As with any practitioner and professional you engage, do your homework with regard to dentists. While the opinion and experience of another person may be helpful, it is important to be responsible to yourself in choosing the dentist who will provide the work you need.  As in medicine, specialties are board certified in Mexico.  While it’s not required that a practitioner be board certified to practice in a particular area, it helps to assure patients that if a dentist says he’s qualified in a particular area, he has met certain standards of expertise.

If you are having major dental work, such as bridges and dentures, root canals, surgery or implants, interview the dentist before you agree to treatment to make sure that you and he/she are understanding each other as to what is wanted and needed.  The extra cost in setting up a few interview appointments prior to procedures might save much costly and difficult reconstructive work that wasn’t done properly the first time.

Many dentists will refer to specialists for work that she/he does not perform in his/her office.  Again, do your homework so that you can feel comfortable with the specialist and what is involved with the treatment.

In the United States the term ‘Cosmetic Dentistry’ is not a recognized specialty, and refers to any procedure which changes the appearance of the teeth or mouth.
No information was found with regard to the use of that term in Mexico.  It is recommended that you ask the dentist what his/her definition of cosmetic dentistry is, and determine how to proceed for yourself.

Some valuable information regarding selecting a dentist can be found at Travel 4 Health and Retirement.

Dental Hygiene in Mexico is most frequently done by the dentist, as there is no dental hygiene profession. There are some trained dental hygienists from outside of Mexico who practice here.
There is no licensure or certification that can be verified.  If you see a free-standing dental hygienist it may be of value to ask to see the credentials from their home country.