Open Bite Malocclusion and Orofacial Dysfunction in Patients with Myotonic Dystrophy Type 1 and Duchenne Muscular Dystrophy

Open bite (OB) is a common malocclusion in individuals with orofacial dysfunction and syndromes, especially in neuromuscular diseases. Objectives: The objectives were to explore the prevalence of OB in myotonic dystrophy type 1 (DM1) and Duchenne muscular dystrophy (DMD) and to create and compare orofacial dysfunction profiles. Methods: In this database study, 143 individuals with DM1 and 99 with DMD were included. The Mun-H-Center questionnaire and observation chart were used together with the Nordic Orofacial Test - Screening (NOT-S) to create orofacial dysfunction profiles. OB was categorised as: lateral (LOB); anterior (AOB); severe anterior (AOBS); or both types of anterior OB (AOB(Tot)). Descriptive and multivariate statistics were used to compare the OB prevalence and to study associations with orofacial variables, respectively. Results: There was a statistically significant difference in OB prevalence between the DM1 (37%) and DMD (49%) groups (p = 0.048). LOB was seen in < 1% of DM1 and 18% of DMD. LOB was associated with macroglossia and closed mouth posture, AOB with hypotonic lips, and open mouth posture and AOBS with hypotonic jaw muscles. The orofacial dysfunction profiles showed similar patterns, although the mean NOT-S total scores for DM1 and DMD were 4.2 +/- 2.8 (median 4.0, min-max 1-8) and 2.3 +/- 2.0 (median 2.0, min-max 0-8), respectively. Limitations: The two groups were not age- or gender-matched. Conclusion: OB malocclusion is common in patients with DM1 and DMD and is associated with different types of orofacial dysfunction. This study highlights the need for multi-disciplinary assessments to support tailored treatment strategies that improve or sustain orofacial functions.