Influence of the Probiotic Lactobacillus rhamnosus on the Physical Properties of Restorative Dental Materials: An In Vitro Study

Highlights

What are the main findings?

• Probiotics are known to promote intestinal homeostasis, and similar biological mechanisms may also be relevant in the oral environment.
• An in vitro experimental model was used to evaluate changes in the microhardness and surface roughness of restorative dental materials following exposure to probiotic yogurt.

What are the implications of the main findings?

• Exposure to probiotic yogurt resulted in statistically significant changes in the microhardness of the tested restorative materials.
• The interaction between probiotics and restorative dental materials may represent a potential component of preventive strategies in contemporary dentistry.

Abstract

Backround: The aim of this study was to evaluate the effects of probiotic yogurt containing Lactobacillus rhamnosus (LGG) on the microhardness and surface roughness of restorative dental materials commonly used in pediatric dentistry. Methods: Three materials were tested: conventional glass ionomer cement Fuji II, high-viscosity glass ionomer cement Fuji IX, and microhybrid composite resin Te Econom. The samples were prepared according to the manufacturers’ instructions, initially stored in distilled water, and subsequently immersed in probiotic yogurt. Microhardness was measured by the Vickers hardness test, and surface roughness was assessed by 3D profilometers. Results: Statistical analysis was performed using the Wilcoxon signed-rank test and the Kruskal–Wallis test. Exposure to probiotic yogurt resulted in increased microhardness for the resin-modified and high-viscosity glass ionomer cements, whereas the microhardness of the microhybrid composite resin decreased. The surface roughness increased for all the tested materials, with statistically significant differences observed in most groups (p < 0.05). Conclusions: These findings indicate that probiotic yogurt can alter the physical properties of restorative dental materials and highlight the importance of careful selection of preventive agents in pediatric dental practice. Further research is needed to clarify the long-term effects of probiotic preparations on dental restorations.

1. Introduction

Recent studies have reported numerous positive effects of probiotics, but their use is still not an integral part of clinical dental practice. They have been shown to be effective in stimulating intestinal homeostasis, and since the oral cavity is the initial part, it is believed that the same mechanisms of action would be effective in the initial part of the gastrointestinal flora [1]. Recent studies have also suggested that probiotics may influence the microhardness and surface roughness of dental restorative materials [2].

The literature consistently shows that filler size, filler distribution, and matrix composition significantly influence surface roughness and microhardness. Larger particles in glass ionomer cements are more prone to surface degradation and ion exchange under acidic conditions, whereas resin-based composites demonstrate greater resistance due to their hydrophobic resin matrix and smaller filler particle size [3].

Glass ionomer cements and composites are dental materials that we use daily in clinical practice. The choice of modern restorative materials in the pediatric population is limited in public health institutions, and the influence of prophylactic agents on the physical properties of the material is certainly interesting.

In addition, probiotic strains should be capable of producing antimicrobial compounds, colonizing the host microbiota, and reducing the harmful effects of toxins [4].

Probiotics are increasingly considered a form of bacteriotherapy, also known as replacement therapy, and may represent a promising approach in the prevention and management of dental caries and periodontal diseases [5]. The antimicrobial activity of these bacteria is attributed primarily to the production of bacteriocins, organic acids, fatty acids, and hydrogen peroxide. The oral microbiome is highly complex and consists of numerous bacterial species inhabiting the teeth, tonsils, tongues, and both the soft and hard palates. These microorganisms play essential roles in maintaining oral health, but they may also contribute to the development and progression of oral diseases when the microbial balance is disrupted.

The development of dental caries is influenced by two major factors: host susceptibility and dietary habits [6]. Under acidogenic conditions, Streptococcus mutans plays a key role because of its ability to metabolize dietary carbohydrates into lactic acid, which leads to demineralization of the tooth surface [7]. Consequently, the formation of carious lesions is associated with disruption of the ecological balance within the oral cavity, where commensal microorganisms normally coexist with potentially pathogenic species in controlled proportions. When the pH of the supragingival biofilm becomes acidic and cariogenic microorganisms predominate, the stability of the oral ecosystem is compromised.

