Mouthguards’ respiratory response to exercise:
Breathing had been defined as the movement of air into and out of the pulmonary system. Breathing and ventilation can be used synonymously to describe the manner that O2 and CO2 are exchanged in the lungs. During the eighteenth century Lavoisier and others of his time believed that “biological oxidation occurred in the lungs.” At this time, ventilation and breathing became known as respiration.(132)
Today, by convention in the study of physiology, the three terms ventilation, breathing, and respiration are used synonymously. Properly speaking, however, ventilation is the breathing of air into and out of the pulmonary system (nose, mouth, trachea, lungs), whereas respiration is the cellular utilization of O2. Ventilation at rest occurs primarily via the nasal route.(133, 134)
As a person begins to exercise, greater demands for oxygen are placed on the body, and breathing changes from a strictly nasal route to an oro-nasal route. Studies had shown that the change from nasal to oro-nasal breathing occured between 30-40 L/min.(133, 135)
On the other hand, it was found that approximately 80% of the breathing at rest occured via the nasal route.(133)
Additionally, others stated that 80% of the breathing during exercise occured via the oro-nasal route.(135)
Maximal VO2 (VO2 MAX) is defined as the maximum amount of physiological work that an individual can do, as measured by oxygen consumption. Also, it is the point at which no further increase in measured VO2 occurs despite an increase in work rate (a plateau is reached) during Graded Exercise Testing (GTX).(136)
It has traditionally been used as the basic standard of cardiorespiratory fitness, as it is considered to be the single physiological variable that best defines the functional capacity of the cardiovascular and respiratory systems. However, it is more appropriate to consider it as an indicator of endurance performance potential.(136, 137)
As previusly reveiwed, use of mouthguards, often results in complaints of discomfort, inability to communicate, and difficulty breathing.
If breathing is more difficult when using a mouthguard, then there may be an obstruction of airflow due to the mouthguard. While at rest, breathing is primarily accomplished through the nose. However, when a person begins to exercise, the breathing pattern changes and breathing occurs through both the nose and the mouth. The majority of inspired air enters the lungs via the oral route during exercise.(138)
While airflow resistance of the nasal airway (RN) is restricted to a relatively narrow range of values, oral resistance (RO) has the potential to vary from infinity (mouth closed) to something approaching zero (mouth widely open).(133)
This means that jaw position, widely open or nearly closed, has the potential to effect airflow. The degree that the oral route is obstructed may be a factor in ventilatory changes during exercise.
Only few published studies pertaining to airflow dynamics while wearing a mouthguard were found in the literature.
In a study of the physiological effects with and without three different types of over-the-counter mouthguards, it was found that although the tested mouthguards restricted forced expiratory airflow, they appeared to be beneficial in prolonging exercise by improving ventilation and economy.(138)
On another study, it was found that although maxillary mouthguards increased airflow resistance, this effect was evident predominantly during resting breathing and when the degree of mouth opening was restricted. Consequently, the authors concluded it appeared that maxillary mouthguards were unlikely to interfere with breathing at high ventilatory rates and where recruitment of compensatory mechanisms was possible.(139)
On evaluating the cardiorespiratory effects of custom made mouthguard, It was found that the recorded values with and without mouthguards showed no significant differences for the evaluated parameters. The authors concluded that athletes could wear custom-made mouthguards without negative effects on their aerobic performance capacity.(140)
Another study studied the effect of a non-custom made bimolar mouthguard on expired ventilation (VE), oxygen uptake (VO2), and heart rate, The authors concluded that non-custom-made bimolar mouthguards might reduce ventilation and oxygen uptake at maximal efforts.(141)
Two different maxillary mouthguards were used in another study. self-adapted and custom-made (SA and CM). The authers concluded that CM or SA maxillary mouthguards do not alter the breathing pattern or the work rate/VO2 ratio. Nevertheless, this conclusion were made with caution regarding SA mouthguards. (142)
Custom pressure-laminated mouthguard was fabricated to athletes and the authers concluded that a custom-made mouthguard did not interfere with maximum exercise performance of professional athletes and wearing a custom-made mouthguard improved the athletes’ attitudes toward the mouthguard after a period of four weeks.(143)
