There are plenty of dental clinics around Qatar. I recently had a filling done at Qatar Medical Centre (Salwa Rd)which I was happy enough with from standard of work & cost. They do root canals but I am unsure of the cost but feel free to contact them via the contact section of their website www.qatarmedicalcentre.com (or if so urgent, try dropping in maybe they can see you at short notice?). Good luck!