Use of Transcutaneous Electrical Nerve Stimulation (TENS) for the Recovery of Oral Function After Orthognathic Surgery
Phase: NA
Conditions: Orthognathic Surgery, Physiology, Transcutaneous Electric Nerve Stimulation
Sponsor: Universidad Complutense de Madrid

 
 
 
STUDY PROTOCOL 
 
 
 
 
Use of transcutaneous electrical nerve stimulation (TENS) for the 
recovery of oral function after orthognathic surgery 
 
 
 
 
 
 
 
 
NCT ID not yet assigned 
 
 
 
 
 
 
 
05/11/2020 
 
 
 
 
 
 
 
 
 

ABSTRACT: 
Oral functions of patients are markedly diminished immediately after orthognathic surgery, 
and novel approaches are needed to accelerate their recovery. The aim of this study will be to 
examine the usefulness of weekly applications of transcutaneous electrical nerve stimulation 
(TENS) for this purpose, based on evidence of its effectiveness in other types of patients with 
muscle alterations. Maximum jaw opening, bite force, pain, and facial inflammation will be 
compared between patients receiving TENS and those receiving sham-TENS for 30 min at 
baseline and weekly over a four-week period after orthognathic surgery and will be also 
compared between before and after each procedure.  
 
 
MATERIAL 
 
The sample will be made up of a sufficient number of patients according to the calculation 
of the sample size who will undergo bimaxillary surgery or mandibular surgery divided between 
experimental (TENS group) and control groups (sham-TENS).  
 
Participants will be selected by non-probabilistic sampling of consecutive patients until the 
estimated sample size is reached. All patients have a skeletal and facial deformity amenable to 
surgery after a pre-surgical orthodontic period, and they will have to signed their informed 
consent after receiving an information sheet on the study. 
 
This study was approved by the ethics committee of the hospital (San Carlos Hospital, 
Madrid, Spain).  
 
Inclusion criterion: 
- programing of bimaxillary or mandibular orthognathic surgery by the same surgeon in 
order to avoid inter-operator variability.  
- no surgery for temporomandibular disorders or more complex syndromes,  
- no presence of muscle or nervous disorders or receipt of medication for such disorders 
 
Exclusion criterion: 
- the impossibility to attend follow-up appointments 
- the refusal of informed consent. 
 
The sample size will be estimated to obtain a statistical power of 80% with an alpha error of 
0.05 and 95% confidence interval to detect a difference in jaw opening ≥ 2.5 mm. 
 
Patients will be randomly assigned to the experimental group for TENS application or the 
control group for sham-TENS and will be blinded to their group assignation, as was the 
researcher responsible for data analyses (single-blind randomized clinical trial). 
 
 
METHOD 
TENS procedure 
An Enraf Nonius® S82 model TENS device will be used, with a maximum frequency of 220 
Hz and an intensity range of 0 to 99.5 mA.  
TENS electrodes will be placed bilaterally on mandibular elevator muscles, on the superficial 
masseter muscle above the gonial angle, and bilaterally on the anterior temporal muscle, 
following the manufacturer’s instructions. The device will be applied in an identical manner to 
all patients in both groups and kept in position for the same time period (30 min); however, the 
device will be not switched on for the control group. 

The stimulation intensity will be adjusted for those in the experimental group to the 
maximum that did not cause discomfort or areas of contraction, maintaining this stimulation 
intensity and frequency throughout the 30-min session.  
Each participant will experience a weekly TENS or sham-TENS session on the same day of 
the week during a four-week period; appointments will be scheduled so as to minimize any 
possible interaction among study participants.  
 
 
 
 
 
Study variables 
Data will be gathered from all patients on jaw opening, bite force, inflammation, and pain 
before surgery and at 7, 14, 21, and 28 days post-surgery, conducting measurements both before 
and after the TENS/sham-TENS session. 
 
Maximum Jaw Opening will be evaluated with patients seated vertically upright in the 
dental chair, using a digital dental caliber (Model R 100110, Mestra®) to measure the maximum 
opening from the incisal margin of upper central incisors to the incisal margin of lower incisors, 
adding the amount (in mm) of overbite or subtracting the amount (in mm) of open bite in 
occlusion.  
 
Bite force will be measured using Dental Prescale Fuji® film, which is formed by 
microcapsules that generate a chemical reaction under pressure, staining the contact area with a 
color density corresponding to the pressure applied.  
A sheet of the film will be placed between the occlusal surfaces of the two arches, and the 
patient will be asked to bite as strongly as possible for 5 sec. This procedure will be repeated three 
times, selecting the sheet with the best-defined tooth print to be photographed with a Canon® 
EOS 500 camera (RAW format, F32, and annular Flash) at the minimum distance permitted by 
the 75-macro lens.  
The image will be processed in a Mac  computer to obtain the color value according to the 
Cie L*a*b* (CIELAB) scale, which gives the color a numerical value. 
The corresponding pressure units (Megapascals, MPa) will be calculated according to Dental 
Prescale specifications, and the bite force (in Newtons [N]) will be obtained by using the following 
formula: 
                    Bite Force= Bite Pressure (MPa) x mm2 print surface. 
 
Pain perceived by patients while autonomously opening and closing their jaws will be 
evaluated using a visual analog scale (VAS).  
 
Facial inflammation will be measured (in mm) with patients seated upright in the dental 
chair, using a soft ruler to obtain a horizontal measurement from the lower border of the earlobe 
to the corner of the mouth and a vertical measurement from the gonial angle to the outer canthus 
of the eye. The soft ruler will be adapted to the contour of the patient's face without exerting any 
pressure. 
 
All of the above measurements provided numeric values for treatment as continuous 
quantitative variables.