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Original Research

Effects of Over-the-Counter Jaw-Repositioning Mouth Guards on Dynamic Balance, Flexibility, Agility, Strength, and Power in College-Aged Male Athletes

Golem, Devon L.1; Arent, Shawn M.2

Author Information
The Journal of Strength & Conditioning Research: February 2015 - Volume 29 - Issue 2 - p 500-512
doi: 10.1519/JSC.0000000000000641
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Abstract

Introduction

Mouth guards are typical safety devices recommended for use by athletes in various sports to decrease the risk of orofacial injuries. Reduced compliance with these recommendations is reported to be due to concerns of decreased performance with mouth guard use (13). Mouth guard manufacturers have responded to this concern with smaller designs that are well-fitted to the teeth of the athletes. The majority of research examining the effects of mouth guards on athletic performance focuses specifically on aerobic aspects and reveals that the above-mentioned design modifications generally prevent any impedance on aerobic capacity and respiratory functional tests (7,9,11). The effects of mouth guards on other aspects of physical performance have not been examined in detail.

The dental technique of jaw repositioning has been incorporated in the design of mouth guards to not only reduce possible negative effects but also promote positive effects on physical performance. The premise to include this technique into mouth guard design stems from the positive effects observed in subjects with and without temporomandibular joint disorder (TMD). Jaw position is correlated with postural control and spinal alignment (6,23,29,34) and has been shown to improve spinal alignment in children with TMD (32). Jaw repositioning has also been observed to improve posture and functional proprioception in adults without TMD (23). Changes in spinal alignment and proprioception induced by jaw repositioning may promote changes in physical movement and performance.

Most of the scientific literature examining the effects of jaw position on physical performance, other than aerobic performance, has focused on muscular strength. It has been consistently found that jaw repositioning, through use of an oral appliance, does not affect strength (1,5,15,22,31,36,37,41). Many types of strength tests were used in these studies, including shoulder adduction and abduction, knee extension and flexion, bench press (BP), and hip sled exercises. Different strength assessments have included isokinetic and maximal strength. Only 1 study reported an increase in peak torque of shoulder extension (SE) and external rotation with the use of a jaw-repositioning appliance (35). However, the improvement in these movements could be associated with changes in flexibility and range-of-motion (ROM) as opposed to the claim of increased strength. To explore the possibility of these effects, flexibility and strength assessments could be simultaneously examined.

Although muscular strength and muscular endurance are not typically observed to be affected by jaw repositioning, muscular power has been shown to be improved (2,5,10). Muscular power is an essential component of athletic performance, as most sports require high power outputs to rapidly accelerate or decelerate (26). The observation of increased muscular power without concurrent increases in muscular strength or endurance leads to questions regarding the effect of jaw-repositioning techniques on these correlates of physical performance. Muscular power differs from strength and endurance in that it requires rapid neuromuscular responses and is time dependent. Commonly known as “speed strength,” muscular power relies on rapid communication between peripheral proprioceptors and central command (18,20). The examination of the effects of jaw repositioning on other aspects of physical performance that require rapid neuromuscular communication may provide more insight regarding mechanism of action.

Only recently has the examination of the influence of jaw-repositioning mouth guards on other aspects of physical performance taken place. Agility, balance, and flexibility are all important correlates of athletic success. Athletic movements require skillful application of force under variable conditions. Part of this skill is demonstrated as agility or the change in movement velocity (26). Any movement requiring rapid change in speed or direction is highly reliant on agility. Retaining balance throughout the execution of these movements is also essential to athletic performance (27). Additionally, optimal movement patterns require flexibility. Flexibility is a measure of ROM that occurs at a joint and is vital for reducing injury. Different optimal levels of flexibility exist for a variety of athletic activities (20). Dynamic balance and agility relate to muscular power as they all require rapid neuromuscular communication (17,33,39,40) and, along with flexibility, are regulated by proprioceptors within the muscle (20). As such, the same neuromuscular factors that govern changes in proprioception (23) may also influence agility, balance, and flexibility. To date, 1 study did not observe any significant differences with the use of an over-the-counter (OTC) performance mouth guard compared with an OTC boil-and-bite mouth guard and to no mouth guard on sit-and-reach flexibility and single-leg medial lateral balance in adult athletes (10). The effects of a jaw-repositioning mouth guard on other measures of flexibility, dynamic balance, and agility have yet to be examined.

