Objective To analyze the repair effect of all-ceramic onlay repair root canal therapy in patients with tooth defect. Methods A total of 80 patients with tooth defects admitted to Yangchun Stomatological Hospital from January 2021 to March 2023 were selected as the research objects. They were numbered according to the time of admission, the odd number was the control group (n=40), and the even number was the observation group (n=40). Both groups received root canal treatment, the control group received all-ceramic crown repair, and the observation group received all-ceramic onlay repair. The clinical efficacy, periodontal and oral function of the two groups were compared. Results The total effective rate of the observation group was 95.00%, which was higher than 80.00% of the control group, and the difference was statistically significant (P<0.05). After treatment, the masticatory efficiency of the observation group was higher than that of the control group, and the GI, SBI, PLI and tooth mobility were lower than those of the control group, the differences were statistically significant (P<0.05). Conclusion The clinical effect of all-ceramic onlay repair root canal treatment for patients with tooth defect is ideal, which can improve the masticatory efficiency and other oral functions of patients, and has important application value.