research dataNathan Dau1, Don Sherman, Richard Bolander, Cynthia Bir, Hermann EngelsBiomedical Engineering Department, Wayne State University, Detroit, USA 
Kinesiology, Health and Sport Studies, Wayne State University, Detroit, USA

The possibility that athletic performance can be affected by a person’s jaw posture during the activity has been of interest to sports practitioners for many years. However, popular claims of the benefits of using mandibular orthopedic repositioning appliances or techniques such as jaw clenching to affect exercise performance are not routinely supported by previous research studies. Of particular interest remains the question of their potential ergogenic value to enhance an athlete’s strength and power generating capacities during high intensity muscular work. Using established elbow and knee flexion/extension testing protocols on a calibrated isokinetic dynamometer (Biodex System 2, Shirley, NY), this study examined selected muscle function characteristics in male NCAA II college football players (n=18) under test conditions in which they wore a professionally-fitted dental appliance (PowerPlus) designed for optimal maxilla-mandibular spacing, a common “boil-and-bite”-type mouth guard (Shock Dr.), and conditions in which they were instructed to have their teeth touch while keeping the jaws relaxed (Relax) or clenched (Clench) without wearing any oral appliances. The four different test conditions were randomly assigned for both isokinetic exercise protocols. Data were statistically analyzed using MANOVA procedures with Bonferroni correction. Results indicated a significant improvement in total work (+9.8%), peak torque/body weight (+10.5%), and average power (+11.25%) for elbow flexion in the PowerPlus relative to the Relax condition. Similarly, knee flexion total work for the PowerPlus was significantly higher compared to both Relax and Clench test conditions. In contrast, no statistically significant differences between conditions were noted for elbow and knee extension total work, maximum repetition work, peak torque/body weight, and average power. The present observations from controlled isokinetic dynamometry testing suggest that wearing a professionally fitted dental appliance may have acute beneficial effects on some aspects of an athlete’s muscular performance. However, additional research is needed to evaluate its usefulness for long term applications and under conditions that represent an athlete’s typical training and competition environment. 

INTRODUCTION: 

Strength and strength training are critical to performance in competitive sports. Many studies have been conducted that evaluate the effect jaw position may have on acute muscle strength. These studies have shown that subjects who suffer from temporomandibular pain dysfunction (TMD) or have a severe vertical dimension of occlusion (VDO) can benefit from a Bite Elevating Appliance (BEA) (Abdallah, Mehta, Forgione, 2004). One such appliance that has been studied in depth is the MORA. This device has shown to improve isometric strength in athlete and non-athlete populations compared to a habitual occlusion and placebo appliance (Gelb, Mehta, Forgione, 1995). The data has shown there is an optimal maxilla-mandibular spacing that can create maximum isometric strength (Chakfa, Mehta, Forgione, 2002). Making the spacing larger or smaller can decrease a subject’s strength. One study compared a BEA created for optimal spacing to a common mouth guard for American football players with TMD. The results showed that isometric strength was improved with a common mouth guard and even more by the BEA (Abduljabbar, Mehta, Forgione, 1997). 

Unfortunately, BEA’s have not proven effective in all studies. In particular, isokinetic strength has not proved to increase with the use of BEA’s (Forgione, Mehta, Westcott, 1991). These tests have been conducted at variousspeeds (60,120, and 240 °/sec) without significant results. If BEA’s can only improve isometric strength they will offer minimal benefit to athletes who rarely perform isometric tasks in competition. The goal of this study was to test the effect of selected oral appliances on isokinetic strength in athletes. The hypothesis is that a BEA designed for optimal maxilla-mandibular spacing can increase isokinetic strength in anathlete population without screening for VDO. The BEA was compared to a common mouth guard in addition to no appliance conditions to ensure that similar results could not be obtained with a simple, off the shelf alternative. 