The primary purpose of this study was to examine the effects of OTC jaw-repositioning mouth guards on muscular strength and power. This information will aid in the determination of whether the jaw-repositioning method of increased dental occlusion will promote similar effects as more expensive, neuromuscular dentistry-designed techniques. As the current literature lacks substantial evidence regarding the effects of jaw repositioning on agility, balance, and flexibility, the secondary purpose of this study was to determine the effects of OTC jaw-repositioning mouth guards on these aspects of physical performance. Overall, based on the proposed mechanisms and previous findings, it is hypothesized that the OTC jaw-repositioning mouth guards will improve agility, balance, and muscular power, whereas strength and flexibility may not be affected.

Methods

Experimental Approach to the Problem

A randomized, blind, placebo-controlled crossover design was used to examine the effects of 2 OTC jaw-repositioning mouth guards on various aspects of physical performance. All subjects completed performance testing in each of 4 conditions in a randomized order: self-adapted jaw-repositioning mouth guard (SA), custom-fitted jaw-repositioning mouth guard (CF), placebo mouth guard (PLA), and a no-mouth guard control (CON). The conditions differed in appearance and feel; yet, the subjects were blinded to the placebo condition and to the jaw-repositioning concept that was being evaluated. All mouth guard fittings were completed in the Human Performance Laboratory at the Rutgers University. The researchers were trained by a dentist on proper fitting procedures and TMD assessment. The subjects completed a familiarization session, which was paired with the fitting session, to control for learning effects on the performance tests, which included dynamic balance, flexibility, power, agility, and strength. After the fitting/familiarization session, subjects completed each of the 4 conditions, which were separated by at least 48 hours to allow for sufficient recovery.

The mouth guards in this study promoted jaw repositioning through a standardized increase in centric dental occlusion (i.e., the space between upper and lower molars). The placement of hard material between the molars promotes a downward movement of the jaw. Unlike typical mouth guards, the material within the OTC jaw-repositioning mouth guards is impervious to dental compression ensuring a permanent increase in dental occlusion. To reduce cost and increase availability, the OTC jaw-repositioning mouth guards evaluated in this study were designed to be constructed without the expertise of a dentist and without use of advanced dental instruments.

Both SA (boil-and-bite) and CF jaw-repositioning mouth guards were evaluated. The design of both mouth guards allowed the material surrounding the teeth to be molded, whereas the material between the dental occlusion was stationary, thus promoting a standardized change in jaw position. Placebo mouth guard had a similar fit around the upper teeth but lacked material between upper and lower molars preventing change in jaw position. Figure 1 shows an illustration of the mouth guard conditions. Dental occlusion under each condition was measured and recorded. A significant difference between conditions was observed (p < 0.001) with CON and PLA having a significantly lower occlusion than the SA and CF conditions (CON: 72.8 ± 4.9 mm; PLA: 73.1 ± 4.7 mm; SA: 75.5 ± 5.0 mm; CF: 75.9 ± 4.8 mm; p < 0.001). The mouth guards effectively increased dental occlusion 2–3 mm.

Figure 1
Figure 1:
Mouth guard conditions. From right to left, the custom-fitted jaw-repositioning mouth guard (CF), the self-adapted jaw-repositioning mouth guard (SA), and the placebo mouth guard control (PLA).

Subjects

Healthy, male collegiate athletes (N = 20; Mweight = 79.8 ± 11.7 kg; Mheight = 176.5 ± 6.5 cm; Mage = 21.5 ± 2.7 years) with 12.4 ± 4.5 years of athletic training experience participated in this randomized crossover study. All subjects participated in sports with which mouth guard use was recommended and were required to wear mouth guards during their athletic career to ensure familiarity with mouth guard use (MGexperience = 7.9 ± 5.4 years). Thirty participants were initially recruited, but 3 were excluded because of lack of mouth guard experience, 3 subjects were injured while training for their sport within the study time period rendering them unable to complete testing, and 4 subjects voluntarily withdrew from participation because of scheduling conflicts. The sports represented by the subject population include mixed martial arts, wrestling, football, soccer, and lacrosse. This study was limited to males to control for muscular power and strength differences that exist between genders (8).

