Simge Gümüş Ayaz
Ezgi Sonkaya
Gökçe Keçeci- 1Department of Restorative Dentistry, Faculty of Dentistry, Batman University, Batman, Türkiye
- 2Department of Restorative Dentistry, Faculty of Dentistry, Cukurova University, Adana, Türkiye
- 3Department of Prosthodontic Dentistry, Faculty of Dentistry, Kahramanmaras Sutcuimam University, Kahramanmaras, Türkiye
The durability of the hybrid layer, which forms the basis of successful bonding in restorative dentistry, depends on the stability of collagen fibrils. Dentin matrix metalloproteinases degrade the collagen structure over time, leading to a reduction in bond strength. Therefore, MMP inhibitors play a crucial role in maintaining bond durability. The study aims to evaluate and compare the short-term (24 h) and long-term (12 months) effects of dentin pretreatment agents -chlorhexidine (CHX), quercetin (QC), naringin (NR), riboflavin (RF), and α-tocopherol (α-TF)- on bond strength. A total of 144 extracted human molars were collected and randomly divided into six groups: control (no treatment), 2% chlorhexidine, 1% QC, 1% Nar, 3% riboflavin, and 10% α-TF. The solutions were prepared and applied to the dentin surfaces for 60 s, followed by the application of All-Bond Universal adhesive and composite resin. Following the bonding procedure, a nanohybrid flowable composite was applied onto the dentin surface of each tooth using a starch tube, forming a cylindrical specimen with a bonding area of 1 mm2 (1 mm in diameter and 1 mm in height). Half of the specimens in each group (n = 12) were tested for micro shear bond strength (μSBS) after 24 h of storage, while the remaining specimens underwent thermocycling to simulate 12 months of aging before μSBS testing. To determine the μSBS, each bonded specimen was subjected to a μSBS test in a universal testing machine (MOD Dental MIC-101, Esetron Smart Robotechnologies, Ankara, Turkey) equipped with a 5-kN load cell and featuring a lower fixed and an upper movable compartment, operating at a crosshead speed of 0.5 mm/min. After μSBS testing, failure modes were determined using a stereomicroscope. Data were analyzed using one-way analysis of variance (ANOVA) followed by Tukey’s post hoc tests with p ˂ 0.05 as the significance level. Results of the one-way ANOVA test revealed that, at the end of 24 h, the highest μSBS was observed in the QC group, followed by CHX and NG, all of which showed significantly higher bond strength than the α-TF group (p < 0.05). After 12 months of aging, an increase in SBS was observed in the QC, RF, and naringin groups, whereas a decrease was noted in the Con, CHX, and α-TF groups. QC and NG are natural and effective agents that can be alternatives to CHX in dentin pretreatment. QC showed promise in terms of long-term success, especially after thermal aging, showing the highest bond strength.
1 Introduction
One of the critical aspects of restorative dentistry is achieving a durable bond between dental restorations and dentin (de Carvalho Beckman et al., 2024). The hybrid layer is responsible for the resin–dentin bond and is formed by the infiltration of resin monomers into partially demineralized dentin. The durability of this layer depends on the stability of collagen fibrils (HS Delgado et al., 2022). Over time, a reduction in resin–dentin bond strength may occur due to the degradation of hydrophilic resin components following water sorption and the degeneration of collagen fibrils within the interface, mediated by dentin-bound enzymes such as matrix metalloproteinases (MMPs) (Epasinghe et al., 2014). Based on previous studies, it has been concluded that incomplete resin infiltration and residual water within the hybrid layer compromise its structural integrity, rendering it susceptible to hydrolysis and collagen denaturation. (Betancourt, 2019). Frassetto et al. demonstrated that cross-linking agents (e.g., EDC). can inactivate gelatinolytic enzymes in situ within the hybrid layer, thereby reducing collagen degradation and preserving interfacial strength (Frassetto et al., 2016). Collectively, these classical studies highlight the multifactorial nature of hybrid layer degradation and emphasize the necessity of strategies, such as MMP inhibition or collagen cross-linking, to enhance bond longevity.
