This typically involves the masseter muscle and the anterior portion of the temporalis (the large outer muscles that clench), and the lateral pterygoids, relatively small bilateral muscles that act together to perform sideways grinding. Multiple causes
The cause of bruxism is largely unknown, but it is generally accepted to have multiple possible causes. Bruxism is a parafunctional activity, but it is debated whether this represents a subconscious habit or is entirely involuntary. The relative importance of the various identified possible causative factors is also debated. Awake bruxism is thought to be usually semivoluntary, and often associated with stress caused by family responsibilities or work pressures. Some suggest that in children, bruxism may occasionally represent a response to earache or teething. Awake bruxism usually involves clenching (sometimes the term "awake clenching" is used instead of awake bruxism), but also possibly grinding, and is often associated with other semivoluntary oral habits such as cheek biting, nail biting, chewing on a pen or pencil absent mindedly, or tongue thrusting (where the tongue is pushed against the front teeth forcefully).There is evidence that sleep bruxism is caused by mechanisms related to the central nervous system, involving sleep arousal and neurotransmitter abnormalities. Underlying these factors may be psychosocial factors including daytime stress which is disrupting peaceful sleep. Sleep bruxism is mainly characterized by "rhythmic masticatory muscle activity" (RMMA) at a frequency of about once per second, and also with occasional tooth grinding. It has been shown that the majority (86%) of sleep bruxism episodes occur during periods of sleep arousal.
Usually lower splints are better tolerated in people with a sensitive gag reflex. Another problem with wearing a splint can be stimulation of salivary flow, and for this reason some advise to start wearing the splint about 30 mins before going to bed so this does not lead to difficulty falling asleep. As an added measure for hypersensitive teeth in bruxism, desensitizing toothpastes (e.g. containing strontium chloride) can be applied initially inside the splint so the material is in contact with the teeth all night. This can be continued until there is only a normal level of sensitivity from the teeth, although it should be remembered that sensitivity to thermal stimuli is also a symptom of pulpitis, and may indicate the presence of tooth decay rather than merely hypersensitive teeth. Splints may also reduce muscle strain by allowing the upper and lower jaw to move easily with respect to each other. Treatment goals include: constraining the bruxing pattern to avoid damage to the temporomandibular joints; stabilizing the occlusion by minimizing gradual changes to the positions of the teeth, preventing tooth damage and revealing the extent and patterns of bruxism through examination of the markings on the splints surface. A dental guard is typically worn during every nights sleep on a long-term basis. However, a meta-analysis of occlusal splints (dental guards) used for this purpose concluded "There is not enough evidence to state that the occlusal splint is effective for treating sleep bruxism. "A repositioning splint is designed to change the patients occlusion, or bite.