In a recent animal study, Cardaropoli et al. (2003) assessed the healing events occurring in the extraction socket following tooth removal. The findings of this study demonstrated that the healing of an extraction socket involved a series of events including the formation of a coagulum that was replaced by a provisional connective tissue matrix, woven bone and lamellar bone and bone marrow. On day 30, mineralized bone occupied 88% of the socket volume. Hard tissue formation had started already after 2 weeks of healing, and then, after a month, the socket was filled with woven bone. Later, the woven bone was gradually replaced by lamellar bone and bone marrow. After 3 months of healing, a hard tissue bridge was consistently found to cover the crestal portion of the extraction site, which was formed by woven bone and lamellar bone. Araújo et al. (2005) analysed in an experimental study in dogs the ridge alterations following the extraction of premolars in the mandible. The authors observed that the resorption of the buccal and lingual walls occurred in two overlapping phases. Phase 1: The bundle bone - that lost its function and blood supply - was resorbed and replaced with woven bone. Vertical resorption was considerably greater on the buccal aspect of the alveolar crest, since this bone wall was much thinner then the lingual wall and was primarily comprised of bundle bone. Phase 2: An additional resorption occurred from the outer surfaces of both bone walls. The reason for this additional resorption has not been clearly ascertained. The hypothesis could be: Impaired superficial vascularisation by raising a mucoperiosteal flap; adjusting to the lack of continuous function; or the reestablishment of the ridge shape, which is genetically determined in the absence of teeth. A recent animal study confirmed that flap elevation plays an important role for a more pronounced superficial bone resorption following extraction , therefore, it seems critical that tooth extraction should be carried out without elevation of a mucoperiosteal flap. Even ridge preservation techniques are not able to prevent the contour changes after tooth extraction.