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12 I I special _ endo-implant algorithm most effective retrograde surgical protocols of all. The literatureisunclearconcerningperi-apicalre-surgery. Gagliani etal.43 compared peri-apical surgery and re-surgery over a five-year follow-up period. Using magnification and microsurgical root-end prepara- tions, the positive outcome for primary surgery was 86% and 59% for re-surgery. While others have shown positive outcomes for re-surgery, the deci- sion remains highly case specific. In spite of our best efforts, negative endodontic treatment outcomes occur and ortho-biological replacement of teeth and their surrounding anchoring structures is an integral part of contemporary foundational treatment plan- ning. A recent article by Assuncao et al.44 describes engineeringmethodsusedindentistrytoevaluatethe biomechanicalbehaviourofosseointegratedimplants. Photoelasticityisusedfordeterminingstress-concen- tration factors in irregular geometries. The applica- tion of strain-gauge methodology to dental implants providesbothinvitroandinvivomeasurementstrains understaticanddynamicloads.Finiteelementanalysis can simulate stress using a computer-generated model to calculate stress, strain, and displacement. An analysis of the impact of mechanical/technical risk factors on implant-supported reconstructions is beyond the scope of this publication; however, the replacement of lost teeth by implants should, without exemption, provide a feeling of restitutioadintegrum. The means by which the restoration of the original condition at the crown–root interface is idealised is detailedinthisarticle. The structure and composition of teeth is perfectly adaptedtothefunctionaldemandsofthemouth,and are superior in comparison to any artificial material. Sofirstofall,donoharm. —Anonymous _Back to the egg An increased uniform amount of coronal dentine significantlyamplifiesthefractureresistanceofendo- dontically treated teeth regardless of the post system used or the choice of material for the full coverage restoration.45 ArecentarticlebyCoppedeetal.demon- strated that friction-locking mechanics and the solid design of internal conical abutments provided greater resistance to deformation and fracture under oblique compressive loading when compared to internal hex abutments.46 Thesetwo‘seemingly’disparateobserva- tions define the inherent continuum between natural tooth engineering and the principles of engineering necessary to ortho-biologically replicating the native state. The use of a ferrule or collet and a bonded or inti- matelyfittedpost-coretorestorefunctionandformto anendodonticallytreatedtoothisanalogoustotheuse ofalong,taperedfriction-fitinterfacewitharetaining screw(Morsetaper)tosecureanabutmenttoafixture. In both cases, the role of contact pressure between mating surfaces in generating frictional resistance provides a locked connection. This has been shown to effect long-term stability of crestal bone support for the overlying gingival tissues and maintain a healthy protective and aesthetic periodontal attachment apparatus.47 The Roman architect Vitruvius’ (Marcus Vitruvius Pollio) description of the perfect human form in geo- metricaltermswasasourceofinspirationforLeonardo da Vinci, who successfully illustrated the proportions outlined in Vitruvius’ work DeArchitectura. The result, the Vitruvian man, is one of the most recognised drawings in the world and is accepted as the standard ofhumanphysicalbeauty.Vitruviustheorisedthatthe essential symmetry of the human body with arms and legs extended should fit into the perfect geometric forms: the circle and the square. Da Vinci recognised that the circle and the square are only tangent at one place, the base. Observe the insert in Figure 8. The stabilising platform for the human form outlined begins at that tangent; the intersection is graphically analogous to the structural configuration of platform switching. The relative simplicity of this construct reinforces the obvious. When we compare design in living things to the artificial designs they inspire, a striking parallel emerges. Almost all the products of man’s technology roots2_2010 Fig. 11a Fig. 11a_The composition of bio- logical width around implants: sulcus depth (SD), distance from peri- implant mucosal margin (PM) to the most coronal point of junctional epithelium (cJE); junctional epithe- lium (JE), distance from cJE to most apical point of the junctional epithe- lium (aJE); connective tissue zone (CT), distance from aJE to the first bone to implant contact (BC).63