[文法] 請問此句的逗點是否可以省略

[peace5566 (和平使者5566)]

Teeth go from being closed, with the tongue just behind the bottom teeth to
parting with the tongue coming through.

問題1.請問請此句的逗點可否省略

問題2.請問 "to parting"的to是介係詞嗎
      不然為什麼是V-ing?

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