Introduction:
The most used type of intra-oral protective splint is a “boil and bite” mouthguard – an appliance adapted by the athlete directly in the oral cavity after its plasticization with hot water. According to the literature, they may have inadequate size and retention.

Aim of the study:
To evaluate the influence of “boil and bite” mouthguards used by mixed martial arts professionals on the stomatognathic system.

Material and methods:
Seventeen male combat sports competitors, professionally training mixed martial arts (MMA) with the “boil and bite” mouthguards were examined. Medical interview and dental examination were performed. The participants answered questions concerning the habits of mouthguard’s use, problems or dysfunctions in the head and mouth area, and maxillofacial trauma which occurred during martial arts training.

Results:
The average participant was 27,16 years (M: 24; SD: 8,67) and had a training experience of 7,94 years (M: 4; SD: 9,07). 76.48% of participants used mouthguards a few times a week. 52.94% of the evaluated group had gum bleeding during toothbrushing, 58.82% teeth clenching during training, and 47.07% headaches after training. 29.41% of athletes taking part in the study reported a concussion during martial arts training, and 23.53% had dentine and enamel fracture. Only 29.41% of participants used a mouthguard that fully covered their teeth, and 35.29% stated that their protective splint is well adapted.

Conclusions:
The use of “boil and bite” mouthguards by mixed martial arts athletes can affect the stomatognathic system. Standard protective splint users should be subjected to regular controls by a dentist.