November 2016

Mouthguard mysteries: Can wearing one really improve athletic performance?

iStock_23905445Multiple studies suggest that mouthguards, designed to protect athletes from dental injuries during contact sports, may also help improve muscle force and power. But plenty of other studies have found no such ben­efits, and even the experts aren’t sure what to believe.

By Cary Groner

Chew on this: Research suggests that what your jaw is doing may have repercussions throughout your body, from brain activity to speed and strength.1

Chomping on something has a long history in stress mitigation, of course. Long before National Football League coach Pete Carroll started chewing gum on the sidelines, gnawing a piece of leather to fight through pain was common practice in the terrifying pre-anesthesia world—a soldier screaming his way through a battlefield amputation or a woman suffering the agonies of childbirth.

In recent, more humane decades, chewing is usually unnecessary for pain control, but even so, studies have shown it increases blood flow to areas of the brain associated with memory, attention, motor control, and planning.2,3 Mastication also destimulates the amygdala, which is associated with emotional reactions;4 activates brain serotonin action; and reduces anxiety while improving alertness.5,6 It improves mental performance and reaction time, too, and appears to help dissipate physiological stress.1

Athletes who wear mouthguards often chew on them, of course. The devices are designed primarily to prevent dental injuries in contact sports—such as football, ice hockey, and lacrosse—by keeping the upper and lower teeth at a courteous distance from each other. But some researchers have suggested there may be performance benefits associated with wearing them, as well. It’s a baffling field full of contradictory claims that have left experts scratching their heads, and though a few
recent papers are shedding light on what may be going on, much speculation remains.

The pros

11cover-istock_48280176-copyCourtenay Dunn-Lewis, PhD, a visiting assistant professor in health and sports medicine at the University of Pittsburgh in Pennsylvania, and colleagues compared neuromuscular force and power production in athletes wearing a customized mouthguard, an over-the-counter (boil-and-bite) guard, or no guard.1 She reported that bench throw power and force were significantly higher with the custom guard than the other conditions in both men and women, and that a plyo press power quotient (3PQ) was higher in terms of both power and force production in men. Similarly, men using the custom guard had a higher rate of power development in the vertical jump, but the researchers found no differences in flexibility, balance, visual reaction time, or sprint time. They concluded that the custom mouthguard improved the performance of upper-body loaded power exercises in both sexes, and lower-body power exercises in men, without compromising other performance measures.

“It may have been that the custom mouthguard helped people stabilize their head and neck by clenching their jaw,” Dunn-Lewis told LER. “That particular guard placed a space between the subjects’ back teeth that they could clench against, and this may activate the muscles a little more, in contrast with slimmer versions primarily used for protection that don’t change the position of the mandible. My impression is that when you do something that requires a burst of effort, and you just clench down and go, that specific guard tends to work. It wouldn’t necessarily have an impact on the rest of the body unless the individual was actively clenching against it.”

As to why women didn’t seem the same lower-body benefits as men, Dunn-Lewis suspected physiological differences between the sexes.

“Women are generally more flexible than men, so it may just be that plasticity of muscle,” she said.

She also speculated about what, more specifically, might cause the effects reported.

“I think the idea of stress attenuation is interesting, that you can just focus all your tension right into the jaw,” she said. “If you want to perform better, you want your core to resist movement, and stabilizing the jaw could theoretically help with that. It’s an interesting question, and I hope that in the future we’ll get more clarity around it.”

Other studies have reported similar findings. For example, in 2008 researchers at Marquette University in Milwaukee found that when study participants exerted maximal clenching on a mouthguard during a countermovement jump, the rate of force development was 19.5% greater than when they didn’t wear the guard.7 Time to peak force was 20.2% lower with the guard, as well, though there were no significant differences in overall peak force between the conditions.

The next year, a study of taekwondo athletes found that custom mouthguards were associated with significant improvement in peak and average power in a Wingate anaerobic test, as well as hamstring isokinetic peak torque.8 Other measures, however—sprint times, jumping tests, isometric leg strength—weren’t affected.

A 2013 paper suggested that, in pro golfers, the gap the guard creates between the teeth may affect performance.9 In that study, golfers performed four trials of 10 driver swings while using a mouthguard, a dental stabilization splint, or nothing. Club speeds and driving distances were significantly increased with the guards or splints, but this advantage decreased when the devices were adjusted to result in molar occlusion.

