Vertical reconstruction of peri-implant soft tissue

For almost one decade, platform switching has been considered to be the most effective way to achieve this outcome. It is so effective that almost all implant companies have implemented platform switching as an essential feature of implant manufacture. It has generally be concluded that implant design is more important than the biology itself. However, recent clinical research conducted by our group has found that soft-tissue thickness is an important factor in preserving crestal bone stability around implants. It was determined that if vertical soft-tissue thickness is 2 mm or less, there will be crestal bone resorption of 1.5 mm in extent during formation of a biological seal between the soft tissue and the implant, abutment or restoration surfaces (Fig. 2).

Furthermore, it was clearly shown that even implants with platform switching could not maintain bone if at the time of implant placement vertical soft tissue was thin (Fig. 3). That returns us to the discussion of whether biology or implant design is more important. Well, we need to understand that vertical soft-tissue thickness is a prerequisite of the biological width around implants. Biological width around implants starts to form at the time of healing abutment connection and is complete after eight weeks. This biological seal is the only barrier protecting the osseointegrated implant from the contaminated intra-oral environment and hence most important. Thus, there is a direct connection between the peri-implant mucosa of an edentulous alveolar ridge and peri-implant soft tissue.

It seems that the soft-tissue thickness required to protect the underlying bone around implants is approximately 4 mm, which is wider than the biological width around teeth. There are two ways in which biological width around implants is formed: with crestal bone loss or without bone resorption. Which one would you like your patient to have? Or which one would you like your mother to have? That is the question we all as clinicians should answer sincerely.
 

So if we diagnose thin vertical tissue at the time of implant placement, what should we do? There are no current guidelines to follow; however, we need to do something, because crestal bone resorption will otherwise result. This is especially important for short implants, which are increasingly being used. Today, an implant of 8 mm in length is no longer considered short, and we have sufficient data to determine that implants of 6 mm in length work as well as longer ones do in the posterior of both jaws. However, imagine the outcome if a 6 mm implant is placed in the posterior mandible, where thin vertical soft tissue is frequently present. We would have approximately 2 mm of bone resorption, due to biological width formation, leaving only two-thirds of the implant surface to become osseointegrated. Such a circumstance poses a risk of implant failure, considering the prosthetic superstructure and implant–crown ratio. Some implant manufacturers have launched implants of 4 mm in length, making soft-tissue thickness even more important for users of these products.

So what should the approach be? There are several options, some of them already researched clinically and some based on clinical experience without any objective evidence. An initial thought may be to place the implant deeper sub-crestally (Fig. 4). Firstly, there must be adequate distance from the alveolar nerve to position the implant sub-crestally in a safe manner. It is advised that the implant stop at least 1 mm from the nerve.

Extensive sub-crestal positioning of the implant, of course, does not prevent crestal bone loss, as the microgap at the implant–abutment interface will form an inflammatory infiltrate, which will cause bone resorption anyway; however, it is likely that the implant will not have soft-tissue recession or rough surface exposure, which usually follow bone resorption. It is well known that the exposure of the rough implant surface enhances plaque accumulation and the development of peri-implantitis. In other words, the future of such an implant would only depend on the scrupulous cleaning abilities of the patient, what is usually not the case.

Another option might be recontouring of the bone during basic implant bed preparation, especially if a narrow ridge is present. Careful reduction and smoothening of the narrow ridge will not only provide a flat bone surface and a sufficiently wide area of bone for implant positioning, but will increase soft-tissue thickness as well (Fig. 5). While the concept of bone removal to preserve the bone might be acceptable to some clinicians, there is no strong clinical evidence that this procedure increases soft-tissue thickness and reduces crestal bone remodelling.

Consequently, we might think in another direction and consider a third option, vertical reconstruction of the soft-tissue thickness, which in my opinion is the most logical approach. Increasing soft-tissue thickness vertically compensates for the lack of vertical tissue. Already in a 2009 paper, we suggested that clinicians “consider the thickening of thin mucosa before implant placement”; therefore, this concept is not entirely new.[1] The idea is to place some sort of autogenous, allogeneic or xenogeneic material over the implant to increase soft-tissue thickness after healing.

A connective tissue graft is considered the gold standard for soft-tissue augmentation around implants. However, this technique has some serious disadvantages, such as donor site morbidity and the difficulty of the harvesting procedure. Therefore, allogeneic substitutes might be considered a viable option to replace autogenous grafts in vertical soft-tissue reconstruction. The use of an acellular dermal matrix is thus far the only approach backed by solid clinical research, including a controlled clinical prospective study.[2] In this study, implants were placed in three groups of patients with (a) thin vertical tissue, (b) thick vertical tissue or (c) thin vertical tissue augmented with an acellular dermal matrix material (AlloDerm, BioHorizons). Radiographic assessment showed a reduction of crestal bone loss from 1.74 mm in the thin-tissue group to 0.32 mm in the augmented group. In addition, soft-tissue thickness increased by 2.33 mm, from 1.50 mm to 3.83 mm, after augmentation with the allograft (Figs. 6a & b). This research proves that the lack of vertical soft-tissue thickness required for biological width formation without crestal bone loss can be compensated for by the use of an acellular dermal matrix material at the time of implant placement.

In conclusion, it must be emphasised that diagnosis of thin vertical soft tissue is very important in implant treatment. Only by acknowledging that tissue thickness is an important factor can we follow protocols that allow us to reconstruct vertical peri-implant tissue and reduce crestal bone loss.

Editorial note: A list of references is available from the publisher.