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What is Ludwig's angina usually begins in which of the following space? and explain in detail?
Ludwig's angina is an acute, potentially life threatening, toxic cellulitis, beginning usually in the submandibular space and secondarily involving the sublingual and submental spaces as well. The disease is not usually considered to be true Ludwig’s angina unless all submandibular spaces are involved. 
Ref: Shafer's textbook of oral pathology 7th edition page 510