Bruxism 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
Grinding (abrasive cutting) work in the machining fields, the term "cutting" is often understood to refer to the macroscopic cutting operations, and "grinding" is often mentally categorized as a "separate" process. This is why the terms are usually used separately in shop-floor practice. Lapping and sanding are subsets of grinding. Selecting which of the following grinding operations to be used is determined by the size, shape, features and the desired production rate. "Surface grinding" uses a rotating abrasive wheel to remove material, creating a flat surface. The tolerances that are normally achieved with grinding are ± for grinding a flat material and ±