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22 I I research _ platform switching implants1_2010 ditions. According to Wolff’s law16 , every change in the form and function of bone is followed by modi- fications in its internal architecture and external conformation. The dimensions and orientation of trabeculae are adaptable in accordance with changes in loading trajectorial vectors and, when equilibrium is found, trabecular patterning repre- sentstheaverageregimeexperiencedbythebone.17 Mechanicalstimuliaffectboneresponseandexert influence on the replication and differentiation of mesenchymalcellstowardtheosteoblastlineage.18 Frost’s theory Frost stated that bone mass changes when ab- solute peak strains induced inside the bone fall either below or above the physiological window estimated between 200 and 1,500 microstrains. The application of this theory Fig. 2 to dental implant rehabilitation explains bone resorption at the crestal level of loaded implants, a condition that may occur because of the stress shielding ef- fect, due to both the solid metal structure of the implantandtheimplantdesign.Thesefeaturescan play a role on load transfer to the bone, reducing strain magnitude under the lower physiologic threshold and, thus, promoting osteoclast resorp- tion at the crestal level. The rigid metal structure of the implant ac- quires most of the occlusal stresses, transferring them deeper into the basal bone, excluding the crestal bone from the physiologic stimulation. Implants with a slim design at the crestal level, for example, demonstrate a wide bone formation, corroborating Frost’s theory. Effect of implant geometry on the marginal bone Implant design consists of the combination of the implant body three-dimensional geometry, presence of threads, thread design, surface topog- raphy and surface treatments that may affect strain stimulation of peri-implant bone.20 Finiteelementanalysisreportedthattaperedim- plants present a better mechanical performance than cylindrical implants to avoid punching stresses.21, 22 It has been demonstrated that threads andtheirlocationontheimplantbodyhavearolein theloadtransferringpressurepatternstothebone.23 The outcome of comparative clinical research on different implant systems have reported analogous marginal bone loss per year (1–3), even if smooth surfacedimplantswithaconicalcollarhavedemon- stratedhigherbonelossthanself-tappingandstan- dard implants.29, 30 In this respect, marginal bone loss might be pri- marilyrelatedtothesmoothnessoftheimplantsur- face, leading to stress protection, and thus, to bone resorption (bone shielding).31 Effect of the implant surface on the peri-implant bone Surface microgeography plays a primary role in facilitating biological interactions between bone precursor cells and implant. Roughimplantsurfacesfacilitatehighosteoblast adhesion levels24 , and since osteoblasts are spread onimplantsurfaces,theroughnessseemstoinduce osteoblaststowardsynthesisandthereleaseofbio- logical factors affecting the tissue response at the interface. Surface roughness is a crucial factor af- fectingboneappositionattheinterfaceandimprov- ing the interface resistance because of better me- chanical interlocking. However,increasedbonemass aroundroughsur- facesmayalsobeattributedtoalowerboneremod- elling level during the early stages of implantation, asreportedinacomparativeresearchstudybetween plasma sprayed and smooth surfaced implants.25, 26 A poor implant design like smooth machined coronal part could be related to a reduction in me- chanical interlocking between implant and crestal bone, acting like a stress shield and inducing crestal bone loss.27, 28 The stability of the peri-implant cervical bone around the neck of the implant and the absence of resorptionarethekeytomaintaininggingivalpapil- lae and bone in the anterior region. Accordingtoreferenceliterature,severalchanges should occur after abutment connection. Bone re- sorption of approximately 2 mm from the implant abutment junction3 should occur circumferentially, noticeable on the buccal plate. Preliminary evidence suggests that anticipated Fig. 2_Frost’s Mechanostat theory. 4,000 – 6,000 microstrains PATHOLOGICAL LOAD =>fracture 1,500 – 4,000 microstrains OVERLOAD => bone resorption 200 –1,500 microstrains PHYSIOLOGICAL LOAD => bone apposition Fig. 2