Aesthetic and durable dental restorations have become a major demand in modern prosthodontics due to the developments in the field of material science and patient expectations.[1] Zirconia-based ceramics have been widely accepted among the restorative materials available because of the improvement in mechanical strength, fracture resistance, and biocompatibility.[2] Zirconia, also known as yttria-stabilized tetragonal zirconia polycrystal, or Y-TZP, is a denture material that exhibits transformation toughening action with a high flexural strength (900–1200 MPa).[3] It is one of the surest materials to use in the fabrication of fixed dental prostheses, especially in the posterior regions.[4] Nevertheless, in spite of all these desirable mechanical properties, the difficulty in ensuring a lasting bond between zirconia and resin-based luting agents is an important clinical problem.

In contrast to silica-based ceramics, zirconia has a polycrystalline structure with low proportions of glass that restricts its capability to be etched by conventional methods of hydrofluoric acid.[4] This chemical inertness leads to lower surface energy and poor micromechanical retention, which eventually leads to a decrease in bond strength with resin cements. It has been demonstrated that the bond strength values of resin cements to untreated zirconia surfaces may be comparatively low, typically between 3 and 8 MPa, based on the cement type and test conditions.[5] Therefore, poor bonding can result in clinical failures like debonding, marginal leakage, and decreased restoration longevity.

To address these shortcomings, several surface modification methods have been proposed, including airborne-particle abrasion (sandblasting), tribochemical silica coating, laser treatment, and the deposition of chemical primers with functional monomers in them, such as 10-MDP. Surface roughening by sandblasting has been demonstrated to provide a significant increase in micromechanical interlocking and improvement in bond strength by increasing the surface area and wettability.[6] There is also an increasing popularity of the self-adhesive resin cements, which have simplified clinical use by removing the need to use two separate clinical steps: etching and bonding, yet offer acceptable bond strength and clinical performance.

Recent research on self-adhesive resin cements has demonstrated good clinical results and retention rates as high as 95% after 24 months when applied to zirconia crowns.[7] Nonetheless, the literature is not consistent on the best surface treatment protocol that is necessary to achieve the maximum bond strength. Although certain reports indicate that varying resin cements display similar values of bond strength (around 11-12 MPa), the effect of surface alteration is a crucial factor that defines the adhesion stability.[8] Moreover, the adhesive interface may also be compromised by other factors like aging, thermocycling, and surface contamination, which may indicate the necessity of standardized and evidence-based procedures.[9]

Despite extensive investigation, the best surface treatment method for strengthening the binding between zirconia restorations and self-adhesive resin cements is still unknown. Most of the available literature either addresses traditional resin cements or considers small-scale surface treatments, which leaves a knowledge gap on the interaction between the new method of surface modification and a simplified luting system. In order to fill this important gap, a comprehensive analysis of the impact of several surface modification techniques on the bond strength of zirconia crowns in conjunction with self-adhesive resin cements was conducted. In addition to improving clinical results, a situation-appropriate methodology is essential for expediting the procedure without compromising the durability of restorations. Finding out how various surface modification techniques affected the bond strength of zirconia crowns bonded with self-adhesive resin cements was the aim of this experimental study.

