The presence of the fourth canal in maxillary first molars is high and nearly 90 percent (depending on the studies and methods, this percentage varies). One of the common causes of root failure failure is the discovery and treatment of this canal, which may cause pain, endotracheal lesions, and even abscesses and swelling. Experienced dentists with an unobtrusive eye may have discovered this channel with a chance of about 30% (depending on the experience, the use of appropriate detergents and the ultrasonic device of this percentage varies). Using eye rings with a magnification of 3.5 times can increase the chance of success by up to 20 percent. However, dental microscopes with a magnification of 10 to 16 times increase this amount by up to 80%. Given the anatomical complexity of the teeth and even the racial variation, root canal therapy (also called neurology) is one of the most complex therapies.