Objective To explore the effect of biologically oriented preparation technique on occlusal function and surface aesthetics of restorations in patients with posterior tooth defect. Methods A total of 80 patients with posterior tooth defect admitted to Huanghua Traditional Chinese Medicine Hospital from January 2025 to December 2025 were selected, and they were divided into the control group and the observation group by the random number table method, with 40 patients in each group. The control group received traditional shoulder preparation, and the observation group received biologically oriented preparation technique. The occlusal function, surface aesthetics of restorations and complication rate were compared between the two groups. Results At 6 months after restoration, the masticatory efficiency and occlusal force in the observation group were higher than those in the control group (P <0.05). The proportions of grade A in marginal adaptation, surface texture and color matching in the observation group were higher than those in the control group (P <0.05). The incidence of complications in the observation group (2.50%) was lower than that in the control group (20.00%) (P <0.05). Conclusion Compared with traditional shoulder preparation, biologically oriented preparation technique for tooth preparation in posterior tooth defect restoration achieves better effects. It can more effectively improve patients’ occlusal function, enhance the surface aesthetics of restorations, and reduce the risk of complications, which is worthy of clinical application.