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  Review Article The Role of Mandibular Third Molars onLower Anterior Teeth Crowding and Relapse afterOrthodontic Treatment: A Systematic Review  Khalid H. Zawawi 1 and Marcello Melis 2 󰀱 Department o Orthodontics, Faculty o Dentistry, King Abdulaziz University, P.O. Box 󰀸󰀰󰀲󰀰󰀹, Jeddah 󰀲󰀱󰀵󰀸󰀹, Saudi Arabia 󰀲 Cranioacial Pain Center, ufs University School o Dental Medicine, One Kneeland Street, Boston, MA 󰀰󰀲󰀱󰀱󰀱, USA Correspondence should be addressed to Khalid H. Zawawi; kzawawi@kau.edu.saReceived 󰀱󰀰 February 󰀲󰀰󰀱󰀴; Revised 󰀴 April 󰀲󰀰󰀱󰀴; Accepted 󰀱󰀱 April 󰀲󰀰󰀱󰀴; Published 󰀳󰀰 April 󰀲󰀰󰀱󰀴Academic Editor: Grant McIntyreCopyright © 󰀲󰀰󰀱󰀴 K. H. Zawawi and M. Melis. Tis is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the srcinal work is properly cited.  Aims . o evaluate the role o third molars in the development o crowding or relapse afer orthodontic treatment in the anteriorsegment o the dental arch.  Methods . PubMed search o the literature was perormed selecting all the articles relevant to the topicandlimitingthestudiestocontrolledtrialsonhumansandwritteninEnglishlanguage.SystematicreviewwasconductedaccordingtothePRISMA(preerredreportingitemsorsystematicreviewsandmeta-analyses)statement. Results .Atotalo󰀱󰀲clinicalstudieswere included in the review. A high risk o bias was ound in most o the articles, either because the relative items assessed wereinadequateorbecausetheywereunclearlydescribed.Tethirdmolarswerenotcorrelatedwithmoresevereanteriortoothcrowdingin most o the studies. However, our o them described a different outcome.  Conclusion . De󿬁nitive conclusions on the role o thethird molars in the development o anterior tooth crowding cannot be drawn. A high risk o bias was ound in most o the trials,and the outcomes were not consistent. However, most o the studies do not support a cause-and-effect relationship; thereore, thirdmolar extraction to prevent anterior tooth crowding or postorthodontic relapse is not justi󿬁ed. 1. Introduction In orthodontics, the most controversial role o the thirdmolars is whether they can contribute to the development o malocclusion or relapse afer orthodontic treatment, partic-ularly in the anterior segment o the dental arch. While thissubject has been discussed and presented in the literature, itis an issue that remains unresolved. It has been hypothesizedthat, while erupting, the tooth could transmit an anteriorcomponentoorcedownthedentalarchconcentratingintheareas o canines and incisors, which results in tooth rotationand misplacement [󰀱, 󰀲]. Based on such theory, Niedzielska suggested that, when a sufficient space is available or theeruption o the third molars, the tooth assumes a normalposition in the dental arch and does not cause displacemento the other teeth; conversely, when the space is de󿬁cient,third molars may aggravate dental crowding [󰀲]. However,several studies did not con󿬁rm these conclusions. Sidlauskasand rakiniene [󰀳] studied a group o ninety-one subjectswith a mean age o 󰀲󰀱 years. Registration o crowding wasbased on the mesiodistal width measurements o the teethin relation to the length o the corresponding segment o thelower dental arch. No statistically signi󿬁cant differences werereported in terms o lower dental arch crowding betweenthe groups with erupted, unerupted, and agenesis o thirdmolars.Teyconcludedthatthereisnoevidencetoimplicatethird molars as etiologic actors in the late lower dentalarch crowding [󰀳]. In addition, Karasawa et al. [󰀴] evaluated three hundred subjects with a mean age o 󰀲󰀰.