ABSTRACT Objectives Crown preparation leads to irreversible dental tissue loss, which affects long‐term restoration success. The advantages of horizontal (chamfer) versus vertical preparation techniques (BOPT, BOPTm) remain debated. This systematic review evaluates which method is most conservative regarding dental structure removal and examines their clinical indications, advantages, and limitations. Materials and Methods This systematic review followed the Cochrane Handbook and PRISMA 2020 guidance. The electronic search was performed in PubMed, Cochrane and Web of Science for studies published between 2012 and 2023. The PROSPERO record (CRD420251161178; registered on 06 October 2025) was retrospective. Clinical studies, in vitro/ex vivo investigations and contextual narrative sources were included for different purposes. The >=6‐month follow‐up criterion was applied only to longitudinal clinical outcome studies; laboratory and descriptive studies were included only for mechanistic or contextual evidence. The primary outcome was direct or indirect quantification of tooth‐structure removal. Secondary outcomes included periodontal health, function, tooth morphology, esthetics, and pulpal implications. Certainty of evidence was evaluated using the GRADE methodology. Results Twenty‐three studies were included. Six studies directly quantified tooth‐structure removal or residual dentin thickness using gravimetric analysis, micro‐CT, digital volumetric analysis, or related methods. Across studies that compared preparation geometries at a comparable margin level, BOPT was generally more conservative than BOPTm; however, supragingival or juxtagingival horizontal chamfer preparations remained the most conservative option when margins could be maintained outside or at the gingival sulcus. Periodontal advantages of BOPT were mainly reported for subgingival clinical scenarios. Conclusions The apparent difference between vertical and horizontal preparations is scenario‐dependent. When a subgingival restorative margin is required, BOPT may preserve more tooth structure than BOPTm and may offer favorable periodontal behavior compared with subgingival horizontal preparations. When margins can be placed supra‐ or juxtagingivally, horizontal chamfer preparations remain the most conservative and clinically predictable approach.
Florescu et al. (Wed,) studied this question.