Risks and benefits were explained to the subjects and all gave written informed consent before participation in the study. All individuals were free from current injuries, dental conditions, and health conditions limiting their ability to complete physiological testing. A health screening was completed with each subject in accordance with the American College of Sports Medicine exercise testing procedures. A TMD screening was completed to ensure adequate dental health (25,29). The study was approved by the Rutgers University Institutional Review Board.

Procedures

After screening, each subject underwent a mouth guard fitting process and completed a familiarization session to control for learning effects (4). The SA jaw-repositioning mouth guards were fitted immediately using a boil-and-bite process. Trained research staff assisted the subjects with the fittings to ensure proper fit. The fitting of the CF jaw-repositioning mouth guard consisted of 2 steps: (a) dental impressions were made in the Human Performance Laboratory by research staff, and (b) these impressions were shipped to the manufacturer for mouth guard construction. The manufacturer used the impressions to construct the CF and the PLA mouth guards for each subject. These were then shipped to the Human Performance Laboratory. It is important to note that these particular CF mouth guards are designed so that the impression can be taken by the individual without requiring clinical fitting by a dentist. Therefore, our procedures enhanced the external validity of the mouth guard use. The first session also consisted of a familiarization practice of every performance test. Each test was demonstrated for the subject while also providing verbal instructions. Each subject completed the physical tests a minimum of 1 time.

The familiarization and fitting session was followed by 4 separate testing sessions once the CF and PLA mouth guards were received. During each testing session, subjects completed 5 different performance tests in the following order: dynamic balance, systemic warm-up on a treadmill, flexibility measurements, countermovement vertical jump (VJ), hexagon (HEX) agility test, and a BP strength test. The order of this battery of physical tests is consistent with the National Strength and Conditioning Association testing order guidelines (16). Participants were instructed to continue with their normal exercise training during the course of the study, but were required to refrain from training for 24 hours before each testing session. Additionally, each subject was tested at the same time of day (±1 hour) to control for diurnal variation that may impact physical performance (3,38). Each testing session was separated by a minimum of 48 hours to allow for recovery. To promote proper use of the mouth guards and ensure that the jaw position of the various conditions was met, subjects were instructed to bite down into the mouth guard immediately before and during each performance test.

Subjects were instructed to arrive for testing normally hydrated, to have eaten and slept per their usual regimen, to maintain consistency in footwear, and to refrain from moderate-vigorous exercise training at least 24 hours before the testing session. Written records of previous meal dietary intake, hours slept the previous night, exercise completed in past 48 hours, and shoes worn were obtained at the beginning of each testing session and were used to assess compliance. No significant differences in energy or macronutrient intake were observed between conditions (p = 0.743). No significant differences between conditions were observed for number of hours of sleep the previous night (p = 0.86) or changes in body weight (p = 0.19). Efforts were made to ensure that the same lighting, temperature, and music within the testing environment remained consistent across all testing sessions.

Performance Measures

Mouth Guard Use

To promote proper use of the mouth guards and ensure that the jaw position of varying conditions was met, subjects were instructed to bite down into the mouth guard immediately before and during each performance test.

Dynamic Balance

Dynamic balance was assessed using the model 16030 Stability Platform (Lafayette Instrument Company, Lafayette, IN, USA). The platform pivots on a center axis from left to right sides. A 5° range of error to either side was designated as “out of center balance.” The subjects used their body to balance the board from leaning laterally during each of four 30-second trials. A 30-second rest was taken between each of the trials. The amount of time to the nearest hundredth of a second to the left, center, and right were recorded for each trial. The highest value for time in center balance was used as the score for each condition. Intraclass correlation coefficient (ICC) for the balance test in our laboratory is r = 0.96.

Flexibility

After a 5-minute systemic warm-up on the treadmill at a self-selected pace, the subjects performed the flexibility tests. The initial self-selected pace for warm-up was repeated for each condition. Given that dynamic flexibility is more closely related to sports performance than static flexibility (14,19), it was the primary emphasis for the flexibility testing used in this study. Hamstring flexibility was assessed using the sit-and-reach method (16). Each subject took off his shoes, sat on a floor mat, and pressed his feet flat against the front of the sit-and-reach box. The subjects leaned forward, with their palms facing the floor and their legs fully extended, and stretched as far as possible holding the position for a minimum of 2 seconds. The sit-and-reach test was completed twice and the highest score was recorded to the nearest 1 cm (16). Intraclass correlation coefficient for the sit-and-reach was r = 0.95.

