IntroductionAngle’s class II division 2 malocclusion has unique characteristicslike•Retroclination of upper incisors and overlapping lateral incisors.•Deep overbite•Retroclined lower incisors•High lower lip line.•Increased perioral muscle activity.•Extra oral features like large nose and prominent chin and shortlower anterior facial height.
RetroclinationRetroclination of the maxillary incisors has been seen in the lateralcephalogram as increased angulation of long axis of crown and root- termedas Collum angle ( Andreasen 1930).Reasons for Collum Angle
Aim of the study:1.To investigate the magnitude of collum angle present in class II division 2malocclusion in comparison to class II division 1 and class I malocclusion.2.To find the relationship between collum angle and lower lip line.
Materials and Methods:Sample : Lateral cephalogram of patients under going orthodontic treatmentSample size = 120 subjectsGroup 1N= 40Class II division 2Group 2N=40Class II division1 malocclusionGroup 3N= 40Class I malocclusion
Inclusion criteria:Class II division 2 malocclusion:Class II division 2 incisor relationshipClass II or end on molar relationANB angle> 4°.Class II division 1 malocclusion:Class II division 1 incisor relationshipClass II or end on molar relationANB angle > 4°.Class I malocclusion:Class I incisor relationshipClass I molar relationANB angle2°± 2°.
Subjects with both hyperdivergent and hypodivergent growth patternwere included.Lateral cephalograms were taken with subjects with centricocclusion with lips reposed in the same for all subjects and in the standardizedposition.Lateral cephalograms were traced with 0.03” acetate paper.
Measurement of Collum angle (Delivanis and Kuftinec, 1980):It involves measurement of long axis of crown and root.Long axis of root(RL) is defined as the line passing through the radiographic apexof the root (Ap) and the midpoint of the lingual and facial projections ofcementoenamel junction (D).Long axis of crown(CL) is defined as the line passing through the incisionsuperious (IS) and the point D.the angle ApDIS is measured as Collum angle.(Figure 1)
Measurement of lower lip line:The lower lip line was measured as the vertical third of the crownof the central incisor (incisal third, middle third, cervical third)at whichthe vermillion border of lower lip was contacting.When the lower lip contacted the labial surface of the incisor atits incisal third it was recorded as the incisal third(I).Similarly it was recordedas middle third(M) and cervical third(C), if the lower lip touched the labialsurface of the incisor in the middle and cervical third respectively.(Figure 1).
ResultsThe mean collum angle in group 1 was 3.24º±4.69º SD.The mean collum angle in group 2 was 0.95º±1.06º SD and in group 3 the mean was1.05º ±1.53º SD(Table 1).Collum angle was statistically significant in three groups( p value=0.000) (table1).In Tukey HSD when comparing the mean collum angle between each groupindividually, it was statistically significant when comparing group 1 & 2 and group 1&3(p=.001) agnd not between group 2 and 3(Table 2).
GroupCollum angle in degrees.p valueMean SDGroup 1 3.4a4.690.000*Group 2 0.95b1.06Group 3 1.05b1.5Table 1 - ANOVA followed by Tukey HSD to test the significance ofcollum angle in groups 1, 2 and 3..*The mean difference is significant at 0.05 level.In Tukey HSD different alphabets indicates the mean difference is significant at 0.05 levelResults
Four lipline categories were compared, the mean collum angle and lower wasstatistically significant( p<0.05) .The mean collum angle was maximum (5.48º±3.68),when the lower lip line was on themiddle third of the labial surface of the central incisor(Figure 2, 5)and it is a negativevalue when the lower lip line is on the cervical third(3.1667±2.04124) indicating morelabial inclination of the root(table 2),(Figure 3,6).The mean collum angle in lip line categories incisal third and no coverage were 0.91º±1.35, 0.83º±0.96respectively (table 2),(Figure 4,7).Results
Lip line collum anglemeanSDP valueNo Coverage 0.83°a0.96 0.000*Incisal third 0.91°a1.35Middle third 5.43°b3.68Cervical third -3.16c2.04Table 2 - ANOVA followed by Tukey HSD to test the significance of relationship between collumangle lower lip line and collum angle*The mean difference is significant at 0.05 levelIn Tukey HSD different alphabet indicates significance at 0.05 levelResults
Etiology of collum angleBacklund (1960)- lingual inclination ofcentral incisors causes increased overbiteIngle(1967) explained dilaceration ascause for collum angleSchulze (1993) heridity as a reason forcollum angle.Influence of lower lip……..
Lower lip influenceLuffingham (1982), suggested strongcorrelation between lip pressure and type ofincisor relationshipAlso stated that stability of maxillary incisorrelationship is strongly dependent on lower lippositionLapatki et al(2002) – lip pressuron maxillary incisors in class IIdivision2 malocclusion is due thigh lower lip line but not due tothe increased thickness of thelip.Theur and Ingervall (1986) – lower lip pressurewas increased on maxillary central incisors inclass II division 2 malocclusion.Mcintyre and Millet(2003)-Class II division 2malocclusion had morethicker and apically placedlower lips
Bending of the incisors at the cervical part from excessivepressure from the lower lip can occur during the eruption ofteeth.The most marked changes in the relationship of thelower lip to the upper incisors is established mostlybetween the age group of 9 and 13 years((Fränkel andFalck20, 1967; Fletcher21, 1975). Vig and Cohen22(1979)
This study showed maximum collum angle in Class II division 2malocclusion.The finding was similar to Delivanis and Kuftinec11 (1980), Williams andWoodhouse23 (1983), Knosel et al25 (2009).The mean collum angle is increased when the lower lip was touching themiddle third (table 2,figure 2) and turned negative when the lower lipheight was at the cervical third of the maxillary incisors (table 2,figure 3).The magnitude of the angle is comparatively decreased when the lip lineis in the incisal third (table 2, figure 4) and there was no coverage.Of all the three groups the percentage of lip line in the middle third ismaximum in class IIdivision 2 malocclusion and lip line in cervical third isseen in only in class II division 2 malocclusion and it is negative value.
The above finding indicates that as the the lower lip line ispositioned cervically, the palatal bending of the roots which is tobe expected is changed to a labial inclination and therefore thenegative value.Hence the lower lip significantly influences the crown- rootangulation of the maxillary incisors and its stability afterorthodontic treatment- Schweitzer and Pancherz (2001).Excessive crown-root angulation may even change the torquerequirements for maxillary central incisors.
ConclusionThe collum angle isincreased in individuals belonging to class IIdivision 2 malocclusion in comparison to class II division 1 andclass I malocclusions.The collum angle is increased when there lower lip line is at themiddle third of the central incisor.The magnitude of the collum angle changes with the position ofthe lower lip line.
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