Enhancement of Zirconia–Resin Bonding by Water Glass Surface Treatment

Enhancement of Zirconia–Resin Bonding by Water Glass Surface Treatment | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Enhancement of Zirconia–Resin Bonding by Water Glass Surface Treatment Kota KOBAYASH, Masaya SHIMABUKURO, Masaomi IKEDA, Kei USHIJIMA, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7571308/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 10 Feb, 2026 Read the published version in Clinical Oral Investigations → Version 1 posted 10 You are reading this latest preprint version Abstract Objectives This study evaluated the effect of water glass [(Na₂O)x(SiO₂)y] surface treatment on the bonding performance of zirconia to veneering porcelain and resin composite. Particular consideration was given to the clinical repair of fractured veneering porcelain on zirconia frameworks. Materials and Methods Zirconia specimens were divided into water-glass-treated and untreated groups, followed by sintering and alumina sandblasting. Surface roughness was analyzed by confocal laser microscopy, and elemental composition was examined using X-ray photoelectron spectroscopy (XPS). For porcelain testing, veneered specimens were subjected to shear bond strength (SBS) testing. For resin testing, specimens were bonded to composite resin with a silane-containing primer and divided into two subgroups: 24 h water storage at 37 °C and thermal cycling (5000 cycles, 5–55 °C). and the SBS was measured. Results Water-glass treatment increased surface roughness and produced a silica-rich layer that persisted after sandblasting. Porcelain SBS was significantly higher in the treated group (29.5 ± 7.3 MPa) compared with the untreated group (15.2 ± 4.3 MPa, p < 0.05). For resin bonding, treated zirconia showed higher SBS under both 24 h (21.0 ± 2.3 vs. 15.6 ± 2.6 MPa) and thermal cycling (13.0 ± 2.4 vs. 7.1 ± 1.9 MPa) (p < 0.001). Conclusions Water-glass treatment enhances resin–zirconia and porcelain–zirconia bonding by forming a durable silica-rich interface that resists sandblasting and promotes silane coupling. Clinical Relevance Water-glass pretreatment strengthens porcelain–zirconia adhesion and provides a stable surface for resin bonding, enabling reliable intraoral repair of porcelain-veneered zirconia crowns. Zirconia Water glass Silane coupling Resin bonding X-ray photoelectron spectroscopy Figures Figure 1 Figure 2 Figure 3 Figure 4 INTRODUCTION Over the past two decades, zirconia dental prostheses have gained widespread popularity due to their excellent mechanical, optical, and biological properties. [1] [2] [3] In addition, zirconia’s highly polished surface results in lower plaque accumulation compared to other materials. (3,[3, 4] Despite these favorable characteristics, the clinical application of zirconia ceramics still presents certain limitations [5] Zirconia framework–veneered ceramic crowns, which combine the high strength of a zirconia core with the superior aesthetics of veneering ceramics, remain vulnerable to chipping and coping failure. These issues often result from separation at the interface between the veneering ceramic and the zirconia framework, which is widely regarded as the restoration’s weakest point. The primary cause of chipping and fracture in zirconia-veneered restorations is the brittle nature of veneering ceramics, which are particularly prone to mechanical failure in posterior teeth, where masticatory forces are highest [6] When these failures occur, clinicians often opt for resin composite repairs rather than complete restoration replacements, particularly in cases without removable implant-supported prostheses [7]. However, unlike glass ceramics, zirconia is resistant to acid etching and does not respond effectively to conventional adhesive procedures. Various methods have been developed to modify the surface of zirconia, including air abrasion with aluminum oxide (Al2O3) particles, acid treatment, laser surface modification, and application of silane or adhesive agents [8, 9]. Reliable adhesion to zirconia can be achieved through chemical bonding using phosphate monomer-containing agents, such as MDP [10]. However, due to zirconia’s polycrystalline, glass-free structure, achieving strong and durable bonding remains a significant challenge. The bond between resin composites and ceramic materials can be significantly enhanced by using silane coupling agents. Silanes are particularly effective for silica-based ceramics, such as porcelain, because they form strong chemical bonds between hydroxyl groups on the ceramic surface and the organic matrix of the resin composite. These agents serve as intermediaries between the inorganic and the organic resin owing to their bifunctional structure—one end binds to the ceramic surface, while the other co-polymerizes with the resin matrix [11]. Additionally, combining air abrasion with silane application has been shown to improve the clinical success of ceramic restoration repairs [12]. Regarding zirconia, a silica-free oxide ceramic, different surface pretreatments are required compared to those used for silica-containing ceramics such as lithium disilicate. One such method is silica coating, which involves air abrasion using aluminum trioxide particles modified with silica [13],[14],[15],[16]. The blasting pressure embeds these silica-coated alumina particles into the ceramic surface, creating a silica-modified layer that is chemically more reactive to resin through silane coupling agents [17]. Despite its potential, however, clinical application and research on silica coating for zirconia remain limited. Water glass, primarily composed of sodium trisilicate (Na 2 O)x(SiO 2 )y​, is a colloidal solution or suspension of aqueous sodium silicate [18]. Its physical properties vary significantly with water content, ranging from a rigid solid glass to a homogeneous viscous liquid, depending on the sodium silicate–water ratio [19]. Water glass demonstrates excellent chemical and thermal stability, making it suitable for use as a binder in refractory adhesives, exterior-grade coatings, and cement-based sealants [20]. Based on these properties, it was considered to infiltrate water glass into partially sintered zirconia to achieve integration. A previous study explored the potential of water glass treatment to improve resin adhesion to zirconia [21]. The findings indicated that water glass treatment forms a stable, silica-rich layer on the zirconia surface, which enhances chemical bonding with silane coupling agents. This silica modification increases the surface reactivity of zirconia, thereby significantly improving the bond strength between the resin composite and zirconia. Porcelain ceramics are commonly veneered onto zirconia frameworks but are susceptible to fracture or chipping. Thus, the bonding characteristics between porcelain and the water glass were considered. Given the vulnerability of zirconia framework–veneered crowns to chipping and coping failure, this study was conducted in the context of clinical repair applications, focusing on enhancing resin bonding for intraoral restorations. The objective was to evaluate the effect of water glass treatment on the shear bond strength between resin composite for repair material and zirconia, as well as its influence on porcelain bonding. The null hypothesis was that no significant difference would be observed between zirconia surfaces with and without water glass treatment. MATERIALS AND METHODS Materials and Water Glass Treatment on Zirconia The materials used in this study are listed in Table 1 . Water glass, represented by the composition formula Na2O・nSiO2・mH2O, is a highly alkaline and viscous sodium silicate solution. For this study, water glass (Type No. 3, T2) was purchased from Toso Sangyo Co., Ltd. (Tokyo, Japan). Its primary components were SiO₂ (28.73 wt%) and Na₂O (9.35 wt%), with a SiO₂/Na₂O molar ratio of 3.2. Trace amounts of iron (0.0029 wt%) and other insoluble substances (0.0080 wt%) were also present, with the remainder consisting of water. The insoluble fraction included alkali metals that are insoluble in hydrochloric acid, mainly aluminum and other metal oxides. Table 1 Materials used in this study Materials Properties Manufacture Porcelain (Cerabien ZR, LT1) Potassium aluminosilicate glass, leucite, etc. Kuraray Noritake Dental, Tokyo, Japan Semi-sintered zirconia disk (Katana Zirconia, UTML, A1) A 5Y-ZP (5 mol % yttria-stabilized zirconia polycrystal Silane coupling agent (CLEARFIL CERAMIC PRIMER PULS) 10-Methacryloyloxydecyl dihydrogen phosphate (MDP), 3-Trimethoxysilylpropyl methacrylate, ethanol Bonding agent (CLEARFIL SE BOND2 BOND) Bis-GMA, 2-hydroxyethyl methacrylate (HEMA), MDP, Hydrophobic aliphatic dimethacrylate, silanated colloidal silica, dl-Camphorquinone, initiators, accelerators Resin composite (ESTELITE UNIVERSAL FLOW High A2) Silica-zirconia filler(filler load 69wt%), Bis-GMA, triethylene glycol dimethacrylate (TEGDMA), Bis-MPEPP, UDMA, 2-(2h-benzotriazol-2-yl)-p-cresol, p-methoxyphenol, 2,6-di-tert-butyl-p-cresol(BTH), titanium dioxide Tokuyama Dental, Tokyo, Japan Bis-GMA; 2, 2-bis [4(2-hydroxy-3-methacryloxy-propyloxy)-phenyl] propane, BisMPEPP;2,2-bis(4-methacryloxy polyethoxyphenyl)propane, UDMA; Bis(2-methacryloxyethyl) N,N'-1,9-nonylene biscarbamate The sample preparation process is illustrated in Fig. 1 . Disk-shaped specimens were designed using 3D modeling software (Geomagic Freeform Modeling Plus, 3D Systems, Rock Hill, SC, USA). Semi-sintered zirconia disks were milled from zirconia blocks (Katana Zirconia, UTML, A1; Kuraray Noritake Dental, Tokyo, Japan) using a milling machine (DWX-50, Roland DG, Hamamatsu, Japan). The final dimensions of the specimens were 12 mm in diameter and 4 mm in height. Specimen surfaces were ground under dry conditions using #600 water-resistant abrasive paper (Water-proof Abrasive Paper Sheet, Sankyo Rikagaku, Tokyo, Japan). The zirconia samples were divided into two groups based on surface treatment: the Zr + SB group received no water glass treatment prior to sandblasting; the Zr + WG + SB group received water glass treatment prior to sandblasting. For the water glass treatment, 3 µL of water glass was applied to each zirconia surface and evenly distributed using a microbrush. The samples were left undisturbed for 30 minutes before sintering. Sintering was performed in a furnace (Esthemat Sinta II, Shofu, Kyoto, Japan) according to the manufacturer's instructions with the following thermal protocol: heating from room temperature to 1550°C at a rate of 10°C/min, holding at 1550°C for 2 hours, and cooling back to room temperature at the same rate. All specimens underwent air-particle abrasion using 50 µm Al2O3 particles (Cobra 1594–1205 50µ, Renfert, Hilzingen, Germany) at 0.2 MPa for 20 seconds, maintaining a 10 mm distance. Abrasion was performed using an