Bruxism often occurs in children who have sleep apnea. However, you must be certain the child has sleep apnea. Clinically the child will mouth breathe at night, have restless sleep, awakens tired, occasional snoring, enuresis, occasional headaches, etc. The etiology is upper airway obstruction due to hypertrophied tonsils and adenoids.
If your child does not exhibit any of these simple clinical stigmata, occasional bruxing is not significant. A few children will awaken bruxing to proprioceptively occlude their teeth and this is not considered pathologic. However, if your child has a history of chronic nocturnal mouth breathing, sore throats and/or earaches you should have an upper airway evaluation.
Check your child several times during deep sleep and be certain there is no chronic nocturnal mouth breathing. If the child is breathing through the nose, the position of the tongue will result in an optimal arch development. However, if the child is chronically mouth breathing, malocclusion will occur often resulting in bruxism, which is a subconscious attempt to establish an optimal occlusion.
It is not just Eustachian tube dysfunction that results in nocturnal bruxism. It is also related to malocclusion resulting in an imbalance between intraoral and extraoral forces on the dentition. When nocturnal mouth breathing occurs, the tongue does not support the extra oral forces from the buccinator mechanism, (orbicularis oris, buccinator and superior constrictor muscles) resulting in an extraoral imbalance with a resultant malocclusion. Children must be chronic nocturnal nose breathers with the exception of the occasional cold.