Background:
Sleep bruxism (SB) and obstructive sleep apnea (OSA) are phenomena that occur during sleep. However, the relationships between them are not fully investigated.

Aim:
The aim of the study was to assess the relationship between SB and OSA and to assess the time dependence of these two phenomena.

Material and methods:
The material for the study consisted of 21 patients with symptoms of OSA determined after clinical examination. PSG examination with electromography of the masticatory muscles are performed in order to evaluate the episodes of apnea and bruxism verified by the analysis of audio-video records.

Results:
PSG study confirmed a strong correlation of the apnea - hypopnea index (AHI) with the number of bruxism episodes (r = 0.62; p = 0.003). Similarly, the bruxism episodes index (BEI) was strongly correlated with the AHI index (r = 0.614, p = 0.003). It has been shown that as the AHI index increases, the number of episodes of bruxism increases. The individual increase in AHI caused an increase in the number of bruxism episodes. on average, by 1.21 and the increase of the bruxism index by an average of 0.03. In addition, there was a strong correlation, almost functional dependence of the variable number of bruxism episodes before apnea and apnea before bruxism (up to 5s interval between events), (r = 0.98, p = 0.000).

Conclusions:
Occurrence of bruxism before apnea and apnea before bruxism despite their significant correlation do not allow for finding casual relationships between these phenomena.