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Changes in mandibular third molar angle and position after unilateral mandibular first molar extraction
ORIGINAL ARTICLE
Changes in mandibular third molar angle and position after unilateral mandibular first molar extraction Sinan Ay,a Ugˇur Agˇar,b A. Altugˇ Bıçakçı,c and H. Hüseyin Kös¸gera Sivas and Kayseri, Turkey Introduction: Third molars often become impacted because of lack of space for their eruption. Because the third molars play an important role occlusally, premolars or second molars are sometimes extracted to create space. First molars are seldom extracted to create space, but they are occasionally extracted for other reasons, especially caries. The aim of this study was to investigate the spontaneous angular and positional changes in mandibular third molars when mandibular first molars are extracted. Methods: The sample consisted of panoramic radiographs of 107 patients (age, 18-40 years; mean, 25.69 years) who had unilateral mandibular first-molar extractions (because of caries) before age 16. Ramus relationship, impaction depth, and angulation of third molars on the extraction and nonextraction sides were assessed. A chi-square test was performed to compare the differences. Results: The prevalence of third molars at the anterior border of the mandibular ramus was significantly greater on the extraction side than on the nonextraction side (P ⬍ .001). Third molars were positioned more occlusally in the mandible on the nonextraction side than on the extraction side (P ⬍ .001). The prevalence of vertically angulated third molars was greater on the extraction side than on the nonextraction side (P ⬍ .001). Conclusions: Mandibular first-molar extraction increases the space for mandibular third-molar eruption and helps the third molars move into better positions. But early extraction can lead to uncontrolled tipping of adjacent teeth into the extraction space. Only third-molar angle and position were evaluated in this study; problems such as dental asymmetry, premature contacts, and uncontrolled tipping should be assessed in the future. (Am J Orthod Dentofacial Orthop 2006;129:36-41)
T
he third molars have the highest rate of impaction of all the teeth.1-4 Lack of space in the arches is a common factor in the etiology of impaction.5-10 When remodeling resorption at the anterior surface of the mandibular ramus is limited, the third molars become impacted.5-7,10 In many patients, mandibular third molars are removed prophylactically, even though they have not caused problems.11-13 But the third molars can be beneficial for orthodontic and prosthodontic treatment and for transplantation. The third molars usually erupt between 16 and 24 years of age14,15; the position of the mandibular third molars changes during development.16-18 Richardson,16 a
Assistant professor, Department of Oral and Maxillofacial Surgery, Cumhuriyet University, Faculty of Dentistry, Sivas, Turkey. b Assistant professor, Department of Orthodontics, Erciyes University, Faculty of Dentistry, Kayseri, Turkey. c Assistant professor, Department of Orthodontics, Cumhuriyet University, Faculty of Dentistry, Sivas, Turkey. ¨ niversitesi Dis¸ Hekimligˇi Reprint requests to: Dr Sinan Ay, Cumhuriyet U Fakültesi, ADÇ Hastalıkları ve Cerrahisi AD, Sivas, Turkey; e-mail, sinanay@ cumhuriyet.edu.tr. Submitted, June 2004; revised and accepted, October 2004. 0889-5406/$32.00 Copyright © 2006 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2004.10.010
36
Shiller,17 and Ventä et al18 showed that the third molars become upright during development, and their angulation improves.19 Other researchers20-24 have shown that mesial movement of the molars because of interproximal attrition and extraction therapy increases eruption space and reduces the frequency of third-molar impaction. However, contradictory results have been noted with both angulation and contact relationship of third molars after the extraction of premolars and second molars.19,22,23,25-27 The teeth most frequently extracted due to caries are the mandibular first and second molars; their incidence of extraction between 11 and 20 years of age is high.28,29 Rindler30 found that 77% of 118 mandibular third molars erupted into good or very good positions after the second molars were extracted, and only 4 third molars in his study were in poor or inadequate positions. Gaumond31 evaluated the eruption of 22 mandibular third molars after the germectomy of second molars and found that 86% achieved a satisfactory or very satisfactory position in the arch (14% were imperfectly positioned). Although many quantitative studies19,22-27,30-32 evaluating third-molar position after second-molar or first premolar extraction have been published, we found
Ay et al 37
American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 1
Fig 1. Panoramic radiograph showing Class I ramus relationship, Class A impaction depth, and vertical angulation on extraction side; Class II ramus relationship, Class A impaction depth, and horizontal angulation on nonextraction side.