This in vitro experimental study was conducted to evaluate the influence of surface modification techniques on the bond strength of zirconia crowns when used with self-adhesive resin cements. The study was carried out in the Department of Dental Materials at equipped with CAD/CAM and material testing facilities. The duration of the study was one year. OpenEpi version 3 was used to calculate the sample size by using the standard formula of proportion estimation. An earlier research provided a prevalence of 85% of better bond strength following surface treatment, which was used with a confidence level of 95 (Z = 1.96) and a margin of error of 8, yielding 49 specimens.[10] In order to provide sufficient group distribution and address potential specimen loss during preparation and testing, the number of final samples was set at 60, with each group having 15 samples. A non-probability consecutive sampling method was employed. Zirconia samples meeting the inclusion criteria were then prepared and incorporated in the order they were available to the point of attaining the desired sample size. The inclusion criteria included zirconia specimens that were produced using CAD/CAM technology, zirconia polycrystal with yttria as a stabilizer, and standardized dimensions with uniform surfaces. Specimens that had visible cracks, porosities, contamination or dimensional errors were eliminated. Moreover, specimens broken in the process of either preparation, surface treatment or mechanical testing were not considered in the final analysis. A total of 60 zirconia specimens that had been sintered in accordance with the manufacturer's instructions were subjected to CAD/CAM milling. Based on the type of surface change, the specimens were split into four groups at random. Group I received no surface treatment; Group II received airborne particle abrasion using 50 µm aluminum oxide particles; Group III received tribochemical silica coating; and Group IV received laser surface treatment. Following surface modification, each specimen underwent a 10-minute ultrasonic cleaning in distilled water before being allowed to air dry. The self-adhesive resin cement was then placed on as per the manufacturer's instructions, and the zirconia specimens were bonded to blocks of composite resin at a constant load to achieve standardized cement thickness. After cementation, each specimen was placed in distilled water at 37°C and allowed to stand for a whole day to simulate oral conditions. To simulate heat stressors in the oral cavity, 500 cycles of thermocycling between 5 and 55 degrees Celsius were performed. A universal testing machine was used to test the bonds' strength. Shear force was applied at a crosshead speed of 0.5 mm/min until the bond failed. Megapascals (MPa) were used to convert the peak failure load, which was measured in Newtons. The manner of failure, which was categorized as adhesive, cohesive, or mixed failure, was also identified using a stereomicroscope (40x). For analysis, the collected data was entered into SPSS 26. The failure mode was the qualitative variable and was displayed as a frequency and a percentage, while bond strength was the quantitative variable and its values were shown as mean and standard deviation. The normality of the data distribution was assessed using the Shapiro-Wilk test. The four groups' mean bond strengths were compared using one-way analysis of variance (ANOVA), and multiple group comparisons were performed using a post hoc Tukey test. Fisher's exact test was used to assess categorical variables, and a p-value of 0.05 or less was considered statistically significant.

A total of 60 standardized zirconia specimens were used in the study and were equally divided into four surface treatment groups. The specimens were all homogeneous in composition (Y-TZP), dimensions, and cementation protocol, which guaranteed homogeneity between groups. The analysis of the bond strength revealed a definite difference in the various surface treatment procedures with the best bond strength being observed in the tribochemical silica coating group (13.02±1.18 MPa), followed by airborne-particle abrasion (11.45±1.35 MPa) and the laser treatment (9.76±1.27 MPa). (Table 1).

Post hoc Tukey test also showed that all the pair comparisons were statistically significant, meaning that each of the surface modification methods influenced bond strength uniquely (Table 2). The highest difference was found between the silica coating and the control group, and this shows the usefulness of surface modification.

Also, failure-mode evaluation revealed that failure modes were more common in the control group (73.3%), where mixed and cohesive failures were more common in treated groups, especially in silica-coated specimens (Table 3). The mode of failure was statistically significantly related to the type of surface treatment (p=0.010), indicating a better bonding integrity with surface modification (Table 3).

Table 1: Comparison of Shear Bond Strength (MPa) and Normality Assessment among Different Surface Treatment Groups

Table 2: Comparison of Mean Shear Bond Strength among Surface Treatment Groups Using One-Way ANOVA and Post Hoc Tukey Test

Table 3: Distribution of Failure Modes and Their Association with Surface Treatment Techniques

The results of this experiment demonstrate that surface modification of zirconia crowns with self-adhesive resin cements greatly increased the bond strength. The tribochemical silica coating group had the strongest bond, followed by airborne particle abrasion, and the control group had the weakest bond. These findings are in excellent agreement with recent research highlighting the importance of surface preparation in enhancing zirconia adhesion. All of the surface-treated groups demonstrated much stronger bonds than untreated zirconia, according to a study published in BMC Oral Health (2023). This result supports the existing conclusion that untreated zirconia has poorer bonding capacity.[11]

Likewise, a recent systematic review and meta-analysis (2023) emphasized that mechanical and chemical surface treatment of zirconia restorations can substantially enhance the bond strength and durability of zirconia restorations in comparison with control groups, which supports the result of the present study.[12] Another meta-analysis further established that the bond strength does not just rely on the surface treatment, but also depends on the aging conditions, whereby treated surfaces have a better duration of existence.[13]

