Excessive mouth breathing may be related to different oral and medical conditions.

Objective: To explore the possible mechanisms involved in the relationship between mouth breathing and some oral and medical conditions. Methods: A review of the literature was performed by using PubMed, Scielo and Hinari. Relevant and updated articles were selected. Results: Mouth breathing has been linked to oral conditions such as dry mouth and lips, dental caries, periodontal disease, secondary halitosis, craniofacial deformity, malocclusion, abnormal swallowing, and to medical conditions such as obstructive sleep apnea, asthma, compromised airway, altered body posture, heart diseases and poor performance. Among the mechanisms that may explain that relationship are chronic hypoxemia with hypercapnia, increased water and energy lose, decreased growth hormone release, inflammatory and oxidative mediators release, large load on the upper back and neck muscles, deformity in the airway passage and craniofacial deformities. Conclusions: Mechanisms underpinning the relationship between mouth breathing and oral and medical diseases vary from biochemical, physiological and immunological deficiencies to anatomical effects. More studies are needed to explore a causal relationship.