Objective To explore the effect of composite resin filling in patients with tooth defect. Methods A total of 80 patients with tooth defect admitted to our hospital from January 2022 to January 2023 were selected as the research objects. They were divided into control group and observation group by random number table method, with 40 patients in each group. The control group was treated with glass ionomer cement filling, and the observation group was treated with composite resin filling. The clinical efficacy, repair effect and adverse reactions 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 (P <0.05). The excellent rate of retention function, masticatory efficiency and aesthetic score of the observation group were better than those of the control group (P <0.05). The incidence of adverse reactions in the observation group was 7.50%, which was lower than 25.00% in the control group (P <0.05). Conclusion Composite resin filling is effective in patients with tooth defect, which can improve the excellent rate of retention function, improve masticatory efficiency, improve aesthetic score, and reduce the incidence of adverse reactions. It is worthy of clinical application.