for many years. Unlike glass ceramics, Y-TZP cannot be etched by hydrofluoric acid under normal conditions (room temperature and ambient atmosphere). [4] Thus, the roughness of Y-TZP surface is generally achieved by grit blasting.Y-TZP is unlikely to react with silane coupling agents because of its low SiO 2 content (less than 1%). [5,6] Thus, primers containing phosphate ester monomers are typically used in combination with alumina grit blasting to improve the chemical bonding between Y-TZP and resin. [7] Among them, 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) is most commonly used. However, the disadvantage of 10-MDP is that it cannot maintain long-term bonding stability in a complex oral environment (0-67 °C); [8] for example, the shear strength of 10-MDP after 10 000 thermocycles is ≈18.0 ± 3.7 MPa. [9] In addition to primers, the bonding strength of Y-TZP/resin has been also increased by depositing SiO 2 films combined with silane coupling agents. [10][11][12][13] Common methods used for SiO 2 film deposition include sol-gel, tribochemical SiO 2 coating, plasma spraying, and chemical vapor deposition; [14][15][16] although, all these methods have their drawbacks. First, the SiO 2 films are not firmly attached to the Y-TZP and thus are easily peeled off. Second, the coverage of the SiO 2 films on the surface of Y-TZP is insufficient and uneven, and the thickness of the films cannot be controlled. [17,18] Plasma spraying requires high temperatures (2700-11 700 °C), which take a long time to reach, and the procedure is relatively complex. [19] These drawbacks limit the clinical applications of SiO 2 film deposition on the bonding surface of Y-TZP prostheses.Atomic layer deposition (ALD) was first proposed by Suntola and Antson in 1977. [20] ALD may produce nanoscale films with high precision, [21] controllable thickness, and extreme uniformity. [22,23] ALD has already been widely used to deposit films on a variety of materials and is thus expected to overcome the drawbacks of other common SiO 2 film deposition methods because of the following ALD advantages. [24] 1. The films are deposited by gas-solid chemical reactions; thus, the films are firmly and stably bonded with the substrate. [25] The retentive strength of zirconia crowns is derived from resin cement, and the weak interface between the two is the main reason for their failure. In this work, nano-thin silica (SiO 2 ) films of precisely controlled thickness are deposited over yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics via atomic layer deposition (ALD). The deposited films are modified using a silane coupling agent, which significantly improves the bonding strength between Y-TZP and resin. Scanning electron microscopy shows that the SiO 2 films deposited by ALD are uniform and can accurately maintain the morphology of grit-blasted Y-TZP. Spectroscopic ellipsometry demonstrates that the films are nano-thin, with thicknesses in the range of 5.58-26.58 nm. The increase in the shear bond strength is attributed to the chemic...