significant difference was detected between all the groups (Figure 4).
Figure 2. Weight changes of different cleaning methods in water.
Figure 3. Thickness changes of different cleaning methods in water.
Figure 4. Surface hardness changes of different cleaning methods in water.
Compare staining effects on denture resin
Figure 5 shows the color changes of different staining. This result came from the test results in the control groups, in which no cleaning treatment was applied while immersed items were in the staining solution. The results showed water made no apparent changes, coffee made color changes, but tea and red wine made a significant change in color of the denture.
Figure 5. Color changes of different staining in control groups.
Compare staining and cleaning effects on denture resin
Different cleaning methods have different abilities to remove stains, and they have different abilities to create defection of the denture at the same time.
Figure 6 shows the results of surface roughness changes of different cleaning methods at the end of treatments, which is 12 months of usage of the denture following different cleaning protocols. It shows that all stains, cleanser, and brush combined cleaning, which ADA recommends, invariably cause the maximum damage. Meanwhile, ultrasound and cleanser ultrasound cleaning methods caused the minimum defects. Figure 7 shows the color changes of different cleaning methods at the end of our treatments. For all stains, cleanser ultrasound and cleanser brush cleaning methods have the best discoloration ability. Unfortunately, according to this result, different cleaning methods’ discoloration and defection abilities are not matched as expected. In this study, the Repeated Measures General Linear Regression Statistical Model was used to measure the weights of different effects (Table 2). Table 3 lists all the test runs on the specimens and the desirability and priority put into the statistical model.
Figure 6. Color changes of different cleaning methods in stains at 48th cycles.
Figure 7. Surface roughness changes of different cleaning methods in stains at 48th cycles.
Table 2. Summary of multiple comparison tests (P-values between each cleaning method) in surface roughness.
Table 3. Statistical model used in data analysis (Repeated measures general linear regression).
After considering the priority and desirability of these statistical models, the result was obtained to choose the optimal cleaning methods for denture resin from different stains. 1. In coffee stains, the cleanser and ultrasonication combined method showed the best for denture resin in most tests, while cleanser and brush clean combined techniques are more efficient in removing the stain. 2. In tea stains, the same patterns were found as the coffee stains. 3. In red wine stains, ultrasound cleaning only showed the best denture resin in most tests, while the cleanser and brush clean combined method was more efficient in removing the stain.
Discussion
The outcomes of this study substantiate the rejection of the null hypothesis, asserting that the amalgamation of ultrasonic treatment with denture cleanser elicits optimal cleaning efficacy. The current investigation aligns harmoniously with the findings of Palenik et al. (27) where ultrasonic devices paired with tap water showcased a cleaning action predominantly propelled by ultrasonic cavitation, rather than the inherent chemical composition. Undoubtedly, this underscores the significant capacity of ultrasonic devices to substantially curtail cleaning time, as reported by Palenik et al. (reduction by 1/420 to 2/3) (28, 29). However, it is imperative to acknowledge the nuanced impact on surface roughness, as elucidated by Palenik et al. and Otake and Yoshida (30).
The assessment of denture color stability involved an examination of the efficacy of various cleaning methods. The susceptibility of dentures to staining was found to be dependent on the staining solution used in this research. Statistical analysis uncovered noteworthy differences in the staining capabilities of various solutions. Notably, red wine and tea exhibited a higher degree of discoloration compared to coffee. The discernible color variations induced by red wine and tea were evident to the human eye (ΔE* > 3.3), aligning with findings from prior studies (31–34). Previous research has suggested that the alcohol content in red wine, as tested in this study, may contribute to surface roughening, thereby facilitating staining by softening the resin matrix. Consistent with our study, the literature indicates that tea tends to exert a more pronounced discoloration effect on polymeric dental materials than coffee (35, 36).
In response to the potential deleterious effects on denture base resin, this study advocates a strategic approach—employing ultrasonic treatment subsequent to the application of denture cleanser. This sequential protocol aims to mitigate the negative repercussions on denture base resin, as expounded upon in this investigation.