air-abrasion unit (Adprep, JMorita, Tokyo, Japan). Surface Characterization Surface roughness of the Zr + WG + SB and Zr + SB groups was analyzed using a confocal laser microscope (CLSM; VK-X 150 series, Keyence, Osaka, Japan). The arithmetical mean height of area (Sa) was used as the surface roughness parameter. The surface morphology of Zr + WG + SB specimens was examined using scanning electron microscopy (SEM; JSM-IT100; JEOL, Tokyo, Japan) at magnifications of 50× and 500× to identify morphological evidence of water-glass residues remaining after sandblasting. Surface chemical composition was investigated by X-ray photoelectron spectroscopy (XPS; JPS-9010MC, JEOL, Tokyo, Japan) for both Zr + WG + SB and Zr + SB groups. Additionally, a Zr + WG group (water-glass-treated without sandblasting) was analyzed by XPS to assess the potential mechanical disruption of the water-glass layer caused by sandblasting. XPS measurements were conducted under a chamber pressure of 1 × 10 –7 Pa, with a detection angle of 90° relative to the sample surface. Measurement conditions included an acceleration voltage of 10 kV and a current of 10 mA using an MgKα X-ray source (energy: 1253.6 eV). Peak intensity were calculated following background subtraction using CasaXPS software (version 2.3.24; Casa Software Ltd., Teignmouth, U.K.), applying Shirley’s method [22]. Sample composition was determined based on the following relative sensitivity factors: C 1s (1.00), O 1s (2.93), Na 1s (8.52), Al 2p (0.54), Si 2p (0.82), and Zr 3d (7.04). Shear Bond Strength Testing of Porcelain Ceramics to Water Glass Treated Zirconia (Fig. 2A) A preliminary study was performed to evaluate the effect of water-glass treatment on shear bond strength (SBS) of porcelain veneered to zirconia, comparing the Zr + WG + SB and Zr + SB groups. Eight specimens were prepared for each group (n = 8). .The specimens for SBS testing were prepared by firing porcelain ceramic (Cerabien ZR, LT1, Kuraray Noritake Dental, Tokyo, Japan) according to the manufacturer’s recommended schedule (starting at 600 °C, heating at 45 °C/min, and holding at 940 °C for 1 min) with porcelain furnace (AUSTROMAT354 press-i-dent, DEKEMA, Freilassing, Germany). After firing, the bonding surface of the porcelain ceramic was adjusted to a diameter of 3 mm. The specimens were embedded in autopolymerizing resin (Unifast Ⅲ, GC, Tokyo, Japan) within a tube (inner = 28 mm, h = 12 mm). The SBS test was performed using a universal testing machine (Autograph AGS-J, Shimadzu, Kyoto, Japan) at a crosshead speed of 1 mm/min. For the Zr + WG + SB samples, the fractured surface characteristic was observed using a confocal laser microscope (CLSM; VK-X 150 series, Keyence, Osaka, Japan). Shear Bond Strength Testing of Resin Composites to Water Glass Treated Zirconia (Fig. 2B) Additional specimens of the Zr + WG + SB and Zr + SB groups were prepared for SBS testing using resin composites, with a total of 20 specimens each group. .Before bonding, the specimens were embedded as above. The surface of specimens was cleaned in 99% ethanol for 5 minutes using an ultrasonic bath (US-2KS, SND Corporation, Nagano, Japan). A silane coupling agent (Ceramic Primer Plus, Kuraray Noritake Dental, Tokyo, Japan) was applied to the adhesive surface for 10 seconds and air-dried for 5 seconds to complete the silane treatment. Next, the specimen surfaces were coated with an adhesive bond (SE bond, Kuraray Noritake Dental, Tokyo, Japan), air-dried for 10 seconds, and light-cured for 20 seconds using a curing device (Pencure 2000, Morita, Osaka, Japan). The treated specimens were then bonded with composite resin (ESTELITE UNIVERSAL FLOW High, Tokuyama Dental, Tokyo, Japan) using a Teflon® tube (inner = 3 mm, h = 4 mm). The composite resin was light-cured for 20 seconds. After curing, the specimens were divided into two groups based on storage conditions. Subgroups were established as follows: The first group (24 h group) was stored in distilled water at 37 °C for 24 hours. The second group (TC group) underwent thermal cycling for 5000 cycles between 5 °C and 55 °C, with a dwell time of 30 seconds per cycle. Following storage, the specimens were subjected to shear loading to measure SBS using a universal testing machine (Autograph AGS-J, Shimadzu, Kyoto, Japan) at a crosshead speed of 1 mm/min. After the SBS tests, failure modes were examined using a stereomicroscope (SMZ1000, Nikon) at 35× magnification. The failure modes were classified as either adhesive or cohesive based on the amount of composite resin remaining on the zirconia surface after debonding [23, 24]. Adhesive failure was defined as failure at the interface between the zirconia and the resin composite, characterized by less than 50% of the zirconia surface covered with residual composite resin. In contrast, cohesive failure was defined as failure within the resin composite itself, indicated by more than 50% of the zirconia surface covered by residual resin. Statistical Analysis A pilot study determined the mean difference and standard deviations of bond strength between experimental groups. Using these values, along with a significance level of 0.05 and a power of 0.8, the required sample size for the t-test was calculated using statistical software (G*power 3.1.9.7, Institute for Experimental Psychology, Dusseldorf, Germany). This calculation established that each group should include eight specimens (n = 8) and ten specimens (n = 10) for ceramics and resin composites, respectively. The distribution and homogeneity of variances were assessed using the Shapiro–Wilk test and Levene’s test, respectively. Surface roughness data were analyzed with a t-test. The SBS data were evaluated using Welch’s t-test. Bonferroni’s correction was applied to adjust the significance level to 5% for multiple comparisons for those of the resin composites group. The frequency of fracture modes was analyzed using Fisher’s exact test. RESULTS Surface Characterization The Sa (µm) results are summarized in Table 2 . Data were analyzed using a t-test (n = 8), which revealed that the Sa value of the Zr + WG + SB group was significantly higher than that of the Zr + SB group (p = 0.0018). SEM images of the Zr + WG + SB surface are presented in Fig. 3 . At the interface without water-glass treatment (Fig. 3 b), polishing streaks caused by abrasive papers remain visible on the zirconia substrate. In contrast, the water-glass-treated surface (Fig. 3 c) shows no visible polishing streaks, suggesting the presence of a residual water-glass layer that remains even after sandblasting. This finding indicates strong adhesion and integration of the water-glass coating with the zirconia surface. Table 2 Surface roughness of the samples, Means ± standard deviations. Data was analyzed by t-test (n = 8, p < 0.05) Group Sa (µm) Zr + SB 2.42 ± 0.36 Zr + WG + SB 3.12 ± 0.32 XPS Analysis The composition analysis results are presented in Fig. 4 . The relative cation fractions of Al, Si, Zr, and Na were calculated from the atomic percentages obtained by XPS. The Si content was higher in the Zr + WG + SB (45%) and Zr + WG (46.3%) groups. Conversely, Al was predominantly observed in the Zr + WG + SB (27.5%) and Zr + SB (44.0%) groups. A small amount of Na (2.5%) was detected only in the Zr + WG + SB group (2.5%), while no Na signal was found in the Zr + WG and Zr + SB groups. SBS of Porcelain Ceramics and Observation of Fractured Surface As in Table 3 . the mean SBS of the untreated zirconia group (Zr + SB) was 15.2 MPa, whereas that of the water glass–treated group (Zr + WG + SB) was 29.5 MPa. The Shapiro–Wilk test confirmed normality, and the non-equality of variances was verified with Levene’s test. Statistical analysis using Welch’s t-test revealed a significant difference between the two groups (p < 0.05, n = 8), with the SBS of the Zr + WG + SB group being significantly higher than that of the Zr + SB group. The fractured surface in the Zr + SB group showed exclusively adhesive failure. In contrast, in the Zr + WG + SB group, remnants of fractured porcelain were observed on the surface, occasionally exposing the underlying zirconia. Due to these remnants of fractured porcelain, the surface in the Zr + WG + SB group appeared irregular, and the deeper regions were presumed to represent the bonding interface with zirconia (Fig. 5 ). Table 3 Shear bond strength of porcelain ceramics to water glass treated zirconia (means ± standard deviation). Welch's t-test showed a significant difference between the groups (p < 0.05, n = 8). Group MPa Zr + SB 15.2 ± 4.3 Zr + WG + SB 29.5 ± 7.3 SBS of Resin Composite and Fracture Mode Analysis The mean SBS values are presented in Fig. 6 . In the 24-hour group, the Zr + WG + SB group (21.0 MPa) showed significantly higher bond strength than the Zr + SB group (15.6 MPa) (p < 0.001). Similarly, in the TC5000 group, the Zr + WG + SB group (13.0 MPa) exhibited significantly greater bond strength than the Zr + SB group (7.1 MPa) (p < 0.001). The frequency of failure modes is summarized in Table 4 . In both the water-glass-treated and untreated groups, the fracture pattern observed after the shear bond test was predominantly adhesive at the zirconia–resin interface, with residual fragments of the fractured resin composite occasionally noted. The means and standard deviations of SBS for the Zr + SB and Zr + WG + SB groups are reported. Two subgroups were evaluated: 24 h (storage in water at 37°C for 24 hours) and TC5000 (subjected to 5000 thermal cycles). Data were analyzed using Welch's t-test, with Bonferroni correction applied to maintain a 5% significance level (n = 10). Horizontal lines indicate statistical differences between specific groups. Table 4 Fracture Surface Classification Storage condition Adhesive failure on Zr Cohesive failure in CR Zr + SB 24h 10 0 TC5000 10 0 Zr + WG + SB 24h 10 0 TC5000 10 0 DISCUSSION SEM analysis confirmed the presence of a water-glass-derived silica layer on the zirconia surface, as indicated by the absence of polishing marks typically produced by #600 grit water-resistant abrasive paper. Moreover, this silica layer remained even after alumina sandblasting, demonstrating a high degree of surface integration and mechanical stability. The water-glass treatment enhanced the bonding of porcelain to zirconia, as reflected by the presence of fractured porcelain remnants on the debonded surface. Furthermore, this study investigated the effects of water glass surface treatment on the properties of zirconia and the bond strength between composite resin and zirconia. Applying water glass slightly increased the surface roughness, and XPS analysis confirmed the presence of a Si-containing layer on the zirconia surface. The SBS of water-glass-treated zirconia was significantly higher than that of untreated zirconia in both the 24-hour and thermal cycling groups. Therefore, the null