It is always a good idea to get them used to the Equine Dentist as soon as possible.  In much the same way  that you would get you horse used to the farrier, it is important that they are also used to the dentist.

Initially your dentist would handle the young horse and then introduce the speculum. the speculum would be opened slightly and your dentist would introduce their hand into the young horses mouth and then close the speculum again. the speculum may be left in place, in the closed position so as not to tax the jaw muscles, to get the young horse familiar with the feel.

This process will also allow the dentist to examine the mouth to ascertain if there is anything e.g. wolf teeth, bone spurs, caps (baby teeth) etc.  which can cause problems for the horse in later life. Your dentist should make this a pleasant experience for the young horse.