Orthodontists and surgeons opinions on the role of third molars as a cause of dental crowding

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1 ORIGINAL ARTICLE Orthodontists and surgeons opinions on the role of third molars as a cause of dental crowding Steven J. Lindauer, a Daniel M. Laskin, b Eser Tüfekçi, c Russell S. Taylor, d Bryce J. Cushing, d and Al M. Best e Richmond, Va Introduction: Despite a substantial body of literature refuting an association between third molar eruption and crowding of the anterior dentition, the issue continues to be controversial. Methods: A survey was developed to evaluate and compare the current opinions of orthodontists (n 393) and oral and maxillofacial surgeons (n 458) regarding the link between third molars and the development of anterior crowding. Results: A smaller percentage of orthodontists than surgeons believed that maxillary (P.0001) and mandibular (P.0001) third molars produce anterior forces during eruption. Similarly, orthodontists were less likely to think that maxillary (P.0001) and mandibular (P.0001) third molars cause anterior crowding and were therefore less likely to recommend prophylactic removal of maxillary (P.0001) and mandibular (P.0001) third molars to prevent crowding. Surgeons were more likely to generally or sometimes (56.9%) recommend prophylactic removal of mandibular third molars to prevent crowding, whereas orthodontists more often said that they rarely or never (64.4%) recommend it. Differences in orthodontists and oral and maxillofacial surgeons beliefs about the association between third molar eruption and the development of crowding were significantly related to graduation year. More recently graduated orthodontists were less likely to recommend prophylactic removal of third molars to prevent crowding, and surgeons were more likely to recommend removal if they graduated in the 1970s or 1980s. Conclusions: Significant disagreement exists among practitioners, including both orthodontists and oral and maxillofacial surgeons, regarding the fundamental issues underlying the role of third molars in dental crowding. (Am J Orthod Dentofacial Orthop 2007;132:43-8) Despite numerous attempts to clarify the role of third molars in causing late anterior dental crowding, the issue remains controversial. Many dental practitioners apparently believe that the eruption of third molars can be a causative factor in the development of this condition. Moreover, orthodontic patients and their parents are often concerned that third molars will threaten the stability of orthodontic results, and former patients frequently cite the eruption of third From the School of Dentistry, Virginia Commonwealth University, Richmond. a Professor and Chair, Department of Orthodontics. b Professor and Chairman Emeritus, Department of Oral and Maxillofacial Surgery. c Assistant professor, Department of Orthodontics. d Dental student. e Associate professor, Department of Biostatistics. Supported in part by the Medical College of Virginia Orthodontic Education and Research Foundation. Reprint requests to: Steven J. Lindauer, Department of Orthodontics, School of Dentistry, Virginia Commonwealth University, PO Box , Richmond, VA ; , sjlindau@vcu.edu. Submitted, March 2005; revised and accepted, July /$32.00 Copyright 2007 by the American Association of Orthodontists. doi: /j.ajodo molars as causing redevelopment of their malocclusions. The issue has been extensively reviewed in the literature, and various authors have come to different conclusions regarding the extent to which third molars are causative agents in the development of late anterior crowding of the dentition. Richardson, 1 who had performed many studies on crowding and third molars, concluded in her review of the relevant literature that The evidence outlined... implicates pressure from the back of the arch and presence of a third molar in the cause of late lower arch crowding. However, she qualified her statement by saying that other factors might also be involved. Bishara, 2 onthe other hand, citing much of the same literature, stated In summary, one has to conclude from the available data that third molars do not play a significant, ie, quantifiable, role in mandibular anterior crowding. Similarly,Beeman, 3 inherarticlemakingacasefor routine removal of third molars in adolescents, stated with regard to many previous studies on the subject that The results have supported both sides of the controversy, convincing most dental practitioners that pres- 43