Additional flexibility assessments included SE, shoulder lateral rotation (SLR), hip flexion (HF) and extension (HE), lumbar spine lateral flexion (LSLF), and lumbar spine rotation (LSR). These 6 movements were selected to represent ROM in the upper, middle, and lower areas of the body's core. The subjects were not assisted through the ROM and used their own muscular force designating these measures of flexibility as dynamic. All measurements were taken with a goniometer on the dominant side of each subject.

Shoulder Lateral Rotation

The subjects laid supine on the floor mat, with their legs extended, and with their head facing the ceiling. Their dominant arm was abducted 90°, so their forearm was perpendicular to the floor. The researchers ensured the alignment of the subject's humerus with their acromion process before using the subject's olecranon process as the axis of rotation. The goniometer was placed along the side of the subject's ulna with the stationary arm perpendicular to the floor and the moving arm along the styloid process (sharp edge of the forearm) of the ulna. The researcher stabilized the distal end of the subject's humerus and scapula. The subjects moved their forearm to the floor away from their body. The angle between the arm and the perpendicular position was recorded. The ICC for SLR was r = 0.89.

Shoulder Extension

The subjects laid prone on a floor mat, with their head turned away from their dominant shoulder, their hands down at their sides, and with slight flexion in their elbows. The goniometer was placed with the axis at the subjects' acromion process. With their palm facing toward their body, the subjects lifted their arm backward/upward to the full ability while a researcher stabilized their scapula. The stationary arm of the goniometer remained along the midaxillary line of the subject while the moving arm was aligned with the subject's arm. The angle from the midaxillary line to the lifted arm was recorded. The ICC for SE was r = 0.92.

Hip Flexion

The subjects laid supine on a floor mat. The subjects bent their testing leg to their chest without assistance. The goniometer axis was placed on the outside of the subject's hip over the greater trochanter. The stationary arm was aligned with the midline of the subject's pelvis and the moveable arm was aligned with the midline of the subject's femur using the lateral epicondyle as a reference point. The angle of HF was recorded. The ICC for HF was r = 0.96.

Hip Extension

The subjects laid prone on a floor mat with their knees extended. The subjects raised their dominant leg while keeping their knees extended. The researcher stabilized the subject's hip from rotating off the floor mat. The goniometer axis was placed on the outside of the hip over the greater trochanter. The stationary arm was aligned with the midline of the subject's pelvis and the moveable arm was aligned with the midline of the subject's femur using the lateral epicondyle as a reference point. The angle of HE was recorded. The ICC for HE was r = 0.91.

Lumbar Spine Lateral Flexion

The subjects stood straight with their feet shoulder width apart and their hands at their sides. The axis of the goniometer was placed over the sacral spine S1 with the arms of the goniometer pointed toward the ceiling along the spine. The subjects performed lateral flexion toward their dominant side. The moveable arm of the goniometer followed the spine directed toward the C7 vertebra. The angle of spinal lateral flexion was recorded. The ICC for LSLF was r = 0.93.

Lumbar Spine Rotation

The subjects sat on a foot stool, facing forward, with their spine erect, their feet on the floor, and their pelvis stabilized. The axis of the goniometer was placed over the center of the cranial aspect of the subjects' heads. The stationary arm of the goniometer was parallel to an imaginary line between the acromion processes. The subjects rotated their spine toward their dominant side to their full ability. The moveable arm of the goniometer followed the imaginary line between the acromion processes, whereas the stationary arm remained in the same position before movement. The angle of lumbar rotation was recorded. The ICC for LSR was r = 0.88.

Power

Lower-body muscular power was assessed with the countermovement VJ test (16) using the JustJump Mat (Probotics, Inc., Huntsville, AL, USA). The subject stood on the mat with his feet shoulder width apart. The subjects performed a rapid countermovement and a subsequent VJ. The remote to the mat indicated height of each jump in inches. A 30-second rest was given between each of the 3 trials. The maximum height of the 3 trials was recorded (16). Power output was calculated with VJ height and body weight using the Sayers formula (30). The ICC for VJ in our laboratory was r = 0.96.

