Objective To compare the long-term effects of all-ceramic onlay and all-ceramic crown in the restoration of dental defect. Methods A total of 120 patients with dental defect who received root canal treatment in our hospital from April 2021 to April 2023 were selected, and they were divided into the control group and the observation group by the random number table method, with 60 patients in each group. The control group was given all-ceramic crown restoration, and the observation group was given all-ceramic onlay restoration. The aesthetic satisfaction of restorations, masticatory function satisfaction, periodontal indexes, long-term effects and complication rate were compared between the two groups. Results The aesthetic satisfaction rate of restorations in the observation group (95.00%) was higher than that in the control group (81.67%) (P <0.05). The masticatory function satisfaction rate in the observation group (91.67%) was higher than that in the control group (78.33%) (P<0.05). The sulcus bleeding index, gingival index and plaque index in the observation group after restoration were lower than those in the control group (P<0.05). The scores of aesthetic appearance and marginal adaptation of restorations in the observation group were higher than those in the control group (P<0.05). There were no statistically significant differences in the scores of restoration integrity and abutment condition between the two groups (P>0.05). There was no statistically significant difference in the incidence of complications between the two groups (P >0.05). Conclusion Compared with all-ceramic crown restoration, all-ceramic onlay restoration has better long-term effects in the restoration of dental defect. It can effectively improve patients' periodontal indexes, help to enhance the aesthetic satisfaction of restorations and masticatory function satisfaction, and does not increase the incidence of complications, which is worthy of clinical application.