2 44 Lindauer et al American Journal of Orthodontics and Dentofacial Orthopedics July 2007 sure from third molars is clearly not the only factor in the development of mandibular crowding. Hicks, 4 in his counterpoint article arguing against prophylactic removal of third molars, offered 2 statements representing opposing viewpoints: The presence of third molars can cause late crowding, and Although some investigators have shown a statistical association of third molars and late anterior crowding, the association is not strong enough to allow prediction of patients at risk. Songetal 5 concluded,afterreviewing40studiesonthe topic, that there is no reliable research evidence to support the prophylactic removal of disease-free impacted third molars. Several studies concluded that the long-held belief that erupting third molars cause crowding of the incisors after orthodontic alignment should be questioned. Ades et al 6 examined orthodontic patients at 10 years postretention and determined that there were no differences in alignment of the incisors in those with bilaterally impacted, erupted, extracted, or absent third molars. In a randomized clinical trial in which postorthodontic patients were assigned to third molar extraction and nonextraction groups, Harradine et al 7 found significantly decreased arch length in the nonextraction group but no significant differences in crowding between groups as evaluated by the irregularity index 8 at a minimum of 5 years postretention. Van der Shoot et al 9 found no differences in the irregularity index in orthodontically treated patients at postretention with erupted, nonerupted, extracted, or congenitally absent third molars. Similarly, Al-Balkhi 10 found no association between condition of the manidublar third molars and lower anterior crowding in a postorthodontic sample of patients without tight interproximal incisal contacts. Laskin 11 reported in 1971 that approximately 65% of both orthodontists and oral surgeons subscribed to the idea that unerupted third molars produced an anteriorly directed force and should be removed to prevent development of crowding of the mandibular incisors. Because of the ongoing state of the controversy and the consequences of believing that third molars cause crowding, the purpose of this study was to evaluate and compare the current opinions of orthodontists and oral and maxillofacial surgeons regarding the link between erupting third molars and anterior crowding of the dentition. MATERIAL AND METHODS A short survey consisting of 6 questions related to the role of third molars as a cause of dental crowding was developed. The questions are shown in Figure 1. Institutional Review Board approval was granted to Fig 1. Survey questions. conduct the study, and the questionnaire was sent to 871 orthodontists and 913 oral and maxillofacial surgeons throughout the United States. Names were systematically chosen from lists provided by the respective specialty organizations and sorted by zip code to assure an even geographic distribution of participants. The surveys were sent by first-class mail with addressed postage-paid return envelopes. A short, explanatory letter requesting voluntary participation was included. There were no identifying markers on the surveys to trace answers back to individual respondents, and no follow-up questionnaires were sent to nonrespondents. Chi-square analysis was used to determine differences in the responses to the questions between orthodontists and oral and maxillofacial surgeons. Logistic regression was used to determine whether there was a relationship between answers to the questions and year of graduation. RESULTS A total of 851 (48%) surveys were returned. There were 393 responses from orthodontists (45% response rate) and 458 responses from oral and maxillofacial surgeons (50% response rate). Answers to all questions were significantly different between the 2 groups. Results from the first 2 questions regarding force exerted during eruption by maxillary and mandibular third molars are shown in Table I. Fewer orthodontists than surgeons answered that maxillary (P.0001) and mandibular (P.0001) third molars produce an anterior component of force during eruption. Twenty-eight percent of orthodontists vs 19.4% of surgeons (P.0005) thought that mandibular but not maxillary third molars produce force during eruption, whereas no orthodontists and only 1 surgeon believed that only maxillary molars produce force. The second set of questions asked whether erupting maxillary or mandibular third molars cause crowding of

