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Dental Tribune Middle East & Africa Edition | 5/2016 implant tribune 2 BySouheilHussaini,Dubai The causes of early implant failures during the osseointegration process include poor quality and quantity of bone and soft tissue,1–8 the patient’s medical condition,2, 6, 8–10 unfavorable patient habits (bruxism, heavy long- term smoking, poor oral hygiene, others),3, 4, 6, 8, 11 inadequate surgical analysis and technique3, 7–9, 11 inad- equate prosthetic analysis and tech- nique,3, 7, 8, 11–13 suboptimal implant design and surface characteristics6, 9, 13 implant position or location14 and unknownfactors. This article attempts to further in- vestigate implant location as one of many factors in early stages of diag- nosis that improves success rate in implant dentistry treatment. Predis- posing factors to implant compli- cations in different jaw regions are discussed. CBCT Zones D1 to D5 is formulated to better analyse implant dentistry procedure preparation during the diagnostic phase based on the lo- cation that has a logical sequence during examination of the alveolar ridge of both maxilla and mandible to have pre-existing information re- garding the demands and the clini- cal requirements in different zones of the jaws. This article identifies the Hounsfield units (HFU) of different alveolar jaw regions, according to which dental implants can be in- serted with better understanding of whattoexpect. Five CBCT zones are identified in this article in a logical sequence: the discreet zone D1 being the anterior mandible, the danger zone D2 being the posterior mandible, the death zone D3 being the anterior maxilla, the demand zone D4 being the pos- terior maxilla and the delicate zone D5 being the posterior maxilla that requiressinusliftprocedure. Zones D1–D5 are related to the bone quality classification of Lekholm & Zarb.15 D1 known as an interforamina area in which a careful diagnosis should be made due to the following procedure, bone density is very high and the osteotomy drills could heat the bone, irrigation temperature could facilitate healing response, dullness of the drills during oste- otomy should be counted for, tap drills are required, arterial supply in the symphasis area should be con- sidered and this area is utilised as a donor site for the chin (symphyseal) block bone graft. D1 includes six an- teriorteeth:fourincisorsandtwoca- nines. A thin alveolar process in this area necessitates implant diameter selection of a narrow-to-standard diameter (3–4 mm). Based on many casereports,apenetrationofthethin lingual mandibular cortex during an implant insertion in this area on oc- casion can lead to serious bleeding withformationofexpandingsublin- gual haematomas.16–24 Haemorrhage from a branch of the sublingual ar- tery (a branch of the lingual artery), the submental artery (from the fa- cial 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-threatening airway compromise.19–22 Tepper et al. dem- onstrated the presence of at least one (sometimes multiple) lingual perforating vascular bone canal(s) andsuggestedaroutineCTexamina- tionpriortoanimplantprocedurein this area.21 A similar report of serious haemorrhagefromanimplantinser- tion in the first mandibular premo- lar position also suggests a common arterial supply of all eight mandibu- lar front teeth and one more reason for including first premolars in this zone.16 A successful placement of two to six implants in this zone in many edentulous arch cases offer a stable foundation for a variety of implant-retained and implant-sup- ported removable and fixed man- dibular prostheses. A symphyseal (chin) monocortical block bone graft harvested in this area is often used for the horizontal augmentation of bone in other regions, especially for theanteriormaxilla. D2 is a bilateral area of the alveolar ridgeoftheposteriormandiblefrom the first premolar to the retromo- lar pad. The mental foramen in the front and the inferior alveolar canal below limits this functional implant zone. An implant’s success in this area relates to the quality (density) of bone and quantity of preserved alveolar ridge, among other factors. The ramus block bone graft is often harvested in the proximity of this zone. Embryologically, this bilateral mandibular alveolar zone develops abovetheinferioralveolarcanal.The alveolar height between the inferior alveolar canal and the alveolar crest is routinely analysed in oral