Efficacy of Denture Cleansers on Impact Strength of Heat polymerized Acrylic Resins.

PURPOSE: The study was aimed to compare and evaluate the changes in the impact strength of heat cure denture base resins when treated using denture cleansers.
METHODOLOGY: Study was conducted with sample size of 40 and dimesion 65 mm length, 10 mm width, and 3 mm thickness as per the ISO 1567. Distilled water has been used as control group, in which 10 samples were immersed of 40 samples. Of remaining 30 samples, 10 were treated with Clinsodent, 10 were treated with VI-Clean, and 10 were treated with Clanden denture cleansers. The impact strength of these specimens from each group was tested with the help of Charpy-type pendulum impact strength tester. The energy absorbed to fracture the specimens was recorded, and impact strength was calculated and was analyzed using Kruskal-Wallis ANOVA and Mann-Whitney test.
RESULTS: Impact strength of samples was significantly reduced after immersion in denture cleansers Clinsodent, VI-Clean, and Clanden solutions when compared to control group.
CONCLUSION: Clinsodent, VI-Clean, and Clanden denture cleansers decrease the impact strength of heat cure denture base resin after immersion. Hence, the study concludes that denture cleansers should be used with caution and advised to follow manufacturer's instructions.

INTRODUCTION

Denture cleansing is an important measure that can prevent cross-contamination and contributes to patient's oral health, denture longevity, and overall quality of life.[1] In patients, particularly those who are very old, have Alzheimer's disease, dementia, or low motor capacity, the use of chemical agents may be the only means of denture hygiene.[2] Denture cleansers can be classified according to their chemical composition, enzymes, alkaline hypochlorite, neutral peroxide with enzymes, acids, disinfectants, and alkaline peroxides.[23] Currently, most commonly used cleansers are alkaline peroxide, which subsequently releases oxygen, thereby enabling a mechanical cleaning by the oxygen bubbles in addition to the chemical cleaning.[4]

Fracture of an acrylic denture base is a common problem due to dropping of denture outside the mouth and occlusal forces during masticatory function inside the mouth because of base deformation and consequent resin fatigue. If denture cleansers negatively affect, the resins decreasing the strength greater incidence of fracture occur. Hence, it is of clinical importance to determine whether denture cleansers alter the properties of acrylic resins.

Many studies revealed that immersion in denture cleansers adversely affects the impact strength property of denture base resin. Very few studies evaluated the effects of impact strength on commercially available denture base resin in denture cleansers.

The purpose of this study was to evaluate the effect certain brands of denture cleansers on impact strength of denture base resins.

METHODOLOGY

Specimen preparation

The metal mold with dimension measuring 65 mm length × 10 mm width × 3 mm thickness was fabricated to make the test samples.

The wax was poured into the die space created within the metal mold to make the wax pattern. The wax patterns obtained were free of voids and inaccuracies. The dental plaster was used for investment of wax pattern in a dental flask (Kavo Germany) following the manufacturer's instructions for water-powder ratio, mixing time, and setting time. Entrapment of air was prevented during investment using mechanical vibrator. Dewaxing was carried out for 10 min after the final set of the plaster and test samples were prepared using the mold space obtained.

Powder-liquid ratio for (Trevalon, Dentsply India, Gurgaon) conventional type of heat cure denture base material is 24 g/10 ml. The material was mixed following the manufacturer's instructions and packed at dough stage. The samples were bench cured for 1 h and polymerized. Processing was carried out, the samples were bench cooled for 1 h, and sand papering was done with various grits (80, 320, 400, and 1000) followed by polishing with pumice. Electronic digital caliper was used to verify the length, width, and thickness of each sample (accurate up to 0.02 mm/0.001 inch Zoom India) and then the samples were stored in distilled water for 24 h.

Immersion procedure

Randomly, thex2 samples were divided into four groups. The control group was immersed in distilled water [Figure 1]. The remaining three groups were immersed in respective denture cleansers according to the manufacturer's instructions. The capacity of the container in which specimens were stored was 400 ml; hence, eight tablets of Clinsodent and Clanden and eight tea spoonfuls of VI-Clan were diluted in 400 ml of water and samples were immersed in it.

Figure 1

Specimens immersed in distilled water

Clinsodent (ICPA) one tablet of 480 mg was diluted in 50 ml of warm water and immersion time is 30 min [Figure 2], VI-Clean one tea spoonful of liquid denture cleanser diluted with 50 ml of water and immersion time is 30 min [Figure 3], and Clanden one tablet of 480 mg is diluted in 50 ml of warm water and immersion time is 3 min [Figure 4].

Figure 2

Specimens immersed in Clinsodent

Figure 3

Specimens immersed in VI-Clean

Figure 4

Specimens immersed in Clanden

To simulate 6 months of cleansing by the patient, the specimens were removed from the cleanser solution, washed thoroughly, and dried with absorbent paper for about 30 times over period of 6 days.

