The Effect of Chitosan Addition in Acrylic Resin Matrix towards the Residual Monomers and Impact Strength

 

Titik Ismiyati1*, Ananto Ali Alhasyimi2

1Faculty of Dentistry, Prostodontic Department, Gadjah Mada University, Indonesia

2Faculty of Dentistry, Orthodontic Department, Gadjah Mada University, Indonesia

*Corresponding Author E-mail: drg_titikis@ugm.ac.id

 

ABSTRACT:

Background: A residual monomer might have impact on the quality of acrylic resin since its caused allergic reactions and inflammation. Chitosan is a biocompatible material and potential to reduce residual monomers and ameliorate the impact strength of acrylic resin Objective of the study: To examine the effect of an acrylic resin matrix mixed with chitosan together with 1% and 2% acrylic acid as denture base and orthodontic material on residual monomers and impact strength. Methodology: There were 30 samples for the test analysis. The impact strength test sample formed with a plate size of 55 × 10 × 10mm, whereas the residual monomer test sample was prepared into powder. The test samples were divided into 3 groups, of 10 samples. Group 1 acrylic resin only, group 2 acrylic resin matrix mixed with chitosan and 1% acrylic acid, group 3 is the same as group 2 but with a concentration of 2% acrylic acid. Gas chromatography was used for measuring the residual monomers. The impact strength was tested by the Charpy impact. The data was evaluated using the ANOVA and correlation test. Results: There were significant differences (p < 0.05) in acrylic resin without addition with the matrix of acrylic resin with chitosan and acrylic acid 1% and 2% to the number of monomers and impact strength. Conclusion: The mixture of acrylic resin with chitosan and acrylic acid 1% and 2% can reduce the amount of residual monomer and increase the impact strength.

 

KEYWORDS: Denture, Orthodontic, Acrylic Resin, Chitosan, Residual Monomer, Impact Strength.

 

 


INTRODUCTION:

Acrylic resin is widely used for manufacturing removable dentures and removable orthodontic appliances because of its low-cost, easily repaired and the manufacturing process is easy. As much as 98% of denture base materials are made of acrylic resin1. The basic criteria for the acrylic resin to be used as a base for denture and orthodontic material are that it must be aesthetically satisfying, color stability can adjust the color of the surrounding tissue, dimensions should be stable and accurate, has good mechanical strength, and is perfectly polymerized2. Acrylic resins, however, have weaknesses in flexural strength and impact, and the presence of residual monomers which causes allergies and irritations. This is because the pores and the simple absorption properties of acrylic resins cause the development of fungi Candida albicans and the molecules contained in saliva3, to form plaque and are supported by the presence of residual monomers, so tissue inflammation, allergic reactions, and cytotoxic cells can occur. The use of dentures can be a factor for inflammation sometimes referred to as stomatitis denture4.

 

Acrylic resin base material is formed due to the polymerization process between polymethyl methacrylate polymer powder and methyl methacrylate monomer liquid. A residual monomer of 0.2%–0.5% will be formed when combined monomers and polymer ratios according to the manufacturer. Residual monomers can cause tissue irritation, allergic reactions and cytotoxic cells5,6. The number of residual monomers depends on the chemical composition, polymerization method, degree of conversion monomers, hydrophilic nature of monomers, storage time and immersion medium for dentures and removable orthodontic appliance. Reducing residual monomers can be achieved by offering additional treatment for polymerization of acrylic resin. Mixing silica with acrylic resin will reduce residual monomers and increase hardness7.

 

Chitosan is a material made from shrimp shells, processed through demineralization, deprotonation, and deacetylation8. Regarding its pharmacology cationic nature, chitosan has numerous physiological and biological properties such as biodegradability, low toxicity, strong biocompatibility and antimicrobial properties9,10. Chitosan is usually soluble at an acidic pH 11,12. Chitosan can also be combined with various various types of biomaterials such as alginate, hydroxyapatite, hyaluronic acid, calcium phosphate and growth factor13 The formation of polyelectrolyte complex by electrostatic interaction between groups from chitosan and COO- groups from polyacrylate acid was shown by evidence from infrared spectra14.

 

Acrylic resin mixture with chitosan can occur with the help of coupling agent material. The use of acrylic acid as a coupling agent material is due to the acrylic acid (CH2CHCO2H) when mixed with chitosan, a complex interpenetrating network bond structure can result in strong adhesion between surfaces. The mixture of thermoplastic nylon with chitosan nanoparticle can produce Candida albicans growth-inhibitory which has been characterized as fungistatic. Acrylic resin mixtures with chitosan at a concentration of 1%, 2% were non-toxic15, It is, necessary to study whether a mixture matrix capable of preventing the growth of Candida albicans can also minimize residual monomers and improve the impact strength.

