Alginate Impression Material Reinforcement Using Polymethyl Methacrylate as Organic Filler

Abstract

Objectives Dental alginate is one of the impression materials used in dentistry to reproduce intra- and extraoral structures. Alginate is a quite affordable and easy-to-use material, but because of its lower tear strength, it still has limitations in terms of accuracy. One way to increase the tear strength of alginate is by adding fillers. Polymethyl methacrylate (PMMA) is an example of an organic filler that can be utilized as an alternative reinforcement that could effectively increase dimensional stability. Thus, the purpose of this study was to evaluate the alginate's tear strength following the addition of PMMA as organic fillers.

Materials and Methods This experimental research consisted of four group samples. Sample A served as controls, while sample B included treated samples with varying PMMA additions of 3wt% (B1), 5wt% (B2), and 7wt% (B3). Each group had five samples. The tear strength test was conducted according to ISO Standard 21563:2021 using a Universal Testing Machine, which was followed by characterization using Scanning Electron Microscope (SEM) and Fourier Transform Infra-Red (FTIR) spectroscopy.

Statistical Analysis The tear strength results were then evaluated by One-Way Analysis of Variance (ANOVA) following Tukey's test (p < 0.05).

Results The tear strength of the control sample (A) was 0.540 N/mm. Meanwhile, the treated samples had tear strengths of 0.612 N/mm (B1), 0.663 N/mm (B2), and 0.596 N/mm (B3). There was a difference between the control and the treated samples that used PMMA fillers (p < 0.05). These results are supported by SEM and FTIR results related to physical closure or blocking of the alginate porous structure and the slight changes in its functional group.

Conclusion The addition of PMMA fillers to dental alginate provides reinforcement as the tear strength increases. This could impact the accuracy of the impression especially when the material is quickly removed from the oral structures. Additional investigation may assess the biocompatibility attributes further.

Keywords

dental alginate - polymethyl methacrylate filler - tear strength - reinforcement

Introduction

The dental materials used in today's era of advanced dentistry are also evolving. A variety of materials that can be used to create tooth impressions are currently needed in the field of dentistry. These imprints are used to create orthodontic appliances, prosthetic teeth, etc. The impression material must be accurate, easy for the dentist to use, comfortable on the mouth, and resistant to tearing when taken out of the mouth.[1] [2] [3]

At the moment, hydrocolloid impression materials are widely utilized in a variety of dental procedures. The most commonly used materials for hydrocolloid impressions are irreversible ones, like alginate. Because it is inexpensive, hydrophilic, and simple to work with, alginate is frequently used as a diagnostic impression material.[1] [4] [5] Another reason alginate is used as an impression material in dentistry is because it has good biocompatibility in the mouth.[2]

Dental alginate is a material with low tear strength, which is one of its drawbacks. The alginate material tears more easily as a consequence of this.[1] [6] Alginate has a tear strength between 0.4 and 0.7 N/mm.[7] Polysulfide is one of the elastomeric impression materials with a tear strength of 2.5 to 7.0 N/mm.[8] This demonstrates that the alginate's tear strength is less than that of other impression materials. Adding a filler is one method of strengthening the impression materials' tear resistance.[1] [9] [10]

In dentistry, fillers are frequently used to enhance dispersion, biocompatibility, and high strength. In general, fillers are used in dentistry at concentrations of 3wt%, 5wt%, and 7wt%.[11] Both inorganic and organic fillers are utilized. When choosing fillers, organic fillers are more biocompatible than inorganic fillers. One of the reasons why organic fillers more advantages is because they have low density, are more affordable, save energy, can be recycled, are widely available throughout the world and long lasting, have nonabrasive properties, are nontoxic, and are easy to process.[12] [13] One of the organic fillers widely used is a filler derived from the methyl methacrylate (MMA) monomer.[14]

MMA is a monomer that can polymerize into the polymer polymethyl methacrylate (PMMA).[15] PMMA has the advantages of being easy to synthesize, economic, translucency, good chemical stability, and easy to catalyze.[14] PMMA is frequently reinforced with fillers to strengthen its use as denture base that can withstand flexural strength and modulus. To the best of the authors' knowledge, PMMA has never been used to enhance alginate impression materials. Even according to research conducted by Acosta et al,[14] MMA, which is polymerized into wood through impregnation, can increase dimensional stability, density, and mechanical properties.[14] [16]

According to the above observations, PMMA as an organic filler might be possible to be used as an alternative filler for improvement of mechanical properties.[8] [17] Therefore, in this research, the aim of the study is to evaluate the tear strength changes that occur by the addition of the PMMA organic filler to the alginate impression materials.

