- Email: [email protected]
Spontaneous third-molar eruption after second-molar extraction in orthodontic patients
ORIGINAL ARTICLE
Spontaneous third-molar eruption after second-molar extraction in orthodontic patients Cristina De-la-Rosa-Gay,a Eduard Valmaseda-Castellón,b and Cosme Gay-Escodac Barcelona, Spain Introduction: This retrospective study was conducted to assess the eruption of third molars by using panoramic radiographs and to identify the variables associated with unsuccessful eruption. Methods: The subjects were 48 patients who had 128 permanent second molars extracted during or before orthodontic treatment. Their ages at extraction were 11 to 23 years. The position of the third molars was assessed from panoramic radiographs taken before second-molar extraction and after third-molar eruption. The median time of eruption was 3 to 4 years (interquartile range, 2 years). A successful final position was defined as eruption with proximal contact with the adjacent first molar and an angle between these 2 teeth of no more than 35°. Results: A total of 96.2% of the maxillary and 66.2% of the mandibular third molars erupted in good positions. The maxillary third molars uprighted and successfully replaced the second molars. In the case of Nolla developmental stage ⬎ 8, the proximal contact could remain open. Most mandibular third molars uprighted and successfully replaced the second molars. Most unsuccessful eruptions of mandibular third molars were due to excessive mesial tilting or lack of proximal contact. Unsuccessful third-molar eruptions occurred in older patients who had higher Nolla developmental stages. Conclusions: Maxillary third molars upright and acceptably replace maxillary second molars after extraction for orthodontic purposes. However, if the Nolla developmental stage is ⬎ 8, proximal contact could remain open. Most mandibular third molars also upright and acceptably replace the second molars after extraction. Unsuccessful third-molar eruption is most common in older patients with higher Nolla developmental stages. Most unsuccessful eruptions are due to excessive mesial tilting or lack of proximal contact. (Am J Orthod Dentofacial Orthop 2006;129:337-44)
he extraction of second molars is an alternative to premolar extraction that causes less retraction of the mandibular incisors1,2 and less augmentation of the interincisal angle.3 Neither the vertical dimension nor the soft tissue convexity (G-Sn-Pg’) seems to be affected by extraction modality, and treatment times appear to be similar.1 Nevertheless, an important concern of second-molar extraction is the prognosis of third-molar eruption. Some authors have recommended not extracting the second molar if the third molar has a buccolingual orientation4 or the angle with the first molar is over 30°.5 However, severely tilted third molars have successfully replaced second molars.6 Maxillary third molars have also been found to replace second molars
T
quite successfully.7,8 There are some concerns about the prognosis of replacement of mandibular second molars by third molars. The ideal moment for extraction of the permanent second molars to optimize the possibilities of third-molar eruption remains unclear. The purposes of this study were to assess the proportion of correctly erupted third molars, the degree of uprighting with respect to the adjacent permanent first molar, and the time elapsed to complete thirdmolar eruption in a sample of patients who had undergone permanent second-molar extraction for orthodontic reasons. Additional aims were to compare correctly erupted with incorrectly positioned third molars in these patients and to identify the variables associated with third-molar eruption failure.
From the School of Dentistry, University of Barcelona, Barcelona, Spain. a Associate professor of orthodontics. b Associate professor of oral surgery and professor of oral surgery and implantology. c Chair, Department of Oral and Maxillofacial Surgery; director, oral surgery and implantology; oral and maxillofacial surgeon, Teknon Medical Center, Barcelona, Spain. Reprint requests to: Dr Cosme Gay-Escoda, Feixa Llarga s/n, Campus de Bellvitge, Pavelló Central, 2a planta, 08097 L’Hospitalet de Llobregat, Barcelona, Spain; e-mail, [email protected]. Submitted, May 2004; revised and accepted, October 2004. 0889-5406/$32.00 Copyright © 2006 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2005.11.002
MATERIAL AND METHODS
A sample of 48 patients (19 male, 29 female) who had completed orthodontic treatment with fixed appliances in both arches was selected. All patients were treated with the Ricketts or the straight-wire technique by the same orthodontist in a private practice in central Catalonia, Spain. The inclusion criteria were extraction of healthy maxillary or mandibular second molars previously or during orthodontic treatment and presence of the third 337
338 De-la-Rosa-Gay, Valmaseda-Castellón, and Gay-Escoda
Table I.
American Journal of Orthodontics and Dentofacial Orthopedics March 2006
Nolla developmental stages
Development of the tooth 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Presence of follicle Initial calcification Third of crown formed Two thirds of crown formed Crown almost fully formed Crown fully formed Third of root formed Two thirds of root formed Root almost formed Closed apex
molar next to the extracted second molar. The exclusion criteria were absence of other posterior permanent teeth in the quadrant in which extractions were made and lack of compliance with clinical recall visits after orthodontic treatment. The patients had been seen annually after orthodontic treatment for 1 to 10 years. All third molars were monitored until occlusion was considered stable or root development was complete and the molar did not move for more than 1 year. Sex, age at extraction of the second molars, and time at which the third molars erupted were retrieved from the clinical records. Panoramic radiographs before second-molar extraction and after third-molar eruption were also retrieved, and the following variables were identified: Nolla developmental stage9 of the third molar at extraction of the adjacent second molar (Table I), and the angle between the third molar and the neighboring first molar at extraction of the second molar and after third-molar eruption (or, in the case of noneruption, after the third molar was considered to be impacted and with totally formed roots). All panoramic radiographs had been obtained with the same equipment (Toshiba Panoura 1-C; Yoshida Dental; Tokyo; Japan). To draw a third molar, the first panoramic radiograph showing that the third molar was level with the occlusal plane and contacted the neighboring first molar was selected; eg, if the mandibular third molars took 1 year more to erupt than the maxillary third molars, the latter were drawn on the old radiograph and the former on the new one. The angles were calculated by drawing 2 lines on the panoramic radiograph: 1 line perpendicular to the occlusal line joining the cusps of the third molar, and the other joining the midpoint of the occlusal surface of the first molar with the midpoint between the 2 roots in the mandibular first molars or the buccal roots in the maxillary first molars. The angle was negative when these lines converged (mesial tilt) and positive when they diverged (distal tilt). One third molar had a major
Fig 1. Construction of angle between third molar and adjacent permanent first molar before extraction of second molar (angle between lines B and C). Line A joins the cusps of the third molar. Line B is perpendicular to Line A. Line C joins the midpoint between the roots of the first molar (buccal roots in upper molars) and the midpoint of its occlusal surface.
axis in the buccolingual direction; this made drawing the line as described impossible, and the angle in this case was considered to be –90°. Figures 1 and 2 represent drawings of constructed angles for the right maxillary and mandibular third molars.
