Effect of premolar extraction and presence of the lower third molar on lower second molar angulation in orthodontic treatment

Accepted Manuscript Effect of premolar extraction and presence of the lower third molar on lower second molar angulation in orthodontic treatment Tae min You , DDS, PhD Bo Hyun Ban , DDS Jin-Sun Jeong , DH Jisun Huh , DDS, MSD Re-Mee Doh , DDS, PhD Wonse Park , DDS, PhD PII:

S2212-4403(14)00467-2

DOI:

10.1016/j.oooo.2014.05.002

Reference:

OOOO 916

To appear in:

Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology

Received Date: 4 February 2014 Revised Date:

22 April 2014

Accepted Date: 5 May 2014

Please cite this article as: You Tm, Ban BH, Jeong J-S, Huh J, Doh R-M, Park W, Effect of premolar extraction and presence of the lower third molar on lower second molar angulation in orthodontic treatment, Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology (2014), doi: 10.1016/ j.oooo.2014.05.002. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Effect of premolar extraction and presence of the lower third molar on lower second molar angulation in orthodontic treatment

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Tae min You, DDS, PhD1, Bo Hyun Ban, DDS2, Jin-Sun Jeong, DH3, Jisun Huh, DDS, MSD3, Re-Mee Doh, DDS, PhD4, Wonse Park, DDS, PhD5

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Assistant Professor, Department of Advanced General Dentistry, Dental Hospital, Dankook

Resident, Department of Advanced General Dentistry, Dental Hospital, Yonsei University, Seoul,

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University, Cheonan, Korea

Korea 3

Researcher, Department of Advanced General Dentistry, Dental Hospital, Yonsei University, Seoul,

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Clinical Assistant Professor, Department of Advanced General Dentistry, Dental Hospital, Dankook

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University, Cheonan, Korea

Associate Professor, Department of Advanced General Dentistry, Dental Hospital, Yonsei University,

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Seoul, Korea

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Address correspondence and reprint requests to: Professor Wonse Park,

Department of Advanced General Dentistry, College of Dentistry, Yonsei University, Yonseiro 50, Seodaemun-gu, Seoul 120-752, Korea E-mail: [email protected] Tel.: +82-2-2228-8980, Fax: +82-2-2227-8906

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ACCEPTED MANUSCRIPT Acknowledgement We have no conflicts of interest in this study; This work was supported by the research fund from Yonsei University College of Dentistry for 2012 (2-2-12-0020)

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Word Count for Abstract: 141 Complete Manuscript Word Count: 2323 Number of References: 42

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Number of Figures/Tables: 5 / 2

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ACCEPTED MANUSCRIPT ABSTRACT Objectives: To evaluate the change in mandibular second-molar angulation (M2) in orthodontic treatment with premolar extraction and lower third molar (M3). Study Design: Panoramic radiographs were evaluated in 3 groups of 129 subjects: (1) control, no orthodontic treatment (n=65),

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(2) extraction, orthodontic treatment with premolar extraction (n=30), and (3) nonextraction, orthodontic treatment without premolar extraction (n=34). The angular difference and ratio of M2 to the first molar (M1), the change in the angulation of M2 between pre- and postorthodontic treatment,

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a distal bone level of M2. Results: Angular difference and ratio of M2 to M1, Angulation change of M2 between pre- and postorthodontic treatment, distal bone level of M2 were higher in the

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nonextraction group than in the control and extraction groups. Conclusion: The successful orthodontic alignment of the M2 might not be achieved in non-extraction cases when the M3s are

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present.

Keywords: mandibular second molar, angulation, nonextraction orthodontic treatment, preorthodontic

Clinical Relevance

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extraction, third molar

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The successful orthodontic alignment of the lower second molar might not be achieved in nonextraction cases when the lower third molars are present. This might be an indication of preorthodontic lower third molar extraction.

