Manuscript 841

Introduction

Angle’s class II division 2 malocclusion has unique characteristics like •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 short lower anterior facial height.

RetroclinationRetroclination of the maxillary incisors has been seen in the lateral cephalogram as increased angulation of long axis of crown and root- termed as 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 2 malocclusion 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 treatment

Sample size = 120 subjects

Group 1N= 40Class II division 2

Group 2 N=40Class II division 1 malocclusion

Group 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 centric occlusion with lips reposed in the same for all subjects and in the standardized position.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 apex of the root (Ap) and the midpoint of the lingual and facial projections of cementoenamel junction (D).Long axis of crown(CL) is defined as the line passing through the incision superious (IS) and the point D.the angle ApDIS is measured as Collum angle.(Figure 1)

Figure 1

Measurement of lower lip line:

The lower lip line was measured as the vertical third of the crown of the central incisor (incisal third, middle third, cervical third)at which the vermillion border of lower lip was contacting.

When the lower lip contacted the labial surface of the incisor at its incisal third it was recorded as the incisal third(I).Similarly it was recorded as middle third(M) and cervical third(C), if the lower lip touched the labial surface of the incisor in the middle and cervical third respectively.(Figure 1).

Results

The 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 was 1.05º ±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 group individually, 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 value

Mean SD

Group 1 3.4a 4.69

0.000*Group 2 0.95b 1.06

Group 3 1.05b 1.5

Table 1 - ANOVA followed by Tukey HSD to test the significance of collum 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 level

Results

Four lipline categories were compared, the mean collum angle and lower was statistically significant( p<0.05) . The mean collum angle was maximum (5.48º±3.68),when the lower lip line was on the middle third of the labial surface of the central incisor(Figure 2, 5)and it is a negative value when the lower lip line is on the cervical third(3.1667±2.04124) indicating more labial 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 angle

mean SD

P value

No Coverage 0.83°a 0.96 0.000*

Incisal third 0.91°a 1.35

Middle third 5.43°b 3.68

Cervical third -3.16c 2.04

Table 2 - ANOVA followed by Tukey HSD to test the significance of relationship between collum angle lower lip line and collum angle

*The mean difference is significant at 0.05 levelIn Tukey HSD different alphabet indicates significance at 0.05 level

Results

Figure 2 Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Discussion

Etiology of collum angle

Backlund (1960)- lingual inclination of central incisors causes increased overbite

Ingle(1967) explained dilaceration as cause for collum angle

Schulze (1993) heridity as a reason for collum angle.

Influence of lower lip……..

Lower lip influence

Luffingham (1982), suggested strong correlation between lip pressure and type of incisor relationship Also stated that stability of maxillary incisor relationship is strongly dependent on lower lip position

Lapatki et al(2002) – lip pressure on maxillary incisors in class II division2 malocclusion is due to high lower lip line but not due to the increased thickness of the lip.

Theur and Ingervall (1986) – lower lip pressure was increased on maxillary central incisors in class II division 2 malocclusion.

Mcintyre and Millet(2003)- Class II division 2 malocclusion had more thicker and apically placed lower lips

Bending of the incisors at the cervical part from excessive pressure from the lower lip can occur during the eruption of teeth.

The most marked changes in the relationship of the lower lip to the upper incisors is established mostly between the age group of 9 and 13 years((Fränkel and Falck20, 1967; Fletcher21, 1975). Vig and Cohen22 (1979)

This study showed maximum collum angle in Class II division 2 malocclusion. The finding was similar to Delivanis and Kuftinec11 (1980), Williams and Woodhouse23 (1983), Knosel et al25 (2009).

The mean collum angle is increased when the lower lip was touching the middle third (table 2,figure 2) and turned negative when the lower lip height was at the cervical third of the maxillary incisors (table 2,figure 3).

The magnitude of the angle is comparatively decreased when the lip line is 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 is maximum in class IIdivision 2 malocclusion and lip line in cervical third is seen in only in class II division 2 malocclusion and it is negative value.

The above finding indicates that as the the lower lip line is positioned cervically, the palatal bending of the roots which is to be expected is changed to a labial inclination and therefore the negative value.

Hence the lower lip significantly influences the crown- root angulation of the maxillary incisors and its stability after orthodontic treatment- Schweitzer and Pancherz (2001).

Excessive crown-root angulation may even change the torque requirements for maxillary central incisors.

Conclusion

The collum angle isincreased in individuals belonging to class II division 2 malocclusion in comparison to class II division 1 and class I malocclusions.

The collum angle is increased when there lower lip line is at the middle third of the central incisor.

The magnitude of the collum angle changes with the position of the lower lip line.

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