The importance of preserving the peri-implant soft tissue barrier

Connective tissue on natural teeth anchor to the cementum using perpendicular collagen fibers called Sharpey’s fibers (Figure 1a, c).^2,3 These fibers ensure a tight seal between the soft tissue and tooth, and contribute mechanically to strengthen the barrier from bacterial infiltration or other foreign body penetration. Conversely, collagen fibers adhere parallel or circumferentially on the transgingival region of abutment surfaces (Figure 1b, d), resulting in a weaker connective interface.^2-4 The modest adhesion of peri-implant fibers cannot withstand mechanical forces as efficiently as the strong attachment of Sharpey’s fibers of natural teeth.^1,5

Moreover, in natural teeth, the blood supply to periodontal tissue is provided by the periodontal ligament, periosteum, and connective tissue. Dental implants do not benefit from the periodontal ligament vasculature and, therefore, the surrounding tissue has a limited blood supply compared to natural teeth.^1,5 Additionally, the surgical trauma of implant placement causes fibrotic tissue to form at the implant-abutment complex, which further limits vascularization to adjacent soft tissue.^1,6 This reduced vascularization can affect the defense of the peri-implant soft tissue against bacterial infiltration.¹

To aid in the prevention of peri-implant disease, this fragile peri-implant soft tissue barrier must be carefully maintained through good oral hygiene and proper soft tissue handling using soft-tissue-friendly prosthodontics.

While there are many factors that contribute to the success or failure of implant-supported restorations, the quality and the quantity of existing or augmented peri-implant mucosa has a critical role to play. In addition to the features discussed above, scientific consensus supports soft tissue site development (tissue grafting) to improve implant outcomes. Especially when the initial soft tissue vertical thickness is less than 2 mm and when the keratinized oral epithelia is limited.^7,8

Prosthodontic considerations for soft tissue management

When using a two-stage procedure with bone-level implants, disconnecting the healing abutment can rupture the adherent epithelial and connective tissue from underlying tissue (Figure 2). The resulting wound exposes the connective tissue (Figure 2a). Repeated abutment disconnection on bone-level implants could harm the mucosal barrier and lead to an apical migration of the biological width and consequently early peri-implant bone loss.^9,10 Abrahamsson et al. originally described this observation in a canine study using a platform-matched connection.¹⁰ Similar results were seen for implants with platform-shifting and internal connection but to a lesser extent.^11,12 Therefore, the number of abutment disconnections should be minimized to prevent damage to the mucosal barrier and peri-implant bone resorption.

According to available data, it would be beneficial to minimize disruption of the soft tissue after implant placement. Unfortunately, with conventional bone-level implants, the soft tissue can be disrupted at numerous points during treatment, such as healing cap removal, impression coping, and definitive prosthesis delivery (Figure 3a). For this reason, the soft-tissue-friendly final abutment at time of implant placement approach was developed. With this method, the final abutment is installed at implant placement and left undisturbed throughout the treatment process.^9,13,14,15
Based on these principles of peri-implant soft tissue preservation, Nobel Biocare developed the On1 concept. The On1 concept has a two-piece abutment with a multi-compatible base that is fixed at implant placement (Figure 3b).