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Dental TribuneAsia Pacific Edition | 9/201510 TRENDS&APPLICATIONS Evidence has shown that one of the biggest challenges facing dentists todayisrestoringseverelydamaged teeth.Inorderfor theserestorations to be long lasting, certain biome- chanical and biochemical criteria need to be met.Even the smallest of cavitiescanresultindramaticfailure owing to poor material choice and incorrect biomechanical interaction betweenthetoothandthematerial. We often see cases where a small cavity was restored with amalgam a few years prior. The amalgam it- self meets the material criteria but the biomechanical issues are clearly evident and cause severe cracks to develop. These cracks could lead to complete failure of the restoration with loss of vitality of the tooth, and possibly even loss of the tooth. Amalgamhaslongbeenreliedupon as a durable restorative material. Butwhatvalueisarestorationitself that lasts for 20 years if the tooth fails? The final objective should be preservation of the tooth and not necessarily preservation of the restoration. Cavity design When it comes to restorations of this nature there are two goals: to stopcrackpropagationandstopping newcracksfromforming.Toachieve this you will need a good material andasoundapproach.Whenitcomes to cavity preparation, the sharper theangles,thehigherthestresscre- ated in the cavity. The difficulty to- dayisthatasdentistsweoftenhave to redo restorations with existing cavity designs for amalgam but re- store those cavities with another material. Inaddition,thetoothwillalsobe damagedtosomeextent.Ourchal- lenge is to minimise this damage by making good choices in cavity designandmaterial.Theprinciples ofcavitydesignarewellestablished: the width of the cavity should not exceedhalfoftheintercuspalwidth. This means the surrounding tooth structure is strong enough to func- tion with the restorative material inside. It is recommended that you needbetween2–2.5mmofwallthick- ness in order to maintain good in- trinsic strength. It is clear that if we don’t respect these criteria and the cavity ends up with very thin and undermined walls, biomechanical failure will occur. Ourbiggestprob- lem here is that we get cavities like this to start with. It’s not necessarily our choice to drill a cav- itylikethisforcariesre- moval. Often times an old amalgam restoration can lead to this type of cavity and the temptation is to keep the remain- ing tooth structure to enable a di- rect restoration. The tendency is to keep those cusp tips, as references for occlusal morphology and to pre- serveasmuchtoothtissueaspossi- ble. Because the walls are clearly not thick enough the load bearing forceswillcreatefatiguewithinthe cusps. Even with a bonded resto- ration, this fatigue will eventually cause the wall to fracture. The fol- lowing clinical situations call for cuspal coverage: 1. A wide isthmus and thin walls. 2. Ifthereisnodentinalsupportand cuspsareundermined—blocking outtheunsupportedenamelwill not solve the problem because curing a composite inside a shell will fracture it. 3. A horizontal crack in the under- mined base of the cusp. 4. A longitudinal MOD crack. 5. Any crack inside the pulp cham- ber. 6. An endodontically treated tooth with MOD restoration requires coverage for all cusps. 7. An endodontically treated tooth withacrackinthepulpalfloorre- quires all cusps to be covered. everX posterior Whatisneededfortheserestora- tions is a material that will bond to the tooth. This is not a guarantee that the restoration will work, but some sort of adhesion is required that is not mechanically retained like amalgam. What is needed is a materialthatbehavesliketooth structure, something that resists fatigue and also in- creasestheloadbearingca- pacity of the total restora- tive complex of the tooth with the restoration. everX Posterior (GC) fibre-rein- forced composite material offers Tips and strategies for restoring large cavities using fibre-reinforced material By Drs Stephane Browet,Belgium,& JavierTapia Guadix,Spain 1g 1h 1i Fig.1a: Pre-operatory.—Fig.1b: Preparation.—Fig.1c: Bonding.—Fig.1d: Enamel wall.—Fig.1e: everX build-up.—Fig.1f: Enamel built-up.—Fig.1g: Staining final.—Fig.1h: Polishing.—Fig.1i: Final. 2i 2j 2k 2l 1a 1b 1c 1f1e1d Fig.2a: Pre-operative view.—Fig.2b: Occlusion and articulation should be considered,they guide the layering for final morphology.Isolation with a rubber dam is recommended for a controlled protocol,optimal view and access.—Fig.2c: Cavity after removal of the old restoration shows decay.—Fig.2d: Another view of the decay under the old amalgam restoration.—Fig.2e: Caries removal and finalisation of the cavity prepara- tion.—Fig.2f:Cavityafterthebondingprocedure.—Fig.2g:Sectionalmatrixplacementandseparationring,awedgeadaptsthematrixtothetoothinthecervicalarea.—Fig.2h:Build-upofthemesialwallintwocon- secutive separately light cured layers.—Fig.2i: Internal build-up with everX Posterior.—Fig.2j: Finalised occlusal morphology.—Fig.2k: Final result.—Fig.2l: Follow up. 2a 2b 2c 2g2f2e 2d 2h DTAP0915_10-12_Browet 08.09.15 09:35 Seite 1 DTAP0915_10-12_Browet 08.09.1509:35 Seite 1