American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 3
De-la-Rosa-Gay, Valmaseda-Castellón, and Gay-Escoda 339
when the tooth had erupted, had proximal contact with the adjacent first molar, and had a final angle between –35° and 35° with the first molar. Occlusion was not considered a success criterion, because, although some third molars were level with the occlusal plane, their antagonists failed to erupt. All measurements were made by the first author. To determine intraobserver concordance, 20 third-molar angles were measured, and the third molars were classified according to Nolla stages9 in 1 session and again 14 days later; comparisons were made with an intraclass correlation coefficient, which was excellent for the angle (lower limit of the 95% CI is 99%) and Nolla stage (95% CI of the intraclass correlation coefficient is 87%-98%). Ages were calculated in years with decimals. All data were processed with the Statistical Package for the Social Sciences (version 10.0; SPSS, Chicago, Ill). RESULTS
Fig 2. Construction of angle between third molar and adjacent permanent first molar after full eruption of third molar (angle between lines B and C). Line A joins the cusps of the third molar. Line B is perpendicular to Line A. Line C joins the midpoint between the roots of the first molar (buccal roots in upper molars) and the midpoint of its occlusal surface.
The final angle between the third and first permanent molars minus the initial angle between them was defined as uprighting of the third molar. Positive uprighting indicated an increase in distal tilting, and a negative value indicated an increase in mesial tilting. Third-molar eruption was considered acceptable
One hundred twenty-eight second molars were extracted (74 mandibular and 54 maxillary). The median age at the second molar extraction was 14.8 years, with an interquartile range of 2.2 years. Figure 3 shows the distribution of ages by sex. Panoramic radiograph images show a patient before (Fig 4, A) and after (Fig 4, B) extraction of the 4 second permanent molars. There was a clear positive correlation between Nolla stage and patient age before extraction of the second permanent molar (Pearson correlation coefficient, r ⫽ 0.732; P ⬍ 0.001). The greater the mesial tilt of the mandibular third molar before extraction of the second molar, the greater the uprighting (r ⫽ 0.799; P ⬍ 0.001). Similarly, the greater the distal tilt of the maxillary third molar, the greater the uprighting (r ⫽ 0.736; P ⬍ 0.001). Uprighting of the mandibular third molars showed a negative correlation to patient age at second-molar extraction (r ⫽ – 0.266; P ⫽ 0.022) and to Nolla developmental stage of the mandibular third molar (r ⫽ ⫺0.403; P ⬍ 0.001). These correlations were not observed in the maxillary third molars. Maxillary molars
Twenty-one maxillary second molars were extracted in males and 33 in females; 26 were on the right side and 28 on the left. All 54 maxillary third molars erupted. Fifty molars erupted successfully (92.6%), but 4 did not reach proximal contact with the adjacent first molar, and 3 more failed to establish occlusal contact with the opposing tooth but were level with the occlusal plane (the opposing tooth did not erupt correctly).
340 De-la-Rosa-Gay, Valmaseda-Castellón, and Gay-Escoda
American Journal of Orthodontics and Dentofacial Orthopedics March 2006
Male 20
Number of cases
10
0 12
13
14
15
16
17
18
19
20
21
22
23
24
Age at extraction (years)
Female 20
Number of cases
10
Fig 4. Panoramic radiograph of 4 second-molar extraction patient (male): A, at age 12 years, immediately before extraction; B, 5 years later, with third molars already in place.
0 12
13
14
15
16
17
18
19
20
21
22
23
24
Age at extraction (years)
Fig 3. Ages of patients (in years, rounded up to next whole number) at extraction of second molars.
The 4 unsuccessfully erupted molars belonged to 3 women aged 20, 21, and 23 (2 molars), and the Nolla developmental stages were 9 in the 2 younger patients and 10 in the older one. Mandibular molars
Thirty-three of the observed mandibular third molars belonged to male patients, and 41 to female patients; 38 were on the left side and 36 on the right. Four mandibular third molars did not erupt (5.4%); 14 failed to establish proximal contact with the adjacent first molar (18.9%), and 10 did not reach occlusion (13.5%). Twenty-five mandibular third molars erupted unsuccessfully. Therefore, the success rate was 66.2%. Four molars did not erupt. The rate of eruption was thus
94.6%. Three of the unerupted third molars had marked final angles (–52°, – 61°, and –74° mesial tilt). Of the 21 erupted third molars with defective positions, 11 had proximal contacts, but their final angles with the mandibular first permanent molar were less than –35° (ie, they were mesially tilted more than 35°, between 37° and 61°), and the remaining 10 did not establish proximal contact. Of these 10 molars with open proximal contact, only 2 showed mesial tilting of more than 35° (– 47° in both cases). Six of the 21 erupted third molars with defective positioning failed to reach occlusion with their antagonists. Fourteen unsuccessfully erupted mandibular third molars were found in males and 11 in females; 9 were on the left side and 16 on the right side. Patients with unsuccessful final positioning of the mandibular third molars were older (Mann-Whitney U-test: P ⫽ .006) (Fig 5), with higher Nolla stages (Mann-Whitney U-test: P ⫽ .002) (Fig 6) at extraction of the second molars. Third molars with defective final positions had significantly less uprighting after extraction of the adjacent second molars (Mann-Whitney U-test: P ⬍ .001) (Fig 7).
American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 3
De-la-Rosa-Gay, Valmaseda-Castellón, and Gay-Escoda 341
Lower third molars
Lower third molars 80 60
20
40 18
20 16
0
14
12
10 N=
49
25
Successful
Unsuccessful
Fig 5. Ages in years (vertical axis) before extraction of mandibular second molars of patients with successful and unsuccessful third-molar final positions. Circles represent outlier values.
Uprighting (degrees)
A g e a t e x t r a c t i o n o f t he se co nd mo l a r ( y ea r s )
22
-20 -40 -60 -80 N=
49
25
Successful
Unsuccessful
Fig 7. Uprighting in degrees (vertical axis) of mandibular third molar with respect to first molar between extraction of second molars and attainment of final third-molar positions. Circle represents outlier values.
Lower third molars 11 10 9 8
Initial Nolla stage
7 6 5 4 3 N=
49
25
Successful
Unsuccessful
Fig 6. Nolla stages (vertical axis) of mandibular third molars before extraction of second molars of patients with successful and unsuccessful third-molar final positions. Circle represents outlier value. Asterisk is extreme value.
