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What is Total space analysis by Merrifield requires: and explain in detail?
Total space analysis by Merrifield;

Requires study casts and cephalograms.
Divides the lower arch into anterior, middle and posterior areas.
The discrepancy for each area is calculated and the resultant value is added to yield the total discrepancy of the arch.

Total space analysis as described by Merrifield is divided into three parts anterior, midarch and posterior.
This is done for simplicity in identifying the area of space deficit or surplus, as well as accuracy in differential diagnosis.
Ref: Graber 6th edition