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implants - international magazine of oral implantology

I special _ endo-implant algorithm The cone-screw abutment has been shown to di- minish micro-movement by reducing the burden of component loosening and fracture. This enables the identificationoftheeffectsoftheparameterssuchas friction, geometric properties of the screw, the taper angle and the elastic properties of the materials on the mechanics of the system. In particular, a relation between the tightening torque and the screw pre- tensionisidentified.Itwasshownthattheloosening torqueissmallerthanthetighteningtorquefortypi- cal values of the parameters. Most of the tightening loadiscarriedbythetaperedsectionoftheabutment, and in certain combinations of the parameters the pre-tensioninthescrewmaybereducedtozero.This tapered abutment connection provides high resist- ancetobendingandrotationaltorqueduringclinical function,whichsignificantlyreducesthepossibilities ofscrewfractureorloosening. _Biomechanics Theseedofatreehasthenatureofabranchortwig orbud.Itisapartofthetree,butifseparatedandset in the earth to be better nourished, the embryo or youngtreecontainedinittakesrootandgrowsinto anewtree. —Isaac Newton Pressure on the cervical cortical plate, micro- movement of the fixture–abutment interface (FAI), and microflora leakage and colonisation at and within the FAI are some of the pathological vectors associated with osseous remodelling, both crestal andperipheraltodentalimplants.48 Occlusalconsid- erations engineered into fixture design should en- able optimum load distribution for permanent load stability during functional loading, reduce func- tional stress transfer to the interfacial tissues, and enhancethebiologicalreactionofinterfacialtissues to occlusally generated stress transfer conditions.49 Future modifications to implant biomechanics should focus on designs wherein the osseous tra- becularframeworkthatretainsthefixturewilladapt to the amount and direction of applied mechanical forces, cope with off-axis loading, compensate for differences in occlusal plane to implant height ra- tios, as well as adjust to mandibular flexion and tor- sion.50 In this new era of implant-driven treatment planning, fixtures should be engineered to support single crowns with cantilevers instead of implant–implant or implant–teeth connections for a span of any degree. These engineering design iter- ations will minimise high-stress torque load at the implant-abutment interface and obviate areas with degrees of bone insufficiency. The goal should be to biomimetically replicate the natural state to the greatestdegreewithregardtoloadbearingcapacity (Figs. 10a & b). Stable crestal bone levels are the yardstick by whichtreatmentsuccessandhealtharemeasuredin theorofacialecosystem,whethersuccessandhealth relatetonaturaltoothretentionorrestorativeand/or replacement rehabilitation. It is therefore surprising thatthetreatmentoutcomestandardsforosseointe- gration accept crestal bone remodelling and resorp- tionofupto1.5to2mminthefirstyearfollowingfix- tureplacementandprostheticinsertion.51 Theconceptofbiologicalwidthoutlinesthemin- imum soft-tissue dimension that is physiologically necessary to protect and separate the osseous crest from a healthy gingival margin surrounding teeth 14 I implants2_2011 Fig. 9 Endo- Restorative Implants BIOLOGY LOAD BEARING CAPACITY LOAD BEARING CAPACITY Mechanical BIOLOGY Mechanical Coronal seal Type of Abutment Joint Bone- implant interface Type of Abutment Joint Compression tension Residual tooth structure Bone quality and quantity Tilted abutment Splinted teeth Length, apical diameter Length, diameter Splinted implants Fig. 9_An arch eliminates tensile stresses in spanning an open space, as all forces are resolved into com- pressive stresses. It requires all of its elements to hold it together, thus making it self-supporting. The incor- poration of platform switching into the design of an implant abutment simulates three oblate spheroid shapes—one vertical, two horizontal. The objective is to ensure that axially vectored compressive stresses are contained within an idealised shape that is structurally enhanced by the useofaprecisefriction-fitconnection. Fig. 10a_Foundational dentistry mandates that the impact of an ortho-biological replacement unit be commensurate with the biological objectives and functional require- ments of the natural tooth. Fig. 10b_As the number of implant-supported single-tooth replacements increases, implant- abutment connection design should ensure that occlusal table replication displays equivalency in both dimen- sion and cuspal inclination with the surrounding natural dentition.