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Article

Shear Bond Strength and Finite Element Stress Analysis of Composite Repair Using Various Adhesive Strategies With and Without Silane Application

by
Elif Ercan Devrimci
,
Hande Kemaloglu
,
Cem Peskersoy
*,
Tijen Pamir
and
Murat Turkun
Faculty of Dentistry, Ege University, Izmir 35030, Turkey
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(15), 8159; https://doi.org/10.3390/app15158159
Submission received: 29 June 2025 / Revised: 19 July 2025 / Accepted: 20 July 2025 / Published: 22 July 2025
(This article belongs to the Special Issue Dental Materials: Latest Advances and Prospects, Third Edition)
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Abstract

This study evaluated the effect of various adhesive systems, particularly silane application, on the repair bond strength of a nanofill resin composite and associated stress distribution using finite element analysis (FEA). A total of 105 composite specimens (4 × 6 mm) were aged by thermal cycling (10,000 cycles), roughened, etched with phosphoric acid, and assigned to seven groups (n = 15): G1. control—no adhesive; G2. Single Bond Universal Adhesive; G3. composite primer; G4. PQ1; G5. Silane + PQ1; G6. Clearfil Universal Bond; G7. All-Bond Universal. Shear bond strength was measured using a universal testing machine (1 mm/min), and failure modes were microscopically classified. FEA was conducted under static and fatigue conditions using 3D models built in Fusion-360. Mechanical properties were obtained from technical data and the literature. A 300 N load was applied and contact detection (0.05 mm) and constraint zones were defined. Statistical analysis was performed using one-way ANOVA and Tukey’s HSD (p = 0.05). Pearson’s correlation was used to assess the relationship between bond strength and von Mises stress. The highest bond strength was found in G2 (21.54 MPa) while G1 showed the lowest (8.86 MPa). Silane-treated groups exhibited favorable stress distribution and a strong correlation between experimental and simulated outcomes. Silane applications significantly enhance composite repair performance.

1. Introduction

In restorative dentistry, there is a growing trend of repairing defective resin composite restorations rather than removing and replacing the complete restoration.
According to FDI criteria, which were improved and modified in 2010, composite restoration repairs may be considered the treatment of choice for several intraoral occurrences, such as chipping; partial or marginal fracturing of restorative material; unacceptable severe staining; secondary caries in accessible locations; the replacement of only one approximal box of Class II MOD restorations; and instances in which the complete removal of an extensive composite restoration would endanger the health of a tooth, such as in composite laminates [1]. Furthermore, restoration repair has gained additional importance due to the worldwide acceptance and implementation of minimally invasive dentistry. There is, however, a possibility that the repair procedure may result in an unacceptably weak restoration. Therefore, an excellent bond between the old and the fresh resin composites is necessary to successfully repair the restorations.
In general, bonding between two fresh composite layers is accomplished in the presence of an oxygen-inhibited layer. However, aged restorations do not have this layer of unreacted monomers on their surfaces. Therefore, repairing aged composites using fresh composites remains a challenge due to the exhaustion of free radicals in the aged composite [2,3]. Several surface conditioning methods have been suggested to improve the composite-to-composite bond strength when adhesive systems are used [3,4,5,6]. These methods include the use of bur roughening of the aged composite surface, silane pretreatment, air abrasion, and application of silane agents, as well as combinations of these procedures [4,5,6]. All these methods increase the reactive surface area for adhesive resins, thereby improving bond strength.
Recently, universal adhesives have been developed and become popular among dentists due to their wide range of application modes, such as self-etch mode, etch-and-rinse mode, or selective enamel etching [7,8,9]. Most of these adhesives contain 10-methacryloyloxy-decyl-dihydrogen-phosphate (10-MDP) as a functional monomer and provide very intense and stable interactions with calcium in hydroxyapatite. Some universal adhesives have silane incorporated into their formulations, in addition to 10-MDP [10]. Silanes rebuild the inhibition layer for safe bonding between old and new resin composites. They also improve surface wetting and chemical bonding between the aged composite and the new composites by activating the inhibition layer. Although the use of so many additional primers with universal adhesives is not suggested when bonding to tooth structures, incorporating silane into these adhesives may help to increase the repair bond strength and eliminate the need for silane pretreatment [11,12].
The complexity of achieving a strong bond between aged and new composites calls for an in-depth exploration of the forces at play, which is where finite element analysis (FEA) becomes an invaluable tool. FEA allows researchers to simulate and analyze the stress distributions within restorative materials, highlighting potential failure points that could compromise the integrity of the repair [13]. By understanding these distributions, modifications in material choices or application techniques can be made to optimize bond strength and reduce failure rates [14]. In this way, FEA supports the investigation of universal adhesives’ effectiveness and helps identify promising avenues for improving restorative practices.
Even though there are several studies [15,16,17,18,19,20,21,22,23] that present alternative methods of composite repair, there is still no consensus as to the best treatment. Thus, the present study aimed to assess the efficiency of different adhesive systems on the repair bond strength of new resin composite bonded to aged resin composite and evaluate the silane effect on the repair bond strength. Additionally, this study employed FEA to simulate and understand the stress distribution and mechanical performance of repaired interfaces under various conditions, providing deeper insights into the efficacy of different adhesive systems. The null hypotheses tested were that (a) the adhesive system used has no effect on the repair bond strength of a resin composite bonded to aged composite; (b) using silane as an additional step for a conventional self-etch adhesive system would not make any difference in the repair bond strength compared to universal adhesives containing silane; and (c) FEA simulations would not significantly alter the understanding or predictions of mechanical performance when compared to empirical results.

