Effect of curcumin on physico-mechanical properties of heat polymerized denture base resin

Abstract

Purpose

Current denture base resins lack adequate strength and antimicrobial properties, necessitating the exploration of alternative solutions. The purpose of this study was to evaluate the effects of curcumin incorporation on the physico-mechanical properties of heat-cured denture base resin, filling a gap in the literature regarding this correlation.

Methods

Heat-cured denture base resin was supplemented with increasing concentrations of curcumin (CR). Groups were designated as CR-0 (0%), CR-0.05 (0.05%), CR-0.10 (0.10%), CR-0.50 (0.50%), and CR-1 (1%), based on the increasing concentrations of curcumin incorporated into the material. Physico-mechanical properties, including flexural strength, surface roughness, fracture toughness, impact strength, and color difference, were evaluated following the testing standards. Statistical analysis involved Kruskal-Wallis ANOVA followed by Dunn’s test for multiple comparisons, with significance set at P ≤ 0.05 and Bonferroni’s correction applied to p-values.

Results

Flexural strength peaked at 153.80 MPa in the CR-0.10 group, while surface roughness was lowest at 0.14 micrometers in the CR-0.50 group. Fracture toughness reached its highest value at 1.80 kJ/m^2 in the CR-0.05 group, and impact strength was greatest at 6.52 Joules in the CR-0.05 group. Additionally, color difference was least pronounced in the CR-0.50 group. Flexural strength, surface roughness, fracture toughness, impact strength, and color difference varied significantly among the control group and different curcumin concentrations (P < 0.05).

Conclusions

Incorporating curcumin into denture base resin alters both optical and mechanical properties. Further research is required to validate the findings and determine the optimal curcumin concentration without compromising the material efficacy.

Introduction

Poly methyl metha acrylate (PMMA) serves as the material of choice for fabrication of dentures [1]. It restores both function, aesthetics and offers numerous advantages. PMMA is preferred material for its favorable aesthetic properties, cost-effectiveness in fabrication and repair, biocompatibility with oral tissues, and ease of manipulation during fabrication. Additionally, PMMA offers excellent color stability and low density, making it an optimal choice for creating dentures that closely mimic natural dentition while ensuring satisfactory function and patient comfort [2]. Despite the widespread utilization of PMMA as denture base resin (DBR), they often face limitations in terms of strength and antimicrobial properties, necessitating efforts to enhance their performance, particularly for long-term clinical use [3, 4].

A composite material is defined as a system comprising two or more distinct materials, where one material, known as the matrix, surrounds and supports another material, known as the filler. For instance, in denture base resins, the matrix is typically the acrylic resin (polymer phase), and fillers such as glass, silica, or metal oxides are added to improve specific properties of the material. This combination allows the material to achieve properties that are superior to those of its individual components [4, 5]. Studies have explored various agents, such as glass fibers, carbon fibers, and zirconia, as well as composite agents like silica and alumina, along with antimicrobial additives [5–7]. These approaches offered numerous advantages that contribute to the functional, aesthetic, and long-term success of dental prostheses. However, the limitations associated with various composite materials include issues such as increased surface roughness, brittleness, reduced strength, and compromised translucency, as well as other functional and aesthetic considerations of the materials [8]. Given these limitations, need persist to explore alternative reinforcement materials that offer superior performance and address the shortcomings of existing options, particularly in strength, durability, PMMA compatibility, biocompatibility, and antimicrobial properties [9–12]. By identifying and utilizing such reinforcement materials, it can aim to develop DBRs that not only meet but exceed the clinical requirements for long-term success and patient satisfaction [13].

Among the incorporated materials, lesser studies evaluated on natural alternatives, such as curcumin. Curcumin is a bioactive compound derived from turmeric, it has multifaceted therapeutic properties, including antioxidant, anti-inflammatory, and antimicrobial effects [14–19]. Initial studies of curcumin suggests that it as a potential adjunctive agent with favorable biocompatibility and pharmacological profile [20–25]. However, comprehensive evaluation of curcumin-incorporated DBRs is less, and it requires further exploration to elucidate their efficacy and safety profiles.