only 1 study32 that examined third-molar position after first-molar extraction. The aim of this study was to compare the spontaneous angular and positional changes between the mandibular third molars in patients with asymmetric mandibular first-molar extraction. MATERIAL AND METHODS
The sample comprised 107 patients (48 men, 59 women), from 18 to 40 years of age (median, 25.69 years). The subjects were selected from the records of the Department of Oral and Maxillofacial Surgery of Cumhuriyet University, Sivas, Turkey, from September 1997 to February 2004. Patients with a history of unilateral mandibular first-molar extraction before 16 years of age and no other missing teeth or prosthetic restorations in the mandible were selected. None of the patients had craniofacial anomalies such as cleft lip or palate. Of the 107 patients, 52 had missing mandibular right first molars, and 57 had missing mandibular left first molars; the roots of 204 third molars were completely formed, and the roots of 10 were two-thirds formed. The locations and positions of the third molars on the extraction and nonextraction sides were classified on the panoramic radiographs (Fig 1). The state of impaction was measured according to the classification of Pell and Gregory33: Class I, the crown is near the anterior border of the mandibular ramus; Class II, the crown is one-half covered by the ramus; Class III, the crown is completely within the mandibular ramus (Fig 2). The impaction depth of the third molars was measured according to the classification of Pell and Gregory33: Class A, the occlusal surface of the impacted tooth is
level or nearly level with the second molar; Class B, the occlusal surface is between the occlusal plane and the cervical line of the second molar; Class C, the occlusal surface is below the cervical line of the second molar (Fig 3). Third-molar angulation was measured with reference to the anterior angle between the occlusal plane of the first and second premolars and a line drawn through the occlusal surface of the third molar (Fig 4). Shiller’s17 method was modified for measuring the angulation of the third molars in our study because the mandibular first molars were always absent on the extraction side in our subjects. The data obtained from panoramic radiographs were classified as follows: vertical, ⬍11°; mesioangular or distoangular, 11°-70°; and horizontal, ⬎70°.17 The results were calculated with the software SPSS for Windows (release 10.0.0, SPSS, Chicago, Ill). The differences between 2 sites were evaluated with the chi-square test. The same investigator (S.A.) made all measurements, and the reproducibility of the method was tested. Twenty-six subjects were randomly selected from the original sample, and the measurements were repeated after 3 weeks. No significant differences between the 2 measurements (P ⫽ .898) were found when tested with the Wilcoxon nonparametric test. RESULTS
Seventy-seven third molars were in Class I ramus relationship on the extraction side compared with 20 on the nonextraction side. The difference was statistically significant (P ⬍ .001). Only 1 third molar was in Class III ramus relationship on the extraction side (Table I). Eighty-two third molars had Class A impaction depths on the extraction side compared with 50 on the nonextraction side. The difference was statistically significant (P ⬍ .001) (Table II). Seventy-eight third molars were in vertical positions on the extraction side compared with 37 on the nonextraction side; the difference was statistically significant (P ⬍ .001). Only 1 third molar was horizontally angulated on the extraction side (Table III). DISCUSSION
Andreasen4 reported that the frequency of thirdmolar impaction was 18% to 32%; Björk et al5 and Ventä et al34 reported frequencies of 22.3% to 66.6%. However, the increase in the eruption space for third molars reduces this range.22-24 Extracting posterior teeth can increase the eruption space through mesial movement of the molars. In this study, we tried to find out whether the spontaneous positional changes in the
38 Ay et al
American Journal of Orthodontics and Dentofacial Orthopedics January 2006
Fig 2. Pell and Gregory classification according to ramus relation.
Fig 3. Pell and Gregory classification according to impaction depth of third molar.
Table I.
Results of chi-square test demonstrating significant differences (P ⬍ .001) in ramus relation of mandibular third molars between extraction and nonextraction sides Class ramus relationship I
II
n
%
n
77 20 97
79.4 20.6
29 62 91
III %
n
%
31.9 1 3.8 68.1 25 96.2 26
Total n
%
107 107 214
50 50
Fig 4. Measurement of ␣ angle to assess angulation of mandibular third molar.