Agility

The HEX test was used to evaluate agility (16). A hexagon was marked on the floor, each of the 6 sides measured at 24 inches and every angle was 120°. The subject began the test standing in the middle, facing toward 1 side of the hexagon. The subjects double-leg hopped from the center over each side and back to the center in a clockwise fashion starting with the side directly in front of them. A total of 3 revolutions around the hexagon while facing forward was completed (16). The test was restarted if the subject landed on the hexagon markings, lost balance, took extra steps, failed to return back to center, or changed direction. The timer was started the moment the subject's feet lifted from the center ground on the first jump. The timer was stopped the moment the feet had returned to the center on completion of the third revolution (16). The subjects performed 3 trials for each condition. Two minutes of rest were provided between each trial. The fastest time (to the nearest 0.1 seconds) of the 3 trials was recorded (16). The ICC for the agility test was r = 0.90.

Strength

Upper-body strength was assessed using the 3-repetition maximum (3RM) testing method for the BP exercise (16). Researchers provided spotting as needed and ensured proper form and technique. The subjects completed 2 warm-up sets. The first warm-up set consisted of 8 repetitions with 65% of estimated 3RM load followed by a 2-minute rest. The second warm-up set consisted of 5 repetitions with 75% estimated 3RM load followed by a 3-minute rest. After the warm-up sets, the subjects attempted 100% of estimated 3RM load. The 3RM load was determined within 3–5 attempts with 3 minutes of rest between each attempt. If the estimated load was too heavy, the load was decreased by subtracting 2.5–5%. If the estimated load was too light, the load was increased by adding 5–10% (16). The highest 3RM load was recorded for each condition. Strength was compared on an absolute basis (total amount of weight lifted for 3 repetitions) and on a relative basis (total weight lifted divided by body weight). A direct relationship exists between strength and muscle size; therefore, athletes with heavier body weights tend to have more total muscle mass compared with those with lower-body weights. Taking this into consideration, in this subject population, body weight is positively related to BP strength. The relative strength (kilogram of load per kilogram of body weight) provides a better comparison measure between subjects. The ICC for 3RM BP testing in our lab was r = 0.94.

Statistical Analyses

All statistical analyses were completed using SPSS statistical software (SPSS version 20; IBM, Armonk, NY, USA). Repeated-measures multivariate analyses of variance were used to assess the effects of the 4 different conditions (CON, PLA, SA, and CF) on flexibility measures (sit-and-reach, SE, SLR, HF, HE, LSLF, and LSR) and related performance variables (VJ, HEX, and BP). Significant multivariate effects were followed by univariate tests. Separate repeated-measures analysis of variance were used to assess the effect of the 4 conditions on time in center balance, adjusted BP (load per kilogram body weight), and adjusted VJ (jump height per kilogram body weight). For each univariate analysis, Huynh-Feldt epsilon was calculated to test the assumption of sphericity. If this statistic was not significant, sphericity was assumed and the unadjusted statistic was used. If this statistic was significant, then sphericity was considered to have been violated and the Huynh-Feldt adjusted statistic was used to test significance.

To evaluate the magnitude of change in each mouth guard condition, effect size (ES) for all variables were calculated using Hedges' g formula. The ES were used to compare magnitude of change as small effects may have a large impact in high-level athletes (24). Table 1 displays all ES values. Data are expressed as mean ± SD and statistical significance was set at a < 0.05 level. Power of 0.8 was calculated for the sample size using the primary variables of interest.

Table 1
Table 1:
Effect size.*

Results

Dynamic Balance

No significant difference in balance was observed between conditions (CON: 19.91 ± 5.6 seconds; PLA: 19.98 ± 5.5 seconds; SA: 20.1 ± 6.3 seconds; CF: 20.1 ± 5.6 seconds; p = 0.99) (Figures 2 and 7).

Figure 2
Figure 2:
Dynamic balance. Time in center balance on the stability platform did not differ between conditions. CF = custom-fitted mouth guard; CON = no-mouth guard control; PLA = placebo mouth guard; SA = self-adapted mouth guard.