 

The impact strength is indicated by the presence of the resilience of the polymer material which results in rupture, for example, acrylic resin dentures or removable orthodontic appliance when falling or in a collision will break. The limitations of the impact strength of acrylic resins against the impact strength are the reasons for the need for reinforcing agents that can be added to acrylic resins. Many techniques have been attempted to increase the shortcomings of the mechanical properties of acrylic resins, including the addition of materials such as chitosan and glass fiber16

 

A gas chromatograph (GC) is a tool used to measure the content of various components in a specimen. Analysis performed by a gas chromatograph is called gas chromatography. The working principle of GC is that the sample solution is injected into the helium or nitrogen gas carrier stream. The residual monomers will separate from other materials and several graphs generated on the screen17,18.

 

Depending on the nature and impact strength of residual monomers produced in the acrylic resin polymerization process, the problem arises if there is an effect of an acrylic resin mixture matrix with chitosan and 1% and 2% acrylic acid on residual monomers and impact strength. This study aims to investigate the effect of the acrylic resin mixture matrix with chitosan and 1% and 2% acrylic acid on residual monomers and impact strength.

 

Method:

The type of this research was a laboratory experimental research. The testing materials and tools include heat-cured acrylic resin (QC-20, Dentstply), plaster casts, Cold Mold Seal (CMS), vaseline, pumice chitosan, acrylic acid, acetone, spatula, rubber bowl. digital scales and measurement cups, stellon pot, cuvette, press, cellophane, brush, crownmess and stone bur, engine polish and vilt cone, tweezers, magnetic stirrer, distillation gray, and gas chromatography (Shimadzu, Japan).

 

The impact strength test sample was formed with a plate of size 55 × 10 × 10mm and in the residual monomer test, the sample was prepared into powder. Samples were divided into 3 groups of 10 samples. Group 1 (control) composed of acrylic resin without chitosan and acrylic acid mixture. Group 2 is made of a mixture of acrylic resin with chitosan and 1% acrylic acid. Group 3 is made of a mixture of acrylic resin with chitosan and 2% acrylic acid. A mixture of group 2 was made by weighing 1gram of chitosan, and then added 100ml of acrylic acid. Alternatively, the mixture of group 3 was made by weighting 2 grams of chitosan and dissolved in 100ml of acrylic acid. We mixed the mixture with a magnetic stirrer without heating and added 100ml of acetone until the material dissolves. The ratio of polymers: monomers: chitosan mixture for the 10 samples was 23gr: 10ml: 0.6ml. The mixture was stirred until phase dough, then put into a cuvette with molds that have been made according to sample size. The polymerization process was carried out with water until it boils (100oC) for 1 hour, followed by 30 minutes after boiling. Wait until the water was cool then remove, clean and polish the sample.

 

Impact strength testing used an 83cm arm length Charpy tool with a weight of 1kg. The test rod was mounted on its position and the pendulum was released, then the test rod is struck by the pendulum and then the pendulum swings until the sample is broken. The pendulum’s effort when hitting the test object or the effort sustained by the test object until it was broken in the form of numbers were then entered into the calculation of the formula for impact strength to obtain the impact strength value.

 

Calculation of residual monomers by immersing the test samples in a distillation flask with ethyl acetate 25ml for the residual monomer leaching process. Reflux was achieved with an oil heater that cooled water at a temperature of 130oC for 1. The solution obtained was then analyzed using a gas chromatograph device. Chromatograph gas devices are regulated according to NMAM (1994) standards for methyl methacrylate analysis. The technique employed was the Flame Ionization Detector (FID) which was specific to the hydrocarbon group. Gas chromatography for the analysis of methyl methacrylate, the carrier gas (Helium) would serve as an eluent that carries the analyte (methyl methacrylate) and the solvent (ethyl acetate) moved in the columns and undergoing an elution process. The movement of the analyte in the column depends on the time taken in the stationary phase and the affinity of the analyte in the stationary phase.

 

A chromatogram with an image of several analyte’s peaks would appear in the detector according to the analyte’s length of time in the stationary phase so that the retention time and retention area were obtained as parameters for calculating the concentration of the sample being sought. The number of residual monomers measured was in grams. Additionally, statistical tests were carried out on the data obtained from the two treatments.

 

RESULTS:

The average results of the acrylic resin matrix residual monomers mixed with chitosan and 1% and 2% acrylic acid, can be seen in Table 1 and Figure 1. The mean and standard deviation results showed that group 3 had the lowest mean results, indicating that compared to control and group 2 the mixture of acrylic resin with chitosan and 2% acrylic acid had the least residual monomers.

