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Comparison of Discoloration of Heat-Curing Resins for Denture Bases
Int J Clin Prev Dent 2022;18(2):53-57
Published online June 30, 2022;  https://doi.org/10.15236/ijcpd.2022.18.2.53
© 2022 International Journal of Clinical Preventive Dentistry.

Seong-Hyuk Bang1, So-Min Kim2

1Best Dental Laboratory, Seoul, 2Department of Dental Technology and Science, Shinhan University, Uijeongbu, Korea
Received May 3, 2022; Revised May 25, 2022; Accepted June 2, 2022.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Objective: This study aims to contribute to the manufacturing of prosthetics with high patient satisfaction by testing and evaluating the discoloration and staining of three commonly used denture base resins (Hipac cozy, Paladent 20, and Rapid Simplified) caused by turmeric, coffee, Polydent, and deionized water.
Methods: After developing a specimen with three types of denture base resin according to the manufacturer’s instructions, samples were made with turmeric, coffee, Polydent, and deionized water, into which five specimens were each deposited. A spectrophotometer was used to measure and compare color change 5, 10, and 15 days after deposit.
Results: While differences with time (p=0.004) were observed, there were no differences among products (p=0.920). Hipac cozy’s color stability was inferior when compared to other denture base resins, and turmeric significantly changed the color of all denture base resins. Additionally, discoloration was severe in areas of the denture specimens where polishing was insufficient.
Conclusion: Clinical observation based on the above results indicates that because the turmeric used in this study caused a significant color change in denture base resins, routine turmeric consumption is unfavorable in terms of color stability.
Keywords : discoloration, heat-curing resin
Introduction

The elderly population is increasing as a result of an aging society. As a result of the denture insurance policy, the number of patients wearing dentures aged ≥65 years is gradually increasing. Endosseous implant treatment is also recommended and widely used in clinical practice to improve denture maintenance. With the announcement of Moon Care (August 9, 2017), the age limit for implants, which were previously applied only to the elderly aged >75 years, was gradually decreased to 65 years, and the copayment was reduced from 50% to 30% (for those covered by health insurance) [1]. Although the copayment cost has been significantly reduced and it is now more easily accessible, implant surgery may still necessitate multiple implant treatments and be economically burdensome. Furthermore, implants may not be appropriate for patients with general health issues or those suffering from other disorders; thus, the need for dentures that use implants or removable implants remains high.

Polymethyl methacrylate (PMMA), a type of acrylic resin, was first introduced to dentistry in the 1930s, and since the 1940s, methyl methacrylate (MMA) polymers and copolymers have been used to manufacture 95% of denture bases [2]. Denture base material is an acrylic resin of PMMA polymerized with MMA that has good esthetics, is lightweight, and has high processability, making it the most widely used denture base material in current clinical practice. Dentures are made up of a denture base and artificial teeth, with the denture base holding the artificial teeth in place. To function stably in the oral cavity, these denture base resins must meet various criteria, including good biocompatibility as they are mounted and in contact with the soft tissues of the oral cavity; an appropriate level of strength for mastication; an oral cavity function; color harmony with the soft tissues of the oral cavity; and resistance to stains and discoloration.

Naturally, denture base resins have lower color stability than other metal prosthetics used in the oral cavity. In addition to having a high cohesive force and repeated loads, the environment within the oral cavity has high temperature fluctuations, is constantly wet with saliva, and has extreme pH changes depending on the food components, all of which adversely affect the physical quality of the resin and can cause discolora-tion [3-5] and further reduce its color stability.

This experiment aims to determine the effect of turmeric, a food ingredient that has recently been regarded as beneficial to health and has influenced dietary changes of Koreans; coffee; Polydent, a denture cleaner; and deionized water (control) on the color of Hipac cozy (Vericom, Chuncheon, Korea), Paladent 20 (Heraeus, Hanau, Germany), and Rapid Simplified (Vertex- Dental, Soesterberg, The Netherlands), which are denture base resins that are currently widely used in clinical practice. Additionally, we aim to establish a standard for clinical application by comparing the properties, characteristics, and strengths and weaknesses of each material.