Extraction side Nonextraction side Total
mandibular third molars were due to mandibular firstmolar extraction. Many orthodontists30,31,35-37 believe that extracting permanent teeth will improve the angulation of the third molars and thus increase the likelihood that they will erupt into good positions. Others disagree, stating that such improvement will occur only if the second molars are extracted, and that extracting the first premolars will not prevent the need for extracting the third molars.26,38,39
Kim et al24 studied the prevalence of third-molar impaction in orthodontic patients treated without extractions and with the extraction of 4 premolars. The impaction scores were 40% for the nonextraction patients and 22% for the extraction patients in the mandible. In our study, the difference between the impaction scores was greater. On the extraction side, 23.5% of the third molars had Class B or C impaction
Ay et al 39
American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 1
Table II.
Results of chi-square test demonstrating significant differences (P ⬍ .001) in impaction depth of mandibular third molars between extraction and nonextraction sides Class impaction depth A n Extraction side 82 Nonextraction side 50 Total 132
B
C
Total
%
n
%
n
%
n
%
62.1 37.9
19 41 60
31.7 68.3
6 16 22
27.3 72.7
107 107 214
50 50
depths, whereas 53% of the third molars on the nonextraction side scored in that range. Although different teeth were extracted, impaction scores for the extraction side are similar to other studies. However, thirdmolar impaction rates were 0% to 4% in studies with second-molar extractions.19,22,23 The closer the third molar is to the extraction site, the less likely it is to become impacted. The differences in ramus relationship between extraction and nonextraction sides were more significant than impaction depth in our study. On the extraction side, 28% of the third molars were in Class II or III ramus relationship compared with 91% on the nonextraction side. These results indicate that the increase in eruption space affects ramus relationship of the third molars much more than the impaction depth. Orton-Gibbs et al,19 Cavanaugh,22 and Richardson and Richardson25 showed the uprighting of third molars in patients whose second molars had been removed before the roots formed on the third molars, and they all concluded that third molars tend to erupt in good or acceptable positions after second-molar extractions. However, Gooris et al23 found that mandibular third molars rarely erupted with both proper angulation and contact relationship after the second molars had been extracted. Similarly, Staggers26 and Staggers et al27 found contradictory results in mandibular third-molar angulation after first-premolar extraction. In our study, 73% of the third molars on the extraction side were found to be vertically angulated compared with just 35% on the nonextraction side. It was also interesting to find 20 horizontally angulated third molars on the nonextraction side compared with only 1 on the extraction side. The uprighting of third molars during development has been shown by Richardson,16 Shiller,17 and Ventä et al.18 Staggers26 examined the records of 22 patients with maxillary and mandibular second-molar extractions
and 22 with maxillary and mandibular first-premolar extractions and evaluated the angulations of the third molars from panoramic radiographs. The maxillary third molars showed improvements in angulation, but the mandibular third molars showed undesirable angular changes. She found this undesirable change “unexpected” and concluded that “one should keep in mind that a favorable change in third molar angulation after second molar extractions does not necessarily mean that third molars will erupt into the mouth with a good inclination, proper contact with the first molar, or acceptable occlusion.” We examined subjects with unilateral extractions to minimize the influence of genetic factors. We selected patients who had their extractions before 16 years of age because eruption of third molars varies but occurs between 16 and 24 years. The teeth were extracted because of caries, and not for orthodontic purposes; none of these patients had undergone orthodontic treatment, and the sample was not derived from the records of the Department of Orthodontics but, rather, from the archives of the Oral and Maxillofacial Surgery Department. When extractions are necessary for orthodontic treatment, orthodontists usually prefer to extract premolars and save first molars because they play an important role in occlusion. However, the results of this study could help orthodontists treating patients whose first molars have poor prognoses because of caries. In such cases, first-molar extractions could be part of an overall orthodontic treatment plan. It would be valuable to have panoramic radiographs taken after the first-molar extractions to evaluate the spontaneous changes. However, it would not be possible to follow patients without applying preventive or prosthetic restorations for ethical considerations. Although early extraction of mandibular first molars could reduce third-molar impaction, adjacent teeth can drift into the extraction space, and an undesired dental asymmetry could occur. This negative side effect was not evaluated in this study and should be investigated in the future. CONCLUSIONS
From the results of this study, the following conclusions can be drawn: 1. Mandibular first-molar extraction increases the space for mandibular third-molar eruption and helps the third molars move into better positions. 2. Early extraction of mandibular first molars can lead to uncontrolled tipping of adjacent teeth into the extraction space. Only third-molar positions were
40 Ay et al
American Journal of Orthodontics and Dentofacial Orthopedics January 2006
Results of chi-square test demonstrating significant differences (P ⬍ .001), except mesioangular, in angulations of mandibular third molars between extraction and nonextraction sides
Table III.
