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Table of Contents
ORIGINAL ARTICLE
Year : 2018  |  Volume : 6  |  Issue : 2  |  Page : 69-73

Assessment of role of mandibular third molar position in lower anterior crowding- A cross sectional study


Department of Orthodontics and Dentofacial Orthopaedics, K M Shah Dental College and Hospital, Sumandeep Vidyapeeth, Vadodara, Gujarat, India

Date of Web Publication26-Feb-2019

Correspondence Address:
Romil B Shah
5/A, Panchratna Society, Gorwa-Refinery Road, Vadodara - 390 016, Gujarat
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/JIHS.JIHS_27_18

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  Abstract 


Objective: To assess the relationship of mandibular third molar position and lower anterior crowding in adult patients. Methodology: A sample of 90 pretreatment casts were divided on the basis of lower third molar position into three groups: erupted, unerupted, and agenesis. Orthopantomograms and dental casts of all 90 samples were procured from the archives of department of orthodontics. The individual quantitative analytical registration of crowding was based on modified arch analysis proposed by Lundstorm. The length of the lower anterior segment was measured with the help of brass wire. Results: Chi-square test and ANOVA statistical tests revealed that there was no statistically significant difference in lower anterior crowding between the groups with erupted, unerupted, and agenesis of third molars on both right and left sides. Conclusion: The third molars do not create statistically significant difference in lower anterior crowding. The recommendation to extract lower third molar to minimize future anterior crowding is thus not justified.

Keywords: Agenesis, lower anterior crowding, third molar position


How to cite this article:
Shah RB, Kanzariya N, Goje SK, Kulkarni N, Joshi H, Chellani S. Assessment of role of mandibular third molar position in lower anterior crowding- A cross sectional study. J Integr Health Sci 2018;6:69-73

How to cite this URL:
Shah RB, Kanzariya N, Goje SK, Kulkarni N, Joshi H, Chellani S. Assessment of role of mandibular third molar position in lower anterior crowding- A cross sectional study. J Integr Health Sci [serial online] 2018 [cited 2019 Mar 22];6:69-73. Available from: http://www.jihs.in/text.asp?2018/6/2/69/252878




  Introduction Top


The problem of late mandibular incisor crowding is a well-established phenomenon, the cause of which has been the substance of considerable debate over the years. Although the terminology is mildly controversial, late incisor crowding (tertiary crowding, late secondary crowding, and postadolescent crowding) is widely regarded as a normal maturation event which is likely to affect most individuals to some extent.[1]

It is illogical to assume a single cause as the beguilingly simple observation of crowding belies the complexity of possible interacting factors. Perhaps it is a capricious combination of: tooth size and arch form; facial growth pattern (differential soft tissue and skeletal maturation); continuing late growth rotations; cumulative effects of resting, functional and parafunctional soft tissue pressures; lack of compensating attrition; and an ill-defined, mesially acting force emanating from the back of the dental arch. The mesially acting force includes pressure from erupting third molars, an inherent mesial migration, continuing mesial and occlusal dental drifting, maturation and contraction of periodontal soft tissues (particularly the transseptal fibers); the anterior component of occlusal forces; and the lower anterior arch contracting influence of the incisor overbite.[2]

Increasing lower dental arch crowding with the age is a recognized clinical problem,[3] and one that has become more apparent in recent years as more adults retain their teeth longer. One of the theories is that the erupting third molars push anterior teeth forward and cause their crowding.[4],[5] On the other hand, a number of studies found no correlation between lower third molars and lower incisor crowding.[6],[7],[8],[9],[10],[11] Because of all these contrasting findings, this study reevaluates correlation between third molars presence and lower dental arch crowding. The role of lower third molar causing lower anterior crowding is controversial.


  Methodology Top


We kept the power of study at 95% confidence interval and level of significance at 0.05. The sample size was calculated using the formula[12] SPSS software version 21 (IBM, USA).



where, n1 = Sample size with finite population correction (56)

N = Population size (72)

Z = Z statistic for level of confidence (1.96)

P = Expected population (if prevalence is 20%, P = 0.2)

D = Precision (if the precision is 50%, than d = 0.05)

The minimum sample size needed was 56.

Null hypothesis

There is no relationship of mandibular third molar position and lower anterior crowding in adult patients.

The approval for the study was given by the Institutional Ethical Committee (Approval no: SVIEC/ON/Dent/SRP/13300). The study completion number is SVIEC/ON/Dent/RP/15035. Ninety dental casts and corresponding orthopantomograms (OPGs) were retrieved from the archives (2015–2016) of the department of orthodontics. Good-quality pretreatment OPG and dental casts of patients above 25 years of age with complete lower dentition and complete root formation of third molar, if present, were included in the study. Samples with a history of previous orthodontic, orthopedic, or facial and surgical treatment; systemic disease, developmental anomalies, or syndromes; abnormal habits and third molar extraction were excluded from the study.

The OPGs and dental casts were divided on the basis of position of lower third molars into three groups: erupted (visible in oral cavity either partially or completely) [Figure 1]a, unerupted (not visible in oral cavity) [Figure 1]b, and agenesis (neither visible in oral cavity nor in OPG) [Figure 1]c.
Figure 1: (a) Erupted third molar, (b) unerupted third molar,(c) agenesis of third molar

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Method for measuring lower anterior crowding

The individual, quantitative, analytical registration of crowding is based on the modified segmented arch analysis proposed by Lundström.[13] Mesiodistal widths of six anterior teeth from canine on one side to canine on contralateral side were measured with the help of a caliper. The length (perimeter) of lower anterior segment (canine to canine) was measured in two segments: canine to central incisor on each side, with the help of brass wire.