3 American Journal of Orthodontics and Dentofacial Orthopedics Volume 132, Number 1 Lindauer et al 45 Table I. Answers to question do erupting third molars exert anterior force? Yes Orthodontists Maxilla 112 (29.6%) 266 (70.4%) Mandible 218 (57.7%) 160 (42.3%) Surgeons Maxilla 255 (59.0%) 177 (41.0%) Mandible 338 (78.2%) 94 (21.8%) the respective anterior dentitions. The results are shown in Table II. Answers between orthodontists and surgeons were significantly different for both maxillary (P.0001) and mandibular (P.0001) third molars. For the maxillary teeth, orthodontists were more likely than surgeons to state that these third molars never cause crowding, and they were also less likely to say that they sometimes cause crowding. In the mandible, orthodontists were less likely than surgeons to report that third molars frequently cause crowding and more likely to say that they rarely or never cause crowding. The last set of questions asked whether the respondent recommended prophylactic removal of third molars to prevent crowding of the anterior dentition. The results are shown in Table III. There were significant differences between orthodontists and surgeons regarding removal of both maxillary (P.0001) and mandibular (P.0001) third molars to prevent crowding. For both maxillary and mandibular third molars, orthodontists were less likely than surgeons to generally recommend removal and more likely to never recommend removal. Effect of year of graduation The relationship between graduation year and the combination of answers given by orthodontists and oral and maxillofacial surgeons to the first 2 questions about whether anterior force is exerted by erupting maxillary and mandibular third molars is shown in Figure 2. There was no significant relationship between graduation year and the answers to these questions by orthodontists (P.25), but surgeons showed a significant association between their answers and graduation years (P.0001). The probability that surgeons would answer yes to both maxillary and mandibular third molars producing an anterior force changed as a function of graduation year; it was highest for graduates in the 1980s and declined in both earlier and later graduates. There were significant associations between graduation year and the opinions of both orthodontists (P No.005) and surgeons (P.0005) regarding whether maxillary third molars cause crowding of the dentition. Orthodontists graduating in the 1970s were more likely to answer rarely and less likely to answer never than earlier or later graduates. Surgeons graduating around 1980 were more likely to answer rarely or sometimes and less likely to answer never than earlier or later graduates. There were also significant relationships for both orthodontists (P.005) and surgeons (P.0001) between graduation year and whether they thought that mandibular third molars cause crowding. Orthodontists graduating in the late 1970s were more likely to answer sometimes and less likely to answer never than earlier or later graduates. There was also a trend for earlier orthodontic graduates to be more likely to answer frequently and later graduates to answer rarely. Surgeons graduating around 1970 were more likely to answer frequently, and those graduating in the late 1980s were more likely to answer sometimes than earlier or later graduates. Those graduating in the early 1980s were less likely than earlier or later graduates to answer never or rarely. The likelihood that both orthodontists (P.001) and surgeons (P.005) would recommend prophylactic removal of maxillary third molars to prevent crowding was significantly related to graduation year. For orthodontists, it became more likely that they would never and less likely that they would rarely recommend prophylactic removal of maxillary molars as graduation year became more recent. For surgeons, the likelihood they would never recommend prophylactic removal was lowest, and the likelihood that they would rarely or sometimes recommend removal to prevent crowding was highest for those graduating around 1980 than earlier or later graduates. There were also significant associations between graduation year and whether orthodontists (P.0001) and surgeons (P.0001) would recommend prophylactic removal of mandibular third molars to prevent crowding. Orthodontists were more likely to never and less likely to generally or sometimes recommend prophylactic removal of mandibular third molars as the graduation year became more recent. Surgeons graduating around 1970 were more likely to generally recommend removal of mandibular third molars than earlier or later graduates. Those graduating in the early 1980s were less likely to never recommend removal, and those graduating in the late 1980s were more likely to sometimes recommend removal of mandibular third molars prophylactically to prevent crowding.