Materials and Methods

Sample Preparation

The study was conducted using a quasi-experimental design and an experimental methodology. Since this study did not directly or indirectly involve humans or animals, ethical approval was not required. The alginate impression material's tear strength was determined in the absence of fillers and in the presence of PMMA fillers. The samples were categorized into four groups with five samples in each group. Sample A served as the control sample without the addition of PMMA fillers, while sample B included treated samples with the addition of 3wt% PMMA fillers (sample B1), 5wt% PMMA fillers (sample B2), and 7wt% PMMA fillers (sample B3).[11] Alginate with the brand Cavex CA37 Normal Set and PMMA powder with the Hillon brand (S Court Limited, England) were used as received. The samples as seen in [Fig. 1] were made using a double pants–shaped polymeric mold with dimensions of 10 cm length, 2 cm width, and 4 mm thickness according to ISO Standard 21563:2021 for Alginate Impression Materials specifications.[18]

Fig. 1 Double pants alginate sample.

Sample A was made by measuring the alginate powder and water according to the manufacture requirements. Alginate powder and water were mixed using a spatula in a rubber bowl according to the alginate working time. The stirred samples were poured into a polymeric mold measuring 10 cm × 2 cm × 4 mm and 90-dgree angle in the middle to facilitate the stress concentration point as seen in [Fig. 1]. The mold was closed and held using a weight of 500 g to ensure that no air was trapped inside.[17] After setting, the samples were removed.

Sample B was made by measuring alginate powder, water, and PMMA filler powder according to the required concentration, which was 3wt% concentration for sample B1, 5wt% concentration for Sample B2, and 7wt% concentration for sample B3. The alginate powder weight was reduced according to the weight percentage concentration of the PMMA powder used. To ensure homogenous mixing, alginate powder and PMMA filler were then mixed and stirred using an overhead stirrer for 2 minutes.[6] The alginate powder and PMMA powder were then mixed using a spatula with water in accordance to the alginate working time. As long as no powder remains unmixed, it will be possible to clearly visually confirm a homogenous mixture. The stirred sample is poured into a polymeric mold with the same size of sample A. The mold was also closed and held using a weight of 500 g.[17] The mold was closed to prevent air bubble formation. After setting, the sample was removed.

Tear Strength Test

The tear strength test can determine the ability of impression materials to withstand pressure during removal from the mouth. The test was carried out using a Universal Testing Machine (Llyod Instruments LRX Plus). The samples were mounted on the machine and was set at 500 mm/min and operated until the sample was a failure, which was indicated by the samples being torn apart.[18] The tear strength was calculated by dividing the force required for tearing by the thickness of the sample.[17] [18] Alginate impression materials must have a minimum tear strength of 0.38 N/mm in accordance with the ISO 21563:2021 specifications.[18] Tear strength data results were then submitted to statistical analysis of variance (one-way ANOVA), following the Tukey test (p < 0.05). The data were then analyzed using IBM SPSS 26.0 software.

Sample Characterization

All of the alginate samples were then characterized using Scanning Electron Microscope (SEM; JSM-6510A) to evaluate the morphological and filler particle interaction. The supported data were also taken also with a Fourier Transform Infra-Red (FTIR) spectrometer (Prestige 21 Shimadzu, Japan) to determine the functional group that allowed for qualitative identification of the material components. The FTIR spectra were obtained by taking 40 measurements at a wavenumber between 4,000/cm and 400/cm at a resolution of 4/cm.

Result

[Table 1] shows that the highest tear strength of the alginate impression material was observed in group B2 (alginate with the addition of MMA fillers with a concentration of 5wt%), which measured 0.663 N/mm. The second highest tear strength was observed in group B1 (alginate with the addition of PMMA fillers with a concentration of 3wt%), the third highest tear strength was observed in group B3 (alginate with the addition PMMA fillers with a concentration of 7wt%), and the lowest tear strength was observed in group A (control group, alginate without the addition of PMMA fillers). Therefore, it could be stated that the tear strength of alginate with the addition of MMA fillers tends to be greater than alginate without the addition of PMMA fillers.

