Dental hygienists can become members of the New Zealand Dental Hygienists' Association. In Ontario, dental hygienists are registered with the College of Dental Hygienists of Ontario (CDHO). This includes&colon; dentists, dental specialists, oral health therapists, dental hygienists and dental assistants. The dental team includes dental assistants, dental hygienists, dental technicians, and sometimes dental therapists. Dentists and dental hygienists can instruct and demonstrate proper brushing or flossing techniques. Dentists and dental hygienists measure periodontal disease using a device called a periodontal probe. Some dental hygienists are licensed to administer local anesthesia and perform dental radiography. Specialists such as Chiropractors, Optometrists, Dentists, and Hygienists travels in every two-three months. Ontario dental hygienists must also prove continuing competence by maintaining a professional portfolio yearly. Oral cancer screening is also recommended by some groups of dental hygienists. These fields include occupations such as dental hygienists, and other professional and sales support. Registered dental hygienists must register every year by December 31. Environmental and occupational hygienists are considered experts in exposure science and exposure risk management. Periodontists and hygienists must visualize plaque and calculus to remove it. Another type is used by industrial hygienists and first responders.