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ENDO CORES FOR PREMOLARS AND MOLARSA TECHNIQUE DISCUSSIONGraeme .comThe techniques described are reliant on total bonding of the final restoration. Cementationof crowns will potentially expose the core to damaging loads and lead to failure.The techniques rely on the retention of the BioRim and the recreation of an adhesivelyattached compression dome to help recreate even distribution of stresses within the tooth,and avoid unnecessary stress concentrations by allowing the tooth, core and adhesive onlayfunction in strain harmony. The techniques for premolars and molars are quite different.RESTORING ENDO PREMOLAR TEETHPremolars that have reached the stage of needing endo most often have severelycompromised crown structure. This exposes the core design and the remaining toothstructure to potentially damaging stresses. The goal is to retain as much remaining toothstructure as possible, and create a core system that will help distribute stresses and avoidweakening the remaining tooth.MATERIALSRIBBOND THIN HIGH MODULUS (THM) ULTRA 2 or 3mmDual-cure bonding system (Total Etch or Self Etch)Dual cure activator for bonding resinDual-cure core paste or flowable bonding paste G W Milicich 2013 all rights reserved. www.advancedental-ltd.comPage 1

(I wonder how long the short core on the second premolar is going to last?)Remove all existing restorationsRemove GP 8-10mm into canals without removing any extra dentin from the wallsAir abrade all exposed dentin surfacesBuccal cavity restored with a bonded composite prior to creating the fibre reinforced core.NOTE: the cusps have been reduced by 1.5mm in height. No further tooth removal on thesound palatal cusp.PREPARATION FOR FIBRE CORE RESTORATIONAfter cleaning the tooth, apply a self-etching bonding primer of your choice. The system youuse must have a dual-cure activator option. When a canal is being used as part of a corebuild up, a dual cure bonding system has to be used to ensure complete polymerization ofthe resin within the depth of the canal. There are many on the market, so the decision as towhich system to use is in the dentist’s hands. Because a dual-cure system is being used, youhave to be organized. Cut two lengths of 2 or 3mm wide Ribbond THM Ultra that are 2.5times the length of the depth of the prepared canal.After applying the SE primer and evaporating the solvent, remove any excess from thedepth of the canal with a paper point.There is one step that has to be understood when using Ribbond as part of the core buildup. Ribbond is plasma etched and will establish a bond and micro-mechanical lock tounfilled resin. With dual cure bonding systems, the fibre should not be wetted with the SEprimer, but with the resin B. However, this is only light cured, so just prior to wetting thefibre, a dual cure activator designed for the bonding system being used, has to be mixedwith resin B, applied to the fibres to wet them, and the excess blotted off with a paper G W Milicich 2013 all rights reserved. www.advancedental-ltd.comPage 2

towel. Immediately place the two lengths of fibre into a cross. A chemical reaction has nowbeen initiated, so efficiency is needed from this stage on.Apply the dual cure resin B into the canal and onto the tooth. The, using a fine mixing tip,inject the dual cure paste into the canal and pulp chamber, place the crossed, dual cureactivated resin impregnated fibres, across the centre of the tooth and using a fine flat endedinstrument, push them to the depths of the canal. Then inject more dual cure paste into thecentral space and allow it to cure chemically. Do not be in a hurry and force the set with acuring light. This will create high C-factor stresses in the core and possible challenge the longterm stability of the seal. After 5 minutes, complete the cure with a curing lightComplete the preparation, retaining as much of the BioRim as possible and restore with anadhesively bonded restoration like e.max or a direct composite onlayCompleted preparation. Note the palatal BioRim has been retained. There is no attempt togain further ferrule retention, that simply removes more critical tootth structure, exposingthe core to increased stresses. There is a small 1mm deep roll over the edge of the palatalcusp to place the underlying tooth structure back into compression when the restoration isloaded. G W Milicich 2013 all rights reserved. www.advancedental-ltd.comPage 3

Completed CADCAM e.max adhesively bonded restoration.MOLAR ENDO COREAll cusps should be overlaid.Failure to do so can lead to catastrophic failure.Cores on endo molars do not have to extend into the canals using posts. This leads to stressconcentration and long term failure G W Milicich 2013 all rights reserved. www.advancedental-ltd.comPage 4