Flexibility and Range-of-Motion

No significant differences between conditions were observed for the flexibility measures obtained for the sit-and-reach, SLR, HE, or LSR. Pairwise comparison revealed that the CON condition had significantly greater HF than the CF condition (CON: 118.85 ± 9.3°; CF: 116.3 ± 9.7°; p = 0.03; ES: −0.27), and the SA condition resulted in significantly greater SE than the CF condition (SA: 36.25 ± 9.0°; CF: 34.85 ± 9.7°; p = 0.014; ES: −0.14). A trend for significance was observed for LSLF as the CF condition had greater ROM than the SA condition (CF: 33.25 ± 9.2°; SA: 31.85 ± 9.3°; p = 0.054; ES: −0.15) (Figures 3 and 8).

Figure 3
Figure 3:
Flexibility. The SA condition had significantly higher shoulder extension flexibility compared with the CF condition. The CF condition had significantly lower hip flexion flexibility compared with the CON condition. No other differences in flexibility were observed between conditions. *p < 0.05 compared with CON; **p < 0.05 compared with CF. CF = custom-fitted mouth guard; CON = no-mouth guard control; PLA = placebo mouth guard; SA = self-adapted mouth guard.

Vertical Jump Height and Power Output

No significant differences were observed regarding VJ height between conditions in absolute (CON: 61.0 ± 7.8 cm; PLA: 60.7 ± 7.7 cm; SA: 60.5 ± 8.2 cm; CF: 60.3 ± 9.1 cm; p = 0.42) or relative terms (CON: 0.78 ± 0.16 cm·kg−1; PLA: 0.78 ± 0.17 cm·kg−1; SA: 0.77 ± 0.16 cm·kg−1; CF: 0.78 ± 0.18 cm·kg−1; p = 0.83). No significant effects were observed between groups in terms of absolute power output (CON: 5,261.4 ± 613.7 W; PLA: 5,230.1 ± 555 W; SA: 5,243.2 ± 636.5 W; CF: 5,212.1 ± 613.6 W; p = 0.78) (Figures 4 and 9). As well, relative power output did not significantly differ between conditions (CON: 66.49 ± 7.2 W·kg−1; PLA: 66.46 ± 7.6 W·kg−1; SA: 66.09 ± 7.6 W·kg−1; CF: 66.12 ± 8.5 W·kg−1; p = 0.88).

Figure 4
Figure 4:
Estimated power output. No significant differences were observed between groups in power output calculated from vertical jump (VJ) and body weight. CF = custom-fitted mouth guard; CON = no-mouth guard control; PLA = placebo mouth guard; SA = self-adapted mouth guard.

Agility

No significant differences were observed between conditions for time to completion of the HEX agility test (CON: 10.9 ± 1.6 seconds; PLA: 10.6 ± 1.0 seconds; SA: 10.5 ± 1.0 seconds; CF: 10.7 ± 1.1 seconds; p = 0.22) (Figures 5 and 10).

Figure 5
Figure 5:
Agility. No significant differences in time to completion of the Hexagon agility test were observed between conditions. CF = custom-fitted mouth guard; CON = no-mouth guard control; PLA = placebo mouth guard; SA = self-adapted mouth guard.

Strength

A trend for a significant effect for absolute strength was observed (p = 0.06). Pairwise comparison revealed that the CON condition resulted in a higher absolute strength compared with the PLA condition (CON: 98.8 ± 17.4 kg; PLA: 97.7 ± 17.6 kg; p = 0.046; ES: −0.06), whereas the absolute strength of the mouth guard conditions did not significantly differ from either CON or PLA conditions (SA: 98.5 ± 17.3 kg, ES: −0.02; and CF: 97.6 ± 17.6 kg, ES: −0.07). No significant differences were observed for relative strength (all conditions: 1.2 ± 0.1 kg of load per kg of body weight; p = 0.47, ES: 0) (Figures 6 and 11).

