Many novel dental ceramic materials that are both aesthetically appealing and extremely durable have recently been discovered. There are several high-strength ceramic systems with different therapeutic indications that are available, including zirconium ox-ide, lithium disilicate, infiltrating alumina, and densely sintered aluminum oxide ceramics (Bajraktarova-Valjakova et al., 2018). Lithium disilicate glass ceramics, a new generation of heat-pressure ceramics, offer greater bending and fracture resistance than the preceding generation of ceramics reinforced by leucite (Phark and Duarte, 2022). In general, lithium disilicate is thought of as an acid etchable ceramic made up of 60%–65% crystals of lithium oxide (Li₂O) embedded in a matrix of silica glass [Zarone et al., 2023].

The cementation process has a major influence on how long ceramic restorations last. A number of clinical studies have suggested that clinical failure could result from the restoration’s insufficient luting performance (Sinha, 2023). Adhesive and non-adhesive cementing techniques are the two varieties. The procedure of adhesive cementation strengthens the bond between the restorative material and substrate by combining adhesive chemical bonding with micromechanical interlocking (Abad-Coronel et al., 2019). Conventional (non-adhesive) cementation fills the area between the restoration and the original tooth with a luting solution and relies only on macro and micromechanical retention (Ghodsi et al., 2021). The indications for each type of cementation are determined by the composition of the ceramic, the available forms for preparation, retention, and resistance, as well as by the field control during cementation. Recent developments in adhesive dentistry have led to numerous studies examining various ceramic restorative surface treatments in an effort to increase bond strength. Like silica coating, sandblasting, and acid etching (Perdigão et al., 2021).

The clinical service outcome of lithium disilicate is significantly influenced by the resin cement and ceramic bond. Robust and strong resin bonding increases marginal adaptation, strengthens fracture resistance, increases retention, and reduces bacterial micro leakage (Simasetha et al., 2022). The cement-ceramic bond can be created by surface wettability, chemical bonding to a silica-based lithium disilicate surface, and micromechanical retention. To achieve micromechanical retention, the surface can be prepared by abrasion with airborne particles or by etching with hydrofluoric acid. Airborne particle abrasion is not recommended since it significantly reduces flexural strength and does not give lithium disilicate a satisfactory bond strength (Blatz et al., 2018).

Hydrofluoric acid etching dissolves the glass phase from the matrix, produces micro-porosity, and increases surface areas. The cement-ceramic surfaces can be chemically coupled by means of a silane coupling agent. The silane coupling agent is a bifunctional chemical that enables covalent connections with hydroxyl (OH) groups on the lithium disilicate surface to facilitate adhesion. One functional group can react with the inorganic lithium disilicate surface, and the other methacrylate group can react with an organic resin matrix (Ramakrishnaiah et al., 2016). Silane and Si-OH combine to generate a condensation reaction bond on a ceramic surface. Methyl methacrylate’s double bonds hold the adhesive to the surface. Applying silane before using resin cement to lute will strengthen the bond by enhancing infiltration into the surface flaws of the etched lithium disilicate. Furthermore, the resin cement has a major impact on the binding to high crystal-line content ceramics. Adhesion between lithium disilicate and resin cement is the outcome of a physico-chemical interaction over the resin-ceramic contact (Fidalgo-Pereira et al., 2023).

The best method to improve the adhesion between resin cement and ceramic surfaces is still up for debate, despite a number of research comparing those various surface treatments (Abad-Coronel et al., 2019; Ghodsi et al., 2021; Perdigão et al., 2021; Simasetha et al., 2022; Blatz et al., 2018; Ramakrishnaiah et al., 2016; Fidalgo-Pereira et al., 2023). Thus, this study’s objective was to assess and compare the effect of different surface treatments including 10% hydrofluoric acid with silane coupling agent, 10% hydrofluoric acid only, Sandblasting with 50 μm Al₂O₃,30 μm silica-coated Al₂O₃ and Er,Cr:YSGG laser on the shear bond strength (SBS) between lithium disilicate and self-adhesive resin cement (RelyXU200). In addition, the surface topography of the surfaces before and after debonding of the tested specimens were also evaluated by using a scanning electron microscope (SEM).