Delving into a meticulous critique of the experiments, this discussion underscores the critical significance of the concurrent utilization of ultrasonic treatment and denture cleanser. A more detailed examination of ultrasonic cavitation as a pivotal cleaning mechanism and its discernible effects on surface roughness now provides a nuanced understanding of the experimental nuances.
The limitations of the study are elucidated in greater detail, encompassing a comprehensive exploration of potential drawbacks. Emphasis is placed on the potential negative influence on denture base resin and the discernible increase in surface roughness, offering a holistic comprehension of the study’s constraints.
The discussion dedicates a considerable segment to delineate potential avenues for future research, emphasizing the necessity for more nuanced investigations. Specifically, it underscores the need for further exploration into diverse chemical compositions within the ultrasonic device, leveraging a meticulously designed clinical trial framework.
Conclusion
Within the scope of this study, the optimal selections of denture base cleaning methods for different stains are suggested. For coffee and tea stains, ultrasonication after cleanser application causes a more negligible effect on physical properties and better efficiency for stain removal than other cleaning methods. For red wine stains, cleaning dentures with ultrasound only causes less impact on physical properties and more efficient stain removal.
References
1. Sumi Y, Miura H, Michiwaki Y, Nagaosa S, Nagaya M. Colonization of dental plaque by respiratory pathogens in dependent elderly. Arch Gerontol Geriatr. (2007) 44:119–24.
2. Sumi Y, Miura H, Sunakawa M, Michiwaki Y, Sakagami N. Colonization of denture plaque by respiratory pathogens in dependent elderly. Gerodontology. (2002) 19:25–9.
3. Yamauchi M, Yamamoto K, Wakabayashi M, Kawano J. In vitro adherence of microorganisms to denture base resin with different surface texture. Dent Mater J. (1990) 9:19–24.
4. Pisani MX, Bruhn JP, Paranhos HF, Silva-Lovato CH, Souza RF, Panzeri H. Evaluation of the abrasiveness of dentifrices for complete dentures. J Prosthodont. (2010) 19:369–73.
5. Richmond R, Macfarlane T, McCord J. An evaluation of the surface changes in PMMA biomaterial formulations as a result of toothbrush/dentifrice abrasion. Dent Mater. (2004) 20:124–32.
6. Paranhos H d, Silva CH, Venezian GC, Macedo LD, Souza RF. Distribution of biofilm on internal and external surfaces of maxillary complete dentures: the effect of hygiene instruction. Gerodontology. (2007) 24:162–8.
7. Paranhos HF, Silva-Lovato CH, Souza RF, Cruz PC, Freitas KM, Peracini A. Effects of mechanical and chemical methods on denture biofilm accumulation. J Oral Rehab. (2007) 34:606–12.
8. Andrade IM, Cruz PC, Silva CH, Souza RF, Paranhos H d, Candido RC, et al. Effervescent tablets and ultrasonic devices against Candida and mutans streptococci in denture biofilm. Gerodontology. (2011) 28:264–70.
9. Budtz-Jorgensen E. Materials and methods for cleaning dentures. J Prosthet Dent. (1979) 42:619–23.
10. Paranhos H d, Peracini A, Pisani MX, Oliveira V d, Souza RF, Silva-Lovato CH. Color stability, surface roughness and flexural strength of an acrylic resin submitted to simulated overnight immersion in denture cleansers. Braz Dent J. (2013) 24:152–6.
11. Polyzois G, Yannikakis S, Zissis A, Demetriou P. Color changes of denture base materials after disinfection and sterilization immersion. Int J Prosthodont. (1997) 10:83–9.
12. Durkan R, Ayaz EA, Bagis B, Gurbuz A, Ozturk N, Korkmaz FM. Comparative effects of denture cleansers on physical properties of polyamide and polymethyl methacrylate base polymers. Dent Mater J. (2013) 32:367–75.
