Study design and participants

A prospective observational clinical study was conducted from November 2021 to December 2022. All the recruited patients were hospitalized for dentofacial deformities and underwent orthognathic surgery. The inclusion criteria were:

Patients aged 18 or over;

Class III malocclusion;

Surgical procedure: Le Fort I osteotomy + Bilateral Sagittal Split Osteotomy (BSSO).

Written consent obtained in accordance with procedures defined and approved by the ethics committee following the registry plan (RP).

The exclusion criteria were: patients under 18 years old; patients with cleft of lip and palate; patients with bone metabolic diseases; patients already included in studies about the use of other treatments (devices or drugs) that may affect the outcome; other types of malocclusions or surgical procedures; failure of the acquisition of three-Dimensional (3D) facial scans; paracetamol allergy.

The ethical approval was obtained from the by the Ethics Committee of Biomedical Sciences of the “Federico II” University of Naples with the protocol number (392/21). The study was conducted in accordance with the Declaration of Helsinki.

All the patients who met the inclusion criteria were enrolled in the study and were divided into two groups: the first group (Standard Group - SD) included patients treated after surgery with glucocorticoids and Hilotherapy face mask; the second group (SD + PEMF) included patients treated after surgery with the standard therapy and PEMF. Assignment to one of the two groups depended on the device availability and on patient’s acceptance of the procedure. All surgical procedures were performed by the same operating team.

Both groups received the same postoperative medical therapy based on ceftriaxone 2 gr i.v. intraoperative and for 3 days after surgery, betamethasone 8 mg i.v. for 3 days and then gradually reduced over the next 6 days, gastric protection and analgesic therapy with ondansetron 8 mg/4mL + ketorolac tromethamine 60 mg/2mL + tramadol 200 mg/2mL through the elastomeric pump for the first 24 h.

All patients received the same amount of postoperative intravenous hydration (1500 cc of fluids for the first 3 days after surgery) and the same post-operative hospital care. All patients in both groups were instructed on face care and oral hygiene measures, including the use of 0.2% chlorhexidine digluconate mouthwash at least twice daily.

Every osteotomy was performed by using piezosurgery (Piezosurgery Plus, Mectron s.p.a. 2014,) to reduce the thermal damage. Both groups of patients received cryotherapy through the facial mask of the hilotherapy system, with a set temperature of 11° C. The facial mask was placed inside the operating theater immediately after surgery and kept on for at least 24 h. It was periodically removed to allow patients to their personal hygiene and to feed themselves. (Fig. 1a)

Fig. 1

Hilotherapy applied facemask on the left and PEMF applied facemask on the right

The SD + PEMF group received PEMF through the electro-medical device SEQEX® FAM (S.I.S.T.E.M.I. srl, Italy) following a protocol drawn up by our Unit according to the scientific literature [7, 16] and to the indications of the technical suppliers. Our protocol has been codified to maximize the swelling prevention efficacy by the emission of low-frequency waves treatment.

SEQEX® FAM is a class IIa medical device, following the essential requirements of the current European directive 93/42 concerning medical devices. The device used in the study consisted in a control console, a power cable and a connector to a specific designed mat, called Anatomical Applicator. The application of magnetic fields modulated in intensity, and frequency and waveform, takes place with the aid of transducers contained within the mat connected to a control console. (Fig. 1b)

The electromagnetic therapy was applied 2 times per day (36 min each), alternately with Hilotherm system. This protocol was performed from 4 h after surgery until the 4th day postop, before discharging the patient from the hospital.

Data sources and collection

Each Patient underwent a 3D facial scan the day after surgery (1d scan) and 4 days after surgery (4d scan), usually the last day in hospital, to obtain a facial volume in milliliters.

Facial scans were acquired by the Shining 3d Ein Scan Pro High Definition (Hangzhou, China, 2019) which has a proven accuracy of 0.045 mm at a working distance of 510 mm. (Fig. 2a) The scans were all performed by the same operator, to reduce the risk of bias.

Fig. 2

Upward the Face Scanning with Shining 3d Ein Scan Pro HD; below the Facial scans cutting on Meshmixer software based on two lines: the first passing between tragus and nasion; the second traced perpendicular to the first; the final scan was used to assess the reduction of volume between the first and the fourth post-operative day

The scans were then uploaded to Meshmixer software ver. 3.5 (Autodesk, 2020). In order to compare 1d scan with 4d scan each mesh derived from the scans was cut by two lines: the first passing through tragus and nasion; the second was traced perpendicular to the first passing through the tragus to obtain comparable facial volumes. The volume in ml of each 3D mesh (1d and 4d) was calculated through the tool mesh analysis. (Fig. 2b, c)

For all patients, a visual analogue scale (VAS) was used to assess pain (0 mm: no pain at 100 mm: disabling pain) and the dose of analgesics administered was recorded. The measurements were carried out after the end of the elastomeric pump (in the second day after surgery), in the total of 4 days of hospitalization and at the seventh day, during the outpatient check-up. The analgesics dose was not considered at 7 days due to the impossibility to control the intake of the drug after discharge from hospital. Paracetamol 1000 mg was used as analgesic for all patients, to standardize the data.

Variables

The primary predictor variable was the facial volume, measured in millimeters, and in particular the facial volume reduction between the 3D scan acquisitions on the first day after surgery and on fourth day after surgery. The secondary variables were the VAS SCORE and the analgesics amounts in mg. All the covariates, such as age, sex, smoke and BMI, were considered to avoid confounding factors.

Statistical methods

The statistical analysis was performed with Statistical Package for Social Sciences, version 16.0, for Windows (SPSS, Chicago, IL, USA) and R (software), version 4.0.2, for Windows (R Foundation for Statistical Computing, Vienna, Austria). To perform the analysis of correlation between the primary variable and the covariates the Pearson’s regression coefficient (r) was used. For each categorical variable, a dummy variable was introduced, taking values of 0 (absence of the character) or 1 (presence of the character). In particular: - For r < 0.1 there is no discernible correlation between the two variables; - For 0.1 < r < 0.3 the correlation between the two variables is weak; - For 0.3 < r < 0.5 the correlation between the two variables is intermediate; - For r > 0.5 the correlation between the two variables is strong. After the analysis, the Pearson’s coefficient was standardized as p-value and a p < 0.05 was considered statistically significant for each correlation analysis.

To compare the facial volume reduction in the two groups, a data distribution test was performed. The data distribution was abnormal due to the small sample size; therefore, a non-parametric test was applied. Using the non-parametric Mann-Whitney U test (group comparison), the data were examined for signs of significant differences. A value of p < 0.05 was considered statistically significant.

To compare the VAS SCORE results and the administrated analgesics in the two groups, the statistical analysis was performed using non-parametric Mann-Whitney U test (group comparison); statistical significance was defined at P < 0.05.