The Characteristics Of The Arch Form Of Skeletal Class â…¢ Occlusion With Normal Maxilla And Protruding Mandible

Objective:The purpose of this study is to study the characteristics of the arch form of skeletal classⅢwith normal maxilla and protruding mandible and to provide evidence for the diagnosis and design of the treatment of orthodontics for classⅢmalocclusion by evaluating differences in dental arch forms between skeletal classⅢwith normal maxilla and protruding mandible and normal occlusion.Materials and Methods:30 skeletal classⅢpatients with normal maxilla and protruding mandible and 30 normal occlusion subjects aged 13～17 years old were selected.Every group includes 15 males and 15 females.Fourteen landmarks, corresponding to the cusp tips and incisor edges,were identified on the upper and lower dental casts of all subjects by three dimension measuring machine and measured.Arch form differences as followings are assessed by Euclidean distance matrix analysis(EDMA):(1)differences of dental arch form between maxilla and mandible of normal occlusion.(2)differences of dental arch form between male and female with normal occlusion.(3)differences of dental arch form between keletal classⅢmalocclusion with normal maxilla and protruding mandible and normal occlusion. Results:(1)In both sexes,arch shape difference was significant betweent the maxilla and mandible of normal occlusion(p＜0.01),by deleting the group of teeth,the results showed that the anterior teeth explain most of the arch-form differences between the two groups.The maxillary arch was larger than the mandibular one.The arch size was 2.2%larger in males and 1.9%larger in females.(2)The normal occlusion data showed no arch-shap difference by sex in either arch,but arch sizes were 2.3%larger in boys in the maxillary arch and 2.1%larger in the mandibular arch.(3)In both sexes,arch shape difference of maxilla was significant betweent skeletal classⅢpatients with normal maxilla and protruding mandible and normal occlusion(p＜0.01),by deleting the group of teeth,the results showed that the posterior teeth explain most of the arch-form differences between the two groups.The maxillary arch of skeletal classⅢpatients with normal maxilla and protruding mandible was larger than that of normal occlusion.The arch size was 2.2%larger in males and 1.9%larger in females.In both sexes,arch shape difference of mandible was also significant betweent skeletal classⅢpatients with normal maxilla and protruding mandible and normal occlusion(p＜0.01),by deleting the group of teeth,the results showed that the anterior teeth explain most of the arch-form differences between the two groups.The mandibular arch of skeletal classⅢpatients with normal maxilla and protruding mandible was larger than that of normal occlusion.The arch size was 2.6%larger in males and 2.4%larger in females.Conclusion:It is concluded that the maxillary and the mandibular arch form of skeletal classⅢsubjects with normal maxilla and protruding mandible significantly differed from that of normal occlusions.The results showed that arch forms in maxillary skeletal classⅢsubjects with normal maxilla and protruding mandible significantly differed from subjects with normal occlusions in both size and shape regardless of sex,and posterior areas contribute most to the arch-form difference.Maxillary posterior arch width was larger than that of normal occlusion.As the same as the maxillary arch,the results showed that arch forms in mandibular skeletal classⅢsubjects with normal maxilla and protruding mandible significantly differed from subjects with normal occlusions in both size and shape regardless of sex,but anterior areas contribute most to the arch-form difference.Mandibular anterior and posterior arch width were both larger than that of normal occlusion.