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ACCEPTED MANUSCRIPT Introduction There are two orthodontic methods for the treatment of arch alignment, which may or may not involve extraction of the premolars. If crowding is severe and there is insufficient arch length available,

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premolar extraction is the preferred method. However, if there is sufficient arch length or the protrusion of the lip is not severe, the orthodontist may choose the nonextraction method. With extraction of the premolars, an anchor loss occurs due to the forward movement of the molar, and a space may develop for eruption of the third molar(M3); however, in the nonextraction method, which

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involves holding back (arch length preservation) or distalization of the permanent molars, the second molar (M2) may move backward, tilt distally, or rotate, so that the area available for M3 eruption may

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be more restricted.1-8 (figure 1,2)

In 1972, Andrews stated in his six keys to normal occlusion that a slight mesial angulation of the crown was in fact normal occlusion.9 Cuoghi et al. compared the mesiodistal axial angulations of the mandibular premolars and molars with or without the presence of the M3 and found that the M2 had a

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slight mesial angulation or was parallel relative to the M1, irrespective of the presence of the M3.10 However, in the Orthodontic treatment without premolar extractions which involves the holding back (arch length preservation) or distalization of M2, the presence or impaction of the lower third molar

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may affect of the angulation of the M2s. In contrast, the lack of mesial movement of the first and second molars and the ‘‘driving’’ of the M2 distally, leads to posterior space deficiencies for the M3 in

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adolescent orthodontic patients. There are many indications for M3 extractions, one of which is the need for orthodontic treatment. There are two theories concerning the influence of M3s on orthodontic treatment. The first is that these teeth are capable of causing interference resulting in the generation of certain irregularities in the positioning of adjacent teeth

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and the second is that they are not.18-23 However, until recently

the removal of M3s to prevent crowding of the lower incisors was not considered warranted according to the data available. Furthermore, early germectomy to prevent impaction or development of crowding was not recommended because the variability in development is too great to allow accurate 4

ACCEPTED MANUSCRIPT prediction.24,25 Although, it is reported in many papers that the presence of M3s is not a direct cause of postorthodontic relapse, some practitioners who believe that the mesial pressure of an erupting M3 is a significant factor for relapse of incisor alignment are likely to recommend early M3 removal before orthodontic treatment.

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But, there is no study which assessed the usefulness of the prophylactic removal of M3 in orthodontic treatment on the grounds of the M2 angulation and M3 extraction not on the grounds of the orthodontic relapse. So, the aims of this study were to evaluate the change in M2 angulation in

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patients treated orthodontically with and without premolar extraction when M3s are present and to ascertain whether there is evidence supporting the prophylactic removal of M3 for adolescent

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orthodontic patients.

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ACCEPTED MANUSCRIPT Materials and methods This retrospective study was approved by the IRB of Yonsei University Dental Hospital. We selected patients who had been subjected to surgical extraction of the M3s in the Department of Advanced General Dentistry, College of Dentistry, Yonsei University, between January 2009 and December 2010.

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The reasons for extraction were pain, food impaction, dental caries, periodontal disease, and referral from orthodontists. Patients with missing teeth, facial asymmetry, a history of orthognathic surgery, or presence of a unilateral M3, or where the image quality was too poor for analysis due to a nonerupted

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M2 were excluded from the study. Of the 1,747 people originally screened, implementation of the exclusion criteria yielded 129 patients who were eligible and selected for study. Of this sample, we

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performed random sampling and classified the patients as follows: (1) control group (n=65 patients, 130 sides) who had no orthodontic treatment, (2) the extraction group (n=30 patients, 60 sides) who had orthodontic treatment with premolar extraction, and (3) the nonextraction group (n=34 patients, 68 sides) who had orthodontic treatment without premolar extraction.

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Measurements

We evaluated the panoramic radiographs of all of our subjects. One observer evaluated each of the radiographs using the Dental Picture Archiving and Communication System twice, with an interval of

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1 week. A midline bisector was drawn at the level of the nasal septum and the anterior nasal spine. A perpendicular line was drawn on this midline bisector that expanded through the palatal shadow

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bilaterally. This constructed plane was termed the horizontal reference plane. The outlines of the mandibular first molars (M1s) and M2s, and their long axes were drawn. The long axes of the M1s and M2s were traced from the midocclusal point through the midpoint of the root bifurcation and the midpoint between the mesial and distal root tips. The M1 and M2 angulations were defined as the outer angles formed by their long axes with the horizontal reference plane. The relative angle ratio of the M2 long axis to the M1 long axis (M2/M1) was calculated to minimize potential errors such as those caused by magnification and distortion of the panoramic radiograph.(Figure 3). In addition, the

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ACCEPTED MANUSCRIPT distal bone level of the M2s was evaluated on panoramic radiographs and classified into three types, 1–3, as shown in Figure 4. Statistical analysis was performed to check the significance of differences in data between the groups.