The modern concept of probiotic replacement therapy is based on the use of inactive or avirulent microorganisms capable of competing with Streptococcus mutans for adhesion sites on the tooth surface [8]. In addition, the oral microbiome may be modified by promoting microbial strains that produce alkaline metabolites, thereby maintaining optimal biofilm pH levels. Another promising approach involves the use of antimicrobial peptides that specifically target Streptococcus mutans [9,10,11]. However, factors such as dosage, frequency of administration, and formulation of probiotic preparations remain important considerations in evaluating their clinical effectiveness.

A reduction in the number of cariogenic microorganisms following probiotic administration supports the hypothesis of their anticariogenic potential. Furthermore, modulation of the oral microbiome may influence environmental pH and contribute to the prevention of periodontal diseases [12]. Under optimal pH conditions, typically between 6 and 7, microbial homeostasis is maintained and the integrity of the tooth surface is preserved. However, disturbances in microbial balance may lead to acidogenic conditions, gingival inflammation, and proliferation of oral pathogens.

To achieve optimal probiotic activity, these microorganisms are commonly administered in various forms, including milk, yogurt, juices, drops, cheeses, toothpastes, mouthwash solutions, and lozenges. Probiotics may also exert antimicrobial effects by reducing adhesion sites for pathogenic microorganisms, competing for nutrients, interfering with toxin-binding mechanisms, and modulating the host immune response [13]. Nevertheless, the optimal dosage, duration of administration, and formulation of probiotic preparations for specific oral conditions remain subjects of ongoing research.

Our country still does not have clear and defined preventive protocols, which is why this topic is particularly challenging.

2. Materials and Methods

The study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of the Faculty of Medicine, University of Banja Luka (number: 18/4. 17/23 of 9 February 2023) and the Ethics Committee of the Public Health Institution of the Institute of Dentistry of the Republic of Srpska (number: 01-461-2/18 of 18 March 2018). The consent of the Public Health Institution of the Institute of Public Health of the Republic of Srpska for the implementation of scientific research was obtained (number: 500-4337-1/17 of 27 December 2017).

This study involved testing the influence of probiotic yogurt cultures on the physical properties of the most commonly used dental restorative materials in the laboratory of the Faculty of Mechanical Engineering. The physical properties that were tested were microhardness and roughness.

The dental materials tested in the laboratory are the most commonly used restorative materials in children’s dentistry:

• conventional glass ionomer (GIC), Fuji II; type: conventional glass ionomer cement, fluoro-alumino-silicate glass + polyacrylic acid, filler particles: ~5–15 µm (average)
• high viscosity glass ionomer (GIC), Fuji IX; type: conventional glass ionomer cement (GIC), fluoro-alumino-silicate glass + polyacrylic acid, filler particles: ~8–12 µm
• Light-curing microhybrid composite (MH COMP Te Econom); type: microhybrid composite (light-cure), organic matrix (dimethacrylates) + inorganic fillers (barium glass, ytterbium trifluoride, silica), filler particles: 0.04–7 µm, average ~0.85 µm

For the probiotic cultures, the effects of the most commonly used probiotic culture were tested:

• LGG Dukat yogurt (Lactobacillus rhamnosus 107 CFU/g).

Restorative materials were prepared by making disks 6 mm in diameter and 2 mm thick in factory molds, with the upper and lower surfaces resting on a glass surface and pressed by the weight of the glass surfaces. A total of 15 disks were made. The samples were made of three different restorative materials:

• Group G1.3 (n = 5): Fuji II disks;
• Group G2.3 (n = 5): Fuji IX disks;
• Group G3.3 (n = 5): Te Econom microhybrid composite disks.

The inner surfaces of the factory mold were insulated with petroleum jelly for easier handling of the samples. Each sample was prepared according to the manufacturer’s instructions. After mixing, the glass ionomer cements were left at room temperature for 15 min, and the microhybrid composite was polymerized for 20 s with an LED lamp with an output power of 1400 mW/c².

The samples were then immersed in 2 mL of distilled water and incubated at 37 °C for 48 h. After basic measurement, the samples were immersed for a period of 20 min in 10 mL of probiotic yogurt at a temperature of 37 °C. The yogurt was not added or refreshed. The short exposure time of the yogurt sample affected the physical properties of the material, so we considered a modified experimental research model.