 

Figure 1: Diagram of mean and standard deviation of residual monomer in control and treatment group

 

Results of normality monomer residual test results using Shapiro–Wilk showed the significance value for each category of study variables > 0.05 so it could be inferred that the data from the study variable had normal distribution data. Levene test results of residual monomer variables had a significance value of 0.176, indicating a significance value > 0.05 so it was concluded that the residual monomer variable produces homogeneous data.

 

To evaluate the difference between the effect of acrylic resin mixture without the addition of chitosan with acrylic acid, and acrylic resin mixed with chitosan with 1% and 2% acrylic acid, it was analyzed using one-way ANOVA and the results can be seen in Table 2.

 


 

Table 1: Mean and standard deviations of residual monomer matrix mixed heat-cured acrylic resin (×10−3gr)

Group

Samples (N)

Mean ± SD

Control

10

0.589 ± 0.028

Group II

10

0.560 ± 0.009

Group III

10

0.536 ± 0.002

Note:

Group I: control group, Group II: matrix of acrylic resin mixed with chitosan and acrylic acid 1%, Group III: matrix of acrylic resin mixed with chitosan and acrylic acid 2%

 

Table 2: ANOVA on the amount of residual monomer of acrylic resin and acrylic resin acrylic matrix mixed with chitosan, and 1% and 2% acrylic acid

 

Number of squares

Degree of freedom

Mid Square

Variant test

Significance

Inter groups

0.013

2

0.006

1301.751

0.000

Intra group

0.000

24

0.000

 

 

Total

0.013

26

0.000

 

 

 


ANOVA results showed a significance of 0.000 (p < 0.05), indicating that the number of residual monomers between the control group and the treatment group (p < 0.05) varied significantly. This shows that the base made of acrylic resin without a mixture with a mixture of acrylic resin, chitosan, and acrylic acid showed a significant difference. The analysis continued with the Post hoc LSD test, the findings were a significant difference between groups 1, 2, and 3 (p < 0.05).

 

The average results of the impact strength among two groups can be seen in Table 3 and Figure 2. In Table 3 and Figure 2, it showed that group 3 had the greatest impact strength compared to group 2 and control.

 

Table 3: Average and standard deviation of impact strength of acrylic resin and acrylic resin matrix mixed with chitosan and acrylic acid

Group

Samples (N)

Mean ± SD

Control

10

5.030 ± 0.464

Group II

10

5.260 ± 0.371

Group III

10

5.980 ± 0.470

Note:

Group I: control, Group II: matrix of acrylic resin mixed with chitosan and acrylic acid 1%, Group III: matrix of acrylic resin mixed with chitosan and acrylic acid 2%

 

 

The normal distribution test using Shapiro–Wilk showed the significance value for each category of study variables > 0.05, group 1 (control) was 0.688, group 2 (treatment) was 0.754 and Group 3 (treatment) was 0.105, so it could be inferred that the impact strength variable data had a normal distribution. The homogeneity test was performed using Levene's test which obtained a significance value of 0.462, indicating it had a homogeneous variance between groups 1 (control), group 2 and group 3.

 


 

Figure 2: Mean and standard deviation diagram of impact strength of acrylic resin, and acrylic resin matrix mixed with chitosan and acrylic acid

 

Table 4: ANOVA on impact strength of acrylic resin without chitosan with acrylic acid and acrylic resin mixed with chitosan, and 1% and 2% acrylic acid

 

Number of squares

Degree of freedom

Mid Square

Variant test

Significance

Inter groups

4.913

2

2.456

12.801

0.000

Intra group

5.181

27

0.192

 

 

 

10.094

29

 

 

 

 


Results of the ANOVA analysis showed variations in the mean impact strength between treatments. Furthermore, an LSD test was performed to determine the location of the average difference in impact strength between treatments. The results showed a significant difference in the mean impact strength between group 1 (control) and group 3 (2%) and between-group 2 (1%) and group 3 (2%). In contrast, there was no significant difference in the mean impact strength between group 1 (control) and group 2 (1%).

 

Correlation analysis was conducted to test the study’s hypothesis 2, regarding the impact strength residual monomers, it was found that a correlation occurred between the residual monomer variables and impact strength variables. Hypothesis testing was performed using product-moment correlation analysis. Before analyzing the product-moment correlation, the normality of data assumptions was tested.

 

The normality test had been conducted with the test results showing the significance value for each study variable > 0.05 and it was concluded that the study variable data had a distribution that was normally distributed. The results of the normality assumption test showed that the study variable data had a normal distribution, so it can be continued with the product-moment correlation analysis and the correlation coefficient results obtained between the residual monomer variables with impact strength variables of −0.682 with a significance value of 0.000. since the significance value was less than α = 0.05 (5%), it means that there was a significant correlation between the residual monomer variables and the impact strength variable. The correlation coefficient was negative meaning the relationship between the two variables was contradictory. The greater the residual monomer, the lower the impact strength, and vice versa.

