No single cause of orofacial myofunctional disorders has been identified, and its causes seem to be multifactorial. Anything that causes the tongue to be misplaced at rest limits lingual excursions within the oral cavity, makes it difficult to achieve acceptable lip closure, and reduces or impedes the ability to obtain and maintain correct oral rest postures leading to an OMD. The following factors may coexist and play a role in OMDs:
- Airway incompetency, due to obstructed nasal passages, either due to nasal structural obstructions (e.g., enlarged tonsils, adenoids, hypertrophied turbinates, and/or allergies, that do not allow for effortless inspiration and expiration) (Bueno, Grechi, Trawitzki, Anselmo-Lima, Felicio & Valera, 2015). These may result in upper airway obstruction and open mouth posture (Abreu, Rocha, Lamounier, & Guerra, 2008; Vázquez-Nava, et al., 2006), as well as an incorrect swallow pattern and mouth breathing (Hanson & Mason, 2003).
- Chronic nonnutritive sucking & chewing habits past the age of 3 years of age (Sousa, et al., 2014; Poyak, 2006; Zardetto, et al., 2002)
- Orofacial muscular/structural differences that encourage tongue fronting could include: delayed neuromotor development, premature exfoliation of maxillary incisors that encourage fronting of the tongue, orofacial anomalies, and ankyloglossia.