After this period, the disks were dried and taken to the Laboratory Research Center of the Faculty of Mechanical Engineering in Banja Luka. Using a Vickers microhardness tester with a force of 100 g for 15 s, measurements were made at three points with a diameter of 6 mm, and the average value was measured. The obtained value for each sample was recorded with the analyzed sample.

To obtain precise data on the impact of probiotic yogurt on a specific type of material and compare it with the basic values of the material, each sample was thoroughly washed with distilled water after being immersed in yogurt culture, dried, and transported to the laboratory.

The microhardness was subsequently measured in the same way as previously described and the values were recorded for each sample and subsequently analyzed. Since surface roughness can affect the adhesion of microorganisms to the surface of a material, surface roughness was measured using the contact profilometry method at the Faculty of Mechanical Engineering in Banja Luka. The profilometer is a Mitutoyo SJ-310 (Kawasaki-shi, Japan, Mitutoyo Corporation). The measuring sensor that slides along the tested profile has a measuring stylus with a diameter of 2 µm under the action of a force F = 0.7 mN. The stylus stroke is defined by the recording length Lt = 5.6. The evaluation length, Lm = 4 mm, and the reference length value (size of the cutoff filter), lc = 0.8 mm, are determined by the choice of Lt according to the ISO standard. The change in the position of the probe relative to the elements of the measuring head is converted into an electrical signal via a transformer. The electrical signal thus marked is amplified and filtered to remove wavelength values that do not correspond to the roughness and obtain the appropriate surface roughness parameters. The parameter most often used to describe surface roughness is the value of the arithmetic mean deviation of the profile (Ra).

For this test, new experimental samples of the material in the form of an elongated cube measuring 30 × 3.3 × 3 mm were made, according to the manufacturer’s instructions, in ready-made plastic molds, insulated with petroleum jelly for easier handling, as follows:

• Sample 1 (U1.3): 5 samples of Fuji II;
• Sample 2 (U2.3): 5 samples of Fuji IX;
• Sample 3 (U3.3): 5 samples of microhybrid composite (Te Econom).

The mixture was then left to stand at room temperature for 15 min for glass ionomers, and the microhybrid composite was polymerized for 20 s. The samples were stored in plastic containers with 2 mL of distilled water at 37 °C for 24 h in the dark, and then transferred to the laboratory of the Faculty of Mechanical Engineering for further analysis of surface roughness. After basic roughness measurement, the samples were immersed in probiotic yogurt, and after rinsing with distilled water and drying, the values of the basic and experimental measurements of the samples were recorded and analyzed.

3. Results

A comparison of the basic microhardness of the restorative materials (first measurement) and the microhardness values after treatment with probiotics (second measurement) between the groups is presented in a table (

Table 1. Analysis of comparisons of basic microhardness of restorative materials (first measurement) and freedom of microhardness of probiotic treated nails (second measurement) between groups.

	G1.3		G2.3		G3.3
First measurement	5	7.80	5	3.20	5	13.00	χ2(2) = 12,500; p = 0.002 a
Second measurement	5	3.20	5	13.00	4	7.80	χ2(2) = 12,500 p = 0.002 a
Wilcoxon signed-ranks test	Z = −2.023; p = 0.043		Z = −2.023; p = 0.043		Z = −1.826; p = 0.068

G1.3—Fuji II samples treated with probiotic yogurt; G2.3—Fuji IX samples treated with probiotic yogurt; G3.3—MH COMP Te Econom composite samples treated with probiotic yogurt. ^a Statistically significant difference between groups G2.3 and G3.3.

), where the Kruskal–Wallis test was used:

A statistically significant difference (p < 0.05) in the microhardness between the Fuji IX probiotic yogurt-treated groups (G2.3) and (G3.3) was observed at the first and second measurements.

