To observe the application effect of all-ceramic crown and onlay in the restoration of posterior dental defect. Methods From January 2022 to January 2023, 80 patients who underwent dental repair after root canal treatment of posterior dental defects in the Department of Stomatology of Libo County People's Hospital were selected as the research objects. They were divided into control group and experimental group by random number table method, with 40 patients in each group. The control group was treated with all-ceramic crown for restoration, and the experimental group was treated with onlay for restoration. The clinical efficacy, oral health status, treatment satisfaction and complications were compared between the two groups. Results The total effective rate of treatment in the experimental group was 97.50%, which was higher than 80.00% in the control group (P <0.05). The oral health score of the two groups after treatment was lower than that before treatment, and that in the experimental group was lower than that in the control group (P <0.05). The satisfaction scores of treatment comfort, treatment skills, treatment quality and treatment effect in the experimental group were higher than those in the control group (P <0.05). The incidence of complications in the experimental group was 2.50%, which was lower than 15.00% in the control group (P <0.05). Conclusion The effect of onlay in the restoration of posterior dental defect is more ideal than that of all-ceramic crown, which can effectively reduce the incidence of complications, improve the treatment effect and treatment satisfaction, and is worthy of clinical application.