The study aimed to evaluate the impact of curcumin on the physico-mechanical properties of DBRs, with a focus on strength enhancement and optical properties. The study investigated the influences of 0, 0.05, 0.10, 0.50, and 1% by weight of curcumin in denture base resin for flexural strength, fracture resistance, impact strength, surface roughness, and color stability of DBRs. The null hypothesis was that the incorporation of curcumin infused DBRs will lead to significant improvements in mechanical and optical properties. By elucidating the potential benefits of curcumin in DBRs, this study aims to contribute to the development of novel biomaterials with enhanced performance and clinical utility in prosthodontic practice.

Materials and methods

The study was approved by the Institutional Review Board of SRM Dental College (SRMDC/IRB/2021/MDS/NO.202). The estimated sample size for the study was 12 per group, with an alpha error of 1% (α = 0.01) and a power of 99%.

Autodesk123D Design software (Autodesk, USA) was used to create computer-aided design (CAD) models. The dies were printed using Anycubic Standard Resin (Anycubic, Shenzhen, China) through the PrusaSlicer software (Prusa Research a.s., Czech Republic) on an Anycubic Photon Ultra SLA printer (Anycubic, Shenzhen, China). Following retrieval, the dies were washed with an alcohol-based solution and light-cured in accordance with the manufacturer’s instructions (Anycubic Wash and Cure Machine, Shenzhen, China). Accuracy was assessed using a digital vernier caliper prior to duplication with putty addition silicone materials.

Wax patterns were fabricated from the putty scaffolds and adjusted to the required dimensions (Table 1). These patterns were then invested in dental flasks, followed by conventional flasking, dewaxing, and packed with heat-cure polymer PMMA denture base resin (Dental Products of India, DPI, India). The resin was polymerized using a long heat-cure cycle-approximately 9 h at 74 °C. Pre-extracted curcumin (Sigma Aldrich, Product No. C1386) was added to the polymer in increasing concentrations of 0, 0.05, 0.10, 0.50, and 1% by weight, forming the study groups: CR-0 (control), CR-0.05, CR-0.10, CR-0.50, and CR-1. The heat-cure resin, with an average particle size of 50 μm, was ball milled for 24 h using a mixture of 5 mm and 10 mm balls. Uniformity of the mixture was confirmed via SEM and FTIR analyses.

Table 1.

Tested parameters and specifications [5]

Property	Standards	Sample dimensions (mm)	Cross sectional speed	Manufacturer details
Flexural strength	ISO 20795-1-2013	64 × 10 × 3.3	5 mm/s	Instron 3365, Norwood, MA, US
Fracture toughness	ISO 20795-1-2013	32 × 4 × 8 Crack length 3 and 0.1	1 mm/s	Instron 3365, Norwood, MA, US
Impact strength	ASTM D-256	55 × 10 × 10	Pendulum load 0.5 Joules	Charpy impact test analyzer. Frank Bacon machinery sales company, Warren, MI
Surface roughness	British standard Institute Specification (1984) no. 771 (B.S.I)	12 × 12 × 3		Talysurf CCI, Taylore Hobson, Precision
Color difference	CIE-2000 ISO 20795-1:2013	50 ± 1 in diameter and 0.5 ± 0.1 thick		Konica Minolta, CM,

Following standard procedures, samples were fabricated, finished, polished, and stored in distilled water at 37 °C for 48 ± 2 h before testing. The established protocol involved mixing heat-cure PMMA powder and methyl methacrylate monomer in a 3:1 weight ratio. The mixture was mixed and dough consistency was achieved, packed into dewaxed molds, and polymerized in a water bath at 74 °C for 90 min, followed by a final cure at 100 °C for 30 min. After polymerization, the samples were deflasked, trimmed, and finished using progressively finer sandpaper (up to 600 grit). Polishing was done with a pumice slurry on a wet rag wheel for 2–3 min, to ensure a smooth, glossy finish free of surface irregularities. The polished samples were stored in distilled water at 37 °C for 48 ± 2 h prior to testing.