• After the microhardness of samples made of resin-reinforced glass ionomer cement RM GICs (FUJI II LC) (first measurement) was determined, it was concluded that after the samples were immersed in probiotic yogurt (second measurement), the microhardness increased samples (Table 2). A statistically significant difference in microhardness (p < 0.05) between the first and second measurements was observed via the Wilcoxon signed-rank test.
• An examination of the microhardness measurement results for samples made from the MH COMP Te Econom Plus composite (first measurement) revealed that after the samples were immersed in probiotic yogurt (second measurement), the microhardness of the samples decreased (Table 3). The application of the Wilcoxon signed-rank test revealed that there was a statistically significant difference in microhardness (p < 0.05) between the first and second measurements.
• The microhardness measurements of the samples made of high-viscosity glass ionomer cement HVGICs (FUJI IX) (first measurement) revealed that after the samples were immersed in probiotic yogurt (second measurement), the microhardness of the samples increased (Table 4). Analysis of the results obtained using the Wilcoxon signed-rank test revealed that there was no statistically significant difference in microhardness (p > 0.05) between the first and second measurements.
• A two-way analysis of variance (two-way ANOVA) was conducted to examine the effects of the material group (Group) and therapy (Therapy), as well as their interaction, on the microhardness of the samples (Table 5). The total number of samples tested was N = 30. The analysis was performed at a significance level of α = 0.05.

Table 2. Ratio of microhardness values before and after immersion of RM GIC samples in probiotic yogurt.

		N	Middle Rank	(Z; p)
Second measurement– First measurement	Second measurement < First measurement	0	0.00	Z = −2.023; p = 0.043
	Second measurement > First measurement	5	3.00
	Second measurement = First measurement	0
	In total	5

Table 2. Ratio of microhardness values before and after immersion of RM GIC samples in probiotic yogurt.

		N	Middle Rank	(Z; p)
Second measurement– First measurement	Second measurement < First measurement	0	0.00	Z = −2.023; p = 0.043
	Second measurement > First measurement	5	3.00
	Second measurement = First measurement	0
	In total	5

Table 3. Ratio of microhardness values before and after immersion of the MH COMP Te Econom Plus samples in probiotic yogurt.

		N	Middle Rank	(Z; p)
Second measurement– First measurement	Second measurement < First measurement	5	3.00	Z = −2.023; p = 0.043
	Second measurement > First measurement	0	0.00
	Second measurement = First measurement	0
	In total	5

Table 3. Ratio of microhardness values before and after immersion of the MH COMP Te Econom Plus samples in probiotic yogurt.

		N	Middle Rank	(Z; p)
Second measurement– First measurement	Second measurement < First measurement	5	3.00	Z = −2.023; p = 0.043
	Second measurement > First measurement	0	0.00
	Second measurement = First measurement	0
	In total	5

Table 4. Ratio of microhardness values before and after immersion of HVGICs samples in probiotic yogurt.

		N	Middle Rank	(Z; p)
Second measurement– First measurement	Second measurement < First measurement	0	0.00	Z = −1.826; p = 0.068
	Second measurement > First measurement	4	2.50
	Second measurement = First measurement	1
	In total	5

Table 4. Ratio of microhardness values before and after immersion of HVGICs samples in probiotic yogurt.

		N	Middle Rank	(Z; p)
Second measurement– First measurement	Second measurement < First measurement	0	0.00	Z = −1.826; p = 0.068
	Second measurement > First measurement	4	2.50
	Second measurement = First measurement	1
	In total	5

Table 5. Two-way ANOVA results for surface microhardness (HV).

Material	Group	N	Means ± SD	F-Value	p-Value	Statistical Significance
HV GIC	Baseline	5	72.38 ± 2.97	62.08	<0.001	Significant
	After	5	75.50 ± 2.52	62.08	<0.001	Significant
RM GIC	Baseline	5	24.54 ± 0.30	62.08	<0.001	Significant
	After	5	40.58 ± 1.78	62.08	<0.001	Significant
Composite	Baseline	5	22.20 ± 1.35	62.08	<0.001	Significant
	After	5	19.84 ± 1.17	62.08	<0.001	Significant

Table 5. Two-way ANOVA results for surface microhardness (HV).

Material	Group	N	Means ± SD	F-Value	p-Value	Statistical Significance
HV GIC	Baseline	5	72.38 ± 2.97	62.08	<0.001	Significant
	After	5	75.50 ± 2.52	62.08	<0.001	Significant
RM GIC	Baseline	5	24.54 ± 0.30	62.08	<0.001	Significant
	After	5	40.58 ± 1.78	62.08	<0.001	Significant
Composite	Baseline	5	22.20 ± 1.35	62.08	<0.001	Significant
	After	5	19.84 ± 1.17	62.08	<0.001	Significant

3.1. Main Effects

The results showed a statistically significant main effect of the material group on microhardness (F(2.24) = 2154.19; p < 0.001).

