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What is Classical monoblock in restorative and endodontic literature is: and explain in detail?
The combined use of a core material and a cement/sealer in contemporary endodontic obturations and fiber post adhesion introduces additional interfaces into a monoblock. 
Secondary monoblocks are those that have two circumferential interfaces, one between the cement and dentin, the other between the cement and the core material. 
A secondary monoblock is the type of monoblock that is classically perceived in the restorative and endodontic literature.