Growth And Rotation Of Jaws In Untreated Class Ⅲ Malocclusion

The growth rotation of jaws plays an important role in the craniofacial growth anddevelopment. The insufficient or excessive rotation can both influence the craniofacialbalance, resulting in malocclusion. It has been reported that mandible rotates forward toolittle in high angle cases, while too much in low angle cases;Compared with Angle Ⅰclass, Angle Ⅱ classmalocclusion expresses a little forward rotation of mandible.Because of the low incidence and the easily early recognition and intervention of Angleclass Ⅲ malocclusion, the longitudinal research data on class Ⅲocclusion is lessworldwide. In recent years, with the wide use of large sample cross-sectional studymethod on craniofacial growth and development, there is a gradual increase of theresearch of the Angle class Ⅲ occlusion.However, domestic reports on the jaw growthrotation of Angle class Ⅲ occlusion havebeen rarely seen by now. Thus, during thisexperiment, the large sample cross-sectional method was applied to study the characteristics of the jaw growth rotation of the Angle class Ⅲocclusion, in order toprovide reference for clinical treatment for Angle class Ⅲocclusion.Object： To observe the characteristics of the jaw growth and development of untreatedpatients of Angle class Ⅲ malocclusion by the Cervical vertebral maturation method(CVM), and study the influence on the growth and rotation of jaw by the eruption of themandibuar third molar(M3). Then provide reference for the orthodontic treatment forpatients of Angle class Ⅲ malocclusion.Material and Methods：Experiment1: The examined sample consisted of pretreatment lateral cephalometricrecords of358(191females with an average age of13.64years old and167males with anaverage age of13.51years old) untreated Class III patients of Chinese,and then it wasgrouped by gender and CVM.The following variables were measured with Winceph8.0Cephalometrics analysis software:(1)jaw growth variables: effective maxillary length(Ar-A),maxillary height(N-A), ramal length (Ar-Go’), mandibular body length (Go’-Me)and effective mandibular length (Ar-Gn);(2) the jaw rotation variables: palatal plane Angle(SN-PP),mandibular true rotation Angle (SN-XiPm),mandibular plane Angle (SN-GoGn),occlusal plane Angle (SN-OP), gonion Angle (ArGo’Me) and facial height ratio(S-Go/N-Me). LSD-t test were used to identify significant differences between all groupsby SPSS16.0software.Experiment2: Files(panoramic radiograph, lateral cephalometric records,physicalexamination,etc.) of131Angle class Ⅲ occlusion cases with M3were collected, with anaverage age of17.80years old,who were divided into two groups based on the status ofM3eruption (the incubating group65cases, the erupted group66cases). Winceph8.0cephalometrics analysis software was used to analyze the following items: the mandibularplane Angle (SN-GoGn), occlusal plane Angle (SN-OP), gonion Angle(ArGo’Me),facialheight ratio(S-Go/N-Me), ramal length(Ar-Go’),mandibular body length (Go’-Me) andeffective mandibular length(Ar-Gn).Data was statistically inferred using the unpaired t-testby SPSS16.0software. Result：1.In males,effective maxillary length (Ar-A) and maxillary height(N-A) sustainedgrowth from CS1to CS5,with no significant difference between adjacent period; ramallength (Ar-Go’), mandibular body length (Go’-Me) and effective mandibular length(Ar-Gn)increased all throughout the whole CVM period, moreover,showed significant increase inCS1-CS2(3.7,6.6and9mm respectively) and in CS4-CS5(5.8,5.8and4.0mmrespectively)(P <0.05).2. In males, no significant difference was identified in terms of palatal plane Angle(SN-PP) from CS1to CS6;gonion Angle(ArGo’Me) reduced4.3°from CS4toCS5(P=0.043), changes of S-Go/N-Me and SN-GoGn were significantly different betweenCS4and CS5(P=0.055).3. In females, effective maxillary length(Ar-A) and maxillary height(N-A) sustainedgrowth from CS1to CS5, and grew significantly in CS1-CS2(3.3and3.7mmrespectively) and CS3-CS4(2.9and3.2mm respectively); ramal length (Ar-Go’),mandibular body length (Go’-Me) and effective mandibular length(Ar-Gn) all increasedthroughout the whole CVM period, moreover, it showed significant increase in CS1-CS2(2.5,4.0and5.9mm respectively),in CS3-CS4(2.7,3.9and6.2mm respectively) andCS4-CS5(3.7,3.9and6mm respectively)(P <0.05).4. In females, no significant difference was identified in terms of palatal planeAngle(SN-PP) from CS1to CS6; mandibular true rotation Angle (SN-XiPm),mandibularplane Angle(SN-GoGn) and occlusal plane Angle (SN-OP),decreased3.1,4.0°and3.5°inCS4-CS5respectively (P <0.05), gonion Angle (ArGo’Me) decreased3.9°in CS4-CS6(P=0.010); corresponding to the SN-GoGn,the significant change of S-Go/N-Me appearedin CS4-CS5groups (P=0.030).5.Ramal length (Ar-Go’), mandibular body length (Go’-Me) and effective mandibularlength(Ar-Gn) increased3.2,3.1and3.9mm respectively (P <0.05)with eruption of M3inAngle class Ⅲ malocclusion patients;gonion Angle (ArGo’Me) of the erupted groupdecreased2.1°,compared to the incubating group (P=0.096). Rest of mandibular rotationmeasurements seemed to be no change. Conclusion1. Maxilla of male subjects with Angle class Ⅲ malocclusion grows slowly, with noobvious growth peak.Mandible grows faster and lasts longer, the growth peak appears inCS4-CS5, there is still growth in CS5-CS6.2. Maxilla of female subjects with Angle class Ⅲ malocclusion grows slowly, with agrowth peak in CS3-CS4.Mandible grows faster and lasts longer, the growth peak appearsin CS4-CS5,and there is still growth in CS5-CS6.3. Maxilla exhibits no growth rotation in cases with Angle class Ⅲ occlusion.4. In both female andmale Class III subjects, mandibular forward rotation occurs inCS4-CS5.But the gonion Angle of men changes obviously, mandibular true rotationAngle,mandibular plane Angle and occlusal plane Angle of women change obviously。5. In Angle class Ⅲ cases, mandible has a small amount of growth with eruption of M3,but it is not clear that this growth is from the promotion of M3, or mandibular growthpotential.6. In Angle class Ⅲ cases, gonion Angle decreases during eruption of M3, butmandibular rotation has not been found.