The highest mean microhardness values were recorded for HVGICs material (M = 73.94 ± 0.60), followed by RM GICs (M = 32.56 ± 0.60), while MH COMP showed the lowest microhardness values (M = 21.02 ± 0.60).

A statistically significant main effect of therapy was also found (F(1.24) = 65.41; p < 0.001).

Compared with the control samples, the yogurt-treated samples had a significantly greater microhardness (M = 45.31 ± 0.49) (M = 39.71 ± 0.49).

3.2. Interaction Effect

A statistically significant interaction between material type and treatment was observed (F(2, 24) = 62.08; p < 0.001). This indicates that the effect of treatment on microhardness depends on the type of material, confirming a material-dependent response, as illustrated in the mean profile plot.

3.3. Post Hoc Analysis

Post hoc analysis (Tukey HSD and Bonferroni tests) for the factor Material revealed significant differences between all groups (p < 0.001). Specifically, HVGICs showed significantly higher microhardness compared to RM GICs (ΔM = 41.38) and the composite (ΔM = 52.92), while RM GICs also had higher values than the composite (ΔM = 11.54). Homogeneous subset analysis confirmed that each material formed a distinct group without overlap.

3.4. Effect Size and Model Fit

The model explained 99.5% of the total variance (R² = 0.995; adjusted R² = 0.994), indicating a very strong effect of the tested factors on microhardness.

Roughness measurements of samples made of resin-reinforced glass ionomer cement RM GICs (FUJI II LC) (baseline) revealed that after immersion of the samples in probiotic yogurt (after), the roughness of the samples increased (

Table 6. Changes in surface roughness (Ra) of RM-GIC (Fuji II LC) before and after probiotic yogurt immersion.

Comparison (After vs. Baseline)	n	Mean Rank	Z-Value	p-Value	Result
After > Baseline	5	3.00	−2.023	0.043 *	Significant increase
After < Baseline	0	0.00
No change	0

Wilcoxon signed-rank test, p < 0.05, * significant difference.

). Analysis of the results, using the Wilcoxon signed-rank test, revealed a statistically significant difference in roughness (p < 0.05) between the first and second measurements.

The results of roughness measurements on samples made from MH COMP Te Econom Plus composites (baseline) show that after the samples were immersed in probiotic yogurt (after), the roughness of the samples increased (

Table 7. Changes in surface roughness (Ra) of composite (MH COMP, TeEconom Plus) before and after probiotic yogurt immersion.

Comparison (After vs. Baseline)	n	Mean Rank	Z-Value	p-Value	Result
After > Baseline	5	3.00	−2.032	0.042 *	Significant increase
After < Baseline	0	0.00	—	—	—
No change	0	—	—	—	—

* significant difference.

). A statistically significant difference in roughness (p < 0.05) between the first and second measurements was confirmed after the Wilcoxon signed-rank test was applied.

The Kruskal–Wallis test was used to compare the roughness values between different groups of materials (

Table 8. Comparison of roughness with basic measurements and after immersion in yogurt.

	Measurement	N	Middle Rank	N	Middle Rank	N	Middle Rank
Roughness	Baseline	U1.3		U2.3		U3.3
		5	7.00	5	7.00	5	6.60
	Kruskal–Wallis test	ꭕ2 = 2.299; p = 0.317		ꭕ2 = 1.836; p = 0.399		ꭕ2 = 1.727; p = 0.422
	After treatment	U1.3		U2.3		U3.3
		5	13.00	5	9.60	5	13.00
	Kruskal–Wallis test	ꭕ2 = 12.500; p = 0.002 a		ꭕ2 = 9.780; p = 0.008 b		ꭕ2 = 9.420; p = 0.009 c

^a The roughness of the samples at the baseline measurement and after immersion in yogurt is statistically significantly different. ^b The samples differ significantly at the baseline measurement and after probiotic treatment. ^c The samples differ significantly at the baseline measurement and after probiotic treatment. U1.3 Fuji II samples treated with probiotic yogurt; U2.3 Fuji IX samples treated with probiotic yogurt; U3.3 samples MH COMP Te Econom treated with probiotic yogurt. The groups U 1.3 and U 3.3 are statistically significantly different in roughness.

