How toothache can cause sinusitis , with knowing the tooth with root canal treatment (upper right first molar)?

Tooth\sinus problems: Toothaches do not cause a sinusitis. If you have an infected upper tooth whose root is near the floor of the maxillary sinus, and it has an infection (whether or not it has had root canal therapy), the infection can spread to the sinus causing a sinusitis or sinus infection. A sinusitis or sinus infection can present as a toothache even if nothing is wrong with the tooth.

Complicated but yes: For an upper molar, the tooth roots are often very close or in the sinus separated by only a small amount of bone and membrane (like very thin skin). So a tooth with (or without) a root canal can develop an infection (full of bacteria) and invade the sinus. As the bacteria go untreated, a sinusitis (inflammation, congestion, some discomfort) can develop. Get the tooth fixed and go from there.

Not unusual: The roots of the upper first molar are often very close in proximity to the maxillary sinus. A sinus infection can cause a toothache, and a tooth infection can cause sinus pain. Or the two can occur independently. This tooth is the most common one for a root canal to fail due to its complexity. Seek evaluation by an endodontist, preferably one with 3-d imaging (cbct). Usually treatable.