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J Appl Oral Sci.

ABSTRACT

www.scielo.br/jaoshttp://dx.doi.org/10.1590/1678-775720130472

Postretention stability after orthodontic closureof maxillary interincisor diastemas

Juliana Fernandes de MORAIS 1, Marcos Roberto de FREITAS 1, Karina Maria Salvatore de FREITAS 2, GuilhermeJANSON 1, Nuria CASTELLO BRANCO 2

1- Department of Pediatric Dentistry, Orthodontics and Community Health, Bauru School of Dentistry, University of So Paulo, Bauru, SP, Brazil.2- Private practice, Bauru, SP, Brazil.

Corresponding address: Juliana Fernandes de Morais - Departamento de Odontopediatria, Ortodontia e Sade Coletiva - Faculdade de Odontologiade Bauru Universidade de So Paulo - Alameda Octvio Pinheiro Brisolla 9-75 - Bauru - SP - 17012-901 - Brazil - Phone/Fax: 55 14 32342650 - e-mail:

[email protected]

Submitted: September 8, 2013 - Modi cation: February 17, 2014 - Accepted: March 15, 2014

Anterior spaces may interfere with smile attractiveness and compromise dentofacialharmony. They are among the most frequent reasons why patients seek orthodontictreatment. However, midline diastema is commonly cited as a malocclusion with highrelapse incidence by orthodontists. Objectives: This study aimed to evaluate the stability ofmaxillary interincisor diastemas closure and the association of their relapse and interincisorwidth, overjet, overbite and root parallelism. Material and Methods: Sample comprised30 patients with at least a pretreatment midline diastema of 0.5 mm or greater aftereruption of the maxillary permanent canines. Dental casts and panoramic radiographswere taken at pretreatment, posttreatment and postretention. Results: Before treatment,midline diastema width was 1.52 mm (SD=0.88) and right and left lateral diastema widths

were 0.55 mm (SD=0.56) and 0.57 mm (SD=0.53), respectively. According to repeatedmeasures analysis of variance, only midline diastema demonstrated signi cant relapse.In the overall sample the average relapse of midline diastema was 0.49 mm (SD=0.66),whilst the unstable patients showed a mean space reopening of 0.78 mm (SD=0.66).Diastema closure in the area between central and lateral incisors showed great stability.Multivariate correlation tests showed that only initial diastema width (=0.60) and relapseof overjet (=0.39) presented association with relapse of midline diastema. Conclusions:Midline diastema relapse was statistically signi cant and occurred in 60% of the sample,while lateral diastemas closure remained stable after treatment. Only initial diastema widthand overjet relapse showed association with relapse of midline diastema. There was noassociation between relapse of interincisor diastema and root parallelism.

Keywords: Diastema. Relapse. Root tip. Corrective orthodontics.

INTRODUCTION

Anter ior d ias temas may interfere wi thsmile attractiveness, compromise dentofacialharmony 7,8,24 , and provoke dyslalias 5. Since they areeasily visible, anterior spaces are one of the mostimportant reasons why patients look for long-lastingstable treatment outcomes 1.

In the primary and mixed dentitions, anteriorspaces are common and considered as normal. In

the permanent dentition, reported incidence rangesfrom 1.7% to 38% 11,13,17,19,23 in different populations.This incidence is higher in black individuals than

among white or yellow racial groups 11,13,17 .Midline diastema is frequently cited as a

malocclusion with high relapse incidence byorthodontists 2,4,15 . Some have suggested thatits recurrence is associated with initial diastemawidth 18 , inadequate root parallelism at the endof treatment 4,15 , sucking habits or imbalancedmusculature 4,15 , abnormal labial frenum 4 , andintermaxillary osseous cleft 18,21 . An increase inoverjet and overbite as the diastema reopens was

also mentioned21

.However, information on stability followingmaxillary diastema closure is limited and the


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majority of reports consists of case reports andauthors opinion. The rare follow-up evaluationson maxillary diastema treatment stability havedivergent results. Edwards 4 (1977) found diastemarelapse on 84% of the sample (recurrent diastemawidth larger than 0.5 mm), and showed a strongcorrelation between labial frenum and diastemarelapse. Contrarily, other studies 18,21 demonstratedthat relapse occurred at about one third of thesubjects, but recurrent diastema widths were near0.6 mm.

To date, no study has evaluated maxillarydiastema relapse between central and lateralincisors, or the association between root parallelismand diastema closure stability.

The objectives of this study were: (1) to describethe frequency and severity of midline and lateralinterincisor diastema relapses in patients withdiastema before treatment; and (2) to identifytreatment and posttreatment factors (interincisorwidths, overjet, overbite and root parallelism) whichcould be associated to space reopening.