4 46 Lindauer et al American Journal of Orthodontics and Dentofacial Orthopedics July 2007 Table II. Answers to question do erupting third molars cause anterior crowding? Frequently Sometimes Rarely Never Orthodontists Maxilla 2 (0.5%) 54 (13.9%) 177 (45.6%) 155 (39.9%) Mandible 28 (7.2%) 126 (32.5%) 127 (32.7%) 107 (27.6%) Surgeons Maxilla 25 (6.4%) 149 (38.4%) 184 (47.4%) 94 (24.2%) Mandible 128 (28.3%) 161 (35.6%) 99 (21.9%) 64 (14.2%) Table III. Answers to question do you recommend removal of third molars to prevent anterior crowding? Generally Sometimes Rarely Never Orthodontists Maxilla 30 (7.6%) 34 (8.7%) 102 (26.0%) 227 (57.8%) Mandible 70 (17.8%) 70 (17.8%) 83 (21.1%) 170 (43.3%) Surgeons Maxilla 99 (21.8%) 78 (17.1%) 142 (31.2%) 136 (29.9%) Mandible 176 (38.7%) 83 (18.2%) 101 (22.2%) 95 (20.9%) Fig 2. Relationship between opinion of whether erupting third molars produce anterior force and year of graduation for orthodontists (not significant, P.25) and surgeons (P.0001). DISCUSSION The role of third molars in creating an anterior component of force during eruption capable of producing crowding is a controversial topic among dental practitioners. This was demonstrated by the wide range of opinions expressed by both the orthodontists and the oral and maxillofacial surgeons surveyed in this study. The survey showed significant differences between the opinions of orthodontists and surgeons regarding the role of third molars in causing crowding of the anterior teeth. Surgeons were more likely than orthodontists to think that both maxillary and mandibular molars exert anterior components of force on the dentition during eruption, more likely to believe that erupting third molars cause crowding, and more likely to recommend prophylactic removal of third molars to prevent crowding of both the maxillary and mandibular teeth. It is not surprising to find such differences in opinion regarding this controversial topic, but it is interesting that there was such a consistent difference in the opinions between the 2 specialty groups. The routine removal of asymptomatic third molars has been widespread for decades. Without clear justification for continuing this practice, 5,12 surgeons might be more likely or more willing to rationalize their decision to extract asymptomatic third molars. Although the focus of this study was on whether practitioners recommended removal of third molars to prevent late anterior crowding, the literature also questions whether asymptomatic third molars should be extracted for other purposes. It is generally agreed that third molars should be removed when there are symptoms or when pathology is present. However, in the absence of pathology, 2 recent comprehensive reviews concluded that it might be more logical to just monitor the third molarsovertime. 5,12 Theserecommendationswerebased on an absence of data documenting the onset of pathology

5 American Journal of Orthodontics and Dentofacial Orthopedics Volume 132, Number 1 Lindauer et al 47 related to these teeth, along with the known risks of postoperative morbidity and the high costs of removal. Since 1971, when 65% of both orthodontists and surgeons reportedly recommended prophylactic removal of mandibular third molars to prevent incisor crowding, 11 the prevalence of belief in the association between third molars and dental crowding has decreased. In this survey, 38.9% of the orthodontists and 56.9% of the oral and maxillofacial surgeons answered that they generally or sometimes recommend removal of mandibular third molars to prevent crowding. For both orthodontists and surgeons, there was substantial consistency between the belief in force of eruption causing crowding and the recommendation for prophylactic removal of third molars to prevent crowding. However, the pattern of agreement between answers to the questions was different for orthodontists and surgeons. Analysis of the data collected to evaluate the level of consistency between answers to various questions showed that 77.9% of orthodontists believed that maxillary third molars rarely or never cause crowding, so they rarely or never recommend removal. For surgeons, this percentage was smaller (54.8%). For surgeons, 32.1% believed that maxillary third molars frequently or sometimes cause crowding, so they generally or sometimes recommend removal. For orthodontists, this percentage was only 8.7%. For mandibular third molars, 54.5% of orthodontists believed that they rarely or never cause crowding, so they rarely or never recommend removal. The rarely or never percentage was 34.0% for surgeons. More oral and maxillofacial surgeons believed that mandibular third molars frequently or sometimes cause crowding and were consistent by generally or sometimes recommending their removal. The percentages were 55.0% for surgeons and 30.3% for orthodontists. Specialists who expressed the belief that neither maxillary nor mandibular third molars produce anterior force during eruption were also very likely (84.0%) to say that they rarely or never cause crowding, and therefore rarely or never recommend removal. Of those who answered that both maxillary and mandibular third molars do produce force during eruption, however, only 43.7% followed through by saying that they recommend removal of those teeth generally or sometimes. Indeed, 29.5% of them said that they rarely or never recommend removal. Likewise, only 