Figure 6
Figure 6:
Strength. Neither of the OTC jaw-repositioning mouth guard conditions (SA nor CF) differed significantly from the CON or PLA conditions in relative terms of bench press 3-repetition maximum performance. CF = custom-fitted mouth guard; CON = no-mouth guard control; PLA = placebo mouth guard; SA = self-adapted mouth guard.
Figure 7
Figure 7:
Dynamic balance spaghetti graph. Time in center balance on the stability platform did not vary significantly between conditions for the majority of subjects. CF = custom-fitted mouth guard; CON = no-mouth guard control; PLA = placebo mouth guard; SA = self-adapted mouth guard.
Figure 8
Figure 8:
Sit-and-reach spaghetti graph. Length of reach during the sit-and-reach test did not vary significantly for all subjects. CF = custom-fitted mouth guard; CON = no-mouth guard control; PLA = placebo mouth guard; SA = self-adapted mouth guard.
Figure 9
Figure 9:
Vertical jump spaghetti graph. Vertical jump height did not significantly vary between conditions for all subjects. CF = custom-fitted mouth guard; CON = no-mouth guard control; PLA = placebo mouth guard; SA = self-adapted mouth guard.
Figure 10
Figure 10:
Hexagon (HEX) test spaghetti graph. With the exception of 1 subject, the time to complete the HEX test did not significantly vary between conditions. CF = custom-fitted mouth guard; CON = no-mouth guard control; PLA = placebo mouth guard; SA = self-adapted mouth guard.
Figure 11
Figure 11:
Relative BP strength spaghetti graph. Performance on the BP test did not significantly differ between conditions for all subjects. BP = bench press; CF = custom-fitted mouth guard; CON = no-mouth guard control; PLA = placebo mouth guard; SA = self-adapted mouth guard.

Discussion

The dental technique of jaw repositioning has been used in the development of potentially ergogenic mouth guards. Previous evidence suggested the possibility of improved athletic performance with the use of some jaw-repositioning mouth guards (2,5,10). This study examined the effects of 2 OTC jaw-repositioning mouth guards on the performance on VJ (power), 3RM BP (strength), 7 flexibility tests, the HEX agility test, and center balance on a balance board (dynamic balance) in 20 college-aged male athletes. The results of this study reveal that neither the SA nor the CF jaw-repositioning mouth guards were effective in promoting a change in performance outcomes of balance, flexibility, muscular power, agility, or strength tests in college-aged male athletes.

The results of this study are consistent with the previous literature in which strength was not affected by jaw repositioning. However, the lack of effect on muscular power contradicts previous evidence. Bates and Atkinson (5) evaluated the effects of a jaw-repositioning appliance compared with a no-appliance control condition, on upper- and lower-body power and muscular strength. In that study, each of the 11 college-aged male subjects completed maximum lifts for BP and hip sled exercises for strength assessment, and VJ for power assessment, with and without use of the oral appliance. Performance on BP and hip sled exercises was not different between the 2 conditions, indicating the absence of an effect of jaw repositioning on upper- and lower-body strength, respectively. However, a significant increase in VJ performance was observed with the use of the oral appliance compared with the controls. Use of the jaw-repositioning appliance led to improvements in power but not strength (5). An increase in VJ and anaerobic power performance with a jaw-repositioning mouth guard was also observed previously in our laboratory (2). We compared a neuromuscular dentistry-designed jaw-repositioning mouth guard to a standard mouth guard in a randomized crossover study evaluating muscular endurance and anaerobic capacity in male athletes. The advanced jaw-repositioning mouth guard led to improved muscular power performance on VJ and a modified Wingate Anaerobic Test (2). More recently, increased power and force on a bench throw test were observed with the use of a customized OTC performance mouth guard compared with an OTC boil-and-bite mouth guard and a no mouth guard control in male and female adults (10). Additionally, the male subjects (n = 26) had higher power and force in the supine plyo press power quotient test while using the customized OTC performance mouth guard compared with the boil-and-bite and no mouth guard conditions (10).

The lack of performance effects in this study may be due in part to the standardized method of jaw repositioning. To decrease costs and increase availability, the manufacturers developed a production system that eliminates the need for dental expertise. However, individuality and precise jaw positioning may not be acquired without the use of advanced dental techniques and direct contact between dental expert and athlete. More advanced dental techniques that are used in the production of TMD treatment devices, such as transcutaneous electric neural stimulation and electromyography (EMG), may be necessary to create an “optimal” jaw-repositioning mouth guard for each individual athlete. Additionally, dental experts are not present when fitting an OTC mouth guard. It is possible that, despite the supervision of trained research staff, improper fitting of the mouth guards used in this study occurred. Although we believe this is unlikely, it does highlight a potential limitation when untrained individuals are expected to properly fit their own mouth guard. Future research should take this into consideration when evaluating the effects of jaw-repositioning mouth guards.

