A Clinical and Cephalometric Study of the Influence of Mandibular Third Molars on Mandibular Anterior Teeth

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1 /jp-journals ORIGINAL ARTICLE Tara Ramprakash Kavra, Etika Kabra A Clinical and Cephalometric Study of the Influence of Mandibular Third Molars on Mandibular Anterior Teeth 1 Tara Ramprakash Kavra, 2 Etika Kabra ABSTRACT Aims and objectives: The aim of this study was to determine the influence of erupted, impacted or missing mandibular third molars on the mandibular anterior teeth. Materials and methods: This study consisted of mixed population of 50 subjects with an age group 17 to 25 years. They were divided into three groups as erupted, impacted and agenesis of mandibular third molars whether they are responsible for crowding of lower anterior teeth. Results and conclusion: It was observed that average size of anterior teeth in erupted and impacted groups and the length of arch when measured from canine to canine found short in both the groups resulting in lower anterior crowding whereas in the case of agenesis of third molar the mean value of teeth size was less than arch length from canine to canine. Various linear and angular measurements from true lateral cephalograms were compared to find the labial inclination of the lower anterior teeth and it was found that it was influenced by the presence of lower third molars. Keywords: Mandibular third molars, Erupted third molars, Impacted third molars, Missing third molars, Mandibular anterior teeth. How to cite this article: Kavra TR, Kabra E. A Clinical and Cephalometric Study of the Influence of Mandibular Third Molars on Mandibular Anterior Teeth. J Ind Orthod Soc 2013;47(4): INTRODUCTION Lower anterior crowding is considered as the most common problem as far as malocclusion is considered. Post orthodontic treatment relapse, especially in lower arches, is common problem faced by many orthodontists in many cases. Laskin 1 and Schulhof 2 have suggested that lower anterior crowding or post orthodontic treatment relapse in lower arches is strongly associated with lower third molar eruption. According to Richardson, 3 third molar impaction is one of the causative factors because anterior crowding is present more often in patients with third molars than in subjects with these teeth absent. In another study, Sidlauskas and Trakiniene 4 evaluated the correlation between third molar presence and lower incisor crowding in 91 subjects. They reported that although differences between the groups were not statistically significant, a greater number of tendencies for crowding in the mandibular anterior teeth were expressed in groups with third molars present than in groups with these teeth missing, supporting the concept of an anterior component of force. In 1 Professor, 2 Private Practitioner 1 Department of Orthodontics, VOS Clinic, Solapur, Maharashtra, India 2 VOS Clinic, Solapur, Maharashtra, India Corresponding Author: Etika Kabra, Private Practitioner, VOS Clinic Solapur, Maharashtra, India, etikakabra@gmail.com Received on: 23/2/12 Accepted after Revision: 14/6/ , Niedzielska 5 reported that if sufficient space is not available for the third molars to erupt, these teeth exert forces on the other teeth, causing crowding. They showed that movement in the buccal segment results in rotation and mesial drift of the canine as it is positioned on the greatest curvature of the dental arch. The resultant force vectors affecting the canines could even cause rotation of the teeth in relation to their original position and this might increase in incisal crowding. In 2009, Tufekci et al 6 concluded that most orthodontists in the United States and Sweden do believe that erupting lower third molars exert an anterior force but these teeth rarely or never cause crowding of the dentition. Lower anterior crowding in early stages mainly results due to factors like tooth size-arch length discrepancy and prolonged retention of deciduous teeth. In late adolescence labioversion and crowding, results due to lower third molars. Lower anterior crowding should be taken care during third molar eruption because it can cause psychological trauma to the patient, dental decay, gum diseases and lack of esthetic. Haralbakis 7 is doubtful whether the 3rd molar in reality interferes with the occlusion of the teeth and is responsible for disturbing the structural arrangement of the alveolar bone of the jaws or the balance of inclination of the long axis of the tooth, though he observes that the 3rd molar poses a problem for the orthodontist and agrees with Anderson 8 that no orthodontist is justified in discharging a patient, prior to the eruption of the 3rd molar or its surgical removal. 390