MATERIAL AND METHODS

A minimum sample size of 20 individuals wasproposed for 80% power at a signi cance level of0.05 to demonstrate a true difference of 0.4 mmin the diastema width, with 0.6 mm of estimatedstandard deviation, according to Sullivan, et al. 24

(2011).Ethical Committee approval was obtained fromthe Research Ethics Committee of Bauru School ofDentistry, University of So Paulo, to perform thisretrospective study.

Thirty subjects were selected (17 female; 13male) with Class I (18 subjects) and Class II (12subjects) malocclusions obtained from the lesof 4,331 patients treated in the OrthodonticsDepartment at Bauru School of Dentistry,University of So Paulo. The subjects were treatednonextraction with standard edgewise appliances(0.022x0.028-inch) by graduate students. Inclusion

criteria were patients presenting with at least amaxillary midline diastema equal to or greaterthan 0.5 mm after maxillary canines full eruption.Subjects with missing anterior teeth, periodontaldisease with bone loss, generalized microdontia,maxillary pathologies, mesiodens , diastema closureby a non-orthodontic method, post-orthodonticrestoration of maxillary anterior teeth resulting inincrease in mesiodistal width, and patients withdeteriorated or missing dental casts or radiographswere excluded. After treatment, patients worea Hawley plate in the maxillary arch. Patientswith maxillary fixed retention were excluded.Pretreatment (T1), posttreatment (T2) andpostretention (T3) mean ages were 12.94 years(SD 1.27), 15.32 years (SD 1.61), and 22.38 (SD3.90), respectively. Dental casts and panoramicradiographs taken at T1, T2 and T3 were used.Periapical radiographs taken at T1 and T2 were alsoevaluated. Treatment changes were calculated asT2-T1, and postretention changes were calculatedas T3-T2. Diastema relapse occurred when diastemawidth at T3-T2 was greater than zero.

Dental cast analysisAll dental cast measurements were made with

a 0.01 mm precision digital caliper (Mitutoyo,Kawasaki, Kanagawa, Japan) at T1, T2 and T3. Theassessed variables were diastema width, overjetand overbite. To measure these variables, the

following concepts were considered:Diastema widths (A, B, C): The smallest distancebetween adjacent teeth at the level of gum papilla(Figure 1).

Overjet (OJ): Distance from the labial aspect ofthe medium point, on mesiodistal direction, of thecentral maxillary incisor incisal edge to the labialsurface of the central mandibular incisor.

Overbite (OB): Distance between the incisaledges of maxillary and mandibular central incisors.

Values of overbite and overjet were obtainedfrom right and left sides and averaged.

Figure 1- (1A) Sites where diastema widths were measured. A: Right lateral diastema; B: midline diastema; C: Left lateraldiastema. (1B) Space width measurement using a round digital caliper

Postretention stability after orthodontic closure of maxillary interincisor diastemas


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Radiographic analysisPanoramic radiographs were taken at T1, T2, and

T3 under standard conditions, with the Frankfurthorizontal plane parallel to oor and the facialmidline plane in a vertical position, by means of theRotograph Plus (Villa Sistemi Medicali, Buccinasco,Milan, Italy) which produces a magni cation factorclose to 25%.

Panoramic radiographs were traced using a 0.5mm pencil on a sheet of acetate paper (14x21cm) placed over the radiographic lm. The inferioroutlines of the zygomatic processes of the maxillaand the contours of the maxillary incisors weretraced. A horizontal reference line (IZP line) wasused, passing through the most inferior point of theright and left zygomatic processes of maxilla (Figure2) 10 . Maxillary incisor angulations were measured,using the following variables: RLI (angle betweenthe long axis of the right maxillary lateral incisorand the IZP line), RCI (angle between the longaxis of the right maxillary central incisor and theIZP line), LCI (angle between the long axis of theleft maxillary central incisor and the IZP line), LLI(angle between the long axis of the left maxillarylateral incisor and the IZP line). Interincisor angleswere assessed by measuring the angles (A, B,C) between adjacent maxillary incisors. Figure2 describes the anatomical structures, lines andangles used in the panoramic radiographic analysis.

Intermaxillary osseous cleft was evaluated by

comparing periapical radiographs taken at T1 andT2, and was considered present when a v-shapedradiolucency in crestal bone between the centralincisors was found in the initial and nal treatmentradiographs 18,21 .