Table 1 Descriptive analysis of tear strength results (N/mm)

Test	Treatment group
	A	B1	B2	B3
	Control	Filler 3wt%	Filler 5wt%	Filler 7wt%
1	0.576	0.572	0.720	0.629
2	0.534	0.629	0.695	0.583
3	0.531	0.576	0.633	0.635
4	0.550	0.624	0.655	0.564
5	0.509	0.660	0.610	0.566
Mean	0.540	0.612	0.663	0.596
Standard deviation	0.025	0.037	0.045	0.034

A one-way ANOVA test was carried out with the confidence level set at 95% and the test error rate (α) at 5%. As shown in [Table 2], by using the p-value criterion, a p-value of 0.001 was obtained, which is less than 0.05. The results of one-way ANOVA test concluded that there were differences in the average tear strength results of alginate impression materials in the four sample groups.

Table 2 One-Way Analysis of Variance (ANOVA) test results

	Sum of squares	df	Mean square	F	Sig
Between groups	0.038	3	0.013	9.861	0.001
Within groups	0.021	16	0.001
Total	0.059	19

As seen in [Table 3], sample B3 had a higher tear strength value of 0.056 N/mm than sample A, but the difference was not significant (Sig 0.109 > 0.05). Sample B1 had a higher tear strength value of 0.072 N/mm than sample A, and the difference was significant (Sig 0.027 < 0.05). Sample B2 had a higher tear strength value of 0.123 N/mm than sample A, and the difference was declared significant (Sig 0.000 < 0.05). Sample B1 had a higher tear strength value of 0.017 N/mm than sample B3, but the difference was not significant (Sig 0.885 > 0.05). Sample B2 had a higher tear strength value of 0.067 N/mm than Sample B3, and the difference was declared significant (Sig 0.042 < 0.05). Sample B2 had a higher tear strength value of 0.051 N/mm than sample B1, but the difference was not significant (Sig 0.160 < 0.05).

Table 3 Details of average differences and significance of further tests (Tukey's test)

Group comparison			Average difference	Sig
Sample A	–	Sample B3	–0.056	0.109
Sample A	–	Sample B1	–0.072	0.027[*]
Sample A	–	Sample B2	–0.123	0.000[*]
Sample B3	–	Sample B1	–0.017	0.885
Sample B3	–	Sample B2	–0.067	0.042[*]
Sample B1	–	Sample B2	–0.051	0.160

^* significant result < 0.05.

[Fig. 2] shows that sample A contains inorganic–inorganic fillers that bond with each other. Sample B2 looks denser compared to samples A, B1, and B3. Meanwhile, sample B3 looks denser than sample A. As observed in [Fig. 3], PMMA filler particles can be seen in samples B1, B2, and B3, which are spherical with a solid consistency. These filler particles were observed filling the porous areas in sample B with the fewest filler particles is seen in sample B1.

Fig. 2 SEM results in 1,000x magnification. (A) Sample A. (B) Sample B1. (C) Sample B2. (D) Sample B3.

Fig. 3 SEM results in 100x magnification. (A) Sample B1. (B) Sample B2. (C) Sample B3.

The FTIR spectra shown in [Fig. 4] revealed OH and (–COOH) functional groups at wavenumbers 3,200 to 3,400/cm detected as alginate molecules. On the other hand, CH₂ stretching was observed at wavenumber 2,928/cm. The stretching vibrations of C–O bonds in sample A appeared at 1,128 and 1,009/cm, and the C–O–C stretching vibration was detected after treatment with PMMA organic fillers. The other observation is the change in stretching vibrations of C–H bonds at 788/cm.[19] The detected functional groups allowed for qualitative identification of the impression material components, distinguishing between native alginate and the treated product.[20]

Fig. 4 Fourier transform infrared result.

Discussion

Alginate is an impression material that has low tear strength. Based on research by Takarini et al,[13] the impression materials with the addition of organic fillers can increase biocompatibility and good strength. Research by Acosta et al[14] shows that if MMA was used as an organic filler, it can increase dimensional stability, density, and mechanical properties. These studies support our findings of an increase in the tear strength of alginate with the addition PMMA fillers. The highest increase occurred in alginate with the addition of filler concentration of 5wt%. The increase in tear strength of alginate after adding the PMMA fillers occurred due to increased dimensional stability. This increase occurs due to the physical bond between PMMA and alginate and physical closure or blocking of the porous structure in the alginate.[14] [19] [21] Increasing dimensional stability can increase mechanical properties, one of which is the tear strength. This is in line with the research by Acosta et al.[14] MMA can improve mechanical properties by physically bonding and physically closing the existing space.