The study was carried out in the Department of Prosthodontics at King Saud University’s College of Dentistry and College of Dentistry Research Center (CDRC) in Riyadh, Saudi Arabia. The CDRC at King Saud University in Riyadh (CDRC # lR 0,466) provided ethical approval.

This study demonstrated that the various surface treatments done to lithium disilicate ceramic had a significant effect on the SBS when using self-adhesive resin cement. The 10% hydrofluoric acid with silane group had the highest mean SBS value (40.48 ± 13.32 MPa), followed by the 10% hydrofluoric acid only group (33.96 ± 11.58 MPa). Nevertheless, there was no discernible statistical difference between the two groups (p > 0.05). The laser group recorded 1.68 ± .37 MPa and the control group recorded 0.94 ± 0.22 MPa, respectively, with no statistically significant difference between the two groups (p > 0.05). The mean values of the Al₂O₃ sandblasting and silica-coated Al₂O₃ coating groups were 23.23 ± 7.15 MPa and 6.70 ± 2 MPa, respectively, with no statistically significant differences (p > 0.05). Nevertheless, both were remarkably higher than the control and laser groups but lower than HFS and HF groups (Table 2).

The most successful surface treatment was 10% hydrofluoric acid with silane, with a mean value noticeably higher than all other groups (p < 0.05) and little difference with the group treated with 10% hydrofluoric acid alone. The laser group, on the other hand, had the least impact on SBS, with a mean value that was considerably lower than that of any other group (p < 0.05) save for the control group. With a mean value significantly higher than the laser and control groups (p < 0.05), but lower than the 10% hydrofluoric acid with saline and 10% hydrofluoric acid groups (p < 0.05), both sandblasting groups demonstrated improvement in SBS. Nonetheless, unimportant in relation to one another (p > 0.05) (Table 3).

At the ceramic-cement interface, adhesive and mixed failure modes were seen in most specimens (Table 4). Compared to the other groups, groups HFS, HF, and AO displayed higher levels of cement-retained on the surface. Some samples of the SC group displayed more than half of the cement retained. Only two samples with retained cement were displayed in the control group, and none at all in the L group. Adhesive failures and combined cement and lithium disilicate failures accounted for the majority of bond failures (Figure 7).

A highly smooth surface was visible in the control group (Figure 3A). Hydrofluoric acid-treated groups generated uniformly retentive, elongated linear crystals (Figures 3B, C). A similar irregularity pattern was produced by airborne abrasion using 30 μm silica particles and 50 μm Al₂O₃ particles (Figures 3D, E). For the test group treated with Er,Cr:YSGG laser, three distinct pilot samples underwent SEM evaluation after being treated with varying powers (1, 2, and 3 W) (Figure 8). A power of 1 W was utilized since surfaces exposed to 2 W and 3 W radiation-induced greater melting than retentive impact. In contrast to the other groups, less retentive regions were discovered under laser irradiation (Figure 3F).

Table 5 displays the Sa values for each of the test groups. The AO group had the highest Sa values (Sa = 4,527.44), followed by the SC group (Sa = 1,054.48) as expected because particles of both these materials were blasted over the ceramic specimens in both groups. The L group, however, had the lowest Sa value (Sa = 257.32), revealing that the laser application had a smoothing impact on the lithium disilicate ceramics' surface.

This study aimed to evaluate the effects of different surface treatments on the self-adhesive resin cement and lithium disilicate ceramic SBS. In this investigation, test specimens with the same dimensions and forms were used to standardize the cementation process and achieve consistency. To find out if the SBS of these surface-treated specimens and resin cement improved, the test specimens' surfaces were subjected to various surface treatments. Using universal testing equipment from Instron, the SBS values of the cemented lithium disilicate specimens were determined in megapascals (MPa). Moreover, a scanning electron microscope (SEM) was used to scan the surface topography of the surfaces both before and after the tested specimens' debonding. Numerous scholars have noted that the method used in this protocol to measure the SBS using universal testing equipment produces reliable results and is one of the most frequently recommended methods (Jayasheel et al., 2017). Measurements of quantitative bond strength have demonstrated the superiority and dependability of universal testing apparatus (El Mourad, 2018; Ismail et al., 2021; Sirisha et al., 2014). The SBS values in MPa continue to be a helpful general bond strength guideline because they are a practical and understandable value that allows the comparison of the SBS values of the tested specimens with different surface treatments and cemented with resin cement, as well as the comparison of the current findings with other studies and standards (Jungbauer et al., 2022). Additional useful information on the SBS values of the materials under test was obtained by using SEM to evaluate the surfaces of the tested specimens.

