Comparison of pull-out bond strength and microleakage of lithium disilicate onlay with and without immediate dentin sealing

Abstract

Background:

Effective adhesion between dentin and resin materials is essential for the long-term durability of onlays, as the strength and durability of the tooth-restoration complex hinge on reliable adhesion. This study aims to enhance the adhesion of lithium disilicate onlays by employing immediate dentin sealing (IDS) and evaluates its effectiveness by comparing pull-out bond strength and microleakage with and without IDS.

Methods:

Extracted human premolars were prepared and categorized into two distinct groups: Group A (with IDS) and Group B (without IDS). In Group A, the dentin surfaces were sealed immediately after tooth preparation using an adhesive resin. In Group B, no sealing was performed before bonding the lithium disilicate restorations. Pull-out bond strength was assessed utilizing universal testing machine. Microleakage was evaluated through dye penetration analysis after thermocycling and sectioning of the samples. For statistical interpretation, one-way ANOVA followed by Tukey’s post-hoc test was applied.

Results:

The pull-out bond strength was significantly higher in Group A compared to Group B (p = 0.0001). Microleakage evaluation revealed less dye penetration in Group A, indicating superior marginal integrity with IDS. The high-resolution images provided clearer visualization of the interfaces and the extent of dye penetration.

Conclusion:

Immediate dentin sealing significantly enhances the pull-out bond strength of lithium disilicate onlay and reduces microleakage. These findings suggest that IDS is a beneficial step in the bonding protocol for lithium disilicate restorations, potentially improving the longevity and performance of the restorations.

Keywords

Immediate dentin sealing pull out bond strength microleakage onlay bonding

Introduction

Restoring posterior teeth requires balancing esthetics and durability, with the choice between direct and indirect methods depending on the cavity’s size and stress demands. Direct resin composites face challenges in achieving proper proximal contacts, anatomical accuracy, mechanical strength, wear resistance, and polymerization shrinkage in large coronal defects. While indirect restorations are preferred for larger cavities due to better management of polymerization shrinkage and stress.

Indirect restorations reduce polymerization shrinkage, enhance esthetics and mechanical qualities through post-curing, ensure optimal occlusal contours, and interproximal contacts.^1,2 These techniques are particularly effective for extensive preparations involving gingival margins within the dentin.³ Advancements in dental adhesive technology have increased the use of tooth-colored onlays for posterior teeth, offering esthetic appeal and functional durability. Adhesively bonded occlusal onlays, with defect-specific and minimally retentive preparations, help preserve natural tooth structure.^4–6 Lithium disilicate onlays with supragingival margins provide an ideal combination of esthetics, strength, and tooth preservation, particularly suited for posterior restorations. Their conservative preparation reduces the risk of pulpal damage and supports long-term vitality. The supragingival margin placement further optimizes adhesive bonding, allowing for secure cementation under controlled conditions, often with rubber dam isolation, which improves marginal integrity and supports gingival health. Additionally, these margins facilitate predictable impressions, whether taken conventionally or digitally, ensuring an accurate fit and seamless integration with the surrounding dentition. Heat-pressed lithium disilicate glass-ceramic is notable for its exceptional optical and mechanical properties, including high fracture strength.⁷ Its etchable microstructure allows for strong bonding with resin cement, contributing to the high survival rates in partial coverage restorations.⁸

Managing dental tissues during preparation and provisionalization is essential for the success of indirect bonded restorations. When dentin remains exposed, it becomes susceptible to bacterial infiltration and subsequent microleakage, leading to microbial colonization, sensitivity, and pulp irritation. Interim cements often fail to seal adequately.⁹ To address these concerns and protect the pulp, Pashley et al. recommended the utilization of dentin-bonding agents directly after tooth preparation.¹⁰

Dentin bonding forms a hybrid layer^11,12 by allowing monomers to penetrate and bond with hard tissues, creating a structural bond similar to that at the dentinoenamel junction¹³ once the resin is polymerized. Key considerations include preventing dentin contamination and avoiding hybrid layer collapse before polymerization. This highlights the significance of sealing dentin immediately after preparing tooth for achieving effective bonded indirect restorations.