There was decreased alginate tear strength after adding PMMA fillers at a concentration of 7wt%. This was probably because of overuse of fillers. Adding too much filler can cause poor physical bonding, which makes the existing porous structure too large to be covered. This can cause a decrease in dimensional stability of the alginate, which reduces the tear strength of the alginate. This is in line with the research by Vallés et al.[22] MMA as a filler can improve the mechanical properties of a material. However, certain concentrations can cause a decrease in the mechanical properties of a material. Based on research by Abdelraouf et al,[6] it was found that adding more powder than the proper ratio could increase the tear strength of the alginate. Alginate has low tear strength when more water is added than the proper ratio. When alginate is added with the PMMA filler powder, the ratio of alginate powder is reduced from the proper ratio, which can cause the water ratio to be more than the powder ratio. Due to the ability of the PMMA filler, reducing the powder ratio should not result in a reduction in the tear strength of the alginate.

Alginate and MMA can also bond chemically. Alginate and MMA require an initiator to chemically bond. The initiator used is benzoyl peroxide. Because there is no addition of initiator in the process, alginate and PMMA fillers only bond physically.[23] Alginate that was added with PMMA fillers only shows physical bonding, as proven by SEM and FTIR characterization. The PMMA fillers are spherical in shape and could be seen filling up the porous area as detected from the SEM result, since the size of the particles itself is around 50 µm, which categorizes these as relatively large filler particles.[24] The predicted bond is only Van der Waals force,[24] which is proven by the stretching vibration of the functional group after treatment with the addition of PMMA fillers supported by the FTIR result.

According to Zafar,[25] if MMA polymerizes, it can increase the toxicity of the material. Self-curing MMA materials have a higher level of toxicity compared to heat-curing MMA materials.[25] [26] In this study, alginate did not chemically bond with MMA, because no initiator was used. Therefore, there is no increase in toxicity of alginate with the addition of PMMA fillers. However, further research is needed regarding the biocompatibility of PMMA if it is used as a filler that physically bonds with alginate. Another factor is the short-term use of alginate impression material in the mouth. Alginate only requires a setting time of 1 minute, so even if an initiator is added to the alginate with PMMA fillers, it will not affect the level of toxicity in the mouth. This is due to the polymerization time of MMA, which takes an estimated 10 minutes.[26] However, further research is needed regarding the use of MMA fillers that polymerize or chemically bond with alginate. The suggestion that can be given is to use heat-curing PMMA fillers that have a lower level of toxicity compared to self-curing MMAs.[26]

One of the mechanical properties of alginate that improve when PMMA fillers are added is the tear strength. This finding is consistent with that of Saskianti et al who found that structural integrity could also be enhanced by the natural properties of PMMA, which is composed of the carbon (C), oxygen (O), and hydrogen (H) elements, which contribute to mechanical stability.[14] [27] Further research could focus on testing other mechanical properties, such as tensile strength or flexural strength, of alginate with the addition of PMMA fillers in order to make this organic filler applicable as a reinforcement for dental impression materials.

Conclusions

The addition of PMMA fillers to alginate in this study resulted in an increase in the tear strength of the alginate. The tear strengths of alginate varied with the addition of different concentrations of PMMA fillers. The highest increase in tear strength in alginate was observed when a PMMA filler concentration of 5wt% was added.

Conflict of Interest

None declared.

