Effects Of Mouth Breathing On Craniomaxillofacial Morphology,Hyoid Position And Upper Airway Sagittal Dimension In Class Ⅱ Malocclusion Patients

Objective: The aim of this study was to observe the effects of mouth breathing on the craniomaxillofacial morphology,hyoid position and sagittal diameter of upper airway in children and adolescents Class Ⅱ malocclusion patients.Methods: The study involved 84 Class Ⅱ malocclusion children who were treated at the Orthodontic Department of the Second Hospital of Hebei Medical University from January 2012 to July 2017.These patients were divided into mouth breathing group and nasal breathing group according to the breathing pattern.There were 42 patients in the mouth breathing group(22 males and 20 females)and 42 patients in the nasal breathing group(16 males and 26 females).The ages of the two groups were 6 to 16 years old.According to the cephalometric radiographs before the treatment of the two groups,the craniomaxillofacial morphology,hyoid position,and upper airway sagittal diameter were measured.SPSS 21.0 statistical software was used to analyze the data.The normal distribution data were analyzed by the independent sample t test.The non-normal distribution data were analyzed by rank sum test.Results: 1.Craniomaxillofacial morphology: 1.1 Vertical measurements: SGn-FH,MP-FH,OP-SN,MP-SN,PP-MP,ANS-Me and ANS-Me/N-Me in mouth breathing patients were greater than nasal breathing patients(P<0.05).There was no statistically significant difference in other items(P>0.05).1.2 Sagittal measurements: The angle of SNB was smaller in mouth breathing group than in nasal breathing group.The angle of ANB in mouth breathing group was greater than that in nasal breathing group(P<0.05),and there was no statistical difference in other measurement items(P>0.05).1.3 Maxillary and mandibular morphology measurements: The results showed no significant difference between the two groups(P>0.05).1.4 Occlusal relationship measurements: The distance of lower central incisor to the NB line of mouth breathing group was larger than that in nasal breathing group(P<0.05).There was no significant difference in other measurement items(P>0.05).2.Hyoid position: The results showed no significant difference between the two groups(P>0.05).3.Sagittal diameter of the upper airway: The measurement results showed that the Mc1-Mc2 in mouth breathing group was smaller than that in nasal breathing group,and there was no difference in other measurement items(P>0.05).Conclusions:By comparing the craniomaxillofacial morphology,hyoid bone position,and sagittal diameter of the upper airway between the patients with mouth breathing and nasal breathing who have Class Ⅱ malocclusion in children and juveniles of this study,we may conclude that:1.Class Ⅱ malocclusion mouth breathing patients mainly present a vertical growth pattern.They are manifested as the clockwise rotation of the mandibular plane and occlusion plane.Their mandibles grow backward and downward,and the anterior lower facial height of these patiens increase.2.Mouth breathing can cause mandible retracted and the lower incisors labial inclined in Class Ⅱ malocclusion patients.3.Mouth breathing has no effects on maxillary length,mandibular body length,mandibular ramus height,chin protrusion and hyoid position in Class Ⅱ malocclusion patients.4.The velopharyngeal segment of the upper airway was narrow in Class Ⅱ malocclusion mouth breathing patients.