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RELATIONSHIP BETWEEN MAXILLARY AND MANDIBULAR EFFECTIVE LENGTHS AND DENTAL CROWDING IN CLASS II MALOCCLUSIONS.

Byline: ADIL KHAN, ULFAT BASHIR, HANNA JALIL and UMAR HUSSAIN

Abstract

The objective of this study was to determine the frequency of crowding in patients with class II malocclusions and to compare the mean maxillary and mandibular apical base lengths in patients with more than 3mm and less than 3mm of crowding in class II malocclusion patients.

This study was a descriptive case series carried out at Islamic International Dental Hospital Islamabad. A total of 95 patients were selected according to the inclusion criteria of a complete (full cusp) bilateral class II molar relationship and presence of all permanent teeth up to the first molars. Patients with an open bite, cross bite, presence of caries or restored teeth were excluded. Measurements were performed on pre-treatment dental casts and lateral cephalograms. Pre-treatment dental casts were used to calculate crowding. The radiographs were traced manually with an acetate paper attached on top and used to calculate the apical base lengths of the maxilla and mandible. The sample was divided into two groups according to severity of mandibular crowding. Group 1 consisted of patients with crowding more than or equal to 3mm.

Group 2 consisted of patients with crowding less than 3mm. Data analysis was carried out using Statistical Package for the Social Sciences (IBM SPSS version 20, Chicago, Ill). Mean mandible length was 124 (+- 7.208) and mean maxilla length was 91.60(+- 6.772) while mean mandible ALD -2.92 (+- 2.866). A comparison of the means with a one sample T-test revealed a P value of 0.000, showing that both the variables were highly significant. The results of this study demonstrate a significant inverse correlation between maxillary and mandibular effective lengths and the severity of dental crowding.

Key Words: Class 2 malocclusion, apical base lengths, dental crowding.

INTRODUCTION

Dental crowding is one of the most prevalent of orthodontic conditions, frequently causing mal-positioned teeth for which patients seek orthodontic treatment. Crowding is defined as a discrepancy between tooth size and arch size that results in malposition and/or rotation of teeth.1 Crowding of the dentition is usually attributed to discrepancies in tooth size and arch length and arch width.2-5 The goal of modern orthodontics is to provide the best possible occlusal relationships within the acceptable framework of facial aesthetics and stability of results. Treating the actual cause of crowding and not just treading along the traditional lines of thought where we simply correlate it with reduced arch dimensions would go a long way in achieving this goal.

Dental crowding has been shown by some studies as being prevalent in as much as 57% of the population.6

Numerous factors such as the direction of mandibular growth, head posture, inclination of teeth and the oral and perioral musculature may affect the development and severity of crowding.7 Research into the relationship between crowding and cephalometric measurements has been sparse. However, the relationship between the base lengths of the jaws and dental crowding has been demonstrated with positive correlation. Studies have shown that short mandibular body lengths, irrespective of arch dimensions, are associated with crowding of the dentition. It is a correlation which exists as early as the early mixed dentition through to the late mixed dentition.7 Longitudinal studies have also shown that mandibular crowding increases over time; the increases being greatest during adolescence and slowing down during adulthood.8,9

Mandibular growth on the other hand, ceases to a great extent after adolescence. Baccetti et al reported an increase of 0.5mm (93.5 to 94.0) in the mean value of maxillary apical base length (Co-A) and an increase of 1.0mm (120.5 to 121.5) in the mean value of mandibular base length (Co-Gn); both termed insignificant.10 Since crowding increases with age regardless of changes in mandibular apical base length, it would make reduced base lengths in childhood a possible indicator for dental crowding in adulthood if a positive correlation existed. Berg's research focused on class I malocclusion patients but more recently, Janson demonstrated weak to moderate correlation between the two variables in class II malocclusions as well.1

Among all the factors responsible for dental crowding, previously only the relationship of the arch dimension to crowding has been investigated in Pakistan. Therefore, the aim of this study is to investigate the relationship between dental crowding and apical base lengths of the jaws in class II malocclusions in the Pakistani population. Significant findings in this study could make mandibular retrognathism an important early indicator of crowding, allowing for timely and appropriate intervention.