44.7% of those who responded that maxillary third molars do not produce force, but mandibular third molars do, also said that maxillary third molars should rarely or never be removed, and mandibular third molars should generally or sometimes be removed to prevent crowding. From these data, it appears that specialists who believe that third molars do not produce an anterior force during eruption consistently and decisively believe that they do not cause crowding and should therefore not be extracted. In contrast, those who thought that third molars do exert force were about equally likely to express that this force will or will not cause crowding, and that removal of those teeth should or should not be recommended. Both orthodontists and oral and maxillofacial surgeons were more likely to implicate mandibular molars than maxillary molars as a cause of force and crowding, and were therefore more likely to recommend their removal. This is consistent with literature on the topic, which more often focuses on the crowding potential of mandibular than maxillary third molars. 1-4,6,7,10,11,13 The relationship between year of graduation and the belief that third molars cause crowding and should therefore be removed prophylactically was somewhat different between orthodontists and surgeons. Recent graduates in both groups were less likely to recommend removal to prevent incisor crowding, indicating familiarity with current literature on this topic. Surgeons graduating before 1970, however, were also less likely to recommend removal prophylactically, possibly reflecting a difference in their original education or a better ability to keep up with current literature. CONCLUSIONS Despite an extensive body of literature addressing this topic, the question of whether third molars should be removed to prevent future crowding of the anterior dentition still is controversial. The results of this survey demonstrate significant disagreement among practitioners, including both orthodontists and oral and maxillofacial surgeons, regarding the fundamental issues underlying this controversy. Surgeons were significantly more likely than orthodontists to believe that erupting third molars produce an anterior component of force and cause crowding of the anterior dentition, and were therefore more likely to recommend prophylactic removal of third molars to prevent crowding. Mandibular third molars were more consistently implicated than maxillary third molars as a cause of crowding and were therefore more likely to be recommended for removal by both orthodontists and oral and maxillofacial surgeons. Opinions about the role of third molars in causing crowding of the anterior dentition were significantly related to year of graduation for both orthodontists and oral and maxillofacial surgeons. Generally, orthodontists became less likely to believe that third molars caused crowding and were less likely to recommend their removal prophylactically when they graduated

6 48 Lindauer et al American Journal of Orthodontics and Dentofacial Orthopedics July 2007 more recently from orthodontic programs. This agrees with most recent literature on the topic that suggests little association between the eruption of third molars and crowding of the anterior teeth. Surgeons were more likely to believe that third molars caused crowding and more likely to recommend their removal to prevent crowding if they graduated in the 1970s or 1980s than earlier or later graduates. REFERENCES 1. Richardson ME. The role of the third molar in the cause of late lower arch crowding: a review. Am J Orthod Dentofacial Orthop 1989;95: Bishara SE. Third molars: a dilemma! Or is it? Am J Orthod Dentofacial Orthop 1999;115: Beeman CS. Third molar management: a case for routine removal in adolescent and young adult orthodontic patients. J Oral Maxillofac Surg 1999;57: Hicks EP. Third molar management: a case against routine removal in adolescent and young adult orthodontic patients. J Oral Maxillofac Surg 1999;57: Song F, O Meara S, Wilson P, Golder S, Kleijnen J. The effectiveness and cost-effectiveness of prophylactic removal of wisdom teeth. Health Technol Assess 2000;4: Ades AG, Joondeph DR, Little RM, Chapko MK. A long-term study of the relationship of third molars to changes in the mandibular dental arch. Am J Orthod Dentofacial Orthop 1990; 97: Harradine NWT, Pearson MH, Toth B. The effect of extraction of third molars on late lower incisor crowding: a randomized controlled trial. Br J Orthod 1998;25: Little RM. The irregularity index: a quantitative score of mandibular anterior alignment. Am J Orthod 1975;68: van der Schoot EAM, Kuitert RB, van Ginkel FC, Prahl- Andersen B. Clinical relevance of third permanent molars in relation to crowding after orthodontic treatment. J Dent 1997;25: Al-Balkhi KM. The effect of different lower third molar conditions on the re-crowding of lower anterior teeth in the absence of tight interproximal contacts one-year post orthodontic treatment: a pilot study. J Contemp Dent Pract 2004;3: Laskin DM. Evaluation of the third molar problem. J Am Dent Assoc 1971;82: Mettes TG, Nienhuijs MEL, van der Sanden WJM, Verdonschot EH, Plasschaert AJM. Interventions for treating asymptomatic impacted wisdom teeth in adolescents and adults [review]. Cochrane Database Syst Rev 2005;18:CD Richardson M. Lower arch crowding in the young adult. Am J Orthod Dentofacial Orthop 1992;101:132-7.