Effect of mandibular advancement splint treatment on tongue shape in obstructive sleep apnea

Mandibular advancement splints (MAS) can effectively treat obstructive sleep apnea (OSA); however, treatment response is variable, and the mechanisms behind differences in treatment outcomes are still not well understood. The aims of this study were (1) to assess the effects of MAS on tongue shape and (2) to compare tongue shape changes with MAS between treatment responders and nonresponders.

Sixty-eight adults with symptomatic mild to severe OSA were included. A custom-made MAS was provided to patients, and treatment outcome was determined by polysomnography. Two-dimensional tongue measurements were evaluated using sagittal and axial MRI image slices without and with MAS in situ. Tongue measurements of height, length, width, area, and shape (height/length) were collected. Additional measurements of surrounding upper airway structures, soft palate length width and area and upper airway area, length and minimum width were measured on sagittal image slices.

Based on polysomnography with MAS in situ, 47 patients were classified as responders (≥50% reduction in apnea-hypopnea index [AHI] from baseline), and 21 were nonresponders (<50% AHI reduction). There was no change in sagittal tongue area with insertion of MAS, although there was a change in most of parameters of tongue shape. Responders showed a greater decrease in tongue length with MAS in situ compared to nonresponders (-0.64 ± 0.46 vs -0.32 ± 0.51 cm, p = 0.016).

This study reports a detailed two-dimensional analysis of tongue dimensions as well as assessment of adjacentsoft palate shape and upper airway structures without and with MAS treatment for OSA. Our finding suggests that MAS does induce changes in tongue shape. MAS treatment responders showed a greater decrease in tongue length (between the tongue tip and hyoid bone) with MAS in situ; whether differences in alteration of tongue position with MAS explain differences in treatment response requires further investigation.