A 2016 paper found that teeth clenching increased the soleus H-reflex regardless of the degree of muscle fatigue.10 One study found that using devices to create unbalanced dental occlusion increased knee muscular performance,11 though another showed the opposite effect.12 The reasons for the disparity, as well as the mechanism itself, remain unclear.

The cons

11cover-shutterstock_87069566-copyIf such positive press has you thinking it might be worthwhile to wear a mouthguard on your next walk in the park, think again. There’s just as much bad news as good.

A 2006 French study found that neither boil-and-bite nor custom mouthguards had a significant effect on a variety of parameters studied, including visual reaction time, explosive power, and ventilation at rest or during exercise.13 Two years later, Swiss researchers reported that a custom mouthguard had no effect on maximal exercise capacity or cardiopulmonary parameters.14 In 2014, investigators at the University of Mississippi in Oxford tested a noncustom mouthpiece (which was designed for bite alignment rather than to prevent injury) and found no significant effects on countermovement jumps or bench presses.15 Finally, a 2016 study from Germany16 reported that specially fitted dental splints had no effect on Wingate anaerobic tests—a finding consistent with those of Dunn-Lewis and others, who’ve reported that mouthguards don’t seem to influence anaerobic tasks such as sprinting.

It’s worth noting that all these studies have been carried out in different countries, with a variety of mouthguard designs and widely disparate outcome measures. It’s a bit like trying to draw conclusions about the biomechanical effects of footwear from studies that include running shoes, ballet slippers, and steel-toed boots, and that evaluate everything from the metatarsals to the hips. Under such conditions, generalizations tend to prove elusive.

“Are there real effects or are there placebo effects?” asked Alison Brooks, MD, MPH, an associate professor in the Department of Orthopedics and Sports Medicine at the University of Wisconsin in Madison. “When athletes wear or do something that they perceive as positive for their performance, it usually is—but not necessarily for any physiologic reason. We always have to account for that.”

Brooks is aware of theories that correlate correct jaw alignment with effects down the kinetic chain,17 but considers much of the research deficient in design and execution.

“Often the number of people in the studies is quite small, or there’s no control group,” she explained. “Every mouthguard company makes anecdotal claims to sell their product, but I don’t put much stock in those. You might find that there’s a statistical difference between people wearing the mouthguard and those who aren’t, but if it’s four one-thousandths of a second, it’s not likely to be clinically meaningful for the average recreational athlete. Though if you’re talking about athletes at the highest level of sports, maybe those minute differences matter.”

A study published this past May in the Journal of Strength and Conditioning Research further supports the notion that mouthguards may not exert significant effects.18 Investigators tested several strength and endurance measures in 10 college football players wearing custom-made, boil-and-bite, or no mouthguards in a crossover study. The custom guards showed no advantage over the other conditions, though, as other research has shown, they didn’t limit performance either.

Lead author Scott Drum, PhD, an associate professor of exercise physiology at Northern Michigan University in Marquette, told LER that the theory being tested had to do with the temporomandibular joint (TMJ).

“The idea is that if you’re relaxing that joint, positioning the jaw to reduce the fight or flight response by inhibiting teeth clenching, and you’re more physically relaxed, then that should enhance performance,” Drum said. “It’s supposed to put you into a state of proper stress—good stress, so you’re not over-amped. It’s an interesting strategy, but we found no difference.”

One telling issue here, however, is that researchers who’ve found performance benefits from mouthguards, such as Dunn-Lewis et al, specifically cited the effects of teeth clenching as potentially contributing to those benefits. So a device (or instructions to the wearer) to reduce clenching might naturally eliminate that effect.

“That’s a really good point, but I think we’re talking about aspects of the same thing,” Drum said. “If somebody isn’t aroused enough to perform well, clenching on a mouthguard may signal just enough stress to get their head into the game. But you want to be on top of that bell curve of stress, without too much or too little, and everybody’s different. If you can identify a given individual who may benefit from more jaw-clenching, then the mouthguard might clue them in to proper alignment and help them be optimal with their stress arousal.”

As Drum points out in his paper, moreover, results like those of Dunn-Lewis aren’t due to clenching per se, but to the space the mouthguard introduces between the teeth so that they’re not occluded by the clench. This invokes the aforementioned study in golfers, in which the advantages associated with the mouthguards disappeared when they were adjusted to eliminate that space.

Drum suspects some of the wide discrepancies in the research may have to do with the heterogeneity of study populations.