METHOD:

Bite Appliance Fitting: The effect of dental appliances on strength was tested in eighteen NCAA Division II American football athletes. The athletes were fitted for two mouth guards typically worn during sport and practice. One mouth guard was the commercially available Shock Doctor Pro (Plymouth, MN). These mouth guards were fitted according to the manufacturer’s instructions, by heating in water and biting the appliance to fit each subject. The other mouth guard was a PowerPlus (Traverse City, MI) mouth guard. This appliance can be customized in many ways. For the purpose of this study, lower dental impressions were taken, and the appliance was fabricated on a stone model for each test subject. The mouth guard was then custom-fitted by a dentist. The PowerPlus mouth guard is a BEA that is designed to optimize the non restrictive jaw position. Each subject’s vertical dimension of occlusion was measured and the mouth guard thickness adjusted to create an optimal vertical dimension of occlusion of 19 mm. 

Data Collection:

The subjects participated in two different strength tests under four different conditions. The conditions included both mouth guards and two conditions without any dental appliance. These conditions required subjects to clench their teeth for one condition (clench) and to have their teeth touching while relaxing their jaw for the other condition (relax). Upper and lower body isokinetic tests were conducted on a Biodex System 2 (Shirley, NY). The subjects performed four sets for both tests, one for each condition. The order of the sets was randomized for each participant. 

The tests were concentric-concentric tests at a velocity of 60°/sec on the subjects’ dominant side. The upper body test was an elbow flexion/extension, and the lower body exercise was knee extension/flexion. Prior to isokinetic exercise testing, each subject completed a standard warm-up protocol that consisted of a 5-min sub maximal upper or lower body cycle ergometry exercise at a moderate intensity. The Biodex device was calibrated before each day of testing and the device was warmed-up according to the manufacturer’s instructions. The Biodex positioning was adjusted for each test subject to ensure proper alignment with joint position. Once the device was positioned properly, the subject was secured in place and allowed to familiarize themselves with the device and the exercise. The subjects performed a set of five repetitions for each of the conditions listed above. The subjects were given a three minute rest period between each of the sets. To diminish effects of position changes on results, the subjects remained in the Biodex chair with the restraints in place during the rest periods. There was no verbal encouragement provided during any of the testing, and the monitor of the Biodex was adjusted so that the test subjects could not observe their performance during testing. The results were not made available to the test subjects until all testing had been completed. 

Data Analysis: 

Four criteria were evaluated for the isokinetic tests: Peak Torque/Body Weight (PT/BW), Max Repetition Work (MRW), Total Work (TW), and Average Power (AP). Since the subjects varied considerably in stature and strength, the data was normalized using the relax condition before statistical analysis was conducted. The relaxed condition was considered the baseline, and was subtracted from all conditions. The other three conditions were evaluated as improvements or degradations from the relax condition. 

The results were analyzed using SPSS 17.0 (Chicago, IL). MANOVA’s were conducted for the upper and lower body isokinetic tests in flexion and extension. Bonferroni post hoc tests were conducted for any conditions that demonstrated a statistical significance (α ≤ 0.05). 

RESULTS: 

In extension, the isokinetic tests did not show statistical significance for any criteria in either test. However, both tests had statistical significance in flexion (Table 1). The upper body tests showed that the PowerPlus had significantly higher results than the relax condition for PT/BW, TW, and AP (α = 0.007, 0.02, and 0.011 respectively). The lower isokinetic tests showed that the PowerPlus was significantly higher than the relax and the clench conditions for TW (α = 0.021 and 0.031 respectively). 

UPPER BODY ISOKINETIC DATA MEANS
 
Cells marked with † are statistically significant (α ≤ 0.05) 

Percent increases were calculated for the data that proved significantly different. The PowerPlus BEA showed mean improvements of 10.5%, 9.8%, and 11.2% from the relax condition in the upper body tests for PT/BW, TW, and AP respectively. The total work for the PowerPlus lower body tests was significantly improved from both the relaxed and the clenched conditions. It provided an increase of 16.8% and 16.0% from the relaxed and clenched conditions, respectively. 