Testing procedures followed ISO standards 20795-1-2013 for assessing flexural strength, fracture toughness, and color difference, ASTM D-256 for evaluating impact strength, and British Standard Institute Specification (1984) no. 771 for analyzing surface roughness [5, 26–28]. Flexural strength was measured using a three-point universal testing machine, fracture toughness was determined with another universal testing machine, and Charpy’s impact strength was evaluated using an impact test analyzer. Surface roughness was assessed using a non-contact testing machine, while color difference was examined using a spectrophotometer under D65 standard illumination. The data was assessed for normality and statistically analysed using IBM SPSS Statistics for Windows, Version 28.0 (IBM Corp., Armonk, NY). A Kruskal-Wallis ANOVA was performed, followed by Dunn’s post hoc test with Bonferroni correction (P ≤ 0.05) Additionally, scanning electron microscopy (SEM) was employed to examine fracture surfaces for detecting porosity, defects, and the distribution of curcumin. Fourier Transform Infrared Spectroscopy (FTIR) was performed to provide insights into the chemical bonds present in the samples, aiding to understand the effects of curcumin addition on the polymer matrix of the denture base resin.

Results

Tables 2 and 3 displayed distinct trends among the experimental groups. The mean flexural strength exhibited a steady increase from CR-0 to CR-0.50, with the CR-0.50 group displaying the highest value. The differences were statistically significant (χ² = 56.689, P < 0.001). The mean fracture toughness was high in the CR-0.05 group and gradually declined towards the CR-1 group. The differences were statistically significant (χ² = 57.535, P < 0.001). Impact strength emulated this pattern, with the CR-0 group exhibiting the highest mean values and the CR-1 group showing the lowest. The differences were statistically significant (χ² = 56.822, P < 0.001). Conversely, the surface roughness demonstrated an inverse trend, with the lowest mean observed in the CR-0.5 group and a progressive increase towards the CR-1 group. Significant differences were evident across groups (χ² = 42.282, P < 0.001), particularly in comparisons between CR-0 and CR-0.05, CR-0 and CR-0.50, CR -0.05 and CR-1, CR-0.10 and CR-1, and CR-0.5 and CR-1 (Fig. 1a and e).

Table 2.

Descriptive statistics of all groups

		N	Minimum	Maximum	MEAN	Std. deviation	Median
	CR-0	12	85.00	88.00	86.20	1.04	86.00
	CR-0.05	12	133.00	135.90	134.51	0.89	134.65
Flexural strength	CR-0.10	12	152.89	154.50	153.80	0.38	153.85
	CR-0.50	12	146.90	148.01	147.70	0.31	147.77
	CR-1	12	90.80	92.90	91.82	0.64	91.85
	CR-0	12	1.71	1.74	1.73	0.01	1.73
	CR-0.05	12	1.79	1.83	1.80	0.01	1.80
Fracture toughness	CR-0.10	12	1.29	1.30	1.30	0.00	1.30
	CR-0.50	12	1.04	1.05	1.04	0.00	1.04
	CR-1	12	0.96	0.98	0.97	0.01	0.97
	CR-0	12	6.21	6.37	6.27	0.04	6.27
	CR-0.05	12	6.49	6.60	6.52	0.03	6.52
Impact strength	CR-0.10	12	4.69	4.81	4.74	0.03	4.74
	CR-0.50	12	4.45	4.65	4.54	0.05	4.53
	CR-1	12	4.30	4.41	4.37	0.03	4.37
	CR-0	12	0.18	0.440	0.31	0.08	0.34
	CR-0.05	12	0.15	0.21	0.18	0.03	0.17
Surface roughness	CR-0.10	12	0.20	0.25	0.22	0.02	0.21
	CR-0.50	12	0.09	0.23	0.14	0.07	0.10
	CR-1	12	0.46	0.88	0.62	0.19	0.53
	CR-0	12	0.44	0.44	0.44	0.00	0.44
	CR-0.05	12	26.00	28.00	27.06	0.50	27.01
Color difference	CR-0.10	12	25.50	26.00	25.72	0.16	25.80
	CR-0.50	12	21.00	22.00	21.51	0.31	21.50
	CR-1	12	26.99	28.90	27.72	0.53	27.85