Another possible explanation for the lack of observed effects in this study includes the specific design of the mouth guards in question. Similar to the OTC boil-and-bite mouth guards used as the control condition by Dunn-Lewis et al. (10), the mouth guards investigated in this study did not elicit an effect on performance when compared with a control without a mouth guard. Perhaps, the structure of the SA and CF mouth guards in this study were too similar to other OTC mouth guards that are not accompanied with claims of increased performance.

A limitation of this study is the lack of comparison to a non–jaw-repositioning OTC mouth guard. Another limitation lies within the PLA mouth guard as the design promoted a lack of fit and was claimed to be uncomfortable by most subjects. The absence of blinding could have potentially been another limitation as the subjects may have preferred one condition over others. To address this limitation, the subjects were encouraged to perform to the best of their ability for each test, despite the condition. As well, the jaw-repositioning design was not disclosed to reduce subject bias. Although many individuals open their mouth when completing activities such as the BP exercise, open-mouth breathing was controlled for during the 3RM BP test, along with all other tests, as the subjects were constantly reminded to bite down while exerting effort.

This was the first study to evaluate the effects of jaw repositioning through a standardized increase in dental occlusion on balance, flexibility, and agility. Although the results were null, the findings lead us to ask other questions regarding the performance claims surrounding these mouth guards and the underlying mechanism of effective jaw-repositioning mouth guards.

Practical Applications

The results of this study indicated that the 2 OTC jaw-repositioning mouth guards were ineffective at enhancing performance of dynamic balance, flexibility, power, agility, and strength in 20 college-aged male athletes. The jaw-repositioning method of producing a standardized increase in dental occlusion may explain the difference in the current power results compared with our previous study (2) that used EMG to determine an optimal resting jaw position for each individual subject. Perhaps, professional manipulation of myofascial activity using advanced dental techniques during mouth guard fitting is necessary to elicit changes in muscular power performance. The purpose of the simplified positioning method used in the mouth guards evaluated in this study was to increase availability and practicality of these jaw-repositioning mouth guards. Eliminating the requirement of dental expertise for the production of these mouth guards enabled the manufacturers to reduce the costs associated with production and sales. These factors make the mouth guards evaluated in this study more practical than the neuromuscular dentistry-designed mouth guards yet less effective as an ergogenic aid in terms of the aspects evaluated in this study.

Although changes in the specific performance aspects of flexibility, balance, agility, power, and strength were not observed with these mouth guards, aerobic performance should not be overlooked. Jaw-repositioning mouth guards may affect aerobic performance in a manner unrelated to proprioceptive movements and therefore may be differentially affected by jaw repositioning. The technique of jaw repositioning has been used to treat breathing disorders by increasing respiratory passageways (12,21,28). Future research should determine whether these OTC jaw-repositioning mouth guards affect aerobic performance in athletes.

This study provides additional support to the evidence that promotes mouth guard compliance as negative performance effects were not observed. Overall, mouth guard use did not negatively affect dynamic balance, flexibility, muscular power, agility, or strength kinetics in college-aged male athletes. The use of mouth guards as a safety device should continue to be encouraged among athletes involved in sports with a high risk of dental injury. The ergogenic effects of OTC jaw-repositioning mouth guards remain questionable as more contradicting evidence is presented. The results of this study indicate that not all OTC jaw-repositioning mouth guards are created equal and therefore not all these mouth guards will impart positive effects on physical performance.

Acknowledgments

This study was funded by a grant from Shock Doctor, Inc. The results of this study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association. We are grateful to the subjects for their participation. We thank Pat Sarcone, Karla Schacher, Pat Davitt, Tony Aboseff, Christina Corino, Laurie Damian, Derek Geischen, Dr. Richard Habeeb, Ryan McCoyd, Alec Moran, Altamash Raja, and Keith Smith for their assistance with recruitment and data collection.

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Keywords:

dental occlusion; athletic performance; temporomandibular; repositioning

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