2 JIOS MATERIALS AND METHODS A Clinical and Cephalometric Study of the Influence of Mandibular Third Molars on Mandibular Anterior Teeth A group of 50 adolescent individuals between the ages of 17 and 25 years were examined at VOS Clinic in Solapur, Maharashtra. Inclusion Criteria Patients in the age group of 17 to 25 years having Angle s Class I dental malocclusion and pleasing facial profile, who wished to be a part of the study, with harmonious dental arches and who did not exhibit edentulous areas mesial to the third molars in the mandible. Twenty patients who had bilaterally erupted mandibular third molars and 20 patients with bilaterally mesioangular impacted mandibular third molars and 10 patients with bilaterally congenitally missing third molars were randomly selected (n = 50). Fig. 1A: Maximum mesiodistal width of lower anterior teeth Exclusion Criteria Patients with history of habits like tongue thrusting, lip biting, mouth breathing or thumb sucking, patients with family history of crowding. Severe horizontal or vertical growth pattern, history of enucleation of lower 3rd molar patients were excluded. Study Tools 1. Clinical examination 2. True lateral cephalogram 3. Stone plaster models 4. Vernier caliper 5. Brass wire. Impressions were taken with alginate and poured in stone plaster and models were prepared for the following study. The maximum mesiodistal width of the six lower anterior teeth and all teeth from second molar to second molar were measured in millimeters with the help of Vernier caliper (Fig. 1A). The length of the arch of the lower anterior region was measured with the help of brass wire from distal of canine to distal of canine on labial as well as lingual sides at same height and mean of these two readings were taken as intercanine arch length (Fig. 1B) and similarly arch perimeter was Fig. 1B: Intercanine arch length measured from distal of second molar to distal of second molar (Fig. 2). True lateral cephalogram were taken for the inclination of lower incisors in erupted, impacted and missing groups for which following variables were measured. Fig. 2: Arch perimeter measured The Journal of Indian Orthodontic Society, October-December 2013;47(4):

3 Tara Ramprakash Kavra, Etika Kabra Table 1: Comparison of mean and standard deviation of different variables among erupted, impacted and missing lower third molars Variables Erupted group Impacted group Missing group Mean SD Mean SD Mean SD Sum of mesiodistal width of lower anterior teeth Intercanine arch length Sum of mesiodistal width of all lower teeth Arch perimeter from distal of right 2nd molar to left 2nd molar Angle between lower incisor and Go-Gn plane Angle between lower incisor and N-Pg plane Angle between lower incisor and N-B plane Lower incisor to N-B distance in mm Table 2: Comparison among erupted, impacted and missing lower third molars (ANOVA) Source of variation Sum of squares df Mean sum of squares F-ratio Sum of mesiodistal width of lower anterior teeth Between (p > 0.05) Error Total Intercanine arch length Between (p > 0.05) Error Total Sum of mesiodistal width of all lower teeth Between (p < 0.01) Error Total Arch perimeter from distal of right 2nd molar to left 2nd molar Between (p > 0.05) Error Total Angle between lower incisor and Go-Gn plane Between (p < 0.01) Error Total Angle between lower incisor and N-Pg plane Between (p < 0.01) Error Total Angle between lower incisor and N-B plane Between (p < 0.01) Error Total Lower incisor to N-B distance in mm Between (p < 0.01) Error Total Lower incisors to Go-Gn plane, N-Pg plane and N-B plane in degrees and millimeters were measured. RESULTS AND FINDINGS In this study, mean, standard deviation, t-test, ANOVA and logistic regression equations were used for statistical analysis of the data. Tables 1 and 2 show that there was no significant difference observed in sum of the mesiodistal width of lower anterior teeth, in intercanine arch length, arch perimeter from distal of second molar to distal of second molar among erupted, impacted and missing group (p > 0.05). There was statistical significant difference observed in sum of mesiodistal width of all lower teeth. There was statistical significant difference between angle of lower incisor to Go- Gn, to N-Pg plane, to N-B plane and distance between lower incisor to N-B plane among erupted, impacted and missing lower 3rd molar groups (p < 0.01). Table 3 shows that there is no statistical significant difference observed in sum of mesiodistal width of lower anterior teeth and intercanine arch length in erupted and missing lower 3rd molar (p > 0.05), but significant difference was observed in impacted lower 3rd molar group (p < 0.01). There was no statistical significant difference observed in sum of mesiodistal width of lower teeth from distal of second molar to distal of second molar and arch perimeter from distal of second molar to distal of second molar among 392

