Abstract: Guided bone regeneration is a core technique for reconstructing alveolar bone defects in implant dentistry，and its success critically depends on the space maintenance component of the PASS principle. Space-maintaining capability directly determines the outcome of bone augmentation and varies significantly across different defect morphologies：favorable bone defects，in which native bony walls constitute a rigid space-maintenance apparatus，generally yielding favorable prognoses，whereas unfavorable bone defects，lacking such natural barriers，must rely on artificial scaffolds for compensation，leading to a markedly elevated risk of augmentation failure. In this context，the present article focuses on unfavorable bone defects，systematically reviewing the advantages and disadvantages of commonly used bone substitute materials and barrier membranes in addressing high-tension space-maintenance demands，highlighting the key operational points and maintenance strength of current mainstream space-maintenance techniques，and，based on the morphological classification of bone defects，presenting a hierarchical surgical recommendation system，with the aim of providing clinicians with a reference for rationally selecting space-maintenance strategies for unfavorable bone defects of varying severity.

Key words: space maintenance, unfavorable bone defects, bone augmentation techniques, bone substitute materials, PASS principle

摘要： 引导骨再生是种植修复中重建牙槽骨缺损的核心技术，其成功与否关键取决于PASS原则中的空间维持环节。空间维持能力直接决定骨增量效果，且在不同骨缺损形态间差异显著。有利型骨缺损因天然骨壁构成刚性空间维持装置，预后良好；而不利型骨缺损因缺乏此类天然屏障，须依赖人工支架代偿，骨增量失败风险显著升高。文章聚焦不利型骨缺损，系统梳理常用骨替代材料与屏障膜在应对高张力空间维持需求时的性能优劣，重点分析当前主流空间维持技术的操作要点与维持强度，并依据骨缺损形态学分型整理出分层级术式推荐体系，以期为临床医生针对不同严重程度的不利型骨缺损合理选择空间维持策略提供参考。

关键词: 空间维持, 不利型骨缺损, 骨增量技术, 骨替代材料, PASS原则