In a systematic review¹⁴ it was found that most common reasons for failure of onlay restoration are fracture, debonding, caries, and deterioration of marginal adaptation. Caries often result from microleakage, which significantly contributes to restoration failure, postoperative sensitivity, and pulpal disease.

Strong adhesion between dentin and resin-based materials is essential for ensuring the durability and longevity of onlays, as the structural integrity and cumulative strength of the restoration-tooth interface counts heavily on effective adhesion. To enhance adhesion, we performed immediate dentin sealing and evaluated adhesion strength through pull-out bond strength testing and microleakage study. Despite known benefits, limited research exists on its impact on pull-out bond strength and microleakage of onlays. This study assessed these factors in lithium disilicate ceramic onlays with immediate versus delayed dentin sealing.

Materials and method

Specimen preparation

The Scientific Review Board - Research Approval (Certificate No: SRB/SDC/ENDO-2201/24/394) provided ethical authorization for this study. Thirty freshly extracted, sound maxillary premolars (MP), free from lesions and cracks, were collected after extraction for orthodontic reasons. Cleaning was performed to strip the teeth of soft tissue and calculus utilizing dental curettes, ultrasonic scaler tips (Woodpecker) and manual scalers, preserved in 0.05% aqueous thymol, and stored in 0.9% sodium chloride solution to maintain hydration.

The MP were randomly assigned into two distinct groups (n = 15 per group) as per the dentin sealing protocol: Immediate Dentin Sealing (IDS) and Delayed Dentin Sealing (DDS). Heat-pressed lithium disilicate glass-ceramic onlays were fabricated for the restoration. To facilitate handling, acrylic bases were prepared, with each tooth embedded 1 mm beneath the cemento-enamel junction. Custom silicone guides were used to ensure consistent preparation thickness across specimens. Teeth were scanned and digitized for precise onlay fabrication. A flow chart summarizing the study design is outlined in Figure 1.

Figure 1.

Study flowchart.

Tooth preparation

Thirty standardized mesio-occlusal-distal (MOD) preparations were performed following the protocol described by.¹⁵ The tooth preparation dimensions were standardized using a split silicone guide, a gingival probe, and Iwanson caliper (GDC). Following preparation, the walls appeared smooth and relatively even, featuring a gingival-occlusal divergence ranging between 6° and 10° per wall. The line angles (both internal and external) were rounded, and 90 ° cavosurface margins were prepared. A reduction of 2 mm was done on the palatal cusp and a 45° angle bevel relative to the long axis of the premolar was given, maintaining 2 mm depth. The margin of the palatal region was a round contoured shoulder with a thickness of 1 mm and aligned at a distance of 2 mm from the tip of the cusp. The height of the axial wall was reduced by 1.5 mm, with a 10° convergence angle maintained along the same draw path as the primary preparation, as illustrated in Figure 2.

Figure 2.

Tooth preparation of maxillary premolar (from left to right) proximal, frontal and occlusal view.

Immediate dentin sealing

The materials employed are detailed in Table 1. The freshly prepared dentin surface was etched with 37% phosphoric acid (H₃PO₄) for 15 s, extending approximately 1 mm beyond the enamel margins. The acid-etched surface was rinsed meticulously and subtly air-dried, leaving the dentin surface visibly moist. A dentin bonding agent was evenly applied across the prepared surface and agitated for 10 s before being air-dried to ensure even distribution. The adhesive film was subsequently light cured for 20 s. Following this, a flowable resin composite was applied in a thin coating to the bonded surface and subjected to an additional 20 s of light curing. The superficial oxygen-inhibited layer (OIL) was gently swabbed away using a cotton pellet moistened in alcohol. To complete the process, the coated surface was covered using glycerine jelly to prevent air inhibition and subjected to a final light polymerization for 20 s. In this study the materials utilized, alongside their registered trade names, manufacturers, and compositions, are listed in Table 1.

Table 1.

The materials used, their commercial names, manufacturers, and compositions, are detailed for each item used.

