Objective To explore the effect of cast ceramic onlay on restoration loss rate and gingival health in patients with short-crown molar defect. Methods A total of 84 patients with short-crown molar defect treated in the Department of Stomatology, Kunshan Hospital of Traditional Chinese Medicine from June 2021 to June 2023 were selected as the research subjects. According to different treatment methods, they were divided into the control group and the observation group, with 42 patients in each group. The control group received zirconia all-ceramic crown restoration, and the observation group received cast ceramic onlay restoration. The restoration loss rate, restoration integrity, marginal adaptation, secondary caries, proximal contact and gingival health were compared between the two groups. Results The restoration loss rate of the observation group was 2.38%, which was lower than 16.67% of the control group (P<0.05). There were no signiffcant differences in restoration integrity, marginal adaptation, secondary caries rate and proximal contact between the two groups (P>0.05). After treatment, the GBI and PD in the observation group were lower than those in the control group (P<0.05). Conclusion Both cast ceramic onlay and zirconia all-ceramic crown achieve favorable clinical effect for repairing short-crown molar defect, while cast ceramic onlay is superior in reducing restoration loss rate and improving gingival health.