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Results

The average angle difference (M2–M1) and the angle ratio (M2/M1) of the M2s and M1s were significantly higher in the nonextraction group than in the extraction and control groups (one-way

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ANOVA and Pearson chi-square test, p-value <0.05, Table 1). Table 2 compares the angular changes between pre- and postorthodontic treatment with and without extraction. The angular change of M2 in

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the extraction group did not differ significantly from that in the control, but that in the nonextraction group did differ. (Paired t-test, p-value <0.05, Table 2).

The distributions of M2 distal bone levels differed significantly between the groups. The most prevalent M2 distal bone level was class 1 in the nonextraction group, but class 3 and 2 in the control

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and extraction groups, respectively (Pearson chi-square test , p-value <0.05, Figure 5)

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ACCEPTED MANUSCRIPT Discussion We evaluated the change in M2 angulation in patients treated orthodontically with and without premolar extraction to ascertain whether there is evidence supporting the prophylactic removal of M3

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for adolescent orthodontic patients from the point of view of the alignment of the M2 and the difficulty of extracting the M3. Our study showed that the angulation of the M2 was a little mesial or parallel to the long axis of the M1 in the control and extraction groups, as described in previous

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studies, but the M2 angulation of the nonextraction group had a high incidence of distoangulation. The distoangulation of the M2 may give rise to problems both surgically and orthodontically. Mild

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distoangulated M2s may require operculectomy or removal of the distal bone so that the clinical crown can be exposed, but in cases of severe distal tilting, some of the clinical crown of the M2 is impacted in the jaw, causing many additional and recurring problems and inflammation.26-29 And the existence of a distally tilting M2 may increase the surgical difficulty during removal of an impacted M3. Surgeons in such cases have poor visibility due to the distal-tilting M2, so that extraction of the

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M3 is difficult in itself. Since the distal side of the M2 is partially covered with gingival tissue, in many cases it is prone to inflammation prior to M3 extraction, and is found to have poor periodontal health after M3 extraction.27,30 One of the indications for M3 removal is the presence of distal caries

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in the M2 and it is more difficult to treat the cervical region of M2s as they have more distal tilting.31

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The eruption and impaction of the M3 is dependent primarily upon the space available at the posterior ends of the arch. This space is influenced by both natural growth and active treatment.32 Growth influences on these spaces may be expressed as arch lengthening by resorption at the anterior borders of the mandibular ramus. When remodeling resorption at the anterior surface of the mandibular ramus is limited, the M3 becomes impacted. Pell and Gregory classified M3 extraction difficulty according to the distance between the distal-most point of the M2 crown and the anterior-most point of the ramus, whereby the M3 extraction difficulty is increased in class III conditions. In our study, Class 1(the distal bone level of the M2 was over half the height of its crown) was prevalent in non 8

ACCEPTED MANUSCRIPT extraction orthodontic treatment. In these cases the difficulty of extracting the M3 is increased because of the small distance between the distal surface of the M2 and the ramus, similar to what is described as class III of the Pell and Gregory classification.33

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There has been considerable research into the influence of orthodontic treatment on the posterior space and subsequent M3 impaction. Growth changes in the retromolar area might have also contributed favorably toward increasing the space available for the M3, as was previously confirmed by Capelli.34 Other authors, such as Richardson, Kim et al and Kaplan have also concluded that

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premolar extractions generally result in greater space in the M3 region, and a general improvement in the angulations of the M3.2,21,32 Most have also found clinically significant reductions in the rate of

without premolar extractions.33,35-38

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impaction of M3 in patients who have had premolar extractions, when compared with those treated Siling stated that the developing M3 continually changes its

angular position, and that nonextraction therapy that holds back the mandibular molars or actively tips them distally may have the effect of encouraging abnormal rotational movements of the M3 crown,

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and thereby increase the possibility of impaction.5 Schulhof, Kim et al. and Kandasamy et al. reported that nonextraction treatment that involves the holding back or attempted posterior movement of the permanent molars may actually reduce posterior arch space, in turn resulting in the impaction of

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M3s.1,2,22 Saysel et al. reported worsening of M3 angulations with nonextraction treatment.4 However, Jain et al. reported that premolar extractions had a positive influence on the developing M3

