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The white line on the side of your tongue is normal if you've been grinding your teeth and likely biting your tongue at night. It is, essentially scar tissue an this is quite common. But if the pain is worsening - not getting better after the recent mouthguard / night guard your dentist may need to adjust the night guard to make it less likely that your tongue will get caught while biting during your sleep. He may be able to do so by simply beveling the area on the night guard where your tongue is being bitten. I would recommend having your dentist do so.
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