What are the signs and symptoms of sleep-related bruxism?
The two most commonly reported symptoms of sleep-related bruxism are sensitivity of the teeth to temperatures and chewing and headaches, usually in the temple region. The following outlines some of the known causes of tooth sensitivity and headaches related to sleep-related bruxism.
Tooth sensitivity is a significant problem in society. Just look at the number or toothpastes and mouth rinses claiming to treat tooth sensitivity. Unfortunately, sleep-related bruxism is rarely considered when tooth sensitivity is being discussed. The following are the ways that sleep-related bruxism can cause tooth sensitivity. Tooth sensitivity is one of the commonly reported symptoms of sleep-related bruxism.
Frequently occurs with longstanding untreated sleep-related bruxism as the side-to-side and front-to-back movements collide the upper and lower teeth together. Many patients with this condition also suffer from GERD (gastroesophageal reflux disorder), or acid reflux during sleep. The powerful hydrochloric stomach acids can soften the enamel accelerating the wear (Figure 1)
Hypersensitivity of the teeth with tooth wear can occur due to loss of the protective enamel and exposure of the sensitive underlying dentin.
The forces generated during sleep bruxism events can exceed the strength of the teeth and they may crack (figure 2). This can be very painful when the crack reaches the nerve inside the tooth. Cracks start small and slowly progress. It is often difficult to identify exactly which tooth actually has the crack, the only symptom is a sharp short-lasting pain when biting harder foods is a region that diminishes once the teeth are separated.
Figure 2: Cracked Teeth
Damaged Periodontal Ligaments:
Teeth are held in by a tiny ligament that surrounds the roots of the teeth. It is called the Periodontal Ligament (PDL) and each ligament system contains tens of thousands of free nerve endings that provide sensory feedback to the brain when chewing, on how hard and what direction we are biting. These free end nerves all connect to the main nerve of the tooth and are carried to the brain on the same pathways as a toothache does.
In sleep-related bruxism, the considerable downward forces (compression) on the teeth excessively stretch or damage these ligaments causing the affected tooth/teeth to be sensitive to biting and to temperature extremes. Over time this can adversely affect nutrition as many foods must be avoided (Figure 3). There are thousands of nerve endings in this ligament that supply the brain with important information on how hard one is chewing. With excessive stimulation form sleep-related bruxism, these nerve endings may be damaged resulting in phantom tooth pain that mimics a tooth ache. The affected teeth may actually feel loose due to stretching of the ligament. Anyone who has had orthodontic treatment can attest to the discomfort some teeth can have. This is due to stretching and shorting of the PDL as the teeth move.
Figure 3: Damage to the PDL due to Tooth Compression: This is a very common cause of tooth sensitivity seen in sleep-related bruxism. As the ligaments are stretched by the extreme compressive forces of sleep-related bruxism, sensory nerves in the ligaments transmit pain sensations to the brain on the same nerve as the tooth. The brain interprets this as tooth pain. Many unnecessary endodontic procedures (root canal therapy) are performed each day that are due to this referred pain of the PDL.
Abfraction lesion is the term given to a loss of enamel at the gumline and the formation of a sensitive notch. These occur usually on the outside of the teeth, but, in severe cases may be seen on the inside as well. These were previously thought to have been caused by excessive or aggressive tooth brushing however this has been dispelled. The extreme side to side and front to back forces of sleep-related bruxism result in this loss of enamel at the gum line and the formation of these painful abfraction lesions on the sides of the affected teeth due bending of the teeth where they exit the jaw bone.
Figure 5: Abfraction Lesions: As they appear clinicallyThe animation in figure 4 demonstrates how forces on a tooth may result in enamel loss at the gum line and figure 5 demonstrates abfraction lesions on a number of teeth. This is a direct result of sleep-related bruxism and many cases are extremely sensitive to touch as well as to hot and/or cold foods and liquids. If fillings are placed to cover these areas, they can help with the sensitivity however the root exposure often requires periodontal surgery to correct. In patients suffering from untreated sleep-related bruxism, the fillings sometimes fail, often repeatedly. With abfraction lesions, there is gum recession and bone loss in the absence of periodontal disease, which can be diagnostic of sleep-related bruxism in some.
Fractured Roots of Teeth:
In severe sleep-related bruxism, the forces can be so great that the roots of the teeth can be fractured. This is more common in root canal treated teeth (which may be more brittle) but can occur in unrestored healthy teeth as well. Figure 6 demonstrates a series of root fractures that may occur due to sleep-related bruxism.
