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T a p e r e d i m p l a n t s f o r b u n d l e b o n e p r e s e r v a t i o n Introduction After loss of a tooth, there is progressive invo- lution of the alveolar bone in both the horizontal and vertical dimensions.4, 5, 17, 18 In addition, the most rapid reduction of alveolar bone after dental extraction occurs during the first months.4, 5 For more than a decade, different clinical studies have demonstrated that immediate implant placement in fresh extraction sites may be an effective therapy not only because it reduces the number of surgical procedures,37, 41 but also because it favors the preservation of the ridges’ morphological contours and simpli- fies clinical techniques. 11, 28, 35, 50, 51 Bone remod- eling begins directly after the preparation of the implant bed, as well as the healing process of the bone. Osteoblast adhesion to the implant surface and the osseointegration process begins approximately 3 weeks after surgery.54 During this healing process, bone remodeling occurs.33, 49 This often results in crestal bone loss.31, 32 How- ever, findings from experiments in humans and dogs have demonstrated that marked reduction in the height of the alveolar ridge occurred con- sistently after tooth extraction4 and that implant placement in fresh extraction sockets had no effect on the process of bone modeling. 5, 9, 17, 18 Several authors have studied the clinical and radiographic changes that occur around dental implants inserted at different levels in relation to the crestal bone. Clinically, implants are often placed subcrestally in esthetic areas to avoid exposure to metals and to create sufficient space to develop a suitable emergence profile.21 Sub- crestal placement of implants may have an addi- tional benefit, as it improves bone–implant con- tact (BIC) in the neck region of the implant.30, 59 Positioning the implant–abutment junction more apically contributes to the maintenance of mucosal texture and tonality and favors the re-establishment of marginal tissue architec- ture.27 Thus, different microgap designs result in different shapes and sizes of the periimplant (dis-shaped) bone defect in submerged implants in either equicrestal or subcrestal positions.58 A previous animal study evaluated bone remodel- ing and BIC after immediate placement at dif- ferent levels in relation to the crestal bone of beagle dogs. Cylindrical and tapered implants were inserted crestally and 2 mm subcrestally. These studies suggested that apical positioning of the top of the implant does not jeopardize bone crest and periimplant tissue remodeling. However, less resorption was observed when implants were placed 2 mm subcrestally. More- over, higher BIC values were found in implants placed subcrestally.38, 39 Bone–implant contact is among the most important factors contributing to implant sta- bility. Thus, many authors have specified the factors that influence BIC levels, implant posi- tion and bone density.23, 24, 26, 46, 56, 57 Experimen- tal and clinical studies have demonstrated that implants designed with a shorter, smooth cor- onal collar caused no additional bone loss and might help reduce the risk of an exposed metal implant margin in areas of esthetic concern.3, 29 The anatomy and surface treatment of the neck of the implant, together with the type of connection between the implant and the pros- thetic components, have been considered as with regard to reducing crestal bone loss.27 Based on the data revised, it is hypothesized that the vertical positioning of the implant platform in relation to the crestal bone may influence the location of the first BIC. As a consequence, the biological width may be established in a more coronal position. Therefore, the objective of this study was to compare the BIC of implants with smooth necks and no microthreads, which rep- resent a rough surface, placed at crestal and subcrestal levels in healed bone and immediately post-extraction in dogs. Materials and methods Six American Foxhound dogs of approximately 1 year of age were used in this study. The Ethics Committee for Animal Research at the Univer- sity of Murcia, Murcia, Spain, approved the study protocol, which followed guidelines established by the European Union Council Directive of Feb- ruary 2013 (R.D.53/2013). Clinical examination determined that all of the animals were in good general health; moreover, all of the animals pre- sented with intact maxillae, without any general occlusal trauma or oral viral or fungal lesions. The choice of this kind of dog was due to these being the animals that we have in our animal facilities approved for research. The ani- mals were quarantined for the application of rabies vaccines and vitamins. The dogs were kept in kennel cages before and after surgery, received appropriate veterinary care, and were allowed free access to water and standard lab- oratory nutritional support throughout the trial period. After surgery, the animals received Journal of Oral Science & Rehabilitation Volume 3 | Issue 3/2017 29