Another study studied wearability and physiological effects of custom-fitted (MG3) vs self-adapted mouthguards (MG2). It was found that MG3 showed the smallest range of changes in players’ performance, suggesting improved fit, comfort, and acceptation compared with MG2. (144)
Mouthguards’ response to muscle strength:
There is a belief on the part of some dentists working in the field of sports that jaw repositioning can increase muscle strength.(145)
Some players testify to ‘‘feeling stronger and being more relaxed’’ when wearing a mouthguard.(146)
MORA Appliance (Gelb splint):
The Mandibular Orthopedic Repositioning Appliance (as described by Dr. Gelb) has been designed to reposition the mandible with its condyle (achieves optimal neuromuscular balance as well as balanced condyle-fossae relationships) .(146)
The Gelb appliance was made covering only the lower premolar and molar teeth. It was used to correct mandibular displacement, reduce TMJ dysfunction and oral/facial pain, and to provide occlusal stability with the patient’s natural dentition serving as the anterior guidance.(146, 147)
Can physiologically balanced mouthguards improve performance by affecting the musculature outside the face and neck (arms, legs, abdomen and back)?(146)
Many athletes with or without occlusal problems are now using MORA supposedly to optimize their performance. The benefits of these appliances for athletes have been widely discussed in popular magazines, newspapers, and radio and television programs, although claims of improved strength and performance have been largely anecdotal and subjective.(147)
Some articles have suggested that the MORA is necessary to help athletes to reach their maximum potential.(148, 149)
A bite-adjusted mouthguards were used with the Philadelphia Eagles football team, which were shown to cause an increase in muscle strength throughout the body.(148)
Additionally, in a 3-year study of long distance runners, it was found that every one of the runners in the study consistently showed an increase in resistance ability, as measured by the muscle resistance test, with the use of an oral appliance. It was further stated that subjective accounts from the runners, all reported an increase in hill performance, more endurance, and lowered perceived exertion.(150)
However, in a double-blind study using 14 male intercollegiate basketball players, it was concluded that bite-positioning appliances did not demonstrate any change in strength.(151)
On the other hand, MORA significantly increased muscle strength while subjects performed vertical jump and the grip test, although it did not significantly increase strength when subjects performed the maximum hip sled and bench press test.(152)
It was also reported that there were no significant differences in muscle strength whether American football players were or were not wearing a MORA while performing the isometric dead lift, two-arm pull and the isokinetic upright rowing.(153)
Additionally, some authors failed to find statistically significant differences in shoulder abduction, shoulder adduction, knee flexion, and knee extension strength whether athletes were wearing a MORA or not.(154)
Moreover, others found no significant differences in shoulder adduction and knee extension whether subjects were or were not wearing interocclusal splints.(155)
However, it must be noted that these experiments did not use statistical tests to verify the results, and neither of these studies used placebo mouth splints.(154)
Other studies, reviewed by Forgione et al., examined the effect of vertical dimension increase in subjects with normal occlusion. The results were conflicting, probably because most of these studies were flawed in their scientific design. Moreover, they mostly measured strength during isometric or isokinetic exercises, whereas muscular performance in contact sports is mainly ballistic.(156)
In another study, the muscle strength of back extension, knee extension, and planter flexion was significantly increased when wearing interocclusal splints, while arm flexion strength and grip strength showed no significant changes.(157)
Moreover, MORA had increased the isometric strength of the muscles around the neck and head in subjects with temporomandibular disorder and/or occlusal problems.(158)
It was found that the functioning of a player’s neck muscles to avoid being hit in the head was not affected by wearing a mouthguard when the player was in the supine position. Additionally, when a person performed muscle strength exercises in the supine position, the functioning of neck muscles in order to fix the head and body trunk was not affected by wearing a mouthguard.(159)
If, in fact, the premise that increased athletic performance could be improved by using a mouthguard, the further development of the ideal mouthguard needs to be pursued.(146)