MMPs are implicated in various stages of both physiological and pathological processes within the pulpodentinal complex (Jiang et al., 2020). Variants such as MMP-2, MMP-8, and MMP-9 have been identified not only in dentin and saliva but also within carious lesions (Jiang et al., 2020; Moradian et al., 2022; Kiuru et al., 2021). The collagen proteins of dentin are degraded by MMP-8, and this degradation is further enhanced by the demineralization of dentin induced by acids present in carious lesions, which activate MMP-2 and MMP-9 (Moradian et al., 2022; Kiuru et al., 2021). Endogenous pro-MMPs within the dentin matrix can be activated in acidic environments—such as those generated by cariogenic bacterial acids or acidic resin monomers—which exposes their catalytic domain. However, once activated, these MMPs display optimal enzymatic activity at neutral pH; after acidification, pH neutralization (e.g., via dentinal buffering or salivary buffers) allows MMPs to degrade the collagen matrix (Chaussain et al., 2013. Moreover, the process of demineralization in clinical conditions is not limited to phosphoric acid etching; the depth and extent of demineralization varies in vivo, and studies have shown that phosphoric acid concentration strongly modulates MMP expression and activity in demineralized dentin (DeVito-Moraes et al., 2016).
Dental adhesive systems have been revolutionary in dentistry, substantially expanding clinicians’ treatment options. Until recently, these systems were manufactured to be used exclusively with either the etch-and-rinse (E&R) or the self-etch (SE) technique; however, universal adhesives, which facilitate clinical ease of application with both E&R and SE approaches, have now been introduced (Yalçin et al., 2025). This technique, which integrates all components into a single bottle to create a one-step clinical system, has become highly popular due to its user-friendliness and ease of application (Apolonio et al., 2017).
Biomodification of dentin has become a popular approach to enhance the reparative potential of the dentin substrate (Epasinghe et al., 2014). To resolve bonding issues, various strategies have been developed, including MMP inhibitors, antibacterial agents, collagen cross-linkers, and remineralization of the hybrid layer (Zhou et al., 2019).
CHX, as an MMP inhibitor, can maintain dentin adhesion, making it a safe option for cavity disinfection by maintaining adequate dentin adhesion (Vegi et al., 2024; Haralur et al., 2022). While numerous studies have shown that chlorhexidine, considered the gold standard for cavity disinfection due to its broad-spectrum activity, increases long-term bond strength, natural and biocompatible alternative materials with lower cytotoxicity potential can be used instead of CHX (Münchow and Bottino, 2017).
Flavonoids are a group of bioactive molecules capable of participating in various biological processes. Quercetin (QC), a type of flavonoid found in citrus fruits, possesses multiple properties, including anti-aggregant, antioxidant, and anti-inflammatory effects (Jiang et al., 2020; Natarajan et al., 2025). QC has been demonstrated to function both as an MMP inhibitor and a collagen cross-linker: in vitro zymography and RSC Advance studies confirm that QC reduces MMP-2/-9 activity in the hybrid layer while forming hydrogen bonds with collagen to stabilize the matrix (Li et al., 2017).
In adhesive dentistry, pretreatment of the dentin surface with a quercetin/ethanol solution has been shown to effectively inhibit MMP activity within the hybrid layer, delay the collapse of the collagen fibrillar network, and further enhance dentin bond longevity (Jiang et al., 2020; Li et al., 2017; Yang et al., 2017). Naringin is a flavanone glycoside found not only in citrus and grape fruits but also in beans, cherries, cocoa, thyme, and tomatoes (Dey et al., 2020). It exhibits potent anti-inflammatory and antioxidant activities (Dey et al., 2020; Chen et al., 2016). Moreover, naringin and its derivatives have been reported to demonstrate antimicrobial effects against pathogenic strains such as Listeria monocytogenes, Escherichia coli, and Staphylococcus aureus (Celiz et al., 2011).
Among vitamins, alpha-tocopherol (α-TF) and riboflavin (RF) derivatives have recently become materials investigated for their potential MMP-inhibitory effects. RF, also known as vitamin B2, is a non-toxic additive widely used in the food industry as a nutritional supplement and food colorant (Beck and Ilie, 2022). When combined with ultraviolet-A (UVA) irradiation, RF has long been used in ophthalmology to strengthen the cornea. Through this photochemical energy, RF disrupts weak intrinsic collagen cross-links and generates reactive oxygen species. Additionally, RF acts as a UVA photosensitizer by promoting the formation of new collagen cross-links (Ashwin and McDonnell, 2010; Daood et al., 2020a). Recent studies have indicated that a stable collagen network—necessary for the formation of the hybrid layer and for preventing its subsequent degradation—can be produced through photoactivated RF. RF-induced collagen cross-linking appears to be a promising adjunctive strategy for enhancing dentin bonding (Fu et al., 2020; Eusufzai et al., 2023). α-TF, one of the most active components of the vitamin E complex, has been investigated to a limited extent regarding its antioxidant properties and its effects on dentin collagen (Whang and Shin, 2015; Marcomini et al., 2024). Some recent studies have demonstrated that this compound has a positive influence on the durability of the adhesive interface (Daood et al., 2020b; Marcomini et al., 2024; Daood et al., 2019).
