Abstract
AimThe 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 MethodsSix 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.ResultsHighly 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.ConclusionExtensive bite loss might be related to diurnal masticatory muscle parafunction but not to parafunction during sleep.Clinical Relevance: Scientific rationale for studyAlthough 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 findingsThis 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 implicationsThe incidence of diurnal phasic contractions could be used for the prognostic evaluation of stomatognathic system stability.
Highlights
Bruxism has caused great concern as a cause of periodontal tissue destruction
Clinical Relevance: Scientific rationale for study: 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
Our results challenge the stereotypical idea of nocturnal bruxism as a strong destructive force
Summary
Bruxism has caused great concern as a cause of periodontal tissue destruction. The relationship between bruxism and tooth loss is not clear, despite the great efforts of epidemiological surveys such as the Study of Health in Pomerania [1]. Increased nocturnal masticatory muscle activity has been thought to cause occlusal overloads, thereby causing clinical complications for teeth and prostheses [2]. Problems possibly related to masticatory muscle forces are periodontal disease and tooth fracture. Houston et al [3] suggested that there is weak or absent correlation between periodontal disease and bruxism, and between bruxism and occlusal status. Bernhardt et al [1] reported that bruxism, as disclosed on questionnaires, as well as occlusal wear into dental hard tissues, protrusive contacts, and elongation of teeth, were not associated with probing depth
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