Aim: This systematic review was conducted to assess the clinical and esthetic outcomes associated with convergent collar implants and compare them to divergent collar implant. The review was registered on the PROSPERO register (registration number: CRD42022326338). Methods: The systematic literature search was conducted in accordance with PRISMA guidelines to identify studies on implant-supported prostheses related to the Biologically Oriented Preparation Technique (BOPT) until June 2023. Inclusion criteria involved experimental and clinical studies published in peer-reviewed journals, excluding expert opinions. Data extraction was performed, adhering to predefined parameters for BOPT, specifications of convergent collar implants, and the assessment of outcomes. Results: The systematic review included 16 studies, comprising 5 prospective cohorts, 3 retrospective cohorts, 3 longitudinal analytic studies, 3 rRandomized Controlled controlled Trialstrials, and 1 non-randomized controlled trial. Periodontal findings were classified into hard and soft tissue changes. Hard tissue changes showed marginal bone loss ranging from 0.071±0.11 mm to 1.44±1.32 mm, with one study reporting bone gain. Soft tissue findings included bleeding on probing (0–9.5%), pocket depth (1.66±0.49–2.84±0.39 mm in BOPT), bleeding index (0.5±0.59), and plaque at 30.8% of implant sites. Additional outcomes revealed statistically greater mucosal thickness in Prama versus Shelta implants, a mean soft tissue volume gain of 38.6±47.3 mm³, and 97.4% of sites with no recession. Hard tissue changes encompassed variable marginal bone loss (0.071±0.11 mm to 1.44±1.32 mm), with one study reporting bone gain. Soft tissue changes covered Bleeding on Probing (0% to 9.5%), Periodontal Pocket Depth (1.66±0.49 to 2.84±0.39 in BOPT groups), Bleeding Index (mean 0.5±0.59), Plaque Index (30.8% of implant sites with plaque), Papillae Gain (variations in mesial and distal papillae), Horizontal mucosa thickness (statistically significant difference between Shelta and Prama implants), Soft tissue volume increase (mean 38.6±47.3 mm³), and Recession (97.4% no recession, 0.4% mild, 1.8% medium, 0.2% severe). Conclusion: Within the limitations of available evidence, convergent collar implants demonstrated favorable preservation of peri-implant bone and soft tissues, suggesting a potential benefit for achieving long-term esthetic stability. Clinically, they may be preferred in anterior or thin-biotype sites requiring enhanced soft-tissue support, whereas divergent collars remain suitable for posterior regions where prosthetic access and retrievability are prioritized. However, heterogeneity across designs and moderate risk of bias among included studies limit the generalizability of these findings. Data indicates that convergent collar implants may improve hard and soft tissue changes. Nevertheless, limited studies and diverse designs underscore the need for standardized research to draw definitive conclusions.
Lawand et al. (Sun,) studied this question.