󰀴 years onthe presence or absence o wisdom teeth and mandibularincisor crowding. Tey also ound no statistically signi󿬁cantassociation between the presence o upper and/or lowerthird molars and anterior mandibular teeth crowding. Teirconclusions stated that evidence on the role o third molarsas etiologic actor in the late lower arch crowding is lacking,similarly to the ones o the previous study [󰀴]. Hindawi Publishing Corporatione Scientific World JournalVolume 2014, Article ID 615429, 6 pageshttp://dx.doi.org/10.1155/2014/615429  󰀲 Te Scienti󿬁c World JournalHarradine et al. [󰀵] described analogous outcome in sub- jects who underwent orthodontic treatment. Tey examinedthe effect o third molar extraction on the development o anterior mandibular dental crowding in a randomized con-trolled study. Te results show minimal difference betweenthegroups(thirdmolarsextractedversusthirdmolarsnonex-tracted), and such difference was not statistically signi󿬁cant.It was also considered clinically nonsigni󿬁cant; thus they concluded that removal o third molars to prevent or reducelate incisor crowding could not be justi󿬁ed [󰀵].In another study our groups o patients treatedorthodontically were compared [󰀶]. Te groups consistedo subjects whose third permanent molar teeth had eruptedinto the mouth, were nonerupted, were extracted, and werecongenitally absent. Te irregularity index used to evaluatetooth misplacement was evaluated beore, immediately afer,and at least three years afer orthodontic treatment; however,no difference was detected among the groups [󰀶]. Te rolethatmandibularthirdmolarsplayinloweranteriorcrowdinghas been discussed and presented ofen in the orthodonticliterature; nonetheless, it is an issue that remains unresolved.Several reviews were discussed this issue. Bishara [󰀷] in hisreview acknowledged this controversial issue; however, hedidnot󿬁ndanyevidencetoimplicatetheseteethasbeingtheonly or even the major etiologic actor in the posttreatmentchanges in incisor alignment. He also suggests that the only relationship between these two phenomena is that they occur at approximately the same time o development. TeNHS Center or Reviews and Dissemination, University o York, UK, in their recommendation to the effectivenessand cost-effectiveness o prophylactic removal o thirdmolars, suggested that there was only a weak associationbetween retention and third molars and crowding. Tey also noted that the methodological quality o the literaturereviews was generally poor and none o the reviews wassystematic [󰀸]. Mettes et al. [󰀹] also showed no evidence to support nor reute regular prophylactic removal o asymptomatic impacted third molars in adults. Tey alsoound prophylactic removal o asymptomatic impacted thirdmolars in adolescents neither reduces nor prevents lateincisor crowding. However, since the review by Mettes et al.