Dental Eruption

Eruption - proceeds throughout the life of equine CT, thought to be between 2 - 4 mm per year. It is this eruption, and subsequent wear of the two softest tooth substances Dentine& Cementum which exposes the relatively unworn harder substance Enamel. It is these Enamel points that cause the majority of the soft tissue traumas.

Deciduous teeth - Between the ages of 2 1/2 and 4 1/2, a horse will need to shed 12 incisor caps and 12 premolar caps. Cap shedding times can vary considerably from breed to breed. Thoroughbreds are generally the earliest with premolars shed around 2.8, 2.10 & 3.10; however this will vary from one continent to another. Cap retention or sometimes, only partial retention along the gum margin is very common. This can cause considerable short term pain, removal giving immediate relief. Asymmetry of shedding will result in imbalances of the Arcades.

Wolf teeth

Anterior- Anterior Maxillary are the most common.

Lingual / Medial - Very common, not always that firmly attached, seem to cause less problems than the rest.

Mandibular - Uncommon, seen a little more often in American trotters

Blind / un erupted - Very common in all breeds, comes in various shapes, sizes and degrees of annoyance for the horse.

Wolf teeth - are the first premolars, a Vestigial tooth that serves no purpose at all. The majority of horses will have Wolf teeth present by the age of two, thoroughbreds by yearlings. They come in various shapes, sizes and locations, not necessarily the largest and most visible causing the most problems. Small, needle like Anterior Maxillary or Mandibular Wolf teeth interfere more with the bit than a large, well rooted wolf tooth or Lingual wolf tooth.

Un erupted or Blind Wolf Tooth are most commonly positioned about 2 1/2 cm Anterior of the 1st CT with the root Caudal to the crown. This angulation of root to crown prevents the tooth from cutting through the tissue, giving the appearance of a wolf tooth not yet ready for removal. In reality, if a wolf tooth hasn’t erupted by the age of two, it’s probably not going to. The best solution for any wolf tooth is early removal.

Developmental disorders/disease

Supernumerary teeth - Are not uncommon in horses, they generally develop caudally to the Maxillary 6th CT & usually abnormal in shape and size. Due to their irregular shape and positioning, Periodontal food pocketing often occurs in the Diastema between them and the 6th CT, as a result, these teeth can become very painful.

Impactions - The Mandible of a young horse commonly has large eruption bumps due to vertical impaction of the developing CT. Excessive angulation of Caudal and Rostral CT leave very little room for eruption of CT in the middle of the arcade. The Mandibular 8s are the teeth that suffer as they are the last premolar to shed, by which time, those around them are already well established. These large eruption bumps can occasionally lead onto Apical infections.

Rotated / displaced cheek teeth - Often the result of overcrowding during eruption, or tooth buds developing too far apart, causing a Diastema, this in turn can cause Periodontal food pocketing (most commonly Bilateral displacements). Insufficient angulation of Caudal & Rostral CTcan also be a contributor.

Diastema and ETR - Transverse ridges on the occlusal surfaces of cheek teeth are very much a part of the horse’s normal dentition; they are vital to their ability to masticate long fibres and should be left well alone. However, exaggerated Transverse ridges should be rectified. These ridges will regularly develop, especially on the occlusal surfaces of CT opposite a Diastema due to lack of attrition. When present, these abnormal ridges will widen and force food into the Diastema. During Mastication, when even more food matter is compressed into the Diastema, causing pressure on the already painful Periodontal area, the horses will probable Quid.

Rostral and Caudal hooks

Focal overgrowths gradually form on the Caudal and or Rostral cheek teeth; this is due to Rostral positioning of the Maxillary CT Arcades in relation to the Mandibular CT Arcades. Even at an early stage, these hooks begin to reduce the amount of Lateral and Anterior / Posterior movement of the Mandible.

Incisor reduction/realignment (Incisor slant)

The differences in chewing patterns from natural rough grasses to processed food causes lack of incisor wear. Over a period of time, the incisors become overlong, this causes a Malocclusion of the molar Arcades and an imbalance of the three balancing points, incisors, molar Arcades and TMJ. With the incisors touching and the molar Arcades completely lifted apart, many horses will exhibit TMJ pain and muscle pain in the neck and poll areas. The most immediate result of overlong incisors is lack of efficiency in Mastication, causing the horse to Quid or try to pass larger than optimal pieces of hay, increasing the risk of impaction colic. Another result of this incisor imbalance is abnormal wear of the molar Arcades.

The incisors should NOT be reduced to the extent there is a gap between the upper and lower incisor occlusual planes causing permanent cheek teeth Occlusion. Free Lateral Excursion and molar table angle is what should cause the incisor separation.  It is not normal for the cheek teeth to be in full Occlusion when the incisors are in a closed and centred position.

Severe incisor slant will dramatically reduce the amount of molar Occlusion during Lateral Excursion on the poor side only. Resulting in excessive wear of occlusal surface and repetitive strain on the large masseter muscle and TMJ on the other side. Focal overgrowths are also likely to form on the side receiving little or no wear; this in turn accentuates the problem.

Diseases

Periodontitis - Displaced and or rotated CT are the most common causes of food pocketing and Focal gingival retraction. Food matter packed between displaced CT is the major contributor of Periodontal disease, which, if effecting the Maxillary CT (1/10, 1/11, 2/10 and 2/11) can result in Secondary Sinusitis.

Trauma

Incisor fractures - Traumatic fractures to the incisors are quite common, although a high percentage of incisor fractures are of the Clinical Crown only, showing no sign of pulpal exposure. In these cases just the fragments can be removed and the root left in place. Loss or mal eruption of incisors can cause uneven occlusal wear that can affect Mastication.