Various testing methods are employed to evaluate the effects of cavity disinfectants, including microtensile bond strength, confocal laser scanning microscopy, microleakage, and microbiological assays. The MicroSBS test, known for its homogeneous stress distribution, was included in the methodology of this study to prevent early failures that may result from microcracks and structural defects (Can et al., 2023).
Although factors affecting the decrease in bond strength over time in universal adhesives have been investigated in numerous studies, the long-term effects of MMP inhibitors such as QC, Nar, RF, and α-TF on bond strength remain under investigation. This study aimed to compare the impact of dentin pretreatment with CHX, QC, Nar, RF, and α-TF on the bond strength of dental adhesives after 24 h and 12 months of thermal aging. The null hypotheses of the study were as follows:
1. The application of different MMP inhibitors (CHX, QC, Nar, RF, and α-TF) to the dentin surface does not have a significant effect on bond strength.
2. There is no significant difference between bond strength values measured after 24 h and 12 months of thermal aging.
2 Materials and methods
Approval for this study was obtained from the Non-Interventional Clinical Research Ethics Committee of Batman University Faculty of Dentistry (approval date: 05/09/2024, approval number: 2024/06–08). The study was conducted by the principles of the Declaration of Helsinki. Sample size calculation was performed using the GPower software (GPower Ver. 3.1.9.2, Kiel, Germany). Considering six groups consisting of experimental and control groups and measurements at two different time points, with a 5% margin of error, 95% confidence level, medium effect size, and theoretical power of 80%, a minimum of 120 observations (10 per group) were planned across 12 groups. To account for possible experimental setbacks that might affect data integrity, the sample size was increased to n = 12 per group, resulting in a total of 144 specimens prepared. The entire experimental procedure is summarized in Figure 1.
Figure 1. Experimental workflow diagram.
2.1 Specimen surface preparation
A total of 150 caries-free human third molars, extracted within the last 2 months, were stored in 0.2% thymol solution at 4 °C for no longer than 3 months. The specimens were subjected to ultrasonic cleaning to ensure the complete removal of surface contaminants and debris. The enamel crown was sectioned using a high-speed diamond bur under water cooling to obtain sound dentin. Teeth were embedded in cylindrical acrylic resin blocks starting 1 mm apical to the cementoenamel junction. In order to obtain a standardized smear layer and flat dentin surface, the specimens were gently ground under slow water flow for 30 s using 600-, 1,000-, and 1200-grit aluminum oxide abrasive papers without applying pressure (Exakt 400 cs Apparatebau, Norderstedt, Germany). Residual debris was removed by rinsing with distilled water for 10 s.
Specimens were randomly divided into six groups (n = 24) according to pretreatment procedures. The application protocols and all materials used in each group are detailed in Table 1. All test solutions were vortexed until a homogeneous mixture was obtained, placed in UV-protected bottles, and used within 24 h after mixing. (The compounds were diluted and homogenized with the aid of a magnetic stirrer and kept in light-proof containers, with their lids closed to prevent solvent evaporation.)
Table 1. Test solutions and application protocols (Moradian et al., 2022; Beck and Ilie, 2022; Turkistani et al., 2024).
The pretreatment solutions were actively applied to the dentin surface by tapping with a microbrush.
For the bonding procedure, a universal adhesive was applied to the pretreated surfaces of all teeth in self-etch mode using a single-use applicator, in accordance with the manufacturer’s instructions. The adhesive was then light-cured using an LED curing unit (Valo, Ultradent, United States) in standard power mode, delivering 1,000 mW/cm2 for 20 s. Before the experiments, the irradiance of the curing unit was measured using a radiometer (SDI Radii Plus, SDI, Bayswater, Australia) to ensure a minimum radiant exposure of 16.8 J/cm2 (Sahadi et al., 2023), thus ensuring complete polymerization. The irradiance measurement was repeated after every five specimens.
