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14 I I special _ endo-implant algorithm are no more than imitations of those in nature and usually, they fail to match the superior design in living things. Consider the engineering per- fection that is the egg. Its strength lies in its oblate spheroid shape. A blow to the side of an egg from a sharp object places pressure along the thin shell and breaks it easily. However;iftheeggissqueezeddirectly on its poles, the vectored pressure is compressed along the surface struc- ture, not across the shell; the egg cannot be broken without extraor- dinary force. However, if a pinhole is created in one of the poles disrupting theintegrityofthestructure,thepressure willreadilybreaktheegg,commensuratewith a sharp blow to the side. In geometry, an oval is a curve that resembles an egg or an ellipse. Architects and engineers have used smooth ovate curves to support the weight of struc- tures over an open space literally since the second millenniumBC.Thesearches,vaultsanddomescanbe seen in buildings and bridges all over the world; the most pervasive example is the keystone arch used by the Romans for aqueducts and mills. An arch directs pressure along its form so that it compressesthebuildingmaterialfromwhichitiscon- structed. Even a concrete block is readily broken if one hitsitonthesidewithasledge.Butundercompression forces from above, the block is incredibly strong and unyielding. Many will remember the weight-bearing tripodexperimentsfromgradeschoolinwhichanegg actsasoneofthreesupportinglegsofasquaresection of wood that bears books as the load. The structure could support over sixty books, almost twenty pounds (9kilograms),beforebreakingthesupportingegg.One need only look at the root trunk and coronal tooth structure of a multi-rooted teeth and it becomes apparentthatstrengthofthetoothformisdependent uponanarchformforitsintegrity(Figs.8&9). Is it possible for this natural feat of engineering to be biomimetically replicated to the design para- meters of osseointegrated implants? There are a number of paradigms that continue to fuel debate in the dental clinical and scientific communities that pertain to the optimal engineering predicates for implant design. These include smooth versus rough surfaces, submerged versus non-submerged installation techniques, mixed tooth-implant ver- sus solely implant-supported reconstructions, Morse taper abutment fixation versus a butt-jointinterface,andtitaniumabut- ments versus aesthetic abutments in clinicalsituationsinwhichaesthetics are of primary concern. Thecone-screwabutmenthasbeen showntodiminishmicro-movementby reducing the burden of component loos- eningandfracture.Thisenablestheidentifica- tion of the effects of the parameters such as friction,geometricpropertiesofthescrew, thetaperangleandtheelasticproperties of the materials on the mechanics of the system. In particular, a relation between the tightening torque and the screw pre-tension is identified. It wasshownthatthelooseningtorqueis smaller than the tightening torque for typical values of the parameters. Most of the tightening load is carried by the tapered section of the abutment, and in certain combinations oftheparametersthepre-tensioninthescrewmaybe reduced to zero. This tapered abutment connection provides high resistance to bending and rotational torqueduringclinicalfunction,whichsignificantlyre- ducesthepossibilitiesofscrewfractureorloosening. _Biomechanics The seed of a tree has the nature of a branch or twig orbud.Itisapartofthetree,butifseparatedandsetin the earth to be better nourished, the embryo or young treecontainedinittakesrootandgrowsintoanewtree. —IsaacNewton Pressureonthecervicalcorticalplate,micro-move- ment of the fixture–abutment interface (FAI), and roots2_2010 Fig. 11b_When a matching implant- abutment diameter is used, the inflammatory cell infiltrate is located at the outer edge of the implant-abut- ment junction close to crestal bone; this close proximity may explain in part, the biological and radiographi- cal observations of crestal bone loss or saucerisation around restored implants. This is not peri-implantitis or mucositis; however, any area of bacterial accumulation and stasis, inaccessible to normal hygiene proto- cols, is a risk factor for exacerbation. Fig. 11c_The Morse taper connec- tion of the Ankylos C/X (internal index) fixture distributes oblique and horizontally applied forces over a large area of the matrix joining surface inside the implant. The connection is therefore only loaded in the vertical direction. The cross- section shows no gap between the abutment taper and the implant which avoids micro-loosening. This is in contrast to systems with internal hex connections (clearance fit) that demonstrate micro-motion and ‘rotational slop’, making them prone to inflammatory reactions at the implant-abutment connection due to micro-leakage. Fig. 11b Fig. 11c

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