Overview

If your jaw is locked or you are having difficulty opening your mouth fully it may be due to trismus, a condition mostly experienced following infections related to teeth (odontogenic) or deep neck infections. To know about trismus you have to know about the infections that lead to trismus and limit your mouth opening. In this case, a bit of knowledge of the anatomy of the mouth, and the muscles (muscles of mastication) that help in chewing food is essential to understand the topic better.

What is trismus?

The term “trismus” refers to the restriction of the range of motions of the jaw. It is also called “ locked jaw” as there is a restriction of the mouth. Amongst many causes, one is due to infections caused by bacteria, viruses, fungi, however, it can also occur from trauma to the TMJ (temporomandibular joint), leading to stiffness and sustained tetanic spasms of the jaw muscles, with a mouth opening less than 15 millimetres (mm).¹

What are the muscles of mastication?

Muscles of mastication are the jaw muscles for chewing and grinding food that aid in digestion. There are two groups of muscles of mastication: 

• The main group comprises masseter, temporalis, medial pterygoid and lateral pterygoid muscles
• The accessory group comprises digastric, buccinator, geniohyoid and mylohyoid muscles

All these muscles coordinate with each other and bring about all the related movements of the upper and lower jaw. The main movements of the lower jaw (mandible) are elevation (upwards), depression (downwards), protrusion (forward), retraction (backwards), and side-to-side movement, all of which aid in chewing and grinding food. Muscle spasms of the jaw can be caused by a tumour or infection of these muscles, leading to its inflammation (myositis) or pain during jaw movement.² 

Figure 1. Sourced from "Muscles of Mastication" article from Earth's Lab, 2018

What are deep neck infections?

In normal healthy people, there are no tissue spaces present. However, during deep neck infections, latent spaces can be formed by the distention of tissues due to the infection from the teeth, bone and periodontal tissue (gum and associated structures), where the infection perforates the cortical plate and discharges into the surrounding spaces. These are also called fascial space infections.³ 

These infections typically arise from local extensions of infections in the tonsils, parotid glands, cervical lymph nodes, and odontogenic (tooth) structures. Symptoms vary depending on which deep neck space is infected (like the parapharyngeal, retropharyngeal, or submental areas) and how serious the infection is. 

Common signs include fever, neck pain, and trouble breathing. Symptoms are often caused by pressure on nearby structures like the respiratory, nervous, or digestive systems, and may include neck swelling, difficulty swallowing (dysphagia), changes in voice (dysphonia), and difficulty opening the mouth (trismus).⁴

Infectious causes of trismus¹

• Peritonsillar abscess and other pharyngeal abscesses: It is one of the most common fascial space infections, also called quinsy. It may occur due to infection in the tonsils (tonsillitis), where pus accumulation takes place near your tonsils. One in every 10,000 people may suffer from this condition. It gradually spreads to the adjacent structures, descending to the parapharyngeal space, and in severe cases, affecting the mouth, neck, chest and lungs⁵
• Tetanus: Toxins produced by the bacterium Clostridium tetani (contamination with dirt) lead to muscle spasms and a locked jaw, initially originating in the face and gradually spreading to the body. It can last for a few minutes to weeks in non-vaccinated individuals. It can be generalised or localised depending on the spread of infection and potentially life-threatening⁶
• Septic arthritis in the temporomandibular joint (TMJ)pyogenic arthritis: A rare occurrence due to the bacteria Staphylococcus aureus, mostly. Symptoms include pain, swelling, tenderness and limited range of motion of TMJ. It can lead to fibrosis, ankylosis, and TMJ dysfunction if left untreated⁵
• Odontogenic (dental) abscess: Tooth decay on the lower second molar or an impacted wisdom tooth leading to poor oral hygiene, or failed root canal treatments of tooth will give rise to odontogenic infections. It may occur due to a periapical abscess (abscess occurring at the root tip of the tooth), or periodontal abscess (abscess occurring in the gums beside the root of the tooth) or both.⁸ Osteomyelitis of the mandible, Ludwig’s angina are the severe forms of dental abscess and are considered life-threatening⁶
• Mumps: A viral contagious infection caused by Rubulavirus affecting the parotid gland and a common childhood disease occurring mostly in unvaccinated individuals. It leads to parotitis- a classic hallmark sign of the disease leading to pain, discomfort, and trismus along with fever, anorexia (unwilling to have food), malaise⁷

Signs and symptoms of trismus

Symptoms of trismus include:

• Jaw stiffness
• Limited jaw movement
• Painful cheek muscles
• Limited and painful mouth opening
• Difficulty in maintaining oral hygiene
• Difficulty in chewing and swallowing food
• Speech difficulty
• Ear-aches
• Headaches

Three-finger test for trismus

You can test the extent of your mouth opening by inserting three fingers vertically into your mouth. The condition is normal if they fit between your top and bottom front teeth. If only two fingers or less are entering your mouth, you may be suffering from trismus.

The three-finger test’s result can be checked by measuring how wide a person can open their mouth, using the TheraBite scale. This tool is placed between the front teeth to measure mouth opening. If the opening is less than about 35 mm, it may suggest trismus.

Figure 2.

Treatment for trismus

• Have a soft diet
• Practice jaw stretching exercises
• Taking pain medications and muscle relaxants as per the doctor’s advice
• Using bite guards/occlusal splints
• Behavioral therapy
• Giving rest to the jaw
• Treating the root cause 

Preventive measures undertaken to avoid trismus

• Go for routine dental check-ups for the detection of caries or impacted wisdom teeth prone to infection
• Maintenance of oral hygiene should be a lifestyle modification to prevent infections
• Tetanus toxoid (tetanus vaccine) is essential for everybody, especially for pregnant women for the development of innate immunity of neonates
• Use of anti-bacterial mouthwash along with salt-infused lukewarm water mouth rinse
• Proper brushing of teeth, especially the molars
• Keep yourself properly hydrated and consume a healthy and balanced diet
• Avoid smoking, chewing tobacco, and areca nuts

FAQs

What is a soft diet?

Tender foods that are easy to chew and digest.

What is behavioural therapy?

Therapy that helps to change unhealthy behaviours, e.g. nail-biting, teeth clenching, or making noises by grinding teeth against each other, especially at night during sleep (bruxism).

What are jaw-stretching exercises?

Doctors/physical therapists teach jaw movements like:

• Opening wide
• Side-to-side movement
• Tongue stretching
• Bringing the lower jaw forward
• Gentle opening and closing of the mouth
• Gently resist opening your mouth by placing your hand on your chin

What is the peritonsillar area?

An area adjacent to the tonsils, a lymphoid tissue that takes part in the body's immunity and defence mechanism against infections.

What are bite guards/occlusal splints?

It is a device that is used to break behavioural abnormalities due to trismus, e.g. teeth-clenching, nail-biting, and teeth grinding (bruxism), thus protecting the teeth and the jaw muscles from further damage.

Summary 

Other causes for trismus (non-infectious) are head-neck cancers, radiation therapy, TMJ disorders, congenital malformations, neurogenic and psychogenic. Smokers and betel leaf orareca nut chewers often present with atrophy (muscle wastage) of the jaw muscles resulting in oral submucous fibrosis. As the saying goes ‘Prevention is better than cure’, you should be on high alert about your teeth health or any prevailing trismus-related disorders and visit your doctor/dentist to prevent further discomfort and complications.