Following the bonding procedure, a nanohybrid flowable composite was applied onto the dentin surface of each tooth using a starch tube, forming a cylindrical specimen with a bonding area of 1 mm2 (1 mm in diameter and 1 mm in height). The composite was then light-cured for 20 s.
Subsequently, the samples were stored in distilled water in a temperature-controlled incubator (FN 500, Nüve, Turkey) at 37 °C and 100% humidity for 1 h. As the starch tube softened, it was gently removed using an explorer, and the specimens were subjected to an additional 20-s light curing (Jiang et al., 2020). To reduce variability, all samples and procedures were performed by a single experienced operator.
Each group was divided into two equal subgroups (n = 12): aged (thermocycled, T+) and non-aged (non-thermocycled, T−). The long-term aging of the specimens was performed using an artificial aging device (Thermocycler THE-1100, SD Mechatronik GmbH, Feldkirchen-Westerham, Munich, Germany). Each cycle consisted of immersing the samples in baths of distilled water. The specimens were subjected to 10,000 thermal cycles between 5 °C and 55 °C, with each cycle consisting of a 25-s immersion in each bath and a 10-s dwell time (Jiang et al., 2020). A total of 10,000 cycles was used to simulate 1 year of clinical aging (Jiang et al., 2020).
Specimens in the T− subgroup were stored in deionized water at 37 °C for 24 h before the micro-shear bond strength (μSBS) test.
2.2 Micro-shear bond strength test
To determine the μSBS, each bonded specimen was mounted on a universal testing machine (MOD Dental MIC-101, Esetron Smart Robotechnologies, Ankara, Turkey) and subjected to a micro-shear bond strength test at a crosshead speed of 0.5 mm/min until failure occurred. The universal testing machine had lower fixed and upper movable compartments which were utilizeu an adjust the attachment jig with screws, with load cell of 5 kN.
The load at failure was recorded in Newtons (N), and the bond strength was calculated in megapascals (MPa) by dividing the load by the bonding area.
2.3 Failure mode analysis
The failure modes were examined under a stereomicroscope (SOIF, Istanbul, Turkey) at ×40 magnification. The failure mode was discovered and categorized as adhesive (debonding at the interface), cohesive (debonding within the tooth structure or composite mass), and mixed (a combination of adhesive and cohesive failures) (Figure 2, Figure 3) (Carvalho et al., 2025).
Figure 2. Cohesive failure.
Figure 3. Mixed failure.
2.4 Statistical analysis
Statistical analyses were performed using SPSS software (version 27 for Windows, SPSS Inc., Chicago, IL, United States). Normality and homogeneity of variances were assessed using the Kolmogorov-Smirnov and Levene tests, respectively. To compare the interaction effects between pretreatment solutions and different time points, one-way analysis of variance (ANOVA) was conducted, followed by post hoc Tukey tests at a significance level of α = 0.05.
3 Results
Among the pretreatment agents, quercetin exhibited the highest μSBS values, whereas riboflavin showed the lowest, and statistical comparisons revealed that the CHX, quercetin, and naringin groups performed significantly better than the riboflavin group, with p-values of 0.004, <0.001, and 0.01, respectively.
The effects of dentin pretreatment agents on subgroups’ μSBS values are summarized in Table 2.
Table 2. Mean and standard deviation (SD) of μSBS values (MPa) for subgroups.
Quercetin (51.03 ± 18.33 MPa) exhibited the highest μSBS values among all subgroups and was significantly higher than the control (both T− and T+), Riboflavin (both T− and T+), and α-Tocopherol (T+) groups (p = 0.005, 0.019, <0.001, <0.001, and <0.001, respectively). Among the tested pretreatment agents, quercetin demonstrated the most stable and durable bonding performance, maintaining relatively high μSBS values even after thermal cycling. In contrast, α-Tocopherol (25.81 ± 9.3 MPa) exhibited lower μSBS after thermal cycling and performed significantly worse than quercetin.
Riboflavin in the non-thermal cycling subgroup (22.58 ± 8.56 MPa) produced the lowest bond strength among all T− groups, showing significantly lower values compared with Quercetin (both T− and T+), CHX (T−), and α-Tocopherol (T−) (p = 0.020, <0.001, 0.012, and 0.022, respectively).