Angulation Vertical
Extraction side Nonextraction side Total
Mesioangular
Distoangular
Horizontal
Total
n
%
n
%
n
%
n
%
n
%
78 37 115
67.8 32.2
25 32 57
43.9 56.1
3 18 21
14.3 85.7
1 20 21
4.8 95.2
107 107 214
50 50 100
evaluated from the panoramic radiographs; problems caused by early extraction, including dental asymmetry, premature contacts, and uncontrolled tipping were not evaluated. REFERENCES 1. Dachi SF, Howell FV. A survey of 3874 routine full-mouth radiographs. II. A study of impacted teeth. Oral Surg Oral Med Oral Pathol 1961;14:1165-9. 2. Bishara SE, Andreasen G. Third molars: a review. Am J Orthod 1983;83:131-7. 3. Grover PS, Lorton L. The incidence of unerupted permanent teeth and related clinical cases. Oral Surg Oral Med Oral Pathol 1985;59:420-5. 4. Andreasen JO, Petersen JK, Laskin DM. Textbook and color atlas of tooth impactions. Copenhagen: Munksgaard; 1997. 5. Björk A, Jensen E, Palling M. Mandibular growth and third molar impaction. Acta Odontol Scand 1956;14:231-72. 6. Björk A. Variations in the growth pattern of the human mandible: longitudinal radiographic study by the implant method. J Dent Res 1963;42:400-11. 7. Silling G. Development and eruption of the mandibular third molar and its response to orthodontic therapy. Angle Orthod 1973;43:271-8. 8. Cahill DR, Marks SC Jr. Tooth eruption: evidence for the central role of the dental follicle. J Oral Pathol 1980;9:189-200. 9. Shafer WG, Hine MK, Levy BM. A textbook of oral pathology. Philadelphia: W.B. Saunders; 1983. 10. Alling CC III, Alling RD. Indications for management of impacted teeth. In: Alling CC III, Helfrick JF, Alling RD, editors. Impacted teeth. Philadelphia: W.B. Saunders; 1993: p. 46-64. 11. Lysell L, Rohlin M. A study of indications used for removal of mandibular third molars. Int J Oral Maxillofac Surg 1988;17: 161-4. 12. Shepherd JP. The third molar epidemic. Br Dent J 1993;174:85. 13. Lopes V, Mumenya R, Feinmann C, Haris M. Third molar surgery: an audit of the indications for surgery, postoperative complaints, and patient satisfaction. Br J Oral Maxillofac Surg 1995;33:33-5. 14. Haralabakis H. Observations on the time of eruption, congenital absence and impaction of the third molar teeth. Trans Eur Orthod Soc 1957:308-9. 15. Hattab FN. Positional changes and eruption of impacted mandibular third molars in young adults. A radiographic 4-year follow-up study. Oral Surg Oral Med Oral Pathol 1997;84:604-8. 16. Richardson ME. The development of third molar impaction. Br J Orthod 1975;2:231-4.
