The simple answer is that your dentist would not visit the yard.
Strangles spreads very quickly and an individual moving from one horse to another can pass blood or saliva which will exacerbate this process. Also, some horses that have recovered from strangles can still harbour the Strep. equi with no outward clinical signs.
Your dentist will take great care to clean and disinfect their tools after each horse, but, even with these precautions the risk of spreading strangles would be too high to take the risk.
The tool in question is referred to as a full mouth speculum. All credible Equine Dentists will use a full mouth speculum to examine and to treat your horses teeth.
Treatment without a speculum is not recommended as the individual would try to control the horses mouth by pulling the tongue outside of the mouth to stop the horse biting down. While moving the tongue might be necessary in a controlled environment for an initial visual appraisal it is not acceptable for working in the horses mouth. If performed incorrectly, it can cause damage to the hyoid apparatus and this will be a problem for the horse. Also, it is only possible, if lucky, to access some of the front teeth this way and does not allow access to the molars.
You should not allow anybody to work in your horses mouth without a speculum. Almost all horses are happy to accept a speculum without any issues if done with care and patience.
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.
In the wild, the horse breeds are usually much purer than domestic horses and ponies. We as humans, have tried to create perfect specimens. If they look nice, move well, jump high or run fast we breed with them, despite their dental problems. Also, horses in the wild will eat for up to 18 hours per day, moving across different terrain and soil types, unlike the horses we keep for our own use. Lastly, if a horse in the wild had poor dental conformation it would not survive and therefore it would not be able to pass on it’s poor dental genetics.
A Category 2 Exemption examination pass from either the WWAED or BEVA. This examination is endorsed by the RCVS and DEFRA and is the only recognised equine dentistry qualification in the UK.