The analysis of thermal cycling effects is presented in Figure 4. Although thermal cycling tended to decrease μSBS values in the Control, Chlorhexidine, and α-Tocopherol groups and tended to increase them in the Quercetin, Riboflavin, and Naringin groups, these differences were not statistically significant within any group.
Figure 4. Distribution of the effect of thermal cycling within the groups.
The frequency distribution of the failure modes examined under a stereomicroscope is presented in Figure 5. The failure mode analysis revealed a predominance of mixed and adhesive failures. Adhesive failure was identified as the most common failure mode in all groups, except for the Quercetin (T−) group. Following thermal cycling, the frequency of adhesive failure decreased in the Chlorhexidine, Riboflavin, and α-Tocopherol groups, whereas it increased in the Control and Quercetin groups, and showed no change in the Naringin group.
Figure 5. Distribution of failure modes for each group subjected to the bond strength test.
4 Discussion
According to the results of this study, among the agents used for dentin pretreatment, QC demonstrated significantly higher bond strength compared to CHX. Therefore, the first null hypothesis (H0) of the study was rejected.
Thermal aging had varying effects on bond strength among the experimental groups. While an increase in bond strength was observed after thermal cycling in the QC, RF, and NG groups, a decrease was noted in the CHX and α-TF groups. Although the group values varied, these differences were not statistically significant; therefore, the second null hypothesis (H0) of the study could not be rejected.
For CHX, the supporting evidence is stronger, and studies reporting generation-dependent effects are available, with CHX demonstrating superior performance particularly in the self-etch (SE) approach. However, for quercetin, naringin, riboflavin, and alpha-tocopherol, there remains a need for more generation-specific (6th vs. 7th) comparative in-vitro studies (Turkistani et al., 2024; Zhao et al., 2022).
In a comprehensive review investigating CHX, it was observed that CHX pretreatment did not improve bond strength or retention rates in follow-up cases at 6, 18, 24, and 36 months (Josic et al., 2021). These findings are consistent with the results obtained in our study. A possible explanation for this outcome could be the diminishing inhibitory effect of CHX on MMP-2, -8, and -9 enzymes over time.
In the present study, a CHX concentration of 2% was selected and applied without rinsing. This specific protocol was chosen in accordance with the manufacturer’s instructions and is supported by literature validating similar approaches (Garlapati et al., 2024). This is because studies have shown that lower concentrations of CHX do not enhance bond strength (Josic et al., 2021; Garlapati et al., 2024). Additionally, higher concentrations of CHX have been reported to cause a decrease in the Ca/P ratio and microhardness (Turkistani et al., 2024).
QC, which is currently a frequently researched agent, has become an effective compound in caries prevention and enhancing bond strength due to its properties such as effective inhibition of MMP activity within the hybrid layer and delay of collagen fibrillar network degradation by reducing reactive oxygen species (ROS) and cyclooxygenase-2 (COX-2) production (Jiang et al., 2020; Moradian et al., 2022; Yang et al., 2017; Hong et al., 2022). Various studies have investigated the optimal effective dose of QC using different concentrations and application techniques; the concentration of 1% and the application method reported by Moradian et al. (2022) have been adopted as references for demonstrating the optimal effect (Moradian et al., 2022). Ethanol is an appropriate solvent for overcoming the limited water solubility of quercetin. Moreover, the inherent antimicrobial and penetrative properties of ethanol further enhance the disinfectant efficacy of quercetin (Dávila-Sánchez et al., 2020).
According to the results of the present study, QC demonstrated significantly higher bond strength values compared to the other groups at 24 h. Although this increase aligns with numerous studies in the literature (Moradian et al., 2022; Porto et al., 2018; de Moraes Porto et al., 2021; Dávila-Sánchez et al., 2020), it is inconsistent with the findings of Yang et al. (Yang et al., 2017). In Yang et al. (2017) study, QC was incorporated into the adhesive system, and this incorporation did not have a significant effect on the immediate bond strength (Yang et al., 2017).