17. Shiller W. Positional changes in mesio-angular impacted mandibular third molars during a year. J Am Dent Assoc 1979;99: 460-4. 18. Ventä I, Murtomaa H, Turtola L, Meurman J, Ylipaavalniemi P. Assessing the eruption of lower third molars on the basis of radiographic features. Br J Oral Maxillofac Surg 1991; 29:259-62. 19. Orton-Gibbs S, Crow V, Orton HS. Eruption of third permanent molars after the extraction of second permanent molars. Part 1: assessment of third molar position and size. Am J Orthod Dentofacial Orthop 2001;119:226-38. 20. Begg PR. Stone Age man’s dentition. Am J Orthod 1954;40:298312. 21. Murphy TR. Reduction of the dental arch by approximal attrition. Br Dent J 1964;116:483-8. 22. Cavanaugh JJ. Third molar changes following second molar extractions. Angle Orthod 1985;55:70-6. 23. Gooris CG, Årtun J, Joondeph DR. Eruption of mandibular third molars after second molar extractions: a radiographic study. Am J Orthod Dentofacial Orthop 1990;98:161-7. 24. Kim TW, Årtun J, Behbehani F, Artese F. Prevelance of third molar impaction in orthodontic patients treated nonextraction and with extraction of 4 premolars. Am J Orthod Dentofacial Orthop 2003;123:138-45. 25. Richardson ME, Richardson A. Lower third molar development subsequent to second molar extraction. Am J Orthod Dentofacial Orthop 1993;104:566-74. 26. Staggers AJ. A comparison of results of second molar and first premolar extraction treatment. Am J Orthod Dentofacial Orthop 1990;98:430-6. 27. Staggers AJ, Germane N, Fortson MW. A comparison of the effects of first premolar extractions on third molar angulation. Angle Orthod 1992;62:135-8. 28. McCaul LK, Jenkins WM, Kay EJ. The reasons for the extraction of various tooth types in Scotland: 15-year follow up. J Dent 2001;29:401-7. 29. Sayegh A, Hilow H, Bedi R. Pattern of tooth loss in recipients of free dental treatment at the University Hospital of Amman, Jordan. J Oral Rehab 2004;31:124-30. 30. Rindler A. Effects on lower third molars after extraction of second molars. Angle Orthod 1977;47:55-8. 31. Gaumond G. Second molar germectomy and third molar eruption. 11 cases of lower second molar enucleation. Angle Orthod 1985;55:77-88. 32. Williams R, Hosila FJ. The effect of different extraction sites upon incisor retraction. Am J Orthod 1976;69:388-410. 33. Pell GJ, Gregory GT. Impacted mandibular third molars: classification and modified technique for removal. Dent Digest 1933; 39:330-8.
American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 1
34. Ventä I, Murtomaa H, Turtola L, Meurman J, Ylipaavalniemi P. Clinical follow-up study of third molar eruption from ages 20 to 26 years. Oral Surg Oral Med Oral Pathol 1991;72: 150-3. 35. Smith DI. The eruption of third molars following extraction of second molars. Dent Pract 1958;8:292-4. 36. Wilson HE. Extraction of second permanent molars in orthodontic treatment. Orthodontist 1971;3:18-24.
Ay et al 41
37. Huggins DG, McBride LJ. The eruption of lower third molars following the loss of lower second molars: a longitudinal cephalometric study. Br J Orthod 1978;5:13-20. 38. Quinn GW. Extraction of four second molars. Angle Orthod 1985;55:58-69. 39. Witzig JW, Sphal TJ. The clinical management of basic maxillofacial orthopedic appliances. Littleton (Mass): PSG Publishing; 1987. p.161-216.