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angulations, but that nonextraction therapy did not have any adverse effects.8 In contrast, Graber and Kaineg, McCoy, and Staggers showed that premolar extraction does not always improve the chances of normal eruption of the M3s.39-42 The M3 angle and position were not included in the assessment in the present study. Orthodontic treatment aimed at treating patients without premolar extractions typically involves the holding back (arch length preservation) or the distalization of the permanent molars. Lack of mesial movement of the first and second molars and the ‘‘driving’’ of the M2 distally, coupled with the lack of resorption at the anterior border of the mandibular rami, inevitably leads to posterior space deficiencies for the M3. This may have a significant effect on developing M3s, such 9

ACCEPTED MANUSCRIPT that they appear to be significantly more likely to become impacted and develop a poor angulation, thus increasing the difficulty associated with M3 extraction after orthodontic treatment. Whether the cause of distal tilting of M2s in nonextraction cases is the result of simple posterior orthodontic forces or impacted M3s that prevent distal movement of the M2 roots remains a matter of

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conjecture, and hence the studies of the angulation of M2 in nonextraction cases with preorthodontic extraction of M3 are needed.

Our study was subject to some limitations. First, it had a retrospective design and hence selection bias

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might have been present; prospective cohort studies are needed to overcome this limitation. Second, dental panoramic radiographs vary in vertical and horizontal magnifications. Caution is thus advised

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when interpreting the measurements taken from panoramic radiographs. Angular distortion is less affected by this problem, and so it is permissible to compare angular measurements taken from similar regions of different films. However, horizontal measurements in particular cannot be relied upon for absolute or comparative purposes. To obviate the effects of angular distortion, we calculated the relative angle ratios of the M2s and M1s, but magnification error remains a possibility when

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measuring M2 distal bone levels. Furthermore, panoramic radiographs are two-dimensional images, which made it impossible to evaluate buccolingual angulation and the position of the teeth. The use of three-dimensional analysis tools, such as cone-beam CT, is needed to overcome this problem. In

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orthodontic patients, mandibular growth and the amount of resorption at the anterior border of the ramus vary depending on age and skeletal pattern. In addition, the degree of M2 distal angulation and

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the posterior space can vary according to the anchorage system and orthodontic force. Other factors, such as molar anchorage considerations, age, and the skeletal classification must be taken into account and included in future studies.

Conclusion The successful orthodontic alignment of the M2 might not be achieved in non-extraction cases when the M3s are present. This might be an indication of preorthodontic extraction of the M3 in adolescent 10

ACCEPTED MANUSCRIPT orthodontic patients because the distoangulation of M2s has the problem of ideal alignment and the

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potential to increase the impaction of M3s and to render subsequent M3 extraction more difficult.

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ACCEPTED MANUSCRIPT lower jaw. Am J Orthod. 1982;81:130-9. 14. Richardson ME. Late lower arch crowding in relation to primary crowding. Angle Orthod. 1982;52:300-12. 15. Richardson ME. Lower molar crowding in the early permanent dentition. Angle Orthod.

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molars to changes in the mandibular dental arch. Am J Orthod Dentofacial Orthop. 1990;97:32335.

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21. Kaplan RG. Some factors related to mandibular third molar impaction. Angle Orthod. 1975;45:153-8.

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23. Shanley SL. The influence of mandibular third molars on mandibular anterior teeth. Am J Orthod.

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24. Beeman CS. Third molar management: a case for routine removal in adolescent and young adult orthodontic patients. J Oral Maxillofac Surg. 1999;57:824-30. 25. Hicks EP. Third molar management: a case against routine removal in adolescent and young adult orthodontic patients. J Oral Maxillofac Surg. 1999;57:831-6. 26. Akadiri OA, Obiechina AE. Assessment of difficulty in third molar surgery--a systematic review. J Oral Maxillofac Surg. 2009;67:771-4. 27. Almendros-Marques N, Berini-Aytes L, Gay-Escoda C. Influence of lower third molar position on the incidence of preoperative complications. Oral Surg Oral Med Oral Pathol Oral Radiol 13

ACCEPTED MANUSCRIPT Endod. 2006;102:725-32. 28. Carvalho RW, do Egito Vasconcelos BC. Assessment of factors associated with surgical difficulty during removal of impacted lower third molars. J Oral Maxillofac Surg. 2011;69:2714-21. 29. Oh YH, Park HS, Kwon TG. Treatment effects of microimplant-aided sliding mechanics on

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distal retraction of posterior teeth. Am J Orthod Dentofacial Orthop. 2011;139:470-81.