In this study, after 12 months of thermal aging, a decrease in the bond strength of QC was observed; however, this reduction was not statistically significant. This finding is consistent with previous studies (Moradian et al., 2022; Porto et al., 2018; de Moraes Porto et al., 2021; Dávila-Sánchez et al., 2020). QC stabilizes collagen through four different forces: van der Waals, electrostatic, hydrogen bonding, and hydrophobic interactions. Although these forces enhance immediate bond strength, some of them diminish over time, leading to a loss of effect (Moradian et al., 2022). Additionally, the decrease in pH levels during the thermal cycling period is considered a significant factor that alters the molecular structure of QC, thereby weakening its effect (Dávila-Sánchez et al., 2020). The reduction in bond strength observed after thermal cycling can be explained by these two mechanisms.
In the literature, there is also research suggesting that the addition of QC to adhesives may reduce bond strength (Dávila-Sánchez et al., 2020). In that study, QC was dissolved in ethanol and applied directly to the dentin surface, which may have more effectively enhanced collagen stabilization.
Another pretreatment agent used in this study, α-Tocopherol (α-TF), showed a significant decrease in bond strength following thermal cycling. This result, consistent with other studies, suggests that hydrophobic antioxidants like α-TF may disrupt polymerization over time, leading to a more linear polymer structure and consequently reduced bond strength (Moradian et al., 2022; Gotti et al., 2015). Additionally, a recent study also reported that α-TF did not enhance bond strength (Silva et al., 2023).
The NG group demonstrated the third highest immediate bond strength values, following QC and CHX. This effectiveness is likely due to the protonation of anionic regions, converting them into cationic sites, which increases the likelihood of these sites reacting with the carbonyl and carboxyl groups of collagen (Epasinghe et al., 2014; Dávila-Sánchez et al., 2020). Furthermore, an increase in bond strength was observed after the thermal aging procedure. This finding is consistent with results reported in similar studies (Dávila-Sánchez et al., 2020; Leme-Kraus et al., 2017).
The effect of flavonoids on bond strength after thermal aging may serve as a useful indirect method to evaluate the substantivity of these therapeutic biomolecules. Studies investigating flavonoids have demonstrated long-term therapeutic effects, which is one of the reasons why flavonoids are currently being extensively researched across various biomedical fields (Dávila-Sánchez et al., 2020; Leme-Kraus et al., 2017; Pietrangelo et al., 2022).
The use of QC or NG as cavity disinfectants in place of CHX in dental practice may offer an advantageous cost–benefit profile owing to their dual antibacterial and MMP-inhibitory effects, biocompatibility, and potential to enhance the long-term stability of bond strength (Liu and Wu, 2025).
Another cavity disinfectant included in this study is RF. However, data regarding the ideal application protocol for RF remains insufficient (de Carvalho Beckman et al., 2024; Eusufzai et al., 2023). Previous studies have investigated RF’s role in collagen cross-linking and enhanced adhesive penetration, leading to improved dentin hybridization (Fu et al., 2020; Daood et al., 2019). Nevertheless, the results concerning bond strength and bonding durability remain inconsistent (Van Meerbeek et al., 2020). As a cross-linking agent, RF can stiffen collagen fibers, thereby limiting protease activity. Additionally, the presence of RF may reduce the degradation of the resin–dentin interface by binding to functional hydroxyl groups in collagen through proline or lysine residues (Daood et al., 2020a). Eltoukhy et al. (2022) described the effects of different aging environments and durations on micro-tensile bond strength. Consistent with their findings, our study also demonstrated a positive change in bond strength following aging (Eltoukhy et al., 2022).
The results of the present study can be explained by the mechanisms of the tested MMP inhibitors. At 24 h, the highest SBS was observed in QC group, followed by CHX and NG, all significantly higher than α-TF. This early pattern aligns with the known mechanisms of these agents: QC and NG inhibit MMP activity and stabilize collagen through cross-linking, whereas CHX preserves the hybrid layer via MMP inhibition (Eusufzai et al., 2023; Hass et al., 2016). After 12 months of aging, SBS increased in the QC, riboflavin (RF), and NG groups, likely due to long-term collagen stabilization and sustained enzymatic inhibition, whereas a decline was observed in the control, CHX, and α-TF groups, reflecting the time-dependent reduction in CHX efficacy and the limited MMP-inhibitory effect of α-TF (Hass et al., 2016; Liu and Wu, 2025; Moradian et al., 2022).