Material	Commercial name	Manufacturer (country)	Composition
Etchant	d-tech etch	(D-tech Orthodontics, Pune, Maharashtra	37% orthophosphoric acid
Dentin bonding agent	Scotchbond Universal	3M ESPE (St. Paul, MN)	2-Hydroxyethyl methacrylate, BIS GMA, 2-propenoic acid, 2-methyl-, reaction products with 1,10-decanediol and phosphorous oxide, ethanol, water, 2-propenoic acid, 2-methyl-, 3-(trimethoxysilyl) propyl ester, reaction products with vitreous silica, copolymer of acrylic and itaconic acid, camphorquinone, dimethylaminobenzoate(−4), (dimethylamino)ethyl methacrylate
Flowable resin composite	Filtek Bulk Fill Flow	3M ESPE (St. Paul, MN)	Silane treated ceramic, UDMA, Substituted Dimethacrylate, Ytterbium Fluoride, BIS GMA, BISEMA-6, TEGDM.
Provisional restoration	Revotek LC	GC Corporation (Tokyo, Japan)	Urethane dimethacrylate (UDMA), trimethacrylate, amorphous silicon dioxide, butylated hydroxytoluene(BHT), titanium dioxide, iron(III) oxide.
Resin Cement	Variolink N	Ivoclar Vivadent (Schaan, Liechtenstein)	Bis-GMA, urethane dimethacrylate, triethylene glycol dimethacrylate, Ba-Al-fluorosilicate glass, barium glass, ytterbium trifluoride, spheroid mixed oxide, initiators, stabilizers, pigments
Hydrofluoric acid	Porcelain Etch	Ultradent Products (UT, USA)	9% buffered Hydrofluoric acid
Silane coupling agent	Silane	Ultradent Products (UT, USA)	MethacryloxypropyltrimethoxySilane, Isopropyl Alcohol

Digital impression

For the Delayed Dentin Sealing (DDS) group, digital scanning was performed immediately after the onlay preparation was completed. In contrast, for the Immediate Dentin Sealing (IDS) group, scanning was done, once the IDS protocol was fully completed, ensuring accurate capture of the sealed dentin surface. Digital impressions were taken using MEDIT T500 Dental 3D Scanner, with single-tooth scanning mode. The scanning protocol ensured high accuracy in capturing preparation margins and surface details. The scanned data were exported in STL format and processed using [EXOCAD 3.2 ELEFSINA] for analysis and onlay fabrication. Scan accuracy was verified through visual inspection before final processing.

Storage

A provisional restoration was placed for a duration of 2 weeks, during which the test specimen were immersed in artificial saliva (Nanochemazone, Mumbai, India) at 37°C to simulate oral conditions. After the 2-week period, the provisional restoration was gently taken out, and the preparation was thoroughly rinsed using an ultrasonic water bath to ensure the removal of any debris or contaminants.

Bonding of onlay

The ceramic onlays were disinfected with 80% ethyl alcohol (Chemtex, West Bengal, India) and the internal surfaces were treated for 20 s with hydrofluoric acid. The onlays were subsequently washed thoroughly in an ultrasonic bath, dried, and treated with two layers of a silane coupling agent, which was allowed to react for 60 s. In the IDS group, the enamel margin of the premolars were treated with phosphoric acid for 15 s to prepare and clean the conditioned surfaces effectively, which were then subsequently rinsed and air dried. Then two layers of dentin bonding agent were carefully coated onto the prepared tooth surface, gently air-dried, and intentionally left uncured to facilitate accurate placement of the onlay. In the DDS group, the enamel surfaces were etched with phosphoric acid for 15 s, subsequently rinsed and subtly air dried. An even layer of dentin bonding agent was coated, lightly air-dried, and light-curing for 10 s was done. The luting of onlay was done using dual-cure resin cement to ensure proper fixation. Initial curing of 5 s was performed with a light curing device, followed by thorough margin cleaning and finally 40 s light curing from all angles to ensure complete polymerization. Finally, the margins were polished and contoured using rubber flame-shaped tips, discs and cones, achieving a smooth surface and optimal fit.

Thermocycling

The test specimens were preserved at 100% relative humidity and 37°C for 24 h. Subsequently, they underwent 500 thermocycles between 5°C and 55°C, with each cycle having a duration of 1 min at each temperature to simulate the thermal stresses experienced in the oral environment.

