A Preliminary Report of Structural Changes to Mouthguards During 1 Season ofHigh School Football

Abstract

Context: Extensive changes to mouthguards may occur as a result of wear and tear and equipment abuse.

Objective: To examine how the shape and thickness of custom-fabricated mouthguards change over the course of a complete season of high school football.

Design: Repeated-measures, case-series study.

Setting: High school.

Patients or Other Participants: Fifteen high school varsity football players aged 15 to 17 years began the investigation; 4 participants lost their mouthguards before the end of the season.

Main Outcomes Measure(s): Custom-made mouthguards were examined before the start of the season, midway through the season, and at the end of the season to document changes to material thickness and shape. Along with evaluating the thickness of mouthguards at the incisor/canine and molar regions, we assessed shape retention by evaluating the width of the mouthguard channel at the first molar.

Results: Material thickness at the incisor/canine region decreased by approximately 16% (F_2,20 = 34.20, P < .001) after 6 weeks of participation. Over the same time period, the mouthguard thickness at the molars decreased by 23% (F_2,20 = 31.92, P < .001), and the shape of the mouthguards changed as well (F_1,11 = 6.01, P = .029).

Conclusions: Although test mouthguards displayed significant deterioration in shape and material thickness, more research is needed to establish wearing length. Frequent inspections of mouthguards are advised to ensure that fit and protective abilities have not been compromised.

Key Points

• Mouthguard shape and thickness had changed significantly by 6 weeks into the football season.

• Frequent inspection of mouthguards is advised to ensure that fit is proper and that protective abilities have not been compromised.

To provide optimal safety during sport participation, the Academy for Sports Dentistry advocates the use of a properly fitted mouthguard and favors the use of a custom-fabricated device.¹ The Academy recommends that mouthguards be sufficiently thick to reduce impact forces and retain their shape so that they are not dislodged on impact. Furthermore, the Academy supports the use of mouthguards that are capable of maintaining these characteristics for, preferably, 1 full season of play.

Few authors have examined whether mouthguards can maintain an appropriate level of material thickness and preserve their shape for an entire athletic season. Initial research by Chaconas et al² revealed that in most cases mouthguard thickness was minimally reduced during the progression of the playing season. However, changes to the protective equipment were tracked for only half the season of play. Recently, Waked et al³ assessed the effects of aging on the retention of mouthguard shape. To impart the characteristics and properties of age, mouthguards were put through a number of cleaning cycles: each mouthguard was soaked in 60°F (16°C) water for 48 hours and then brushed 100 times with a soft toothbrush in soapy water at 140°F (60°C). This aging regimen, designed to represent the cleaning cycles of mouthguards in regular use, resulted in significant dimensional changes to the central incisor region of the mouthguard. Although simulations such as these might reproduce changes that are perhaps the result of regular usage patterns, they cannot, unfortunately, account for certain aspects of aging, such as mouthguard abuse (eg, from excessive biting).

In truth, one cannot obtain an accurate indication of the lasting effects of a mouthguard if the assessed changes are not the result of actual use or if the investigation is not extended for a reasonable length of time. Our objective was to evaluate the magnitude of structural changes (ie, to material thickness and shape) that occur in custom-fabricated mouthguards during a 12-week season of high school football.

METHODS

In this repeated-measures, case-series design study, we considered 3 dependent variables: mouthguard thickness at the labial and occlusal surfaces and mouthguard shape. These measures depended on a single experimental condition or independent variable: time.

Participants

Only subjects using mouthguards constructed in the same manner with the same type of material were considered for this investigation. To meet this requirement, all subjects were recruited from a single sport team. A local high school that supplied all members of its varsity football team with custom-fabricated mouthguards granted us permission to complete this investigation at their institution. Of the 39 athletes on the varsity football team, only 15 (age range, 15–17 years) agreed to participate in this study, which was approved by the Western Institutional Review Board on behalf of the university. Assent and consent were obtained from subjects and parents or guardians, respectively.

