Introduction 

Trismus is a condition that is also known as "lockjaw". This is due to a hindrance in opening the mouth because of long spasms in the chewing muscles, mainly hitting the jaw joint and nearby muscles. It may be for a short time or forever, greatly affecting day-to-day activities like eating and talking.¹

Preventing trismus is needed in cancer care. It helps improve the quality of life, aids mouth care, and eating and talking work well. Taking steps early can solve the big problems linked to fewer jaw movements, which may last forever if not managed right.^2,3 

The common causes of trismus in cancer patients are:^,2,4

• Radiation therapy. Exposure to radiation makes the muscles stiff and scarred, particularly affecting the muscles around the jaw and muscles used for chewing
• Surgery. Getting surgically operated on around the jaw may cause scar tissue that limits how the jaw can move
• Fibrosis. Damage from both radiation and surgery can make the jaw muscles stiff, making trismus worse

Risk factors for trismus in cancer treatment 

Radiation therapy to the head and neck

Radiation intervention for treating individuals around the head and neck area is a big risk for trismus in cancer care, mostly for those with head and neck cancers. A study showed that trimus was seen in 45% of people who received curative doses of radiation therapy for head and neck cancer.⁵

Surgical procedures involving the jaw or surrounding tissues

Surgery procedures performed around the jaw, or surrounding areas, are seen as a major risk of getting trismus during cancer care, mainly in people getting treatments for head and neck cancers. The reasons behind trismus occurring before surgeries include associated harm due to trauma, scarring, and bone death from radiation.⁴

Tumour location and infiltration

The location of a tumour can be a risk factor for trismus. Tumours near the jaw muscles or the jaw joint can make it hard to open your mouth. A study compared mouth opening in people with big tumours and small tumours. The TNM classification is used to stage cancer tumours, specifically, letter T refers to the size of the tumour. According to the study, people with big tumours, which are seen in T3 and T4 stages, could not open their mouths as wide as those with small tumours, like in T1 and T2 stages. This shows that big and deep tumours increase the risk.⁴ 

Tumours by the upper jaw, lower jaw, cheek, or big spit glands also have a high chance of causing trismus. The spreading of tumours into nearby tissues can worsen the risk of trismus. If cancer cells move into muscle or connecting tissue, they can cause inflammation, fibrosis, and then scarring. This reduces the muscles' function and limits how much the jaw can move. For example, if a tumour grows into the masticator space, it can stop the mouth from opening wide. This is often seen as a T4b level in staging systems.^6,7 

Chemotherapy-induced fibrosis

Chemotherapy-induced fibrosis is another contributor to trismus in cancer care, even for those who get both chemotherapy and radiation for head and neck cancers. A review showed that the chance of getting trismus was 2.55 times higher in patients with both treatments than in those with just radiation. Studies have found that trismus can start soon after treatment begins, with an increased occurrence of cases in the first six months after therapy. Patients often say they have less mouth opening, which describes a reduced Maximal Interincisal Opening (MIO), which tells us trismus is there.⁸ 

Pre-existing dental or muscular conditions

People who already have teeth problems, like losing teeth, gum disease, or mouth infections, face a high risk of getting trismus when they go through cancer care. Research shows that in patients with bad growths in the mouth area, 42% had trismus before they began treatment. It's important to note that trismus was a lot more common in those without any teeth than in those with all or some of their teeth.⁹ Another study showed that trismus gets worse when tumours spread into the chewing muscles and muscles around the jaw, noting that people already having muscle issues might find these risks grow bigger during cancer treatments.¹⁰ 

Preventive strategies 

Pre-treatment interventions

Pre-treatment interventions are important and an effective strategy for reducing the risk of trismus developing in cancer treatment. Below are three important areas in pre-treatment interventions for trismus.

Patient education and awareness

Educating people is necessary in preventing trismus. Giving patients information about the risks linked to cancer care, like surgery and radiation, can help them take up proactive measures early. Studies show that utilising educational approaches boosts patients' knowledge about trismus and how it affects them. Those who get a detailed education on the need for continuous oral exercises and steady check-ups take better care of themselves. This care is vital to keep the jaw working well during and after care. Also, educating patients by creating awareness using flyers, clips, or phone applications makes it clearer for patients and helps them follow the appropriate advice. These aids can send tips to do oral exercises and to keep appointments with a doctor, helping them stick to care steps to avoid issues.¹¹

Baseline assessment of jaw function

Assessing how well the jaw works before starting cancer therapy is key to finding those who may be at risk of getting trismus. This assessment often looks at how wide the jaw can open, that is, the MIO and its movement range. Studies show that knowing the jaw's state early helps doctors plan better care. A study revealed that people who already had stiff jaws were more prone to develop more significant trismus after therapy. Also, identifying individuals with low MIO early means starting specific interventions or treatments to keep the jaw working during care. Keeping track with regular check-ups helps see if these methods work well.¹¹

Dental evaluations and preventive care

It is important to check the teeth before cancer treatments to spot risks that might make trismus happen. People who already have teeth issues, like gum disease or no teeth, could get trismus because these problems change how the jaw moves. Using fluoride, learning how to care for your mouth, and getting your teeth checked often can help prevent trismus from occurring.^6,9

During treatment strategies

Exercise programs 

Exercising can prevent trismus in those receiving care for head and neck cancers. Many studies have shown that people who did planned jaw and mouth-opening exercises faced a much lower chance of getting trismus than those with usual care. The risk dropped, making it a protective measure. These exercise movements keep the jaw loose and strong, improve mouth use while in treatment. Follow-up programs through phone calls or reminders can boost adherence to the workout plan and bring better results.³ 

Manual therapy 

Manual therapy (MT) is also a better way to help deal with mouth stiffness from radiation in those who have had head and neck cancer. In a study of 49 people, MT made it easier to open the jaw, showing an increase of about 4.1 mm after one time and 6.4 mm after a few times. MT uses ways like manipulating inside the mouth and moving the head and neck from the outside to aim at the jaw muscles. The improvement noticed after the first session shows that MT might work well as a first try treatment, mostly for those who do not respond well to just doing exercises or those with more complicated diseases.¹²

Emerging technologies and approaches

Manual therapy

Manual therapy (MT) has been seen to make the jaw open wider better after just one session, helping even individuals with advanced cancer or those who are not responding to exercises. MT may be a first choice, using hands to help make jaw moves better and not be hurtful.¹²

Adjunctive treatments

Involves using low-level laser therapy (LLLT) and low-intensity pulsed ultrasound (LIPUS), combined with exercise, can improve the wider opening of the mouth than using mouth exercises alone. These ways cut down swelling and help fix tissues. Also, phone apps giving alerts, learning stuff, and online meet-ups can make folks stick to their care plan and boost how well it works.¹¹

Summary

It is necessary to use effective plans to stop trismus to ensure that cancer patients receive better care. Pre-treatment techniques, such as educating patients, assessing them, and full teeth checks on them, are must-dos to find people at risk and ensure that the mouths of patients are healthy before treatment. While receiving care, exercises have been shown to cut the risk of jaw lock, and hand treatments help the jaw work right away. A team of health experts should join in planning teeth care, teaching patients, and working together to improve these preventive strategies and help patients do well.