2. Materials and Methods

This study was conducted as an in vitro experimental comparison of different adhesive strategies, with and without silane application, to assess their effect on composite repair bond strength. Additionally, finite element analysis was employed to simulate stress distribution under standardized loading conditions.

2.1. Sample Preparation

The materials used in this study, along with their application techniques, are presented in Table 1.
The sample size was determined based on a power analysis using G*Power software (v3.1; Heinrich Heine University, Düsseldorf, Germany). A minimum of 15 specimens per group was calculated to detect a medium effect size (f = 0.40) with a statistical power of 0.80 and an alpha level of 0.05 using one-way ANOVA. A total of 105 samples were fabricated from a nanofill resin composite (Clearfil Majesty Esthetic, Kuraray, Japan) using a Teflon mold with a diameter of 4 mm and a height of 6 mm. Specimens were prepared by inserting uncured resin composite into the mold placed on a glass slide covered by a mylar strip and covered by a second strip and a glass slide to stabilize the mold. The specimens were light-cured every 2 mm increment from the top, according to the manufacturer’s specifications, using a light-curing device (Elipar 10, 3M ESPE, St. Paul, MN, USA). The specimens were stored in distilled water for 14 days prior to aging. They were then subjected to thermal cycling 10,000 times (≈1 year of aging) between 5 and 55 °C, with a dwell time of 20 s and a transfer time of 3 s. After the aging process, the aged specimens were roughened with a silicon carbide grinding paper (320-grit) to standardize the surfaces, then etched with phosphoric acid for 10 s, washed, and dried with air/water spray.
One hundred and five specimens were randomly allocated to seven groups (n = 15) according to the repair procedures to be tested: G1. control—no adhesive; G2. Single Bond Universal Adhesive; G3. composite primer; G4. PQ1; G5. Silane + PQ1; G6. Clearfil Universal Bond; G7. All-Bond Universal. Randomization was performed using a computer-generated random sequence created in Microsoft Excel. The group assignments were carried out by an independent researcher who was blinded to the adhesive protocols to minimize selection bias. G1 was considered as a negative control group with no treatment, and the adhesives in the other groups were applied according to the manufacturers’ instructions for composite repair, as shown in Table 1. For all groups, the specimens were then placed in a mold with a diameter of 4 mm and a height of 12 mm, and the same fresh resin composite was inserted against the treated side of the aged specimen in increments and light-cured for 20 s. Repaired samples (4 mm in diameter and 12 mm in height) were stored in distilled water for 24 h at 37 °C before shear bond testing (Figure 1).

2.2. Shear Bond Testing (SBT)

The immediate shear bond strengths were measured using a universal testing machine (AG-S 5kN Shimadzu, Tokyo, Japan) (Figure 1). The load (max. 300 N) was applied with a crosshead speed of 50 mm/min until fracture. The maximum load force and stress (bond strength) values were recorded. Subsequently, the exact type of fracture was classified as adhesive, cohesive, or mixed under a stereomicroscope at 40× magnification.

