implants - international magazine of oral implantology

I special _ endo-implant algorithm Fig. 3_Two different retreated teeth; two different potential treatment out- comes. The root-canal system of both teeth has been re-engineered in its anatomic entirety; however, the treatment outcome after restoration for both is unlikely to be the same. Regenerative technologies incorpo- rating mesenchymal stem cells derived from dental tissues may one day obviate the concern. Fig. 4_Less porous, less hydrated and highly mineralised outer dentine (a); pulp canal space (b); more porous, more hydrated and less mineralised inner dentine (c); water in the dentinal tubules and pulp space is held in a confined environ- ment under hydrostatic pressure (d). Fig. 5_Primary causes of fracture include excessive structure loss, loss of free unbound water from the root-canal lumen and dentinal tubules, age-induced changes in the dentine and restorations and restorative procedures. Secondary causes of fracture include the effects of endodontic irrigants and medicaments on dentine, the effects of bacterial interaction with dentine substrate and bio-corrosion of metallic post-cores. Understandingthemechanicalpropertiesofteeth isessentialinordertoaddressthemostcommonclin- ical problem affecting all endodontically treated teeth, fracturing, which in spite of even minimal loss of tooth structure may be severe enough to necessi- tateremoval.22–24 Thehypothesisthatdentinebrittle- ness increases with diminished moisture content has been debunked; conserving bulk dentine is the sine quanonoffractureprevention.Kuttleretal.reported that dentine thickness correlates inversely to post- space diameter in the distal roots of mandibular mo- lars.25 A size #4 Gates-Glidden drill caused strip per- forations in 7.3% of canals studied. The authors rec- ommend that Gates-Glidden drills no larger than a size #3 be used. After endodontic treatment, dentine thickness on the furcation side was less than 1mm in 82% of the distal roots studied (Fig. 4). There are pri- mary causes that predispose teeth to fracturing and secondary causes that predispose teeth to fracturing afteraperiodoftime(Fig.5).Endodonticsisacompo- nentofaninterdisciplinaryprocessandachainisonly as strong as its weakest link. Subsequent to any en- dodonticprocedure,intensityofstressconcentration and tensile stresses within an endodontically treated tooth will depend upon: 1) thematerialpropertiesofthecrown,post,andcore material chosen; 2) the shape of the post; 3) the adhesive strength at the crown–tooth, core– tooth, core–post, and post–tooth interfaces; 4) the magnitude and direction of occlusal loads; 5) the amount of available tooth structure; and 6) the anatomy of the tooth. Anycombinationofvectoredstressconcentration andhightensilestresseswillpredisposetheseteethto fracturing without an adequately engineered restorative design. _Re-engineering Re-engineering negative treatment outcomes is a significant part of the contemporary endodontic oeuvre. The presence of apical periodontitis may affecttheoutcomeofinitialendodontictreatment;26 however, there is general consensus that apical periodontitis is the most important variable that in- fluences a positive outcome with non-surgical and surgical retreatment.27–29 Positive treatment out- comesmaybemorelikelyincertainteethwithacom- bination of both procedures, rather than with one or the other alone (Fig. 6). The premise that non-surgical retreatment im- proves the outcome of peri-apical surgery has been supportedbybothhistoricalandcurrentstudies.30–32 Apical surgical ‘correction’ of intra-canal infections may isolate, but not eliminate, the residual mi- croflora of the root-canal space. It should therefore be limited to situations in which non-surgical re- treatment is judged impractical. With the range of sophisticated equipment and material in the con- ventional endodontic armamentarium, this is a re- mote consideration at best. When the aetiology is 10 I implants2_2011 Fig. 3 Fig. 4 Fig. 5