DISCUSSION
In most reports, the patients’ age range at secondmolar extraction was narrow, thus enhancing the study’s internal validity. In our sample, the age range was broad (11-23 years), allowing us to see how third molars perform when the second molars are extracted at various ages and in different developmental stages. Patients who had their second molars extracted but did not report for the recalls were excluded from the
study. This could constitute a limitation if an association existed between reporting to follow-up visits and eruption of the third molars. However, it is unclear whether patients with badly positioned third molars seek more treatment. Defective eruptions were followed for a shorter time than correct eruptions. The reason for this shorter follow-up period is that unsuccessful final positioning corresponded to older patients, and their third molars took less time to reach a final position, because they were in higher Nolla developmental stages. In these cases, it is unlikely that their positioning could have improved much even if the follow-up period had been longer, since they were in occlusion with the antagonist, had proximal contact with the adjacent first permanent molar, or had fully formed roots that prevented further movement. Despite causing magnification and distortion of the image, panoramic radiographs allow the measurement of angles, and the consistency between measurements can be assessed if the device and settings are the same.10,11 Although lateral radiographs show less distortion and have been extensively used for evaluating thirdmolar eruptions after second-molar extractions,4,7,8,12-16 panoramic radiographs are the usual exploration modality for dental screening, and additional radiographs were not considered necessary for assessing third-molar eruption. Unfortunately, panoramic radiographs do not allow assessment of buccolingual dimension or quantification of molar rotation. Some authors have claimed that extraction of the second molars should not be indicated
342 De-la-Rosa-Gay, Valmaseda-Castellón, and Gay-Escoda
Table II.
American Journal of Orthodontics and Dentofacial Orthopedics March 2006
Variables for maxillary third molars Successfully erupted (n ⫽ 50)
Age (y) Angle before extraction (°) Angle after eruption (°) Uprighting (°) Nolla stage Time to erupt (y)
Mean (SD)
Median (IQR)
Min/max values
15.1 (2.6) 20.4 (14.6) 7.9 (8.2) ⫺12.4 (14.6) 6.6 (1.1) 4.4 (1.9)
14.6 (1.8) 22.0 (16.3) 8.0 (12.0) ⫺12.5 (17.3) 7.0 (1.0) 3.9 (1.9)
12.3/22.8 ⫺15/52 ⫺20/23 ⫺38.0/20 5/10 1/10
Min, Minimum; max, maximum.
Table III.
Variables for mandibular third molars Successfully erupted (n ⫽ 49)
Age (y)* Angle before extraction (°) Angle after eruption (°) Uprighting (°)* Nolla stage* Time to erupt (y)
Mean (SD)
Median (IQR)
Min/max values
14.5 (2.1) ⫺36.4 (16.2) ⫺21.1 (6.9) 15.3 (14.8) 6.2 (1.2) 4.5 (1.9)
14.2 (2.0) ⫺35.0 (19.0) ⫺21.0 (10.5) 14.0 (20.0) 6.0 (1.0) 4.3 (2.6)
11.4/20.9 ⫺90/⫺10 ⫺35/⫺9 ⫺15.0/59.0 4/10 1/10
*Significant differences between successfully and unsuccessfully erupted third molars with P ⬍ .01 (U-Mann-Whitney test). Min, Minimum; max, maximum.
if the third-molar germ is orientated in a severe buccolingual direction.4 However, 1 mandibular third molar had a marked buccolingual orientation (90°) that attained an acceptable result. Thus, although this restriction seems logical, it cannot be considered an absolute contraindication. Orthodontic treatment is usually carried out before third-molar eruption. Because of this, in some studies dealing with third-molar eruption after second-molar extraction for orthodontic purposes, only an improvement in third-molar tilting was observed, but the actual rate of third-molar eruption was not assessed.1,2,7 The general improvement in the position of both maxillary and mandibular third molars (with the exception of a few mandibular molars) contrasts with the findings of a study reporting improvement in the maxillary third molars but also worsening of mandibular third-molar positioning.1 In our sample, most of the mandibular third molars improved their positions, and worsening (increased mesial tilting) was the exception, not the rule. The main problems of the mandibular third molars were lack of proximal contact and excessive mesial tilting. These problems are probably related, because third molars (both maxillary and mandibular) without proximal contacts increase their mesial tilt to reach it.
For the mandibular third molars, increased age and Nolla developmental stage before second-molar extraction were clearly associated with deficient eruption. Probably the space balance was better for the maxillary third molars, because they do not have the anatomic limitation of the ramus and can erupt in a buccal position. On the other hand, although all observed maxillary third molars erupted, the association of increased patient age, Nolla stage, and defective final positioning (ie, lack of proximal contact) was also clear. Because age and Nolla stage were strongly correlated, this confirmed that the chances of replacing the second permanent molar with the third clearly depend on the timing of extraction. However, many maxillary and mandibular third molars with higher developmental stages or increased patient ages at extraction of the adjacent second molars reached acceptable final positions. Therefore, these 2 variables are associated with negative third-molar eruption prognosis but do not contraindicate second-molar extractions. On the other hand, early mandibular second-molar extraction is not a guarantee of good thirdmolar positioning, because some patients who underwent extraction as early as 13 years of age (in Nolla stage 5) had deficient positioning. The eruption prognosis of maxillary third molars
American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 3
Table II.
De-la-Rosa-Gay, Valmaseda-Castellón, and Gay-Escoda 343
Continued Unsuccessfully erupted (n ⫽ 4)
Total (n ⫽ 54)
Mean (SD)
Median (IQR)
Min/max values
Mean (SD)
Median (IQR)
Min/max values
22.2 (1.7)) 1.8 (30.0) 15.3 (6.8) ⫺17.0 (23.2) 9.5 (0.6) 2.8 (0.3)
22.5 (3.1) 1.5 (54.8) ⫺15.5 (12.8) ⫺17.0 (42.0) 9.5 (1.0) 2.8 (0.6)
20.2/23.6 ⫺27/31 ⫺22/⫺8 ⫺39.0/5.0 9/10 2/3
15.6 (3.1) 19.0 (16.5) 6.2 (10.1) ⫺12.8 (15.1) 6.9 (1.3) 4.3 (1.9)
14.7 (1.9) 22.0 (16.8) 7.5 (12.0) ⫺12.5 (21.5) 7.0 (1.0) 3.8 (2.0)
12.3/23.6 ⫺27/52 ⫺22/23 ⫺39/20 5/10 1/10
Table III.
