Abstract
Introduction: Bite raising occlusal attachments or bite blocks are commonly integrated into clear aligner treatments. They aim to prevent posterior extrusion and promote active intrusion of posterior teeth by enhancing masticatory muscle activity (MMA) and associated occlusal forces on the dentition. However, the putative mechanism of their effect remains largely anecdotal.
Aims: 1) Investigate the effect of aligners with bite raising occlusal attachments on habitual MMA, compared to attachment-free control aligners. 2) Determine whether bite raising induces transient signs and symptoms of masticatory muscle pain.
Methods: Twelve volunteers were recruited for this randomised, cross-over study. Deambulatory recordings of MMA including amplitude, duration, frequency and workload were taken using a wearable electromyographic (EMG) device over a period of 5 hours in a natural environment while wearing: 1) no aligners; 2) control aligners; and 3) aligners with occlusal attachments that encroached into their free-way space (FWS) for eight days. Participants’ FWS, occlusal discomfort (OD), stress levels and temporomandibular disorder (TMD) symptoms were monitored. Descriptive statistics and linear mixed modelling were used to analyse the results.
Results: Bite raising attachments significantly influenced MMA, resulting in an increase in the mean number of contraction episodes per hour (i.e. +55%; 95%CI +12%-67%) and muscle workload, from day one to day eight of wearing bite raising aligners. Compared to baseline values, both aligners resulted in significant increases in FWS, with the bite raising aligner showing the most pronounced (i.e. +114%; 95%CI +85%-144%) increase. Participants experienced significant occlusal discomfort during the first three days, regardless of the type of aligner. None of the participants were diagnosed with TMDs.
Conclusions: There is a transient increase in MMA when aligners encroach into the FWS in a group of healthy young adults. The increase was despite adaptation to the aligners as shown by diminishing discomfort and a newly established FWS. Occlusal attachments may aid in control of the occlusal vertical dimension.