Materials and Methods

1. Experimental materials

Three types of thermally polymerized resins for denture bases (Hipac cozy, Paladent 20, and Rapid Simplified) widely used in the market were used for this experiment (Table 1).

Table 1 . Heat-curing resin for denture bases

Product nameMain ingredientManufacturerManufacturing country
Hipac cozyPMMAVericomKorea
Paladent 20PMMAHeraeusGermany
Rapid SimplifiedPMMAVertex-DentalThe Netherlands

PMMA: polymethyl methacrylate.



Turmeric, which has recently been increasingly consumed by Koreans; coffee; and Polydent, a denture cleaner, were used as samples, with deionized water serving as a control (Table 2). deionized water was obtained using PURELAB Flex3 (ELGA LabWater, Woodridge, IL, USA), an ultrapure water production device. For color measurement, spectrophotometer SP 62 PURELAB Flex3 (X-RITE, Grand Rapids, MI, USA) was used. OVEN LB30575054 (Thermo Fisher Scientific, Dreieich, Germany) was used to keep the specimens at a constant tem-perature.

Table 2 . Solutes and solutions

VariableProduct nameManufacturerManufacturing country
TurmericPEACOCK turmericDongwon Home foodKorea
CoffeeMocha gold mildMaximKorea
Polydent PolydentStafford Miller Ltd.Ireland
Deionized waterPrepared using an ultrapure water production device


2. Specimen preparation

Five specimens for color measurement were prepared after flasking using a boxing wax and polymerized according to the manufacturer’s instructions with a length and width of 20 mm each and a thickness of 2 mm. After polymerization, each specimen was polished to #800 with sandpaper, washed using ultrasonic and steam cleaners, and dried with compressed air before testing.

3. Incubation

The specimen was deposited in a beaker containing 400 ml of deionized water and stored for 24 hours in an oven at 37℃, a temperature similar to that of the human body.

4. Color measurement

1) Treatment before staining

Before staining, the specimens were stored in deionized water for 24 hours, washed and dried, and the color tone was measured using a spectrophotometer.

2) Preparation of the sample solution

For turmeric and coffee, the sample solution was prepared by mixing 400 ml of deionized water with 8 g of powder, and a stock solution was used for Polydent and deionized water.

3) Color measurement after staining

Specimens stored for 24 hours in deionized water were deposited in samples of turmeric, coffee, Polydent, and deionized water, and color was measured after 5, 10, and 15 days. On each day, the specimens were washed with a brush under running water for 30 seconds and dried before being measured. After calibrating the spectrophotometer, color measurement was conducted; the specimen was placed in close contact with the optical unit, and three locations per specimen were selected and measured three times, with the average of these values used.

Results

The color of the specimens was measured before they were placed in turmeric, coffee, Polydent, and deionized water samples, and the color changes were measured using a spectrophotometer after 5, 10, and 15 days. The following results were obtained after measuring color changes.

For deionized water, Hipac cozy had the highest value at 1.29 after 10 days, and the average color change was high in the order of Hipac cozy, Rapid Simplified , and Paladent 20 (Table 3).

Table 3 . Color differences (ΔE*) of denture base resins in deionized water at different times (n=5)

Product nameBeforeAfter 5 daysAfter 10 daysAfter 15 days
Hipac cozy0.000.66±0.261.29±0.840.81±0.17
Paladent 200.000.45±0.240.51±0.210.62±0.53
Rapid Simplified0.000.66±0.450.66±0.450.54±0.23

Values are presented as mean±standard deviation.



Turmeric showed high color differences in all specimens (Table 4).

Table 4 . Color differences (ΔE*) of denture base resins in turmeric at different times (n=5)

Product nameBeforeAfter 5 daysAfter 10 daysAfter 15 days
Hipac cozy0.0037.40±7.2042.96±1.7944.36±1.97
Paladent 200.0039.20±3.2441.17±1.8040.77±2.24
Rapid Simplified0.0038.01±1.1239.86±1.0240.59±1.47

Values are presented as mean±standard deviation.



