Three-dimensionl Analysis Of Maxillary Dental Arch And Basal Bone In Skeletal Class Ⅲ Malocclusion

ObjectiveIn this study,we established the maxillary three-dimensional coordinate system of skeletal Class Ⅲ malocclusion.The three-dimensional coordinate ranges of the maxillary dental arch landmarks and the basal bone landmarks were preliminarily counted.To study the incoordination and compensation,we compared the three-dimensional difference of maxillary teeth and basal bone between skeletal ClassⅢ malocclusion and individual normal occlusion.The research results provide theoretical basis of compensation and guidance for orthodontists,so that the teeth are located in the normal position and the treatment effect remains more stable.MethodsWe selected 50 patients with skeletal Class Ⅲ malocclusion(25 females:22.87 ±3.12 years old,25 males : 22.54 ± 2.32 years old)who were treated in the Orthodontics Department of Tianjin Stomatological Hospital from September 2017 to September 2019 and 50 normal patients(25 females : 22.23 ± 3.47 years old,25males:23.89 ± 2.28 years old).CBCT images were taken as experimental group and control group respectively.The image data was converted to the Invivo 5.3 software,a three-dimensional coordinate system of the maxillary region was established.The dental arch landmarks and the basal landmarks of upper jaw were marked and their three-dimensional coordinates were recorded.SPSS 22.0 was used to analyze independent t-test samples between two groups.The items include three-dimensional coordinates of dental arch points,basal points,and differences between dental arch points and basal points,which indicate the three-dimensional characteristics and compensation of maxillary dental arch and basal bone.Results1.In the three-dimensional coordinate system of this study,three-dimensional coordinate range of the maxillary dental arch and the basal bone landmarks of skeletal Class Ⅲ malocclusion was preliminarily calculated.Comparison ofmaxillary dental arch coordinate between skeletal Class Ⅲ malocclusion and individual normal occlusion: There was no difference in X coordinates;Y coordinates were smaller than the individual normal occlusion,and the direction was sagittal to negative;The Z coordinate value of second molar was smaller than individual normal occlusion.2.Comparison results of maxillary basal bone coordinates between skeletal Class Ⅲ malocclusion and individual normal occlusion: The X coordinate values of canine to second molar were smaller than individual normal occlusion;The Y coordinate values of posterior region were smaller;The Z coordinate values of the first premolar to the first molar were smaller than that of normal occlusion,that is,the height was lower.3.Comparison of the difference coordinates between the maxillary dental arch and base: compared to normal occlusion,The X coordinate value of the skeletal ClassⅢ malocclusion was larger in the first premolar to the second molar area.The maxillary molars were inclined to buccal side;Except for the maxillary canine and second molar,Y coordinates of the other teeth were larger than that of individual normal occlusion,and the direction was negative;The absolute value of the Z coordinates of the first premolar to first molar were smaller than that of normal occlusion,and the height in the vertical direction was decreased,but the absolute value of second molar was larger than the normal occlusion,and the height in the vertical direction was increased.Conclusions1.The development of maxillary dental arch of skeletal Class Ⅲ malocclusion is normal in the horizontal direction.And the maxillary teeth have sagittal compensation.The height of the second molar is lowered vertically.2.The maxillary base bone of skeletal Class Ⅲ malocclusion is underdeveloped in horizontal,sagittal and vertical directions.3.The maxillary dental arch of skeletal Class Ⅲ malocclusion is compensated for the incoordination of basal bone.The maxillary incisors incline to labial side.The posterior teeth incline to buccal and mesial,and the height is lowered.So thecompensation of maxillary dental arch and basal bone should be considered in orthodontic treatment plan.