From the biological point of view, the apicocoronal positioning of an implant, particularly those of tissue-level design, should follow the principle of “as shallow as possible, as deep as necessary” (Buser and coworkers 2004) in order to avoid deep peri-implant probing depths, taking into account the prosthetic and esthetic factors in the area.
This concept has recently been confirmed in a case-control study on 19 patients that evaluated the modifying effect of a deep mucosal tunnel (DMT, ≥ 3 mm) on the induction and resolution phases of experimental peri-implant mucositis (Chan and coworkers 2019). All patients, each with a properly placed tissue-level implant, were assigned either to the test group (DMT, depth ≥ 3 mm) or to the control group (shallow mucosal tunnel, SMT, ≤ 1 mm). The subjects underwent a standard experimental peri-implant mucositis protocol, characterized by an oral-hygiene optimization phase, a three-week induction phase using an acrylic stent to prevent self-performed oral hygiene at the experimental implant, and a three-plus-two-week resolution phase.
The modified plaque index (mPI), gingival index (mGI), and IL-1β concentrations in the peri-implant sulcus fluid were determined over time. Both the mPI and the mGI increased during the induction phase. After normal oral hygiene had resumed, the mPI and mGI resolved towards baseline values in the SMT group, while they diverged in the DMT group. Although plaque accumulation was resolved in the DMT group, the resolution of inflammation was delayed and found to be of smaller magnitude during the first three weeks after resumption of oral hygiene. IL-1β Concentrations were significantly higher in the DMT group at the end of induction and during the resolution phase, corroborating the clinical findings. Removal of the crown and submucosal professional cleaning were needed to revert mGI to baseline values in the DMT group.
The fact that the depth of the peri-implant sulcus influenced the resolution of experimental mucositis raised doubts as to the efficacy of self-performed oral hygiene in scenarios where implants are placed too deeply. Therefore, since the risk of mucositis evolving into peri-implantitis appears to be higher in such clinical situations, clinicians should make every effort to place implants properly—not only for esthetic, but also for biological reasons (Berglundh and coworkers 2018).
It should be noted that, from a clinical point of view, this may be more easily achievable for implants without adjacent teeth, but more challenging if the implant has to be placed between two teeth, particularly if these teeth are periodontally compromised. Figures 1a-b show examples of correct implant positioning. Figures 2a-b show examples of incorrect implant positioning.
The ideal implant position for optimal soft-tissue integration should be planned before removing the teeth. Ridge preservation is one of the treatment options after tooth extraction, particularly in situations where one or more socket walls are missing (Roccuzzo and coworkers 2014c; Mardas and coworkers 2015). The rationale for this approach is that the maintenance of the ridge contour often facilitates subsequent treatment steps and limits the risk of an improper position of the implant collar, creating an ideal soft-tissue seal (MacBeth and coworkers 2017). Figures 3a-i show an example of long-term soft-tissue stability after implant placement following ridge preservation. The correct positioning of an implant, with a shallow peri-implant sulcus, could be particularly difficult in areas where the mucosa is too thick. Here an appropriate flap design is mandatory, especially if cemented restorations are planned. Figures 4a-h show an example of implant positioning in the posterior maxilla where a tissue excess needed to be removed.
One of the challenges in optimal flap design around non-submerged implants is the circumferential closure around the implant collar, especially when the soft tissues present anatomical irregularities. Figures 5a-k show an example of soft-tissue management for non-submerged tissue-level implants in the posterior maxilla with an irregular soft-tissue morphology.
Creating an optimal flap for ideal transmucosal healing becomes even more difficult if no keratinized mucosa is present at all. In these circumstances, a free gingival graft may be advised, especially if bone regeneration is required, as discussed in Chapter 4.1.
Often, a small quantity of keratinized tissue will be sufficient to create a soft-tissue cuff around the implant collar, provided the tissue is properly surgically managed. Figures 6a–I show an example of soft-tissue management around a tissue-level implant in conjunction with bone regeneration in a case where there does not appear to be any keratinized tissue available.