Pull out bond strength

After the onlays were cemented, the samples were mounted in acrylic resin to ensure stability during testing. The mounted samples were then positioned in a universal testing machine (Besmak Ltd., Ankara, Turkey; Figure 3). Pull-out bond strength (PBS) measurements were determined utilizing this apparatus. The acrylic resin blocks were firmly held in place by securing it with two clamps and exposed to tensile force at a steady rate of 1 mm/min. The test proceeded until the onlays were entirely detached out of the samples (Figure 3) . The resulting pull-out force measurement, recorded in Newtons (N), were precisely logged and stored in a Microsoft Excel sheet for subsequent analysis.

Figure 3.

Mounted samples and debonded onlay in a universal testing machine (Besmak Ltd., Ankara, Turkey).

Microleakage

The apical regions of all teeth were sealed using composite resin, followed by two layers of nail varnish coated over the whole tooth surface, maintaining a 1–2 mm margin around the restoration edges to limit dye penetration. The samples were then submerged in a 0.5% Rhodamine B dye for 48 h. Post-immersion, the radicular sections were separated, and both the coronal and radicular portions were thoroughly rinsed and embedded in acrylic resin. The embedded samples were then dissected along the buccolingual plane, passing across the middle of the cavity, resulting in two mesial and distal halves. Each section was subsequently examined under a Confocal Laser Scanning Microscope (CLSM) to evaluate microleakage at the restoration margins.

Statistical analysis

A sample size determination was executed using G*Power 3.1 software (Heinrich Heine University, Düsseldorf, Germany), indicating that 30 samples were needed in order to achieve a statistical power of 91%. Statistical evaluation was carried out using SPSS Statistics version 22.0 software (IBM Corp., Armonk, NY, USA). The collected data were analyzed through one-way ANOVA, followed by Tukey’s post-hoc test to compare the groups and identify statistically significant differences. The results were compiled and presented in a tabular format to ensure clarity and facilitate a better understanding of the findings.

Results

The pull-out bond strength findings are summarized in Table 2. Group 1 demonstrated significantly higher maximum force and tensile strength compared to Group 2. The mean maximum force for Group 1 was 555.67 ± 74.86 N, with a corresponding tensile strength of 8.43 ± 1.04 MPa. In contrast, Group 2 showed a mean maximum force of 272.60 ± 39.08 N and a tensile strength of 4.01 ± 0.68 MPa. A statistically significant difference between the two groups (p < 0.001) was seen. The graph (Figure 4) illustrates a significant improvement in both mean maximum force and mean tensile strength for samples treated with IDS compared to those without IDS. The mean maximum force with IDS was 555.67, almost double the 272.60 observed without IDS, while the mean tensile strength with IDS reached 8.43, significantly higher than the 4.01 recorded without IDS.

Table 2.

Comparison of maximum force and tensile strength between experimental groups.

Group	Maximum force [N]	Tensile strength [MPa]
Group-1	555.67 ± 74.86	8.43 ± 1.04
Group-2	272.60 ± 39.08	4.01 ± 0.68
SIG	0.000	0.000

Figure 4.

Graph illustrates the comparison of mean maximum force (left) and mean tensile strength (right) between interventions with and without IDS (Immediate Dentin Sealing). Error bars represent the 95% confidence interval.

The Confocal Laser Scanning Microscope (CLSM) images were captured in both fluorescent and reflected modes as shown in Figure 5. In Group 1, no microleakage was observed at the junction between the tooth surface and the restoration, indicating excellent adaptation of the restorative material. Conversely, Group 2 displayed visible microleakage along the junction connecting the tooth surface and restoration, although the material demonstrated good overall adaptation. These findings suggest superior sealing in Group 1 compared to Group 2.

Figure 5.

CLSM images of onlay restoration with IDS (a and b), and without IDS (c and d).