hypothesis was rejected, as significant improvements in SBS were observed for both porcelain–zirconia and resin–zirconia with water glass treatment. The zirconia surface treated with water glass exhibited significantly greater surface roughness compared to the untreated group. Because micromechanical retention depends on surface texture, this increase in roughness likely contributed to the improved bond strength. Surface roughness, characterized by microscopic irregularities, can enhance mechanical interlocking and promote adhesion [25]. However, chemical bonding also plays a crucial role in achieving durable adhesion of resin composite as well as porcelain to zirconia. Although a clear difference in surface roughness was observed between the two groups, the extent to which this factor alone influenced the tensile bond strength remains uncertain. The elevated bond strength in the water glass–treated group was more likely attributable to chemical modification of the zirconia surface. In particular, water glass treatment formed a silica-rich layer that facilitated effective silane coupling, thereby enhancing chemical adhesion to both resin composite and porcelain ceramics. Although various silica-coating techniques have been developed to facilitate silane bonding to zirconia, achieving consistent and complete surface coverage remains challenging. For instance, silica airborne abrasion systems, such as the Rocatec method, improve bond strength by embedding silica particles onto the surface before silane application [26–28]. However, this approach often results in a nonuniform silica layer. Similarly, applying a SiO₂–ZrO₂ slurry has been investigated as an alternative method [28]. While this technique can enhance bond strength by forming a SiO₂–ZrO₂ coating after sintering, achieving complete surface coverage continues to be a limitation [28], [29]. In the present study, water glass application, as illustrated in Fig. 3 , produced high silica coverage on the zirconia surface that was resistant to removal by alumina air abrasion. This surface modification was clearly confirmed by XPS analysis, which quantified the relative elemental composition and demonstrated a high abundance of silicon on the zirconia surface. Furthermore, Si remained on the zirconia surface even after alumina blasting, indicating that a solid Si layer was formed by the water glass application. This Si layer may consist of polymerized SiO₂ network structures, including various polymorphs, on the zirconia surface. Similar polymerization has been reported during the high-temperature treatment of silica gel powders [30]. In this study, the semi-sintered zirconia treated with water glass was sintered at 1550°C—well above the melting points of sodium silicate (1088°C) and Na₂O (1132°C) [30]. This high-temperature process likely caused sodium volatilization and the formation of a stable SiO₂ phase on the zirconia surface. Since dental zirconia is typically sintered above 1170°C, this surface modification technique may be applicable to other pre-sintered zirconia products. On the other hand, XPS detected Zr on the water-glass-treated surface, suggesting that the silica layer formed by water glass has an amorphous network structure with nanoscale porosity. Water glass-derived silica layers are known to exhibit porosity, especially after drying or thermal treatment. During these processes, the removal of water and volatilization of sodium ions result in a hydrated, silica-rich network containing nanoscale voids and irregularities typical of porous structures. The structure closely resembles silica gels, which are nanoporous due to their particulate and polymerized silicate frameworks. Water glass-derived silica layers, in particular, are known to be porous after drying or thermal treatment, as elimination of water and sodium leads to a silica-rich, hydrated network. This structure typically exhibits nanoscale porosity similar to that found in leached silicate glasses or silica gels [31]. XPS is particularly suitable for analyzing such surfaces, as it can precisely determine the elemental composition and chemical states of atoms within ultrathin films. Porcelain-veneered zirconia crowns are clinically prone to chipping and fracture, which often requires intraoral repair. In such situations, sandblasting is typically applied to the fractured surface to prepare it for resin bonding. While this procedure may occasionally remove residual porcelain fragments, XPS analysis indicates that the silica-rich water glass layer deposited on the zirconia surface remains intact. This characteristic is of particular importance because zirconia itself provides an inherently unfavorable substrate for resin adhesion. By preventing direct exposure of the zirconia substrate, the water glass layer offers a more favorable surface for silane coupling and subsequent resin bonding. These findings suggest that water glass treatment could contribute to more durable and predictable clinical repair outcomes. Achieving durable resin bonding to zirconia under intraoral conditions is a critical clinical challenge. In the present study, a ceramic primer containing both a silane coupling agent and an MDP monomer was applied to all specimens, regardless of water glass treatment. The water-glass-treated zirconia group demonstrated significantly higher SBS than the untreated group under both 24-hour and thermocycled conditions (p < 0.05). This improvement is likely due to effective adhesion through silane coupling to the SiO₂ layer, Since resin cement bond strength is known to deteriorate after thermal aging [23, 24, 29, 32], thermal cycling was performed to evaluate the durability of adhesion.. Although bond strength decreased following thermal cycling, it remained at 15.8 MPa, indicating that the bond between the silica phase and zirconia was stable under thermal stress [33, 34]. These findings suggest that water glass treatment may contribute to more durable and predictable resin bonding in clinical repair situations. Within the limitations of this study, zirconia surfaces treated with water glass, followed by sintering, utilized the silane coupling effect to achieve a stable chemical bond between zirconia and composite resin. Therefore, water glass treatment shows promise for repairing chipped zirconia-veneered crowns with composite resin. Further research is needed to verify the effectiveness of this treatment using other bonding systems and composite resins. Additionally, in vivo clinical evaluations are necessary to confirm its practical effectiveness. CONCLUSION The silica layer formed on the water-glass-treated zirconia surface remained intact after sandblasting. The water-glass treatment improved the bonding of porcelain to zirconia, as evidenced by the presence of fractured porcelain remnants on the debonded surfaces. The silane coupling agent effectively bonded to this silica layer, directly enhancing the bond strength with the resin composite. Consequently, bond strength was significantly improved and maintained even after thermal loading. Declarations Ethical approval: No human participants or animals were involved in this study. Conflict of Interest: The authors declare that they have no conflict of interest. Funding: This research received no external funding. Author Contribution Author Contributions•N.H. M.S. and M.I. conceived and designed the study, supervised the project, and critically revised the manuscript.•N.H. and M.I. provided conceptual advice on water-glass treatment•K.K and N.H. drafted the initial manuscript.•K.K., K.U. and M.I. performed specimen preparation and carried out shear bond strength testing. •K.K., M.S., M.K. and N.H. conducted surface analyses including confocal microscopy and XPS, and contributed to data interpretation.•K.K. and K.U. assisted with thermal cycling experiments and SEM fracture surface evaluation.•M.K and Y.S. critically revised the manuscript and contributed to manuscript editing.All authors reviewed and approved the final manuscript and agree to be accountable for the integrity of the work. Data Availability All data and materials supporting the findings of this study are available within the paper References Piconi C and Maccauro G (1999) Zirconia as a ceramic biomaterial. Biomaterials 20:1-25. doi: 10.1016/s0142-9612(98)00010-6 Thompson JY, Stoner BR, Piascik JR and Smith R (2011) Adhesion/cementation to zirconia and other non-silicate ceramics: where are we now? Dent Mater 27:71-82. doi: 10.1016/j.dental.2010.10.022 Gautam C, Joyner J, Gautam A, Rao J and Vajtai R (2016) Zirconia based dental ceramics: structure, mechanical properties, biocompatibility and applications. Dalton Trans 45:19194-19215. doi: 10.1039/c6dt03484e Taran PK and Kaya MS (2018) A Comparison of Periodontal Health in Primary Molars Restored with Prefabricated Stainless Steel and Zirconia Crowns. Pediatr Dent 40:334-339. Cevik P, Cengiz D and Malkoc MA (2016) - Bond strength of veneering porcelain to zirconia after different surface treatments. - 30:- 2476. Agingu C, Zhang C, Jiang N, Cheng H, Özcan M and Yu H (2018) Intraoral repair of chipped or fractured veneered zirconia crowns and fixed dental prosthesis: clinical guidelines based on literature review. JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY 32:1711-1723. doi: 10.1080/01694243.2018.1443639 Özcan M (2015) Intraoral repair protocol for chipping or fracture of veneering ceramic in zirconia fixed dental prostheses. J Adhes Dent 17:189-90. doi: 10.3290/j.jad.a34175 Mesquita AMM, Al-Haj Husain N, Molinero-Mourelle P and Ozcan M (2021) An Intraoral Repair Method for Chipping Fracture of a Multi-unit Fixed Zirconia Reconstruction: A Direct Dental Technique. Eur J Dent 15:174-178. doi: 10.1055/s-0040-1716311 Yoo JY, Yoon HI, Park JM and Park EJ (2015) Porcelain repair - Influence of different systems and surface treatments on resin bond strength. J Adv Prosthodont 7:343-348. doi: 10.4047/jap.2015.7.5.343 Han A, Hiraishi N, Tsoi J, Matinlinna JP, Tagami J and Hayashi F (2025) The influence of pH on the adhesive performance of phosphoric ester monomers with zirconia. Dent Mater 41:495-502. doi: 10.1016/j.dental.2025.02.004 Matinlinna JP, Lung CYK and Tsoi JKH (2018) Silane adhesion mechanism in dental applications and surface treatments: A review. Dent Mater 34:13-28. doi: 10.1016/j.dental.2017.09.002 Kimmich M and Stappert CF (2013) Intraoral treatment of veneering porcelain chipping of fixed dental restorations: a review and clinical application. J Am Dent Assoc 144:31-44. doi: 10.14219/jada.archive.2013.0011 Peutzfeldt A and Asmussen E (1988) Silicoating: evaluation of a new method of bonding composite resin to metal. Scand J Dent Res 96:171-6. doi: 10.1111/j.1600-0722.1988.tb01425.x Ozcan M, Pfeiffer P and Nergiz I (1998) A brief history and current status of metal-and ceramic surface-conditioning concepts for resin bonding in