What is the relationship between mouthguard use and concussion incidence in professional male rugby union?

Objective
To investigate the association between mouthguard use and match concussion incidence.
Design
Case-control (cases: match concussions, controls: non concussion contact injuries).
Setting
All participating teams in the top tier of professional rugby union in England, 2013–2019.
Participants 1436 male professional rugby union players.
Interventions (or Assessment of Risk Factors)
Medical staff reported mouth guard use at the time of injury/concussion. Outcome
Measures Odds of sustaining a match concussion when wearing a mouth guard or not.
Main Results
Match concussion incidence (2013–19) was 17 per 1000 hours (95%CI:14–20). Sixty-five percent of cases and54%of controls wore mouthguards. Mouthguard use was associated with concussion injury (adjusted odds ratio: 1.51, 95%CI:1.25–1.82). Median number of days absent due to injury was equal for both cases and controls (9days). Sustaining a concussion in the current or previous season was associated with a nearly three-fold increased odds of concussion (odds ratio: 2.98, 95%CI:2.58–3.44). Age and position had no significant effect on concussion risk (OR: 0.99, 95% CI:0.97–1.01andOR: 1.05, 95%CI:0.88–1.27, respectively). Conclusions
The use of mouthguards in this professional rugby setting was associated with increased odds of concussion. This was an unexpected finding and the reasons for it are unclear. Mouthguards protect against dental injuries and should still be recommended, but further evidence is needed to understand the relationship with concussion, in particular regarding mouthguard use in non-injured populations, risk taking behaviours of concussed vs non-concussed athletes and mouthguard type (boil and bite/custom fit).