It looks like a muscle spasm from prolonged mouth opening during treatment. It generally gets better overtime, however if you have taken a medicine for it and still are not getting cured then you should visit a TMJ disorders expert so that they can rule out any possibility of joint related issues.

Since your root canal treatment, you have developed restricted mouth opening that has persisted for more than a month. This can occur due to muscle spasm/trismus or a temporomandibular joint disorder, particularly after prolonged mouth opening during dental treatment. However, the exact cause cannot be confirmed without examining your jaw movements and measuring your mouth opening. Since there has been no significant improvement after a 7-day course of medication, I would recommend an evaluation by a dentist/oral & maxillofacial surgeon or a clinician experienced in TMD rather than starting another medication on your own.

Put a damp warm cloth on the side of your face  and gently massage the tight jaw muscles and relax.

Hi sir it seems like you had a lock jaw ( based on history given) .You need to visit a dentist and get it treated properly to improve your  mouth opening. Do you have any pain while mouth opening because your doctor prescribed a pain medication.Take a opg to assess the TMJ or any other reasons.You need mouth opening exercises for better opening.

Limited mouth opening after a dental procedure can sometimes occur due to muscle spasm or strain from keeping the mouth open for a prolonged period. However, since your problem has continued for more than a month despite medication, it should be examined rather than taking another medicine on your own. A dentist should assess your mouth opening, jaw muscles, TMJ and the tooth that underwent root canal treatment to identify the exact cause. Depending on the findings, treatment may include warm compresses, appropriate jaw-opening exercises/physiotherapy and medication if required. Avoid forcefully stretching the mouth or repeatedly trying to open it wide without an examination. Please schedule an in-person dental/TMJ evaluation, especially if the opening is worsening, painful, associated with swelling, or affecting eating.

Hlo sir…TMJ problems after an RCT can occur due to keeping mouth open for a long time,muscle strain,prolonged procedures,or an altered bite from a high temporary or permanent restorations. But if the pain persists even after 1 month of treatment may not be due to root canal treatment itself.common reasons include:- 1.prolonged mouth opening during rct 2.High bite after RCT or crown placement/restoration 3.Muscle spasm/Myofascial pain 4.pre existing tmj problem 5.u clench ur teeth while asleep 6.pain referred from treated tooth or another tooth.

Can you specify which tooth was treated??? And do you experience pain while opening your mouth or any other pain near or in front of the ear??? For care from your side you can use cold compression for next 2 days and then moderate warm compression along with taking care of your oral health - rinse off with water after every meal And visit the doctor after you complete your medication dose.