2.3. Finite Element Analysis

Finite element analysis was employed to determine the shear bond strength under both static and fatigue conditions (Figure 2).
Mesh validation was performed using a mesh convergence study while tetrahedral meshing was applied with an average element size of 0.2 mm. The model was re-meshed with finer elements until further mesh refinement resulted in a von Mises stress value change of less than 5%, ensuring computational accuracy and stability. To simulate the virtual bond strength tests, Fusion 360 (v2603.0.86, Autodesk Inc., San Francisco, CA, USA) CAD software was used. Physical properties of the study materials, including Young’s modulus, the shear and tensile strength, and Poisson’s ratio, were collected from manufacturers’ technical data or FEA studies, as shown in Table 2.
Subsequently, static and dynamic FEA analyses were utilized for calculations, with a 0.05 mm automatic contact detection tolerance, and three sides (both sides of the 3D resin block) were selected as constraints. The load (max. of 300 N) was then applied in accordance with the load-to-failure test to each specimen, considering the ultimate tensile strength (MPa) data as the main safety factor, and data were recorded for each model. In the present study, all materials in the finite element analysis (FEA) were modeled under the assumption of linear elastic material behavior under static loading condition. Boundary conditions were also simplified: three sides of the resin composite blocks were constrained with fixed displacement boundary conditions to simulate immobilization during shear bond testing, while a static load of 300 N was applied on the opposing surface, in alignment with the experimental setup. These simplifications allow for effective stress distribution analysis while maintaining computational efficiency and relevance to clinical composite repair scenarios.

2.4. Statistical Analyses

Data were imported into SPSS analysis software (v27.0, IBM Corp., Chicago, IL, USA), and a one-way analysis of variance (ANOVA) along with post hoc Tukey’s HSD multiple comparisons were employed to assess statistical differences in repair bond strengths among groups at a significance threshold of 0.05.
The correlation between shear bond strength values and von Mises stress values was analyzed using Pearson’s correlation (r) test for the finite element analysis (FEA) results. Comparisons were conducted on FEA results to evaluate consistency and reliability across various surface treatments and assess their impact on mechanical performance predictions.

3. Results

The mean shear bond strengths and differences among groups are illustrated in Figure 3 and shown in Table 3.
The highest bond strengths were recorded in specimens repaired with Single Bond Universal Adhesive (21.54). These data were comparable to the data regarding specimens repaired with Clearfil Universal Bond GC (21.17), silane/PQ1 (20.43), and composite primer (17.15) (p > 0.05). The lowest repair strengths were obtained from specimens in the control group, in which the resin composite was repaired without any adhesive layer (8.86 MPa). Specimens repaired with PQ1 had a mean value of 12.90, which is significantly different than all the other groups (p < 0.05). All-Bond Universal (15.92) presented significantly similar strength values to those of the composite primer and silane/PQ1 (p > 0.05).
Fracture analysis revealed that all test groups presented cohesive failures in the aged composite, except for one specimen in PQ1 and one specimen in the All-Bond Universal adhesive groups. These two specimens and all the specimens in the control group presented adhesive failures (Figure 4).
The finite element analysis (FEA) results indicate variations in von Mises stress values across different surface treatments. The control group exhibited the lowest von Mises stress (9.91 MPa) and, correspondingly, had the lowest mean bond strength (8.86 MPa). In contrast, the highest von Mises stress was observed for Single Bond Universal (26.963 MPa), which also demonstrated one of the highest bond strengths (21.54 MPa). These findings indicate a positive correlation between shear bond strength values and von Mises stress values (r = 0.825). In contrast, this correlation was not found to be statistically significant for the GC Composite Primer and PQ1 + silane groups (p > 0.05).
The displacement findings reveal notable differences among the treatments. The All-Bond Universal and Silane + PQ1 groups showed minimal displacement (0.071 mm and 0.055 mm, respectively), suggesting a more stable bond. Conversely, PQ1 exhibited the highest displacement (1.521 mm), indicating a less stable interface despite its moderate bond strength (12.90 MPa). Overall, treatments with higher bond strength, such as Clearfil Universal Bond and Single Bond Universal, also demonstrated relatively low displacement values (0.093 mm and 0.097 mm, respectively) (p < 0.05).

