The relationship between form and function within the craniofacial complex has been investigated by several Authors. However, there is still controversy regarding the different electromyographic activation patterns of the elevator muscles of the jaw. One particularly contentious area of enquiry is whether it is facial morphology that determines the strength of muscle activation, or whether a strong musculature can influence skeletal growth processes.
In light of the aforementioned considerations, the objective of the current clinical observational study was to investigate the potential correlation between the electromyographic activity of selected masticatory muscles (masseter, anterior temporalis and suprahyoid) and the craniofacial morphology of subjects under examination, with a particular focus on elucidating the mechanical advantage derived from different sagittal relationships between the maxillae. The electromyographic evaluation is carried out before the beginning of the orthodontic treatment (T0).
Patients needing an orthopaedic and/or orthodontic treatment
Deciduous, mixed, or permanent dentition
Systemic diseases or congenital anomalies affecting craniofacial growth or development
Signs or symptoms of temporomandibular disorder (TMD)
Dental Pain
Past maxillofacial surgery
Patients willing to begin orthopedic/orthodontic treatment
Case-only
Prospective
EMG
Diagnostic testDisposable bipolar surface electrodes will be used. The patient's skin will be clean with cotton gauze soaked in alcohol before electrodes placement to reduce skin impedance. The operator will palpate the muscle belly while the patient clenches his teeth and will position surface electrodes in parallel to the muscular fibres. Doing so the position of the electrodes results as follows: Masseters electrodes will be fixed parallel to the exocanthion-gonion line and with the upper pole of the electrode under the tragus-labial commissural line. Temporalis electrodes will be positioned along the anterior margin of the muscle (corresponding to the frontoparietal suture). Suprahyoid muscles electrodes will be placed in the submental area nearly 1 cm posterior to the mental symphysis, paramedian to the midline and lightly diverging. A reference electrode will be applied to the forehead of the patient.
Percentage Overlapping Coefficient - POC %
It indicates in % the ratio between the activation of the left muscle compared to the right one and its value is between 0 and 100%. A POC of 100% identifies two muscles that activate symmetrically. A lower value shows a greater asymmetry of muscles activation. 95% of subjects without muscular imbalances of dental origin exhibits POC values between 80 and 90%. The POC detected are: Temporalis Anterioris, Masseter Muscle and mean.
Asymmetry index - ASIM %
It compares the influence of dental contacts on the total activity of the right MM and TA with respect to the left MM and TA. Its value varies between -100% and +100%. A negative value indicates a greater differential activity of the left muscles; conversely, a positive value indicates a greater differential activity of the right muscles. 95% of subjects without muscular imbalances of dental origin exhibits values of asymmetry between ± 10% .
Activation Index - ATTIV %
3.It compares the influence of dental contacts on the TA activity in relation to MM activity. A negative value implies greater differential recruitment of TA, while a positive value implies greater differential recruitment of the MM. 95% of subjects without muscular imbalances of dental origin exhibits activation values between ± 10%.
TORQUE %
Torque measures the differential activity of the right TA and left MM in relation to the antagonist torque. A prevalence of the right TA and left MM muscles, or right MM and left TA, may result in twisting forces on the jaw resulting in laterodeviation. This index ranges between -100% and +100%. -100% indicates the total prevalence of left TA and right MM, + 100% indicates the total prevalence of right TA and left MM. 95% of subjects without muscular imbalances of dental origin exhibits torque values between ±10%.
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