The excellent performance of silica coating in the current study is in line with other recent studies. It has been demonstrated that tribochemical silica coating improves micromechanical retention as well as chemical bonding via silane coupling and thus achieves greater bond strength than alternative methods. Conversely, airborne-particle abrasion has been cited as the most favorable approach in some studies. Although other techniques also shown a considerable increase in bond strength above control groups, a 2024 study published in BMC Oral Health found that airborne-particle abrasion had the best binding strength between various types of zirconia.[14] This minor discrepancy could be explained by the variations in zirconia composition, particle size, and experimental procedures.

The results of the current study are also consistent with the study by Swarnakar et al. (2022), which revealed much greater bond strength values of sandblasted zirconia than unblasted ones, which proves the significance of surface roughening in strengthening adhesion.[15] Moreover, researchers in 2023 have stressed that mechanical and chemical surface treatments show better bonding results in comparison to single-modality strategies, which also aligns with the high performance in the silica-coated group in the current study.[16]

Moreover, recent studies on the topography and wettability of surfaces have shown that a high degree of surface roughness and wettability is also a crucial factor in the strengthening of zirconia bonds.[17] This is in line with the current results, in which the bond strength was significantly greater in treated groups with modified surface properties than in the smooth and untreated control group.

The fact that the majority of adhesive failures occurred in the control group and mixed/cohesive failures in the treated groups in this study further confirms the enhancement in bonding that was attained due to surface modification. The same trends have been observed in the current literature, with stronger adhesion being linked to cohesive or mixed failures, which provides a more stable and lasting bond interface. Recent 2023 studies have continued to show this reduction in failure mode with enhanced surface treatments.[11, 18]

Although the overall consensus is there, there are slight differences in the studies on the best surface treatment method. Although the current research has found silica coating to be the best method, there are studies that have preferred airborne-particle abrasion or a combination of both protocols. Such variations can be attributed to differences in experimental design, type of resin cement, thermocycling conditions, and zirconia composition, especially differences in yttria content, which is observed to affect bonding behavior.[14, 19]

In general, the results of this research are in line with the existing literature, as they prove that the surface modification is a key to optimal bond strength in zirconia restorations.[20, 21] The findings also indicate that the more complex surface treatments, especially those involving both mechanical and chemical processes, can offer better bonding efficacy and could increase the clinical efficacy of zirconia-based restorations in the long term.

This study had many limitations that should be taken into account when evaluating the findings. Since it is an in vitro study, the full simulation of the oral environment was not possible, especially salivary enzymes, masticatory forces, pH changes, and long-term thermal aging, which was not subjected to the thermal thermocycling program. The sample size was relatively small, statistically sufficient, but it included only standardized zirconia discs and not full-contour crowns, which might not be a complete replication of clinical conditions. Moreover, only one type of self-adhesive resin cement was tested, which limits the ability to generalize the results to other cement systems. The fact that operator-dependent procedures and surface treatment parameters, including pressure and time spent in airborne abrasion or laser settings, varied might also have affected the results, even though an effort was made to standardize them.

The binding strength of zirconia crowns treated with self-adhesive resin cements was found to be significantly impacted by surface modification techniques within the limitations of this experimental study. The highest bond strength was demonstrated by the tribochemical silica coating, which was followed by laser treatment and airborne particle abrasion, while untreated zirconia had the lowest bond strength. Surface treatment also positively contributed to the pattern of failure as it enhanced mixed and cohesive failures, which are indicative of enhanced interfacial bonding. These findings clearly show that in order to optimize the adhesive properties of zirconia restorations, appropriate surface modification is essential. This has the potential to improve zirconia restorations' lifespan and clinical performance in the context of restorative dentistry.

