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The soft sac containing fluid is a
MUCOCELE which is formed either due to trauma to any minor
salivary gland or its ducts or any traumatic
injury to the duct of major salivary gland and as it is under tongue it can be due to either submandibular or Submental salivary glands which are major salivary glands..
You can also have a
Sialolith or salivary gland stone and it can cause swelling under jawline and floor of mouth but a blue black swelling is a MUCOCELE most probably..
You should
consult a dentist and get evaluated..
1. For Mucocele mostly treatment is not required but if it doesn't resolve surgical removal has to be done..
2. For salivary gland stone take more of citrus foods and candies that simulate saliva flow and small stones can be flushed off with saliva flow..
Large stones need either manual removal by an expert or surgical removal has to be done..
Hope this information helps..
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Thanks and regards.Dr.Honey Nandwani Arora..