[󰀹] almost ten years ago there have been several additionalstudies added to the literature. Tereore, in the light o thedifferent results in the literature, the aim o this study wasto review the articles published on the topic by ollowingthe preerred reporting items or systematic reviews andmeta-analyses (PRISMA) statement [󰀱󰀰], in order to clariy the role o mandibular third molars on lower anterior teethcrowding and relapse afer orthodontic treatment. 2. Materials and Methods 󰀲.󰀱. Literature Search.  wo reviewers (Marcello Melis andKhalid H. Zawawi) independently perormed an electronicsearch o the literature using PubMed according to theollowingcriteria.Keytermsincludedinthesearchwere third molar/molars and wisdomtooth/teeth ononesideand relapse,anterior crowding, alignment, post retention, anterior post retention, incisor relapse,  and  incisor crowding   on the otherside. All key words were included both as medical subjectsheadings (MeSH) terms and text words. Afer combining theresults, selections were limited to the English language andhumans. Afer reading the titles and the abstracts selected,only srcinal articles relevant to the topic were included inthe review. Additionally, a manual search was carried out by examiningthereerencesotheincludedarticles.Finally,only controlled trials o the articles collected were selected. 󰀲.󰀲. Quality Assessment o the Studies.  o evaluate the quality othestudiesincludedinthereviewtheollowingitemswereassessed as described by Vos et al. [󰀱󰀱]:(󰀱) sequence generation and concealed allocation,(󰀲) size and composition o the studied groups,(󰀳) blinding o participants, clinicians, and investigators,(󰀴) application o inclusion and exclusion criteria orsubjects,(󰀵) descriptions o loss to ollow-up,(󰀶) adequacy o statistical analysis.wo reviewers (Marcello Melis and Khalid H. Zawawi)independentlyratedeachstudyscoringitas“adequate”whentherelativeitemwasjudgedtobeassociatedwithalowrisko bias, “unclear” when lack o inormation on the relative itemdid not allow evaluating the risk o bias, and “inadequate”when the relative item was judged to be associate with highrisk o bias.Sequence generation and concealed allocation were con-sidered adequate when the group assignment was random-ized and the clinician was blind to such assignment. Sizeand composition o the studied groups were consideredadequate when the size o the groups was approximately equalandageandgenderwereequallyrepresentedamongthegroups. Blinding o participants, clinicians, and investigatorswas considered adequate when at least the investigator whoanalyzed the results was blind to the condition o thesubjects.However,blindingoparticipantsandclinicianswasconsideredimpossibledueto theeaturesothetherapy(e.g.,orthodontic treatment and dental extraction). Application o inclusion and exclusion criteria or subjects was consideredadequatewhentheywereproperlydescribedbeoretheinclu-sion o the subjects. Descriptions o loss to ollow-up wereconsidered adequate when the number o withdrawals romthe groups was clearly indicated. However, such evaluationwas not applicable or cross-sectional studies, where lossto ollow-up cannot occur. Adequacy o statistical analysiswas considered adequate when all subjects included wereanalyzedandstatisticaltestswereconsideredappropriate.Anexpert in statistics evaluated the appropriateness o statisticaltests. 