Importance and justification The importance of carrying out this study is to verify the electrical activity generated by the masticatory muscles to be able to have clarity of their performance in the development of orthopedic treatment, thus complementing the diagnosis to achieve a more successful treatment with myofunctional device SN1 in Class II malocclusions.

In addition, with the results of this study, treatment prediction criteria are provided to the clinician, depending on the thickness of the muscle, more specific equipment will be chosen to solve the malocclusion and prognosis when using the SN1 myofunctional device in class II malocclusions.

Additionally, it has academic utility, since there is little scientific evidence about myofunctional SN1 device and its impact on masticatory muscles, thus opening the door to a line of research where this study can be used as a basis for future orthopedic clinical research. in UNICIEO.

Added to this and according to the results, the knowledge about the SN1 will be updated, thus providing evidence for the teaching of orthopedics for the students; and also a measurement protocol with electromyography for children will be provided Overall objective To evaluate the electrical activity of the masseter and temporal muscles in patients from 7 to 12 years of age, with skeletal class II who are under treatment with myofunctional apparatus (Sn1), in the UNICIEO orthopedics clinic by means of kinesiological electromyography compare with a control group without use of the device Specific objectives

• Determine the activity of the masseter and temporal muscles of patients at rest (without functional orthopedic apparatus) in the two study groups.
• To determine the activity of the masseter and temporal muscles of the patients after the use of functional orthopedic equipment (Sn1), after six months of treatment and in the control group without treatment.

Study design Prospective nonrandomized controlled clinical trial, 1: 1 allocation Participants Study group. Boys and girls between 7 and 12 years skeletal class II, for the study group the individuals will be selected from the UNICIEO postgraduate clinic of orthopedic clinic orthodontics after conducting a full clinical case study exposed to a board of specialist teachers in orthodontics, where by means of several diagnostic methods a skeletal class II is confirmed that involves a treatment with myofunctional apparatus SN1; patients presenting syndromes that generate craniofacial alterations, patients with previous orthopedic treatment, patients with signs of condyle lesions, patients with Pierre Robin syndrome or any form of slit will be excluded.

Control group. Children aged between 7 and 12 years diagnosed with class II dental classification, who attend the Leonardo Da Vinci School after carrying out an intraoral and extraoral photography study and diagnostic impressions with study models accepting participation in the study, children over the age of 12 will have to sign an agreement, patients who present syndromes that generate craniofacial alterations, patients with previous orthopedic treatment, patients with Pierre Robin syndrome or any form of slit will be excluded.

Interventions or independent variables

• Use of Sn1 equipment in the study group: the study participants are placed, which correspond to the study group, the Sn1 apparatus of which is composed of dorsal arches with an hourly intensity of 12 hours a day, where a control will be carried out monthly.
• Six months of observation in the control group: patients in the control group will be given informed consent, children over the age of 12 will have to sign an informed consent, then a photographic study of intraoral and extraoral photos will be made, impressions to obtain models and have an observation of the molar classification, and verify if it has the inclusion criteria of the study, once that participation is confirmed, the muscular activity of the masticatory muscles will be observed, in two times, at the beginning and at six months after.

Results or dependent variables.

Masseter and temporal muscle activity measured with EMG (microvolts) in the following moments:

Moment of measurement: the electrical activity will be taken at 2 moments of the study.

T0: Initial Moment

1. Rest: A record of electromyography will be taken where the patient has a natural position of the head and is in complete rest, resting time (60 seconds)
2. Maximum intercuspidation: The patient will be instructed to perform a force that will be measured with a dynamometer where it generates a dental tightening, to verify the electrical activity that is generated in that maximum contraction of masseter muscles captured by the electromyograph.
3. Use of the device: a record of the muscular activity will be made at the moment the patient puts on the Sn1 device.

T1: six months of use of functional equipment (Sn1)

1. Rest: A record of electromyography will be taken where the patient has a natural position of the head and is in complete rest, resting time (60 seconds)
2. Maximum intercuspidation: The patient will be instructed to perform a force that will be measured with a dynamometer where it generates a dental tightening, to verify the electrical activity that is generated in that maximum contraction of masseter muscles captured by the electromyograph.
3. Use of equipment (study group) will be a record of muscle activity at the time the patient puts on the Sn1 device

Sample size To date, no similar studies have been located, therefore a pilot test will be carried out with 10 patients from each group and with the result the sample size of the study will be calculated.

Statistical Methods The data will initially be tested using the Shapiro-Wilk test. Maximum changes in molar bite force during treatment or observation (T0 - T1) will be evaluated, and t-paired tests will be used to evaluate the statistical significance within each group. A comparison of the changes between the treatment and control groups will also be carried out using t-unpaired tests. Parametric analyzes will be used: Anova, Multivariate analysis of variance (Manova), T2 Hotelling test. All correlations were considered significant with p <0.05.

Inclusion Criteria:

• Boys and girls from 7 to 12 years old with class II skeletal classification attending a consultation in the dental clinic of the UNICIEO foundation, to be fitted with myofunctional apparatus type Sn1

Exclusion Criteria:

• Patients who have had previous orthopedic treatment
• Patients with signs of condyle injuries
• Patients of Pierre Robin or any form of cleft
• Patients with syndromes that associate craniofacial anomalies and muscle alterations.