A magnetic resonance imaging study to compare structural changes of the temporomandibular joint disk during mandibular advancement between Angle Class Ⅰ and Class Ⅱ in adult males / 中国组织工程研究

ABSTRACT

BACKGROUND: Mandibular advancement devices are commonly used in patients with mild to moderate obstructive sleep apnea hypopnea syndrome. But wearing with mandibular protraction appliance makes the mandible in an abnormal position, and inevitably affects the temporomandibular joint (TMJ). As one of the important components of the TMJ, can structural changes of the joint disk impair the TMJ? Are there any differences in the TMJ structure between Angle Class Ⅰ and Class Ⅱ? What will happen to the TMJ structure in the Angle Class Ⅰ and Class Ⅱ during mandibular advancement? Is there a same law of TMJ changes for Angle Class Ⅰ and Class Ⅱ? All of these are undetermined systematically. OBJECTIVE: To compare the changes in the structure of TMJ disk and the differences during mandible advancement between Angle Class Ⅰ and Class Ⅱ adult males. METHODS: Forty non-apnea adult males were divided into two groups (n=20 per group), including Class Ⅰ and Class Ⅱ groups, according to the Angle's classification and sagittal skeletal facial type. Each volunteer was scanned by MRI in three positions, including central occlusion (F0), 75% of the maximum mandible advancement (F75) and maximum of the mandible advancement (F100). These indexes that were correlated with morphology of the joint disk in different mandible advancement positions were measured and calculated by MRI, and then analyzed statistically. RESULTS AND CONCLUSION: In F0, the ratio of disk anterior displacement in the Class Ⅱ group was higher than that in the Class Ⅰ group (P< 0.01). The angle A was decreased as the mandible advanced in both groups from F0to F75(P < 0.01). The rotational angular dimension was increased as the mandible advanced, and the sizes from F0to F100were bigger than those from F0to F75(P < 0.05). Some differences existed in the structure of TMJ disk between Angle Class Ⅰ and Ⅱ adult males. In summary, appropriate mandibular advancement may play a positive role in patients with anterior displacement of the joint disk, but excessive mandible advancement is likely to impair the TMJ disk.