Error studyAfte r a month in te rva l f rom the f i r s t

measurement, 30 randomly selected dental castsand 30 panoramic radiographs were reevaluatedby the same examiner (JFM). The casual error

was calculated according to Dahlbergs formula(S 2=d 2 /2n) 3, where S2 is the error variance andd is the difference between two determinationsof the same variable. The systematic errors wereevaluated with dependent t tests at P


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J Appl Oral Sci.

changes during and after treatment, despite theangle between central incisors (B) diverged about3 degrees with treatment (Table 1).

Since only midline diastema (B) demonstrated

signi cant relapse, correlation of this diastemarelapse and its possible associated variables wasexclusively analyzed. Midline diastema relapseshowed statistically signi cant correlation withinitial diastema widths (A, B, C T1), nal rightlateral diastema width (A - T2), and postretentionchange of overjet (Table 2). Thus, these variableswere selected to be included in a multiple regressionanalysis to assess the level of relationship betweenmidline diastema relapse and the selected variables.

Eight subjects showed intermaxillary osseouscleft. Initial midline diastema width and its relapsewere larger in these patients than in subjects withnormal crestal bone (Table 3). These findingssuggest that intermaxillary osseous cleft could bea predisposing factor for midline diastema relapse.

Therefore, this variable was also selected to beincluded in the multiple regression analysis.

Multivariate correlation tests showed thatonly initial diastema width (=0.60) and relapse

of overjet (=0.39) presented association withrelapse of midline diastema. Association betweenrelapse of midline diastema and root parallelismor intermaxillary osseous cleft was not observed(Table 4).

DISCUSSION

Only midline diastema showed statisticallysigni cant relapse (Table 1) and occurred in 60%of patients. However, the diastema width at T3 wassigni cantly smaller than its distance at T1. Thisresult was also observed by most authors 4,18,21,22 ,which means that there is only partial relapse.Contrarily to our results, a previous study 18 showed stability of diastema closure in 75% of the

Variables Normal crestal bone (N=22) V-shaped crestal bone (N=8) P

Unit Mean SD Mean SD

B (T1) mm 1.25 0.6 2.25 1.15 0.004*B (T3-T2) mm 0.24 0.41 1.02 0.89 0.003*

RCI (T1) 90.91 3.07 90.12 3.91 0.569

RCI (T2) 89.43 3.79 89.00 1.83 0.761

RCI (T3) 88.77 3.29 90.31 3.29 0.267

RCI (T3-T2) -0.66 3.04 -1.52 3.42 0.14

LCI (T1) 89.14 3.75 89.87 4.51 0.655

LCI (T2) 87.45 3.47 88.31 4.65 0.589

LCI (T3) 87.77 3.57 87.38 3.06 0.782

LCI (T3-T2) 0.32 4.17 -0.94 3.75 0.461

B (T1) -0.43 4.28 0.1 5.57 0.823

B (T2) -3.09 5.71 -2.69 5.06 0.862

B (T3) -3.45 5.9 -2.31 4.03 0.618

B (T3-T2) -0.36 5.43 0.38 5.04 0.74

*Statistically signi cant at P


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patients. One reason for this divergence may be thedifference between sample inclusion criteria, sincethey included patients who were still using xed orremovable retention and the mean pretreatmentspace width was 1.22 mm. In our study, the meanpretreatment midline diastema width was slightlylarger (1.52 mm) and the patients were at least 1.8years out of retention, with an average postretentionperiod of 5.6 years. Sullivan, et al. 21 (1996) foundspace closure stability in 66% of the patients, andthe sample selection criteria were similar to ours,except for the minimum postretention time thatwas 1 year. Analyzing the relapse amount, moststudies 18,21,22 also showed small space reopening.On the other hand, Edwards 4 (1977) demonstratedgreater relapse, between 2.4 and 2.7 mm in 84%of the patients, in a sample consisting of patientswith an average pretreatment midline diastema of3.2 mm (minimum 2 mm). Therefore, the initialdiastema width might explain the discrepancybetween our ndings and Edwards 4. Unlike midlinediastema area, lateral space closure appearedto be stable (Table 1). Although lateral spacerelapse had not been investigated yet, it waspreviously observed that, when relapse occurs,even in patients presenting generalized anteriorspacing before treatment, it is usually located atthe midline 21 . Whereas only 22 patients presentedlateral diastemas before treatment, pos t-hoc power analysis calculation showed that a sample

composed of 18 subjects provides 91.4% powerat a signi cance level of 0.05 to detect a minimumdifference of 0.1 mm, with standard deviation 0.12.

