Occlusal (Mouth) Guards – Designing Criteria

As dentists we have to diagnose for and make mouth guards for patients for the purpose of defeating the habit of teeth grinding or clenching. Yet in most dental practices the design of this occlusal device is usually determined largely by the efficacy of the dental lab the office works with, in making a device that requires minimal chair time to fit it to the patient. The underlying concepts of occlusion, TMJ ( joint) health status and the accurate analysis of the underlying cause of associated symptoms plays an even larger role in the design than dental lab’s efficiency. However these topics can be intimidating to the average practitioner because it involves not just gathering a good understanding of the concepts but also developing the deliberate discipline to utilize these skills in the office as a matter of routine. This is my attempt at a decision tree that will help in the analysis and determination of the design of the occlusal guard for most patients.

The simplest classification of occlusal guards is based on the material used – soft or hard plastic. For the purpose of this discussion I will be focusing on the hard occlusal guards. The soft ones are largely for a temporary relief of muscle and joint discomfort.

The hard plastic occlusal guards can be classified by area of coverage such as full arch, anterior coverage only, with or without a bite plane or a bite ramp. But it is more effective to classify them for the purpose they are intended for.

Even though the occlusal guards are for the treatment of teeth clenching and grinding habits, the design criteria will depend on

  1. a) Whether the patient admits to the awareness or knowledge of these habits or the dentist discovers signs and symptoms usually associated with these habits namely teeth wear, cracked fillings or teeth, teeth sensitivity, abfractions
  2. b) Symptoms and signs indicating involvement of masticatory muscles such as headaches and neck cramping
  3. c) In extreme instances accompanying joint related symptoms also.

Mouth guards can therefore be for intervening a habit without associated symptoms in the muscles and joints or for specifically alleviating the associated symptoms also.

Patient with healthy TMJ:

The principle of the mouth guard is to move the bite as forward as possible using either a flat anterior bite plane or an anterior guidance bite ramp. The size of the mouth guard can be a full arch or limited to a few front teeth like the NTI design.

Full arch with anterior flat plane

NTI appliance

Both these designs tend to help reduce the musculature stress and also helps the jaws to realgin to a Centric relationship position.

The two instances when a full arch design will not work is when the teeth are buccally or lingually or labially tipped which makes seating of the mouth guard difficult or when there is supra eruption of the back molars. The ‘front-limited coverage only’ mouthguards like the NTI have there own limitations such as lack of retention on short teeth, uncomfortable bite when the opposing arch is uneven due to misalignment. Because of its tendancy to reposition the jaws into ‘centric’ these mouth guards might have unintended consequences of the patient experiencing premature contacts at the second molars and sometimes even an anterior open bite. These are purely due to the change in the positional relationship of the lower jaw to the upper jaw.

Patients with joint pathology:

The designs discussed in the earlier paragraph will not be inappropriate for patients with Symptomatic TMJ.

The jaw-joint acts as a class 3 lever.

For a person with inflamed TMJ the difference in the effect of a bite at the incisor end is easily elicited when comparing trying to bite a soft material like cheese vs a hard substance like a nut. The latter bite will definitely be more uncomfortable but if the same nut is positioned at the molar area it might be better tolerated. In the design of the mouth guard therefore it would help to build a bite contact in the molar areas and even avoid an anterior contact.

Anterior bite plane helps in seating the condyles into the fossa in the skull and this will increase the stress on the joint and its structures. Healthy joint is capable of absorbing this stress but joints with dislocated discs or arthritic breakdown or inflammation of the retrodiscal tissue will be further aggravated if the Joint is seated more into the fossa and subject to increased loading stress. Creating a bite or point of contact in the posterior will act to reduce the stress in the TMJ. Likewise translating the joint forwards will also prevent the load on the joint which is why a MI (Maximum Intercuspation) bite or even a bite in a forward translated position of the lower jaw will reduce discomfort in the joint.

If the patient suffers from TMJ pathology and has additional sore masticatory muscles the design will include (in MI bite or bite that is comfortable) the anterior discluding ramps- anterior or canine guidance.

Modifying a lab fabricated occlusal guard for anterior disclusion:

1.

Guard made to MI Bite. Most patient without associated musculature symptoms will be able to get relief with this design.

A Mandibular design is usually a design of choice for patients wanting to wear the mouth guard during daytime versus those who prefer a night time device.

2.

Lack of anterior guidance in lateral positions. This design will work well if the patient had accompanying TMJ symptoms or pathology. This reduces the stress on the TMJ

3.

To modify the occlusal guard to provide anterior guidance use cold cure acrylic. Anterior guidance will reduce masticatory muscle stimulation.

Finally mouth guards are not to be worn 24/7 but if they need to be then the design will have to be a full coverage with bite in CR or MI or the position of comfort but without any posterior disclussion except by design in translation positions only, otherwise it might lead to supraeruption of the discluded teeth.

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