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ePaper created 2016-03-31, 16:35:38 | version 1.38.0
fibre post restorations literature review | 25roots1 2016 time/output, results in better composite polymeri- sation. Theindirectcastgold/metal/zirconiapostandcore has been largely replaced with a one appointment restoration of a direct post and core. Fibre posts such as the Ultradent Unicore Fiber Post, the quartz fibre posts manufactured by RTD (St. Egreve, France), the Macro-LockX-RO(RTDSt.Egreve,France),andtheDT Light-Post (RTD St. Egreve, France) have many physi- cal characteristics that make them more desirable clinically, rather than metal and zirconia posts: 1. The elastic modulus (or a material’s stiffness) of fibre posts more closely approximates that of den- tine (18.6 Gigapascals—GPa) allowing some slight flexinfunction,dissipatingstressandreducingthe likelihoodofdamagetotheroot.20, 21 Stainlesssteel has an elastic modulus of about 200 GPa, titanium alloy 110 GPa and Zirconia 300 GPa.22 The stiffness of metal and zirconia posts creates more internal stress, zones of tension and shear during function and parafunction,23 which can result in unrestor- able catastrophic root fractures. 2. Fibre posts have a high flexural strength, and in a studybyStewardson,‘theflexuralstrengthoffibre reinforced composite endodontic post materials exceedtheyieldstrengthofgoldandstainlesssteel and two of the FRC (fibre reinforced composite) posts were comparable to the yield strength of ti- tanium’.24 It must be noted here that not all fibre posts are created equal. There are differences in fracture load, flexural strength, fibre diameter, fi- bre/matrix ratio, type of fibre (with quartz fibre postshavinghigherfailureresistance),lighttrans- mission, shape, post surface adhesion, quality of fibre, structural defects/voids and manufacturing quality, which all affect the clinical outcome and longevity.25–29, 16 The clinician must make an in- formed choice for choosing a fibre post—looking for the best attributes above—in order to select the post with superior properties based on indepen- dent research. The dental practitioner must also be aware of the best adhesive combinations and techniques, as there are some incompatibilities between dual-cure core materials and simplified acidic adhesives due to residual acidity. There is a variation in the results of the scientific literature when evaluating fibre posts, not only because of thedifferencesinthepoststhemselves,butalsobe- causeofthecementing/bonding/adhesivesystems used. To date, multiple articles in the scientific lit- erature support the statement that ‘only specific combinations of dentin adhesives and luting ce- ments prove efficient, with total etch adhesives combined with dual-cure cement (composite) ap- pearing to be the best choice’.30, 31 3. Fibre posts are not subject to galvanic or corrosion activity. The corrosion of base metals predisposes to a high percentage of failures with cast posts, whichcanalsocreateanegativeaestheticoutcome of a dark root and darkening of the gingival collar (Fig. 6a).32, 33 Milnar and others have published ex- cellentpapersshowingthattheuseofalighttrans- mitting post can eliminate this common aesthetic challenge, allowing not only light transmission down the canal eliminating the dark gingival co- lour, but also the creation of superb clinical aes- theticswithtranslucentceramicsoveracomposite core (Fig. 6b).34–36 4. Clinically, heavily restored teeth may hold up to normalocclusalfunctionbutmanyfailincyclicfa- tigue–repeatedfunctionalstressandtorque.21 Fibre posts are more fatigue resistant than metal posts, and the quartz fibre post is found to be more than twice as fatigue resistant as the stainless and tita- nium alloy posts.37 During repeated fatigue load- ing, the flexural strength of metal posts can de- crease by 40 %, while there is only a 14 % decrease in a fibre composite post.38 5. Endodontic procedures do fail, either due to faulty technique,theinabilitytoaccessorcompletelyde- Fig.2:To seat the inserted parallel sided post into the tapered canal would require more apical removal of vital dentinal structure needlessly weakening the root and creating an apical stress point. Fig.3:The taper of the Macro-Lock post allows respect for the dentine and ensures a more even and minimal amount of surrounding composite resin,thereby reducing polymerisation contraction forces. Fig.2 Fig.3