Sunday, January 08, 2012
An example of a claim that mouthguards reduce concussions that can be found in the popular press was the following statement by Ron Wilson, head coach of the Toronto Maple Leafs: "We're trying to get all our players to wear mouthguards. If you get hit and you're wearing a proper mouthguard, it lessens the chance of a concussion." The theory is that a mouth guard prevents concussions after a blow to the jaw (in which forces are thought to move upwards to the base of the brain) by positioning the jaw in such a manner that it absorbs the impact forces instead of the brain. Now let us examine what the data shows in terms of whether mouthguards actually reduce concussion.
Review of the evidence
The most comprehensive scientific review on the topic of mouthguards and concussions was conducted by Knapik et al. (2007). Their conclusion was as follows: "However, the evidence that mouth guards protect against concussion was inconsistent, and no conclusion regarding the effectiveness of mouth guards in preventing concussion can be drawn at present.” (p. 118). Note that all underlined sections in this article are emphasized by myself and not the original authors. The authors also discuss “…a lack of evidence for concussion prevention (regarding mouth guards). The inconsistency among studies is problematic and makes it impossible to determine conclusively whether mouthguards reduce concussion risk at present.” (p. 139). In fact, the authors even cite some evidence that concussion rates are higher among mouth guard users than non-mouth guard users. Lastly, the authors state, “There is currently insufficient evidence to determine whether mouthguards offer protection against concussion injury, and more work of good methodological quality is needed.” (p.140).
Review of specific studies
Here are some reviews of articles on the topic of mouthguards and concussions that were found during a literature search on PubMed, and what these articles say on the topic.
BARBIC ET AL. (2005). These authors performed a multicenter randomized controlled study and concluded that, “In this study, concussion rates were not significantly different for varsity football and rugby players who wore the WIPSS Brain-Pad mouth guard compared with other types of mouth guards.” (p. 94). The American Academy of Neurology’s (AAN’s) definition of concussion was used. The based on observations by trained health care professionals, not a survey.
BLIGNAUT ET Al. (1987). The authors performed a cross-sectional study of 321 college rugby players who did or did not use mouthguards. The authors stated, “We conclude that injuries sustained at rugby in this study were not associated with the use or non-use of mouthguards.” (p. 5). These injuries included concussion. The study, however, is flawed because it is based on survey data and does not provide a definition of concussion.
GARON ET AL. (1986). This study is based on survey data from 754 male football players who were asked about mouthguard use and history of various injuries, including concussion. The study is flawed because it is based on survey data and does not provide a definition of concussion. The authors found 15 concussions reported in the mouthguard use group and 14 reported in the non-mouthguard use group. This is not a significant difference and does not provide any evidence of mouthguard effectiveness for concussion reduction.
LABELLA ET AL. (2002). In this study of male Division I college basketball players (also flawed due to survey data and not clearly defining concussion in the article) the authors concluded, “Custom-fitted mouthguards do not significantly affect rates of concussions or oral soft tissue injuries, but can significantly reduce the morbidity and expense resulting from dental injuries in men’s Division I college basketball.” (p. 41).
MARSHALL ET AL (2005). This was a study of rugby players assessed weekly for injuries based on whether they did or did not wear mouthguards. The authors found that, “The risk of concussion was not lessened by the use of padded headgear (RR = 1.13, 95% CI: 0.40–3.16) or mouthguards (RR = 1.62, 95% CI: 0.51–5.11)” (p. 113). Unfortunately, no definition of concussion was provided by the authors and information was based on self-report only.
MIHALIK ET AL. (2007). These authors found that mouthguard use does not decrease the severity of concussion and that neurocognitive deficits after concussion did not differ between athletes who used mouthguards compared to those who did not. The study involved 180 athletes who were followed prospectively after a baseline cognitive assessment was performed. Unfortunately, the definition of concussion used in this study was not described. It was also not specified how a concussion was identified beyond having athlete’s complete self-report questionnaires.
TAKEDA ET AL. (2005). These authors performed experiments in which they struck an artificial skull model with a pendulum. They found that use of a mouthguard significantly decreased distortion of the mandibular bone and acceleration of the head. Based on this, the authors theorized that mouthguards may have the potential to reduce concussions. However, this is speculative and is not data that allows one to make any firm conclusions about this topic in living human beings.
WISNIEWSKI ET AL. (2004). The authors studied 87 Division I College football teams and found no advantage of wearing a custom made mouthguard over a boil-and-bite mouthguard to reduce the risk of concussion. Concussions were recorded by athletic trainers but the definition of concussion was not described.
Why the Myth Continues
The main reason why the mouthguard myth continues is because people misread (or do not read) peer reviewed research articles, authors make misleading statements, and/or because authors cite flawed studies to support their claims without noting the caveats. An example can be found in the study by Kemp et al. (2008). If one were to just review the abstract of the paper, one would see the following statement: “Mouthguard and headgear usage was associated with a reduced incidence of concussive injury.” (p.227). However, it is not until one reads the actual manuscript where it is found that this statement is misleading. Specifically, the manuscript states, “The incidence of concussions sustained by players not wearing mouthguards was higher than those wearing mouthguards, but it did not reach statistical significance; the average severity of concussions was similar for wearers and nonwearers.” (p. 229). In science, if a difference is not statistically significant, there is no real difference between the two groups. In fact, the authors later go on to state the following: “Similarly, research to date indicates that the wearing of mouthguards does not reduce the incidence of concussion in rugby.” (p. 232-233).
It should not come as a surprise to anyone keeping up with the research literature on this topic that there is no conclusive evidence that mouthguards prevent concussions since McCrory addressed this very topic in 2001. In that paper, McCrory noted that, “The ability of mouthguards to protect against head and spinal injuries in sport falls into the realm of ‘neuromythology’ rather than hard science.” McCrory shows how two often cited papers have been used to perpetuate this myth.
