Growth And Rotation Of Jaws In Class Ⅱ Malocclusion

The growth of craniofacial is the foundation of orthodontics. Since Bjork put forward the concept of jaw rotation, orthodontic doctors began to focus on the importance of jaw rotation. Rotation plays an important role in the growth and development of craniofacial. The direction and amplitude of rotation can affect the growth of cranial and maxillofacial balance and lead to malocclusion.Class Ⅱ is one of common malocclusion. Depending on the anterior labial inclination, it was divided into Class Ⅱ1 and Class Ⅱ2 malocclusion. The article of growth and development of jaws in Class Ⅱ is commonly seen, however, there is no research on the characteristics of various periods in growth and development, especially for the analysis of rotation. This study evaluated the gender difference of the jaw growth and development of Angle class II malocclusion by the Cervical vertebral maturation method(CVM), and compared the differences in Class Ⅱ1, Class Ⅱ2 and Class I. Object:To observe characteristics of jaw rotation of Class Ⅱ1 and Class Ⅱ2 with various Cervical vertebral maturation stage and compare differences in rotation of Class Ⅱ1, Class Ⅱ2 and Class I.Material and Methods:Part I: A cohort of 663 individuals, including 422 Class Ⅱ1(197 males, 225 females), 241 Class Ⅱ2(91 males, 150 females), selected from of class II malocclusion patients in the fourth military medical university stomatological hospital orthodontic department were enrolled. Basic data and pretreatment lateral cephalometric records were collected, which were grouped by CVM and gender. Each lateral cephalometric was analyzed by winceph8.0 cephalometric software and the statistics were calculated by SPSS16.0 software using LSD-t test.Part II: The sample was same to Part I, T test were used for analysis of the differences in the growth and development period of same sex’s Class Ⅱ and Class I.Part III: A cohort of 302 Class I(162 males, 140 females) which from the fourth military medical university stomatological hospital were enrolled. Basic data and new head lateral slice which were grouped by CVM and gender were collected. Each lateral cephalometric was analyzed by winceph8.0 cephalometric software and the statistics were calculated by SPSS16.0 software. The t-test analysis was used to compare jaw growth rotation difference in class I, Class Ⅱ1 and Class Ⅱ2Result: 1. The characteristic of jaw rotation in Class Ⅱ1.For males of Class Ⅱ1, PP-SN in CS1-CS2 decreased about 0.33°, increased in CS2-CS4 about 1.21°, then decreased in CS5-CS6 about 1°. It rotated counterclockwise overall. Xi Pm- SN increased by 0.82 ° in CS1-CS6, which showed a trend of downward and forward rotation; Go Gn-SN in CS1-CS3 period increased continuously about 1.22°, decreased about 1.23 °in CS3-CS5, increased little in CS6 which increased about 0.65 °overall. OP- SN in CS1-CS6 overall decreased about 1.68°. Ar-Go-Me increased in CS1-CS3, decreased 3.16 ° in CS3-CS6 period. S-Go/N-Me in CS1–CS4 decreased slightly(about 0.3%), then increased significantly(about 1%).For females of Class Ⅱ1, PP-SN changed slightly overall and the upper jaw rotated forward and upwards. Xi Pm-SN decreased about 0.55 °from CS1 to CS6. The overall of Go Gn-SN decreased about 2.71°, which rotated counterclockwise. OP-SN in CS1-CS6 period decreased about 5.51° slowly. Ar-Go-Me decreased 7.65 ° in CS1-CS6 period and changed obviously in CS1- CS3. S-Go/N-Me increased about 2.4% in CS1-CS2 period, then changed slightly.2. The characteristic of jaw rotation in Class Ⅱ2 For males of class II2, PP-SN decreased significantly about 2.61° in CS1-CS2(P< 0.05). Xi Pm-SN reduced 0.59° and 2.13°in CS3 and CS5, respectively. Go Gn-SN reduced obviously about 3°in CS5. OP-SN significantly reduced 5°(P<0.05) in CS4-CS5 and increased about 3°(P<0.05) in CS5-CS6; S-Go/N-Me increased 3.46% overall, but changed irregularly in each period. Ar-Go-Me reduced significantly about 4.59 ° in CS5(P<0.05).For females of class II2, PP-SN significantly increased about 2°in CS2, significantly reduced about 2.61 ° in CS3. Xi Pm-SN, Go Gn-SN, and OP-SN in each period changed in the same trend and decreased about 0.74°, 1.34°, 1° in CS1-CS6 respectively, but there were no significance difference in each period. S-Go/N-Me greatly increased about 2.16% in CS2-CS3 period and decreased about 2.84%(P<0.05). Ar-Go-Me overall decreased in CS1-CS6 and increased about 2.56°in CS4.3. The difference of jaw rotation of males in Class Ⅱ1 and Class Ⅱ2.Compared with males of Class Ⅱ1, the PP-SN of Class Ⅱ2 increased 3.6° in CS2(P<0.05), then the PP-SN decreased in next periods. The Xi Pm-SN of Class Ⅱ2 decreased 1.66° averagely in each periods. Angle on Y axis of males in Class Ⅱ2 decreased 1.96° in CS5(P<0.05). The OP-SN of Class Ⅱ2 decreased in each periods compared with Class I, especially in CS4(almost decreased 3.11°,P<0.05). With growth and development, the Go Gn-SN of Class Ⅱ2 increased. It increased 3.51° in CS5 compared