Relationship Between Angle of Incisal Path and Characteristics of Bruxism

Objectives: Sleep bruxism (SB) is harmful parafunction during sleep, however, the influence of anterior guidance to SB is still unclear. The purpose of this study was to investigate the relationship between angle of incisal path and characteristics of jaw movement and masseter muscle activity types during SB.
Methods: We recorded jaw movement, biological signals (respiration, EEG, EOG, ECG, EMG) and audio-visual record of 10 adult healthy volunteers (25.9 ± 5.8 yrs old) for two nights by using a six-degree-of-freedom measurement system of jaw movements during sleep. This system consists of an electromagnetic jaw tracking device with intra-oral sensor, an ambulatory polysomnograph and AV Monitor. The second night data was used for analysis. SB event was defined as elevation of RMS masseter EMG activity above 5% maximal voluntary contraction level. These SB events were classified into 5 jaw movement type (chopping, excursion, eccentric clenching, intercuspal clenching and mixed type) and 3 EMG activity types (tonic, phasic and mixed type) separately. Frontal and horizontal angle of incisal path were calculated when jaw was moved into the lateral excursion of 3 mm on border movement path. Spearman correlation was performed to measure the strength of the relationship between the angle of incisal path and 8 SB types.
Results: SB events were observed 3.3 times per hour. In chopping and eccentric clenching type, there were significant correlations between the frequency of SB events and frontal angle of incisal path (R = 0.840, 0.65 respectively; p < 0.05). In excursion type, there was a significant correlations between the frequency of SB events were and horizontal angle of incisal path (R = 0.64; p < 0.05). However, no significant correlation was observed between angle of incisal path and 3 EMG activity types of SB.
Conclusions: The jaw movement type of SB was related to anterior guidance.