dentistry. Quintessence Int 29:713-24. Ozcan M (2002) The use of chairside silica coating for different dental applications: a clinical report. J Prosthet Dent 87:469-72. doi: 10.1067/mpr.2002.124365 Ozcan M and Niedermeier W (2002) Clinical study on the reasons for and location of failures of metal-ceramic restorations and survival of repairs. Int J Prosthodont 15:299-302. Ozcan M and Vallittu PK (2003) Effect of surface conditioning methods on the bond strength of luting cement to ceramics. Dent Mater 19:725-31. doi: 10.1016/s0109-5641(03)00019-8 Hribar U, Østergaard MB, Iversen N, Spreitzer M and König J (2023) The mechanism of glass foaming with water glass. J Non-Cryst Solids 600:122025. Mohsin H, Maron S, Maurin I, Burov E, Tricot G, Devys L, Gouillart E and Gacoin T (2021) Thermal behavior of waterglass: foaming and xerogel-to-glass evolution. J Non-Cryst Solids 566:120872. Zhang X, Liu X, Yang S, Long K and Wu Y (2012) Effect of carboxyl methyl cellulose on the adhesion properties of sodium silicate wood adhesive. Book title. IEEE, Ushijima K, Hiraishi N, Ikeda M, Tsuji Y, Tsuchida Y and Shimada Y (2024) Effect of water glass treatment for zirconia and silane coupling on bond strength of resin cement. Clinical oral investigations 28:305. doi: 10.1007/s00784-024-05680-9 Shirley DA (1972) High-Resolution X-Ray Photoemission Spectrum of Valence Bands of Gold. Phys Rev B 5:4709-&. doi: DOI 10.1103/PhysRevB.5.4709 Khanlar LN, Takagaki T, Inokoshi M, Ikeda M, Nikaido T and Tagami J (2020) The effect of carboxyl-based monomers on resin bonding to highly translucent zirconia ceramics. Dent Mater J 39:956-962. doi: 10.4012/dmj.2019-312 Alsandi Q, Ikeda M, Nikaido T, Tsuchida Y, Sadr A, Yui N, Suzuki T and Tagami J (2019) Evaluation of mechanical properties of new elastomer material applicable for dental 3D printer. J Mech Behav Biomed Mater 100:103390. doi: 10.1016/j.jmbbm.2019.103390 Carek A, Slokar Benić L, Komar D and Krebelj E (2022) Roughness of the Surface of Zirconia Reinforced Lithium Disilicate Ceramic Treated by Different Procedures. Materials (Basel) 16. doi: 10.3390/ma16010265 Maciel LC, Amaral M, Queiroz DA, Baroudi K and Silva-Concílio LR (2020) The effect of repeated surface treatment of zirconia on its bond strength to resin cement. J Adv Prosthodont 12:291-298. doi: 10.4047/jap.2020.12.5.291 Buyukcavus E, Ugurlu M and Buyukcavus MH (2022) Shear bond strength of orthodontic molar tubes to composite restoration bonded with particular adhesives after different surface pre-treatments. Orthod Craniofac Res 25:541-548. doi: 10.1111/ocr.12567 Du Q, Cui T, Niu G, Qui J and Yang B (2023) Improving Bond Strength of Translucent Zirconia Through Surface Treatment With SiO2-ZrO2 Coatings. Oper Dent 48:666-676. doi: 10.2341/22-121-l Nagaoka N, Yoshihara K, Tamada Y, Yoshida Y and Meerbeek BV (2019) Ultrastructure and bonding properties of tribochemical silica-coated zirconia. Dent Mater J 38:107-113. doi: 10.4012/dmj.2017-397 Li Z-J, Liu C-R and Zhao Q-S (2000) Effect of heat treatment on the pore structure properties of silica gel powders derived from water glass. J Non-Cryst Solids 265:189-192. Banerjee J, Bojan V, Pantano CG and Kim SH (2018) Effect of heat treatment on the surface chemical structure of glass: Oxygen speciation from in situ XPS analysis. J Am Ceram Soc 101:644-656. R AN, Gupta R and Weber DK (2025) Zirconia Biomaterials. Book title. StatPearls Publishing Copyright © 2025, StatPearls Publishing LLC., Treasure Island (FL) Villanova M, Carvalho Prado M, Neves Y, Annese E, Archanjo B, Simão R, Dos Santos HE and Prado M (2023) The Effect of Colloidal Silica and Glaze Coatings on the Adhesion of Zirconia with Various Ytrria Concentration. Eur J Prosthodont Restor Dent 31:346-357. doi: 10.1922/EJPRD_2491Villanova12 Lima RBW, Silva AF, da Rosa WLO, Piva E, Duarte RM and De Souza GM (2023) Bonding Efficacy of Universal Resin Adhesives to Zirconia Substrates: Systematic Review and Meta-Analysis. J Adhes Dent 25:51-62. doi: 10.3290/j.jad.b3868649 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 10 Feb, 2026 Read the published version in Clinical Oral Investigations → Version 1 posted Editorial decision: Revision requested 15 Dec, 2025 Reviews received at journal 20 Nov, 2025 Reviews received at journal 20 Nov, 2025 Reviewers agreed at journal 26 Oct, 2025 Reviewers agreed at journal 24 Oct, 2025 Reviewers agreed at journal 22 Oct, 2025 Reviewers invited by journal 15 Sep, 2025 Editor assigned by journal 12 Sep, 2025 Submission checks completed at journal 12 Sep, 2025 First submitted to journal 09 Sep, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7571308","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":515735422,"identity":"5e8ad73d-e144-4f57-a100-f1e6ed4ad82d","order_by":0,"name":"Kota KOBAYASH","email":"","orcid":"","institution":"Institute of Science Tokyo","correspondingAuthor":false,"prefix":"","firstName":"Kota","middleName":"","lastName":"KOBAYASH","suffix":""},{"id":515735423,"identity":"a8ee302a-dbbb-4ff6-91a8-325f390cc00a","order_by":1,"name":"Masaya SHIMABUKURO","email":"","orcid":"","institution":"Institute of Science 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1","display":"","copyAsset":false,"role":"figure","size":105810,"visible":true,"origin":"","legend":"\u003cp\u003eSample preparation process of water glass treatment on zirconia.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7571308/v1/07c077d46bc14eca71a83947.png"},{"id":92022943,"identity":"045f68ff-6798-4f11-9dbf-de4fe14de8e5","added_by":"auto","created_at":"2025-09-23 18:11:04","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":134988,"visible":true,"origin":"","legend":"\u003cp\u003eSample preparation process of shear bond strength test for porcelain ceramics (A) and resin composites (B) on zirconia.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7571308/v1/983d94fd51368476c45c8ca9.png"},{"id":92023484,"identity":"77784035-7ac3-4c2e-bd40-52c85a084d81","added_by":"auto","created_at":"2025-09-23 18:19:04","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":110219,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative SEM images of the Zr+WG+SB surface: (a) Zr+WG+SB showing the interface between the water glass treated and untreated areas (×50); (b) Zr+SB representing the non-treated surface (×500); and (c) Zr+WG+SB showing the water-glass-treated surface (×500).\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7571308/v1/c414a69be9e1734237d2eabb.png"},{"id":92022945,"identity":"c20b4e42-47e0-4bfa-8225-ff86794248e8","added_by":"auto","created_at":"2025-09-23 18:11:04","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":90143,"visible":true,"origin":"","legend":"\u003cp\u003eXPS analysis showing the relative cationic composition of the surfaces of Zr+SB+WG, Zr+WG, and Zr+SB sepcemens.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7571308/v1/ef0aef649eff4e32987f3cb4.png"},{"id":102786731,"identity":"a6395c00-23ac-41e3-be5a-8a0a7952ed18","added_by":"auto","created_at":"2026-02-16 16:15:00","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1123408,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7571308/v1/8870c827-8367-43be-bcf0-a4cdff9d9014.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Enhancement of Zirconia–Resin Bonding by Water Glass Surface Treatment","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eOver the past two decades, zirconia dental prostheses have gained widespread popularity due to their excellent mechanical, optical, and biological properties. [1] [2] [3] In addition, zirconia\u0026rsquo;s highly polished surface results in lower plaque accumulation compared to other materials. (3,[3, 4] Despite these favorable characteristics, the clinical application of zirconia ceramics still presents certain limitations [5]\u003c/p\u003e\u003cp\u003eZirconia framework\u0026ndash;veneered ceramic crowns, which combine the high strength of a zirconia core with the superior aesthetics of veneering ceramics, remain vulnerable to chipping and coping failure. These issues often result from separation at the interface between the veneering ceramic and the zirconia framework, which is widely regarded as the restoration\u0026rsquo;s weakest point. The primary cause of chipping and fracture in zirconia-veneered restorations is the brittle nature of veneering ceramics, which are particularly prone to mechanical failure in posterior teeth, where masticatory forces are highest [6]\u003c/p\u003e\u003cp\u003eWhen these failures occur, clinicians often opt for resin composite repairs rather than complete restoration replacements, particularly in cases without removable implant-supported prostheses [7]. However, unlike glass ceramics, zirconia is resistant to acid etching and does not respond effectively to conventional adhesive procedures. Various methods have been developed to modify the surface of zirconia, including air abrasion with aluminum oxide (Al2O3) particles, acid treatment, laser surface modification, and application of silane or adhesive agents [8, 9]. Reliable adhesion to zirconia can be achieved through chemical bonding using phosphate monomer-containing agents, such as MDP [10]. However, due to zirconia\u0026rsquo;s polycrystalline, glass-free structure, achieving strong and durable bonding remains a significant challenge.\u003c/p\u003e\u003cp\u003eThe bond between resin composites and ceramic materials can be significantly enhanced by using silane coupling agents. Silanes are particularly effective for silica-based ceramics, such as porcelain, because they form strong chemical bonds between hydroxyl groups on the ceramic surface and the organic matrix of the resin composite. These agents serve as intermediaries between the inorganic and the organic resin owing to their bifunctional structure\u0026mdash;one end binds to the ceramic surface, while the other co-polymerizes with the resin matrix [11]. Additionally, combining air abrasion with silane application has been shown to improve the clinical success of ceramic restoration repairs [12].\u003c/p\u003e\u003cp\u003eRegarding zirconia, a silica-free oxide ceramic, different surface pretreatments are required compared to those used for silica-containing ceramics such as lithium disilicate. One such method is silica coating, which involves air abrasion using aluminum trioxide particles modified with silica [13],[14],[15],[16]. The blasting pressure embeds these silica-coated alumina particles into the ceramic surface, creating a silica-modified layer that is chemically more reactive to resin through silane coupling agents [17]. Despite its potential, however, clinical application and research on silica coating for zirconia remain limited.