), i.e., the basic roughness (baseline) and after immersion in probiotics (after treatment):

-

For samples made from the Fuji IX material (first measurement), there was a statistically significant difference in roughness (p < 0.05) between the first measurement and after immersion in the probiotic yogurt (second measurement).

-

For samples made from the Te Econom Plus composite material (baseline), there was a statistically significant difference in roughness (p < 0.05) compared to the measurement after immersion in probiotic yogurt (after treatment).

-

Compared with the samples from the first measurement, the Fuji II samples from the probiotic yogurt had a significantly greater roughness.

Clinical threshold: Ra > 0.2 µm indicates an increased risk of biofilm accumulation.

All the baseline values were near the threshold, whereas the posttreatment values exceeded clinically relevant limits in all the materials (

Table 9. Surface roughness (Ra, µm) before and after probiotic yogurt exposure (Wilcoxon signed-rank test).

Material	Group	Mean ± SD	Median	Min–Max	Δ Change	p-Value	Sig.
Fuji IX (Conventional GIC)	Baseline	0.25 ± 0.02	0.25	0.22–0.27
	After	2.42 ± 0.39	2.79	2.25–2.93	+2.17	0.043	*
Fuji II LC (RMGIC)	Baseline	0.33 ± 0.04	0.32	0.28–0.39
	After	1.31 ± 0.07	1.28	1.24–1.43	+0.98	0.043	*
Composite (MH COMP)	Baseline	0.80 ± 0.03	0.81	0.75–0.84
	After	1.61 ± 0.29	1.51	1.41–2.13	+0.81	0.043	*

* p < 0.05 (statistically significant difference).

).

For the Wilcoxon signed-rank test, p < 0.05 was considered significant.

4. Discussion

In everyday clinical practice, there is a need for the restoration of dental surfaces with materials that are biocompatible, simple to apply, easy to handle, and acceptable even to the youngest patients. The smoothness and microhardness of dental restorative materials are key factors in clinical practice, as they directly affect the resistance of the material to wear, biofilm accumulation, durability of fillings, and success of long-term dental therapy.

The most commonly used restorative materials are the subject of research in this study. However, modern dentistry, which strives to establish a clear protocol of preventive work methods, often uses prophylactic agents, the application of which in the oral cavity and the impact on restorations have not yet been sufficiently proven. Probiotics show the ability to modulate the oral microbiome but also have an impact on dental materials when they are applied in the appropriate amount and for an adequate period of time.

Probiotics in the form of probiotic yogurt can modify the properties of restorative materials that are often used in pediatric dentistry, as they affect the microhardness and roughness of dental restorations. The immersion of probiotic yogurt increased the microhardness of high-viscosity glass ionomer cement and resin-reinforced glass ionomer cement, whereas the microhardness of the composite materials decreased. Immersion in probiotic yogurt increases the roughness of high-viscosity glass ionomer cement and composites.

Probiotic liquids such as kefir or probiotic mouthwash do not have a strong negative effect on the surface properties of restorative materials or tooth enamel under laboratory conditions, although the effect depends on the type of material being tested. In this study, we investigated that yogurt did not have negative effects, but rather improved some properties, such as microhardness, especially in glass ionomer cement.

A limitation of the study is certainly the small number of samples that were taken due to limited economic resources and time constraints. The sample size limits the possibility of generalization. However, the consistent patterns in the results warrant further research on a larger population.

Similar studies to ours have been reported in the literature, showing an increase in the microhardness of resin-reinforced and high-viscosity glass ionomer cements [14] and a decrease in the microhardness of hybrid composites [15]. The exposure and immersion of materials in different solutions (such as yogurt) can result in different degrees of water absorption and affect the matrix structure of each tested material [16]. In this way, physical properties, such as the microhardness and roughness of the material, are modified.

Studies on glass ionomer cements have demonstrated that water sorption and solubility correlate strongly with changes in microhardness, suggesting that aqueous penetration into the matrix can alter mechanical resistance, but few studies have confirmed the underlying mechanisms with structural analyses [17]. Furthermore, microstructural investigations via SEM/EDX can reveal ionic exchange layers and filler distributions that may explain the observed microhardness behavior; however, these findings are lacking in the current manuscript [18]. Similar research on composite resins reported that water can act as a plasticizer in the polymer network, lowering the microhardness and reinforcing the need for sorption and FTIR/SEM evaluation [19].