13. Saraç D, Saraç Y, Kurt M, Yüzbaşioğlu E. The effectiveness of denture cleansers on soft denture liners colored by food colorant solutions. J Prosthodont. (2007) 16:185–91.
14. Nikawa H, Hamada T, Yamashiro H, Kumagai H. A review of in vitro and in vivo methods to evaluate the efficacy of denture cleansers. Int J Prosthodont. (1999) 12:153–9.
17. Abere D. Post-placement care of complete and removable partial dentures. Dent Clin North Am. (1979) 23:143–51.
18. American Dental Association.Guide to Dental Materials and Devices. 6th ed. Chicago: American Dental Association (1974).
19. Dyer D, MacDonald E, Newcombe RG, Scratcher C, Ley F, Addy M. Abrasion and stain removal by different manual toothbrushes and brush actions: studies in vitro. J Clin Periodontol. (2001) 28:121–7.
20. Satoh Y, Ohtani K, Maejima K, Morikawa M, Matsuzu M, Nagai E, et al. Wear of artificial denture teeth by use of toothbrushes. J Nihon Univ Sch Dent. (1990) 32:247–58.
21. Sexson J, Phillips R. Studies on the effects of abrasives on acrylic resins. J Prosthet Dent. (1951) 1:454–71.
22. Patel S, Gordan V, Barrett A, Shen C. The effect of surface finishing and storage solutions on the color stability of resin-based composites. J Am Dent Assoc. (2004) 135:587–94.
23. Pitt W, Ross S. Ultrasound increases the rate of bacterial cell growth. Biotechnol Prog (2003) 19:1038–44.
24. Morris D, Elliott R Jr. Effect of ultrasonic cleaning upon stability of resin denture bases. J Prosthet Dent. (1972) 27:16–20.
25. Barbosa DB, Souza RF, Pero AC, Marra J, Compagnoni MA. Flexural strength of acrylic resins polymerized by different cycles. J Appl Oral Sci. (2007) 15:424–8.
26. Kurtulmus-Yilmaz S, Deniz S. Evaluation of staining susceptibility of resin artificial teeth and stain removal efficacy of denture cleansers. Acta Odontol Scand. (2014) 72:811–8.
27. Palenik C, Miller C. In vitro testing of three denture-cleaning systems. J Prosthet Dent. (1984) 51:751–4.
28. Saitoh M, et al. A study on denture cleansers – effects on the surface of denture base resin for a long period. Jpn J Dent Practice Admin. (2000) 35:268–75.
29. Shiota Y, et al. A study on denture cleansers – cleaning effects using an ultrasonic cleaning system. Jpn J Dent Practice Admin. (2002) 37:294–301.
30. Otake M, Yoshida T. Discoloration and weight change of denture resin and dental alloy for clasp in immersion denture cleaner. J Jpn Soc Dent Prod. (2001) 15:20–36.
31. Guler AU, Yilmaz F, Kulunk T, Guler E, Kurt S. Effects of different drinks on stainability of resin composite provisional restorative materials. J Prosthet Dent. (2005) 94:118–24.
32. Rutkunas V, Sabaliauskas V, Mizutani H. Effects of different food colorants and polishing techniques on color stability of provisional prosthetic materials. Dent Mater J. (2010) 29:167–76.
33. Sepúlveda-Navarro WF, Arana-Correa BE, Borges CPF, Jorge JH, Urban VM, Campanha NH. Color stability of resins and nylon as denture base material in beverages. J Prosthodont. (2011) 20:632–8.
34. Ruyter I, Nilner K, Moller B. Color stability of dental composite resin materials for crown and bridge veneers. Dent Mater. (1987) 3:246–51.
35. Khokhar Z, Razzoog M, Yaman P. Color stability of restorative resins. Quintessence Int. (1991) 22:733–7.
36. Um C, Ruyter I. Staining of resin-based veneering materials with coffee and tea. Quintessence Int. (1991) 22:377–86.
© The Author(s). 2024 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.