Procedures

Each of the study participants was provided 1 laminated, custom-fabricated mouthguard at the beginning of the football season. The football season was 12 weeks long and consisted of 7 games. The test mouthguards used by the athletes were all produced at one dental laboratory, and each was manufactured in the same manner to create mouthguards with similar specifications. Mouthguards were all produced from impressions of the maxillary teeth and were constructed using the same colored ethyl vinyl acetate material. Although the prefabrication thickness of the mouthguard material was 4 mm (2 sheets), the thermoforming process employed in the fabrication of the mouthguards resulted in an approximately 50% reduction in material thickness (Table 1). Furthermore, none of the mouthguards were constructed with balanced occlusion, as only impressions of the maxillary teeth were made available to the laboratory. When occlusion is balanced, the total biting surface of the maxillary mouthguard is in contact with the mandibular teeth. Any participant who lost the original mouthguard or required a new mouthguard at any time during the season was provided a replacement mouthguard but was excluded from the study at that point.

Table 1. Thickness of Mouthguard Material as Mean (SD) in mm (n = 11).

Before the mouthguards were distributed to the athletes, we noted various baseline thickness measurements and shape characteristics. To accurately assess the material thickness of the mouthguards, we obtained measurements using a spring-loaded caliper gauge accurate to 0.1 mm. Each measurement was repeated twice and the average thickness recorded. The occlusal thickness at the chewing surface of the mouthguards was assessed by obtaining measurements from the distobuccal and distolingual cusps of the second molars on both the right and left sides (Figure). If the second molar was missing, measurements were completed at the first molar. Measurements of the labial thickness (ie, the surface adjacent to the lips) were collected from the central incisors and both the right and left canines. Along with a baseline assessment recorded before the start of the season, the aforementioned measurements were repeated at the midpoint (6 weeks) and again at the end of the playing season (12 weeks). The overall average thickness at the occlusal and labial regions was then calculated using both right and left side measurements, and the mean was included in the statistical analysis.

Locations of mouthguard measurements. a, Channel width at the left first molar. b, Occlusal thickness at the distolingual cusp of the right second molar. c, Occlusal thickness at the distobuccal cusp of the right second molar.

In addition to thickness measures, changes to mouthguard shape were determined by evaluating the changes to the width of the mouthguard channel at the location of the first molar (Figure). Width measurements were achieved using a digital caliper (model MT5-00193; Mitutoyo American Corp, Aurora, IL). Shape retention was assessed once on both the right and left sides of the mouthguards, and these measurements were then repeated on 2 other occasions after the initial assessment (midseason and end of the season). Width data obtained from the right and left sides were then combined, and the average of these measurements was used for statistical analysis.

Data Analysis

We calculated a 1 (group) × 3 (time) analysis of variance with repeated measures to evaluate changes in each of the 3 dependent variables considered in this study: mean occlusal thickness, mean labial thickness, and average channel width (right and left sides). Post hoc pairwise comparisons with Bonferroni adjustments were calculated when necessary. All statistical analyses were performed using SPSS statistical software (version 11.5; SPSS Inc, Chicago, IL), with the level of significance for all statistical tests set a priori at α ≤ .05.

RESULTS

Our investigation began with 15 subjects, but only 11 completed the study, as 4 mouthguards were lost after the midpoint of the season. Rather than impute data for the missing values, we only analyzed data from the 11 subjects who completed the study.

Statistical tests performed on thickness data collected from the labial surface of both the incisors and canines revealed a significant main effect (F_2,20 = 34.20, P < .001, Mauchly W = .832, P = .437; Table 1). The labial thickness decreased about 16% from preseason to midseason and decreased an additional 2% to 3% from the middle of the season to the end of the season. Post hoc tests revealed a significant difference between the preseason and midseason labial thickness (P < .001), as well as between preseason and end-of-season thickness (P < .001). No difference was noted between midseason and end-of-season measurements (P = 1.0).

The thickness at the occlusal surface changed significantly over the course of the season (F_2,20 = 31.92, P < .001, Mauchly W = .762, P = .295). Decreases in occlusal thickness were 23% and 26%, respectively, when comparing preseason mouthguard thickness with midseason and end-of-season measurements. Again, post hoc tests revealed a significant change between the preseason measurement and the midseason measurement (P < .001) and between baseline and end-of-season measurements (P < .001) only.