\u003c/p\u003e\u003cp\u003eWater glass, primarily composed of sodium trisilicate (Na\u003csub\u003e2\u003c/sub\u003eO)x(SiO\u003csub\u003e2\u003c/sub\u003e)y​, is a colloidal solution or suspension of aqueous sodium silicate [18]. Its physical properties vary significantly with water content, ranging from a rigid solid glass to a homogeneous viscous liquid, depending on the sodium silicate\u0026ndash;water ratio [19]. Water glass demonstrates excellent chemical and thermal stability, making it suitable for use as a binder in refractory adhesives, exterior-grade coatings, and cement-based sealants [20]. Based on these properties, it was considered to infiltrate water glass into partially sintered zirconia to achieve integration. A previous study explored the potential of water glass treatment to improve resin adhesion to zirconia [21]. The findings indicated that water glass treatment forms a stable, silica-rich layer on the zirconia surface, which enhances chemical bonding with silane coupling agents. This silica modification increases the surface reactivity of zirconia, thereby significantly improving the bond strength between the resin composite and zirconia.\u003c/p\u003e\u003cp\u003ePorcelain ceramics are commonly veneered onto zirconia frameworks but are susceptible to fracture or chipping. Thus, the bonding characteristics between porcelain and the water glass were considered. Given the vulnerability of zirconia framework\u0026ndash;veneered crowns to chipping and coping failure, this study was conducted in the context of clinical repair applications, focusing on enhancing resin bonding for intraoral restorations. The objective was to evaluate the effect of water glass treatment on the shear bond strength between resin composite for repair material and zirconia, as well as its influence on porcelain bonding. The null hypothesis was that no significant difference would be observed between zirconia surfaces with and without water glass treatment.\u003c/p\u003e"},{"header":"MATERIALS AND METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eMaterials and Water Glass Treatment on Zirconia\u003c/h2\u003e\u003cp\u003eThe materials used in this study are listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Water glass, represented by the composition formula Na2O・nSiO2・mH2O, is a highly alkaline and viscous sodium silicate solution. For this study, water glass (Type No. 3, T2) was purchased from Toso Sangyo Co., Ltd. (Tokyo, Japan). Its primary components were SiO₂ (28.73 wt%) and Na₂O (9.35 wt%), with a SiO₂/Na₂O molar ratio of 3.2. Trace amounts of iron (0.0029 wt%) and other insoluble substances (0.0080 wt%) were also present, with the remainder consisting of water. The insoluble fraction included alkali metals that are insoluble in hydrochloric acid, mainly aluminum and other metal oxides.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eMaterials used in this study\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMaterials\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eProperties\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eManufacture\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePorcelain (Cerabien ZR, LT1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePotassium aluminosilicate glass, leucite, etc.\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eKuraray Noritake Dental, Tokyo, Japan\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSemi-sintered zirconia disk (Katana Zirconia, UTML, A1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eA 5Y-ZP (5 mol % yttria-stabilized zirconia polycrystal\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSilane coupling agent\u003c/p\u003e\u003cp\u003e(CLEARFIL CERAMIC PRIMER PULS)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10-Methacryloyloxydecyl dihydrogen phosphate (MDP), 3-Trimethoxysilylpropyl methacrylate, ethanol\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBonding agent\u003c/p\u003e\u003cp\u003e(CLEARFIL SE BOND2 BOND)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eBis-GMA, 2-hydroxyethyl methacrylate (HEMA), MDP, Hydrophobic aliphatic dimethacrylate, silanated colloidal silica, dl-Camphorquinone, initiators, accelerators\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eResin composite\u003c/p\u003e\u003cp\u003e(ESTELITE UNIVERSAL FLOW High A2)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSilica-zirconia filler(filler load 69wt%), Bis-GMA, triethylene glycol dimethacrylate (TEGDMA), Bis-MPEPP, UDMA, 2-(2h-benzotriazol-2-yl)-p-cresol, p-methoxyphenol, 2,6-di-tert-butyl-p-cresol(BTH), titanium dioxide\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eTokuyama Dental, Tokyo, Japan\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e\u003cp\u003eBis-GMA; 2, 2-bis [4(2-hydroxy-3-methacryloxy-propyloxy)-phenyl] propane, BisMPEPP;2,2-bis(4-methacryloxy polyethoxyphenyl)propane, UDMA; Bis(2-methacryloxyethyl) N,N'-1,9-nonylene biscarbamate\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe sample preparation process is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Disk-shaped specimens were designed using 3D modeling software (Geomagic Freeform Modeling Plus, 3D Systems, Rock Hill, SC, USA). Semi-sintered zirconia disks were milled from zirconia blocks (Katana Zirconia, UTML, A1; Kuraray Noritake Dental, Tokyo, Japan) using a milling machine (DWX-50, Roland DG, Hamamatsu, Japan). The final dimensions of the specimens were 12 mm in diameter and 4 mm in height. Specimen surfaces were ground under dry conditions using #600 water-resistant abrasive paper (Water-proof Abrasive Paper Sheet, Sankyo Rikagaku, Tokyo, Japan). The zirconia samples were divided into two groups based on surface treatment: the Zr\u0026thinsp;+\u0026thinsp;SB group received no water glass treatment prior to sandblasting; the Zr\u0026thinsp;+\u0026thinsp;WG\u0026thinsp;+\u0026thinsp;SB group received water glass treatment prior to sandblasting. For the water glass treatment, 3 \u0026micro;L of water glass was applied to each zirconia surface and evenly distributed using a microbrush. The samples were left undisturbed for 30 minutes before sintering. Sintering was performed in a furnace (Esthemat Sinta II, Shofu, Kyoto, Japan) according to the manufacturer's instructions with the following thermal protocol: heating from room temperature to 1550\u0026deg;C at a rate of 10\u0026deg;C/min, holding at 1550\u0026deg;C for 2 hours, and cooling back to room temperature at the same rate. All specimens underwent air-particle abrasion using 50 \u0026micro;m Al2O3 particles (Cobra 1594\u0026ndash;1205 50\u0026micro;, Renfert, Hilzingen, Germany) at 0.2 MPa for 20 seconds, maintaining a 10 mm distance. Abrasion was performed using an air-abrasion unit (Adprep, JMorita, Tokyo, Japan).\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eSurface Characterization\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSurface roughness of the Zr + WG + SB and Zr + SB groups was analyzed using a confocal laser microscope (CLSM; VK-X 150 series, Keyence, Osaka, Japan). The arithmetical mean height of area (Sa) was used as the surface roughness parameter. The surface morphology of Zr + WG + SB specimens was examined using scanning electron microscopy (SEM; JSM-IT100; JEOL, Tokyo, Japan) at magnifications of 50× and 500× to identify morphological evidence of water-glass residues remaining after sandblasting. Surface chemical composition was investigated by X-ray photoelectron spectroscopy (XPS; JPS-9010MC, JEOL, Tokyo, Japan) for both Zr + WG + SB and Zr + SB groups. Additionally, a Zr + WG group (water-glass-treated without sandblasting) was analyzed by XPS to assess the potential mechanical disruption of the water-glass layer caused by sandblasting. XPS measurements were conducted under a chamber pressure of 1 × 10\u003csup\u003e–7\u003c/sup\u003e Pa, with a detection angle of 90° relative to the sample surface. Measurement conditions included an acceleration voltage of 10 kV and a current of 10 mA using an MgKα X-ray source (energy: 1253.6 eV). Peak intensity were calculated following background subtraction using CasaXPS software (version 2.3.24; Casa Software Ltd., Teignmouth, U.K.), applying Shirley’s method [22]. Sample composition was determined based on the following relative sensitivity factors: C 1s (1.00), O 1s (2.93), Na 1s (8.52), Al 2p (0.54), Si 2p (0.82), and Zr 3d (7.04).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eShear Bond Strength Testing of\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ePorcelain Ceramics to Water Glass Treated Zirconia (Fig. 2A)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA preliminary study was performed to evaluate the effect of water-glass treatment on shear bond strength (SBS) of porcelain veneered to zirconia, comparing the Zr + WG + SB and Zr + SB groups. Eight specimens were prepared for each group (n = 8). .The specimens for SBS testing were prepared by firing porcelain ceramic (Cerabien ZR, LT1, Kuraray Noritake Dental, Tokyo, Japan) according to the manufacturer’s recommended schedule (starting at 600 °C, heating at 45 °C/min, and holding at 940 °C for 1 min) with porcelain furnace (AUSTROMAT354 press-i-dent, DEKEMA, Freilassing, Germany). After firing, the bonding surface of the porcelain ceramic was adjusted to a diameter of 3 mm. The specimens were embedded in autopolymerizing resin (Unifast Ⅲ, GC, Tokyo, Japan) within a tube (inner = 28 mm, h = 12 mm). The SBS test was performed using a universal testing machine (Autograph AGS-J, Shimadzu, Kyoto, Japan) at a crosshead speed of 1 mm/min. For the Zr + WG + SB samples, the fractured surface characteristic was observed using a confocal laser microscope (CLSM; VK-X 150 series, Keyence, Osaka, Japan).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eShear Bond Strength Testing of Resin Composites\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eto Water Glass Treated Zirconia (Fig. 2B)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAdditional specimens of the Zr + WG + SB and Zr + SB groups were prepared for SBS testing using resin composites, with a total of 20 specimens each group. .Before bonding, the specimens were embedded as above. The surface of specimens was cleaned in 99% ethanol for 5 minutes using an ultrasonic bath (US-2KS, SND Corporation, Nagano, Japan). A silane coupling agent (Ceramic Primer Plus, Kuraray Noritake Dental, Tokyo, Japan) was applied to the adhesive surface for 10 seconds and air-dried for 5 seconds to complete the silane treatment. Next, the specimen surfaces were coated with an adhesive bond (SE bond, Kuraray Noritake Dental, Tokyo, Japan), air-dried for 10 seconds, and light-cured for 20 seconds using a curing device (Pencure 2000, Morita, Osaka, Japan). The treated specimens were then bonded with composite resin (ESTELITE UNIVERSAL FLOW High, Tokuyama Dental, Tokyo, Japan) using a Teflon® tube (inner = 3 mm, h = 4 mm). The composite resin was light-cured for 20 seconds. After curing, the specimens were divided into two groups based on storage conditions. Subgroups were established as follows: The first group (24 h group) was stored in distilled water at 37 °C for 24 hours. The second group (TC group) underwent thermal cycling for 5000 cycles between 5 °C and 55 °C, with a dwell time of 30 seconds per cycle. Following storage, the specimens were subjected to shear loading to measure SBS using a universal testing machine (Autograph AGS-J, Shimadzu, Kyoto, Japan) at a crosshead speed of 1 mm/min.