4 JIOS A Clinical and Cephalometric Study of the Influence of Mandibular Third Molars on Mandibular Anterior Teeth Table 3: Comparison between sum of mesiodistal width of lower anterior teeth with intercanine arch length and sum of mesiodistal width of all lower teeth with arch perimeter from lower right 2nd molar to lower left 2nd molar among erupted, impacted and missing lower third molar Mean Standard deviation t-test p-value Erupted lower third molar Sum of mesiodistal width of lower anterior teeth >0.05 Intercanine arch length Impacted lower third molar Sum of mesiodistal width of lower anterior teeth Intercanine arch length <0.01 Missing lower third molar Sum of mesiodistal width of lower anterior teeth Intercanine arch length >0.05 Erupted lower third molar Sum of mesiodistal width of all lower teeth Arch perimeter from distal of right 2nd molar to left 2nd molar >0.05 Impacted lower third molar Sum of mesiodistal width of all lower teeth Arch perimeter from distal of right 2nd molar to left 2nd molar >0.05 Missing lower third molar Sum of mesiodistal width of all lower teeth Arch perimeter from distal of right 2nd molar to left 2nd molar <0.01 erupted and impacted lower 3rd molar (p > 0.05) while significant difference was observed in missing lower 3rd molars (p < 0.01). The Pearson correlation test showed that there was strong positive correlation. Regression analysis showed depended relationship on each other. DISCUSSION Influence of lower third molars on the lower anterior crowding has been a subject of considerable controversy for the past 150 years. Their influence is not clearly established, but certainly they may contribute to the development of lower anterior crowding. Several workers among them, Richardson, 9 Lambardi 10 and Broadbent 11 have found that the incidence of lower anterior crowding is common observation frequently associated with the development and eruption of lower third molars. Stainly, 12 Garn and Lewis 13 have found a reduction in size of anterior teeth in patient with agenesis of third molar. Keene and Commander 14 have further observed that in the cases of agenesis of lower third molars, the lower anteriors were well aligned without crowding. PR Begg 15 and those who profound the theory that lower molars are not the only cause of anterior crowding. Anterior crowding can be due to the neuromuscular influence, discrepancy between jaw size and tooth dimensions, mouth breathing and relapse after orthodontic therapy, but they too agree that the lower third molars may be the factor in anterior crowding and procumbency up to certain extent. The data of this study suggest that there is a role of third molars on crowding of lower anterior teeth, and statistical analysis shows significant results as far as lower anterior crowding and impacted third molars are concerned; also statistically significant results are seen in procumbency of lower anterior teeth. In 1971, survey of more than 600 orthodontists and 700 oral surgeons, Laskin 1 found that 65% were of opinion that third molars sometimes produce crowding of mandibular anterior teeth. In 2006, Sidlauskas and Trikinene 4 studied to see effect of lower third molar on the lower dental arch and found that lower dental arch crowding over the age of 17 years but do not create statistically significant difference of crowding in lower dental arch when compared with agenesis, removed and present third molars. The average size of the anterior teeth had no significant difference in erupted, impacted and missing groups. The length of the arch when measured from canine to canine was found to be short in both the groups (erupted and impacted), resulting in lower anterior crowding, whereas in the cases of agenesis of the third molars the mean value of the teeth size was less than the arch length from canine to canine due to the fact that arch length was greater thereby indicating that the basal bone was sufficient to accommodate all the teeth. Keene and Commander 14 findings coincide with the findings of the present study. From the study, it was observed that the arch perimeter from the distal of lower right second molar to lower left second molar was deficient and could not accommodate the teeth in erupted and impacted groups, whereas arch perimeter was sufficient to accommodate the teeth in the agenesis group as the posterior teeth were comparatively smaller and arch perimeter was more resulting in spacing between them. Thus concluding that the size of posterior teeth in the patient showing agenesis of third molar was comparatively smaller than where the third molars were present. Garn and Levis 13 have also confirmed the finding of this study. The Journal of Indian Orthodontic Society, October-December 2013;47(4):