Continued Unsuccessfully erupted (n ⫽ 25)
Total (n ⫽ 74)
Mean (SD)
Median (IQR)
Min/max values
Mean (SD)
Median (IQR)
Min/max values
16.7 (2.6) ⫺29.8 (16.0) ⫺39.3 (13.7) ⫺9.4 (14.5) 7.8 (1.4) 3.3 (2.0)
16.0 (5.0) ⫺32.0 (13.5) ⫺40.0 (20.0) ⫺11.0 (19.5) 8.0 (2.0) 2.9 (1.3)
13.0/20.5 ⫺60/9 ⫺74/⫺11 ⫺39.0/18.0 5/10 1/10
15.3 (2.4) ⫺34.2 (16.3) 27.3 (13.0) 6.9 (18.8) 6.8 (1.5) 4.1 (2.0)
14.7 (2.5) ⫺34.0 (17.5) ⫺25.0 (17.0) 8.0 (24.0) 7.0 (1.0) 3.5 (2.2)
11.4/20.9 ⫺90/9 ⫺74/⫺9 ⫺39.0/59.0 4/10 1/10
after second-molar extraction, especially if extraction has been done at an early age, is good (over 90% of eruptions), although a 31% incidence of rotations has been reported7 (the maxillary third molar seemingly replaces the second by rotating its vestibular aspect to the proximal area). The case of mandibular third molars is different. Depending on the criteria used to assess their final position after extraction of the second molars, the success rate varies from 35% to 99%.6,11,17-21 In our sample, 5.4% of the mandibular third molars did not erupt, and 19% had deficient proximal contacts; this coincides with other reports.11 Although only a limited sample has been published,22 early enucleation of the second molars does not seem to prevent deficient eruption of the third molars. A study based on radiographs and stone casts has shown that the main problems with replacing mandibular second molars with third molars are occlusion (good in only half of the subjects) and proximal contact (good in only 62%).17 Tipping and rotation seem to be good in 90%. The different methodology and the fact that many patients in that study did not undergo orthodontic treatment could explain the difference. We did not take into account possible movement of the first permanent molars during orthodontic treatment; movement could be limited in the mandible but more extensive in the maxilla. A more recent study6 showed
that 12% of replacing third molars lacked proximal contact; this is more in line with our results and other reports.19 In our study, there was general improvement in the angle of the maxillary and mandibular third molars, which became more parallel to the first molars, with the exception of a few mandibular molars that failed to erupt correctly and increased their angles as they tilted mesially, as has also been reported in other studies.11,23,24 This general improvement is consistent with other reports on third-molar eruption.25,26 Although an angle of the mandibular third molar before extraction of the second molar of more than 25° has been associated with poorer results,27 and an angle more than 30° has been identified as a contraindication to extraction,5 our results do not support this recommendation. However, another report also described an association between mesial tipping of the mandibular third molar and lack of proximal contact11; this agrees with our results, because third molars without proximal contact tipped toward the first permanent molar. No corrections were made in the positions of the third molars, and probably the positions of many could have been improved by using simple uprighting mechanics.28 However, the patients had finished orthodontic treatment some years ago and were unwilling to wear appliances again. Thus, some minor third-molar
344 De-la-Rosa-Gay, Valmaseda-Castellón, and Gay-Escoda
eruption problems leading to classification as “defectively erupted” molars are the result of spontaneous eruption and are easy to correct. CONCLUSIONS
Maxillary third molars upright and acceptably replace second molars after extraction for orthodontic purposes. However, if the Nolla developmental stage is more than 8, proximal contact could remain open. Most mandibular third molars also upright and acceptably replace the second molars after extraction for orthodontic purposes. Unsuccessfully erupted third molars were found in older patients with higher Nolla developmental stages. Most unsuccessful eruptions are due to excessive mesial tilting or lack of proximal contact.
REFERENCES 1. Staggers JA. A comparison of results of second molar and first premolar extraction treatment. Am J Orthod Dentofacial Orthop 1990;98:430-6. 2. Jager A, el-Kabarity A, Singelmann C. Evaluation of orthodontic treatment with early extraction of four second molars. J Orofac Orthop 1997;58:30-43. 3. Stellzig A, Basdra EK, Kube C, Komposch G. Extraction therapy in patients with Class II/2 malocclusion. J Orofac Orthop 1999;60:39-52. 4. Battagel JM, Ryan A. Spontaneous lower arch changes with and without second molar extractions. Am J Orthod Dentofacial Orthop 1998;113:133-43. 5. Foster TD. A textbook of orthodontics. Oxford: Blackwell Scientific Publications; 1990. 6. 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. 7. Moffitt AH. Eruption and function of maxillary third molars after extraction of second molars. Angle Orthod 1998;68:147-52. 8. Basdra EK, Stellzig A, Komposch G. Extraction of maxillary second molars in the treatment of Class II malocclusion. Angle Orthod 1996;66:287-92. 9. Nolla C. Development of the permanent teeth. J Dent Child 1960;27:254-66.
American Journal of Orthodontics and Dentofacial Orthopedics March 2006
10. Larheim TA, Svanaes DB. Reproducibility of rotational panoramic radiography: mandibular linear dimensions and angles. Am J Orthod Dentofacial Orthop 1986;90:45-51. 11. 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. 12. Richardson ME. Lower arch crowding in the young adult. Am J Orthod Dentofacial Orthop 1992;101:132-7. 13. Richardson ME. Late lower arch crowding: the role of differential horizontal growth. Br J Orthod 1994;21:379-85. 14. Richardson ME. Late lower arch crowding in relation to skeletal and dental morphology and growth changes. Br J Orthod 1996;23:249-54. 15. Capelli J Jr. Mandibular growth and third molar impaction in extraction cases. Angle Orthod 1991;61:223-9. 16. Romanides N, Servoss JM, Kleinrock S, Lohner J. Anterior and posterior dental changes in second molar extraction cases. J Clin Orthod 1990;24:559-63. 17. Richardson ME, Richardson A. Lower third molar development subsequent to second molar extraction. Am J Orthod Dentofacial Orthop 1993;104:566-74. 18. Dacre JT. The criteria for lower second molar extraction. Br J Orthod 1987;14:1-9. 19. 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. 20. Lawlor J. The effects on the lower third molar of the extraction of the lower second molar. Br J Orthod 1978;5:99-103. 21. Rindler A. Effects on lower third molars after extraction of second permanent molars. Angle Orthod 1977;47:55-8. 22. Gaumond G. Second molar germectomy and third molar eruption. 11 cases of lower second molar enucleation. Angle Orthod 1985;55:77-88. 23. Richardson ME. Changes in lower third molar position in the young adult. Am J Orthod Dentofacial Orthop 1992;102:320-7. 24. Hattab FN, Alhaija ES. Radiographic evaluation of mandibular third molar eruption space. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;88:285-91. 25. Efstratiadis SS, Kent RL Jr, Lebret LM, Moorrees CF. Spatial position of mandibular third molars in monozygotic twins. Angle Orthod 1984;54:271-82. 26. Sewerin I, von Wowern N. A radiographic four-year follow-up study of asymptomatic mandibular third molars in young adults. Int Dent J 1990;40:24-30. 27. Ryu YK. [The study on third molar changes following second molar extraction (1)]. Taehan Chikkwa Uisa Hyophoe Chi 1990;28:1069-79. 28. Bishara SE, Ortho D, Burkey PS. Second molar extractions: a review. Am J Orthod 1986;89:415-24.