As with thickness measurements, width measurements collected from the right and left sides of the mouthguards were combined for statistical analysis. A significant change was noted in mouthguard width (F_1,11 = 6.01, P = .029; Mauchly W = .158, P < .001); therefore, the Huynh-Feldt adjustment for degrees of freedom was applied. Unfortunately, post hoc tests did not reach statistical significance when the Bonferroni correction was applied. Thus, a measure of effect size (ie, Cohen d) was computed for each comparison. A large effect size (ie, any value greater than 0.8) was recorded for the preseason to midseason and preseason to postseason comparisons for both labial (2.40 and 2.38, respectively) and occlusal (1.77 and 1.94, respectively) thicknesses, whereas only a small effect size was noted at both mouthguard areas for the midseason to postseason comparison. This finding indicates that although significance was lost subsequent to the Bonferroni correction, it was not because of a low effect size but probably because of our small sample size. Table 2 presents the average change in channel width over time.

Table 2. Right and Left Side Channel Width at the First Molar as Mean (SD) (n = 11).

DISCUSSION

A number of authors have demonstrated that the level of protection offered by mouthguards is related to material thickness.^4–9 Both laboratory studies and in situ tests have revealed that as the material content of mouthguards is reduced, the ability of these protective devices to absorb impact energy decreases. Naturally, with more force transmitted to the teeth, a greater risk of injury exists.^8,9 In one laboratory study, decreasing the thickness of mouthguard material from 2.0 mm to 1.5 mm resulted in an increase of approximately 30% in the peak force transmitted during a drop ball test, and visible deformation occurred with further reductions. In our investigation, the material thickness at the occlusal surface decreased by nearly the same amount (approximately 0.48 mm) after only 6 weeks. By comparison, this change was greater than the amount reported by Chaconas et al,² who revealed that after half a season of football, the average amount of thinning that resulted at the occlusal surface of the first molar was less than 0.1 mm. This discrepancy in mouthguard performance might be related to manufacturing differences. In our study, mouthguards were fabricated from 2 sheets of thermoplastic ethyl vinyl acetate laminated together (ie, fused using high heat and pressure). In the study by Chaconas et al,² mouthguards were fabricated from prelaminated material. The 2-ply material used by Chaconas et al² consisted of a thin, soft inner layer with a slightly thicker, more rigid outer layer for added strength. Additionally, Chaconas et al² reported that the mouthguards used in their study were 3 mm thick, whereas in our study, the average postfabrication thickness at the occlusal surface was just over 2 mm.

Previously we mentioned that the mouthguards tracked in this investigation lacked a balanced occlusion. In the absence of a balanced occlusion, the maxillary and mandibular occlusal surfaces do not match up completely, and occlusal contact is likely to occur primarily at the molar area instead of over the entire set of teeth. As a result, it is quite possible that this misalignment could have promoted the excessive amount of wear we observed at the occlusal region. Furthermore, the poorly aligned occlusion could also explain the disproportionate rate of deterioration we reported between the first and second half of the football season, as occlusal contact would be expected to continue at the molar region until the area leveled off and the distribution of contact forces balanced out. Then again, the discrepancy in deterioration rate might also be related to the greater number of practices and increased intensity of practices during the early part of the season.

We found that along with thickness changes, significant alterations to shape also occurred very early in the course of the season. The average change in mouthguard shape we detected was slightly greater than the deformation reported by Waked et al,³ who also examined width changes in the same general location. However, the different outcomes in our study and that of Waked et al³ were not unexpected, given the artificially reproduced aging process in their study. It should be noted that although the average change in shape observed by the midpoint of the season was approximately 9%, in some cases, the range of change to channel width was noticeably greater. In those few instances, the extreme alterations in shape were presumably the result of mouthguard abuse.