Discussion

Immediate dentin sealing (IDS) has gained attention for its potential to enhance adhesion by protecting freshly cut dentin and preventing contamination before final cementation. Given that bond strength and marginal integrity are critical factors for the sustained effectiveness of ceramic onlays, it is essential to fully understand how IDS influences these critical parameters. Lithium disilicate, widely favored for its esthetic and mechanical properties, presents challenges in achieving optimal adhesion to dentin, particularly in mitigating microleakage and preventing restoration failure over time. Based on this background, the study was designed to analyze the impact of IDS on the pull-out bond strength and microleakage of lithium disilicate onlays by conducting a comparative analysis between samples with and without IDS treatment. The primary goal was to enhance the long-term reliability and durability of adhesive ceramic restorations

Achieving effective dentin bonding is crucial in clinical settings for procedures like onlays, inlays, veneers, and dentin-bonded porcelain crowns. This is attributed to the overall strength of the restored tooth structure, which relies significantly on the quality of the adhesive techniques used.¹⁶ Certain key principles must be adhered to throughout the procedural technique of dentin-resin hybridization, with two critical concerns being (1) the potential for contamination of the dentin surface and (2) the vulnerability of the hybrid layer to disintegrate before polymerization. Considering these factors is particularly important for bonded indirect restorations, like adhesive porcelain restorations. This method emphasizes the importance of sealing dentin directly after preparing teeth, prior to impression taking. This method, referred to as the Immediate Dentin Sealing (IDS) technique, offers numerous benefits. The advantages include a bacterial leakage reduction, reduced post-procedural sensitivity, and minimized crevice formation. Additionally, IDS enhances the bond strength, improves the mechanical durability of the restoration and helps reinforce the tooth structure. Given that debonding and secondary caries are among the most frequent causes of restoration failure, and the performance and durability of onlays are largely influenced by effective adhesion, the current study intends to evaluate the effectiveness of the IDS protocol. In clinical practice, debonding of onlays often results in the restoration being completely separated from the prepared tooth surface, often due to minimal retentive design of onlay. By replicating this common failure mechanism, the pull-out test delivers essential understanding of the retention characteristics and performance of restorations. This method simulates realistic clinical conditions, allowing for a more accurate assessment of how well the restoration adheres to the tooth structure under stress, ultimately helping to evaluate its long-term stability and effectiveness.¹⁷

Achieving effective dentin bonding is essential for the success of dentin-bonded onlays, as it contributes substantially to the overall performance of the restoration. In the DDS protocol, dentin sealing is performed after the provisionalization stage, specifically during the final cementation procedure. This approach has been demonstrated to result in weaker bond strength when compared to Immediate Dentin Sealing (IDS).¹⁸ Additionally, DDS can lead to incomplete seating of the restoration, increasing the risk of microleakage, secondary caries formation and reduced longevity. Several factors contribute to the improved bond strength observed in the IDS group. One key reason is the avoidance of dentin contamination, which commonly occurs during the provisionalization phase. Dentin contamination has been shown to significantly reduce bonding potential, as demonstrated by multiple studies conducted by Paul and colleagues.^19,20 Clinically, freshly exposed dentin is available instantaneously after preparation of tooth and before taking impressions, defining this the optimal moment for coating the bonding agent to maximize adhesion. The unpolymerized dentin–resin hybrid layer in the DDS group is prone to collapse under compression applied, while placing the composite or while positioning of the restoration. This collapse compromises the integrity of the bond between the dentin and the restorative material, potentially leading to reduced adhesion strength and increasing the risk of microleakage and restoration failure.^21–23 Studies^10,22 have reported that the thickness of polymerized dentin bonding agent (DBA) layers typically ranges between 60 and 80 μm on smooth, convex surfaces and can extend to 200–300 μm in concave areas, including marginal chamfers. This increased thickness can hinder the complete seating of restorations, which could be a reason for microleakage observed in the DDS group. To address this, the dentin bonding agent (DBA) is left uncured until the restoration is correctly positioned and seated. However, this approach introduces two potential issues: (a) during restoration insertion, the external flow of dentinal fluid may weaken the bonding agent, obstructing the micropores that resin typically infiltrates^24,25; and (b) excessive pressure applied by the luting agent during placement may lead to collapse of demineralized dentin collagen, ultimately compromising adhesion. These challenges can be effectively mitigated by applying the Immediate Dentin Sealing (IDS) protocol immedia-tely after preparing teeth and before taking the final impression. When employing the Immediate Dentin Sealing (IDS) protocol in bonded indirect restorations, delaying the seating of the final restoration and deferring bite forces allows the dentin bond to strengthen naturally, not being exposed to immediate stress. This delay provides an optimal environment for the bonding interface to mature and achieve greater stability, ultimately enhancing the durability and performance of the restoration. In this study a flowable resin composite was applied in a thin coating over the bonded surface since lightly filled DBA (Scotchbond Universal–SBU) was used. This is known as the “reinforced IDS” approach.²⁶

