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. 2025 Jun 2;25:874. doi: 10.1186/s12903-025-06321-7

Effect of addition of hemp fiber and lignin-pectin-free hemp fiber to poly(methyl methacrylate) on surface roughness property

Süha Kuşçu 1,✉, Fatma Dilara Baysan 2, Nesrin Korkmaz 3
PMCID: PMC12128366  PMID: 40457295

Abstract

Background

This study aimed to evaluate the effect of hemp fiber (HeF) and lignin-pectin-free HeF addition on the surface roughness of poly(methyl methacrylate) (PMMA) together with the Finishing and Polishing process.

Methods

HeF and lignin-pectin-free HeF were used at a rate of 1%. This study uses three groups: Finishing groups (FG), Universal Polishing Paste groups (UP), and Lesk Polishing Liquid groups (LP). Each group has subgroups consisting of PMMA, PMMA + 1% HeF, and PMMA + 1% lignin-pectin-free HeF. ‘finishing’ and ‘polishing’ processes were applied to the prepared samples. Surface roughness was measured ‘finishing’ and ‘polishing’ processes using a profilometer. SEM and EDX analyses were performed in the characterization. One-way ANOVA evaluated surface roughness. P = 0.05 was set as the level of statistical significance.

Results

Statistical analysis showed that there were significant differences in surface roughness between the sample materials for PMMA + 1% HeF + ‘finishing’ (FG2) group in the ‘finishing’ process and PMMA + 1% HeF + Universal Polishing Paste (PG2) group in the ‘polishing’ process (p < 0.05). The mean Ra values ​​of the PG group in the ‘polishing’ process were found to be significantly higher than those of the PMMA + Lesk Polishing Liquid (LP) group (p < 0.05). The null hypothesis was rejected, and HeF increased surface roughness. ‘finishing’, with varying results, Polishing depending on the paste (PG) or liquid material (LP) used. Reducing surface roughness in dental materials is crucial to minimize microbial adhesion and colonization.

Conclusion

The findings suggest that hemp fibers increase roughness before polishing, and effective polishing can alleviate this, potentially reducing microbial adhesion and improving overall oral hygiene in clinical settings.

Keywords: Hemp fiber, PMMA, Surface roughness

Background

Poly(methyl methacrylate) (PMMA) is widely used for prosthetic bases due to its workability and aesthetics [1–6]. It is utilized in various prosthetics, including removable partial and complete dentures, space maintainers, overdenture prostheses, and maxillofacial prostheses [7, 8]. Dental prostheses mimic the lost hard and soft tissues within the oral cavity. They redirect the forces generated during chewing to the underlying alveolar bone [8, 9]. The most commonly used removable space maintainers to prevent space loss in multiple early primary tooth loss in children are simple acrylic and removable partial dentures. Removable partial dentures are preferred because they help to chew, improve aesthetics, and prevent unwanted tongue habits [10]. Removable space maintainers used in children are prone to cracking or fracturing due to occlusal forces and fatigue caused by insertion and removal [11, 12]. Therefore, dental prostheses and removable space maintainers must resist chewing forces, cracking, and fracturing. Additionally, they should have minimal surface roughness to reduce plaque accumulation.

Although PMMA is the most commonly used material for prosthetic bases, its mechanical properties impose certain limitations on the material [13, 14]. Various fibers have been incorporated to enhance the mechanical properties of PMMA. In recent years, the focus on natural fibers has increased [15]. Natural fibers have become an economically viable, more sustainable, and environmentally friendly alternative to composite materials than artificial or traditional synthetic fibers [16]. Reinforcing polymers with natural fibers has become an important research topic in dentistry.

