Background <p>To evaluate the effect of fiber-reinforced composites on fracture-strength (FS) values of nanoceramic CAD/CAM restoration materials with different thicknesses.</p> Methods <p>One-hundred extracted, caries-free human maxillary premolars were divided into two main groups based on the thickness of the nanoceramic CAD/CAM restorative material (2&#xa0;mm and 3&#xa0;mm). Within each main group, five subgroups were formed: one control, one non-fiber (G-ænial Universal Flo), and three fiber-reinforced experimental subgroups (Ribbond, EverStick NET, and EverX Flow). Standardized MOD cavities were prepared in all experimental groups, extending 2&#xa0;mm below the cementoenamel junction and 3&#xa0;mm wide on the proximal walls. All restorations were fabricated using Cerasmart blocks and cemented with G-CEM Link Force dual-cure resin cement. FS testing was performed, and the data were statistically analysed (<i>p</i> &lt; 0.05).</p> Results <p>Ribbond significantly increased fracture resistance compared to the control group (<i>p</i> = 0.047), while other fiber materials showed no significant difference (<i>p</i> &gt; 0.05). An increase in restorative material thickness enhanced fracture resistance in fiber-reinforced groups (<i>p</i> &lt; 0.001). In the control group, variation in the remaining tooth structure height did not significantly affect fracture resistance (<i>p</i> = 0.078). There was also no significant difference in the interaction between the fiber-reinforced composite type and restoration thickness (<i>p</i>&gt;0.05).</p> Conclusion <p>Although the thickness of the restorative material may influence FS, the use of fiber-reinforced composites does not appear to significantly affect the fracture resistance of nanoceramic CAD/CAM restorations.</p>