Under certain circumstances tooth extraction is inevitable and consequently requires consideration of tooth replacement options. As tooth extraction induces trauma on the surrounding soft and hard tissues, a cascade of biological events is subsequently triggered. These biological events following tooth extraction have been intensively studied in pre-clinical studies (Cardaropoli et al. 2003, Araujo & Lindhe 2005). The trauma on the adjacent bundle bone, which is a tooth-dependant structure, induces osteoclastic activity and as a consequence bone resorption (Araujo & Lindhe 2005). As thin buccal bone plates often consist entirely of bundle bone, bone resorption is followed by an invagination of the surrounding soft tissues with potentially insufficient ridge dimensions for future dental implant placement.

Systematic reviews have shown that tooth removal induces a marked reduction in the ridge dimensions, in particular in the first three months following tooth extraction (Van der Weijden et al. 2009, Tan et al. 2012). These soft and hard tissue alterations are more pronounced in the horizontal than in the vertical aspect of the alveolar ridge. A rapid progression of tissue remodeling is seen within the first 3 - 6 months after tooth extraction, followed thereafter by a gradual reduction in ridge dimensions. On average a clinician can expect bone reduction of 29 - 63% (3.79 +/- 0.23 mm) in the oro-facial aspect and 11 - 22% (-1.24 +/- 0,11 mm) in the vertical aspect (Tan et al., 2012). It has to be considered, however, that several clinical factors such as thickness of the buccal bone wall (Spinato et al. 2014), flapless/flapped extraction (Fickl et al. 2008a) and the location of the extraction site (Misawa et al., 2016) have an impact on the shrinkage process.

As long-term clinical research articles have shown that a certain amount of hard tissue structure on the buccal side of a dental implant is necessary to retain long-term function and esthetics (Buser et al. 2013a, Buser et al. 2013b), these atrophic changes following tooth extraction can jeopardize optimal three-dimensional implant placement or may require extensive additional or even staged grafting procedures.

With respect to these volumetric alterations, the correct timing of implant placement post-extraction is an important decision to achieve an optimal treatment outcome with long-term stability. This has been addressed in a series of ITI Consensus Conferences leading to a Type I-IV classification (Morton et al. 2014). Type I (immediate implant placement) is only used in optimal clinical situations with intact soft and hard tissue structures (Buser et al. 2017). This will be discussed in detail in the article by Stephen Chen. Type II (4 - 8 weeks after tooth extraction) and type III (12 - 16 weeks after tooth extraction) have been very well documented by the Bern group and are seen as an optimal alternative to the highly technique-sensitive Type I procedure and the prolonged treatment time of Type IV interventions. These will be addressed in detail in the paper by Daniel Buser. If Type I, II and III procedures are not used, late implant placement (Type IV) in a healed site with at least 6 months of healing time has to be applied. In order to limit the above-described dimensional alterations, alveolar ridge preservation or socket grafting is strongly recommended.

Various techniques have been developed to avoid tissue loss post-extraction and are defined as alveolar ridge preservation or socket grafting. These techniques are used to counteract changes in soft and hard tissue following tooth extraction and facilitate the placement of dental implants in a prosthetically ideal position without the need for further augmentation. This includes filling the socket with a biomaterial and additional measures to close the socket orifice through application of a barrier material or a soft tissue graft/soft tissue xenograft.

In a series of pre-clinical and clinical studies, our group showed that socket grafting and socket sealing can reduce dimensional alterations on a hard and soft tissue level, but fail to entirely counteract tissue resorption following tooth extraction (Fickl et al. 2009a, Fickl et al. 2008a, Fickl et al. 2008b, Fickl et al. 2009b, Fickl et al. 2008c, Thalmair et al. 2013, Fickl et al. 2017). These mostly pre-clinical data were confirmed in a review article showing that alveolar ridge preservation resulted in significantly less vertical and horizontal resorption of the alveolar bone crest when compared to spontaneous healing (Vignoletti et al. 2012). It can therefore be concluded that alveolar ridge preservation can attenuate the physiological dimensional bone changes that typically follow tooth extraction with spontaneous healing. However, there is no scientific evidence about the superiority of any hard and soft tissue socket grafting procedure. Therefore, it is the goal of this article to show possible clinical options for alveolar ridge preservation combined with or without socket sealing to facilitate late implant placement.