METHODOLOGY

* Study design: Descriptive case series

* Setting: Islamic International Dental Hospital, Islamabad

* Duration: Six months after the approval of synopsis

* Sample technique: Non-probability consecutive

* Sample size: 95

* Confidence interval: 95%

* Anticipated population: 56.66%

* Absolute precision: 10%

* Inclusion criteria:

1 Complete (full cusp) bilateral class II molar relationship

2 Presence of all permanent teeth up to the first molars

* Exclusion criteria:

1 Open bite - Lack of vertical overlap of the mandibular dentition by the maxillary dentition

2 Cross bite - One or more teeth in the maxillary anterior or buccal segment is lingual to one or more of the opposing teeth in the mandibular arch in maximum intercuspation

3 Presence of caries

4 Presence of restorations.

After approval of the study by the institute's ethical committee, 95 patients were randomly selected according to our selection criteria. Informed consent was taken from all the patients selected for the study.

Measurements were performed on pre-treatment dental casts and lateral cephalograms. Pre-treatment dental casts were used to calculate crowding. Mandibular and maxillary crowding were calculated as the difference between arch perimeter and the sum of the mesio-distal dimensions of the teeth, in millimetres, from the second premolar on one side of the arch to the second premolar on the other side. The mesio-distal dimensions were measured with a digital vernier calliper (Mitutoyo Corp., Kawasaki, Japan). The arch perimeter was measured from the mesial marginal ridge of the permanent first molar on one side to the mesial marginal ridge of the permanent first molar on the other side with a brass wire of 0.5mm diameter.

All the lateral cephalograms were taken by the same operator on Rotograph Plus at 80 kvp, 10 mA and 0.8-second exposure time using 8 x 10 inch Kodak green film with the patient's head in the natural head position. The radiographs were traced manually with an acetate paper attached on top. Tracing was done with a lead pencil in a dark room on a radiograph viewer. A single investigator manually conducted anatomic tracings and location of dento-skeletal landmarks. The base length of the maxilla was taken as the linear distance between the condylion and point A (Co-A). The base length of the mandible was measured as the linear distance between the condylion and gnathion (Co-Gn). The readings were recorded and noted in the data collection proforma by the trainee researcher. Tracings were repeated after a minimum of two months by the trainee researcher and two colleagues for intra and inter operator reliability.

The sample was divided into two groups according to severity of mandibular crowding. Group 1 consisted of patients with crowding more than or equal to 3mm. Group 2 consisted of patients with crowding less than 3mm.

Data analysis was carried out using Statistical

Package for the Social Sciences (IBM SPSS version 20, Chicago, Ill). For the quantitative variables; age, mandibular base length and maxillary base length, mean and standard deviation were calculated. For the qualitative variables; sex and crowding, frequency and percentages were calculated. T-test was used to compare mean maxillary and mandibular base lengths. P value of [?] 0.05 was taken to be significant.

TABLE 1: AGE DISTRIBUTION (N=95)

Age (years)###Frequency (n)###Percent

12-16###75###78.9

17-21###12###12.6

22-27###8###8.4

TABLE 2: GENDER DISTRIBUTION (N=95)

Gender###Frequency (n)###Percent

Male###48###50.5

Female###47###49.5

TABLE 3: MAXILLARY LENGTH DISTRIBUTION

Length (mm)###Frequency (n)###Percent

100###10###10.5

TABLE 4: MAXILLARY CROWDING DISTRIBUTION

ALD (mm)###Frequency (n)###Percent

10###1###1.1

TABLE 5: MANDIBULAR LENGTH DISTRIBUTION

Length (mm)###Frequency (n)###Percent (%)

130###13###13.7

TABLE 6: MANDIBULAR CROWDING DISTRIBUTION

ALD (mm)###Frequency (n)###Percent

4mm) and that when the accumulated mass of 20 permanent teeth is 140mm or more, the clinician may consider treatment with extractions.13 These findings and the results of our study may suggest that beyond the arch length analysis, the sum of mesio-distal widths of the teeth and the length of apical base should be considered in the formulation of the orthodontic treatment plan, especially in borderline cases where there may be an element of doubt about extraction of permanent teeth.

CONCLUSION

Subjects with complete Class II malocclusion and moderate to severe mandibular crowding have significantly smaller effective apical base lengths than subjects with the same malocclusion and slight mandibular crowding.

The results of this study demonstrate a significant inverse correlation between maxillary and mandibular effective lengths and the severity of dental crowding.

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Publication:Pakistan Oral and Dental Journal
Article Type:Report
Date:Jun 30, 2017
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