**1. Introduction**

This chapter analyses the effects of Rapid Maxillary Expansion (RME) and Extraoral Traction Appliances (ETA) on children with a high prevalence of specific otorhinolaryngologic pathology like persistent nasal obstruction and/or repeated upper respiratory infections (three episodes over six months or four episodes in a year nasal obstruction).

This type of obstructive symptomatology is common in Down syndrome (DS) children [1] but may occur in children with other syndromes or diseases, and even in healthy persons.

Other possible causes of breathing difficulty are related to muscle weakness. If we look to the population that uses Noninvasive Ventilation (NIV), we identify the significant groups of risk, where respiratory muscles are weakened, or the airway is obstructed: Obstructive sleep apnea (OSA), Neuromuscular disorders (ND), Cystic fibrosis, Children with Obesity and Down syndrome (DS).

Upper airway obstruction may have several causes, and accumulated secretions augment the obstruction. Adenoidectomy and tonsillectomy are common to remove the obstruction, but many times, not enough. Another cause related to obstruction, often forgotten, is a constricted and/or retruded maxilla. In most cases, we find the presence of lateral crossbite and/or evidence of maxillary compression.

A diminished transverse dimension of the maxilla reduces the nasal cavities, thereby reducing the airflow into the lungs [2].

The nasal respiratory space represents a vital role in the craniofacial skeleton growth and development (the most important stimuli for the growth of the midface is ventilation by the nose).

The respiratory pattern can determine an altered mandibular posture, allowing compensatory oral ventilation. When the tongue does not occupy a stable position in the oral cavity, the entire balance that keeps the teeth in their typical situation changes, allowing the occurrence of malocclusion.

The occlusion between the maxilla and mandible is essential to choose the type of therapy to use.

Based on scientific evidence and clinical practice, this chapter supports a better understanding of these treatments that improve oral functions and the child's general development.