The biomechanical performance of lithium disilicate onlays is influenced by bond strength, adhesive interface stability, and stress distribution. In a study,¹⁵ onlays demonstrated sufficient fracture resistance, with values exceeding typical masticatory forces. IDS significantly improved fracture strength compared to DDS, likely due to better adhesive layer integrity and stress distribution. The most common failure mode was restoration fracture with a small portion of the tooth, while root fractures were more frequent in DDS, suggesting IDS may better distribute occlusal stresses. These findings emphasize the clinical significance of optimizing bonding protocols to enhance restoration durability. Future studies should explore fatigue resistance and long-term stress analysis under extreme loading conditions.

Hydrofluoric acid (HF) etching plays a critical role in achieving strong adhesion between lithium disilicate ceramics and resin cements by selectively dissolving the glassy phase and exposing the crystalline microstructure. Studies have shown that an optimal etching time of 60s with 9.5% HF provides superior bond strength without excessive material degradation.²⁷ However, prolonged etching may compromise ceramic integrity by over-dissolving the surface, potentially reducing fracture resistance. While our study does not evaluate HF etching effects directly, these findings highlight the importance of controlled etching protocols in achieving durable adhesive bonding for lithium disilicate restorations

The adhesive system chemical composition also plays a crucial role in determining its bonding efficacy.²⁸ The 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) monomer in the adhesive system, which contributes to the acidity necessary for etching the dentin surface. This acidic monomer promotes demineralization of dentin, enabling the adhesive to infiltrate and interact with the demineralized dentin matrix.^29,30 A key feature of 10-MDP is its ability to form a chemical bond with the inorganic content (hydroxyapatite) in both enamel and also in dentin, enhancing the adhesion to dental structures.^30–32 In self-etching adhesive systems, the remaining hydroxyapatite enveloping the collagen fibrils act as a binding site for 10-MDP, facilitating chemical interactions that improve the adhesive’s overall performance.

Scotchbond Universal contains a copolymer of polyalkenoic acid that forms a chemical bond with the calcium present in hydroxyapatite.³³ The polyalkenoic acid copolymer has carboxyl functional groups present which facilitate interactions with hydroxyapatite. These carboxyl groups substitute phosphate ions on the substrate, forming ionic bonds with calcium.³⁴ The polyalkenoic acid copolymer contributes to the stability of the adhesive bond to dentin. Additionally, this copolymer likely contributes to the improved dentin bonding performance of Scotchbond Universal adhesive. One study by Perdigão et al.³⁵ demonstrated that Scotchbond Universal achieved higher dentin bond strength than Clearfil SE Bond.

The polymerization efficiency of dual-cured resin cements significantly influences their bond strength, mechanical properties, and durability. This study by Pereira et al.³⁶ highlights that immediate light activation leads to higher polymerization rates, particularly for highly filled resin cements. Delayed photo-activation did not show significant improvements in conversion, reinforcing that early curing is optimal for maintaining bond integrity. Additionally, light curing plays a critical role in controlling polymerization shrinkage and stress distribution at the adhesive interface. While dual-cure cements provide chemical polymerization in areas where light cannot reach, light activation remains essential for maximizing polymer cross-linking and mechanical stability. For indirect restorations, selection of the appropriate curing protocol is crucial. Highly filled cements, such as Panavia F 2.0 and Variolink II, require immediate photo-activation for optimal conversion. These findings emphasize the importance of optimizing light curing strategies to enhance the longevity of bonded restorations.