1. Hoseini, M.S. and S.K. Naeeni, Aesthetic Considerations in Prosthodontics: A Literature Review. Journal of Oral and Dental Health Nexus, 2025. 2(1): p. 27-39.
2. Zhong, C. and X. Wang, Advancements and challenges in the application of zirconia ceramics for dental restorations. Ceram. Silikáty, 2024. 68: p. 610-623.
3. Almirabi, R.S. and K.M. Alzahrani, Effect of the intaglio surface treatment and thickness of different types of yttria-stabilized tetragonal zirconia polycrystalline materials on the flexural strength: In-vitro study. Materials, 2024. 17(21): p. 5256.
4. Malallah, A.D. and N.H. Hasan, Classification and generations of dental zirconia, in Zirconia-New Advances, Structure, Fabrication and Applications. 2023, IntechOpen.
5. Lee, H., R.J.Y. Kim, and D.-G. Seo, Shear bond strength of dual-cured resin cements on zirconia: The light-blocking effect of a zirconia crown. Journal of Dental Sciences, 2024. 19(1): p. 162-168.
6. Lin, S.-C., et al., Evaluation of the bonding strength between various dental zirconia models and human teeth for dental posts through in vitro aging tests. Coatings, 2021. 11(9): p. 1017.
7. Alrashdi, M. and A. Alhunti, Clinical outcome of prefabricated zirconia crowns cemented with self-adhesive resin and pure glass ionomer on primary teeth: a retrospective cohort study. Children, 2024. 11(8): p. 991.
8. Murugesan, S., In vitro Comparison of Shear Bond Strength of Various Cements for Zirconia Crowns. Journal of Pharmacy and Bioallied Sciences, 2025. 17(Suppl 1): p. S510-S512.
9. Ayedi, L., et al., Which Bonding Protocol Provides the Most Durable Zirconia Adhesion after In Vitro Artificial Aging: A Systematic Review. The Journal of Contemporary Dental Practice, 2026. 26(12): p. 1215-1227.
10. Özcan, M. and M. Bernasconi, Adhesion to zirconia used for dental restorations: a systematic review and meta-analysis. J Adhes Dent, 2015. 17(1): p. 7-26.
11. Sarıkaya, I. and Y. Hayran, Adhesive bond strength of monolithic zirconia ceramic finished with various surface treatments. BMC Oral Health, 2023. 23(1): p. 858.
12. Kumar, R., et al., Effect of surface treatment of zirconia on the shear bond strength of resin cement: a systematic review and meta-analysis. Cureus, 2023. 15(9).
13. Rigos, A.E., K. Sarafidou, and E. Kontonasaki, Zirconia bond strength durability following artificial aging: A systematic review and meta-analysis of in vitro studies. Japanese Dental Science Review, 2023. 59: p. 138-159.
14. Falahchai, M., et al., Effect of different surface treatments on shear bond strength of zirconia with various yttria contents. BMC Oral Health, 2024. 24(1): p. 1520.
15. Swarnakar, A., et al., Comparative Analysis of Three Surface Treatments on the Bond Strength of Zirconia to Resin-luting Agents: An In Vitro Study. J Contemp Dent Pract, 2022. 23(9): p. 883-888.
16. Limpuangthip, N., A. Surintanasarn, and P. Vitavaspan, Mechanical and chemical surface treatment enhances bond strength between zirconia and orthodontic brackets: an in vitro study. BDJ open, 2023. 9(1): p. 53.
17. Wongsue, S., et al., Effect of surface topography and wettability on shear bond strength of Y-TZP ceramic. Scientific reports, 2023. 13(1): p. 18249.
18. Sokolowski, G., et al., The shear bond strength of resin-based luting cement to zirconia ceramics after different surface treatments. Materials, 2023. 16(15): p. 5433.
19. Alnazzawi, A.A., et al., Effect of different surface treatments on the bond strength of different monolithic zirconia with dentin. International Dental Journal, 2025. 75(4): p. 100812.
20. Szawioła-Kirejczyk, M., et al., Adhesive cementation of zirconia based ceramics-surface modification methods literature review. Coatings, 2022. 12(8): p. 1067.

21.         Lupu, I.-C., et al., Bonding Strategies for Zirconia Fixed Restorations: A Scoping Review of Surface Treatments, Cementation Protocols, and Long-Term Durability. Biomimetics, 2025. 10(9): p. 632.