Sample

Thirteen healthy patients aged between 18 and 40 years participated in this study. All subjects were male, had a normal occlusion and all of their teeth (except third molars), had no comorbidities, and did not present extensive excoriations or lacerations of the face that would prevent the fixation of surface electrodes. They had no median or paramedian fractures of the maxilla, no Le Fort I type fractures, mandibular fractures, or dentoalveolar injuries. All of the patients included in the sample were conscious on arrival at the hospital and did not have skull base fractures or neurological injuries. However, three patients did not attend the pre-established study follow-up appointments (1, 2, 3, and 6 months). Therefore, the final sample included 10 men.

The study patients were divided into two groups: group I comprised men (average age 34.5 years) with Le Fort III type fractures ( n = 3) and left zygomatic orbital fractures ( n = 1) treated surgically using the coronal approach with pre-auricular extension, as described by Ellis and Zide ; group II comprised men (average age 24.8 years) with frontal bone fractures ( n = 3) and naso-orbito-ethmoid fractures associated with Le Fort II type fractures ( n = 3) treated surgically using the coronal approach, as described by Ellis and Zide.

Patients who had zygomatic, naso-orbito-ethmoid, and Le Fort fractures required additional surgical incisions, such as subciliary and intraoral buccal incisions. A single surgeon performed the fracture surgery. There was no difference in the anchorage system used for the fractures (1.5-mm plates and screws system, Tóride; Tóride Implantes Ind. Com. Ltda, Mogi Mirim, SP, Brazil). All patients received preoperative cephalexin 2 g at 1 h before surgery and took 1 g every 8 h while hospitalized; after discharge they took cephalexin 500 mg every 6 h for 7 days, ketoprofen 100 mg every 8 h for 3 days, and dipyrone as a painkiller in the case of pain in the first week.

All fractures were middle and upper third, caused by a high-energy trauma. The most prevalent aetiology of the fractures was traffic accidents; however physical aggression and falls were also among the causes. One patient in group 1 and one patient in group 2 had transient neuropraxia of the frontal branch of the facial nerve for 15 days after the surgery. No patient included in the study had a postoperative infection, or wound dehiscence or bruising that could interfere with the study. The average duration of hospitalization was 3 ± 2 days.

The control group comprised healthy subjects with a normal occlusion and no temporomandibular dysfunction. These subjects were matched to the study group subjects by age, sex, height, and weight. They had electromyographic (EMG) data, molar bite force, and jaw mobility values within the normal range.

Bite force

A digital dynamometer (model IDDK; Kratos, Cotía, SP, Brazil) was used to analyse the bite force in the first molar region on both sides. The patients were instructed to bite the dynamometer with maximum force three times (2-min rest interval). The maximum molar bite force (the largest number) was obtained.

Electromyographic data

Muscular activity was evaluated using EMG recordings of the masseter and temporalis muscles in the following conditions: rest (5 s), teeth clenching in maximum voluntary contraction (MVC) (4 s), maximum right (5 s) and left (5 s) laterality with dental contact (canine guidance), and maximum protrusion with dental contact in anterior guidance (5 s), presenting the Christensen phenomenon.

EMG activity was evaluated using a Myosystem-Br1 apparatus (DataHominis Tecnologia Ltda, Uberlândia, MG, Brazil). The EMG analysis was performed by one trained professional. The electrodes were placed on the masticatory muscles in the intermediate region between the centre of the innervation zone (motor point) and the muscle tendon, aligned longitudinally and parallel to the direction of the muscle fibres, as this was considered the most suitable place. To ensure precise location of the muscles, specific palpation manoeuvres in MVC were carried out. To avoid cross-talking, a reference electrode was placed in a region distant from the muscles to be tested. The EMG analysis was performed by one trained professional.

Mandibular mobility

A digital pachymeter (Mitutoyo, Santo Amaro, São Paulo, Brazil) was used to measure mandibular mobility, considering the maximum standards for mouth opening, as well as right and left lateral movement and protrusion. The necessary instructions and explanations were given, and the patient was always asked to remain as calm as possible and to breathe slowly. The mandibular mobility benchmarks were the dental midlines. The calliper was positioned in the incisal and mesial region of the maxillary right central incisor and the incisal and medial region of the lower right central incisor.

Statistical analysis

The raw electromyographic signal was used to derive electromyographic amplitude values obtained by calculating the root mean square (RMS). The EMG, bite force, and mandibular mobility data were tabulated and submitted to statistical analysis using the repeated measures test (IBM SPSS Statistics version 21.0; IBM Corp., Armonk, NY, USA). A 95% level of significance was adopted ( P ≤ 0.05).