Spontaneous third-molar eruption after second-molar extraction in orthodontic patients Cristina De-la-Rosa-Gay,a Eduard Valmaseda-Castellón,b and Cosme Gay-Escodac Barcelona, Spain Introduction: This retrospective study was conducted to assess the eruption of third molars by using panoramic radiographs and to identify the variables associated with unsuccessful eruption. Methods: The subjects were 48 patients who had 128 permanent second molars extracted during or before orthodontic treatment. Their ages at extraction were 11 to 23 years. The position of the third molars was assessed from panoramic radiographs taken before second-molar extraction and after third-molar eruption. The median time of eruption was 3 to 4 years (interquartile range, 2 years). A successful final position was defined as eruption with proximal contact with the adjacent first molar and an angle between these 2 teeth of no more than 35°. Results: A total of 96.2% of the maxillary and 66.2% of the mandibular third molars erupted in good positions. The maxillary third molars uprighted and successfully replaced the second molars. In the case of Nolla developmental stage ⬎ 8, the proximal contact could remain open. Most mandibular third molars uprighted and successfully replaced the second molars. Most unsuccessful eruptions of mandibular third molars were due to excessive mesial tilting or lack of proximal contact. Unsuccessful third-molar eruptions occurred in older patients who had higher Nolla developmental stages. Conclusions: Maxillary third molars upright and acceptably replace maxillary second molars after extraction for orthodontic purposes. However, if the Nolla developmental stage is ⬎ 8, proximal contact could remain open. Most mandibular third molars also upright and acceptably replace the second molars after extraction. Unsuccessful third-molar eruption is most common in older patients with higher Nolla developmental stages. Most unsuccessful eruptions are due to excessive mesial tilting or lack of proximal contact. (Am J Orthod Dentofacial Orthop 2006;129:337-44)
he extraction of second molars is an alternative to premolar extraction that causes less retraction of the mandibular incisors1,2 and less augmentation of the interincisal angle.3 Neither the vertical dimension nor the soft tissue convexity (G-Sn-Pg’) seems to be affected by extraction modality, and treatment times appear to be similar.1 Nevertheless, an important concern of second-molar extraction is the prognosis of third-molar eruption. Some authors have recommended not extracting the second molar if the third molar has a buccolingual orientation4 or the angle with the first molar is over 30°.5 However, severely tilted third molars have successfully replaced second molars.6 Maxillary third molars have also been found to replace second molars
T
quite successfully.7,8 There are some concerns about the prognosis of replacement of mandibular second molars by third molars. The ideal moment for extraction of the permanent second molars to optimize the possibilities of third-molar eruption remains unclear. The purposes of this study were to assess the proportion of correctly erupted third molars, the degree of uprighting with respect to the adjacent permanent first molar, and the time elapsed to complete thirdmolar eruption in a sample of patients who had undergone permanent second-molar extraction for orthodontic reasons. Additional aims were to compare correctly erupted with incorrectly positioned third molars in these patients and to identify the variables associated with third-molar eruption failure.
From the School of Dentistry, University of Barcelona, Barcelona, Spain. a Associate professor of orthodontics. b Associate professor of oral surgery and professor of oral surgery and implantology. c Chair, Department of Oral and Maxillofacial Surgery; director, oral surgery and implantology; oral and maxillofacial surgeon, Teknon Medical Center, Barcelona, Spain. Reprint requests to: Dr Cosme Gay-Escoda, Feixa Llarga s/n, Campus de Bellvitge, Pavelló Central, 2a planta, 08097 L’Hospitalet de Llobregat, Barcelona, Spain; e-mail, [email protected]. Submitted, May 2004; revised and accepted, October 2004. 0889-5406/$32.00 Copyright © 2006 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2005.11.002
MATERIAL AND METHODS
A sample of 48 patients (19 male, 29 female) who had completed orthodontic treatment with fixed appliances in both arches was selected. All patients were treated with the Ricketts or the straight-wire technique by the same orthodontist in a private practice in central Catalonia, Spain. The inclusion criteria were extraction of healthy maxillary or mandibular second molars previously or during orthodontic treatment and presence of the third 337
338 De-la-Rosa-Gay, Valmaseda-Castellón, and Gay-Escoda
Table I.
American Journal of Orthodontics and Dentofacial Orthopedics March 2006
Nolla developmental stages
Development of the tooth 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Presence of follicle Initial calcification Third of crown formed Two thirds of crown formed Crown almost fully formed Crown fully formed Third of root formed Two thirds of root formed Root almost formed Closed apex
molar next to the extracted second molar. The exclusion criteria were absence of other posterior permanent teeth in the quadrant in which extractions were made and lack of compliance with clinical recall visits after orthodontic treatment. The patients had been seen annually after orthodontic treatment for 1 to 10 years. All third molars were monitored until occlusion was considered stable or root development was complete and the molar did not move for more than 1 year. Sex, age at extraction of the second molars, and time at which the third molars erupted were retrieved from the clinical records. Panoramic radiographs before second-molar extraction and after third-molar eruption were also retrieved, and the following variables were identified: Nolla developmental stage9 of the third molar at extraction of the adjacent second molar (Table I), and the angle between the third molar and the neighboring first molar at extraction of the second molar and after third-molar eruption (or, in the case of noneruption, after the third molar was considered to be impacted and with totally formed roots). All panoramic radiographs had been obtained with the same equipment (Toshiba Panoura 1-C; Yoshida Dental; Tokyo; Japan). To draw a third molar, the first panoramic radiograph showing that the third molar was level with the occlusal plane and contacted the neighboring first molar was selected; eg, if the mandibular third molars took 1 year more to erupt than the maxillary third molars, the latter were drawn on the old radiograph and the former on the new one. The angles were calculated by drawing 2 lines on the panoramic radiograph: 1 line perpendicular to the occlusal line joining the cusps of the third molar, and the other joining the midpoint of the occlusal surface of the first molar with the midpoint between the 2 roots in the mandibular first molars or the buccal roots in the maxillary first molars. The angle was negative when these lines converged (mesial tilt) and positive when they diverged (distal tilt). One third molar had a major
Fig 1. Construction of angle between third molar and adjacent permanent first molar before extraction of second molar (angle between lines B and C). Line A joins the cusps of the third molar. Line B is perpendicular to Line A. Line C joins the midpoint between the roots of the first molar (buccal roots in upper molars) and the midpoint of its occlusal surface.
axis in the buccolingual direction; this made drawing the line as described impossible, and the angle in this case was considered to be –90°. Figures 1 and 2 represent drawings of constructed angles for the right maxillary and mandibular third molars.