with Class Ⅱ2(P<0.05). Compared with Class Ⅱ2 the Ar-Go-Me of Class Ⅱ1 increased in each periods, there was statistical difference in CS5. In CS1, the S-Go/N-Me of Class Ⅱ2 was littlesmaller, after that, each periods lager than Class Ⅱ1 and it increased 2.31% in CS5(P<0.05).4. The difference of jaw rotation of females in Class Ⅱ1 and Class Ⅱ2 Compared with females of Class Ⅱ1, PP-SN of females in Class Ⅱ2 changed irregularly. Xi Pm-SN of females in Class Ⅱ2 was larger about 1.42° and 2.51° in CS1 and CS2 period than Class Ⅱ1, respectively. There was no statistical difference in the rest period. Comparing females of class II1, angle on Y axis of females in Class Ⅱ2 reduced 1.45° and 0.19° in CS3 and CS4, respectively. OP-SN of females in Class Ⅱ2 changed irregularly.,which was larger respectively about 3.98°,2.02°,3.19° than females of Class Ⅱ1 in CS2,CS5,CS6(p<0.05)。There were statistical significance of OP-SN between females of Class Ⅱ1 and Class Ⅱ2 in CS2, CS5, CS6(P<0.05). There were no statistical differences of Go Gn-SN and S-Go/N-S in females of Class Ⅱ1 and Class Ⅱ2. Ar-Go-Me of females of class II1 more increased significantly about 1.1 °in CS5 than females in class II2(P<0.05).5. The difference in Class Ⅱ1 and Class I Compared with Class I of males, the PP-SN of Class Ⅱ1 decreased 1.73°(P<0.05). The Xi Pm-SN of Class Ⅱ1 of males increased among all period, especially increased 4.75° and 3.68° in CS2, CS4(P<0.05), respectively. The angle on Y axis of males in Class Ⅱ1 increased overall period. In CS4, the angle on Y axis increased 1.17°(P<0.05). The OP-SN and Go Gn-SN of Class Ⅱ1 decreased 0.14° and 1.03° in CS1, respectively. In the rest periods, the OP-SN and Go Gn-SN increased. The Ar-Go-Me of Class Ⅱ1 in CS1-6 were less than Class I 0.55°-4.25°.Compared with Class I of females, the PP-SN of Class Ⅱ increased in CS1-3. The PP-SN of Class I of females was larger 0.81° than Class Ⅱ1. The PP-SN of Class I decreased in CS5-6. The Xi Pm-SN of Class I increased in all period which increased 3.02°, 5.20°, 3.53° and 3.52° in CS2, CS4, CS5 and CS6, respectively. The angle on Y axis of females in Class Ⅱ1 increased in overall period compared with Class I, but this was not statistical significance. The Go Gn-SN only decreased in CS3 and increased in the rest of period. The Go Gn-SN increased 3.05° in CS4(P<0.05). The Ar-Go-Me of Class Ⅱ1 decreased 4.03°(P<0.05). The S-Go/N-ME of Class Ⅱ1 decreased 2% compared with Class I(P<0.05). There were no statistical significance in rest stages.6 The difference in Class Ⅱ2 and Class ICompared with Class I of males, the PP-SN of Class Ⅱ2 of males increased 2.99° in CS2, however, in the rest of periods, the PP-SN decreased. The Xi Pm-SN averagely increased 1.08°. The Ar-Go-Me of Class Ⅱ2 increased 4.03° and 3.62° in CS2 and CS4, respectively,compared with Class I(P<0.05). Except for Go Gn-SN of Class Ⅱ2 increased 0.67° in CS4, other periods decreased. The Ar-Go-Me of Class Ⅱ2 decreased 5.58°, 7.02°, 4.32° and 5.04° in CS1,CS2,CS3 and CS5,respectively(P<0.05). The number of S-Go/N-ME of Class Ⅱ2 increased in CS2-6 compared with Class I, but there were no statistical significance.Compared with Class I of females, the PP-SN of Class Ⅱ2 of females increased 2.61° in CS2(P<0.05), however, in the rest of periods, there were no statistical significance. The Xi Pm-SN increased 4.38, 5.53, 4.96, 3.34 and 4.89 in CS1, CS2, CS4, CS5 and CS6, respectively(P<0.05). The Go Gn-SN of Class Ⅱ2 of females were merely less than Class I in CS3 and increased 4.74 in CS4°(P<0.05). The Ar-Go-Me of Class Ⅱ2 of females increased 5.56°, 2.89° and 2.9° in CS2, CS5, and CS6,respectively, compared with Class I of females(P<0.05). The Ar-Go-Me decreased 4.32° in CS3 compared with Class I(P<0.05). The S-Go/N-Me of Class Ⅱ2 of females increased 2.93% and 3.46% in CS3 and CS4, respectively, compared with Class I(P<0.05).Conclusion 1. The maxillary of Class Ⅱ1 rotated forward and upwards. The mandible was rotated clockwise. The OP-SN rotated counterclockwise. The Ar-Go-Me decreased in the process of growth and development.2. The maxillary of Class Ⅱ2 rotated small scope. The Xi Pm-SN, Go Gn-SN, OP-SN rotated counterclockwise. The S-Go/N-Me increased. The Ar-Go-Me changed acutely.3. Compared with Class Ⅱ1, the OP-SN of Class Ⅱ2 rotated clockwise and the mandible rotated counterclockwise. The Ar-Go-Me were relatively smaller. The S-Go/N-Me were relatively larger.4. The maxillary of Class Ⅱ1 were protrusion compared with Class I and the mandible were retrusion.5. Compared with Class I, the maxillary of Class Ⅱ1 was normal developed and the mandible were retrusion. The the mandible rotated clockwise, the difference were more obviously in females than males.6. Compared with Class I, the maxillary of Class Ⅱ2 was normal developed and the mandible was retrusion, especially in length of mandible body. The direction of mandible true rotation was clockwise. The Ar-Go-Me were relatively smaller. The S-Go/N-Me were relatively larger.