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ePaper created 2014-07-29, 09:08:59 | version 1.30.01
case report I I 35implants2_2014 volume is very high and critical because of very severe boneloss,especiallysitesinwhichmostofthenewbone tissue will receive and support the implant load, autol- ogous bone blocks stabilised by screws are the more suitable and predictable material for the graft. Mandibularbonewithitspredominantlycorticalmicro- architecture exhibits a small volume loss and achieves good integration after a short healing period.27–29 In comparison with cortical bone grafts, autologous can- cellous bone grafts have been thought to be more os- teogenic because spaces within their structure allow thediffusionofnutrientsandtherebylimitedrevascu- larisation by micro-anastomosis of the blood ves- sels.30–32 A cancellous graft is a good space filler, but it doesnotsupplysubstantialstructuralsupport.Because only the endosteal and osteoblasts cells on the grafts’ surface survive the transplant, a cancellous graft basi- callybehavesasanosteoconductivesubstrate.33 Thisef- fectively supports the ingrowth of new blood vessels and the infiltration of new osteoblasts and osteoblast precursors.33 Cancellous grafts do not provide direct structuralsupport,buttheyquicklyintegrate.Withinsix to twelve months, they finally reach a structural strength that is equivalent to that of cortical grafts.34 Severalauthorshaveobservedthatcorticalbonegrafts willmaintaintheirvolumebetterthancancellousbone grafts will.35, 36 Cancellous bone grafts revascularise much more quickly than cortical bone grafts do; how- ever,corticalboneismuchstronger.37 Thecombination ofcorticalandcancellousboneingraftspromotesearly vascularisation and maximum graft maintenance.38 Thus,beta-TCP(-TCP)wasusedinthiscasebecauseit promotesresorptionsimilartocancellousboneandcor- tical bone was harvested from the mandibular ramus. Structurally,porous -TCPhasacompressivestrength andtensilestrengthsimilartocancellousbone.39 Stud- ieshavesuggestedthatthemorbiditywhenharvesting bone from the mandibular symphysis is higher than whenharvestingfromtheretromolarregion,29,40–43 and veryfewcomplicationswithintra-oralboneharvesting occur at the lateral ramus/corpus of the mandible. The lackofadaptationofboneblocksintherecipientsiteor the presence of gaps can cause the interposition of fi- brous tissue.44 Therefore, filling these spaces is neces- sary and autologous bone scrapings,45 platelet-rich plasma46 orbiomaterialscanbeusedforthispurpose.47 Furthermore,bonegraftsubstitutesareusedtoprevent resorptionandtoproduceasmoothoutline.Theuseof bonegraftsubstitutesreducestheamountofbonetobe harvested from the donor site and thereby improves post-operative recovery. In the case presented, which wasfollowedforfouryears,itwasobservedthatthema- terial (calc-i-oss) was replaced by new bone formed throughtheintegrationoftheautologousblocks,facil- itatingbetteradaptationinthisarea. _Conclusion Theprincipalproblemsregardingtheuseofautolo- gous bone for regeneration are limited availability and donorsitemorbidity;therefore,thereisaneedforbone graftsubstitutes.Thecombinationofsmallautologous blocks with -TCP offers a good alternative for recon- struction in critical areas and reduces post-operative complications. In the case presented, excellent bone volumewasobservedafterfouryears._ Figs. 14 & 15_Photograph and tomography image after 4 years; maintenance of bone in the palatine and vestibular portions of the implant is illustrated (yellow arrow). Fig. 13 Fig. 14 Fig. 15 Dr Sergio Alexandre Gehrke Rua Dr.Bozano,571 97015-001 – Santa Maria (RS) – Brazil Tel./Fax:+55 55 3222 7253 sergio.gehrke@hotmail.com _contact implants