In equine dentistry one must be able to access and inspect the inside of the horse's mouth both visibly and palpably in order to fully examine it. By palpably I mean that it must be felt or touched(palpated) with the hand. The majority of issues inside a horse's mouth simply can't be identified by sight, and the ones that are able to be seen, still cannot be properly evaluated until having felt them. A loose tooth is the obvious example of an issue that can't be detected just by looking at it.
Here's a 39 second video of a woman putting a speculum on a horse.
So a full-mouth speculum is used to hold the horse's mouth open in order to be able to insert a hand, as well as a good bit of the forearm, inside the horse's mouth to feel around.
When a speculum is put on the average horse, he will typically show a small degree of anxiety for a moment or two and then gradually accept it. Very few horses will not accept a speculum, and those who don't, will then need to be sedated before having their mouth inspected.
It's very quick and easy to put a speculum on a horse. You then rinse the mouth out and palpate(feel) throughout the entire mouth for anything which may be abnormal. Very quick and easy, and essential. The only other thing than a speculum necessary for the proper inspection of a horses mouth is a person properly trained in equine dental science who is willing to do a thorough and careful job.
The speculum is an indispensable part of the formula in adequately checking any horse who is showing signs of being compromised by a problem inside his mouth. I'll give you an illustration of how badly things can go wrong when proper inspection standards are not followed and a speculum is not used.
A farrier customer of mine has a 27 year old horse who had just lately been eating less and less of it's usual daily rations. The equine practitioner there giving a mid-winter Coggins test was asked to check the horse's mouth for any potential problems. The vet checked the horses mouth, without the use of a speculum, and subsequently gave the horse a clean bill of health. And in particular, that the horse had no loose teeth.
On my next farrier visit there they asked me to check the horse's teeth. They told me the horse was doing poorly and they were not convinced that there was not a problem inside the mouth. I checked and found a lose, sideways tooth, that not only couldn't bear weight without considerable pain, being in a sideways and impossible weight-bearing position, but had long been rubbing, blistering and callousing the cheek next to it as well. Not only could the horse not chew on that side of its mouth but it had a much larger problem. A horse cannot chew efficiently on only one side of its mouth. Right, a horse does indeed chew on only one side of its mouth at a time, but its method of processing the food that enters it's mouth requires chewing ultimately on both sides of its mouth. Since food inevitably migrates it's way to the bad side of the mouth, the horse is faced with the painful need of having to do something with that food, or swallowing it whole, and the painful predicament leaves the horse to slowly lose interest in eating much at all.
The horse and the owner are now left in a disastrous condition, horse having been diagnosed as having no problem in the mouth and now left to continue to deteriorate-the result of having been attended to by someone who is not an honest dental practitioner-when a problem this common should have easily been remedied, by after properly inspecting the horses mouth in the first place, merely lifting the offending tooth out of the horses mouth, allowing it to eat freely again, and live.
Instead of coming back the next day and pulling it out myself, since I didn't have my molar pullers with me, I suggested that the equine vet would appreciate knowing what had been missed, rather than hearing about it at some later date, and be allowed to come back and correct it.
The equine practioner came back in a week and pulled out not one but two loose teeth.
The lesson to be learned here is that the horse's mouth can have any number of serious issues needing attention which will be left undiagnosed and untreated without the use of a speculum; not to mention without the necessary integrity of the attending practitioner. The illustration above helps us understand why this is important information to have. Also why second opinions can be vey useful.
The full mouth inspection of a horse without the use of a speculum cannot be done. A very valuable point to bear in mind come dental evaluation time.