Changes in mandibular third molar angle and position after unilateral mandibular first molar extraction Sinan Ay,a Ugˇur Agˇar,b A. Altugˇ Bıçakçı,c and H. Hüseyin Kös¸gera Sivas and Kayseri, Turkey Introduction: Third molars often become impacted because of lack of space for their eruption. Because the third molars play an important role occlusally, premolars or second molars are sometimes extracted to create space. First molars are seldom extracted to create space, but they are occasionally extracted for other reasons, especially caries. The aim of this study was to investigate the spontaneous angular and positional changes in mandibular third molars when mandibular first molars are extracted. Methods: The sample consisted of panoramic radiographs of 107 patients (age, 18-40 years; mean, 25.69 years) who had unilateral mandibular first-molar extractions (because of caries) before age 16. Ramus relationship, impaction depth, and angulation of third molars on the extraction and nonextraction sides were assessed. A chi-square test was performed to compare the differences. Results: The prevalence of third molars at the anterior border of the mandibular ramus was significantly greater on the extraction side than on the nonextraction side (P ⬍ .001). Third molars were positioned more occlusally in the mandible on the nonextraction side than on the extraction side (P ⬍ .001). The prevalence of vertically angulated third molars was greater on the extraction side than on the nonextraction side (P ⬍ .001). Conclusions: Mandibular first-molar extraction increases the space for mandibular third-molar eruption and helps the third molars move into better positions. But early extraction can lead to uncontrolled tipping of adjacent teeth into the extraction space. Only third-molar angle and position were evaluated in this study; problems such as dental asymmetry, premature contacts, and uncontrolled tipping should be assessed in the future. (Am J Orthod Dentofacial Orthop 2006;129:36-41)
T
he third molars have the highest rate of impaction of all the teeth.1-4 Lack of space in the arches is a common factor in the etiology of impaction.5-10 When remodeling resorption at the anterior surface of the mandibular ramus is limited, the third molars become impacted.5-7,10 In many patients, mandibular third molars are removed prophylactically, even though they have not caused problems.11-13 But the third molars can be beneficial for orthodontic and prosthodontic treatment and for transplantation. The third molars usually erupt between 16 and 24 years of age14,15; the position of the mandibular third molars changes during development.16-18 Richardson,16 a
Assistant professor, Department of Oral and Maxillofacial Surgery, Cumhuriyet University, Faculty of Dentistry, Sivas, Turkey. b Assistant professor, Department of Orthodontics, Erciyes University, Faculty of Dentistry, Kayseri, Turkey. c Assistant professor, Department of Orthodontics, Cumhuriyet University, Faculty of Dentistry, Sivas, Turkey. ¨ niversitesi Dis¸ Hekimligˇi Reprint requests to: Dr Sinan Ay, Cumhuriyet U Fakültesi, ADÇ Hastalıkları ve Cerrahisi AD, Sivas, Turkey; e-mail, sinanay@ cumhuriyet.edu.tr. Submitted, June 2004; revised and accepted, October 2004. 0889-5406/$32.00 Copyright © 2006 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2004.10.010
36
Shiller,17 and Ventä et al18 showed that the third molars become upright during development, and their angulation improves.19 Other researchers20-24 have shown that mesial movement of the molars because of interproximal attrition and extraction therapy increases eruption space and reduces the frequency of third-molar impaction. However, contradictory results have been noted with both angulation and contact relationship of third molars after the extraction of premolars and second molars.19,22,23,25-27 The teeth most frequently extracted due to caries are the mandibular first and second molars; their incidence of extraction between 11 and 20 years of age is high.28,29 Rindler30 found that 77% of 118 mandibular third molars erupted into good or very good positions after the second molars were extracted, and only 4 third molars in his study were in poor or inadequate positions. Gaumond31 evaluated the eruption of 22 mandibular third molars after the germectomy of second molars and found that 86% achieved a satisfactory or very satisfactory position in the arch (14% were imperfectly positioned). Although many quantitative studies19,22-27,30-32 evaluating third-molar position after second-molar or first premolar extraction have been published, we found
Ay et al 37
American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 1
Fig 1. Panoramic radiograph showing Class I ramus relationship, Class A impaction depth, and vertical angulation on extraction side; Class II ramus relationship, Class A impaction depth, and horizontal angulation on nonextraction side.