Table 3.

Multiple pairwise comparison using Dunn’s post hoc test

Dependent variable	group	group	Z statistic	P value
Flexural strength	CR-0	CR-0.05	-24	0.008
		CR-0.10	-48	0.000
		CR-0.50	-36	0.000
		CR-1	-12	0.923
	CR-0.05	CR-0.10	-24	0.008
		CR-0.50	-12	0.923
		CR-1	-12	0.923
	CR-0.10	CR-0.50	-12	0.920
		CR-1	-36	0.000
	CR-0.50	CR-1	-24	0.008
Fracture toughness	CR-0	CR-0.05	-12	0.899
		CR-0.10	12	0.899
		CR-0.50	24	0.007
		CR-1	36	0.00
	CR-0.05	CR-0.10	24	0.007
		CR-0.50	36	0.00
		CR-1	48	0.00
	CR-0.10	CR-0.50	12	0.899
		CR-1	24	0.007
	CR-0.50	CR-1	12	0.899
Impact strength	CR-0	CR-0.05	-12	0.919
		CR-0.10	12	0.919
		CR-0.50	24	0.007
		CR-1	36	0.000
	CR-0.05	CR-0.10	24	0.007
		CR-0.50	36	0.000
		CR-1	48	0.000
	CR-0.10	CR-0.50	12	0.919
		CR-1	24	0.007
	CR-0.50	CR-1	12	0.919
Surface roughness	CR-0	CR-0.05	20.17	0.046
		CR-0.10	8.46	1.000
		CR-0.50	23.38	0.010
		CR-1	-17	0.168
	CR-0.05	CR-0.10	-11.71	0.996
		CR-0.50	3.21	1.000
		CR-1	-37.17	0.000
	CR-0.10	CR-0.50	14.92	0.359
		CR-1	-25.46	0.003
	CR-0.50	CR-1	-40.38	0.000
Color difference	CR-0	CR-0.05	-38.25	0.000
		CR-0.10	-24.04	0.007
		CR-0.50	-12	0.907
		CR-1	-45.71	0.000
	CR-0.05	CR-0.10	14.21	0.452
		CR-0.50	26.25	0.002
		CR-1	-7.46	1.000
	CR-0.10	CR-0.50	12.04	0.896
		CR-1	-21.67	0.023
	CR-0.50	CR-1	-33.71	0.007

Fig. 1.

(a) 3D surface analysis image of control group specimen. (b) 3D surface analysis image of CR-0.05 specimen. (c) 3D surface analysis image of CR-0.10 specimen. (d) 3D surface analysis image of CR-0.50 specimen. (e) 3D surface analysis image of CR-1 specimen

The color difference unveiled significant variations across all groups, with the highest discrepancy observed in the CR-1 group and these variations were statistically significant (χ² = 56.822, P < 0.001).

SEM analysis depicted a uniform surface with increasing concentrations of curcumin, though revealing fine cracks attributed to differences in agglomerates and uneven particle distribution in the matrix (Fig. 2a and e).

Fig. 2.