implan- tology when posterior mandibular implants are considered. A heavy masticatory demand during func- tion, especially for people with par- afunctional habits, necessitates an insertion of two to three implants into this region for replacement 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 inci- sors and two canines. Part of the an- terior maxilla is a protruding alveo- lar process with thin labial and thick palatal cortical plates covering and protecting the upper front teeth. A prominent position of the anterior maxilla and upper front teeth in the face is responsible for bone and soft- tissue injuries.25 Fracture of crowns and roots, subluxation, displace- ment and avulsion of teeth are fre- quent in this zone.25 The main blood supply to the anterior maxilla is de- rived from the branches of the max- illary artery: the anterior superior alveolar artery (from the infraorbital artery), the greater palatine artery, and the nasopalatine artery. A mid- dle superior alveolar artery is occa- sionally described as a branch of the infraorbital artery that supplies the region of the canine tooth. The an- terior and middle superior alveolar arteries anastomose with the poste- rior superior alveolar artery to form an arterial network feeding both en- dostealandperiodontalplexuses. Anothertraumaticeventinthelifeof the alveolar ridge is a tooth loss. A tooth extraction, or periodontal disease also leads to bone resorption. The progression of heal- ing after a tooth extrac- tion goes through certain resorptive stages of fibrin clot organisation (first four weeks), immature (woven) bone formation (four to eight weeks), mature (la- mellar) bone development (eight to twelve weeks), and bone stabilisation stage (twelve to 16 weeks or about four months).26–28 Post ex- traction bone resorption is always 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 hori- zontal bone loss occurs within three months and one-third takes place within the remaining nine months ofthefirstyearpostextraction. 29 A mean reduction of the width of the ridge has been reported to be 5 to 7 mm within a six-month period or 50 per cent during the twelve monthsfollowingtoothextraction.29 The loss of bone height is smaller, re- ported to be about 1 mm within the first six months post extraction.20, 29 If a bone grafting and implant treat- ment approach is not considered soonaftertrauma,theatrophyofthe alveolar process of the anterior max- illa continues with time. Resorption of the buccal plate compromises the anatomy of the edentulous alveolar ridge and makes it difficult to place Bone quality related to implant location CBCT zones of the jaw Technical Data Anodevoltage 60–90kV Anodecurrent 1–14mA Focalspot 0.5mm,fixedanode Imagedetector Flat panel Imageacquisition Single200degreerotation Scantime 7.5–27s Reconstructiontime 2–25s Table1 Average HFU of different areas in the mouth Zones(D1–D5) No.ofCases Avg.HFUperzone 1 14 655 2 33 599 3 31 562 4 19 529 5 3 213 Total 100 Table2 an implant in the prosthetically favourable position.31 Even when a dental implant is placed, its strength is diminished without the presence ofabuccalcorticalplate.Usingatwo- dimensional finiteelement model for stress analysis, Clelland and asso- ciatesdemonstratedlowstressesand highstrainssurroundedtheimplant for the all-cancellous (lack of cortical plate) bone model.32 When a layer of thick cortical bone was added to the model, it had a significant impact and improved stresses and strains ontheimplant. D4 is related to first and second pre- molars in the maxillary region and rarely first and second molars. Al- though this area is not considered the maxillary anterior teeth, it is still a prime concern for the patients during conversation and smiling. In addition to two anterior premolar teeth, two posterior molars are not considered as a separate class in this group if sinus lift is not required due totheircommonbonequality.These implants once restored are the long- est support in front of maxillary si- nuses. Park, Hyo-Sang et al. reported that the cortical bone density of the maxilla ranged approximately between 810 and 940 HFU at the al- veolar bone except for the maxillary tuberosity (443 HFU at the buccal and 615 HFU at the palatal alveolar bone),andbetween835and1,113HFU at the basal cortical bone except for tuberosity (542 HFU).33 The cortical bonedensityofthemandibleranged between800and1,580HFUattheal- ÿPage 3 114655 233599 331562 419529 53213