Although CHX is recognized as a highly effective MMP inhibitor for preserving long-term resin–dentin bonds, its protective effect has been reported in some studies to diminish after 18–24 months depending on concentration, application protocol, and aging conditions (Kiuru et al., 2021). Nevertheless, flavonoid agents such as QC and NG, as well as RF and α-TF not only inhibit MMP activity but also stabilize collagen through cross-linking, thereby contributing to the more durable preservation of the hybrid layer. Long-term in vitro studies using universal adhesives have shown that the incorporation of QC, NG, RF, and α-TF significantly enhances bond strength and reduces nanoleakage after aging, suggesting that these agents could serve as viable alternatives to CHX in maintaining adhesive interface integrity over time (Falconi-Páez et al., 2025).
In clinical practice, MMP inhibitors such as chlorhexidine (CHX), quercetin, naringin, riboflavin, and alpha-tocopherol can be applied as a pretreatment to the dentin surface prior to adhesive placement, aiming to stabilize the collagen matrix and reduce enzymatic degradation. This approach is particularly relevant in high-caries-risk patients or in cases requiring deep dentin bonding, where the hybrid layer is more susceptible to hydrolytic and enzymatic breakdown. Clinical protocols typically involve a brief application of the MMP inhibitor solution, careful drying, followed by adhesive placement. Both in vitro and in vivo studies have demonstrated that this procedure improves bond durability without compromising adhesive performance (Breschi et al., 2010; Falconi-Páez et al., 2025). Therefore, incorporating MMP inhibitors into routine adhesive procedures may provide a practical strategy to enhance long-term restorative outcomes.
Adhesive failure was predominant across all experimental groups. This finding is consistent with similar studies reported in the literature (Moradian et al., 2022). It is believed that the weakest point in the resin-dentin bond occurs within the hybrid layer, leading to adhesive failure.
This study was conducted under in vitro conditions, and thus, the physiological dynamics of the oral environment could not be fully replicated. Future studies may strengthen the analysis by testing different adhesive systems and composite brands. Additionally, similar in vivo studies should be conducted to further support the results.
5 Conclusion
According to the results of this in vitro study, quercetin and naringin are natural and effective agents that may serve as alternatives to chlorhexidine for dentin pretreatment. Quercetin demonstrated the highest bond strength, particularly after thermal aging, indicating promising potential for long-term clinical success. In contrast, α-tocoferol and riboflavin exhibited lower and more variable bond strength values. These findings support the clinical applicability of quercetin and naringin in dentin pretreatment; however, further clinical studies are warranted to confirm these results.
Data availability statement
The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.
Ethics statement
The studies involving humans were approved by Ethical approval for this study was granted by the Non-Interventional Clinical Research Ethics Committee of Batman University Faculty of Dentistry. (approval date: 05/09/2024, approval number: 2024/06–08). The studies were conducted in accordance with the local legislation and institutional requirements. The human samples used in this study were acquired from gifted from another research group. Written informed consent for participation was not required from the participants or the participants’ legal guardians/next of kin in accordance with the national legislation and institutional requirements.
Author contributions
SG: Formal Analysis, Methodology, Resources, Writing – original draft. EA: Funding acquisition, Supervision, Validation, Visualization, Writing – review and editing. GK: Conceptualization, Data curation, Investigation, Project administration, Software, Writing – original draft.
Funding
The author(s) declared that financial support was received for this work and/or its publication. This study was supported by Çukurova University Scientific Research Projects under the project number TSA-2024–16656.
Acknowledgements
The authors would like to extend their sincere appreciation to Batman University, Batman, Turkiye, for its continuous support.
Conflict of interest
The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Generative AI statement
The author(s) declared that generative AI was not used in the creation of this manuscript.
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Keywords: cavity disinfectants, chlorhexidine, dentin pretreatment, flavonoid, micro shear bond strength (μSBS), naringin, quercetin
Citation: Gümüş Ayaz S, Sonkaya E and Keçeci G (2025) Comparative analysis of the impact of modern cavity disinfectants on dentin bond strength. Front. Mater. 12:1718129. doi: 10.3389/fmats.2025.1718129
Received: 03 October 2025; Accepted: 09 December 2025;
Published: 19 December 2025.
Edited by:
Daochen Zhu, Jiangsu University, ChinaReviewed by:
Aastha Buch, Dharmsinh Desai University, IndiaMarina Ciccone Giacomini, University of São Paulo, Bauru, Brazil
Copyright © 2025 Gümüş Ayaz, Sonkaya and Keçeci. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Simge Gümüş Ayaz, ZHRzaW1nZWd1bXVzQGdtYWlsLmNvbQ==