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAfter the SBS tests, failure modes were examined using a stereomicroscope (SMZ1000, Nikon) at 35× magnification. The failure modes were classified as either adhesive or cohesive based on the amount of composite resin remaining on the zirconia surface after debonding [23, 24]. Adhesive failure was defined as failure at the interface between the zirconia and the resin composite, characterized by less than 50% of the zirconia surface covered with residual composite resin. In contrast, cohesive failure was defined as failure within the resin composite itself, indicated by more than 50% of the zirconia surface covered by residual resin.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStatistical Analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA pilot study determined the mean difference and standard deviations of bond strength between experimental groups. Using these values, along with a significance level of 0.05 and a power of 0.8, the required sample size for the t-test was calculated using statistical software (G*power 3.1.9.7, Institute for Experimental Psychology, Dusseldorf, Germany). This calculation established that each group should include eight specimens (n = 8) and ten specimens (n = 10) for ceramics and resin composites, respectively. The distribution and homogeneity of variances were assessed using the Shapiro–Wilk test and Levene’s test, respectively. Surface roughness data were analyzed with a t-test. The SBS data were evaluated using Welch’s t-test. Bonferroni’s correction was applied to adjust the significance level to 5% for multiple comparisons for those of the resin composites group. The frequency of fracture modes was analyzed using Fisher’s exact test.\u0026nbsp;\u003c/p\u003e\u003c/div\u003e"},{"header":"RESULTS","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003eSurface Characterization\u003c/h2\u003e\u003cp\u003eThe Sa (\u0026micro;m) results are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Data were analyzed using a t-test (n\u0026thinsp;=\u0026thinsp;8), which revealed that the Sa value of the Zr\u0026thinsp;+\u0026thinsp;WG\u0026thinsp;+\u0026thinsp;SB group was significantly higher than that of the Zr\u0026thinsp;+\u0026thinsp;SB group (p\u0026thinsp;=\u0026thinsp;0.0018). SEM images of the Zr\u0026thinsp;+\u0026thinsp;WG\u0026thinsp;+\u0026thinsp;SB surface are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. At the interface without water-glass treatment (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb), polishing streaks caused by abrasive papers remain visible on the zirconia substrate. In contrast, the water-glass-treated surface (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec) shows no visible polishing streaks, suggesting the presence of a residual water-glass layer that remains even after sandblasting. This finding indicates strong adhesion and integration of the water-glass coating with the zirconia surface.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eSurface roughness of the samples, Means\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviations. Data was analyzed by t-test (n\u0026thinsp;=\u0026thinsp;8, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05)\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGroup\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSa (\u0026micro;m)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eZr\u0026thinsp;+\u0026thinsp;SB\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.36\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eZr\u0026thinsp;+\u0026thinsp;WG\u0026thinsp;+\u0026thinsp;SB\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.32\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eXPS Analysis\u003c/h3\u003e\n\u003cp\u003eThe composition analysis results are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The relative cation fractions of Al, Si, Zr, and Na were calculated from the atomic percentages obtained by XPS. The Si content was higher in the Zr\u0026thinsp;+\u0026thinsp;WG\u0026thinsp;+\u0026thinsp;SB (45%) and Zr\u0026thinsp;+\u0026thinsp;WG (46.3%) groups. Conversely, Al was predominantly observed in the Zr\u0026thinsp;+\u0026thinsp;WG\u0026thinsp;+\u0026thinsp;SB (27.5%) and Zr\u0026thinsp;+\u0026thinsp;SB (44.0%) groups. A small amount of Na (2.5%) was detected only in the Zr\u0026thinsp;+\u0026thinsp;WG\u0026thinsp;+\u0026thinsp;SB group (2.5%), while no Na signal was found in the Zr\u0026thinsp;+\u0026thinsp;WG and Zr\u0026thinsp;+\u0026thinsp;SB groups.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003eSBS of Porcelain Ceramics and Observation of Fractured Surface\u003c/h2\u003e\u003cp\u003eAs in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. the mean SBS of the untreated zirconia group (Zr\u0026thinsp;+\u0026thinsp;SB) was 15.2 MPa, whereas that of the water glass\u0026ndash;treated group (Zr\u0026thinsp;+\u0026thinsp;WG\u0026thinsp;+\u0026thinsp;SB) was 29.5 MPa. The Shapiro\u0026ndash;Wilk test confirmed normality, and the non-equality of variances was verified with Levene\u0026rsquo;s test. Statistical analysis using Welch\u0026rsquo;s t-test revealed a significant difference between the two groups (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05, n\u0026thinsp;=\u0026thinsp;8), with the SBS of the Zr\u0026thinsp;+\u0026thinsp;WG\u0026thinsp;+\u0026thinsp;SB group being significantly higher than that of the Zr\u0026thinsp;+\u0026thinsp;SB group. The fractured surface in the Zr\u0026thinsp;+\u0026thinsp;SB group showed exclusively adhesive failure. In contrast, in the Zr\u0026thinsp;+\u0026thinsp;WG\u0026thinsp;+\u0026thinsp;SB group, remnants of fractured porcelain were observed on the surface, occasionally exposing the underlying zirconia. Due to these remnants of fractured porcelain, the surface in the Zr\u0026thinsp;+\u0026thinsp;WG\u0026thinsp;+\u0026thinsp;SB group appeared irregular, and the deeper regions were presumed to represent the bonding interface with zirconia (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eShear bond strength of porcelain ceramics to water glass treated zirconia (means\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation). Welch's t-test showed a significant difference between the groups (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05, n\u0026thinsp;=\u0026thinsp;8).\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGroup\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMPa\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eZr\u0026thinsp;+\u0026thinsp;SB\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15.2\u0026thinsp;\u0026plusmn;\u0026thinsp;4.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eZr\u0026thinsp;+\u0026thinsp;WG\u0026thinsp;+\u0026thinsp;SB\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e29.5\u0026thinsp;\u0026plusmn;\u0026thinsp;7.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003eSBS of Resin Composite and Fracture Mode Analysis\u003c/h2\u003e\u003cp\u003eThe mean SBS values are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e6\u003c/span\u003e. In the 24-hour group, the Zr\u0026thinsp;+\u0026thinsp;WG\u0026thinsp;+\u0026thinsp;SB group (21.0 MPa) showed significantly higher bond strength than the Zr\u0026thinsp;+\u0026thinsp;SB group (15.6 MPa) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Similarly, in the TC5000 group, the Zr\u0026thinsp;+\u0026thinsp;WG\u0026thinsp;+\u0026thinsp;SB group (13.0 MPa) exhibited significantly greater bond strength than the Zr\u0026thinsp;+\u0026thinsp;SB group (7.1 MPa) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). The frequency of failure modes is summarized in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. In both the water-glass-treated and untreated groups, the fracture pattern observed after the shear bond test was predominantly adhesive at the zirconia\u0026ndash;resin interface, with residual fragments of the fractured resin composite occasionally noted.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe means and standard deviations of SBS for the Zr\u0026thinsp;+\u0026thinsp;SB and Zr\u0026thinsp;+\u0026thinsp;WG\u0026thinsp;+\u0026thinsp;SB groups are reported. Two subgroups were evaluated: 24 h (storage in water at 37\u0026deg;C for 24 hours) and TC5000 (subjected to 5000 thermal cycles). Data were analyzed using Welch's t-test, with Bonferroni correction applied to maintain a 5% significance level (n\u0026thinsp;=\u0026thinsp;10). Horizontal lines indicate statistical differences between specific groups.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eFracture Surface Classification\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eStorage condition\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eAdhesive failure on Zr\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCohesive failure in CR\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eZr\u0026thinsp;+\u0026thinsp;SB\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e24h\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTC5000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eZr\u0026thinsp;+\u0026thinsp;WG\u0026thinsp;+\u0026thinsp;SB\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e24h\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTC5000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eSEM analysis confirmed the presence of a water-glass-derived silica layer on the zirconia surface, as indicated by the absence of polishing marks typically produced by #600 grit water-resistant abrasive paper. Moreover, this silica layer remained even after alumina sandblasting, demonstrating a high degree of surface integration and mechanical stability. The water-glass treatment enhanced the bonding of porcelain to zirconia, as reflected by the presence of fractured porcelain remnants on the debonded surface. Furthermore, this study investigated the effects of water glass surface treatment on the properties of zirconia and the bond strength between composite resin and zirconia. Applying water glass slightly increased the surface roughness, and XPS analysis confirmed the presence of a Si-containing layer on the zirconia surface. The SBS of water-glass-treated zirconia was significantly higher than that of untreated zirconia in both the 24-hour and thermal cycling groups. Therefore, the null hypothesis was rejected, as significant improvements in SBS were observed for both porcelain\u0026ndash;zirconia and resin\u0026ndash;zirconia with water glass treatment.