The crowding was calculated separately for the right and left lower anterior dental arch segments (central incisor to canine) based on the difference between the tooth size and arch length discrepancy. To determine the reliability, 20 dental casts were selected randomly and analyzed by the same investigator and a coinvestigator at different time-points.

Method for locating lower third molar position

With the help of the position of third molar on the OPG and dental casts (other than in case of agenesis), it was decided whether the third molar is erupted, unerupted, or absent for right and left sides, respectively.

Statistical analysis

Descriptive statistics was used to compare the gender distribution. Chi-square test was used to compare crowding (right and left side) and third molar position. One-way ANOVA was used to compare the mean crowding (SPSS version 21).


  Results Top


[Table 1] shows the gender distribution of the samples; male-to-female ratio is 4:5. [Table 2] shows the distribution of severity of crowding in the absent, erupted, and unerupted third molar groups on the left side. There were 58 samples with erupted third molar, 18 with unerupted, and 14 samples where third molar was absent. In the erupted group of 58 samples, 37.9% had 2–3 mm crowding.
Table 1: Sample distribution

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Table 2: Comparisons between crowding (left side) and third molar position

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On using Chi-square test [Table 3] and [Table 4], it shows that there was no statistically significant third molar presence-specific differences in lower anterior crowding between the groups with erupted, unerupted, and agenesis of third molars on the left and right sides.
Table 3: Chi-square test for comparisons between crowding (left side) and third molar position

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Table 4: Chi-square test for comparisons between crowding (right side) and third molar position

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[Table 5] shows the distribution of severity of crowding in the absent, erupted, and unerupted third molar groups on the right side. There were 61 samples with erupted third molar, 20 with unerupted 3rd molar, and 9 samples where the third molar was absent. In the erupted group of 61 samples, 54.1% had 1–3 mm crowding.
Table 5: Comparisons between crowding (right side) and third molar position

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As per [Table 6] and [Table 7], the mean crowding in the erupted group on the left side is 1.672 mm. However, the ANOVA test shows that there is no statistically significant difference between the mean lower anterior crowding and third molar position in all the three groups.
Table 6: Comparisons of means using ANOVA (left side)

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Table 7: ANOVA table (left side)

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As per [Table 8] and [Table 9], the mean crowding in the erupted group on the right side is 2.025 mm. However, the ANOVA test shows that there is no statistically significant difference between the mean lower anterior crowding and third molar position in all the three groups. Although differences between the groups were not statistically significant, some tendency for crowding in the anterior part of lower dental arch was more expressed in the groups with erupted third molars than with agenesis and unerupted third molars bilaterally.
Table 8: Comparisons of means using ANOVA (right side)

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Table 9: ANOVA table (right side)

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  Discussion Top


One of the long-held dental and orthodontic tenets that have been refuted in the last decade has been the extraction of third molars to prevent late lower incisor crowding. Many potential etiological factors have been attributed to lower arch or incisor crowding.[9],[12],[14],[15],[16],[17],[18],[19],[20],[21],[22],[23],[24],[25]

It would appear that the etiology behind the late incisor crowding phenomenon is one that is multifactorial in nature. It involves a decrease in arch length, jaw/tooth size, shape and relationship, narrowing of the intercanine width, retroclination of the lower incisors, mesial movement of the posterior teeth, and skeletal and soft tissue changes during growth and the natural ageing process.

The present study shows that there is no statistically significant correlation between third molar position and lower anterior crowding in all the three groups and also for right and left sides. Although there is an increase in the mean crowding in the erupted group in comparison with unerupted and absent group bilaterally, the association between the third molar position and lower anterior crowding is more on right side compared to left side.

While no similar prospective study exists in the literature, the results of this investigation supports the work of the Linquist and Thilander[8] who extracted third molars unilaterally and Vego[5] who examined aplasia of third molars, both of whom found a very small increase in crowding with third molars present but no clinically significant effect. Similar conclusion was drawn by Ades et al.,[26] in their retrospective study of patients who had received orthodontic treatment. This study does not support the conclusions of Schwarze[27] based on a retrospective study of nonrandomized extractions that third molar extractions are clearly beneficial in reducing later anterior irregularity,

The findings of this study are in concurrence with studies done by Shanley,[28] Buschang and Shulman,[29] Kaplan,[6] Little[7] Richardson,[30] Harradine et al., (1998)[1] and van der Linden et al.[21] The findings of this study are not in correlation with previous studies done by Bergstorm and Jensen.[31] The possible reason for this might be as suggested by Niedzielska who said that when a sufficient space is available for the eruption of the third molars, the tooth assumes a normal position in the dental arch and does not cause displacement of the other teeth; conversely, when the space is deficient, third molars may aggravate dental crowding.[32]

Further, a recent review of literature showed that 83% of included articles (n = 10/12) did not find any significant relationship between lower third molar and mandibular dental anterior crowding.[33] As a result, the removal of third molars on the sole basis of preventing lower incisor crowding is unsubstantiated and should be based on other more sound reasons.


  Conclusion Top


The third molars do not create statistically significant difference in lower anterior crowding, when compared to subjects with erupted, unerupted, and absent third molars. Hence, the position of third molar plays no role in lower anterior crowding. The recommendation to extract third molars in the lower jaw has to have a justifiable reason and cannot be solely based on the doubtful rationale to minimize present or future crowding of the lower anterior teeth.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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    Figures

  [Figure 1]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9]



 

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