Along with normal wear and tear, a user might engage in a variety of practices that could accelerate changes to material thickness or mouthguard shape. Mouthguard thinning at the occlusal surface is certainly magnified if wearers exert excessive biting pressure or if they grind their teeth abnormally. Also, removing the mouthguard from its position in the mouth and chewing on various locations along its margins or fringes can affect labial thickness and may even result in tears or punctures of the mouthguard. We believe that these destructive tendencies could be responsible for the larger-than-anticipated degree of thinning we detected along the labial surface of test mouthguards. Another habit too often witnessed among football players is the temporary wedging or extended storage of mouthguards between the face mask and helmet. This routine not only distorts the shape of the mouthguard but may also increase exposure of the mouthguard to the sun, which should be avoided. Waked et al³ also called attention to the fact that the cleaning process itself, if exaggerated or too vigorous, may alter the structural stability of a mouthguard. Furthermore, improper cleaning technique, such as using markedly hot water, can also result in distortion, because most mouthguards are made of thermoplastic material.³

Many of the reasons proposed to explain the extensive changes to both thickness and retention of shape are related to the abuse of mouthguards. If mouthguard abuse is in fact contributing to the deterioration of these protective devices, scheduling periodic inspections of the equipment throughout the athletic season might be helpful to verify that both fit and functionality are preserved but also to perhaps discourage athletes from causing any detrimental changes to their mouthguards. Of course, a greater amount of responsibility must also be deferred to the users to maintain and care for the mouthguards. To assist with this process, athletes must be provided with educational resources to make certain that mouthguards are used correctly, remain in good condition, and stay functional throughout the season. Additionally, preventive measures, such as providing athletes with a storage case or, when possible, attaching mouthguards to a face mask using a latch or lanyard, may help to minimize the tendency for athletes to unconsciously alter their mouth protector.

In anticipation of the thinning that may occur, one might be tempted to fabricate or distribute thicker mouthguards. Reports^9–11 indicate, however, that a drop in compliance tends to accompany significant increases in material thickness. Waked and Caputo¹² indicated that based upon the normal physiologic interocclusal space at rest (that is, the space between the maxillary and mandibular occlusal surfaces), the maximum thickness that would be comfortable and still be tolerated is approximately 4 mm.

As with most experimental research, the generalizability of our study results is limited. For example, the participants recruited for this investigation all played football. We recognize that football is not the only sport that requires mouth protection. In those sports in which athletes do not spend much time waiting to become involved or active, the level of deterioration might be different because of fewer opportunities to chew and deform the mouthguards.

In addition, although the participants in our investigation wore custom-made mouthguards, most high school athletes are provided with over-the-counter products (eg, a boil-and-bite mouthguard), which are inexpensive and readily available. Having studied how custom-fabricated mouthguards deteriorate over time, we cannot comment on the durability of other styles of mouthguards (such as the boil-and-bite variety), nor can we infer how mouthguards made of different materials or of different material thicknesses would hold up over the course of an entire season of play. We know, for instance, that although mouthguards supplied to athletes in this investigation were made of ethyl vinyl acetate, materials with different levels of hardness are available for equipment fabrication. Also, researchers^7,9,13,14 have recommended using mouthguards that are thicker than those provided to our study participants because of the added protection afforded the user, but another potential benefit of thicker material is that it might result in a product that is better suited to resisting breakdown.

One other aspect of the current study that restricts the generalizability of the results is the small sample size. With any research investigation, subject dropout is always a risk. This was an issue with our study, just as it was for Chaconas et al,² who reported a 35% dropout rate with one particular test group and indicated that only 13 participants from that group completed the investigation. Notwithstanding our small sample size, the preliminary data presented in this investigation have drawn attention to the durability of custom-fabricated athletic mouthguards. Clearly, more research is needed to establish the wearing length of both these and over-the-counter athletic mouthguards.

In summary, significant changes to both shape and thickness occurred before the midpoint of the athletic season. These findings indicate that it may be necessary to examine mouthguards on a regular basis throughout the season to ascertain that they have not lost their structural characteristics or protective attributes. To increase wearing length, dentists and others responsible for fabricating mouthguards may want to consider enhancing these devices by increasing (within reason) the material thickness or by using more durable material. Finally, educating athletes on the importance of maintaining and caring for mouthguards may also help to increase the length of time these protective devices remain suitable for use.