3. Results A total o 󰀹󰀶 articles were 󿬁rst ound by combining the key words and limiting the studies to English and human. Aferexaminingthetitlesandtheabstracts,twenty-sixstudieswere  Te Scienti󿬁c World Journal 󰀳 󰁡󰁢󰁬󰁥 󰀱: Literature review search 󿬂ow chart.Steps Key words Selections󰀱“third molar” [MeSH] OR “third molar” [ext Word] OR “third molars” [MeSH] OR “third molars” [ext Word]OR “wisdom tooth” [MeSH] OR “wisdom tooth” [ext Word] OR “wisdom teeth” [MeSH] OR “wisdom teeth”[ext Word]󰀸󰀱󰀷󰀶󰀲“relapse” [MeSH] OR “relapse” [ext Word] OR “anterior crowding” [MeSH] OR “anterior crowding” [extWord] OR “alignment” [MeSH] OR “alignment” [ext Word] OR “post retention” [MeSH] OR “post retention”[ext Word] OR “incisor relapse” [MeSH] OR “incisor relapse” [ext Word] OR “incisor crowding” [MeSH] OR “incisor crowding” [ext Word] OR “anterior post retention” [MeSH] OR “anterior post retention” [ext Word]󰀳󰀲󰀷󰀶󰀲󰀸󰀳 Combining 󰀱 and 󰀲 󰀱󰀱󰀷󰀴 󰀳 limited to English and human 󰀹󰀶󰀵 󰀴 title and abstract based selection (topic, srcinal studies) 󰀲󰀶󰀶 󰀵 reerences hand search +󰀵󰀷 󰀵 + 󰀶 controlled trials 󰀱󰀲󰁡󰁢󰁬󰁥 󰀲: Quality assessment o the studies.Author 󰀱 󰀲 󰀳 󰀴 󰀵 󰀶Shanley 󰀱󰀹󰀶󰀲 [󰀱󰀲] U U U U N/A ASheneman 󰀱󰀹󰀶󰀹 [󰀱󰀳] U U U U U UKaplan 󰀱󰀹󰀷󰀴 [󰀱󰀴] I A U A U ALindqvist and Tilander 󰀱󰀹󰀸󰀲 [󰀱󰀵] A A U I U ARichardson 󰀱󰀹󰀸󰀲 [󰀱󰀶] I I U I U AAdes et al., 󰀱󰀹󰀹󰀰 [󰀱󰀷] I I A A U A van der Schoot et al., 󰀱󰀹󰀹󰀷 [󰀶] I I U A U AHarradine et al., 󰀱󰀹󰀹󰀸 [󰀵] A A A A A ALittle 󰀱󰀹󰀹󰀹 [󰀱󰀸] I I U I U UBuschang and Shulman 󰀲󰀰󰀰󰀳 [󰀱󰀹] A A U A N/A ANiedzielska 󰀲󰀰󰀰󰀵 [󰀲] I A U A A ASidlauskas and rakiniene 󰀲󰀰󰀰󰀶 [󰀳] I I U A N/A U 󰀱: sequence generation and concealed allocation; 󰀲: size and composition o the studied groups; 󰀳: blinding o participants, clinicians, and investigators; 󰀴:application o inclusion and exclusion criteria or subjects; 󰀵: descriptions o loss to ollow-up; 󰀶: adequacy o statistical analysis; A: adequate; U: unclear; I:inadequate. identi󿬁ed, and 󰀵 additional publications were added afer themanualsearchotheirreerences.Sevenarticlesthatwere󿬁rstselectedbythetitleorurtherevaluationcouldnotbeound,mainly because the year o publication was very old. Tus,a total number o 󰀱󰀲 controlled studies were included in thereview (able 󰀱) [󰀲, 󰀳, 󰀵, 󰀶, 󰀱󰀲–󰀱󰀹]. Te quality assessment o the selected studies revealed ahigh risk o bias in most o the articles, either because therelative items assessed were inadequate or because they wereunclearly described. Generally, quality tended to improve inthemorerecenttrialswithrespecttotheoldest,butalsomorecontemporarystudies obtaineda very low qualityevaluation.Te only article that scored “adequate” in all items was theone by Harradine et al. [󰀵]; detailed assessment is shown inable 󰀲.Othe󰀱󰀲studiesincludedinthereview,󰀹werelongitudi-nal studies (󰀳 o them prospective longitudinal and 󰀶 o themretrospective longitudinal based on patients’ records) and󰀳 were cross-sectional studies. Te prospective longitudinalstudiesanalyzedorthodonticallytreatedoruntreatedsubjectsdivided into different groups according to the presence orabsence in occlusion o the third molars. Te absence o thethird molars in unctional occlusion was due to extractions,impaction, or agenesis. One prospective longitudinal study did not divide the subjects into groups but used one side o the mandible as a control or the opposite side [󰀱󰀵]. Subjectswere ollowed up to detect the development o anteriortooth crowding or a de󿬁ned