only 1 study32 that examined third-molar position after first-molar extraction. The aim of this study was to compare the spontaneous angular and positional changes between the mandibular third molars in patients with asymmetric mandibular first-molar extraction. MATERIAL AND METHODS
The sample comprised 107 patients (48 men, 59 women), from 18 to 40 years of age (median, 25.69 years). The subjects were selected from the records of the Department of Oral and Maxillofacial Surgery of Cumhuriyet University, Sivas, Turkey, from September 1997 to February 2004. Patients with a history of unilateral mandibular first-molar extraction before 16 years of age and no other missing teeth or prosthetic restorations in the mandible were selected. None of the patients had craniofacial anomalies such as cleft lip or palate. Of the 107 patients, 52 had missing mandibular right first molars, and 57 had missing mandibular left first molars; the roots of 204 third molars were completely formed, and the roots of 10 were two-thirds formed. The locations and positions of the third molars on the extraction and nonextraction sides were classified on the panoramic radiographs (Fig 1). The state of impaction was measured according to the classification of Pell and Gregory33: Class I, the crown is near the anterior border of the mandibular ramus; Class II, the crown is one-half covered by the ramus; Class III, the crown is completely within the mandibular ramus (Fig 2). The impaction depth of the third molars was measured according to the classification of Pell and Gregory33: Class A, the occlusal surface of the impacted tooth is
level or nearly level with the second molar; Class B, the occlusal surface is between the occlusal plane and the cervical line of the second molar; Class C, the occlusal surface is below the cervical line of the second molar (Fig 3). Third-molar angulation was measured with reference to the anterior angle between the occlusal plane of the first and second premolars and a line drawn through the occlusal surface of the third molar (Fig 4). Shiller’s17 method was modified for measuring the angulation of the third molars in our study because the mandibular first molars were always absent on the extraction side in our subjects. The data obtained from panoramic radiographs were classified as follows: vertical, ⬍11°; mesioangular or distoangular, 11°-70°; and horizontal, ⬎70°.17 The results were calculated with the software SPSS for Windows (release 10.0.0, SPSS, Chicago, Ill). The differences between 2 sites were evaluated with the chi-square test. The same investigator (S.A.) made all measurements, and the reproducibility of the method was tested. Twenty-six subjects were randomly selected from the original sample, and the measurements were repeated after 3 weeks. No significant differences between the 2 measurements (P ⫽ .898) were found when tested with the Wilcoxon nonparametric test. RESULTS
Seventy-seven third molars were in Class I ramus relationship on the extraction side compared with 20 on the nonextraction side. The difference was statistically significant (P ⬍ .001). Only 1 third molar was in Class III ramus relationship on the extraction side (Table I). Eighty-two third molars had Class A impaction depths on the extraction side compared with 50 on the nonextraction side. The difference was statistically significant (P ⬍ .001) (Table II). Seventy-eight third molars were in vertical positions on the extraction side compared with 37 on the nonextraction side; the difference was statistically significant (P ⬍ .001). Only 1 third molar was horizontally angulated on the extraction side (Table III). DISCUSSION
Andreasen4 reported that the frequency of thirdmolar impaction was 18% to 32%; Björk et al5 and Ventä et al34 reported frequencies of 22.3% to 66.6%. However, the increase in the eruption space for third molars reduces this range.22-24 Extracting posterior teeth can increase the eruption space through mesial movement of the molars. In this study, we tried to find out whether the spontaneous positional changes in the
38 Ay et al
American Journal of Orthodontics and Dentofacial Orthopedics January 2006
Fig 2. Pell and Gregory classification according to ramus relation.
Fig 3. Pell and Gregory classification according to impaction depth of third molar.
Table I.
Results of chi-square test demonstrating significant differences (P ⬍ .001) in ramus relation of mandibular third molars between extraction and nonextraction sides Class ramus relationship I
II
n
%
n
77 20 97
79.4 20.6
29 62 91
III %
n
%
31.9 1 3.8 68.1 25 96.2 26
Total n
%
107 107 214
50 50
Fig 4. Measurement of ␣ angle to assess angulation of mandibular third molar.
Extraction side Nonextraction side Total
mandibular third molars were due to mandibular firstmolar extraction. Many orthodontists30,31,35-37 believe that extracting permanent teeth will improve the angulation of the third molars and thus increase the likelihood that they will erupt into good positions. Others disagree, stating that such improvement will occur only if the second molars are extracted, and that extracting the first premolars will not prevent the need for extracting the third molars.26,38,39
Kim et al24 studied the prevalence of third-molar impaction in orthodontic patients treated without extractions and with the extraction of 4 premolars. The impaction scores were 40% for the nonextraction patients and 22% for the extraction patients in the mandible. In our study, the difference between the impaction scores was greater. On the extraction side, 23.5% of the third molars had Class B or C impaction
Ay et al 39
American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 1
Table II.