“Some individuals are undertrained,” he said. “I could see that in a highly stressful competitive situation with elite athletes, eking out a half percent of relaxation could be a viable difference. Even if the benefits are the result of a placebo effect, by all means wear the mouthguard, because the placebo effect is well-studied and real, and the mouthguard isn’t going to do any harm. I just think it’s a red flag when manufacturers make blanket statements about improving strength, endurance, agility, skill, and balance.”

Both sides now

Few researchers are better positioned to look at both sides of the issue than Shawn Arent, PhD, director of the IFNH (Institute for Food, Nutrition, and Health) Center for Health & Human Performance, and of the Graduate Program in Kinesiology & Applied Physiology at Rutgers University in New Brunswick, NJ. Some of Arent’s research has shown performance benefits associated with mouthguards, but not all of it has.

11cover-shutterstock_348218759-copy

For example, in a 2010 paper, Arent and his colleagues compared the effects of a neuromuscular dentistry-based mouthguard—which emphasizes alignment of the TMJ—to a standard boil-and-bite guard in 22 high-level male athletes who performed vertical jumps, bench presses, and variations of a Wingate anaerobic test.19 When the participants wore the dentistry-based mouthguard, they had significantly better performance in peak power output and repeated maximal efforts than when they wore the boil-and-bite device.

By contrast, in a 2015 paper studying four conditions—a custom-fitted jaw-repositioning mouthguard, a boil-and-bite guard, a placebo guard, and no guard—Arent and his coauthors reported no significant differences between the mouthguards in terms of muscular strength or power, dynamic balance, or agility.20

“In the first study, the custom guard involved a forty-five minute fitting process that included hooking the subject up to a TENS [trans­cutaneous electrical nerve stimulation] unit to relax the jaw, ideally into its true resting alignment,” Arent said. “They took the bite impression at that point, and I think that process was associated with a lot of the expense of those guards, which cost fifteen hundred to two thousand dollars.”

Arent said that in the second study, that fitting process wasn’t used.

“Those guards were just trying to create occlusal space, and we didn’t see any significant effects, which leads me to wonder if there was something important about that fitting process in the earlier study.” (Arent said the mouthguard company in question eventually abandoned the process and sold its technology, in any case.)

Like the other experts LER spoke with, Arent felt that even when the guards seemed to work, the associated mechanism of action remained unexplained. He thought it might have something to do with the TMJ and its effect on the cranial nerves that pass nearby.

“The idea is that if the TMJ is not in an optimal position—if it impinges on anything—it may affect the descending cranial nerve,” he said.

Unfortunately, there isn’t much research that would shed light on this possibility, one way or another. A 2012 literature review in the Journal of Oral Rehabilitation found no evidence for a predictable relationship between occlusal and postural features, and found that TMJ pain wasn’t associated with postural abnormalities;21 but of course, posture and performance, while often related, aren’t the same thing. Later, a 2016 study reported that patients with lower-limb disease who used a TMJ exerciser experienced gait improvements;22 however, it was a small study and results were inconsistent across the 11 participants.

“This may just be one area where you get what you pay for,” Arent said. “As ridiculous as it seems, we didn’t see the same effects with cheaper mouthguards as we did with those that cost fifteen hundred dollars and involved the more extensive fitting process. Can we replicate that? After [the company] stopped doing it, we never had the opportunity to.”

Arent agreed with Alison Brooks that an athlete’s degree of training may affect the relative effects of a mouthguard on performance, however.

“My guess is that in highly trained athletes, even a small adjustment can make a difference,” he said. “When you’re talking about races won or lost by hundredths of a second, you might not need a big effect from the mouthguard to see benefits. Then it becomes a question of cost versus utility—is it just part of the arsenal?”

Arent emphasized that the current state of the evidence does address a few important issues, however.

“One is whether athletes in noncontact sports should wear mouthguards, and I don’t think anything supports that at this point,” he said. “But would it hurt? No; for me, one of the most important things to come out of these studies is that none of the mouthguards interfered with performance. And if you have an athlete in a sport for which a mouthguard is recommended, the logic for refusing isn’t good. They protect from injury, and some research shows performance benefits even if the reasons aren’t well established from a mechanistic standpoint. Again—for an elite athlete, even a modest effect could be beneficial; it’s just part of the whole equation of your preparation and training.”

Cary Groner is a freelance writer in the San Francisco Bay Area.