\u003c/p\u003e\u003cp\u003eThe zirconia surface treated with water glass exhibited significantly greater surface roughness compared to the untreated group. Because micromechanical retention depends on surface texture, this increase in roughness likely contributed to the improved bond strength. Surface roughness, characterized by microscopic irregularities, can enhance mechanical interlocking and promote adhesion [25]. However, chemical bonding also plays a crucial role in achieving durable adhesion of resin composite as well as porcelain to zirconia. Although a clear difference in surface roughness was observed between the two groups, the extent to which this factor alone influenced the tensile bond strength remains uncertain. The elevated bond strength in the water glass\u0026ndash;treated group was more likely attributable to chemical modification of the zirconia surface. In particular, water glass treatment formed a silica-rich layer that facilitated effective silane coupling, thereby enhancing chemical adhesion to both resin composite and porcelain ceramics.\u003c/p\u003e\u003cp\u003eAlthough various silica-coating techniques have been developed to facilitate silane bonding to zirconia, achieving consistent and complete surface coverage remains challenging. For instance, silica airborne abrasion systems, such as the Rocatec method, improve bond strength by embedding silica particles onto the surface before silane application [26\u0026ndash;28]. However, this approach often results in a nonuniform silica layer. Similarly, applying a SiO₂\u0026ndash;ZrO₂ slurry has been investigated as an alternative method [28]. While this technique can enhance bond strength by forming a SiO₂\u0026ndash;ZrO₂ coating after sintering, achieving complete surface coverage continues to be a limitation [28], [29].\u003c/p\u003e\u003cp\u003eIn the present study, water glass application, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, produced high silica coverage on the zirconia surface that was resistant to removal by alumina air abrasion. This surface modification was clearly confirmed by XPS analysis, which quantified the relative elemental composition and demonstrated a high abundance of silicon on the zirconia surface. Furthermore, Si remained on the zirconia surface even after alumina blasting, indicating that a solid Si layer was formed by the water glass application. This Si layer may consist of polymerized SiO₂ network structures, including various polymorphs, on the zirconia surface. Similar polymerization has been reported during the high-temperature treatment of silica gel powders [30]. In this study, the semi-sintered zirconia treated with water glass was sintered at 1550\u0026deg;C\u0026mdash;well above the melting points of sodium silicate (1088\u0026deg;C) and Na₂O (1132\u0026deg;C) [30]. This high-temperature process likely caused sodium volatilization and the formation of a stable SiO₂ phase on the zirconia surface. Since dental zirconia is typically sintered above 1170\u0026deg;C, this surface modification technique may be applicable to other pre-sintered zirconia products.\u003c/p\u003e\u003cp\u003eOn the other hand, XPS detected Zr on the water-glass-treated surface, suggesting that the silica layer formed by water glass has an amorphous network structure with nanoscale porosity. Water glass-derived silica layers are known to exhibit porosity, especially after drying or thermal treatment. During these processes, the removal of water and volatilization of sodium ions result in a hydrated, silica-rich network containing nanoscale voids and irregularities typical of porous structures. The structure closely resembles silica gels, which are nanoporous due to their particulate and polymerized silicate frameworks. Water glass-derived silica layers, in particular, are known to be porous after drying or thermal treatment, as elimination of water and sodium leads to a silica-rich, hydrated network. This structure typically exhibits nanoscale porosity similar to that found in leached silicate glasses or silica gels [31]. XPS is particularly suitable for analyzing such surfaces, as it can precisely determine the elemental composition and chemical states of atoms within ultrathin films.\u003c/p\u003e\u003cp\u003ePorcelain-veneered zirconia crowns are clinically prone to chipping and fracture, which often requires intraoral repair. In such situations, sandblasting is typically applied to the fractured surface to prepare it for resin bonding. While this procedure may occasionally remove residual porcelain fragments, XPS analysis indicates that the silica-rich water glass layer deposited on the zirconia surface remains intact. This characteristic is of particular importance because zirconia itself provides an inherently unfavorable substrate for resin adhesion. By preventing direct exposure of the zirconia substrate, the water glass layer offers a more favorable surface for silane coupling and subsequent resin bonding. These findings suggest that water glass treatment could contribute to more durable and predictable clinical repair outcomes.\u003c/p\u003e\u003cp\u003eAchieving durable resin bonding to zirconia under intraoral conditions is a critical clinical challenge. In the present study, a ceramic primer containing both a silane coupling agent and an MDP monomer was applied to all specimens, regardless of water glass treatment. The water-glass-treated zirconia group demonstrated significantly higher SBS than the untreated group under both 24-hour and thermocycled conditions (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). This improvement is likely due to effective adhesion through silane coupling to the SiO₂ layer, Since resin cement bond strength is known to deteriorate after thermal aging [23, 24, 29, 32], thermal cycling was performed to evaluate the durability of adhesion.. Although bond strength decreased following thermal cycling, it remained at 15.8 MPa, indicating that the bond between the silica phase and zirconia was stable under thermal stress [33, 34]. These findings suggest that water glass treatment may contribute to more durable and predictable resin bonding in clinical repair situations.\u003c/p\u003e\u003cp\u003eWithin the limitations of this study, zirconia surfaces treated with water glass, followed by sintering, utilized the silane coupling effect to achieve a stable chemical bond between zirconia and composite resin. Therefore, water glass treatment shows promise for repairing chipped zirconia-veneered crowns with composite resin. Further research is needed to verify the effectiveness of this treatment using other bonding systems and composite resins. Additionally, in vivo clinical evaluations are necessary to confirm its practical effectiveness.\u003c/p\u003e"},{"header":"CONCLUSION","content":"\u003cp\u003eThe silica layer formed on the water-glass-treated zirconia surface remained intact after sandblasting. The water-glass treatment improved the bonding of porcelain to zirconia, as evidenced by the presence of fractured porcelain remnants on the debonded surfaces. The silane coupling agent effectively bonded to this silica layer, directly enhancing the bond strength with the resin composite. Consequently, bond strength was significantly improved and maintained even after thermal loading.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eEthical approval:\u003c/h2\u003e\u003cp\u003eNo human participants or animals were involved in this study.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eConflict of Interest:\u003c/strong\u003e\u003cp\u003eThe authors declare that they have no conflict of interest.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e\u003cp\u003eThis research received no external funding.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAuthor Contributions\u0026bull;N.H. M.S. and M.I. conceived and designed the study, supervised the project, and critically revised the manuscript.\u0026bull;N.H. and M.I. provided conceptual advice on water-glass treatment\u0026bull;K.K and N.H. drafted the initial manuscript.\u0026bull;K.K., K.U. and M.I. performed specimen preparation and carried out shear bond strength testing. \u0026bull;K.K., M.S., M.K. and N.H. conducted surface analyses including confocal microscopy and XPS, and contributed to data interpretation.\u0026bull;K.K. and K.U. assisted with thermal cycling experiments and SEM fracture surface evaluation.\u0026bull;M.K and Y.S. critically revised the manuscript and contributed to manuscript editing.All authors reviewed and approved the final manuscript and agree to be accountable for the integrity of the work.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eAll data and materials supporting the findings of this study are available within the paper\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003ePiconi C and Maccauro G (1999) Zirconia as a ceramic biomaterial. Biomaterials 20:1-25. doi: 10.1016/s0142-9612(98)00010-6\u003c/li\u003e\n\u003cli\u003eThompson JY, Stoner BR, Piascik JR and Smith R (2011) Adhesion/cementation to zirconia and other non-silicate ceramics: where are we now? Dent Mater 27:71-82. doi: 10.1016/j.dental.2010.10.022\u003c/li\u003e\n\u003cli\u003eGautam C, Joyner J, Gautam A, Rao J and Vajtai R (2016) Zirconia based dental ceramics: structure, mechanical properties, biocompatibility and applications. Dalton Trans 45:19194-19215. doi: 10.1039/c6dt03484e\u003c/li\u003e\n\u003cli\u003eTaran PK and Kaya MS (2018) A Comparison of Periodontal Health in Primary Molars Restored with Prefabricated Stainless Steel and Zirconia Crowns. Pediatr Dent 40:334-339. \u003c/li\u003e\n\u003cli\u003eCevik P, Cengiz D and Malkoc MA (2016) - Bond strength of veneering porcelain to zirconia after different surface treatments. - 30:- 2476. \u003c/li\u003e\n\u003cli\u003eAgingu C, Zhang C, Jiang N, Cheng H, \u0026Ouml;zcan M and Yu H (2018) Intraoral repair of chipped or fractured veneered zirconia crowns and fixed dental prosthesis: clinical guidelines based on literature review. JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY 32:1711-1723. doi: 10.1080/01694243.2018.1443639\u003c/li\u003e\n\u003cli\u003e\u0026Ouml;zcan M (2015) Intraoral repair protocol for chipping or fracture of veneering ceramic in zirconia fixed dental prostheses. J Adhes Dent 17:189-90. doi: 10.3290/j.jad.a34175\u003c/li\u003e\n\u003cli\u003eMesquita AMM, Al-Haj Husain N, Molinero-Mourelle P and Ozcan M (2021) An Intraoral Repair Method for Chipping Fracture of a Multi-unit Fixed Zirconia Reconstruction: A Direct Dental Technique. Eur J Dent 15:174-178. doi: 10.1055/s-0040-1716311\u003c/li\u003e\n\u003cli\u003eYoo JY, Yoon HI, Park JM and Park EJ (2015) Porcelain repair - Influence of different systems and surface treatments on resin bond strength. J Adv Prosthodont 