Oleiwi et al. (2017) investigated the enhancement of tensile properties in PMMA resin by incorporating Siwak and bamboo fibers at various lengths and weight ratios. They found that increasing fiber length and weight ratio increased in tensile strength and elastic modulus [17]. A 2018 study investigated the flexural and impact strength of PMMA resin reinforced with Hibiscus sabdariffa fibers at various weight fractions. This study demonstrated that increasing the fiber weight fraction of this fiber enhanced both flexural and impact strength [18]. Such studies have shown that it is possible to achieve improved mechanical properties of dental materials with an environmentally friendly approach. However, the effects of adding natural fibers on the surface structure have also become an important issue, enhancing the mechanical strength of materials. Polishing and smoothing prosthetic surfaces are essential for achieving optimal aesthetics and maintaining long-term oral hygiene [19]. It has been reported in the literature that adding hemp fiber to PMMA improves mechanical properties, but there is no study on the effect of hemp on the surface roughness of PMMA [20, 21]. Hemp fibers, among the most potent natural fibers after ramie, are less affected by temperature and can withstand high temperatures [22, 23].

Surface roughness (Ra) measures the microscopic variations and irregularities on the surface of an object [4]. High Ra values in prosthetic base resins can lead to staining and discoloration of the prosthesis, compromising aesthetics. This situation may negatively affect patient satisfaction [24, 25]. Furthermore, in many studies, it has been shown that rough prosthetic bases exhibit increased plaque and bacterial retention compared to a smooth surface [9, 26–28]. Microorganisms adhering to rough surfaces can proliferate, leading to fungal and bacterial infections and contributing to dental caries and periodontal diseases [29–31]. The Ra value of prosthetic bases is influenced by the structure of the base material, reinforcement, polishing techniques, polymerization time, and patients dental hygiene [24, 25]. Therefore, ensuring that a prosthesis has a smooth, polished surface is essential for optimal oral health [1]. A prosthesis with a surface structure exceeding the acceptable Ra value can increase wear and plaque accumulation [32]. Consequently, dental technicians must use effective polishing methods for acrylic resin prosthetic bases to ensure proper maintenance and hygiene [9].

This study used polishing techniques to evaluate the effect of HeF and lignin-pectin-free HeF added to PMMA on surface roughness. The null hypothesis of our research is that adding hemp fiber does not affect the surface roughness of PMMA.

Methods

Preparation of hemp fibers

This study utilized hemp fibers sourced from Yozgat Bozok University. Trials began in May 2022 under field conditions, with plants maturing physiologically between August and September. After harvesting, plants were dried to standardize fiber moisture levels. The fibers separation occurred at the Faculty of Agriculture, Yozgat Bozok University. The hemp fibers used in this study underwent two trials. In the first trial, harvested hemp fibers were tested in pure form (HeF). In the second trial, thinning with NaOH was applied to remove lignin and pectin (lignin-pectin-free HeF), creating a second experimental group for comparison. Figures 1a and 2a show images of HeF and lignin-pectin-free HeF. The HeF and lignin-pectin-free HeF were characterized using SEM and EDX analysis. The SEM image obtained from HeF shows that the fibers are more compact due to lignin-pectin-free HeF (Fig. 1b). EDX analysis of the HeF revealed that it contains 61.23% C, 38.21% O, and trace amounts of 0.22% K and 0.33% Ca elements (Fig. 1c). Upon examining the EDX analysis of the lignin-pectin-free HeF, it was determined that they contain 54.33% C, 45.11% O, and 0.56% Na elements (Fig. 2c). Although the fibers were rinsed three times with pure water after the thinning process, the presence of Na element here is attributed to the impurity originating from the NaOH used in the thinning process.

Fig. 1.

Fig. 1

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For HeF (a) Powder HeF, (b) SEM image of HeF (c) EDX analysis of HeF

Fig. 2.

