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I case report _ ridge preservation and GTR 18 I implants3_2011 ticles of the graft material. All samples showed new boneformationwiththenewlyformedbonestrongly adherent to the bone graft particles. _Discussion The aim of this case report is to evaluate guided bone regeneration after tooth extraction with a xenograft material. The use of a bone substitute can avoid bone harvesting from a donor site, thus reduc- ing patient discomfort post-operatively. Inarandomisedclinicalstudy,Baroneetal.(2008) comparedextraction-onlytreatmenttoridgepreser- vation with xenograft (cortico-cancellous porcine bone) and collagen membrane. Seven months after toothextraction,agreaterhorizontalwidthreduction of the residual alveolar ridge (8.1mm versus 6.3mm) in the extraction-only group was observed. A reduc- tion of vertical ridge height was also observed. These findings were in agreement with previous studies (Iasella et al. 2003). Deproteinized bovine bone has proven to be a highly biocompatible and osteo-con- ductive material that acts as a natural scaffold for boneformation,andhasalowrateofresorption(Car- magnola etal. 2003; Barone etal. 2008). The absence of inflammatory signs around the xenograft particles suggests that this is a safe and biocompatiblebiomaterial(Baroneetal.2008).Many studies have demonstrated the absence or a minimal amount of inflammatory infiltrate (Cardaropoli & Cardaropoli 2008), but in a clinical and histological study evaluating ridge preservation with xenografts in humans, Vence et al. (2004) observed some histo- logical inflammation, primarily polymorphonuclear neutrophils in the trabecular spaces, in three of 12 treated sockets, at four months. However, there was no clinical inflammation, and all sites had complete soft-tissue closure by three weeks. The authors sug- gest that the inflammation may have been related to resorption of the graft particles. The efficacy of a xenograft as an alveolar bone graft material may be the result of a combination of factors:itsosteo-conductivecapacity,theincreaseof mineral content in the grafted area necessary for boneformationanditsdensityinordertoprovidesta- bility to the graft and to persist for many months (Barone etal. 2008; Artzi etal. 2000). The histological analysis revealed that in all sam- ples there are residual particles of the xenograft, in- cluding studies at nine months (Artzi etal. 2000). Ac- cording to studies, the volume of residual bone graft material may vary between 16 and 30%. The volume of new bone formation varies between 23 and 46% (Table I). Histological and histo-morphometric studies have observed that the formation of new bone and theresorptionofthexenograftparticlesisaslowand gradualprocess.Inanine-yearstudyofasinuseleva- tion with a xenograft, Traini etal. (2007) observed an increase in bone formation over time, a decrease in the marrow spaces and a slow resorption of the bio- material. Sartori etal. (2003) presented a case of a si- nus augmentation with a xenograft and histo-mor- phometric evaluation after ten years; he observed that the absorption of the xenograft is slow but con- stant. He saw a resorption of 3.6% per year for the first two years and a significant decrease in the next eightyears,withanaveragerateofresorptionof0.58 % per month. Accordingtoseveralstudies,oncethexenograftis in contact with mineralised bone, it acts similarly to thehostbone,providingabiologicsupportfordental implants (Haas et al. 1998). The success of implants placedinregeneratedareasofupto40%ofxenograft residual particles seems to be similar to those placed in native bone (Carmagnola etal. 2003). _Conclusion The ridge preservation technique limits hard-tis- sue resorption following tooth extraction. A xenograft with a resorbable collagen membrane has been proven to be a clinically successful means of restoringabonedefect.Thehistologicalexamination confirmed the presence of newly formed vital bone almost completely surrounding xenograft particles throughout the biopsy samples._ Interviews for candidates to the 3 year Postgraduate Program (2011-14) in Periodontology at Universitat Internacional de Catalunya are opened until the end ofApril.AllcandidatesmustbeDDSandfluentinEng- lishandSpanish. Editorial note: A list of references is available from the pub- lisher. Prof José Nart Chairman and Programme Director Department of Periodontology Universitat Internacional de Catalunya C/ JosepTrueta s/n 08195 Sant Cugat delVallès (Barcelona),Spain Tel:+34 935 042 030 E-mail:jose@nartperiodoncia.com _contact implants