period o time [󰀲, 󰀵, 󰀱󰀵]. Te retrospective longitudinal studies were carried out retrievingthe clinical charts and dental models o orthodontically treated or untreated patients and assessing the associationbetween the presence or absence o the third molars and thedevelopment o anterior tooth crowding [󰀶, 󰀱󰀳, 󰀱󰀴, 󰀱󰀶–󰀱󰀸]. Cross-sectional studies analyzed orthodontically untreatedsubjects and correlated the presence or absence in occlusiono the third molars with the presence o anterior toothcrowding [󰀳, 󰀱󰀲, 󰀱󰀹]. Te presence o the third molars was not correlated withmore severe anterior tooth crowding in most o the studies[󰀳, 󰀵, 󰀶, 󰀱󰀲, 󰀱󰀴, 󰀱󰀷–󰀱󰀹]; however, some o them described  󰀴 Te Scienti󿬁c World Journal 󰁡󰁢󰁬󰁥 󰀳: Summary o included studies.Author Study groups Sample size ype o study  ResultsShanley 󰀱󰀹󰀶󰀲 [󰀱󰀲]Orthodontically untreated subjects withmandibular 󰀳rd molars:(󰀱) bilaterally impacted(󰀲) bilaterally erupted(󰀳) bilaterally congenitally absent󰀴󰀴 Cross-sectional No differencesbetween the groupsSheneman 󰀱󰀹󰀶󰀹 [󰀱󰀳]Orthodontically treated subjects withmandibular 󰀳rd molars:in occlusionuneruptedmissing󰀴󰀹 Retrospective/longitudinalMore stability inpatients withcongenital missing󰀳rd molars than inthose whose 󰀳rdmolars were presentKaplan 󰀱󰀹󰀷󰀴 [󰀱󰀴]Orthodontically treated subjects withmandibular 󰀳rd molars:(󰀱) bilaterally erupted into unction(󰀲) bilaterally impacted(󰀳) bilateral agenesis󰀷󰀵 Retrospective/longitudinal No differencesbetween the groupsLindqvist andTilander 󰀱󰀹󰀸󰀲 [󰀱󰀵]Orthodontically untreated subjects withmandibular 󰀳rd molar:Extracted on one sideRetained on the contralateral side󰀵󰀲 Prospective/longitudinalExtraction side had amore avorabledevelopment than thecontrol sideRichardson 󰀱󰀹󰀸󰀲 [󰀱󰀶]Orthodontically untreated subjects withmandibular 󰀳rd molars:(󰀱) Bilaterally impacted(󰀲) Bilaterally nonimpacted󰀵󰀱 Retrospective/longitudinalIndividuals whose 󰀳rdmolars becomeimpacted tend to havemore tooth crowdingAdes et al., 󰀱󰀹󰀹󰀰 [󰀱󰀷]Orthodontically treated subjects withmandibular 󰀳rd molars:(󰀱) impacted(󰀲) erupted into unction(󰀳) congenitally absent(󰀴) Extracted at least 󰀱󰀰 years earlier󰀹󰀷 Retrospective/longitudinal No differences amongthe groups van der Schoot et al.,󰀱󰀹󰀹󰀷 [󰀶]Orthodontically treated subjects with 󰀳rdmolars:(󰀱) erupted(󰀲) nonerupted(󰀳) extracted(󰀴) congenitally absent󰀹󰀹 Retrospective/longitudinal No differences amongthe groupsHarradine et al., 󰀱󰀹󰀹󰀸[󰀵]Orthodontically treated subjects with 󰀳rdmolars:(󰀱) extracted(󰀲) nonextracted󰀱󰀶󰀴 Prospective/longitudinal No differencesbetween the groupsLittle 󰀱󰀹󰀹󰀹 [󰀱󰀸]Orthodontically treated subjects withmandibular 󰀳rd molars:(󰀱) impacted(󰀲) erupted(󰀳) extracted(󰀴) agenesis󰀹󰀷 Retrospective/longitudinal No differencesbetween the groupsBuschang andShulman 󰀲󰀰󰀰󰀳 [󰀱󰀹]Random sample o orthodontically untreated subjects as part o the TirdNational Health and NutritionExamination Survey 󰀹.󰀰󰀴󰀴 Cross-sectionalErupted 󰀳rd molarsnot associated withincreased toothcrowdingNiedzielska 󰀲󰀰󰀰󰀵 [󰀲]Orthodontically untreated subjects withmandibular 󰀳rd molars:(󰀱) bilaterally extracted(󰀲) unilaterally extracted(󰀳) bilaterally retained(󰀴) unilaterally retained󰀴󰀷 Prospective/longitudinalRetained 󰀳rd molarsassociated withincreased toothcrowding in relationto Ganss ratio
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