Fig. 2

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For lignin-pectin-free HeF (a) Powder lignin-pectin-free HeF (b) SEM image of lignin-pectin-free HeF (c) EDX analysis of lignin-pectin-free HeF

Preparation of samples

Acrylic powder (Acron Duo, Associated Dental Products) was mixed with HeF and lignin-pectin-free HeF at a ratio of 1% by weight to ensure uniform distribution. The mixture was then stirred for 5 min using a homogenizer (Weightlab instrument, Overstirree). The acrylic molds were prepared as a 65 mm × 10 mm × 3.3 mm (ISO 20795-1:2013) [33]. After conducting a power analysis, a power value of 80% was used for sample size determination, resulting in 10 samples being taken in each subgroup (Table 1). Sixty wax samples (Cerewax Modelling Wax, Pera Dental) were prepared using a standard metal mold. The prepared samples were embedded in hard plaster (Moldano, Heraeus Kulzer) for wax elimination and placed inside a flask. The flask was closed with its lid, and pressure was applied using a pressurizing device. The flask and the samples inside were placed in a wax elimination device and kept at 100 °C for 8 min. After removal from the hot water bath, the flask was held under running water to facilitate wax elimination. The edges of the flask were isolated, except for the areas where wax voids formed. The heat-polymerized acrylic base material powder-to-liquid ratio was prepared at 25 g/10 ml. Acrylic powder was incorporated into the liquid and mixed for the recommended time specified by the manufacturer to achieve the acrylic dough. Polymerization of the traditional acrylic was carried out according to ADA Standard No:12 [34]. After removing all acrylic test samples from the flask, ‘finishing’ and ‘polishing’ procedures were applied.

Table 1.

Finishing and Polishing study groups

Finishing groups (FG)
FG1 PMMA + Finishing (n = 20)
FG2 PMMA + 1% HeF + Finishing (n = 20)
FG3 PMMA + 1% lignin-pectin-free HeF + Finishing (n = 20)
Universal Polishing Paste groups (UP)
PG1 PMMA + Universal Polishing paste (n = 10)
PG2 PMMA + 1% HeF + Universal Polishing paste (n = 10)
PG3 PMMA + 1% lignin-pectin-free HeF + Universal Polishing Paste (n = 10)
Lesk Polishing Liquid groups (LP)
LP1 PMMA + Lesk Polishing Liquid (n = 10)
LP2 PMMA + 1% HeF + Lesk Polishing Liquid (n = 10)
LP3 PMMA + 1% lignin-pectin-free HeF + Lesk Polishing Liquid (n = 10)
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Finishing and Polishing

Firstly, all sample surfaces were processed with a tungsten carbide burr (Schliff Cut Denture 20; Edenta AG, ISO No. 500 104 194 140 060) at a speed of 10,000 revolutions per minute [35]. Subsequently, silicon carbide discs with increasing particle sizes (600, 1200) were polished underwater for 30 s at 150 rpm using a polishing machine (Buehler, Lake Bluff). All samples were then cleaned with cotton and alcohol (Alcohol 70ºGL) for 20 s [36]. These procedures apply to all sample surfaces are called ‘finishing’. Before subjecting all samples to ‘polishing’, they were immersed in distilled water at 37 °C for 10 min. Samples separated according to the content of acrylic resin material underwent two different ‘polishing’ processes. The first involved applying a Universal Polishing Paste (Ivoclar Vivadent), composed of aluminium oxide, onto a single surface of the samples using a soft leather polishing wheel for 90 s at 3000 rpm with a polishing unit (Kavo, Biberach, Germany) [9]. The second type of ‘polishing’ involved applying a Lesk Polishing Liquid (Interdent), containing abrasives, onto a single surface of the samples using a soft leather polishing wheel for 90 s at 3000 rpm with a polishing unit. Each sample in the respective group received this treatment for 90 s [9]. The ‘polishing’ process was standardized using a balance load weight system-based saw (Isomet Precision; Buehler). As recommended, a force of 3 to 5 N was applied to the saw. This system includes a weight arm and a counter arm attached to the handpiece. The acrylic resin sample was positioned under the polisher and manipulated freely by the operator. Before the ‘polishing’ procedure, the gravity loading was calibrated to apply a pressure of 400 g on the surface of the silicone polisher [9]. All ‘finishing’ and ‘polishing’ procedures are described in Table 2.

