The relationship between arch width and vertical dimension of skeletal III malocclusion

Objective To analyze the relationship between width and vertical dimension of dental arches in skeletal class Ⅲ malocclusion. Methods 56 adults with skeletal class Ⅲ malocclusion (female 29, male 27) of orthodontic department in the stomatology hospital of Lanzhou university were selected. Their initial plaster models and lateral cephalograms were collected. According to the value of mandibular plane angle (MP-FH, SN-MP), they were divided into three groups (high-angle, average-angle and low-angle groups). Maxillary and mandible dental arch width and alveolar arch width at levels of inter-canine, inter-first-premolar and inter-molar were measured. The differences between the maxillary and mandibular width of each sample were calculated. Normality and homogeneity of the data were tested, and one-way ANOVA and Pearson's rank correlation with mandibular plane angle were analyzed. Results In skeletal class Ⅲ malocclusion, the width of the maxillary and mandibular molar alveolar arch in the high-angle group were significantly larger than that in the average-angle group and the low-angle group (P<0.05). There was no significant difference for the rest measured values of the three groups. Pearson correlation test showed that the dental arch width of maxillary first premolar was negatively correlated with mandibular plane angle, maxillary and mandibular alveolar arch width difference of the first premolar was negatively correlated with the mandibular plane angle in skeletal class Ⅲ malocclusion. There was no significant difference for the rest measured values of the three groups. Conclusions High-angle patients with skeletal class Ⅲ malocclusion had a tendency of excessive development of maxillary and mandibular alveolar arch width. There was correlation between maxillary middle arch width and vertical facial type in skeletal class Ⅲ malocclusion. Key words: Skeletal class Ⅲ malocclusion; Arch width; Facial vertical skeletal types