Figure 7 demonstrates the various types of root fractures. In most cases, removal of the affected tooth is required, unless it is caught in the very early stages. Sometimes a crown can be placed to stabilize the fracture however even with a crown, the long-term prognosis is poor for these teeth. It is accepted that if a crown is placed within the 1st year of sensitivity, the tooth should last a lifetime. The later the crown is placed, the worse the long term prognosis is. When cracks occur, the tooth may be painful only to chewing certain-type foods, such as hard foods, that open the crack. When the biting stops the pain subsides. In more advanced cracks, the tooth mat be intensely painful all of the time. Left untreated for years, an abscess or infection can develop. Endodontic treatment (root canal therapy) is rarely successful when there is a crack into the nerve chamber of the tooth. Extraction is often the only course of action.
Headaches are one of the most common disorders in our society. Tension occura in up to 80% of the population intermittently and migraine headaches occur in 18% of women and 6% of men. These account for the bulk of headaches and there are billions of dollars each year paid for pain medications to treat tension and migraine headaches.
Interestingly, headaches are the second most commonly reported symptom of sleep-related bruxism and can occur as a tension-type headache or as a migraine-type headache (without aura). These headaches can occur in the night, waking the patient, upon waking in the morning, or even later in the day. Most headaches are due to muscle spasms in the head (jaw muscles) and neck. Many of the neck muscles are also involved in sleep-related bruxism, as the neck muscles are accessory chewing muscles, supporting the skull when chewing. With sleep-related bruxism, it is not only the jaw muscles that are strained, but the neck muscles are also often involved.
Referred Pain from Injured Jaw Muscles:
Referred pain can occur anywhere in the body. For example, heart attacks can often only be felt by a sharp pain at the angle of the lower jaw or down the right arm. In sleep-related bruxism, the masseter and temporalis muscles (Figure 9, 10), can refer pain to the teeth, jaw, and temple regions.
Sleep-related bruxism forces the masseter and temporalis muscles to contract with maximum force during sleep-related bruxism events (Figure 9). The muscles become fatigued and may be injured (figure 10). When this occurs, painful areas of the muscle called” trigger points” may refer pain to adjacent regions. The teeth commonly experience pain being referred from these two powerful muscles and can mimic a toothache very accurately. As with periodontal ligament pain, the pain is diffuse and hard to localize to one tooth. More importantly, these muscles refer pain to the side of the head and temple regions. This is intense pain in most and is resistant to pain medications. Message therapy main reduces the headache pain temporarily however the headache pain returns the next day after a night of sleep-related bruxism. Over time this can be very disturbing for many and pain-related depression is known to be associated with sleep-related bruxism.
The pain referral pattern from the temporalis muscle (figure 10) is across the side of the head and into the upper teeth occurs very frequently as a headache as well as hypersensitivity of the teeth to chewing and temperatures. The pain referral pattern for the masseter (figure 10) is to the temple region as well as both upper and lower back teeth.
The referred pain from these two powerful chewing muscles accounts for the headaches seen in sleep-related bruxism, one of the most commonly reported symptoms.
Other Affected Areas
The excessive pressure of sleep-related bruxism, over time, often causes other permanent alterations of the bones of the jaws. These are discussed below.
Antigonial Notching of the Mandible:
In many patients with long-standing untreated sleep-related bruxism, the masseter muscle will compress the lower border of the mandible resulting in a distinct bend in the lower jaw. This is termed antigonial notching and is a permanent change resulting in the shortening of the masseter muscles and deformation of the mandible. The antigonial region of the mandible is at the lower border of the lower jaw (Figure 11)
Figure 12 demonstrates a panoramic radiograph of severe antigonial notching of the mandible in a sleep-related bruxism patient.
Coronoid Process Elongation:
This occurs from excessive pulling forces of the temporalis muscle as it attaches to the coronoid process of the mandible. Figure 12 demonstrates how this occurs.
The coronoid process of the mandible is stretched upward inside of the cheekbone. In extreme cases, there is a restriction of side-to-side movement as the coronoid process collides with the cheekbone preventing complete movement. The coronoid process is the upper part of the mandible that extends under the cheekbone. This is where the temporalis muscle attaches to the jaw. Figure 13 demonstrates a panoramic radiograph of a patient with significant coronoid elongation. The normal height is indicated with the yellow dot, the orange dashed line is the actual height. This length would likely restrict side to side movement of the lower jaw.
Other Osseous (Bone) Changes:
Exostosis is the medical term for bone outgrowths. in the mouth, these can occur due to excessive side-to-side sleep-related bruxism. The forces on the roots of the teeth stimulate bone apposition or growth to prevent fracturing of the jaw. There are different types seen depending upon where the forces are concentrated.
These occur on the inside of the lower jaw, usually in the regions of the cuspids or 1st bicuspids extending back as far as the molars in some. They are as a rule painless but can be difficult to clean under if food traps under them. This also reduces the volume of space for the tongue and may encourage sleep apnea, if large. Figure 14 demonstrates various mandibular tori.