The first paper often cited was by Stenger et al. in 1964. In this study, the authors reported their observations of a season of Notre Dame University football. They anecdotally reported one case in which they felt that mouthguard use abolished the symptoms of repeat concussion. The case includes the implausible claim that the patient could not recall a game or scrimmage dating back to highschool in which he had not either partly or completely lost consciousness. Despite this claim of losing consciousness every game and scrimmage, the patient made his way onto a Division I football team as an All-American. In the Stenger paper, there were 10 cases of concussion during the entire season, which did not provide enough data to perform statistical analysis of a protective effect. In addition, all of their data was speculative. The most the authors could do was speculate that mouthguards may reduce concussions since mouthguards alter the position of the mandible.
The second paper often cited is by Hickey et al. (1967). This study did not even examine living people, but instead used mouthguards fitted to cadavers (also known as dead people). The author showed that mouthguards could reduce forces applied to the head after a blow to the jaw. This was then used by later authors as evidence that mouthguards reduce concussion risk in living people, although Hickey et al. never made such a claim. The problem is that this is obviously a huge generalization which does not provide any direct proof of reduced concussion risk in living humans. In addition, the degree to which a cadaver’s skull responds to trauma is different from how the skull of a living human would respond.
In 1998, a review by Chalmers (1998) stated, “Moreover, there is evidence that mouthguards are effective in protecting against concussion and injuries to the cervical spine.” (p. 339). He cites numerous studies as evidence to support his statement. These studies are Clegg (1969), Fricker (1983), Kerr (1986), Jagger and Milward (1995), Johnsen and Winters (1991), Powers et al. (1984), Stenger at al. (1964), and Chapman (1985). Let us examine these studies one by one.
CHAPMAN (1985a): The author states that “The use of mouthguards should be encouraged in all contact sports as the most important value of the mouthguard is the concussion saving effect following impact to the mandible. This fact alone should make the wearing of mouthguards compulsory in all contact sports.” (p. 27). The problem is that no references are listed to support the claim. However, earlier in the article, the authors reference the Hickey et al. study (see above for discussion) as support for wearing a mouthguard in sports.
CLEGG (1969): Regarding mouthguards, the author states, ”It reduces the incidence of concussion caused by blows from under the chin.” (p. 341). No references were cited by Clegg to support the statement.
FRICKER (1983): Not a single mention of concussion or brain injury is made in the article.
JAGGER (1995): The author states that, “The increased separation between the head of the glenoid fossa that occurs at the increased vertical dimension should also decrease the transmission of force from the mandible to the cranial base and thus reduce the risk of concussion.” (p. 31). The reference was Chapman (1985b). Chapman (1985b) stated: “Thus, standard mouthguards protect against orofacial injuries (dental injuries, intraoral and circumoral lacerations and jaw fractures) and concussion.” (p. 25). The references cited were Clegg (1969; see above), Davis and Knott (1984) and Chapman (1985c). Davis and Knott (1984) is a dental article with no mention of concussion. Chapman (1985c) states that mouthguards result in reduced injury to facial regions and “…a reduction in the concussion force from a blow to the mandible.” (p. 34). The references were Clegg (1969; see above), Upson (1982) and Davies et al. (1977). The articles by Davies and Upson (1982) make no mention of mouthguards reducing concussions.
JOHNSEN & WINTERS (1991): The authors state that, “The use of mouthguards reduces the likelihood of concusssions, cerebral hemorrhage, unconsciousness (“knock-out“), or other serious central nervous system injuries and even death.“ (p. 658). Three references were cited, a) Hickey et al. (see above), b) Stenger et al. (see above), and c) Godwin et al. (1968). The reference to Godwin is odd because it is a dental article that does not contain a single mention of concussions or any other type of central nervous system problem.
KERR (1986): The author states that mouthguards “…prevents fractures, dislocations, and concussions.” (p. 417). The author references Hickey et al. (see above) and Cathcart (1959). Note that the reference in the text is to Cathcart (1959) yet the biography lists Cathcart (1952) and that the actual reference is really from 1951. The Cathcart article does not make a single mention of concussions.
POWERS ET AL. (1984): The authors state that, “The mouth protector reduces forces that may cause concussions, neck injuries, and jaw fractures.” (p.84). The reference? You guessed it. Hickey et al. yet again (see above). A few sentences later the authors state: “According to some observers, an additional benefit was a reduction in the number of concussions and neck injuries occurring among football players.” (p. 84). The reference was Stenger et al. (see above) and News of Dentistry (1972). The News of Dentistry reference discussed the 1971 University of Connecticut football program. It stated that no players wearing a mouthguard suffered a concussion but two players who wore a mouthguard did not. This was what was offered as support for “key protection” when the reality is that the numbers are too small to make any sweeping generalizations about a protective effect.
STENGER ET AL. (1964): See above.
As this article has demonstrated, there is no strong scientific evidence that mouthguards prevent or reduce concussive injuries. Despite this, a myth continues to exist in the media, among coaches, the public, and some health care providers that mouthguards prevent or reduce concussions. As was detailed above, this belief owes its historical roots to the citation of articles that do not support the claim. Many of the cited articles contain no mention of concussions or refer back to two articles from the 1960s based on one living person and one dead person. This article highlights the need for statements to be based on evidence and for people to check the sources of information and critically analyze them before believing a particular claim. Mouthguards do play a role in reducing dental and oral-facial injuries and are recommended by many physicians for this express purpose.
Barbic et al. (2005). Comparison of Mouth Guard Designs and Concussion
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Cathcart, J. (1951). Mouth protectors for contact sports. Dental Digest, 57, 346-348.
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