Brief Answer:
Send clear picture of the white patch.

Detailed Answer:
Hi.
Thanks for the query.

Well, once the root canal treatment is completed there should be no pain by now.
So first of all get an x ray of the tooth done and send it to me.
Before I advise you further please let me know the following:

-Is there pain on chewing and biting only or is there pain all the time?
-Is there any swelling also present on cheek or gum?
-Is the cap placed again after root canal? If yes, is there any feeling that cap is too high?
-Are you taking the prescribed medication and if yes, do you have any improvement or pain is the same?
-Do you have any medical problems or are you on any medication?
-Any known allergies?

Now about the white patch.
- First of all click a clear picture and upload, the picture that you have sent is blurring on magnification.
- Is the patch painful?
- From how long it is present?
- Have you experienced tongue bite recently or any injury to the area of white patch with any dental instrument?
-Is the patch scrapable?
-Do you chew tobacco or smoke?

Please write back.

Regards.

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Brief Answer:
Well, then it can be a traumatic ulcer

Detailed Answer:
Hi.
Thanks for writing back

Well, as per your explanation, the patch is due to injury caused by dental instrument causing inflammation and ulceration..

To reduce pain and discomfort do warm salt water gargles.
You can gargle with numbing mouthwash especially before meals.
Suck ice pops.
Avoid hot spicy and sour foods.
Drink plenty of cool water and eat soft foods.

Hope this helps.

Thanks.

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