This specific research will investigate the effects of experimental muscle tenderness on your facial sensitivity, blink reflex, jaw muscle motor cortical activity, bite force, and jaw muscle activity during sleep.
In order to achieve that, I will measure your motor cortical activity using transcranial magnetic stimulation (TMS), which is a non-invasive and pain-free method to stimulate the human cortex. In addition, you will be asked to sleep for 8 nights with a medical device that can record the activities of your temple muscle (GrindCare ® ) with the aid of surface electromyography (EMG). GrindCare is also non-invasive and it will not interfere with your usual sleep. Please, visit https://www.grindcare.com/global for more information. You will also be asked to bite a gauge with your back teeth to assess how strong you can bite. The blink reflex tests how strong and fast you can blink when an electrical stimulation is applied using a very small electrode placed on the infraorbital region (below your eyes). The stimulus is electrical, and you might feel the sensation of a "blunt needle" or a "sharp needle". Also, we are going to measure your facial sensitivity with some devices that apply standardized pressure, touch with Nylon filaments and pinprick weights. This facial sensitivity will be assessed before and after 30 min of application of capsaicin cream 1% on the skin overlying the right jaw muscle. Capsaicin is the chemical compound of chili peppers. When capsaicin cream is applied to the skin you may feel a "heat" or "burning" sensation. Capsaicin cream 1% is safe, although you might experience temporary side effects, for example, redness, itching, swelling, blistering and burning sensation in the area of capsaicin during the application or immediately after its removal. Finally, some questionnaires about your mood, sleep, facial pain and mastication will also be applied.
The study design is as follows: a) in the first appointment you are going to be interviewed about your medical history in order to check if you are indeed eligible to participate and you are going to receive your GrindCare (no experiment will be done this day ); b) 4 days after starting using GrindCare you will come back for the session 1. Therefore, we will perform TMS and bite force assessment; c) 1 day after session 1 you will come for session 2, where we will evaluate the facial sensitivity and blink reflex before and after the application of capsaicin cream 1%. In the end, you will either receive an injection of nerve growth factor (NFG) or isotonic saline (control injection) into your right masseter muscle. NGF injected into the masseter muscle of pain-free volunteers does not provoke spontaneous pain and it is a safe procedure, but mechanical sensitivity (tenderness to palpation or pain evoked by chewing, for instance) can last up to 7-10 days. Isotonic saline injection is also a safe procedure and did not provoke pain at all.So, you have a 50% chance of getting the non-painful injection ; d) 2 days after session 2 you will come back for session 3. Thus, we will again evaluate the facial sensitivity and blink reflex before and after the application of capsaicin cream 1%; e) 1 day after session 3 you will come back for session 4 and, again, we will perform TMS and bite force assessment and the GrindCare device should be returned. In this last session you will do a series of tooth clenching tasks before the TMS assessment.
The majority of the procedures are non-painful or slightly painful, with the exception of the NGF injection that may cause muscle tenderness and pain evoked by jaw functions like chewing or yawning. Also, like after any injection, there is a risk of hematoma, which will not require any treatment but will disappear in a couple of weeks. There is also a theoretical risk of infection after any injection. If this should occur against our expectations, it will be treated. The Section of Orofacial Pain, Department of Dentistry Aarhus University is responsible for all the experimental testing and techniques. Likewise,capsaicin cream 1% is safe, although you may experience temporary side effects, for example, redness, itching, swelling, blistering and burning sensation in the area of capsaicin during application or immediately after its removal. These side effects do not require any specific treatment and will disappear in a couple of hours. The electrical stimulation for the blink reflex could also be painful (sensation of a “sharp needle”).
After successful completion, you will receive 1500 DKK. The duration of the 4 experiment sessions is around 2.5 hours, so approximately 10 hours in total.
Besides a good general and oral health status without any history of head / face trauma or major surgery and systematic condition like heart disease, hypertension diabetes, recurrent / frequent headaches, or dental problems (eg, cavities, periodontal disease or ongoing orthodontic treatment), you should not have any complain of pain or discomfort in the jaw or temple area in the last 30 days. Also, you should not have metal implants in the head or use pacemaker / medicine-pump, history of epilepsy / seizure. If you are a woman, you should not be pregnant. If you have a full beard, it also will not be possible to participate, since it can interfere with the EMG recordings that are going to be made. So, a clean-shaven is necessary (at least the masseter region should be). Finally, if you are more than 50 years old it will not be possible to include you.
Also, you should not make regular intake of medications (antiepileptics, antidepressants, anxiety drugs or analgesics). Please, note that you will be asked about these in the first appointment and that you may be declining participation if not fulfill the eligibility criteria. Finally, you must be able to communicate in English.
If you would like to book the first appointment to get your GrindCare, please, reply that you would like to participate, and we will send you an email for booking.
I really appreciate your help and interest and I hope you can join me.
If you have any further question, please do not hesitate to contact me.
Looking forward to hearing from you.