Table 2.

Finishing and Polishing procedures

Product Components Manufacturer Technique
Finishing Tungsten bur 0320.023HP tungsten carbide bur Edenta AG Dentalprodukt 10 s-10,000 rpm

Silicon carbide abrasive paper

(600 and 1200)

 Silicon carbide Norton 30 s − 150 rpm
Cotton and alcohol Alcohol 70ºGL Tupi Brazil 20 s
Polishing

Universal Polishing

Paste for Resins

and Metals

Loose abrasives (aluminum oxide-Al2O3)

in paste

 Ivoclar Vivadent, Schaan, Liechtenstein 90 s-3000 rpm
Lesk Polishing Liquid Loose abrasives in liquid Interdent, Celje, Slovenia 90 s-3000 rpm
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Surface roughness

All samples were ultrasonically cleaned in deionized water (Pro-Sonic 600; Sultan Healthcare) for 10 min, then dried with compressed air. Sample thickness was measured using a digital caliper (Absolute Digimatic). The average surface roughness (Ra) was assessed initially and after polishing using a stylus profilometer (Taylor Hobson Surtronic 25) with a 0.25 mm cutoff value. Measurements were taken at a constant speed of 0.5 mm/s to determine the average roughness profile (Ra) in micrometers. The profilometer was calibrated before each group of measurements (n = 10). Surface roughness was measured at the center of each sample, with three measurements taken per sample to calculate the average Ra value. A reduction in the Ra value signifies a smoother surface [37].

Scanning Electron microscope (SEM)

After polishing, a piece of acrylic resin measuring 5 mm x 35 mm from each sample was cut using an Isomet 1000 Precision Saw (Buehler) and prepared for scanning electron microscopy (SEM) analysis. The samples were cleaned with 70% alcohol in an ultrasonic cleaner and then sputter-coated with gold. The surfaces of the acrylic resin were examined with a scanning electron microscope (JEOL JSM 5800; JEOL Ltd, Tokyo, Japan) at 7 to 8 keV, and photomicrographs were captured at magnifications of 200, 1000, and 5000.

Statistical method

The data were analyzed using SPSS 17 software, and a significance level of p < 0.05 was adopted. The One-way ANOVA test was applied to determine whether there was a difference in the surface roughness of acrylic resin materials. A Post Hoc Tukey HSD test was conducted to identify which group was responsible for the significant difference in surface roughness as revealed by the One-way ANOVA test.

Results

It was proven with Levene statistics that we can use the One-way ANOVA test to understand whether there is a difference between the surface roughness of PMMA materials before ‘finishing’ (F (5, 54) = 4.160, p = 0.003). According to the One-way ANOVA test, a significant difference was observed between the surface roughness of the PMMA materials ‘finishing’ (F (5, 54) = 5.372, p = 0.000) (Table 3) (Fig. 3). Post hoc Tukey HSD test to find the group that caused the difference showed that the Mean value of FG2 was significantly higher than that of FG1 (p = 0.000) and FG3 (p = 0.003). However, there was no significant difference between the Mean values ​​of the other groups (p > 0.05) (Table 3).

Table 3.

Descriptive statistics for finishing and polishing

One-way ANOVA
Groups N Mean SD Tukey HSD Post Hoc p df F p
Finishing FG1AB* 20 0.3687 0.1150 FG2 > FG1 0.000 5 5.372 0.000
FG2B 20 0.4788 0.0783 FG2 > FG3 0.003 54
FG3AB 20 0.4162 0.1299 59
Total 60 0.3767 0.1007
N Mean SD Games-Howell Post Hoc p
Polishing** PG1 10 0.1821 0.0466 PG2 > PG1 0.004 5 8.410 0.000
PG2 10 0.2679 0.0407 PG2 > PG3 0.003 54
PG3 10 0.1773 0.0488 PG2 > LP1 0.000 59
LP1 10 0.1767 0.0327 PG2 > LP3 0.003
LP2 10 0.2372 0.0467 LP1 > LP2 0.039
LP3 10 0.1945 0.0278
Total 60 0.2060 0.0527
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*Values followed by the same letter in the column are not significantly different

**Robust ANOVA

Fig. 3.