For coffee, Hipac cozy had the highest value, and the average color change appeared in the order of Paladent 20 and Rapid Simplified , but there was no significant difference (Table 5).

Table 5 . Color differences (ΔE*) of denture base resins in coffee at different times (n=5)

Product nameBeforeAfter 5 daysAfter 10 daysAfter 15 days
Hipac cozy0.002.39±0.575.40±4.033.28±0.59
Paladent 200.002.04±0.362.04±0.292.69±0.45
Rapid Simplified0.002.11±0.472.06±0.382.24±0.24

Values are presented as mean±standard deviation.



Polydent showed similar results with Rapid Simplified and Hipac cozy, and Paladent 20 had the lowest value (Table 6).

Table 6 . Color differences (ΔE*) of denture base resins in Polydent at different times (n=5)

Product nameBeforeAfter 5 daysAfter 10 daysAfter 15 days
Hipac cozy0.000.96±0.291.33±0.221.22±0.72
Paladent 200.000.58±0.320.61±0.190.43±0.17
Rapid Simplified0.001.20±0.811.29±0.901.18±0.84

Values are presented as mean±standard deviation.


Discussion

Dentures made with the help of computer-assisted design/computer assisted manufacturing (CAD/CAM) systems and CAD printers are becoming increasingly popular in the current dental industry. The CAD/CAM system improves the quality and reproducibility of restorations by maximizing standardization and precision using three-dimensional oral data [6]. Unlike other types of prosthetics, denture bases made of resin and artificial teeth can be easily grafted onto a CAD printer, so continuous research on materials will be required in the future. The penetration rate of CAD/CAM systems in dental engineering is estimated to be 60%. Therefore, it is thought that active research and studies should be conducted on resins that can facilitate the use of CAD printers in the dental field. Resin, which fixes and maintains artificial teeth and is the basic frame of denture bases, must not only function in the oral cavity but also be esthetically pleasing. As a result, its strength and esthetics are being emphasized. Because the esthetic aspect is significantly associated with food ingredients consumed, the resin must also be color stable. Because foods that affect color stability cannot be avoided, resin must be manufactured to withstand staining and discoloration.

Discoloration is pigmentation and is related to the state of polishing, and Wendt [5] demonstrated that the rougher the surface, the lower the color stability. It is believed that the bubbles formed during resin polymerization as a result of various components used by different manufacturers also influence color stability. Therefore, to minimize color stability, the surface polishing of the denture base resin was polished to 800 grits for this experiment. Additionally, bubble formation during polymerization can affect color change in different products. According to Strohaver and Mattie [7], thermally polymerized resin has fewer air bubbles and better color stability than visible light-polymerized resin. As a result, resin does not form bubbles during its manufacturing process and can be a better prosthetic when polished well. However, regardless of how well the prosthetic is made during the manufacturing process, discoloration of the denture will occur quickly if the patient consumes foods that easily lead to staining. Therefore, patients with dentures will be able to use their prosthetics longer if they pay attention to the foods they consume.

Conclusion

This experiment aims to determine the color stability of three types of resin (Hipac cozy, Paladent 20, and Rapid Simplified) that are widely used in clinical practice using turmeric, a food ingredient whose consumption has recently increased among Koreans; coffee; Polydent, a denture cleaner; and deionized water as a control for color comparison. The color at different times was measured, and the following conclusions were reached:

1. Differences according to time (p=0.004) and no differences among products (p=0.920) were observed.

2. Hipac cozy has inferior color stability compared with other denture base resins.

3. Turmeric significantly changed the color of all denture base resins.

4. Discoloration was severe in regions of the denture base resin specimens with insufficient polishing.

According to the above findings, routine turmeric consumption is likely to be detrimental to color stability because it caused significant color changes in the resin specimens used in this study.

Conflict of Interest

No potential conflict of interest relevant to this article was reported.

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June 2022, 18 (2)