Specific diurnal EMG activity pattern observed in occlusal collapse patients: relationship between diurnal bruxism and tooth loss progression

Abstract

Aim: The role of parafunctional masticatory muscle activity in tooth loss has not been fully clarified. This study aimed to reveal the characteristic activity of masseter muscles in bite collapse patients while awake and asleep.

Materials and methods: Six progressive bite collapse patients (PBC group), six age- and gender-matched control subjects (MC group), and six young control subjects (YC group) were enrolled. Electromyograms (EMG) of the masseter muscles were continuously recorded with an ambulatory EMG recorder while patients were awake and asleep. Diurnal and nocturnal parafunctional EMG activity was classified as phasic, tonic, or mixed using an EMG threshold of 20% maximal voluntary clenching.

Results: Highly extended diurnal phasic activity was observed only in the PBC group. The three groups had significantly different mean diurnal phasic episodes per hour, with 13.29±7.18 per hour in the PBC group, 0.95±0.97 per hour in the MC group, and 0.87±0.98 per hour in the YC group (p<0.01). ROC curve analysis suggested that the number of diurnal phasic episodes might be used to predict bite collapsing tooth loss.

Conclusion: Extensive bite loss might be related to diurnal masticatory muscle parafunction but not to parafunction during sleep.

Clinical relevance scientific rationale for study: Although mandibular parafunction has been implicated in stomatognathic system breakdown, a causal relationship has not been established because scientific modalities to evaluate parafunctional activity have been lacking.

Principal findings: This study used a newly developed EMG recording system that evaluates masseter muscle activity throughout the day. Our results challenge the stereotypical idea of nocturnal bruxism as a strong destructive force. We found that diurnal phasic masticatory muscle activity was most characteristic in patients with progressive bite collapse.

Practical implications: The incidence of diurnal phasic contractions could be used for the prognostic evaluation of stomatognathic system stability.

Figure 1. Typical panorama x-ray view of Eichner Index B4 patient.

Note the absence of posterior occlusal support with highly resorbed alveolar bone (white arrow).

Figure 2. Typical diurnal phasic EMG activity observed in the PBC group.

MVC, EMG activity during maximal voluntary clenching.

Figure 3. Incidence of phasic episodes relative to the duration of each episode (threshold: >20% MVC).

Diurnal phasic episodes of long duration were most frequently observed in the PBC group. Note that all the subject, in MC and YC groups, showed episodes less than twice per hour.

Figure 4. Incidence of phasic, tonic, and mixed episodes >20% MVC for YC, PBC, and MC groups.

Note that, during waking hours, all the subjects in PBC group showed high prevalence of phasic episodes. On the other hand, despite the fact that most of the subjects in PBC group showed high prevalence of tonic and mixed episodes, some of the subjects in PBC group showed only few episodes of these types, which seemed to be almost equivalent with those in YC and MC groups. Incidence of phasic episodes during sleep for PBC, MC and YC groups were remarkably low compared to those in waking hours (p = 0.008).

Figure 5. ROC curve for phasic, tonic, and mixed episodes (threshold: >20% MVC).

a. ROC curve for episodes during waking hours, b. ROC curve for episodes during sleep.