Cheek teeth fractures - traumatic fractures from a kick or fall are not uncommon but Pathological fractures are probably the largest contributor. Degenerative dental disease i.e. infundibular Necrosis comes in the form of "Decay" caused by the loss of Cement in the infundibular (cementumhyperplasia) This Decay creates a weakness running the length of the tooth, a major contributor to sagital fractures. It is very common to have Bilateral pathological fracture of this type.

Molar extractions - Diagnosis of Apical infection requires X-Rays, not just to confirm an infection, but, if considering extraction, to be absolutely sure it‘s the tooth you think it is, and to check the exact angle of the Reserve Crown. When possible, oral extraction of affected CT is advocated, it reduces the risk of general anaesthesia and has much less post-extraction aftercare than CT repulsion or buccotomy. Oral extractions of CT, unless relatively loose, are best carried out in a clinical situation.

Molar X-Ray	(Extracted cheek tooth showing signs of chronic Apical infection) (Picture courtesy of Jan Hagstrom,Sweden)

Anterior / Posterior (A/P Movement ) (and Lateralmandibular block - Anterior / Posterior and Lateral movement in a horse is essential if a horse is to have optimum efficiency in Mastication, be balanced and be relaxed through the poll and neck, and without an over elevated head carriage. When a horse elevates its head, the Mandible slides in a Posterior direction, returning to normal when the head is lowered. When lowered, it slides in at Anterior direction. A small amount of Anterior / Posterior movement, and uninhibited Lateral Excursion is also vital to normal Mastication. When these Rostral or Caudal Hook, or in fact any focal overgrowth forms on the occlusal surface, essential Anterior / Posterior slide is compromised. This movement is also effected by severe incisors angulation.

Vertical and Lateral balance

Balance is the basis of any discipline; you need both vertical and Lateral balance. The vertical balance is determined by the position of the horse’s head which in return affects the position of the body. When a horse is vertically balanced the horse’s nose is neither pointing forwards, causing the body to tip too far forward, or the head over elevated, making the body tip backwards.

Lateral balance requires the horse to have even weight distribution, this is impossible if the head is too low, over elevated, or tilting to one side. For instance, if the head tilts with the nose to the left and ears to the right, automatically, the weight is transferred into the offore leg, making the horse heavy in the rider’s right hand. Many of these problems are caused by focal overgrowths!

Vertical Balance	Lateral Balance

Myth and Truth

Myth:  Power equipment takes too much tooth off! 

Truth:  Do NOT blame the tools! The person using the power equipment took too much tooth off, which they also could just as easily have done using a sharp rasp! Some, but not all power equipment enables a competent person to accurately correct a cheek tooth overgrowth by taking miniscule amounts of tooth off at a time!

Myth:  The dentist took so much tooth off, my horse was Quidding hay for three days.

Truth:  Your horse was a little uncomfortable and took a couple of days to readjust; if he'd had too much occlusal surface removed, he would Quid for months NOT a few days!

Myth:  You can fix everything in every horse's mouth with a rasp and without ever using sedation.

Truth:  Most horse's will happily let you do the 'routine' rasping without sedation. BUT, if you NEVER use sedation and only use a hand rasp, you are missing a lot of corrective work which later in life will manifest as advanced dental disorders!

Myth:  Power equipment over heats the teeth

Truth: Please read 'Study on thermal damage' below

Study on Thermal Damage

A veterinary study took place were a series of teeth were taken from horses skulls, isolated, with no adjacent teeth, and with no normal bone, gum tissue, blood supply or cheek touching them. A Power Float was then applied to each tooth for varying amounts of time and the temperature of the teeth were recorded with a heat monitor embedded in the tooth. The findings were, after a full minute, at full speed, in one spot, the temperature rise was found to be non damaging! With increased application of two full minutes, on the same tooth, a rise in temperature was recorded that could be harmful to living teeth.  

Conclusion:   Yes, you should be careful not to keep a power float on one tooth for long periods of time, why would you? You should also only use well maintained sharp equipment that doesn’t create heat build up or transfer heat from cutting tool to the tooth.

Equipment

The majority of ‘routine’ dentistry, can be performed using hand rasps with good quality blades. Most well mannered horses will not only tolerate routine dentistry, but, a high percentage, will behave like they almost enjoy it. Doing most routine dentistry using hand rasps, also means fewer horses will require sedation. When I say 'routine dentistry, I am referring to dentistry performed on horses with good mouths at six monthly intervals. I have found a lot of people who are anti sedation and power tools, are oftern the same people who only get their horses teeth done every five years after they have already developed a problem.

Advanced dentistry however, is a different story all together. Large Cheek Tooth ‘CT’ overgrowths, especially those on the 6th Mandibular CT, can NOT be satisfactorily reduced using hand rasps! By being able to accurately reduce ONLY the tooth concerned, and NOT rasping the adjacent teeth while trying to get to the problem area, (contrary to popular believe), using power equipment to reduce focal overgrowths actually saves more vital tooth material than using hand rasps. This is in part due to rasp blades generally being 3 ¼ inches in length, and CT crowns being about 1 ½ inches from front to back. Therefore, a rasp blade will cover just over two CT, and that’s before you start to move it backwards and forwards. It doesn’t take a scientist to work out, by trying to use a hand rasp to bring a CT overgrowth in line with the rest of the occlusal surface, will sacrifice vital chewing surface of the adjacent teeth!

 I use a quiet, high torque and low speed power tool, this reduces heat build up and makes a lighter sedation possible.

Conclusion: Do routine dental maintenance where possible with hand tools, But, don’t ruin a horse’s dentition trying to perform advanced dentistry with basic equipment!

Dental equipment should be kept in a Clean and hygienic condition. A stainless steel bucket containing a chlorhexidine solution is used to soak rasps and speculum.

Clean Equipment	Chlorhexidine solution for soaking rasps