A periodontist is a dentist who specializes in the prevention, diagnosis, and treatment of periodontal disease, and in the placement of dental implants. Periodontists are also experts in the treatment of oral inflammation.
Ground speed. Ground speed is the horizontal speed of an aircraft relative to the ground. An aircraft heading vertically would have a ground speed of zero. Information displayed to passengers through the entertainment system often gives the aircraft ground speed rather than airspeed.
Court speeds. The ITF do categorize surfaces, category 1 (slow), category 2 (medium/medium fast) and category 3 (fast), though the time of day, weather, temperature and type of ball being used all have a bearing on how fast the courts play.