4. Discussion

This study aimed to investigate the effects of different adhesive systems on the repair bond strength of a resin composite bonded to an aged composite. The results showed that adhesive systems were necessary when adding fresh composite to aged composite, and differences in the adhesive systems influenced the repair bond strength of a resin composite bonded to aged resin composite. Therefore, the first null hypothesis, i.e., that the adhesive system used does not affect the repair bond strength of a resin composite bonded to aged composite, was rejected.
In order to achieve successful results in repairing composite restorations, it is necessary to create a durable bond between the old restoration and the new resin composite. The structure of the old composite, the time it spends in the mouth, and the method of repair are important factors affecting the success of the new restoration [33]. Therefore, the surface of the old restoration should be altered in order to provide a proper bonding surface [21,22], adhesion should be provided with a suitable adhesive system, and a pairing composite resin should be used [18,19]. This approach, as in the present study, was deliberately chosen to eliminate variables related to differences in composite composition, ensuring that the observed bond strength outcomes were attributable solely to the adhesive systems tested.
The highest bond strength was obtained when the Single Bond Universal Adhesive system was used. This outcome should be interpreted in light of its chemical formulation, which includes both MDP and silane, two components known to enhance adhesion and interfacial stability. As stated by the manufacturer, Single Bond also has Vitrebond copolymer in addition to MDP and silane in its composition. Vitrebond allows the product to bond in a moist environment, which could be important in repairing aged composites, since these are fully saturated with water during the thermal cycling procedure. The results obtained from using Single Bond in the composite-to-composite repair procedure can be explained by the agent’s enhanced chemical content and structure. However, the superior performance of this group must be viewed cautiously, as other adhesives demonstrated variable results that were influenced by their distinct chemical compositions. For instance, the relatively lower bond strength of PQ1 may be attributed to its lack of functional monomers and absence of silane. Similarly, the moderate performance of All-Bond Universal, despite containing MDP, could be due to the absence of silane and differences in solvent content or pH.
The aging process of composites plays an important role in the bond strength of composite repairs [4,34,35]. Since there is no standard protocol for the artificial aging process, different aging procedures have been applied in many composite repair studies [36,37,38,39,40,41]; thermal cycling has been the most frequently used method [39,40,41]. During this process, the composites and the adhesive interfaces undergo a process of degradation due to water absorption and constant temperature changes. In the present study, 10,000 thermal cycles were employed to simulate intraoral aging of the substrate composite. According to the recent literature, this protocol approximates one year of clinical service, based on the frequency of daily thermal fluctuations resulting from routine consumption of food and beverages [39,40]. As such, the applied aging procedure reflects an early-stage degradation scenario that is representative of clinical conditions in which restoration repair may be considered. Following the thermal aging process applied only to the substrate composite surfaces, the repair protocol was subsequently performed. The repaired specimens were then stored in distilled water at 37 °C for 24 h prior to bond strength testing. The immediate shear bond tests of the samples after 24 h showed cohesive failure patterns in the aged composite, indicating that the bond strength was higher than the inherent strength of the aged composite. The required reference value for the ideal bond strength needed after composite repair must be in the range of 15 to 25 MPa [42]. In this study, all the groups, except for the control and PQ1, yielded optimal repair bond strength. It should be noted that in the present study, the repaired specimens were stored in distilled water for 24 h prior to bond strength testing. While this short-term storage period allows for the assessment of immediate bond performance, it may not sufficiently reflect the long-term hydrolytic and mechanical degradation observed clinically. Previous studies have demonstrated that extended water storage and post-repair thermocycling can adversely affect bond durability by promoting water sorption, plasticization of the resin matrix, and interfacial degradation over time [35,37]. Therefore, incorporating additional aging protocols following the repair procedure would decrease the predictive value of in vitro testing and may hinder a clearer evaluation of the clinical performance of adhesives.