In the current study, the SBS between resin cement and lithium disilicate dental restorative material with different surface treatments was examined. Lithium disilicate ceramic has grown a lot in popularity and is utilized a lot, particularly in circumstances that are quite attractive. It can be applied in a range of clinical settings and has shown to be an extremely durable substance. Understanding the intricacy of this material’s structure is crucial to be able to use it confidently as a ceramist, technician, or clinician. The physical qualities of this material are greatly influenced by its microstructure, which can be altered by various surface treatments (Zarone et al., 2019). This can change the material’s bond strength with resin cement which is the cement of choice when using glass ceramics (Zarone et al., 2016). The goal of the current study was to evaluate and examine how various surface treatments affected the lithium disilicate bond strength with resin cement. The study’s findings demonstrated that all surface treatments—except laser irradiation—improved the self-adhesive resin to lithium disilicate ceramic’s SBS, therefore, the null hypothesis stating that various surface treatments have no effect on the shear bond strength between lithium disilicate and resin was thus disproved.

The clinical performance, success, and longevity of the ceramic restorations are significantly influenced by the cementation technique and adhesive cement type employed (Vargas et al., 2011; Chirca et al., 2021). When entire ceramic crowns were bonded with resin cement, their fracture resistance rose (Jurado et al., 2023). This was because the resin filled in the imperfections on the restoration’s inside surface, halting the spread of cracks (Fathy et al., 2022; Tyor et al., 2023). Moreover, resin cement is superior to other forms of cement on the market in terms of its mechanical, physical, and aesthetic qualities (Muhammed et al., 2023). To offer acceptable surface qualities, several procedures such as acid etching, laser irradiation, diamond rotary tools, airborne particle abrasion with silica or aluminum oxide, and combinations of any of these are commonly utilized (Bajraktarova-Valjakova et al., 2018; Berk et al., 2008). Because the microstructure has a major impact on the bond strength, it is imperative to choose the right surface treatment for the type of ceramic (Limpuangthip et al., 2023).

The surfaces treated with 10% hydrofluoric acid and silane coupling agent had the highest SBS values in the current study, with a mean value of (40.478 Mpa). This was in line with an earlier investigation by Lyann et al. (2018), who demonstrated similar SBS values of (40.6 ± 6.3 Mpa) when using acid etching with hydrofluoric acid and silane coupling agent. Hydrofluoric acid etching and silanization, in which the silica particles react with the hydrofluoric acid, make up the micromechanical and chemical bonding mechanism of silica-based ceramics (Yavuz and Eraslan, 2016). Acid etching increases the free energy microporosity and surface area, which lowers the contact angle and enhances the wettability of resin cement and lithium disilicate (Levartovsky et al., 2021). Little, randomly oriented, interconnecting, densely packed, needle-like lithium disilicate crystals make up the architecture of lithium disilicate, to which even smaller secondary lithium orthophosphate crystals are added. By dissolving and eliminating the glassy matrix including silica and silicates, HF etching creates a porous surface. Increased surface micromechanical retention is provided by the secondary crystal phase (Li et al., 2019). HF, in particular, has the potential to break down the glassy matrix of the ceramic, leaving the lithium disilicate surface with an uneven microstructure. This impact increased the surface area for micromechanical bonding and interlocking, which increased the bond strength (Ersu et al., 2009; Fischer et al., 2008).

