A Novel Framework for Optimizing Peri-Implant Soft Tissue in Subcrestally Placed Implants in Single Molar Cases: Integrating Transitional and Subcrestal Zones for Biological Stability

Background: The peri-implant soft tissue seal plays a critical role in the long-term success of subcrestally placed implants (SPIs). However, conventional biologic width models, originally developed for natural teeth, fail to fully account for the complex three-dimensional peri-implant soft tissue adaptation. This study introduces a novel framework that integrates the concepts of the Transitional Zone (TZ) and Subcrestal Zone (SZ) to optimize peri-implant soft tissue stability and function. Methods: A three-dimensional peri-implant soft tissue analysis (3DSTA) was conducted using CBCT imaging and clinical evaluation. This study defines key parameters, including Crest to Restoration Distance (CRD), Soft Tissue Thickness (STT), and Self-Sustained Soft Tissue (SSST), to assess the biologic and structural adaptation of peri-implant soft tissue in SPI cases. Results: A mathematical model was developed to determine optimal implant placement depth, considering emergence angle (EA), soft tissue thickness (STT), and peripheral crestal offset (PCO). SSST, composed of TZ and SZ, was identified as a critical factor in maintaining peri-implant health by providing a wider biologic width and enhancing resistance to microbial infiltration. The importance of sub-mucosal coronal flaring in SPI was highlighted, demonstrating that a broader contact zone improves peri-implant tissue adaptation and biologic stability. Implant Paper Point Probing (IPPP) was introduced as a novel diagnostic tool to assess the peri-implant sulcus seal and differentiate healthy peri-implant soft tissue from pathological pockets. Conclusions:This study presents a novel peri-implant soft tissue framework, shifting from a two-dimensional biologic width model to a three-dimensional analytical approach. By integrating TZ and SZ as components of SSST, this model provides clinical guidelines for optimal emergence profile design, SPI placement depth, and peri-implant soft tissue management. Future studies should focus on validating these findings through histological investigations and long-term clinical trials to refine peri-implant soft tissue optimization strategies.