The adhesive systems used in this study were selected based on their distinct chemical compositions to enable a comparative evaluation of bonding strategies in composite repair. Most of the adhesives contained 10-MDP as a functional monomer, while others included both MDP and silane, or monofunctional methacrylate [10,11,19]. PQ1, a conventional etch and rinse adhesive lacking both MDP and silane, was deliberately included to represent earlier-generation adhesive systems. Its inclusion allowed for the assessment of how modern formulations particularly those incorporating silane, either as a separate pretreatment or within universal adhesives perform in comparison to traditional products. Notably, PQ1 was also selected because it permits combination with separate silane application, allowing the study to isolate and examine the specific contribution of silane to the repair bond strength. Accordingly, an additional group utilizing silane pretreatment followed by PQ1 application was tested. This group exhibited significantly higher bond strength compared to PQ1 alone, underscoring the essential role of silane in promoting chemical adhesion to aged composites [2]. Silane molecules contain two functional groups: silanol groups that bond with the inorganic filler particles, and organofunctional methacrylate groups that copolymerize with resin monomers [43]. This dual reactivity enhances both chemical bonding and surface wettability, which may explain the improved performance observed in the silane/PQ1 group [2,44].
The results obtained from Single Bond Universal and Clearfil Universal Adhesive were comparable to those of the silane/PQ1 group, indicating that both strategies effectively enhanced the repair bond strength of aged resin composites. This suggests that the application of silane either as a separate step or incorporated into universal adhesive formulations can significantly improve bonding performance [45]. Given the similar outcomes observed between these two approaches, silane-containing universal adhesives may be preferred in clinical practice due to their simplified application, reduced technique sensitivity, and lower risk of procedural errors. Therefore, the second hypothesis stating that “the use of separate silane pretreatment would not significantly differ in effectiveness from universal adhesives containing silane” was accepted. Additionally, the GC Composite Primer group, which contains monofunctional methacrylate according to the manufacturer, showed bond strength values comparable to the silane-containing groups. In contrast, adhesives without silane (e.g., PQ1) exhibited significantly lower bond strength, further emphasizing the importance of silane in achieving effective chemical bonding to aged composites.
All-Bond contains 10-MDP, which is the main component of many resin-based materials and is the most frequently used acidic monomer. The dihydrogen phosphate group of MDP is used for etching tooth substrates, and the methacrylate group is used for cross-linking with other resin monomers [46]. 10-MDP is known to interact most intensively with hydroxyapatite and to form a hydrolytically stable bond with calcium [46]. Indeed, many promising results have been obtained from various investigations on the enamel and dentine bonds of 10-MDP [10]. In the present study, the shear bond strength of All-Bond in the repair process was significantly lower than that of Clearfil Universal and Single Bond Universal. This result can be attributed to the lack of hydroxyapatite in the resin composite samples for MDP to bond with.
In this study, only the effect of adhesive systems on repairing composite resins was tested, so the repair composite used was chosen to be the same as the aged composite. Usually, in repair studies, the substrate and the adherent composites are chosen to be different in order to reflect clinical conditions wherein the type of composite to be repaired is unknown [47]. It has likewise been stated in a study [48] that the composite type influences the repair bond strength of the restorations. For instance, Baur and Ilie [48] demonstrated that the type of composite plays a critical role in the repair bond strength, with significant differences observed between nano-hybrid and microhybrid composites. Although using the same composite material for both aged and repair specimens’ controls for compositional variability and isolates the effect of adhesive systems, clinical situations often involve repair on unknown or different original composites. A recent systematic review and meta-analysis found no significant difference in repair bond strength between similar and dissimilar composite combinations, suggesting that well-established repair protocols may still be effective even when the substrate composite is unknown [49]. Nonetheless, it remains important to test mismatched composite pairings in future studies to further validate clinical applicability across a wider range of materials. Additionally, with the increasing adoption of three-dimensional (3D) printed dental composites in restorative dentistry, there is a growing need to investigate whether conventional adhesive strategies, including silane application, perform similarly on these novel materials. Recent studies have reported distinct surface characteristics and layer-by-layer structural differences in 3D printed composites compared to traditionally fabricated resin composites, which may affect the repair bond strength and adhesive behavior [50]. Therefore, future studies should investigate various composite types, including 3D printed dental composites, to validate the applicability of the present findings across different clinical scenarios.
However, in this study, we preferred to repair the substrates with the same resin composite to eliminate bonding failures that can be caused by differences in the compositions of resin composites. Nevertheless, it should be acknowledged that the use of different composite materials in clinical situations may result in varying repair outcomes due to differences in filler morphology, resin matrix composition, and degree of conversion. These material dependent variables can influence the effectiveness of the adhesive interface and the chemical compatibility between the aged and fresh composites [49]. Therefore, future research evaluating repair bond efficacy among various composite combinations would yield a more thorough comprehension relevant to practical clinical situations.