Airborne abrasion with Al₂O₃ is another effective method that is often used on oxide ceramics (Fidalgo-Pereira et al., 2023). In order to improve the surface area by producing more micromechanical cuts for the cement interlocking, several manufacturers proposed utilizing airborne particle abrasion to increase surface roughness (Fischer et al., 2008). As shown by SEM Figure 2, increasing the powder size from 30 μm to 50 µm has enhanced the surface roughness while maintaining a constant duration and pressure. However, excessive roughness on ceramic surfaces might lead to weak interfacial interactions instead of strong ones in certain cases (De Jager et al., 2000; Erdemir et al., 2014).

Consistent with earlier studies (Fischer et al., 2008; Hummel and Kern, 2004; Sadan et al., 2003), the Al₂O₃ sandblasting group in our study showed significantly higher SBS values (23.23 ± 7.15 MPa) than the control group. However, the current study found no statistically significant differences between 30 μm silica particles and 50 μm Al₂O₃. In the present investigation, the use of advanced surface pretreatments techniques beyond the commonly used standard surface treatments were studied, including Er,Cr:YSGG laser irradiation to evaluate its effect on SBS. It is expected that silica-based ceramics will lose their glass phase when exposed to laser light, resulting in a rough surface (Yavuz et al., 2017). However, the current results showed that Er,Cr:YSGG laser irradiation had no effect on the bonding strength with resin cement when compared to the control samples. Similar findings were reached by Foxton et al. (2011) when they examined the effect of the Er:YAG laser on the SBS of resin cement and alumina ceramics. Additionally, similar SBS values of (3.88 ± 1.94 MPa) using laser-irradiation with a power of 1.5 were reported in another investigation by Kursoglu et al. (2013).

The mode of failure in the current study correlated to the shear bond strength values, in other words, it was predominantly cohesive failure in the groups that displayed higher shear bond strength values such as the HFS, HF and AO groups, and as the shear bond strength decreased such as in the group treated with laser, the adhesive failure mode was predominating. It is reasonable to explain such correlation to the fact that the stronger the bond between the cement and the ceramic surface, the more cement portions retain on the ceramic surface. Understanding the bonding mechanisms with the different surface treatment modalities used in the current investigation may be partially aided by the results of the Sa measurements conducted using a profilometer. The maximum Sa values were shown by airborne-particle abrasion with 50 μm Al₂O₃ particles. This was also supported by the SEM pictures, which showed rough and uneven surfaces at varying depths and heights. In contrast to the control, laser-treated, and silica-coated groups, these morphological alterations produced interlocking retentive structures in the lithium disilicate surface, resulting in a micromechanical bond that increased the SBS. The SBS of the AO samples was lower than that of the hydrofluoric acid with and without silane, despite the fact that they seemed the roughest of all the examined groups. This result was consistent with previous studies that showed the strongest bonds were created by hydrofluoric acid treatment followed by silane application (Abdulkader et al., 2021; Ayad et al., 2008; Şişmanoğlu et al., 2020). When combined with silane, the roughness of the ceramics produced by hydrofluoric acid etching resulted in an efficient production of siloxane linkages upon mixing with the acid solution, according to Ayad et al. (Ayad et al., 2008). In terms of shear bond strength, this chemical link was superior than the micromechanical characteristics of the acid-etched HFS and HF groups, which were visible in SEM images as grooves and pores. However, the lowest Sa values were obtained after laser treatment. SEM examination validated this conclusion by demonstrating that laser treatment created smooth surface topography devoid of retentive micromechanical features, which may account for the low SBS values that did not differ significantly from the control groups.

The present investigation had certain limitations. Although standard protocols were followed during sample fabrication, specimen’s surface characteristics may have been affected during manufacturing process, besides, handling of the materials during production might have an impact on the outcome. Moreover, the study only used one type of self-adhesive resin cement; therefore, greater investigation into other types of cements is strongly advised in order to better understand the long-term behavior of SBS. Additionally, as this study was conducted in vitro, it was unable to account for all the factors that might be present in the oral media, such as fatigue and pH changes. Considering the aforementioned constraints, it is imperative to carefully evaluate the current study’s findings.

Based on the findings of the study, it can be concluded that.

• Using 10% hydrofluoric acid with silane coupling agent effectively improved the shear bond strength between lithium disilicate ceramics and self-adhesive resin cement.