American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 3
De-la-Rosa-Gay, Valmaseda-Castellón, and Gay-Escoda 339
when the tooth had erupted, had proximal contact with the adjacent first molar, and had a final angle between –35° and 35° with the first molar. Occlusion was not considered a success criterion, because, although some third molars were level with the occlusal plane, their antagonists failed to erupt. All measurements were made by the first author. To determine intraobserver concordance, 20 third-molar angles were measured, and the third molars were classified according to Nolla stages9 in 1 session and again 14 days later; comparisons were made with an intraclass correlation coefficient, which was excellent for the angle (lower limit of the 95% CI is 99%) and Nolla stage (95% CI of the intraclass correlation coefficient is 87%-98%). Ages were calculated in years with decimals. All data were processed with the Statistical Package for the Social Sciences (version 10.0; SPSS, Chicago, Ill). RESULTS
Fig 2. Construction of angle between third molar and adjacent permanent first molar after full eruption of third molar (angle between lines B and C). Line A joins the cusps of the third molar. Line B is perpendicular to Line A. Line C joins the midpoint between the roots of the first molar (buccal roots in upper molars) and the midpoint of its occlusal surface.
The final angle between the third and first permanent molars minus the initial angle between them was defined as uprighting of the third molar. Positive uprighting indicated an increase in distal tilting, and a negative value indicated an increase in mesial tilting. Third-molar eruption was considered acceptable
One hundred twenty-eight second molars were extracted (74 mandibular and 54 maxillary). The median age at the second molar extraction was 14.8 years, with an interquartile range of 2.2 years. Figure 3 shows the distribution of ages by sex. Panoramic radiograph images show a patient before (Fig 4, A) and after (Fig 4, B) extraction of the 4 second permanent molars. There was a clear positive correlation between Nolla stage and patient age before extraction of the second permanent molar (Pearson correlation coefficient, r ⫽ 0.732; P ⬍ 0.001). The greater the mesial tilt of the mandibular third molar before extraction of the second molar, the greater the uprighting (r ⫽ 0.799; P ⬍ 0.001). Similarly, the greater the distal tilt of the maxillary third molar, the greater the uprighting (r ⫽ 0.736; P ⬍ 0.001). Uprighting of the mandibular third molars showed a negative correlation to patient age at second-molar extraction (r ⫽ – 0.266; P ⫽ 0.022) and to Nolla developmental stage of the mandibular third molar (r ⫽ ⫺0.403; P ⬍ 0.001). These correlations were not observed in the maxillary third molars. Maxillary molars
Twenty-one maxillary second molars were extracted in males and 33 in females; 26 were on the right side and 28 on the left. All 54 maxillary third molars erupted. Fifty molars erupted successfully (92.6%), but 4 did not reach proximal contact with the adjacent first molar, and 3 more failed to establish occlusal contact with the opposing tooth but were level with the occlusal plane (the opposing tooth did not erupt correctly).
340 De-la-Rosa-Gay, Valmaseda-Castellón, and Gay-Escoda
American Journal of Orthodontics and Dentofacial Orthopedics March 2006
Male 20
Number of cases
10
0 12
13
14
15
16
17
18
19
20
21
22
23
24
Age at extraction (years)
Female 20
Number of cases
10
Fig 4. Panoramic radiograph of 4 second-molar extraction patient (male): A, at age 12 years, immediately before extraction; B, 5 years later, with third molars already in place.
0 12
13
14
15
16
17
18
19
20
21
22
23
24
Age at extraction (years)
Fig 3. Ages of patients (in years, rounded up to next whole number) at extraction of second molars.
The 4 unsuccessfully erupted molars belonged to 3 women aged 20, 21, and 23 (2 molars), and the Nolla developmental stages were 9 in the 2 younger patients and 10 in the older one. Mandibular molars
Thirty-three of the observed mandibular third molars belonged to male patients, and 41 to female patients; 38 were on the left side and 36 on the right. Four mandibular third molars did not erupt (5.4%); 14 failed to establish proximal contact with the adjacent first molar (18.9%), and 10 did not reach occlusion (13.5%). Twenty-five mandibular third molars erupted unsuccessfully. Therefore, the success rate was 66.2%. Four molars did not erupt. The rate of eruption was thus
94.6%. Three of the unerupted third molars had marked final angles (–52°, – 61°, and –74° mesial tilt). Of the 21 erupted third molars with defective positions, 11 had proximal contacts, but their final angles with the mandibular first permanent molar were less than –35° (ie, they were mesially tilted more than 35°, between 37° and 61°), and the remaining 10 did not establish proximal contact. Of these 10 molars with open proximal contact, only 2 showed mesial tilting of more than 35° (– 47° in both cases). Six of the 21 erupted third molars with defective positioning failed to reach occlusion with their antagonists. Fourteen unsuccessfully erupted mandibular third molars were found in males and 11 in females; 9 were on the left side and 16 on the right side. Patients with unsuccessful final positioning of the mandibular third molars were older (Mann-Whitney U-test: P ⫽ .006) (Fig 5), with higher Nolla stages (Mann-Whitney U-test: P ⫽ .002) (Fig 6) at extraction of the second molars. Third molars with defective final positions had significantly less uprighting after extraction of the adjacent second molars (Mann-Whitney U-test: P ⬍ .001) (Fig 7).
American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 3
De-la-Rosa-Gay, Valmaseda-Castellón, and Gay-Escoda 341
Lower third molars
Lower third molars 80 60
20
40 18
20 16
0
14
12
10 N=
49
25
Successful
Unsuccessful
Fig 5. Ages in years (vertical axis) before extraction of mandibular second molars of patients with successful and unsuccessful third-molar final positions. Circles represent outlier values.
Uprighting (degrees)
A g e a t e x t r a c t i o n o f t he se co nd mo l a r ( y ea r s )
22
-20 -40 -60 -80 N=
49
25
Successful
Unsuccessful
Fig 7. Uprighting in degrees (vertical axis) of mandibular third molar with respect to first molar between extraction of second molars and attainment of final third-molar positions. Circle represents outlier values.
Lower third molars 11 10 9 8
Initial Nolla stage
7 6 5 4 3 N=
49
25
Successful
Unsuccessful
Fig 6. Nolla stages (vertical axis) of mandibular third molars before extraction of second molars of patients with successful and unsuccessful third-molar final positions. Circle represents outlier value. Asterisk is extreme value.