Ideally, the repair bond strength should be similar to the cohesive strength of the repaired resin composite. In this study, all failure types were cohesive in the aged composite for all groups, except for one in the PQ1 group (93.3%) and one in the All-Bond Universal group (93.3%). In addition, all the specimens in the control group experienced adhesive failures (100%). However, the overall analysis revealed 96.6% cohesive failure in the aged composites among all adhesive groups, indicating that adhesive bonding is stronger than cohesive bonding of the aged composites in all test groups, which were treated using different adhesive systems.
Traditional bond strength tests, such as shear and microtensile methods, have long served as the primary means of evaluating the effectiveness of dental adhesive systems. However, their ability to accurately simulate intraoral conditions remains questionable. Variations in test geometry, the load application angle, and specimen dimensions can lead to inconsistent results, failing to reflect the true performance of materials in clinical practice. Several studies have highlighted these limitations. For instance, Oh et al. [51] emphasized that standardized laboratory bond strength tests only provide limited predictive power for clinical outcomes. Similarly, a study conducted by Abo-Alazm et al. [52] demonstrated that shear bond strength tests resulted in more uniform stress distributions and fewer pretest failures compared to microtensile tests, especially when analyzed via FEA. This method also proved essential in visualizing how stress concentrates at the adhesive interface, allowing for a more precise evaluation of bond performance.
In the present study, both shear bond strength (SBS) testing and FEA were employed to assess the impact of silane-containing adhesive systems on the repair bond strength of resin composites. While SBS tests revealed significant improvements in bond strength when silane was incorporated, the FEA results added an essential layer of understanding by illustrating reduced stress concentrations at the interface, particularly for silanized surfaces. This aligns with the findings of Saleh et al. [53], who confirmed the critical role of silane in stabilizing the adhesive layer, improving stress transfer. Additionally, Ismail et al. and Campos et al. [13,14] emphasized that laboratory testing alone might overlook such subtle mechanical effects, and combining it with FEA provides a more clinically relevant perspective. In contrast, the results obtained in studies by Perdigão et al. and Frankenberger et al. [54,55] showed some inconsistencies in silane efficacy, likely due to differences in substrate conditioning protocols or material aging, which again highlights the value of mechanical modeling in standardizing evaluation. In addition to bond strength values, the displacement results obtained from FEA provided further insight into the mechanical stability of the adhesive interface. Lower displacement values, as observed in the silane-treated groups such as Silane + PQ1 and All-Bond Universal, indicate reduced interfacial deformation under applied stress. Clinically, this may translate into better load distribution and improved resistance to functional forces during mastication. Conversely, the higher displacement observed in the PQ1 group suggests increased flexibility or a weaker interface, which could potentially compromise the long-term stability of the repair. Therefore, adhesives that achieve both high bond strength and minimal displacement may offer superior clinical performance in composite repair applications.
Finally, these findings support the notion that conventional bond strength tests should be supplemented with numerical analyses, such as FEA, to better approximate the clinical reality. FEA allows for not only essential verification of test-derived bond strength values but also enables the prediction of failure modes under various loading conditions. This dual approach “combining empirical testing with simulation” offers a more robust framework for evaluating adhesive systems, particularly when considering complex substrates or multi-material restorations.
This study presents several limitations that should be acknowledged. First, the same nanofilled composite material was used for both the aged and repair layers, which may have favored inter-material compatibility and potentially exaggerated the bond strength results. While this choice minimized compositional variability, it limits generalizability to clinical cases where materials often differ. Second, the in vitro nature of the study does not replicate complex oral conditions such as saliva, occlusal forces, or long-term degradation, which may affect adhesive performance. Third, the finite element analysis did not include mesh convergence testing or sensitivity analysis, and while boundary conditions were standardized, further refinement is required to enhance clinical relevance. Finally, displacement values observed in FEA were interpreted within the constraints of simplified loading protocols; future research should integrate cyclic fatigue testing and multi-material interfaces to better reflect functional longevity in clinical scenarios.
Based on the results of this study, both silane-containing universal adhesives and the combination of separate silane pretreatment with a conventional adhesive significantly improved the repair bond strength. However, given the comparable performance of these two approaches and the simplified application protocol, universal adhesives with integrated silane may be preferred in clinical practice. They reduce the number of steps and the potential for operator error, offering a more efficient and predictable option for composite repair without compromising bond effectiveness.