Microhardness is an extremely important physical property of restorative dental materials in everyday work, because the durability and resistance of the restoration largely depend on both the conditions in the oral cavity and the agents we use in the everyday prevention and prophylaxis of oral diseases. In our research, we could conclude that the selection of an appropriate prophylactic agent is extremely important because its applicability is reflected both in prophylactic application and in the modification of the physical properties of dental restorations. The use of probiotics and their effects on increasing the microhardness of glass ionomer cements, which are exceptionally important in everyday clinical practice, have been described in numerous studies [14]. Different types of probiotic cultures have been investigated for the purpose of potential modification of dental restorations in recent studies [19]. Probiotic strains are bound to the nanoparticles of the material, which significantly increases the microhardness of the glass ionomer cement, and the combination of probiotics with synthesized nanoparticles could be a hypothesis for future research [20].

Roughness was generally pronounced after treatment with probiotic yogurt, according to the results of our research, but greater deviations were still observed in the composite material and in the resin-modified glass ionomer cement. The importance of polishing the surface of dental restorations is manifold. Facilitated maintenance of oral hygiene, difficult accumulation of oral biofilms, prevention of the appearance of secondary carious lesions and prevention of marginal microcracks are more easily carried out on well-polished restorative material. Smoothness also plays a large role in the stability and durability of fillings.

Similar results for roughness to those in our study emphasize the possibility of degradation of the surface of glass ionomer restorations due to the influence of preventive agents on the matrix between glass particles, which has been reported in the literature [21]. The dissociation and release of fluoride ions from the surface of glass ionomer cements, which are widely applied in pedodontics precisely because of this property, promote an anticariogenic effect and affect the appearance of surface roughness [22]. Probiotic cultures can increase the roughness of mineralized oral surfaces, which may have implications for the adhesion of microorganisms and long-term effects on dental materials [23], which may be the subject of further research with the aim of developing individual preventive protocols.

One of the reasons for the increase in roughness among dental restorative materials is their chemical composition, where they react differently with applied varnishes and solutions. This theory has been confirmed in the literature, where the importance of fillers of composite materials on resistance to oral environmental conditions has been investigated, with composites with smaller filler particles being more homogeneous and showing less roughness [24]. The results of the increase in roughness, such as those given in this study, have also been confirmed in similar studies [25,26,27]. According to these authors, the change in roughness occurs as a consequence of the frequency of application and concentration of the solution, and the duration of prophylaxis.

Prophylactic solutions have the greatest effect on the composition of resin filler particles, i.e., inorganic particles [28]. Some prophylactic solutions can increase the surface roughness of composites because of their effects on the polymer matrix and the release of fillers [29]. A similar study describes an increase in material roughness after the application of prophylactic solutions [30]. Rough surfaces of dental restorations reduce the wear resistance of the material, which reduces the quality of everyday work. Therefore, careful selection and application of preventive agents are extremely important.

Resin-reinforced glass ionomer cements and conventional glass ionomers show an increase in surface roughness after exposure to probiotic cultures, which is attributed to water absorption and the action of acidic metabolites of probiotics. Compared with glass ionomers, composite materials presented a smaller change in roughness after exposure to probiotic solutions, which suggests that their matrix structure is more resistant to interactions with water and bacterial metabolites.

When glass ionomer cements harden, the presence of water in the liquid medium causes their instability and porosity. However, the ability to release fluoride and the effects achieved by remineralizing dental tissues with the use of glass ionomer cements in the pediatric population represent a greater benefit to the health of the individual than the potential damage to the surface of the dental restoration that can occur as a result of the use of prophylactic agents, including probiotic cultures.

5. Conclusions

Exposure to probiotic yogurt resulted in a significant increase in microhardness for resin-modified and high-viscosity glass ionomer cements, whereas a reduction in microhardness was observed in the microhybrid composite resin. Additionally, surface roughness increased in all tested materials, with the majority of changes reaching statistical significance (p < 0.05).

These results suggest that probiotic yogurt has the potential to influence the physical characteristics of restorative dental materials and emphasize the need for careful selection of preventive agents in pediatric dentistry. Additional studies are needed to better understand the long-term impact of probiotic products on dental restorations.