Mouthwear

Since the lower jaw forms a bilateral joint with the base of the skull at the glenoid fossa, blows to this mobile jaw may drive the jaw up and back, creating a transfer of energy from the lower jaw to the temporomandibular joint (TMJ) and base of the skull. Dr. Robert Cantu4 stated that blows to the chin, which acts as a lever, produce maximal forces. This fact has long been known in boxing, where the prime target for the opposing combatants has always been the chin. Stewart and Witzig19 have estimated that in athletes, over 90% of concussions resulting in unconsciousness are the result of blows to the lower jaw.

Although boxing serves as a prime example of the effects of direct blows to the lower jaw, even athletes wearing face shields and helmets are at risk of TMJ and traumatic brain injury from lower jaw impacts. Tim Walilko at the Wayne State School of Medicine demonstrated that the impact of a hockey puck traveling at 64 mph into a face shield is capable of creating enough energy transfer (shield – chin rest – lower jaw – TMJ – basal skull ) to create a 20% likelihood of mTBI.20

Standard National Operating Committee on Standards in Athletic Equipment (NOCSAE) football helmet drop test studies21 have shown that impact to the football helmet faceguard can displace the helmet and pull on the chin strap, causing a similar transfer of energy exceeding the pass/fail criteria set for helmets themselves.21,22 The ability of standard design mouthguards to protect against concussion has long been an area of debate. Barth has pointed out the theoretical and mathematical basis for a role of mouthguards in protecting the brain during lower jaw impacts if the mouthguard is fitted to provide vertical separation between the condyle and glenoid fossa. He also pointed out that the protective effect is limited to blows of a vertical nature only.23 Blows with a horizontal component are still capable of driving the lower jaw posteriorly, imparting impact energy at the TMJ area.17

Unfortunately, most blows to the lower jaw in sports arrive from the front and side,24-26 and carry a significant component of horizontal force. Additionally, little protection is available if the jaw is open during impact.27 Without the ability to lock the lower jaw into position, standard design mouthguards are capable of providing only unidimensional protection (Figure 4).

A prime determinant of the effectiveness of an appliance in reducing the risk of brain injury is the ability of the appliance to prevent displacement of the lower jaw during lower jaw impacts from any direction. When considering risk reduction for TMJ and brain injury in sports, we must begin to distinguish between the uni-dimensional protection afforded by standard design mouthguards and the multidimensional support provided by a new class of intraoral guard known as jaw joint protectors (Figure 5).
INTRAORAL GUARDS TO REDUCE LOWER JAW IMPACT TRAUMA

Classification of Mouthguards in Sports

Types of athletic mouthguards have traditionally been classified based on fabrication or design, as follows27:

(1) Classification by fabrication.
Stock mouthguard cannot be custom sized and should not be used
Boil and bite can be custom sized by molding when soft after boiling
Custom made dentist prescribed and laboratory fabricated mouthguards.

(2) Classification by design.
Single-arch design covers only one arch of teeth (usually the maxillary)
Dual-arch design covers both the maxillary and mandibular arches.

A NEW CLASSIFICATION FOR INTRAORAL SPORTS APPLIANCES

If we are to consider an expanded role of intraoral appliances in reducing the risk of concussion, traumatic brain injury, and jaw joint injury, we need to begin considering appliances based on classification by function, as follows:

(1) Mouthguard an intraoral appliance designed to protect the teeth and the oral tissues.

(2) Jaw joint protector (or brain injury risk-reducing appliance) an intraoral appliance designed to protect the teeth and oral tissues and the jaw joint and associated basal skull surface and brain during lower jaw impacts.

APPLIANCE DESIGN REQUIREMENTS FOR MINIMIZATION OF CONCUSSION RISK

An intraoral appliance designed to protect the brain and jaw joint should have the following features:

(1) It must prevent posterior and superior displacement of the lower jaw during impact, by fixing the mandible into position. This can only be accomplished by a dual-arch appliance.17

(2) The appliance must exhibit rigidity and resistance to deformation during lower jaw impact and during clenching (a normal and beneficial physiological response of athletes during maximal performance).27

(3) An appliance must fit properly. Compliance of wear is dependent on comfort, and comfort is dependent on fit. Proper fit is also required in order to provide retention. Only a properly retained mouthguard can be relied upon to be properly positioned at the time of impact.27,28

(4) The appliance must provide for adequate breathing during clenching.28,29 Prevention of lower jaw displacement during impacts is possible only when the mandibular dentition is firmly seated within the appliance. Therefore, an airway opening is of the utmost importance in order to allow both mouth and nasal breathing.

AN INTRAORAL APPLIANCE TO REDUCE THE RISK OF CONCUSSION

The limitations of single-arch appliances during lower jaw impact have also been recognized by athletes and dental professionals. Boxers have utilized numerous dual-arch dentist-fabricated appliances in the past, and various manufacturers (Everlast, Shock Doc) have had versions of dual-arch appliances meant to address lower jaw impact. Control of anteroposterior positioning of the mandible to create a horizontal separation of the TMJ and skull was not specifically addressed by these appliances. Compliance of wear by athletes is limited when breathing is compromised28,29 or when an airway breathing space is not incorporated or inadequate.

Dr. E. Williams designed an appliance to address the issue of lower jaw impacts and repetitive trauma in boxers. The appliance was designed to overcome previous limitations of dual-arch appliances, and is now utilized and endorsed by most major boxing, martial arts, and contact sport organizations. It is marketed as a jaw joint protector (Brain-Pad, WIPSS Products Inc). The appliance can be boil- and bite-fitted by dentists, athletes, or parents for general application, although custom fit by dental professionals may be recommended in cases of malocclusion, orthodontic therapy, or other special circumstances.

The Brain-Pad is fabricated with the following features to address the specific problem of energy transfer to the basal skull area during lower jaw impact:

(1) Dual-arch design with upper and lower bite channels to lock and hold the lower jaw into a down and forward position, creating a multidimensional safety space in the jaw joint area.

(2) Frontal airway space allows mouth breathing and speech while clenching the teeth. Dual material design allows for thermoplastic fitting as well as rigidity to maintain the airway space.

(3) A protective lower lingual flange guard minimizes posterior displacement of the mandible during impact.

(4) Down and forward mandibular positioning increases the airway space to optimize breathing during maximal exertion.

Impact to the lower jaw is transmitted to the appliance, which locks the lower jaw in position, and thus the forces are dissipated through the appliance into the maxillary arch. The risk reduction capacity of the Brain-Pad was evaluated by Voigt Hodgson at the Wayne State School of Medicine.22 In standard NOSCAE drop tests, the Brain-Pad design provided significant protection in the TMJ basal skull area, while standard design custom or boil and bite mouthguards did not meet the pass/fail criteria

The increase in bulk of a dual-arch appliance may be an initial concern for athletes accustomed to standard single-arch designs, but even younger athletes quickly adapt to the appliance. The Brain-Pad is not recommended for patients with class III malocclusion.