|Year : 2018 | Volume
| Issue : 2 | Page : 69-73
Assessment of role of mandibular third molar position in lower anterior crowding- A cross sectional study
Romil B Shah, Nikita Kanzariya, Santosh Kumar Goje, Narayan Kulkarni, Harshil Joshi, Samarth Chellani
Department of Orthodontics and Dentofacial Orthopaedics, K M Shah Dental College and Hospital, Sumandeep Vidyapeeth, Vadodara, Gujarat, India
|Date of Web Publication||26-Feb-2019|
Romil B Shah
5/A, Panchratna Society, Gorwa-Refinery Road, Vadodara - 390 016, Gujarat
Source of Support: None, Conflict of Interest: None
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 Jul 23];6:69-73. Available from: http://www.jihs.in/text.asp?2018/6/2/69/252878
| Introduction|| |
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.
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.
Increasing lower dental arch crowding with the age is a recognized clinical problem, 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., On the other hand, a number of studies found no correlation between lower third molars and lower incisor crowding.,,,,, 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|| |
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 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.
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. 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.
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|| |
[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 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.
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.
| Discussion|| |
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.,,,,,,,,,,,,,
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 who extracted third molars unilaterally and Vego 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., in their retrospective study of patients who had received orthodontic treatment. This study does not support the conclusions of Schwarze 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, Buschang and Shulman, Kaplan, Little Richardson, Harradine et al., (1998) and van der Linden et al. The findings of this study are not in correlation with previous studies done by Bergstorm and Jensen. 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.
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. 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|| |
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
Conflicts of interest
There are no conflicts of interest.
| References|| |
Harradine NW, Pearson MH, Toth B. The effect of extraction of third molars on late lower incisor crowding: A randomized controlled trial. Br J Orthod 1998;25:117-22.
Samspon WJ. Current controversies in late incisor crowding. Ann Acad Med Singapore 1995;24:129-37.
Sidlauskas A, Trakiniene G. Effect of the lower third molars on the lower dental arch crowding. Stomatologija 2006;8:80-4.
Bergstrom K, Jensen R. Responsibility of the third molar for secondary crowding. Svensk Tandlak Tskr 1961;54:111-24.
Vego L. A longitudinal study of mandibular arch perimeter. Angle Orthod 1962;32:187-92.
Kaplan RG. Mandibular third molars and postretention crowding. Am J Orthod 1974;66:411-30.
Little RM, Wallen TR, Riedel RA. Stability and relapse of mandibular anterior alignment-first premolar extraction cases treated by traditional edgewise orthodontics. Am J Orthod 1981;80:349-65.
Lindqvist B, Thilander B. Extraction of third molars in cases of anticipated crowding in the lower jaw. Am J Orthod 1982;81:130-9.
Southard TE, Southard KA, Weeda LW. Mesial force from unerupted third molars. Am J Orthod Dentofacial Orthop 1991;99:220-5.
Pirttiniemi PM, Oikarinen KS, Raustia AM. The effect of removal of all third molars on the dental arches in the third decade of life. Cranio 1994;12:23-7.
Fastlicht J. Crowding of mandibular incisors. Am J Orthod 1970;58:156-63.
Björk A, Skieller V. Facial development and tooth eruption. An implant study at the age of puberty. Am J Orthod 1972;62:339-83.
Lundström A. Changes in crowding and spacing of the teeth with age. Dent Pract Dent Rec 1969;19:218-24.
Björk A, Skieller V. Normal and abnormal growth of the mandible. A synthesis of longitudinal cephalometric implant studies over a period of 25 years. Eur J Orthod 1983;5:1-46.
Broadbent BH. Ontogenic development of occlusion. Angle Orthod 1941;11:223-41.
Moss JP, Picton DC. Experimental mesial drift in adult monkeys (Macaca irus
). Arch Oral Biol 1967;12:1313-20.
Southard KA, Behrents RG, Tolley EA. The anterior component of force Part 1 Relationship with dental malalignment. Am J Orthod Dentofac Orthop 1989;96:493-500.
Southard TE, Behrents RG, Tolley EA. The anterior component of occlusal force. Part 2. Relationship with dental malalignment. Am J Orthod Dentofacial Orthop 1990;97:41-4.
van Beek H, Fidler VJ. An experimental study of the effect of functional occlusion on mesial tooth migration in macaque monkeys. Arch Oral Biol 1977;22:269-71.
Begg PR, Kesling PC. Begg Orthodontic Theory and Technique. Philadelphia: W.B. Saunders Company; 1971.
van der Linden FP. Genetic and environmental factors in dentofacial morphology. Am J Orthod 1966;52:576-83.
Wood DP, Floreani KJ, Galil KA, Teteruck WR. The effect of incisal bite force on condylar seating. Angle Orthod 1994;64:53-61.
Bjork A. Some biological aspects of prognathism and occlusion of the teeth. Acta Odontol Scand 1950;9:1-40.
Norderval K, Wisth PJ, Böe OE. Mandibular anterior crowding in relation to tooth size and craniofacial morphology. Scand J Dent Res 1975;83:267-73.
Peck S, Peck H. Othodontic aspects of dental anthropology. Angle Orthod 1975;45:95-102.
Ades AG, Joondeph DR, Little RM, Chapko MK. A long-term study of the relationship of third molars to changes in the mandibular dental arch. Am J Orthod Dentofacial Orthop 1990;97:323-35.
Schwarze CW. The influence of third molar germectomy – A comparative long term study. Abstract of Third International Congress; 1973. p. 551-62.
Shanley LS. Influence of mandibular third molars on mandibular anterior teeth. Am J Orthod 1962;48:786-7.
Buschang PH, Shulman JD. Incisor crowding in untreated persons 15-50 years of age: United states, 1988-1994. Angle Orthod 2003;73:502-8.
Richardson M. Lower arch crowding in the young adult. Am J Orthod Dentofacial Orthop 1992;101:132-7.
Fastlicht J. Crowding of mandibular incisors. Am J Orthod 1970;58:156-63.
Zawawi KH, Melis M. The role of mandibular third molars on lower anterior teeth crowding and relapse after orthodontic treatment: A systematic review. ScientificWorldJournal 2014;2014:615429.
Genest-Beucher S, Graillon N, Bruneau S, Benzaquen M, Guyot L. Does mandibular third molar have an impact on dental mandibular anterior crowding? A literature review. J Stomatol Oral Maxillofac Surg 2018;119:204-7.
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9]