There iss sufficient tooth structure to provvide an effeective energgy sink and retention withoutwusing thhe root canaals for retenntion. The ccase being demonstratded is a commplex one involvinga missinng wall in thhe pulp chamber.MATERRIALSRIBBONND THM OR THM ULTRA. Two or t hree piecessRIBBONND WETTINGG RESIN (doo not use th is in premoolar Ribbondd posts – it iis only lightt cured)RIBBONND STICKY FLOW (do noot use this i n premolarr Ribbond posts – it is oonly light cuured)SE DENTTIN BONDINNG SYSTEM. This does not have too be dual cuure becausee light can reeach tothe deppths of the pulppchambber on mola rs with this techniqueGaeniall Bond, Scootchbond Unniversal, Opptibond FL(ttotal etch), Clearfil SE Bond 2, Cleearfil SEProtect, PQ1 to name a few, area all suita ble.POSTERRIOR COMPOSITE. GC everXeposteerior. A fibre reinforcedd compositee, or any highstrength posterior composite like Clearfi l APX.TOOTH PREPARATTIONFollowing endo, reemove all reemaining re storations. Reduce all cusps by 1.55mm, with a slight1mm roolled chamffer margin.Ensure there is a slight mechaanical underrcut in the internalipulp chamber shape. Thiss isgenerallly present anyway.aIn thist case, thhe mesial wallw of the pulp chambeer is missingg andneeds tto be restored. The goal is to creaate a fibre reeinforced toorsion box iin the pulp GWMMilicich 20133 all rights reeserved. wwww.advancedeental-ltd.commPage 5

chambeer to help distribute strresses evennly throughoout the tootth and avoidd stressconcenttrations. WeW are tryingg to create strain harmmony between the coree system annd theremainiing tooth.PREPARRATION FORR FIBRE CORE RESTORRATIONIf the coore of the toooth is intact, two lenggths are neeeded. If a wallw has to b e rebuilt, thhreelengths of Ribbondd will be neeeded, one oof sufficientt length to wrapwright aaround the pulppchambeer walls. Deepending onn the size off the pulp chamber,ceitther 3mm oor 4mm RibbondTHM is needed.The Ribbbond is wetted with normal resinn, blotted drry with tissuue paper annd then stickky flowis applieed to the uppper surface.If a circumferential wrap is beeing used in the case off a missing wall,w the Ribbbond can bewrappeed around a composite roller and ssticky resin applied. Leeave the Ribbbond on thheroller annd use this to place it insideithe ppulp chambeer. Cover with a light pproof lid unttilneededd.TOOTH PREPARATTION GWMMilicich 20133 all rights reeserved. wwww.advancedeental-ltd.commPage 6

Remove GP 1.5mm into the canals and seal with glass ionomer. Once set, remove anyexcess GIC from the pulp chamber walls and floor to expose clean dentin. Air abrade allexposed dentin surfaces.If a direct bonded composite is used to restore the tooth, selectively acid etch all enamelmargins, rinse and then apply SE bond to all surfaces as per manufacturer’s instructions, airthin and cure. Then apply the first circumferential wrap of Ribbond, ensuring it is closelyadapted to the chamber walls. Close adaptation of Ribbond to the underlying dentin is mostdesirable because this provides the greatest reinforcing effects to the underlying toothstructure.Note the missing mesial wall is now replaced by a layer of Ribbond. Remove excess stickyflow from the occlusal surface and cure. G W Milicich 2013 all rights reserved. www.advancedental-ltd.comPage 7

The seccond piece ofo Ribbond is placed buuccolingually and closeely adapted to the first layerand curred. If a direect compossite is going to be placeed, keep thee Ribbond wwithin the heighthofthe pulpp chamber. If an indireect restoratiion is beingg placed, it doesn’tdmattter, it will bereducedd during final contouring of the onnlay preparation. If the volume off the pulp chambercis signifficant, or there has beeen significannt loss of toooth structure, a third mmesiodistal strip ofRibbondd can be plaaced.Example: Circumfeerential wraap, followedd by buccolingual layer, followed by mesiodiistallayer. GWMMilicich 20133 all rights reeserved. wwww.advancedeental-ltd.commPage 8

The centre of the core is then filled with layers of everX Posterior (a Fibre reinforcedcomposite from GC) or posterior composite until filled, then contoured for the finaladhesive restoration.Continuing with the initial case. The core can then be filled with layers of everX Posterior orother posterior composite and then contoured for an adhesive onlay restoration, retainingas much of the BioRim as possible.Note the overlay contours that put the retained Biorim (red) back into compression whenthe onlay is loaded. This design is also retaining as much enamel on the margins as ispossible. The bonded fibre reinforced core provides a large volume that helps dissipateloads and stresses throughout the tooth in all directions, minimizing damaging stressconcentrations.If a direct composite is going to be placed, two further strips of Ribbond are laidbuccolingually across the tooth to tie the cusps together.Then the composite restoration is completed with posterior composite using incrementallayers. This restoration can be viewed as an interim stabilization of the tooth and allows forthe placement of an adhesive indirect onlay at a later stage without having to go back andreaddress the core status. Removal of the overlaying composite takes you back to theoriginal onlay design and a bonded e.max onlay can be placed. If a bonded e.max onlay isbeing placed straight away, the horizontal layers of Ribbond are not required. G W Milicich 2013 all rights reserved. www.advancedental-ltd.comPage 9