Fig. 3

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Box-plot diagram of the distribution of Ra data according to tested groups

Instead, according to the Welch statistics, FWelch(5, 24.991) = 7.742, p = 0.000 was obtained, so the Robust ANOVA test was performed. According to the Robust ANOVA test, a significant difference was observed between the surface roughness of the PMMA materials after ‘polishing’ F (5, 54) = 8.410, p = 0.000. Post hoc Games-Howell test to find the group causing the difference showed that the Mean value of PG2 (0.2679) was significantly higher than that of PG1 (0.1821), PG3 (0.1773), LP1 (0.1767), and LP3 (0.1945) (p < 0.05) (Table 3). Again, according to the Post hoc Games-Howell test, the Mean value of LP1 (0.1767) was significantly higher than that of LP2 (0.2372) (p < 0.05). However, there was no significant difference between the Mean values ​​of the other groups (p > 0.05) (Table 3).

A One-Way ANOVA was also performed by taking the difference between the surface roughness values ​​of the PMMA materials in the ‘finishing’ and ​​’polishing’ process. Accordingly, Levene Statistic confirmed that One-Way ANOVA could be performed with F(5, 54) = 6.572, p = 0.000. ANOVA performed using the surface roughness differences between the ‘finishing’ and ‘polishing’ showed that there was a difference between the groups with F (5, 54) = 3.885, p = 0.004. Post hoc Tukey HSD test performed to find the group causing the difference showed that the Mean value of PG3 (0.2389) was significantly higher than that of LP1 (0.1277), LP2 (0.1282) and LP3 (0.1323) (p < 0.05) (Table 4) (Fig. 4). However, there was no significant difference between the Mean values ​​of the other groups (p > 0.05) (Table 4).

Table 4.

Descriptive statistics for differences in surface finishing and Polishing

Groups N Mean SD Tukey HSD Post Hoc p
Difference PG1AB* 10 0.1866 0.1428 PG3 > LP1 0.026
PG2AB 10 0.2108 0.0487 PG3 > LP2 0.027
PG3B 10 0.2389 0.0863 PG3 > LP3 0.037
LP1A 10 0.1277 0.0421
LP2A 10 0.1282 0.0508
LP3A 10 0.1323 0.0371
Total 60 0.1707 0.0863
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*Values followed by the same letter in the column are not significantly different

Fig. 4.

Fig. 4

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Means of Difference and Box-plot graph of the differences between ‘finishing’ and ‘polishing’ Ra data

Analysis of differences between groups with univariate analysis of variance gives us information about whether our independent variables surface treatment and their interaction have a statistically significant effect on the dependent variable Sample type (FG, PG, and LP). When the groups were examined, a statistically significant difference was observed in the means of PG1&PG2 [F (1, 16) = 5.675, p = 0.030], PG1&PG3 [F (1, 16) = 17.077, p = 0.001], PG2&PG3 [F (1, 16) = 57.890, p = 0.000], LP1&LP2 [F (1, 16) = 4.624, p = 0.047] and LP2&LP3 [F (1, 16) = 6.787, p = 0.019] (Table 5).

Table 5.