Hybrid layer degradation is a major factor affecting the longevity of bonded restorations. Incomplete resin infiltration into the demineralized dentin matrix leaves exposed collagen fibrils vulnerable to enzymatic degradation by MMPs and hydrolysis, leading to bond deterioration over time. Additionally, the presence of hydrophilic monomers in adhesive systems facilitates water uptake, weakening the hybrid layer through phase separation and inadequate polymerization at deeper regions, which contribute to nanoleakage and restoration failure.^37,38

The wet bonding technique enhances initial bond strength by maintaining collagen fibril expansion for better resin penetration. However, residual water retention within the hybrid layer compromises polymerization and activates MMPs, accelerating bond degradation. To counteract these effects, MMP inhibitors (e.g. chlorhexidine) and collagen cross-linking agents (e.g. proanthocyanidins, curcumin) have been explored, though their clinical feasibility remains limited. Ethanol-wet bonding and self-etch primers with hydrophobic monomers offer alternative strategies to improve resin infiltration and hybrid layer stability. While these approaches show promise, further research is needed to develop bioactive adhesives that inhibit enzymatic degradation and enhance bonding performance, thus ultimately improving the longevity of bonded restorations

CAD/CAM technology has significantly improved the accuracy, fit, and marginal adaptation of bonded restorations, reducing microleakage, and improving bond longevity.³⁹ Digital workflows eliminate manual errors, ensuring greater precision and reproducibility in restorative design. Studies confirm that CAD/CAM-fabricated lithium disilicate and zirconia restorations exhibit superior adhesion and fracture resistance, particularly when combined with optimized surface treatments. Future research should explore scanning accuracy, milling precision, and AI-driven workflows to further enhance bond stability and clinical efficiency.

Limitations

The experiments were conducted under dry and static conditions, which do not fully replicate the wet and dynamic environment of the oral cavity. In this study, only one type of bonding agent was used. Given the variety of bonding systems available, the results may not be generalizable to other bonding agents. Moreover, the study did not account for the variability of intraoral forces, which differ in magnitude, application, speed, and direction. This study did not evaluate hybrid layer thickness, which is a critical factor influencing long-term adhesion performance. Future studies should employ nanomechanical testing methods to assess the mechanical properties of the hybrid layer, particularly in high-stress posterior restorations. This study did not assess the effects of prolonged thermomechanical aging on the resin-dentin interface. Future research should incorporate high-resolution imaging techniques to analyze microstructural changes over time, providing deeper insights into bond durability under functional stresses.

Conclusion

In conclusion, Immediate Dentin Sealing (IDS) provides superior bond strength and longevity for indirect adhesive restorations compared to Delayed Dentin Sealing (DDS). IDS reduces bacterial leakage, microleakage, and gap formation, while enhancing the mechanical stability of the restoration. The technique also prevents dentin contamination during provisionalization and allows stress-free maturation of the adhesive bond, improving overall performance. Utilizing IDS ensures stronger adhesion and long-term success in restorative dentistry.

Future recommendation

The findings of this study suggest that incorporating multiple dentin bonding agents (DBAs) into immediate dentin sealing (IDS) procedures could offer clinicians a broader range of choices and improve the applicability of IDS techniques. Future clinical studies are essential to assess the impact of factors such as pulpal pressure, aging, bacterial contamination, and biocorrosion, which may influence the clinical significance of the in vitro results obtained in this study. The impact of nanoscale defects at the dentin-resin interface on restoration failure needs to be explored through atomic force microscopy and advanced computational modeling to predict long-term outcomes. The effectiveness of alternative dentin sealing techniques, such as plasma surface modification and self-etching nanotechnology, in improving resin infiltration and bonding stability should be investigated for next-generation adhesive systems.

Footnotes

Acknowledgements

The authors express their thanks and gratitude to AlMaarefa University, Riyadh, Saudi Arabia to support the current research.

Author contributions

Conceptualization: N.A, and M.I.K; Data curation: A.K., and N.A; Formal analysis: M.F., and N.M.; Investigation: A.K; Methodology: A.K; N.A; and M.I.K.; Project administration: N.A., M.I.K.; Resources: M.F., and N.M; Software: N.M; Supervision: M.I.K; Validation: M.F.; Visualization: M.F; and N.M; Writing – original draft: A.K, N.A, and M.I.K; Writing – review & editing: M.F, N.M., and M.I.K.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Ethics approval and consent to participate

In compliance with local and national guidelines, the Scientific Review Board of Saveetha Dental College and Hospitals, Saveetha Institute of Medical and Technical Sciences, Saveetha University, Chennai, Tamil Nadu, India (Certificate No: SRB/SDC/ENDO-2201/24/394) provided ethical authorization for the current study.

ORCID iD

Mohmed Isaqali Karobari

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