Objective To compare the clinical effects of IPS e.max Press cast ceramic onlay and resin onlay for posterior tooth defect after root canal therapy. Methods A total of 128 patients with posterior tooth defect after root canal therapy admitted to our department from January 2022 to January 2024 were selected, and they were divided into the control group (n=65) and the observation group (n=63) by the random number table method. The control group was restored with resin onlay, and the observation group was restored with IPS e.max Press cast ceramic onlay. The clinical effect and patient satisfaction at 2 years after restoration were compared between the two groups. Results At 2 years after restoration, the grade A rates of restoration integrity, marginal adaptation, proximal contact, secondary caries, periodontal response, marginal discoloration and restoration color in the observation group were higher than those in the control group, and the grade A rate of antagonist wear in the observation group was lower than that in the control group (P<0.05). The satisfaction rate of the observation group (90.47%) was higher than that of the control group (84.61%), but the difference was not statistically signiffcant (P>0.05). Conclusion IPS e.max Press cast ceramic onlay presents stable long-term clinical efffcacy, high restoration success rate and favorable aesthetic effect for posterior tooth defect after root canal therapy, which can meet patients’ demands, but long-term antagonist wear may occur.