Testing the impact strength

Testing was done by using a Charpy-type digital impact testing machine (ATS FAAR Company, Italy). Ten specimens of each group were used for impact strength determination (n = 40). The test specimens were placed on the platform of the impact testing machine with their unnotched side facing away from the pendulum [Figures 5 and 6]. A pendulum of 2 J testing capacity was used and the impact speed of pendulum was 3.46 m/s. The energy absorbed by the test specimen at the time of fracture was given by a calibrated scale. Impact strength was calculated using the following formula:

Figure 5

Notched specimens for impact strength test

Figure 6

Charpy-type pendulum impact strength tester

Where E = energy absorbed by specimen at breaking and A = area of cross-section (30 mm2).

Statistical analysis

Impact strength results were analyzed statistically using the Statistical Package for the Social Sciences version 17.0 (SPSS Inc, US). Results were expressed in frequencies. Nonparametric tests namely Kruskal–Wallis ANOVA test and Mann–Whitney U-test were used for testing the statistical significance, and P ≤ 0.05 was considered for statistical significance.

RESULTS

The results are presented as average mean values of impact strength of heat cure denture base materials in Table 1 and Graph 1. In terms of denture cleansers, there was a statistical difference between all groups [Table 2]. Clinsodent group showed highest reduction in the impact strength of heat cure denture base resin, followed by Clanden and VI-Clean denture cleansers [Table 3].

Table 1

The mean and standard deviation of impact strength of various groups

Graph 1

Comparison of mean impact strength of various group tested

Table 2

Kruskal–Wallis (ANOVA) used to analyze the total impact strength data

Table 3

The descriptive statistics of intergroup comparison

DISCUSSION

Poly methyl methacrylate (PMMA) has been used as a denture base material for more than 70 years and was introduced in 1937 by Dr. Walter Wright.[5] Since then, it has been successfully used for fabrication of denture bases, artificial teeth, and impression trays and many more application in dentistry. The properties that have contributed the most to the success are excellent appearance and processing is simple and easy to repair.

An inherent disadvantage is the liability of an acrylic resin to break as a result of base deformation and consequent resin fatigue. If denture cleansers negatively affect, the resins decreasing the strength greater incidence of fracture occur. Hence, the present study conducted and compared the effect of denture cleansers on impact strength property of heat cure denture base resins.

Results of the present study showed that when compared to the control group, the impact strength of the denture base resin significantly decreased after immersion in denture cleanser solutions (Clinsodent, VI-Clean, and Clanden). The impact strength decreased due to the chemical interactions of denture cleansers with methyl methacrylate which have an influence on the bond strength of denture base resins. As a result, the chains of polymers move far apart from each other results in decrease strength of the material. Amin et al. in their study concluded that the decrease in the impact strength of in the both the studies may be due to the reason that long-term exposure to denture cleansers results in absorption of organic and inorganic components of denture cleansers by the polymer network. Water molecules incorporated in between the polymer chains cause swelling of the meshwork and reduce the frictional forces in between the chains.[6] Machado et al. in their study of Charpy tests were performed to calculate the impact strengths; thermocycling reduced the impact strength. The decrease in impact strength due to the dissolution of the polymer from both bonding surfaces followed by the interdiffusion of polymer chains.[7]

Faot et al. were observed in their study that impact strength in microwave-polymerized acrylic resins varies according to the period of irradiation. Denture base resins exhibited a high number of brittle fractures. The SEM study had shown that brittle fractures showed in well-organized crystallographic planes, whereas the intermediate fractures had a disorganized appearance irrespective of the processing technique.[8]

Ahmad in her study showed that conventional heat-cured acrylic cannot be safely soaked in (4% tartaric acid) causes decreases the impact strength because which contains isopropyl alcohol, so it is advised not to use solutions containing alcohol as acrylic denture cleansers. Lacalut dent is an oxygenating denture cleanser that had the lowest adverse effects on the impact strength of heat-cured acrylic.[9]

Ragher et al. in their study showed that immersion of heat-cured acrylic resins in denture cleanser decreases the flexural strength due to chemical interaction of denture cleanser with methyl methacrylic having an influence on the bond strength.[10]

Anusavice reported that water molecules interfere with the PMMA polymer chains and act as a plasticizer and interfere with its mechanical properties, thus decreasing acrylic resin strength.[11]

These studies emphasize that denture cleansers reduce the impact strength, resulting in fracture of denture. Inappropriate use of denture cleansers should be avoided and patient should be instructed to follow manufacturer guidelines.

CONCLUSION

Within the limitations of the study such as the denture bases are not exposed to varying magnitudes acting in different directions as in oral cavity and also the clinical situations a uniform thickness of denture base resin may not be 3 mm as used in the study, following conclusions were made that there were significant decreases in the impact strength of heat-polymerized denture base resins when immersed in denture cleanser solutions Clinsodent, VI Clean, and Clanden. In that, Clinsodent shows more reduction in the impact strength, followed by Clanden and VI-Clean denture cleansers.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.