By Laura Osman THE CANADIAN PRESS OTTAWA- The Parliamentary Budget Officer estimates the promised federal dental insurance plan will cost $2.9 billion less than the government budgeted, assuming provincial governments don’t drop their coverage. The Liberals promised a stand-alone dental insurance plan for low- and middle-income Canadians who don’t have private insurance as part of its supply and confidence deal with the NDP last year. The program is expected to launch before the end of the year, starting with qualifying people under the age of 18, people with disabilities and seniors. The Liberals initially set aside $5.3 billion over five years to launch the program, but increased that amount to $13 billion in the last federal budget based on internal estimates about the true cost of the program. The Parliamentary Budget…