 

Also, the correlation graph presented in Figure 3 shows the correlation between residual monomer variables and impact strength variables. On the correlation graph between residual monomer variables with impact strength variables known determination coefficient (R Sq Linear) values of 0.465, which 46.5 % of the impact strength variation can be explained by residual monomers, while 53.5 was due to other factors.

 

Figure 3: Correlation graph of residual monomers and impact strengths

 

DISCUSSION:

In this study, the concentration of chitosan mixture with 2% acrylic acid showed a significant advantage in reducing the amount of residual monomer matrix of acrylic resin, chitosan, and acrylic acid mixtures. The decrease in residual monomers was due to the formation of chemical bonds between chitosan with polymers and monomers in acrylic resins with the help of acrylic acid which acts as a binder (coupling agent). Acrylic acid was added to reinforce the complex tissue. The hydroxyl group from acrylic acid may be an active binding site for chitosan and acrylic resin. Acrylic acid had carboxylic acid (COOH) and double bonds (C = O). Acidic carboxylates react with NH2 from base chitosan, while the acrylic acid double bond (C = O) reacts with acrylic resin monomers. The reaction will form polymer chains and cross bonds15.

 

If there will still be a residual monomer in the reaction of an acrylic resin mixture that is between a polymer and a monomer, the residual monomer formed will be reduced with the addition of chitosan and acrylic acid. This is because in polymerization, the monomers in the acrylic resin bind to form polymer bonds. Normally there is a residual monomer of 0.2 - 0.5% after the polymerization process, residual monomers can also reduce the mechanical strength of acrylic resins5,6. The 2% concentration of acrylic acid coupling agent material will help the processing of the residual monomer in the acrylic resin mixture forming a polymer bond of ± 0.18%.

 

In this study, the difference in impact strength between the control and treatment is probably due to the mixture of two materials which can produce a mixture of materials containing the properties of the two components such that other properties tend to make the mixture material into a matrix with better strength properties. This can be seen in the acrylic resin matrix mixture with chitosan and acrylic acid, the greater the concentration shows an increase in impact strength. Besides that, the possibility of influencing factors during the mixing and polymerization process that cannot be controlled during the study, including time and technique, and the imperfect stirring speed causes the homogeneous imperfect mixture such that the monomers remain residual, which was also observed in the impact strength properties during the analysis. The impact strength obtained from a mixture of acrylic resin matrix with chitosan and acrylic acid with a concentration of 1% and 2% was higher than that of 0.2 - 0.9 relatives to the standard acrylic resin without a mixture (control). The crossed carbon double bonds react with the oligomer during the reaction as it polymerized, forming bonds with the filler into a polymer matrix. This bond can add strength to the nature of physical strength, namely impact strength. The difference in impact strength decrease between the two groups of samples was in the range of impact strength values which were approximately the same so that there was no statistically significant difference.

 

In this study, a significant correlation was identified between residual monomer variables and impact strength variables. the correlation coefficient between the residual monomer variable and the impact strength variable was −0.6682. The negative correlation coefficient means the relationship between the two variables was the opposite. The greater the residual monomer, the lower the impact strength, and vice versa. It is possibly the residual monomer that can act as a plasticizer causing the acrylic resin to become more plastic and lower impact strength.19

 

Most residual monomers in the acrylic resin react to form a cross bond in a mixture of chitosan acrylic resin and with an acrylic acid coupling agent. Owing to the balance of strength between polar bonds and covalent bonds in the polymer chain, the change from residual monomers to polymers results in optimum mechanical strength3. The chain length of a molecule is indicated by the molecular weight. Long polymer chains mean it has a high molecular weight. The strength of a polymer to accept a load depends on the molecular weight of the polymer.5

 

CONCLUSION:

A mixture of acrylic resin with chitosan and acrylic acid 1% and 2% can reduce the amount of residual monomer and increase the impact strength.

 

ACKNOWLEDGMENT:

This work was supported by Faculty of Dentistry, Universitas Gadjah Mada.

 

CONFLICT OF INTEREST:

No competing interests were disclosed.

 

CONTRIBUTION OF AUTHORS:

Titik Ismiyati: Conceptualization, Data Curation, Funding Acquisition, Investigation, Methodology, Supervision, Validation, Visualization, Writing – Original Draft Preparation. Ananto Ali Alhasyimi: Conceptualization, Data Curation, Writing – Review and Editing

 

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Received on 21.04.2020            Modified on 29.05.2020

Accepted on 24.06.2020         © RJPT All right reserved

Research J. Pharm. and Tech. 2021; 14(4):2280-2285.

DOI: 10.52711/0974-360X.2021.00403