7:343-348. doi: 10.4047/jap.2015.7.5.343\u003c/li\u003e\n\u003cli\u003eHan A, Hiraishi N, Tsoi J, Matinlinna JP, Tagami J and Hayashi F (2025) The influence of pH on the adhesive performance of phosphoric ester monomers with zirconia. Dent Mater 41:495-502. doi: 10.1016/j.dental.2025.02.004\u003c/li\u003e\n\u003cli\u003eMatinlinna JP, Lung CYK and Tsoi JKH (2018) Silane adhesion mechanism in dental applications and surface treatments: A review. Dent Mater 34:13-28. doi: 10.1016/j.dental.2017.09.002\u003c/li\u003e\n\u003cli\u003eKimmich M and Stappert CF (2013) Intraoral treatment of veneering porcelain chipping of fixed dental restorations: a review and clinical application. J Am Dent Assoc 144:31-44. doi: 10.14219/jada.archive.2013.0011\u003c/li\u003e\n\u003cli\u003ePeutzfeldt A and Asmussen E (1988) Silicoating: evaluation of a new method of bonding composite resin to metal. Scand J Dent Res 96:171-6. doi: 10.1111/j.1600-0722.1988.tb01425.x\u003c/li\u003e\n\u003cli\u003eOzcan M, Pfeiffer P and Nergiz I (1998) A brief history and current status of metal-and ceramic surface-conditioning concepts for resin bonding in dentistry. Quintessence Int 29:713-24. \u003c/li\u003e\n\u003cli\u003eOzcan M (2002) The use of chairside silica coating for different dental applications: a clinical report. J Prosthet Dent 87:469-72. doi: 10.1067/mpr.2002.124365\u003c/li\u003e\n\u003cli\u003eOzcan M and Niedermeier W (2002) Clinical study on the reasons for and location of failures of metal-ceramic restorations and survival of repairs. Int J Prosthodont 15:299-302. \u003c/li\u003e\n\u003cli\u003eOzcan M and Vallittu PK (2003) Effect of surface conditioning methods on the bond strength of luting cement to ceramics. Dent Mater 19:725-31. doi: 10.1016/s0109-5641(03)00019-8\u003c/li\u003e\n\u003cli\u003eHribar U, \u0026Oslash;stergaard MB, Iversen N, Spreitzer M and K\u0026ouml;nig J (2023) The mechanism of glass foaming with water glass. J Non-Cryst Solids 600:122025. \u003c/li\u003e\n\u003cli\u003eMohsin H, Maron S, Maurin I, Burov E, Tricot G, Devys L, Gouillart E and Gacoin T (2021) Thermal behavior of waterglass: foaming and xerogel-to-glass evolution. J Non-Cryst Solids 566:120872. \u003c/li\u003e\n\u003cli\u003eZhang X, Liu X, Yang S, Long K and Wu Y (2012) Effect of carboxyl methyl cellulose on the adhesion properties of sodium silicate wood adhesive. Book title. IEEE, \u003c/li\u003e\n\u003cli\u003eUshijima K, Hiraishi N, Ikeda M, Tsuji Y, Tsuchida Y and Shimada Y (2024) Effect of water glass treatment for zirconia and silane coupling on bond strength of resin cement. Clinical oral investigations 28:305. doi: 10.1007/s00784-024-05680-9\u003c/li\u003e\n\u003cli\u003eShirley DA (1972) High-Resolution X-Ray Photoemission Spectrum of Valence Bands of Gold. Phys Rev B 5:4709-\u0026amp;. doi: DOI 10.1103/PhysRevB.5.4709\u003c/li\u003e\n\u003cli\u003eKhanlar LN, Takagaki T, Inokoshi M, Ikeda M, Nikaido T and Tagami J (2020) The effect of carboxyl-based monomers on resin bonding to highly translucent zirconia ceramics. Dent Mater J 39:956-962. doi: 10.4012/dmj.2019-312\u003c/li\u003e\n\u003cli\u003eAlsandi Q, Ikeda M, Nikaido T, Tsuchida Y, Sadr A, Yui N, Suzuki T and Tagami J (2019) Evaluation of mechanical properties of new elastomer material applicable for dental 3D printer. J Mech Behav Biomed Mater 100:103390. doi: 10.1016/j.jmbbm.2019.103390\u003c/li\u003e\n\u003cli\u003eCarek A, Slokar Benić L, Komar D and Krebelj E (2022) Roughness of the Surface of Zirconia Reinforced Lithium Disilicate Ceramic Treated by Different Procedures. Materials (Basel) 16. doi: 10.3390/ma16010265\u003c/li\u003e\n\u003cli\u003eMaciel LC, Amaral M, Queiroz DA, Baroudi K and Silva-Conc\u0026iacute;lio LR (2020) The effect of repeated surface treatment of zirconia on its bond strength to resin cement. J Adv Prosthodont 12:291-298. doi: 10.4047/jap.2020.12.5.291\u003c/li\u003e\n\u003cli\u003eBuyukcavus E, Ugurlu M and Buyukcavus MH (2022) Shear bond strength of orthodontic molar tubes to composite restoration bonded with particular adhesives after different surface pre-treatments. Orthod Craniofac Res 25:541-548. doi: 10.1111/ocr.12567\u003c/li\u003e\n\u003cli\u003eDu Q, Cui T, Niu G, Qui J and Yang B (2023) Improving Bond Strength of Translucent Zirconia Through Surface Treatment With SiO2-ZrO2 Coatings. Oper Dent 48:666-676. doi: 10.2341/22-121-l\u003c/li\u003e\n\u003cli\u003eNagaoka N, Yoshihara K, Tamada Y, Yoshida Y and Meerbeek BV (2019) Ultrastructure and bonding properties of tribochemical silica-coated zirconia. Dent Mater J 38:107-113. doi: 10.4012/dmj.2017-397\u003c/li\u003e\n\u003cli\u003eLi Z-J, Liu C-R and Zhao Q-S (2000) Effect of heat treatment on the pore structure properties of silica gel powders derived from water glass. J Non-Cryst Solids 265:189-192. \u003c/li\u003e\n\u003cli\u003eBanerjee J, Bojan V, Pantano CG and Kim SH (2018) Effect of heat treatment on the surface chemical structure of glass: Oxygen speciation from in situ XPS analysis. J Am Ceram Soc 101:644-656. \u003c/li\u003e\n\u003cli\u003eR AN, Gupta R and Weber DK (2025) Zirconia Biomaterials. Book title. StatPearls Publishing\u003c/li\u003e\n\u003cli\u003eCopyright \u0026copy; 2025, StatPearls Publishing LLC., Treasure Island (FL)\u003c/li\u003e\n\u003cli\u003eVillanova M, Carvalho Prado M, Neves Y, Annese E, Archanjo B, Sim\u0026atilde;o R, Dos Santos HE and Prado M (2023) The Effect of Colloidal Silica and Glaze Coatings on the Adhesion of Zirconia with Various Ytrria Concentration. Eur J Prosthodont Restor Dent 31:346-357. doi: 10.1922/EJPRD_2491Villanova12\u003c/li\u003e\n\u003cli\u003eLima RBW, Silva AF, da Rosa WLO, Piva E, Duarte RM and De Souza GM (2023) Bonding Efficacy of Universal Resin Adhesives to Zirconia Substrates: Systematic Review and Meta-Analysis. J Adhes Dent 25:51-62. doi: 10.3290/j.jad.b3868649\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"clinical-oral-investigations","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cloi","sideBox":"Learn more about [Clinical Oral Investigations](http://link.springer.com/journal/784)","snPcode":"784","submissionUrl":"https://submission.nature.com/new-submission/784/3","title":"Clinical Oral Investigations","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Zirconia, Water glass, Silane coupling, Resin bonding, X-ray photoelectron spectroscopy","lastPublishedDoi":"10.21203/rs.3.rs-7571308/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7571308/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eObjectives\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study evaluated the effect of water glass [(Na₂O)x(SiO₂)y] surface treatment on the bonding performance of zirconia to veneering porcelain and resin composite. Particular consideration was given to the clinical repair of fractured veneering porcelain on zirconia frameworks.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMaterials and Methods\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eZirconia specimens were divided into water-glass-treated and untreated groups, followed by sintering and alumina sandblasting. Surface roughness was analyzed by confocal laser microscopy, and elemental composition was examined using X-ray photoelectron spectroscopy (XPS). For porcelain testing, veneered specimens were subjected to shear bond strength (SBS) testing. For resin testing, specimens were bonded to composite resin with a silane-containing primer and divided into two subgroups: 24 h water storage at 37 °C and thermal cycling (5000 cycles, 5–55 °C). and the SBS was measured.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWater-glass treatment increased surface roughness and produced a silica-rich layer that persisted after sandblasting. Porcelain SBS was significantly higher in the treated group (29.5 ± 7.3 MPa) compared with the untreated group (15.2 ± 4.3 MPa, p \u0026lt; 0.05). For resin bonding, treated zirconia showed higher SBS under both 24 h (21.0 ± 2.3 vs. 15.6 ± 2.6 MPa) and thermal cycling (13.0 ± 2.4 vs. 7.1 ± 1.9 MPa) (p \u0026lt; 0.001).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWater-glass treatment enhances resin–zirconia and porcelain–zirconia bonding by forming a durable silica-rich interface that resists sandblasting and promotes silane coupling.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical Relevance\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWater-glass pretreatment strengthens porcelain–zirconia adhesion and provides a stable surface for resin bonding, enabling reliable intraoral repair of porcelain-veneered zirconia crowns.\u003c/p\u003e","manuscriptTitle":"Enhancement of Zirconia–Resin Bonding by Water Glass Surface Treatment","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-23 18:10:59","doi":"10.21203/rs.3.rs-7571308/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-12-15T07:47:27+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-21T01:37:55+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-20T09:24:39+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"82283072676492330446378670335391818008","date":"2025-10-26T16:50:20+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"208663625040527783970698493607107333175","date":"2025-10-24T04:50:13+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"273881226826622441657918429542245138937","date":"2025-10-23T01:33:42+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-09-15T21:48:43+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-09-12T09:51:51+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-09-12T09:51:13+00:00","index":"","fulltext":""},{"type":"submitted","content":"Clinical Oral Investigations","date":"2025-09-09T08:10:52+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"clinical-oral-investigations","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cloi","sideBox":"Learn more about [Clinical Oral Investigations](http://link.springer.com/journal/784)","snPcode":"784","submissionUrl":"https://submission.nature.com/new-submission/784/3","title":"Clinical Oral Investigations","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"8379be1d-3429-4fa1-836e-97ec29b5f5a9","owner":[],"postedDate":"September 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-02-16T16:14:56+00:00","versionOfRecord":{"articleIdentity":"rs-7571308","link":"https://doi.org/10.1007/s00784-026-06747-5","journal":{"identity":"clinical-oral-investigations","isVorOnly":false,"title":"Clinical Oral Investigations"},"publishedOn":"2026-02-10 15:58:12","publishedOnDateReadable":"February 10th, 2026"},"versionCreatedAt":"2025-09-23 18:10:59","video":"","vorDoi":"10.1007/s00784-026-06747-5","vorDoiUrl":"https://doi.org/10.1007/s00784-026-06747-5","workflowStages":[]},"version":"v1","identity":"rs-7571308","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7571308","identity":"rs-7571308","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}