Palatal Torus: As the name implies, this occurs in the palate (figure 15). The compression of the upper jaw into the skull, as is seen in sleep-related bruxism, places pressure on the nasal septum that runs from to back in the middle of the palate. In response, the nasal septum and palate generate an exostosis in the palate termed a torus (tori is the plural form). When large, the nasal sinus may grow down inside the torus making surgical removal impossible (a hole would be left in the palate requiring surgical closure).
As with mandibular tori, these are usually painless but reduce the volume of space for the tongue.
Of clinical significance, I have seen tori, both mandibular and palatal in children as young as 14, already developing when sleep-related bruxism is present at this age.
In some, there will be an apposition or formation of bone outgrowths on the outer surface of the upper and lower jaws. These can become quite large in some and cause irritation of the cheeks when chewing. Figure 16 demonstrates the appearance of these. These are made of solid bone.
All of the bone overgrowths shown are a direct result of sleep-related bruxism and the extreme forces placed on the bones of the face and skull. Of significance, if dentures must be fitted, all of these overgrowths must be removed before the dentures can be placed!
The Cardiovascular System:
In recent years there has been a growing body of evidence that has shown that sleep-related bruxism affects the cardiovascular system adversely. With each sleep-related bruxism event, there is a stimulation of a powerful cranial reflex known as the “Trigeminal Cardiac Reflex” or TCR. This reflex affects the central nervous system, specifically the autonomic nervous system. It primarily acts on the parasympathetic nervous system resulting in bradycardia (slowing of the heart), hypotension (a drop in blood pressure), apnea (slowing of respiration), and changes in acid production in the stomach. It is medically accepted that there must be a change in heart rate of greater than 20% before it may be stated the TCR was involved.
Sleep-related bruxism is unique in its effect on the TCR. Instead of the expected parasympathetic effect, it has the opposite sympathetic effect and results in tachycardia, hypertension, increased irregular respiration, and GERD (gastroesophageal reflux disorder).
Figure 17 is an animation of how this reflex is thought to work in sleep-related bruxism. The stimulation of the TCR occurs at the Gasserion (trigeminal) ganglion, travels to the trigeminal sensory nucleus in the brainstem, then to the vagus motor nucleus, and then on to the heart, lungs, and stomach.
Sleep-related bruxism is unique in that it affects the TCR opposite all other regions of simulation. All other areas result in a parasympathetic stimulation (slowing of heart rate, breathing, drop in blood pressure, etc) whereas sleep-related bruxism is a sympathetic stimulation (tachycardia, increased rate of breathing, increase in blood pressure, etc.). More information on the TCR can be found here.
In Figure 18, percent the heart rate is the lowest tracing, the sleep-related bruxism events in the most upper. In the tracing, heart rate can be seen as very erratic, increasing in response to the sleep-related bruxism events. In this sleep study, there was an increase in heart rate of 110%. It is medically accepted that a change of greater than 20% in the heart rate must occur before one can state the TCR has been involved. Sleep-related bruxism far exceeds the 20% threshold. Recent studies have investigated if this increase, and resulting increase in blood pressure, had negative effects on the heart and cardiovascular system. It is now medically accepted that it does.
Figure 19: Activation of TCR in Sleep-Related Bruxism
In the sleep study shown in Figure 19, the heart rate increased from 62 to 95 beats per minute, an increase of 33%. Of note: this only occurs during the sleep-related bruxism events and is clear evidence of activation of the trigeminal cardiac reflex, exceeding the 20% threshold requirement. Also, note that the heart rate rapidly increases and then returns to normal rapidly. This is a requirement to state activation of the TCR, the stimulation must occur and diminish rapidly. Sleep-related bruxism has been shown in the research not to just stimulate the TCR, it hyper-stimulates it!
One would expect that these sudden increases of heart rate and blood pressure would be hard on the heart and blood vessels. This is the case and new research is confirming this to be true.
Sleep-related bruxism is classified by the World Health Organization (WHO) as a motion-type sleep disorder, similar to restless leg syndrome (which also activates the TCR and is considered a risk factor for cardiovascular disease). Every time a sleep-bruxism event occurs, there is a sleep arousal, taking the patient into shallower sleep, preventing deep, restorative sleep. Daytime tiredness (figure 20) is measured by various questionnaires such as the Epworth Sleepiness Scale. Sleep-related bruxism patients frequently score similar to mild obstructive sleep apnea. Sleep-related bruxism primarily occurs in stages N1 and N2 of sleep (see Figure 21).
The result is a dramatic reduction in stages N3 and REM sleep, which are considered deep restorative sleep. This reduction results in the daytime sleepiness seen in sleep-related bruxism (Epworth Sleepiness scale scores of 5-9). In REM sleep, memories are consolidated, or made permanent. Reductions in REM sleep may result in memory problems in many.
Sleep deprivation is common with sufferers of sleep-related bruxism and is a significant risk factor for auto accidents and industrial accident and injuries. It is also a significant cause of loss of productivity in the workplace.