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implants_international magazine of oral implantology No. 2, 2016

| research 08 implants 2 2016 ­anterior teeth: four incisors and two canines. A thin alveolar process in this area necessitates implant ­diameter selection of a narrow-to-standard diame- ter (3–4 mm). Based on many case reports, a pene- tration of the thin lingual mandibular cortex during animplantinsertioninthisareaonoccasioncanlead to serious bleeding with formation of expanding ­sublingual haematomas.16–24 Haemorrhage from a branch of the sublingual artery (a branch of the lin- gual artery), the submental artery (from the facial artery), or the mylohyoid artery (from the inferior ­alveolar artery, a branch of the maxillary artery) or their anastomoses can in some cases cause a life-threateningairwaycompromise.19–22 Tepperetal. demonstrated the presence of at least one (some- times multiple) lingual perforating vascular bone canal(s) and suggested a routine CT examination prior to an implant procedure in this area.21 A similar report of serious haemorrhage from an implant in- sertioninthefirstmandibularpremolarpositionalso suggests a common arterial supply of all eight man- dibularfrontteethandonemorereasonforincluding firstpremolarsinthiszone.16 Asuccessfulplacement oftwotosiximplantsinthiszoneinmanyedentulous arch cases offer a stable foundation for a variety of implant-retained and implant-supported removable and fixed mandibular prostheses. A symphyseal (chin) monocortical block bone graft harvested in this area is often used for the horizontal augmen­ tation of bone in other regions, especially for the ­anterior maxilla. D2isabilateralareaofthealveolarridgeofthepos- terior mandible from the first premolar to the retro- molar pad. The mental foramen in the front and the inferior alveolar canal below limits this functional implantzone.Animplant’ssuccessinthisarearelates to the quality (density) of bone and quantity of pre- served alveolar ridge, among other factors. The ra- mus block bone graft is often harvested in the prox- imity of this zone. Embryologically, this bilateral mandibularalveolarzonedevelopsabovetheinferior alveolar canal. The alveolar height between the infe- rior alveolar canal and the alveolar crest is routinely analysed in oral implantology when posterior man- dibularimplantsareconsidered.Aheavymasticatory demand during function, especially for people with parafunctional habits, necessitates an insertion of two to three implants into this region for replace- ment of missing first, second premolar, first molar, and occasionally the second molar. D3 is a zone of the alveolar ridge of the anterior maxilla (aesthetic area), including six front teeth: four incisors and two canines. Part of the anterior maxilla is a protruding alveolar process with thin la- bialandthickpalatalcorticalplatescoveringandpro- tecting the upper front teeth. A prominent position of the anterior maxilla and upper front teeth in the faceisresponsibleforboneandsoft-tissueinjuries.25 Fracture of crowns and roots, subluxation, displace- mentandavulsionofteetharefrequentinthiszone.25 The main blood supply to the anterior maxilla is de- rived from the branches of the maxillary artery: the anterior superior alveolar artery (from the infra­ orbital artery), the greater palatine artery, and the nasopalatineartery.Amiddlesuperioralveolarartery is occasionally described as a branch of the infra­ orbital artery that supplies the region of the canine tooth. The anterior and middle superior alveolar ­arteries anastomose with the posterior superior al­ veolar artery to form an arterial network feeding both endosteal and periodontal plexuses. Another traumatic event in the life of the alveolar ridge is a tooth loss. A tooth extraction, or periodon- taldiseasealsoleadstoboneresorption.Theprogres- sionofhealingafteratoothextractiongoesthrough certain resorptive stages of fibrin clot organisation (firstfourweeks),immature(woven)boneformation (four to eight weeks), mature (lamellar) bone devel- opment (eight to twelve weeks), and bone stabili­ sation stage (twelve to 16 weeks or about four months).26–28 Post extraction bone resorption is al- ways three-dimensional, with the greatest loss of bone in the bucco-palatal or horizontal direction (the width) and occurring mainly on the buccal side of the alveolar ridge.28 Schropp et al. reported that two thirds of the horizontal bone loss occurs within three months and one-third takes place within the remaining nine months of the first year post ex- traction.29 Ameanreductionofthewidthoftheridge hasbeenreportedtobe5to7 mmwithinasix-month period or 50 per cent during the twelve months ­following tooth extraction.29 The loss of bone height is smaller, reported to be about 1 mm within the first sixmonthspostextraction.20, 29 Ifabonegraftingand implant treatment approach is not considered soon after trauma, the atrophy of the alveolar process of the anterior maxilla continues with time. Resorption of the buccal plate compromises the anatomy of the edentulous alveolar ridge and makes it difficult to place an implant in the prosthetically favourable ­position.31 Even when a dental implant is placed, its strength is diminished without the presence of a ­buccalcorticalplate.Usingatwo-dimensionalfinite- elementmodelforstressanalysis,Clellandandasso- ciates demonstrated low stresses and high strains surroundedtheimplantfortheall-cancellous(lackof cortical plate) bone model.32 When a layer of thick corticalbonewasaddedtothemodel,ithadasignif- icant impact and improved stresses and strains on the implant. D4 is related to first and second premolars in the maxillary region and rarely first and second molars. 22016

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