5. Conclusions

Within the limitations of this study, the following conclusions were drawn:
  • The repair bond strength between aged and fresh composite resin was significantly influenced by the adhesive system used.
  • Both silane-containing universal adhesives and separate silane pretreatment significantly improved repair bond strength, with no statistical difference between the two approaches.
  • The incorporation of silane into the adhesive protocol significantly reduced interfacial stress concentrations, indicating improved mechanical stability at the repair interface.

Author Contributions

Conceptualization, H.K. and M.T.; methodology, H.K. and C.P.; software, C.P.; validation, T.P. and M.T.; formal analysis, H.K. and C.P.; investigation, E.E.D. and H.K.; resources, E.E.D. and T.P.; data curation, E.E.D. and T.P.; writing—original draft preparation, E.E.D.; writing—review and editing, C.P., H.K. and M.T.; visualization, E.E.D., H.K. and C.P.; supervision, T.P. and M.T.; project administration, H.K.; funding acquisition, T.P. and M.T. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
FEAFinite Element Analysis
SBSShear Bond Strength

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Figure 1. The preparation of the specimens for shear bond testing. (a): Fabrication of composite specimens using cylindrical Teflon molds, (b): Placement of aged specimens into 12 mm molds, (c): Incremental placement of fresh composite onto aged surface, (d): Repaired samples, (e): Shear bond testing of the adhesively bonded specimens.
Figure 1. The preparation of the specimens for shear bond testing. (a): Fabrication of composite specimens using cylindrical Teflon molds, (b): Placement of aged specimens into 12 mm molds, (c): Incremental placement of fresh composite onto aged surface, (d): Repaired samples, (e): Shear bond testing of the adhesively bonded specimens.
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Figure 2. Von Mises stress and displacement values obtained using FEA. Finite element analysis (FEA) results showing von Mises stress distribution (left) and displacement values (right) for composite repair specimens treated with different adhesive protocols. Blue regions represent areas of minimal stress or displacement, while red regions indicate peak values after a static load of 300 N similar to the shear bond tests was applied in the direction indicated by the blue arrows.
Figure 2. Von Mises stress and displacement values obtained using FEA. Finite element analysis (FEA) results showing von Mises stress distribution (left) and displacement values (right) for composite repair specimens treated with different adhesive protocols. Blue regions represent areas of minimal stress or displacement, while red regions indicate peak values after a static load of 300 N similar to the shear bond tests was applied in the direction indicated by the blue arrows.
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Figure 3. Bar graph showing the mean shear bond strength values (MPa) of composite specimens repaired with different adhesive protocols.
Figure 3. Bar graph showing the mean shear bond strength values (MPa) of composite specimens repaired with different adhesive protocols.
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Figure 4. Failure mode distribution acquired from shear bond testing of repaired composite specimens.
Figure 4. Failure mode distribution acquired from shear bond testing of repaired composite specimens.
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Table 1. Materials, compositions, and instructions for use.
Table 1. Materials, compositions, and instructions for use.
Materials and Manufacturer DetailsComposition Directions for Use
ControlNo treatment
Single Bond Universal Adhesive
(3M ESPE, St. Paul, MN, USA)		10-MDP, HEMA, silane,
dimethacrylate resins,
Vitrebond copolymer, filler, ethanol, water, initiators
✓
Apply the adhesive to the entire tooth structure and rub it in for 20 s.
✓
Direct a gentle stream of air over the liquid for about 5 s.
✓
Harden the adhesive with commonly used light curing for 10 s.
Composite Primer
(GC Corporation, Tokyo, Japan)		Monofunctional methacrylate, urethane dimethacrylate (UDMA), camphorquinone
❖
Apply a thin layer of composite primer to surface.
❖
Light cure using an LED curing unit for 20 s.
PQ1
(Ultradent Products Inc.,
South Jordan, UT, USA)		Mineral 2-hydroxyethyl methacrylate, camphorquinone, ethyl alcohol
➢
Apply PQ1 to the entire prepped area. Rub with moderate pressure for 10 s.
➢
Thin/dry with a focused air stream with 1/2 air pressure at 10 mm for 10 s. to remove alcohol solvent.
➢
Light cure for 20 s. with LED curing unit.
Silane + PQ1
(Ultradent Products Inc.,
South Jordan, UT, USA)		Silane: Methacryloxypropyl
Trimethoxysilane
PQ1: Mineral 2-hydroxyethyl methacrylate, camphorquinone, ethyl alcohol
○
Apply silane with a mini brush tip. Let it evaporate for 60 s.
○
Then, apply PQ1, as described in G4.
Clearfil Universal Bond
(Kuraray Noritake Dental Inc.,
Okayama, Japan)		Bis-GMA, HEMA, ethanol,
10-MDP, hydrophilic aliphatic dimethacrylate, colloidal silica, DL-camphorquinone, silane coupling agent, accelerators
□
Apply bond to the entire adherend surfaces. Light-cure bond with a dental curing unit for 10 s.
All Bond Universal
(Bisco Inc., Schaumburg, IL, USA)		Bis-GMA, 10-MDP, HEMA, ethanol, initiators, water
▪
Apply 1 coat of All-Bond Universal to the repair site and air dry to remove excess solvent.
▪
Light cure for 10 sec. with LED curing unit.
Table 2. The mechanical properties of the materials used for FEA.
Table 2. The mechanical properties of the materials used for FEA.
MaterialsPoisson’s RatioYoung’s Moduli (GPa)Tensile Strength (MPa)Source
Silane
(Monobond) *		0.3118.640.14Alsadon et al., 2017 [24]
PQ1 *0.331.0029.45Mollica et al., 2004 [25]
De Santis et al., 2005 [26]
All-Bond
Universal *		0.301.5933.81Bonilla et al., 2024 * [27]
GC Composite Primer0.352.1935.90Masouras et al., 2008 [28]
Pirmoradian et al., 2024 [29]
Clearfil Universal Bond0.247.7018.40Calinoiu et al., 2023 [30]
3M Single Bond Universal0.4611.7628.00Anatavara et al., 2016 [31]
Clearfil
Majesty		0.2221.71117.00Papadogianis et al., 2011 [32]
* Young’s moduli and tensile strength data were acquired from manufacturers’ safety data sheet (MSDS) or official scientific documentation.
Table 3. The bond strength, von Mises stress, and significance among the test groups.
Table 3. The bond strength, von Mises stress, and significance among the test groups.
Surface TreatmentsMean Bond
Strength (MPa)		von Mises Stress Value (MPa)Displacement (mm)r
Control8.869.911.0440.276
PQ112.9014.075 a1.5210.152
All-Bond Universal15.92 a17.671 b0.071 a0.835
GC Composite Primer17.15 ab14.991 a0.691−0.694
Silane + PQ120.43 ab18.312 b0.055 a−0.461
Clearfil Universal Bond 21.17 b22.4550.093 b0.066
3M Single Bond Universal21.54 b26.9630.097 b0.724
p0.0010.0010.001
Values with the same superscript letters in the same column/row are not significantly different (p > 0.05).
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MDPI and ACS Style