DISCUSSION
In most reports, the patients’ age range at secondmolar extraction was narrow, thus enhancing the study’s internal validity. In our sample, the age range was broad (11-23 years), allowing us to see how third molars perform when the second molars are extracted at various ages and in different developmental stages. Patients who had their second molars extracted but did not report for the recalls were excluded from the
study. This could constitute a limitation if an association existed between reporting to follow-up visits and eruption of the third molars. However, it is unclear whether patients with badly positioned third molars seek more treatment. Defective eruptions were followed for a shorter time than correct eruptions. The reason for this shorter follow-up period is that unsuccessful final positioning corresponded to older patients, and their third molars took less time to reach a final position, because they were in higher Nolla developmental stages. In these cases, it is unlikely that their positioning could have improved much even if the follow-up period had been longer, since they were in occlusion with the antagonist, had proximal contact with the adjacent first permanent molar, or had fully formed roots that prevented further movement. Despite causing magnification and distortion of the image, panoramic radiographs allow the measurement of angles, and the consistency between measurements can be assessed if the device and settings are the same.10,11 Although lateral radiographs show less distortion and have been extensively used for evaluating thirdmolar eruptions after second-molar extractions,4,7,8,12-16 panoramic radiographs are the usual exploration modality for dental screening, and additional radiographs were not considered necessary for assessing third-molar eruption. Unfortunately, panoramic radiographs do not allow assessment of buccolingual dimension or quantification of molar rotation. Some authors have claimed that extraction of the second molars should not be indicated
342 De-la-Rosa-Gay, Valmaseda-Castellón, and Gay-Escoda
Table II.
American Journal of Orthodontics and Dentofacial Orthopedics March 2006
Variables for maxillary third molars Successfully erupted (n ⫽ 50)
Age (y) Angle before extraction (°) Angle after eruption (°) Uprighting (°) Nolla stage Time to erupt (y)
Mean (SD)
Median (IQR)
Min/max values
15.1 (2.6) 20.4 (14.6) 7.9 (8.2) ⫺12.4 (14.6) 6.6 (1.1) 4.4 (1.9)
14.6 (1.8) 22.0 (16.3) 8.0 (12.0) ⫺12.5 (17.3) 7.0 (1.0) 3.9 (1.9)
12.3/22.8 ⫺15/52 ⫺20/23 ⫺38.0/20 5/10 1/10
Min, Minimum; max, maximum.
Table III.
Variables for mandibular third molars Successfully erupted (n ⫽ 49)
Age (y)* Angle before extraction (°) Angle after eruption (°) Uprighting (°)* Nolla stage* Time to erupt (y)
Mean (SD)
Median (IQR)
Min/max values
14.5 (2.1) ⫺36.4 (16.2) ⫺21.1 (6.9) 15.3 (14.8) 6.2 (1.2) 4.5 (1.9)
14.2 (2.0) ⫺35.0 (19.0) ⫺21.0 (10.5) 14.0 (20.0) 6.0 (1.0) 4.3 (2.6)
11.4/20.9 ⫺90/⫺10 ⫺35/⫺9 ⫺15.0/59.0 4/10 1/10
*Significant differences between successfully and unsuccessfully erupted third molars with P ⬍ .01 (U-Mann-Whitney test). Min, Minimum; max, maximum.
if the third-molar germ is orientated in a severe buccolingual direction.4 However, 1 mandibular third molar had a marked buccolingual orientation (90°) that attained an acceptable result. Thus, although this restriction seems logical, it cannot be considered an absolute contraindication. Orthodontic treatment is usually carried out before third-molar eruption. Because of this, in some studies dealing with third-molar eruption after second-molar extraction for orthodontic purposes, only an improvement in third-molar tilting was observed, but the actual rate of third-molar eruption was not assessed.1,2,7 The general improvement in the position of both maxillary and mandibular third molars (with the exception of a few mandibular molars) contrasts with the findings of a study reporting improvement in the maxillary third molars but also worsening of mandibular third-molar positioning.1 In our sample, most of the mandibular third molars improved their positions, and worsening (increased mesial tilting) was the exception, not the rule. The main problems of the mandibular third molars were lack of proximal contact and excessive mesial tilting. These problems are probably related, because third molars (both maxillary and mandibular) without proximal contacts increase their mesial tilt to reach it.
For the mandibular third molars, increased age and Nolla developmental stage before second-molar extraction were clearly associated with deficient eruption. Probably the space balance was better for the maxillary third molars, because they do not have the anatomic limitation of the ramus and can erupt in a buccal position. On the other hand, although all observed maxillary third molars erupted, the association of increased patient age, Nolla stage, and defective final positioning (ie, lack of proximal contact) was also clear. Because age and Nolla stage were strongly correlated, this confirmed that the chances of replacing the second permanent molar with the third clearly depend on the timing of extraction. However, many maxillary and mandibular third molars with higher developmental stages or increased patient ages at extraction of the adjacent second molars reached acceptable final positions. Therefore, these 2 variables are associated with negative third-molar eruption prognosis but do not contraindicate second-molar extractions. On the other hand, early mandibular second-molar extraction is not a guarantee of good thirdmolar positioning, because some patients who underwent extraction as early as 13 years of age (in Nolla stage 5) had deficient positioning. The eruption prognosis of maxillary third molars
American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 3
Table II.
De-la-Rosa-Gay, Valmaseda-Castellón, and Gay-Escoda 343
Continued Unsuccessfully erupted (n ⫽ 4)
Total (n ⫽ 54)
Mean (SD)
Median (IQR)
Min/max values
Mean (SD)
Median (IQR)
Min/max values
22.2 (1.7)) 1.8 (30.0) 15.3 (6.8) ⫺17.0 (23.2) 9.5 (0.6) 2.8 (0.3)
22.5 (3.1) 1.5 (54.8) ⫺15.5 (12.8) ⫺17.0 (42.0) 9.5 (1.0) 2.8 (0.6)
20.2/23.6 ⫺27/31 ⫺22/⫺8 ⫺39.0/5.0 9/10 2/3
15.6 (3.1) 19.0 (16.5) 6.2 (10.1) ⫺12.8 (15.1) 6.9 (1.3) 4.3 (1.9)
14.7 (1.9) 22.0 (16.8) 7.5 (12.0) ⫺12.5 (21.5) 7.0 (1.0) 3.8 (2.0)
12.3/23.6 ⫺27/52 ⫺22/23 ⫺39/20 5/10 1/10
Table III.
