Incisors And First Molars Inclination Of Adult Skeletal Class â…¢ Malocclusion With Different Facial Growth Patterns

Objective:By measuring the labial or lingual inclination of incisors and the mesiodistal inclination of first molars in different growth patterns with adult skeletal class Ⅲmalocclusion through lateral cephalograms,to explore the dentoalveolar compensation mechanism in line with the vertical skeletal discrepancy, and provide reference for orthodontist.Methods:In the light of inclusion criteria,the value of FHI and the angle of MP-SN,adult skeletal class Ⅲ malocclusion patients were selected as experimental group including horizontal,average,vertical growth patterns,20 cases in each pattern.The same number of angle’s classⅠand skeletal classⅠwere selected as control group.12 angle parameters were measured to asses incisors’ or first molar’ inclination.These data in control and experimental group were analyzed by analysis of variance and SNK-q test separately,the differences between the two groups were compared using two-sample t-test.Results:1.Angle’s classⅠand skeletal classⅠmalocclusion measurement results:The result of ∠U1-SN and ∠L1-MP decreased with facial growth patterns increasing;∠U6-SN,∠U6-FH,∠L6-MP decreased according to horizon,average and vertical growth patterns,all of the differences had statistic significance,suggesting that incisors tended to be upright and first molars tended to tip distally with facial growth patterns increased,There were no significant differences in intermolar angulation amongdifferent facial growth patterns.2.Skeletal class Ⅲ malocclusion measurement results:∠U1-SN in vertical growth patterns were smaller than them in horizontal and average growth patterns,∠L1-MP decreased in turn with horizontal,average and vertical growth patterns.∠U6-SN and ∠L6-MP decreased with the same order,∠U6-FH in average and vertical growth patterns were smaller than them in horizontal growth patterns.All of the differences had statistic significance,indicating that the compensatory trend of incisors and first molars was in keeping with control group.3.Skeletal class Ⅲ malocclusion and angle’s classⅠand skeletal classⅠmalocclusion comparison results:Compared with angle’s classⅠand skeletal classⅠmalocclusion,∠U1-SN in adult skeletal class Ⅲ malocclusion with different growth patterns were greater,while ∠U1-MP were smaller,suggesting that the upper incisors were more proclined,whereas the lower incisors were more retrolined.∠U6-SN in vertical and average growth patterns were larger than them in control group,∠U6-FH,∠U6-PP in vertical growth patterns were larger also,indicating that the upper first molars tended to tip mesially compared with control groups.∠L6-SN and ∠L6-PP in adult skeletal class Ⅲ malocclusion with average and vertical growth patterns were greater than them in control groups,whereas ∠L6-MP were smaller,making clear that lower first molars tended to tip distally.The upper incisors’ compensatory changes relative to anterior granial base plane in average and vertical growth patterns were 5.00° and 4.15° seperately,the upper first molars’ were 2.85° and 3.25°,the lower incisors’ compensatory changes relative to mandibular plane were 7.15° and 9.7°,the lower first molars’ were 2.75° and 2.85°,suggesting that the incisors’ compensatory changes were more obvious than first molars’.Conclusions:1.Adult skeletal class Ⅲ malocclusion have the coincident compensation trends with adult angle’s classⅠand skeletal classⅠmalocclusion.With the facial growth pattern increasing, the incisors tend to be upright, the first molars tend to tip distally.2.Adult skeletal class Ⅲ malocclusion’s upper incisors have the sloping trend toward proclined direction,whereas the lower incisors have the sloping trend toward retrolined direction;the upper first molars in average and vertical growth patterns have the sloping trend toward mesial direction,whereas the mandibular first molars have the sloping trend toward distal direction.The compensatory trend of incisors may be more obvious than first molars’.