Devrimci, E.E.; Kemaloglu, H.; Peskersoy, C.; Pamir, T.; Turkun, M. Shear Bond Strength and Finite Element Stress Analysis of Composite Repair Using Various Adhesive Strategies With and Without Silane Application. Appl. Sci. 2025, 15, 8159. https://doi.org/10.3390/app15158159

AMA Style

Devrimci EE, Kemaloglu H, Peskersoy C, Pamir T, Turkun M. Shear Bond Strength and Finite Element Stress Analysis of Composite Repair Using Various Adhesive Strategies With and Without Silane Application. Applied Sciences. 2025; 15(15):8159. https://doi.org/10.3390/app15158159

Chicago/Turabian Style

Devrimci, Elif Ercan, Hande Kemaloglu, Cem Peskersoy, Tijen Pamir, and Murat Turkun. 2025. "Shear Bond Strength and Finite Element Stress Analysis of Composite Repair Using Various Adhesive Strategies With and Without Silane Application" Applied Sciences 15, no. 15: 8159. https://doi.org/10.3390/app15158159

APA Style

Devrimci, E. E., Kemaloglu, H., Peskersoy, C., Pamir, T., & Turkun, M. (2025). Shear Bond Strength and Finite Element Stress Analysis of Composite Repair Using Various Adhesive Strategies With and Without Silane Application. Applied Sciences, 15(15), 8159. https://doi.org/10.3390/app15158159

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