The platysma muscle sheet rises up over the mandible & inserts near the corners of the mouth, so it seems possible that overtightening could cause this. Among other functions, the platysma is a lip depressor - it balances the smile http://www.michaelevansachs.com/newyorkplasticsurgerynyc/plasticsurgeryresearchdocs/TotalPlatysmaResection.pdf Tho this article is about crooked smiles where the platysma is NOT PULLING on one side, it does convey what may happen if there's TOO MUCH PULL. Arguably, overly tight medial plication may pull the mouth corners down & inwards, while over tightening to behind the ear lobes could create a low wide sardonic grin. Comments please from surgeons?