• References

• 1 Singh S, Mishra SK, Kumar P. An in-vitro evaluation of impact of water hardness on tear strength of alginate impression material. Rama Univ J Dent Sci 2021; 7 (04) 9-13
• 2 Adamiak K, Sionkowska A. State of innovation in alginate-based materials. Mar Drugs 2023; 21 (06) 1-26
• 3 Chandran SK, Jaini JL, Babu AS, Mathew A, Keepanasseril A. Digital versus conventional impressions in dentistry: a systematic review. J Clin Diagn Res 2019; 13 (04) ZE01-ZE06
• 4 Zdiri K, Cayla A, Elamri A, Erard A, Salaun F. Alginate-based bio-composites and their potential applications. J Funct Biomater 2022; 13 (03) 1-31
• 5 Helmiyati AM. Characterization and properties of sodium alginate from brown algae used as an ecofriendly superabsorbent. IOP Conf Ser Mater Sci Eng 2017; 188: 012019
• 6 Abdelraouf RM, Bayoumi RE, Hamdy TM. Effect of powder/water ratio variation on viscosity, tear strength and detail reproduction of dental alginate impression material (in vitro and clinical study). Polymers (Basel) 2021; 13 (17) 1-11
• 7 Fayaz A, Noori A. Evaluation of tear strength of two types of Iralgin and its comparison with similar alginate impression material. J Dent Sch 2016; 34 (01) 28-33
• 8 Anusavice KJ, Shen C, Rawls HR. Phillips's Science of Dental Materials. 12th ed.. St. Louis, MO: Elsevier Inc.; 2013: 152-181
• 9 Kaidi S, Bentiss F, Jama C. et al. Isolation and structural characterization of alginates from the kelp species Laminaria ochroleuca and Saccorhiza polyschides from the Atlantic Coast of Morocco. Colloids Interfaces 2022; 6 (04) 51
• 10 Vaderhobli RM. Advances in dental materials. Dent Clin North Am 2011; 55 (03) 619-625 , x
• 11 Alhotan A, Yates J, Zidan S, Haider J, Silikas N. Flexural strength and hardness of filler-reinforced PMMA targeted for denture base application. Materials (Basel) 2021; 14 (10) 1-14
• 12 Ali U, Karim KJBA, Buang NA. A review of the properties and applications of poly (methyl methacrylate) (PMMA). Polym Rev 2015; 55 (04) 678-705
• 13 Takarini V, Asri LATW, Suratman R, Hadi BK. The potential use of Indonesian glutinous rice flour as nanoparticles organic filler for dental impression materials. IOP Conf Ser Mater Sci Eng 2020; 1007: 012003
• 14 Acosta AP, Labidi J, Schulz HR. et al. Thermochemical and mechanical properties of pine wood treated by in situ polymerization of methyl methacrylate (MMA). Forests 2020; 11 (07) 1-10
• 15 Zhang Y, Wang Y, Kong X, Zhao D. Mechanical properties of methyl methacrylate copolymers. Presented at: Asia-Pacific Energy Equipment Engineering Research Conference (AP3ER 2015); June 13–14, 2015; Zhuhai, China
• 16 Dong X, Sun T, Liu Y, Li C, Li Y. Structure and properties of polymer-impregnated wood prepared by in-situ polymerization of reactive monomers. BioResources 2015; 10 (04) 7854-7864
• 17 Singer L, Bourauel C. Mechanical and physical properties of an experimental chemically and green-nano improved dental alginate after proven antimicrobial potentials. Gels 2023; 9 (05) 1-12
• 18 International Organization for Standardization (ISO). ISO 21563:2021: Dentistry—Hydrocolloid Impression Materials. Geneva, Switzerland: ISO; 2021
• 19 Abdollahi H, Najafi V, Amiri F. Determination of monomer reactivity ratios and thermal properties of poly(GMA-co-MMA) copolymers. Polym Bull 2021; 78 (01) 493-511
• 20 Raszewski Z, Mikulewicz M, Brzakalski D, Pakula D, Przekop RE. Comparison of the bioactive and bacteriostatic performance of different alginate-based dental prosthetic impression materials with and without zirconium phosphate-based ion exchange resin containing silver: an in vitro study. Appl Sci 2023; 13 (21) 11639
• 21 Abdelraouf RM. Chemical analysis and microstructure examination of extended-pour alginate impression versus conventional one (characterization of dental extended-pour alginate). Int J Polym Mater 2018; 67 (10) 612-618
• 22 Vallés C, Papageorgiou DG, Lin F. et al. PMMA-grafted graphene nanoplatelets to reinforce the mechanical and thermal properties of PMMA composites. Carbon 2020; 157: 750-760
• 23 Salisu A, Sanagi MM, Karim KJA, Pourmand N, Ibrahim WAW. Adsorption of methylene blue on alginate-grafted-Poly (methyl methacrylate). J Teknol 2015; 76 (13) 19-25
• 24 Meincke DK, Ogliari AdeO, Ogliari FA. Influence of different fillers on the properties of an experimental vinyl polysiloxane. Braz Oral Res 2016; 30 (01) 1-10
• 25 Zafar MS. Prosthodontic applications of polymethyl methacrylate (PMMA): an update. Polymers (Basel) 2020; 12 (10) 1-35
• 26 Arenas-Arrocena MC, Argueta-Figueroa L, García-Contreras R. et al. New trends for the processing of poly(methyl methacrylate) biomaterial for dental prosthodontics. In: Reddy BSR. eds. Acrylic Polymers in Healthcare. London: Intech Open; 2017: 43-74
• 27 Saskianti T, Purnamasari S, Pradopo S. et al. The effect of mixed polymethylmethacrylate and hydroxyapatite on viability of stem cell from human exfoliated deciduous teeth and osteoblast. Eur J Dent 2024; 18 (01) 314-320

Publication History

Article published online:
20 January 2025