Continued Unsuccessfully erupted (n ⫽ 25)
Total (n ⫽ 74)
Mean (SD)
Median (IQR)
Min/max values
Mean (SD)
Median (IQR)
Min/max values
16.7 (2.6) ⫺29.8 (16.0) ⫺39.3 (13.7) ⫺9.4 (14.5) 7.8 (1.4) 3.3 (2.0)
16.0 (5.0) ⫺32.0 (13.5) ⫺40.0 (20.0) ⫺11.0 (19.5) 8.0 (2.0) 2.9 (1.3)
13.0/20.5 ⫺60/9 ⫺74/⫺11 ⫺39.0/18.0 5/10 1/10
15.3 (2.4) ⫺34.2 (16.3) 27.3 (13.0) 6.9 (18.8) 6.8 (1.5) 4.1 (2.0)
14.7 (2.5) ⫺34.0 (17.5) ⫺25.0 (17.0) 8.0 (24.0) 7.0 (1.0) 3.5 (2.2)
11.4/20.9 ⫺90/9 ⫺74/⫺9 ⫺39.0/59.0 4/10 1/10
after second-molar extraction, especially if extraction has been done at an early age, is good (over 90% of eruptions), although a 31% incidence of rotations has been reported7 (the maxillary third molar seemingly replaces the second by rotating its vestibular aspect to the proximal area). The case of mandibular third molars is different. Depending on the criteria used to assess their final position after extraction of the second molars, the success rate varies from 35% to 99%.6,11,17-21 In our sample, 5.4% of the mandibular third molars did not erupt, and 19% had deficient proximal contacts; this coincides with other reports.11 Although only a limited sample has been published,22 early enucleation of the second molars does not seem to prevent deficient eruption of the third molars. A study based on radiographs and stone casts has shown that the main problems with replacing mandibular second molars with third molars are occlusion (good in only half of the subjects) and proximal contact (good in only 62%).17 Tipping and rotation seem to be good in 90%. The different methodology and the fact that many patients in that study did not undergo orthodontic treatment could explain the difference. We did not take into account possible movement of the first permanent molars during orthodontic treatment; movement could be limited in the mandible but more extensive in the maxilla. A more recent study6 showed
that 12% of replacing third molars lacked proximal contact; this is more in line with our results and other reports.19 In our study, there was general improvement in the angle of the maxillary and mandibular third molars, which became more parallel to the first molars, with the exception of a few mandibular molars that failed to erupt correctly and increased their angles as they tilted mesially, as has also been reported in other studies.11,23,24 This general improvement is consistent with other reports on third-molar eruption.25,26 Although an angle of the mandibular third molar before extraction of the second molar of more than 25° has been associated with poorer results,27 and an angle more than 30° has been identified as a contraindication to extraction,5 our results do not support this recommendation. However, another report also described an association between mesial tipping of the mandibular third molar and lack of proximal contact11; this agrees with our results, because third molars without proximal contact tipped toward the first permanent molar. No corrections were made in the positions of the third molars, and probably the positions of many could have been improved by using simple uprighting mechanics.28 However, the patients had finished orthodontic treatment some years ago and were unwilling to wear appliances again. Thus, some minor third-molar
344 De-la-Rosa-Gay, Valmaseda-Castellón, and Gay-Escoda
eruption problems leading to classification as “defectively erupted” molars are the result of spontaneous eruption and are easy to correct. CONCLUSIONS
Maxillary third molars upright and acceptably replace second molars after extraction for orthodontic purposes. However, if the Nolla developmental stage is more than 8, proximal contact could remain open. Most mandibular third molars also upright and acceptably replace the second molars after extraction for orthodontic purposes. Unsuccessfully erupted third molars were found in older patients with higher Nolla developmental stages. Most unsuccessful eruptions are due to excessive mesial tilting or lack of proximal contact.
REFERENCES 1. Staggers JA. A comparison of results of second molar and first premolar extraction treatment. Am J Orthod Dentofacial Orthop 1990;98:430-6. 2. Jager A, el-Kabarity A, Singelmann C. Evaluation of orthodontic treatment with early extraction of four second molars. J Orofac Orthop 1997;58:30-43. 3. Stellzig A, Basdra EK, Kube C, Komposch G. Extraction therapy in patients with Class II/2 malocclusion. J Orofac Orthop 1999;60:39-52. 4. Battagel JM, Ryan A. Spontaneous lower arch changes with and without second molar extractions. Am J Orthod Dentofacial Orthop 1998;113:133-43. 5. Foster TD. A textbook of orthodontics. Oxford: Blackwell Scientific Publications; 1990. 6. 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. 7. Moffitt AH. Eruption and function of maxillary third molars after extraction of second molars. Angle Orthod 1998;68:147-52. 8. Basdra EK, Stellzig A, Komposch G. Extraction of maxillary second molars in the treatment of Class II malocclusion. Angle Orthod 1996;66:287-92. 9. Nolla C. Development of the permanent teeth. J Dent Child 1960;27:254-66.
American Journal of Orthodontics and Dentofacial Orthopedics March 2006
10. Larheim TA, Svanaes DB. Reproducibility of rotational panoramic radiography: mandibular linear dimensions and angles. Am J Orthod Dentofacial Orthop 1986;90:45-51. 11. 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. 12. Richardson ME. Lower arch crowding in the young adult. Am J Orthod Dentofacial Orthop 1992;101:132-7. 13. Richardson ME. Late lower arch crowding: the role of differential horizontal growth. Br J Orthod 1994;21:379-85. 14. Richardson ME. Late lower arch crowding in relation to skeletal and dental morphology and growth changes. Br J Orthod 1996;23:249-54. 15. Capelli J Jr. Mandibular growth and third molar impaction in extraction cases. Angle Orthod 1991;61:223-9. 16. Romanides N, Servoss JM, Kleinrock S, Lohner J. Anterior and posterior dental changes in second molar extraction cases. J Clin Orthod 1990;24:559-63. 17. Richardson ME, Richardson A. Lower third molar development subsequent to second molar extraction. Am J Orthod Dentofacial Orthop 1993;104:566-74. 18. Dacre JT. The criteria for lower second molar extraction. Br J Orthod 1987;14:1-9. 19. 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. 20. Lawlor J. The effects on the lower third molar of the extraction of the lower second molar. Br J Orthod 1978;5:99-103. 21. Rindler A. Effects on lower third molars after extraction of second permanent molars. Angle Orthod 1977;47:55-8. 22. Gaumond G. Second molar germectomy and third molar eruption. 11 cases of lower second molar enucleation. Angle Orthod 1985;55:77-88. 23. Richardson ME. Changes in lower third molar position in the young adult. Am J Orthod Dentofacial Orthop 1992;102:320-7. 24. Hattab FN, Alhaija ES. Radiographic evaluation of mandibular third molar eruption space. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;88:285-91. 25. Efstratiadis SS, Kent RL Jr, Lebret LM, Moorrees CF. Spatial position of mandibular third molars in monozygotic twins. Angle Orthod 1984;54:271-82. 26. Sewerin I, von Wowern N. A radiographic four-year follow-up study of asymptomatic mandibular third molars in young adults. Int Dent J 1990;40:24-30. 27. Ryu YK. [The study on third molar changes following second molar extraction (1)]. Taehan Chikkwa Uisa Hyophoe Chi 1990;28:1069-79. 28. Bishara SE, Ortho D, Burkey PS. Second molar extractions: a review. Am J Orthod 1986;89:415-24.