5 Tara Ramprakash Kavra, Etika Kabra Vego 16 claims that, with eruption of third molar, there is loss in the arch perimeter which was also observed in the present study. This study further indicated that those patient showing congenitally missing lower third molar had greater reduction in the size of posterior teeth whereas anterior teeth was observed to be of normal size. Keene and Commander 10 found that the mesiodistal dimension of the crown of the lower first molar was to be smaller in agenesis of lower third molar. The average of the angulations of lower incisor to Go-Gn (mandibular), N-Pg plane, N-B plane in degree and N-B in millimeters showed a significant difference between erupted, impacted and missing groups, whereby erupted and impacted groups definitely show labial inclination greater than that showed in the missing group. The labial inclination of lower incisor to mandibular plane as observed in Indian population is considered to be normal at 99.9 (Kundan 17 ). In this study, when the third molars were missing very close angulation was observed The impacted and erupted group showed higher angulations of lower incisors. Thus concluding that, in the erupted and impacted groups, the lower anterior were proclined. The logistic regression equations were obtained for angulation of lower incisor teeth in erupted, impacted and missing lower 3rd molar groups. The percentage of correct classification showed whether teeth are within range or labially placed, 95% in erupted group, 70% in impacted group and 98% in missing lower 3rd molars. CONCLUSION The study has been carried out with primary objective whether lower anterior crowding is influenced by lower third molars. Various measurements were done as size of the arches, linear and angular measurements on true lateral cephalogram. The following conclusion were drawn from the present studies: The size of lower anterior teeth was practically same in all three groups, but posterior teeth were smaller in size in agenesis of lower third molar group. The arch length was insufficient to accommodate lower anterior teeth in erupted and impacted but sufficient in missing lower third molars. Arch perimeter was comparatively less, when the lower third molars were present, and sufficient in missing lower third molars. The inclination of lower incisors to mandibular plane, NB plane and facial plane in all cases showed proclination but more in erupted, less in impacted and least in missing group. Statistically, there was significant difference among all three groups. These all findings conclude that lower third molars were responsible for labioversion of lower anterior teeth and lower anterior crowding in impacted lower third molars, so we as orthodontist must consider this factor. REFERENCES 1. Laskin DM. Evaluation of the third molar problems. J Am Dent Assoc 1971 Apr;82(4): Schulhof RJ. Third molar and orthodontic diagnosis. J Clin Orthod 1976 Apr;10(4): Richardson ME. The role of the third molar in the cause of late lower arch crowding: a review. Am J Orthod Dentofacial Orthop 1989 Jan;95(1): Sidlauskas A, Trakiniene G. Effect of the lower third molars on the lower dental arch crowding. Stomatologija 2006;8(3): Niedzielska I. Third molar influence on dental arch crowding. Eur J Orthod 2005 Oct;27(5): Tüfekçi E, Svensk D, Kallunki J, Huggare J, Lindauer SJ, Laskin DM. Opinions of American and Swedish orthodontists about the role of erupting third molars as a cause of dental crowding. Angle Orthod 2009 Nov;79(6): Haralabakis H. Observations on the time of eruption, congenital absence and impaction of 3rd molar teeth. Trans Europ Orthod Soc 1959: Chaconas SJ. Letter to the editor: more on third molar enucleation. Am J Orthod 1976 Jun;69(6): Richardson ME, Dent M. Some aspects of lower third molar eruption. Angle Orthod 1974 Apr;44(2): Lambordi AR. Mandibular incisor crowding in completed case. Am J Orthod 1972 Apr;61(4): Broadbent BH. The influence of third molar on alignment of teeth. Am J Orthod Oral Surg 1943;29: Garn SM, Lewis AB. The gradient and the pattern of crown size reduction in simple hypodontia. Angle Orthod 1970 Jan;40(1): Garn SM, Lewis AB. The relationship between third molar agenesis and reduction in tooth number. Angle Orthod 1962 Jan;32(1): Keene HJ. Third molar agenesis, spacing and crowding of teeth and tooth size in caries-resistant naval recruits. Am J Orthod 1964;50(6): Begg, PR.; Kesling, Peter C. Begg orthodontic theory and technique. Philadelphia: WB Saunders Co., p. 16. Vego L. A longitudinal study of mandibular arch perimeter. Angle Orthod 1962 Jul;32(3): Kundan. A cephalometric appraisal of the axial inclination of position of teeth in Indian adults with nuestro-occlusion. India: Dissertation of Bombay University; 1961 Oct. 394