30. Leone SA, Edenfield MJ, Cohen ME. Correlation of acute pericoronitis and the position of the mandibular third molar. Oral Surg Oral Med Oral Pathol. 1986;62:245-50.

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31. McArdle LW, Renton TF. Distal cervical caries in the mandibular second molar: an indication for the prophylactic removal of the third molar? Br J Oral Maxillofac Surg. 2006;44:42-5.

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32. Richardson ME, Dent M. Some aspects of lower third molar eruption. Angle Orthod.

33. Pell GJ, Gregory GT. Impacted mandibular third molars; classification and modified technique for removal. Dent Dig 1933;39:330-8.

34. Capelli J, Jr. Mandibular growth and third molar impaction in extraction cases. Angle Orthod.

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1991;61:223-9.

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36. 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.

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37. Rindler A. Effects on lower third molars after extraction of second molars. Angle Orthod. 1977;47:55-8.

38. Smith DI. The eruption of third molars following extraction of second molars. Dent Pract 1958;8:292-4.

39. Wilson HE. Extraction of second permanent molars in orthodontic treatment. Orthodontist. 1971;3:18-24. 40. Graber TM, Kaineg TF. The mandibular third molar--its predictive status and role in lower incisor crowding. Proc Finn Dent Soc. 1981;77:37-44. 14

ACCEPTED MANUSCRIPT 41. McCoy JR. A study of growth potential. From observations made in over 50 years of orthodontic practice. Am J Orthod. 1965;51:79-97. 42. Staggers JA, Germane N, Fortson WM. A comparison of the effects of first premolar extractions

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on third molar angulation. Angle Orthod. 1992;62:135-8.

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Figure Legends Figure 1.Clinical feature of distoangulated lower second molar. This makes the surgery more

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difficult and evokes postoperative recurrent inflammation and poor periodontal condition.

Figure 2.Panoramic radiograph of distoangulated lower second molar in nonextraction

Figure 3.Measurements made on panoramic radiographs.

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premolar orthodontic treatment.

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Figure 4.Classification of distal bone level of M2s. Class 1: the distal bone level reaches up to half of the height of the crown of the M2 or more. Class 2: the distal bone level reaches up to half of the height of the crown of the M2 [i.e., up to its cementoenamel junction (CEJ). Class 3:

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the distal bone level is lower than the CEJ of the M2.

Figure 5.Distribution of M2 distal bone level classifications among the control, extraction, and

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nonextractiongroups.

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ACCEPTED MANUSCRIPT Table 1. Second and first mandibular molars (M2 and M1): angular differences and relative ratios in the three treatment groups: control (no orthodontic treatment), extraction (orthodontic treatment with premolar extraction), and nonextraction (orthodontic treatment

M2 M1

0.39±6.01

Extraction (n=60)

Non-Extraction (n=68)

0.09±6.45

2.32±6.11

0.012* 0.01*

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Control (n=130)

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without premolar extraction).

0.99±0.08

1.00±0.09

1.03±0.09

M2/M1≤1

58.46%

51.67%

38.24%

41.54%

48.33%

* One-way ANOVA, P < 0.05

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M2/M1>1

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** Pearson chi-square test, P < 0.05

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M2/M1

61.76%

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0.044**

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Post-

treatment

M2/M1

0.66±8.17 0.99±0.12

orthodontic

P***

treatment

treatment 0.09±6.45

0.45

1.00±0.09

0.6

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P*** : paired t-test p-value, P < 0.05

orthodontic

0.82±6.09

orthodontic

0.99±0.09

P***

treatment

2.32±6.11

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orthodontic

Post-

Pre-

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Pre-

M2-M1

Non-Extraction (n=68)

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Extraction (n=60)

1.03±0.09

< 0.0001 < 0.0001

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ACCEPTED MANUSCRIPT Clinical Relevance The successful orthodontic alignment of the lower second molar might not be achieved in nonextraction cases when the lower third molars are present. This might be an indication of

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preorthodontic lower third molar extraction.