REFERENCES
  1. Dunn-Lewis C, Luk HY, Comstock BA, et al. The effects of a customized over-the-counter mouthguard on neuromuscular force and power production in trained men and women. J Strength Cond Res 2012;26(4):1085-1093.
  2. Momose T, Nishikawa J, Watanabe T, et al. Effect of mastication on regional cerebral blood flow in humans examined by positron-emission tomography with 15O-labeled water and magnetic resonance imaging. Arch Oral Biol 1997;42(1):57-61.
  3. Hirano Y, Obata T, Kashikura K, et al. Effects of chewing in working memory processing. Neurosci Lett 2008;436(2):189-192.
  4. Berridge CW, Mitton E, Clark W, Roth RH. Engagement in a non-escape (displacement) behavior elicits a selective and lateral lies the suppression of frontal cortical dopaminergic utilization and stress. Synapse 1999;32(3):187-197.
  5. Zibell S, Madansky E. Impact of gum chewing on stress levels: online self-perception research study. Curr Med Res Opin 2009;25(6):1491-1500.
  6. Scholey A, Haskell C, Robertson B, et al. chewing gum alleviates negative mood and reduces cortisol during acute laboratory psychological stress. Physiol Behav 2009;97(3-4):304-312.
  7. Ebben WP, Flanagan EP, Jensen RL. Jaw clenching results in concurrent activation potentiation during the countermovement jump. J Strength Cond Res 2008;22(6):1850-1854.
  8. Cetin C, Kececi AD, Erdogan A, Baydar ML. Influence of custom-made mouthguards on strength, speed and anaerobic performance of taekwondo athletes. Dent Traumatol 2009;25(3):272-276.
  9. Pae A, Yoo RK, Noh K, et al. The effects of mouthguards on the athletic ability of professional golfers. Dent Traumatol 2013;29(1):47-51
  10. Mitsuyama A, Takahashi T, Ueno T. Effects of teeth clenching on the soleus H reflex during lower limb muscle fatigue. J Prosthodont Res 2016 Jun 24. [Epub ahead of print]
  11. Jung JK, Chae WS, Lee KB. Analysis of the characteristics of mouthguards that affect isokinetic muscular ability and anaerobic power. J Adv Prosthodont 2013;5(4):388-395.
  12. Grosdent S, O’Thanh R, Domken O, et al. Dental occlusion influences knee muscular performances in asymptomatic females. J Strength Cond Res 2014;28(2):492-498.
  13. Bourdin M, Brunet-Patru I, Hager PE, et al. Influence of maxillary mouthguards on physiological parameters. Med Sci Sports Exerc 2006;38(8):1500-1504.
  14. Von Arx T, Flury R, Tschan J, et al. Exercise capacity in athletes with mouthguards. Int J Sports Med 2008;29(5):435-438.
  15. Allen CR, Dabbs NC, Zachary CS, Garner JC. The acute effect of a commercial bite-aligning mouthpiece on strength and power in recreationally trained men. J Strength Cond Res 2014;28(2):499-503.
  16. Fischer H, Weber D, Beneke R. A neuromuscular fitted dental splint does not improve sprint performance. Int J Sports Physiol Perform 2016 June 13. [Epub ahead of print].
  17. Heit T, Derkson C, Bierkos J, Saqqur M. The effect of the physiological rest position of the mandible on cerebral blood flow and physical balance: an observational study. Cranio 2015;33(3):195-205.
  18. Drum SN, Swisher AM, Buchanan CA, Donath L. Effects of a custom bite-aligning mouthguard on performance in college football players. J Strength Cond Res 2016;30(5):1409-1415.
  19. Arent S, McKenna J, Golem D. Effects of a neuromuscular dentistry-designed mouthguard on muscular endurance and anaerobic power. Comp Exerc Physiol 2010;7(2):73-79.
  20. Golem DL, Arent SM. Effects of over-the-counter jaw-repositioning mouthguards on dynamic balance, flexibility, agility, strength, and power in college-aged male athletes. J Strength Cond Res 2015;29(2):500-512.
  21. Manfredini D, Castroflorio T, Perinetti G, et al. Dental occlusion, body posture and temporomandibular disorders: where we are now and where we are heading for. J Oral Rehabil 2012;39(6):463-471.
  22. Chung GY, Choi GS, Shin KY, Park IS. Gait changes after using a temporomandibular joint exerciser in patients who underwent lower limb joint surgery. J Phys Ther Sci 2016;28(5):1584-1587.
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