Tests of between-subjects effects

Dependent Variable: PG and LP Polishing
Source statistics F Source statistics F
PG1&PG2 F(1, 16) = 5.675, p = 0.030 LP1&LP2 F(1, 16) = 0.070, p = 0.795
Finishing F(1, 16) = 1.987, p = 0.178 Finishing F(1, 16) = 4.624, p = 0.047
PG1&PG3 F(1, 16) = 17.077, p = 0.001 LP1&LP3 F(1, 16) = 0.002, p = 0.967
Finishing F(1, 16) = 1.529, p = 0.234 Finishing F(1, 16) = 2.548, p = 0.130
PG2&PG3 F(1, 16) = 0.251, p = 0.623 LP2&LP3 F(1, 16) = 0.056, p = 0.816
Finishing F(1, 16) = 57.890, p = 0.000 Finishing F(1, 16) = 6.787, p = 0.019
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The surface morphological patterns of ‘finishing’ and ‘polishing’ materials are shown in Fig. 5 through SEM analysis. SEM images indicate that changes occurred in the surface topography of all materials after the process, with a decrease in surface roughness observed for all. According to SEM analysis, the smoothest surface was observed for Universal Polishing Paste groups (PG1-3). The surfaces of the groups with HeF and lignin-pectin-free HeF were displayed in Fig. 5 at 5000x magnification. When the SEM images of the HeF and lignin-pectin-free HeF groups were examined, a significant difference in the surface contour between the groups was observed, regardless of the form of the hemp fibers. This situation was shown in the SEM image of the groups, which is consistent with the surface roughness analysis.

Fig. 5.

Fig. 5

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SEM image of the sample groups; original magnification 5000x

Discussion

The literature contains numerous studies on the reinforcement of PMMA, the most commonly used material in dental prosthesis fabrication, with various fiber additives to enhance its physical properties. Understanding how the addition of materials to PMMA affects the mechanical properties of heat-polymerized acrylic PMMA and its surface roughness is an important research topic. One of the most crucial requirements for a successful prosthesis is to have a well-polished, smooth surface. An increase in surface roughness creates areas conducive to the adherence of microorganisms on the prosthesis. This can increase the incidence of dental caries, periodontal diseases, and prosthetic stomatitis. Therefore, the surface roughness value (Ra) of the prosthesis should be low. According to the in vivo studies by Bollen et al. [38] and Quirynen et al. [39], the clinically acceptable roughness (Ra) of hard surfaces in the oral environment should not exceed 0.2 μm after ‘polishing’. The Ra values observed after ‘polishing’ could have been influenced by the pressure the hydraulic press machine applied on the mold surface, and the high temperatures during the polymerization process may have contributed to surface degradation [40]. Previous studies have reported surface roughness values for acrylic PMMA ranging from 0.03 to 1.06 μm, depending on the ‘finishing’ and ‘polishing’ techniques employed [1, 9, 19, 25, 31, 41, 42]. In our study, like other studies, all groups exhibited surface roughness values lower than the clinically accepted threshold of 0.2 μm after ‘polishing’ [9, 24]. Furthermore, after the ‘polishing’ process using Universal Polishing Paste, less surface roughness was achieved compared to the ‘polishing’ process using Lesk Polishing Liquid [9].

In recent years, various synthetic fibers have been explored as alternatives to natural fibers in the reinforcement of PMMA-based denture materials. For instance, studies have demonstrated the incorporation of glass fibers and carbon fibers, which are known for their superior mechanical properties and durability. These synthetic fibers have been shown to enhance the mechanical strength and wear resistance of PMMA, which is essential for improving the longevity of denture bases. However, unlike natural fibers such as hemp, synthetic fibers often raise concerns regarding their environmental impact and sustainability. In contrast, hemp fibers offer an environmentally friendly and sustainable alternative. Studies have shown that natural fibers, including hemp, can significantly improve the mechanical and biological properties of PMMA without compromising the environment [43, 44]. Hemp fibers are among the most potent natural fibers, following ramie fibers, and they withstand high temperatures [23, 45]. The structure of hemp fibers comprises approximately 70–74% cellulose, 15–20% hemicellulose, 3.5–5.7% lignin, 0.8% pectin, and 1.2–6.2% beeswax [22, 23].