Results of chi-square test demonstrating significant differences (P ⬍ .001) in impaction depth of mandibular third molars between extraction and nonextraction sides Class impaction depth A n Extraction side 82 Nonextraction side 50 Total 132
B
C
Total
%
n
%
n
%
n
%
62.1 37.9
19 41 60
31.7 68.3
6 16 22
27.3 72.7
107 107 214
50 50
depths, whereas 53% of the third molars on the nonextraction side scored in that range. Although different teeth were extracted, impaction scores for the extraction side are similar to other studies. However, thirdmolar impaction rates were 0% to 4% in studies with second-molar extractions.19,22,23 The closer the third molar is to the extraction site, the less likely it is to become impacted. The differences in ramus relationship between extraction and nonextraction sides were more significant than impaction depth in our study. On the extraction side, 28% of the third molars were in Class II or III ramus relationship compared with 91% on the nonextraction side. These results indicate that the increase in eruption space affects ramus relationship of the third molars much more than the impaction depth. Orton-Gibbs et al,19 Cavanaugh,22 and Richardson and Richardson25 showed the uprighting of third molars in patients whose second molars had been removed before the roots formed on the third molars, and they all concluded that third molars tend to erupt in good or acceptable positions after second-molar extractions. However, Gooris et al23 found that mandibular third molars rarely erupted with both proper angulation and contact relationship after the second molars had been extracted. Similarly, Staggers26 and Staggers et al27 found contradictory results in mandibular third-molar angulation after first-premolar extraction. In our study, 73% of the third molars on the extraction side were found to be vertically angulated compared with just 35% on the nonextraction side. It was also interesting to find 20 horizontally angulated third molars on the nonextraction side compared with only 1 on the extraction side. The uprighting of third molars during development has been shown by Richardson,16 Shiller,17 and Ventä et al.18 Staggers26 examined the records of 22 patients with maxillary and mandibular second-molar extractions
and 22 with maxillary and mandibular first-premolar extractions and evaluated the angulations of the third molars from panoramic radiographs. The maxillary third molars showed improvements in angulation, but the mandibular third molars showed undesirable angular changes. She found this undesirable change “unexpected” and concluded that “one should keep in mind that a favorable change in third molar angulation after second molar extractions does not necessarily mean that third molars will erupt into the mouth with a good inclination, proper contact with the first molar, or acceptable occlusion.” We examined subjects with unilateral extractions to minimize the influence of genetic factors. We selected patients who had their extractions before 16 years of age because eruption of third molars varies but occurs between 16 and 24 years. The teeth were extracted because of caries, and not for orthodontic purposes; none of these patients had undergone orthodontic treatment, and the sample was not derived from the records of the Department of Orthodontics but, rather, from the archives of the Oral and Maxillofacial Surgery Department. When extractions are necessary for orthodontic treatment, orthodontists usually prefer to extract premolars and save first molars because they play an important role in occlusion. However, the results of this study could help orthodontists treating patients whose first molars have poor prognoses because of caries. In such cases, first-molar extractions could be part of an overall orthodontic treatment plan. It would be valuable to have panoramic radiographs taken after the first-molar extractions to evaluate the spontaneous changes. However, it would not be possible to follow patients without applying preventive or prosthetic restorations for ethical considerations. Although early extraction of mandibular first molars could reduce third-molar impaction, adjacent teeth can drift into the extraction space, and an undesired dental asymmetry could occur. This negative side effect was not evaluated in this study and should be investigated in the future. CONCLUSIONS
From the results of this study, the following conclusions can be drawn: 1. Mandibular first-molar extraction increases the space for mandibular third-molar eruption and helps the third molars move into better positions. 2. Early extraction of mandibular first molars can lead to uncontrolled tipping of adjacent teeth into the extraction space. Only third-molar positions were
40 Ay et al
American Journal of Orthodontics and Dentofacial Orthopedics January 2006
Results of chi-square test demonstrating significant differences (P ⬍ .001), except mesioangular, in angulations of mandibular third molars between extraction and nonextraction sides
Table III.
Angulation Vertical
Extraction side Nonextraction side Total
Mesioangular
Distoangular
Horizontal
Total
n
%
n
%
n
%
n
%
n
%
78 37 115
67.8 32.2
25 32 57
43.9 56.1
3 18 21
14.3 85.7
1 20 21
4.8 95.2
107 107 214
50 50 100
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