(a) SEM image of control group specimen. (b) SEM image of CR-0.05 specimen. (c) SEM image of CR-0.10 specimen. (d) SEM image of CR-0.50 specimen. (e) SEM image of CR-1 specimen

FTIR analysis focused on the polished surfaces of the test samples to determine the incorporation of curcumin into the polymer matrix and its effect on the overall chemical structure of the denture base resin. Fourier Transform Infrared Spectroscopy (FTIR) was employed to examine the chemical bonds in the denture base resin samples both with and without curcumin. Characteristic absorption bands of curcumin were identified, including a strong band around 1620 cm⁻¹ corresponding to C = O stretching, aromatic C = C stretching between 1500 and 1600 cm⁻¹, and O-H stretching vibrations observed around 3200–3500 cm⁻¹ (Fig. 3).

Fig. 3.

FTIR analysis of various concentrations of curcumin in denture base resin

Discussion

The study rejected the null hypothesis due to the observed variations in both mechanical and physical properties in the experimental groups. The study meticulously evaluated and compared the physico-mechanical properties of denture base resins incorporating curcumin. The results demonstrated an enhancement in flexural properties at the CR-0.10 concentration, followed by a decline at higher percentages. Conversely, CR-0.05 exhibited the highest impact strength, suggesting a concentration-dependent effect. Similarly, fracture toughness was high in the CR-0.05 group, indicating the potential of curcumin to reinforce the material.

The findings align with previous research which investigated the impact of curcumin on acrylic resin flexural strength [11, 15]. The study revealed that lower concentrations (1% and 3%) had no significant adverse effects, while 5% curcumin led to a notable decrease in flexural strength. This emphasizes the concentration-dependent nature of curcumin’s influence on mechanical properties, consistent with our observations.

The incorporation of curcumin into PMMA resin demonstrates a concentration-dependent effect on flexural strength. The study found that lower concentrations of curcumin enhance the material’s flexural strength, while higher concentrations result in a decrease. This phenomenon may be attributed to several underlying mechanisms. At lower concentrations, curcumin could facilitate improved polymerization by enhancing the cross-linking density within the resin matrix, leading to increased structural integrity. Additionally, curcumin’s antioxidant properties may play a role in reducing free radicals during the curing process, further promoting optimal mechanical properties. Conversely, at higher concentrations, the presence of curcumin might lead to agglomeration or uneven distribution within the matrix, adversely affecting the polymer’s mechanical performance. This aligns with findings from Khan et al. [9, 10] which emphasize that the mechanical properties of modified denture base materials can be compromised by excessive filler concentrations due to poor dispersion and increased viscosity. The concentration-dependent effects of curcumin on the flexural strength of PMMA is critical for optimizing its application in prosthodontics. Further investigation into the specific mechanisms at play will provide a deeper understanding of how curcumin modifications can be effectively utilized to enhance denture base materials [15–17].

He Y et al. [29] and Bhatt et al. [30] highlighted curcumin’s impact on surface properties. The reduction in surface roughness in the CR-0.5 group suggests curcumin’s potential to contribute to smoother surfaces, offering advantages in applications requiring improved tactile qualities. Conversely, the increase in surface roughness in the CR-1 group may pose challenges in biomedical applications where smoother surfaces are crucial.

Mirizadeh A et al. [6] and Puri G et al. [10] observed curcumin’s potential as a toughening agent for polymers. The highest fracture toughness observed in the CR-0.05 group implies that curcumin, at this concentration, may enhance the material’s ability to resist fracture, thus enhancing its suitability for structural applications.

The addition of curcumin can enhance fracture resistance in denture base resins through several mechanisms. Curcumin acts as a natural filler, providing reinforcement to the polymer matrix. Its incorporation can improve the dispersion of the resin and create a more homogeneous material, which contributes to better load distribution during stress. Unlike traditional fiber reinforcements that often rely on chemical bonding or silanization, curcumin can interact with the polymer matrix through hydrogen bonding and other intermolecular forces. This can enhance the interfacial adhesion between the curcumin and the acrylic polymer, leading to improved mechanical properties. Curcumin has a unique structure that can absorb energy, which helps to dissipate stress during loading. This energy absorption can lead to increased toughness and resistance to crack propagation. Curcumin’s antioxidant properties may also contribute to the longevity and durability of the denture base resin, reducing degradation over time and maintaining fracture resistance. While traditional reinforcements like fibers and fillers depend on specific bonding mechanisms, the addition of curcumin can improve fracture resistance through a combination of physical reinforcement, chemical interactions, and enhanced toughness. (15 –17)