Our study investigated the effect of adding hemp fibers to heat-polymerized acrylic PMMA and the influence of two different polishing techniques on surface roughness. HeF and lignin-pectin-free HeF were added to the heat-polymerized acrylic PMMA. To the best of our knowledge, no other studies in the literature investigate the effect of hemp fiber addition on the surface roughness of heat-polymerized acrylic resin. According to the ‘finishing’ process, the surface roughness of the HeF + PMMA was statistically significantly higher than that of the PMMA and lignin-pectin-free HeF + PMMA. According to this result, it is observed that the addition of HeF to PMMA increases surface roughness regardless of polishing. The higher surface roughness of the HeF + PMMA compared to the group PMMA and lignin-pectin-free HeF + PMMA is thought to be not attributed to the lignin and pectin present in the hemp primary bast fibers. Based on this, it can be interpreted that the aggregation of HeF increases surface roughness. In ‘finishing’ and ‘polishing’ statistical analysis, the mean surface roughness value of the acrylic resin group containing HeF of the polishing with Universal Polishing Paste was statistically significantly higher than that of the acrylic resin group, as well as the group containing lignin-pectin-free HeF. Similarly, the mean surface roughness value of the acrylic resin group polished with Lesk Polishing Liquid was statistically significantly higher than that of the group containing HeF.

When using Universal Polishing Paste for HeF + PMMA groups, higher surface roughness was observed compared to both PMMA and lignin-pectin-free HeF + PMMA groups. This difference suggests that lignin and pectin in the fiber-added group contribute to increased surface roughness. However, when using Lesk Polishing Liquid for polishing acrylic resin with HeF addition, lower surface roughness was observed compared to the group without HeF addition. This indicates that the type of polishing affects surface roughness differently in acrylic resin with HeF addition.

Future studies are planned to expand on the current findings in several ways:

  1. Higher Fiber Concentrations: We intend to investigate the effects of different concentrations (e.g., 2%, 3%, and 5%) of both untreated and lignin-pectin-free hemp fibers on PMMA to better understand the concentration-dependent changes in surface characteristics.

  2. Mechanical and Biological Properties: In addition to surface roughness, future work will evaluate the mechanical strength, color stability, and microbial adhesion potential of the fiber-reinforced PMMA materials.

  3. Long-Term Aging Studies: The performance of these materials under thermal and mechanical aging will be assessed to simulate clinical conditions and determine their long-term durability.

  4. Alternative Polishing Systems: The comparison of additional polishing agents and protocols will help identify the most effective method for achieving clinically acceptable smoothness in fiber-reinforced PMMA.

  5. In Vitro Microbial Studies: To directly relate surface roughness to biological outcomes, in vitro tests using common oral pathogens will be conducted to assess bacterial adhesion and biofilm formation.

Conclusion

The addition of hemp fiber significantly increased the surface roughness of PMMA, especially after the ‘finishing’ procedure. However, appropriate ‘polishing’ particularly with effective materials substantially reduced this roughness. These findings emphasize the importance of ‘polishing’ in improving the surface quality and cleanability of fiber-reinforced denture base resins.

This study’s limitations include manual force and the non-uniform distribution of polishing paste. Further research is needed to investigate the effects of other chemicals, such as denture cleansers and artificial saliva, on surface roughness. The surface roughness test was performed from five different points, and the average was calculated when evaluating the results. In contrast, the SEM analysis was performed from a single point, which is a limitation of this study.

Acknowledgements

The authors thank the Yozgat Bozok University Research Foundation (THD-2023-1193) for financial support.

Author contributions

S.K. designed the research, supervision, project administration, writing–review&editing; F.D.B., and N.K. methodology, analysed data, investigation, validation, writing– original draft.

Funding

The authors thank the Yozgat Bozok University Scientific Research Projects Unit for their financial support under project number THD-2023-1193.

Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethical approval

Not applicable.

Consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

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