## 4 Discussion
However, these protocols allow no room for soft tissue improvement and pose possible risks for the final outcome. In case the prosthesis applies any pressure to the buccal soft tissue and/or the gingival biotype is thin, there is a risk for soft tissue recession, compromising the end result [56]. On the contrary, with MMC, all the support of the supra-crestal soft tissue is provided not by the prosthesis, but instead by the BRG and the membrane. The only prosthetic material that is present sub-gingivally is a narrow portion of the titanium abutment which provides the necessary space and a biocompatible surface that enhance the soft tissue adaptation in a more favorable and predictable way [57]. The MMC protocol involves the use of a second temporary restoration, which we call transitional restoration. The latter is used in order to take advantage of the improved soft tissue quantity and quality achieved by the first phase of treatment and condition of the soft tissue by utilizing the principles of proper cervical tissue conditioning [8; 58]. The transitional restoration at this stage comprises an anatomically shaped submergence profile, which applies lateral pressure to the soft tissue, forcing the gingival fibers to obtain an oblique orientation [59]. This lateral pressure also leads the coronally migrated buccal tissue to its final vertical location. This vertical location is level with the zenith of the transitional prosthesis, which mimics the desired final prosthesis, and it is located more apically. This apically forced shift of the marginal, matured soft tissue is accompanied by an increase of its thickness [8]. These two factors increase the marginal tissue thickness and oblique orientation of gingival fibers, in combination, improving the tone and color appearance of the soft tissue [8]. The conditioning of the tissue per se also allows the fabrication of a prosthesis with proper cervical contour that achieves ideal esthetic appearance [29]. The process of the final impression can involve any technique, either digital or analogic. It is important, at this stage, to capture the tissue topography accurately and thus, if needed, it is recommended to utilize proper protocols of impression post customization [60]. During the lab stage, the most critical factor refers to proper communication between the clinician and the lab technician as per standard practice. The only restriction that the MMC proposes is the use of a final abutment that comprises a shoulder that is identical to the one of the temporary abutment used for the support of the transitional restoration. It is understood that an intermediate abutment or a CAD abutment milled in-office can also be utilized in order to serve more options of final abutment-prosthesis assembly, as long as these abutments respect the aforementioned requirements with regards to their design and are used at all involved restorative stages. The difference between the temporary abutments used for the support of the temporary (first) restoration and the transitional restoration refers to their margin. The margin of the temporary restoration extends up to 0.5 mm apical to the existing free gingival margin, while the one of the transitional restoration extends 0.5 mm apical to the future zenith point of the prosthesis. The reason behind this difference is that the first supra-structure is designed in order to allow space for gain in soft tissue height, while the second (transitional) supra-structure is designed in order to condition the soft tissue at the ideal height for the final prosthesis. Since the MMC allows the soft tissue to migrate coronal to the zenith point of the future prosthesis, the transitional prosthesis will now condition/push this tissue laterally and apically and this way will further improve its thickness. The MMC has been tested for sites presenting limited soft tissue recession. Further investigation is required to evaluate the efficiency of the technique in cases involving more severe recessions.