The color differences observed in this study were significant. The ΔE values suggest that while the addition of curcumin introduced a perceivable color change and it remained within acceptable clinical limits for denture base materials. Curcumin’s inherent yellow pigmentation likely contributes to the color changes. However, the concentration-dependent nature of curcumin incorporation means that higher concentrations can lead to more pronounced changes in the shade of the resin. Despite these changes, the results indicate that at lower concentrations, the color difference is subtle and clinically acceptable. The results align with previous studies on the incorporation of pigments or natural compounds into PMMA, where the balance between concentration and aesthetic acceptability is critical [9, 10]. Future studies can investigate the optimizing concentration of curcumin to maintain mechanical properties while minimizing the impact on color.

The incorporation of curcumin into denture base resins enhanced the mechanical and physical properties. However, careful consideration of curcumin concentration is essential to optimize these properties for specific applications, with potential implications for material performance in diverse clinical and biomedical settings. Further research exploring the multifaceted effects of curcumin on material properties is essential to unlock its full potential for prosthetic applications.

The study provides valuable insights into the effects of curcumin incorporation on denture base resins, but it is not without limitations. The study focused on mechanical and physical properties, without exploring other potential benefits or drawbacks of curcumin incorporation, such as its effect on microbial adhesion or biocompatibility over longer periods. Additionally, the study evaluated curcumin concentrations up to 1%, but higher concentrations may yield different results that warrant investigation. Furthermore, the study design did not account for potential variations in curcumin distribution within the resin matrix, which could influence the observed properties. Future studies could employ advanced imaging techniques, such as confocal microscopy, to analyze the spatial distribution of curcumin and its impact on material properties more comprehensively. Moreover, the study was conducted under controlled laboratory conditions, and the findings may not fully translate to clinical settings. Long-term clinical trials are needed to assess the performance of curcumin-incorporated denture base resins in real-world scenarios, including their durability, biocompatibility, and resistance to staining or degradation over time.

Despite these limitations, the study provides a foundation for further research into the potential applications of curcumin in dental materials. Clinically, incorporating curcumin into denture base resins could enhance durability and offer antimicrobial benefits, potentially improving patient satisfaction and reducing infection risks. Future investigations can explore novel formulations, delivery methods, or combinations with other bioactive agents to optimize the properties of denture base resins for improved patient outcomes and satisfaction.

Conclusion

The study revealed the following insights on the effects of curcumin in denture base resins:

1. Optimal flexural strength was achieved at 0.10% curcumin concentration, with strength decreasing at higher concentrations, showing a concentration-dependent impact.

2. Surface roughness varied, with CR-1 having the highest and CR-0.50 the lowest, likely due to curcumin concentration affecting surface quality.

3. CR-0.05 exhibited the highest impact strength, while CR-1 had the lowest, suggesting curcumin’s role in improving material durability.

4. CR-0.05 also showed the highest fracture toughness, indicating curcumin’s ability to enhance material resilience and fracture resistance.

5. CR-1 displayed the highest color difference, highlighting significant alterations in physical and optical properties even with small curcumin concentrations. Thus, careful curcumin level management is crucial for maintaining desired color stability in dental prostheses.

Author contributions

A.M: Data curation, investigation, Resources, Reviewing.N.G.C: Conceptualisation, Methodology, Original draft preparation, Data Interpretation Resources, Reviewing and Editing.M.B : Resources, Data interpretation, Reviewing.

Funding

No external grants or funds received.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Competing interests

The authors declare no competing interests.