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).

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).

Muscle activity is commonly recorded by means of surface electromyography (sEMG). However, sEMG data can be affected by various artifacts, resulting in questionable interpretation of the results. A standardisation procedure allows to reduce variability of the assessment of masticatory muscle activity during static and dynamic tasks.

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 on the forehead of the patient. The sEMG analysis will be composed of four parts:

1. Masticatory muscle standardisation procedures (repeated thrice): two 10 mm thick cotton rolls will be positioned on the mandibular posterior teeth of each participant, and a 5 second maximum voluntary contraction will be recorded to standardize anterior temporalis and superficial masseters sEMG signals. The mean sEMG potential obtained in the first acquisition was set at 100%, and all further ssEMG potentials will be expressed as a percentage of this value (μV/μV × 100).
2. Maximum voluntary teeth clenching: patients will be asked to clench their teeth in maximum intercuspation as hard as possible for 5 seconds.
3. Submental muscle standardisation procedures: participants will be asked to push their tongue against the palate (without teeth clenching), and a 5 seconds sEMG suprahyoid muscles activity will be recorded. All further sEMG potentials will be expressed as a percentage of this value (μV/μV × 100).
4. Saliva swallowing: participants will be asked to keep their mouth open to accumulate saliva and, when needed, to swallow "freely" (as usual) and a 5 seconds sEMG activity will be recorded.

Inclusion Criteria:

• Patients needing an orthopaedic and/or orthodontic treatment
• Deciduous, mixed, or permanent dentition

Exclusion Criteria:

• 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

Data will be available upon motivated request to the Principal Investigator.