Objective: To explore the effects of different tooth preparation morphologies (traditional shoulder preparation and bio-guided preparation techniques) on the restoration of occlusal function and surface aesthetics of tooth crowns in posterior tooth defect repair. Methods: A total of 80 patients with posterior tooth defect who were admitted from January 2025 to December 2025 were selected and randomly equally divided into the observation group (bio-guided preparation technique, 40 cases) and the control group (traditional shoulder preparation, 40 cases) using the digital table method. Results: Compared with the control group, 6 months after restoration, the chewing efficiency and bite force of the observation group were higher (P < 0.05), the A-level scores for marginal fit, surface texture and color matching were better (P < 0.05), and the complication rate was lower (P < 0.05). Conclusion: In posterior tooth defect repair, using bio-guided preparation technique for tooth preparation compared with traditional shoulder preparation can more effectively improve the occlusal function of patients and enhance the surface aesthetics and marginal fit of the tooth crown, and it is recommended for promotion.