LOWER BODY ISOKINETIC DATA MEANS
 
Cells marked with † are statistically significant (α ≤ 0.05) 

DISCUSSION: 

These results indicate BEA devices can increase isokinetic strength in athletes without screening for severe VDO. This implies that an average athlete population could benefit from the device. Some subjects may observe a larger benefit due to their predisposition, but it appears there is a benefit to the general population. During the fitting of the BEA, the VDO was measured for each subject, and these measurements could be utilized to compare groups based on their VDO. The improvements in strength could be compared between large and small VDO groups to determine if there is a significant difference between the groups. 

Future studies could examine the long term effects of BEA’s on strength and performance. Athletes could be evaluated over the length of an off-season strength conditioning program. Strength improvements could be compared between subjects who are provided a BEA to wear during strength training to a control group participating in the same conditioning program. Other studies have required subjects to wear their BEA for a week before testing (Allen, Walter, McKay, Elmajian, 1984). This study did not find any statistical significance, but week to week performance variability for test subjects could have diminished results. 

The ultimate goal of improving an athlete’s strength is to improve their sport-specific performance. One study examined a test more applicable to sports, the in-flight velocity of golf balls (Egret, Leroy, Loret, Chollet, Weber, 2002). This study found that velocity increased and was more consistent with the BEA. Future studies should examine other sport-specific tests to determine if BEA’s can improve performance. American football athletes could perform a battery of tests included in the NFL combine (40 yard dash, standing long jump, bench press, etc.). 

CONCLUSION: 

These data indicate dental appliances designed for optimal maxilla-mandibular spacing can improve isokinetic strength in flexion. The PowerPlus BEA provided improvements in both upper and lower body isokinetic flexion. These results differ from previous studies. The PowerPlus device provided statistically significant increases in three of the four criteria evaluated (PT/BW, TW, and AP) compared to the relax condition in elbow flexion. It provided increases of 10.5%, 9.8%, and 11.2% for these criteria respectively. In isokinetic knee flexion, the PowerPlus increased TW by 16.8% and 16.0% compared to the relaxed and clenched conditions. 

These improvements were not present with a common mouth guard. These data show that an average athlete population can benefit from a specifically designed BEA, and that a common mouth guard does not provide the same benefit. 

REFERENCES: 

Abdallah EF, Mehta NR, Forgione AG, et al. (2004). Affecting upper extremity strength by changing maxillo-mandibular vertical dimension in deep bite subjects. Cranio, 22, 268-275. 

Abduljabbar T, Mehta NR, Forgione AG, et al. (1997). Effect of increased maxillo-mandibular relationship on isometric strength in TMD patients with loss of vertical dimension of occlusion. Cranio, 15, 57-67. 

Allen ME, Walter P, McKay C, Elmajian A. (1984). Occlusal splints (MORA) vs. Placebos show no difference in strength in symptomatic subjects: double blind/cross-over study. Can J of App Sport Sci, 9, 148-152. 

Chakfa AM, Mehta NR, Forgione AG, et al. (2002). The effect of stepwise increases in vertical dimension of occlusion on isometric strength of cervical flexors and deltoid muscles in nonsymptomatic females. Cranio, 20, 264-273. 

Egret C, Leroy D, Loret A, Chollet D, Weber J. (2002). Effect of mandibular orthopedic repositioning appliance on kinematic pattern in golf swing. Int J Sports Med, 23, 148-152. 

Forgione AG, Mehta NR, Westcott WL. (1991). Strength and bite, Part 1: An analytical review. Cranio, 9, 305-315. 

Gelb H, Mehta NR, Forgione AG. (1995). Relationship of muscular strength to jaw posture in sports dentistry. N Y State Dent J, 61, 58-66. 

Gelb H, Mehta NR, Forgione AG. (1996). The relationship between jaw posture and muscular strength in sports dentistry: a reappraisal. Cranio, 14, 320-325. 

Acknowledgement 

The authors would like to thank Bulent Ozkan for his assistance with statistical analysis, Paul Harker and Paul Winters for allowing their players to participate in the study, all the athletes who took the time to participate in the study, and Dr. Thomas Birk for the use of his lab equipment and time.