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CAD/CAM 3 2016 | cone beam supplement research 48 Although this area is not considered the maxillary anterior teeth, it is still a prime concern for the pa- tientsduringconversationandsmiling.Inadditionto twoanteriorpremolarteeth,twoposteriormolarsare not considered as a separate class in this group if sinus lift is not required due to their common bone quality.Theseimplantsoncerestoredarethelongest supportinfrontofmaxillarysinuses.Park,Hyo-Sang et al. reported that the cortical bone density of the maxilla ranged approximately between 810 and 940HFUatthealveolarboneexceptforthemaxillary tuberosity (443 HFU at the buccal and 615 HFU at the palatal alveolar bone), and between 835 and 1,113HFUatthebasalcorticalboneexceptfortuber- osity (542 HFU).33 The cortical bone density of the mandible ranged between 800 and 1,580 HFU at the alveolar bone and 1,320 and 1,560 HFU at the basal bone. The highest bone density in the maxilla was observedinthecanineandpremolarareas,andmax- illary tuberosity showed the lowest bone density. Density of the cortical bone was greater in the man- dible than in the maxilla and showed a progressive increase from the incisor to the retromolar area. D5, known as the sinus zone, is a bilateral zone of the alveolar ridge of posterior maxilla located at the baseofthemaxillarysinusfromthesecondpremolar to pterygoid plates. There are certain common fea- turesofreplacementofmissingtoothorteeth(rarely two premolars and commonly one or two molars) with dental implants in this zone. It often relates to thedegreeofsinuspneumatisationandverticalbone deficiency that may require supplemental surgical procedures in the subantral area in order to place endosseous implants. Thisbilateralmaxillaryposteriorzonethatextends from the second premolar to the pterygoid plates is located at the base of maxillary sinuses (antra of Highmore). Embryologically, the hard palate and the alveolar process of the maxilla form the barrier be- tween the maxillary sinus and the oral cavity. The bone height between the floor of the maxillary sinus andthealveolarcrestisroutinelyanalysedinoralim- plantology when posterior maxillary implants are contemplated. An increase of sinus volume or sinus pneumatisation after a loss of posterior tooth/teeth often necessitates vertical bone augmentation with a sinus lift procedure. The bone of this region is also known to have compromised bone quality (types 3 and 4) that can increase an implant failure rate. The main blood supply to the posterior maxilla derives from the posterior superior alveolar artery, the greater and lesser palatine arteries (all from the maxillary artery), the ascending pharyngeal branch of the external carotid artery, and the ascending palatine branch of the facial artery. An injury to the posterior superior alveolar artery during the lateral approach for subantral augmentation can cause haemorrhage that may require coagulation. Materials and method Fromadatabaseof1,134patientswhohadreceived 4,800 dental implants from 2001 till August 17, 2015, randomly a prosthodontist with no knowledge of these criteria was requested to select 100 files from the data base and present them for this study. The 100 files had received panoramic and cone beam computed tomography (CBCT, Table 1) during their diagnostic visit. The average HFU of the randomly selected 100 cases was calculated. Results Hounsfield unit: The data in table #1, out of 100 samples, demonstrated that the average HFU was the minimum in D5 (213 HFU), and followed by D4 (528 HFU), D3 (561 HFU), D2 (599 HFU) and D1 (654 HFU) in ascending order respectively (Fig. 1 and Table 2). Discussion There are few literature reports that attempt to study implant location, among a multitude of other factors, to determine its influence on the success or failure of dental implant treatment. Becker et al. evaluated 282 implants placed in the maxillary and mandibular molar positions in a prospective study.34 The six-year cumulative success rate (CSR) for maxillary posterior implants was 82.9 percent, for mandibular posterior, 91.5 percent. He concluded thatCSRintheposteriorregionsislowerthanusually reported for anterior regions of the maxilla and mandible due to differences in bone quality and quantity. Eckert et al. assessed 1,170 endosseous implants placed in partially edentulous jaws in a Technical data Anode voltage 60–90 kV Anode current 1–14 mA Focal spot 0.5 mm, fixed anode Image detector Flat panel Image acquisition Single 200 degree rotation Scan time 7.5–27 s Reconstruction time 2–25 s Table 1 32016