Ideal Occlusion

Meaning (n): The relationship existing when all teeth are perfectly placed in the arcades of the jaws and have a normal anatomic relationship to each other.  When the teeth are brought into contact the cusp-fossa relationship is considered the most perfect anatomic relationship that can be attained.

In the practice of equine dentistry the goal of the Equine Dental Practitioner is to achieve ‘ideal occlusion’ for the client, then maintain that ‘balance’ throughout their association with that animal.

It is not possible to achieve ideal occlusion and then maintain it if the practitioner has no concept of exact base normal or what would be ideal occlusion for the animal being treated.

This may seem like a simple concept, but the truth is with the proliferation of quick educational techniques and the availability of more effective sedation and power equipment, very few of the practitioners performing equine dental treatments have a true understanding of the physiological changes they are initiating or ceasing.

The normal physiological changes to teeth are initiated by the usual forces applied i.e. genetic, congenital, traumatic chemical, thermal, environmental etc and in most instances of normal life these changes are slow bordering on microscopic; however in some cases such as trauma the changes can be rapid.

When practicing equine dentistry the changes initiated would be more in line with trauma than normal physiological wear; that is not to say that procedures shouldn’t be performed or that you shouldn’t perform some treatments more aggressively if necessary.

One obvious example is a horse with large caudal hooks – those hooks took a long time to evolve but in most cases would be removed in one treatment – the certainty of this treatment is there will be dramatic secondary effects to the stomatognathic system as a whole; therefore it is essential to ensure the prognosis of these changes is positive or as positive as can be achieved.

A major concern when diagnosing a treatment for an individual case is the prognosis for the immediate and long term future of the animal. This cannot be achieved without knowledge of the animal’s history and his present situation. This knowledge is paramount as it gives the practitioner an insight into the path of wear the mouth is taking along with a combined knowledge of ‘ideal ‘balance’ or the closest the individual could come to ‘ideal balance’.

The variance between these two mouths would be:

  1. The mouth as is

  2. Hypothetically how the mouth could or should be

This determines the best course of treatment for the animal concerned.  If the best possible result is not achieved on completion and for many reasons it is not always possible to achieve ‘ideal balance’ (i.e exodontics) then there will be negative physiological changes that need to be considered.

When ‘ideal occlusion balance’ is achieved in an individual the best possible normality of the stomatognathic system is achieved on a number of very complex levels i.e. muscular balance and health, cardiovascular health, nervous system function, saliva flow and viscosity chemical balance, structural soundness of head, neck, back, tongue, digestive system and indeed the whole body.

When ‘ideal occlusal balance’ is not achieved the animal’s body will do the best it can to recreate normal occlusal balance as rapidly as possible, not always to good effect e.g. laying of sclerotic or tertiary dentin, cementoblastic proliferation, rapid eruption of teeth, osteo clast/blast changes to move out occluding teeth to normalise pressure.

If teeth are left too low or reduced below the ideal occlusal levels they will erupt rapidly so as to recreate more normal occlusal pressures. If teeth are left too high, bone will redevelop and shift teeth to reduce occlusal pressures to normal. Normal occlusal pressures are registered by the mechanoreceptors located in the periodontal ligament – in humans the most sensitive of these receptors is located in the fulcrum of the tooth and the least sensitive at the apex. Horses (due to reserve crown differences) would probably vary but would be unlikely to vary to much from this concept.

These receptors are involved in the:

  1. Jaw opening reflex (mediated by low threshold receptors)

  2. Tactile sensation in the control of the maximum biting force

  3. The masticatory salivary reflex (probably more important in horses)

Imbalances to occlusal pressures created by equine dentistry, which do not achieve ideal occlusion (not always adverse or severe) will allow the animal’s body to initiate changes to recreate ideal occlusion.

If a practitioner has a clear understanding of true ideal balance then these processes may be used to the animal’s advantage over a period of time to better achieve a positive prognosis for the animal being treated.

If the practitioner has little or a poor understanding of ideal occlusal balance the future prognosis for these animals is poor.

As an example a modern misconception is that bite realignment should be carried out every time a horse has its teeth treated. This train of thought is one of the more detrimental concepts to emerge with modern dentistry and has been developed to justify sedation with every treatment.

Let us look at this concept more closely so what we are trying to achieve we first understand.

There are two major components to dental equilibration (the modification of occlusal forms of teeth by grinding with the intent to equalise occlusal stress):

  1. Realignment
    Realignment is the art of resetting the balance of the dental arcades in an attempt to achieve ‘ideal balance’ of the horse’s mouth.  If realignment is performed incorrectly this will cause a condition called ‘Pathogenic Occlusion’ which will always have a detrimental effect on all the stomatognathic systems.  Chronic Pathogenic Occlusion is now a common phenomenon.

  2. Reduction
    Mechanical reduction of teeth is called occlusal equilibration and is a common component of equine dentistry, however once ideal occlusion is achieved the amount of reduction should be minor at the occlusion level and would be more to do with unworn enamel points. Chronic over reduction would be a catalyst for pathogenic occlusion and is a major contributor to hyper wear/eruption and stomatognathic system failure.

If we realign and re-establish normal occlusal heights and angles the incisors stay at a normal angle and height and if ideal occlusal balance is achieved then reduction is not required for approximately 10 years in most cases.

However, realignment is totally different in a malocluding situation, as the mouth may require realignment more regularly.

To confuse reduction with realignment will shorten a horses dental longevity; in the case of central incisors by between a 1/3 and a ½ of the normal life.  The normal enamel component of an average sized horse will be approx 50mm long at first occlusion stage (around 3yrs of age) and will be worn to the apex around 21 years.  This represents 18 years of normal wear (individual horses may vary, but this would be typical) and averages wear at 2.78mm per year throughout the enamels life.  If we reduce this enamel and an additional 1mm every year this enamel will last 13 years or be finished at 16 years of age.  If we reduce by an additional 2mm per year this will result in a life expectancy of 10.5 years or worn out at 13-14 years of age.

This process applies to all ‘over reduced’ teeth which is not to say reduction of teeth is bad but chronic reduction techniques are detrimental once ideal occlusal balance has been achieved.

Equine dentition that conforms to the requirements of ideal occlusal balance will show less individual tooth wear and therefore the prognosis for longevity in the individual is greatly increased.

Chronic over equilibration will lead to shortened life expectancy and in extreme cases (which are not uncommon) will lead to systemic failures and serious secondary pathologic conditions.

Warwick Behrns

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