Regarding the contributing factors for midlinediastema relapse, spaces A, B, and C at T1, spaceA at T2, and posttreatment changes (T3-T2) inOJ showed signi cant association when tested byunivariate correlation test (Table 2). On the otherhand, no association between midline diastemarelapse and root angulations or parallelism werefound.

It is suggested that root parallelism in uencesthe stability after orthodontic closure of anteriordiastema 4,15 . However, the present results did notcon rm any in uence of root tip on space relapse(Table 2) and so did the ndings presented in aprevious study 14 . Additionally, it was found thatthe slight mesial crown tip of the maxillary incisorsoccurred during the space closure remained stableposttreatment 14 .

An intermaxillary osseous cleft, which is alsoa contributing factor for diastema relapse 4,20 waspresent in eight patients. These patients showedlarger initial midline diastema and greater relapsethan those with normal intermaxillary crestal bone

(Table 3). Nevertheless, multivariate analysisdemonstrated that there was no associationbetween intermaxillary osseous cleft and diastema

reopening (Table 4). Therefore, it seems that theactual contributing factor for the greater midlinediastema relapse in the osseous cleft group was itslarger width at the pretreatment stage.

According to the multivariate analysis, initialdiastema width (B T1) was the only pretreatmentsigni cant factor associated to its relapse (B T3-T2)(Table 4). This association was also supported byothers 18,22 and con rmed by the great reopeningtendency found in Edwards sample 4. Conversely,spaces between lateral and central incisors showedno correlation with midline diastema relapse.Previous results showing no association betweendiastema reopening and initial generalized anteriorspacing 21 support this nding. Contrarily, otherstudy veri ed that generalized spacing arches weremore likely to suffer midline diastema recurrence 18 .

Among the treatment and posttreatment factors,only OJ T3-T2 presented signi cant associationwith diastema relapse (Table 4). As the overjetincreased, so did the midline diastema. Musclefunction and relapse of Class II malocclusion mayexplain this association. Forward tongue postureinduces incisor proclination, increase in arch lengthand anterior space opening. If tongue pressureis stronger on the maxillary incisors, the overjetincreases. Camouflage orthodontic treatmentof Class II division 1 malocclusion usually isreached by maxillary incisor retroclination andgreat overjet decrease. Therefore, patients with

this malocclusion might be more prone to relapseof overjet and, consequently, diastema relapse.Association between diastema reopening and incisorproclination was previously determined 21 .

Treatment nishing with interincisor spacesremaining is another factor that might havein uenced diastema relapse in this study, becauseeight patients nished without complete closureof anterior spaces. This could induce tongueabnormal pressure 5 and, secondarily, provokeanterior space enlargement. Studies focusing onClass II malocclusion, on muscle function, andon treatment nishing as contributing factors fordiastema relapse may be of interest in the future.

Some investigators have suggested that labialfrenum may contribute to diastema development 2,4,8 .Due to the retrospective follow-up study design,information about frenum anatomy would beavailable on clinical charts, photographies, orstudy models. These methods could be consideredquestionable 21 , and a previous study found noassociation between frequency of relapse andabnormal frenum 18 . Therefore, assessment of thein uence of labial frenum on diastema relapse wasnot performed.

Image magnification and distortion limitdimensional accuracy in panoramic radiography 9.This is more critical for linear measurements.

Postretention stability after orthodontic closure of maxillary interincisor diastemas


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Contrarily, angular measurements in panoramicradiography showed less distortion 6,12 , especiallyin the anterior region 16 . Panoramic radiographywas used because it is a low-dose radiographictechnique which provides a comprehensive view ofthe entire maxillomandibular complex in a single

lm. Additionally, it is routinely required in theorthodontic practice and its use for this researchavoided extra radiation exposure of the patientswho comprised this sample.

This study showed that midline diastemaclosure is highly unstable. The amount of relapseis proportional to its pretreatment width andoccurs associated with increase in the overjet.It is suggested lifetime wear of a well-adaptedmaxillary xed retainer on any patients with midlinediastema, especially in cases with initial largespaces and/or muscle unbalance.

CONCLUSIONS

Midline diastema relapse was statisticallysigni cant and occurred in 60% of the sample, whilelateral diastemas showed great stability.

Only initial diastema severity width and overjetrelapse showed association with relapse of midlinediastema.

There was no association between relapse ofinterincisor diastemas and root parallelism.

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stability of spaced dentition. Angle Orthod. 1985;55:321-8.20- Stubley R. The in uence of transseptal bers on incisor positionand diastema formation. Am J Orthod. 1976;70:645-62.21- Sullivan TC, Turpin DL, Artun J. A postretention study ofpatients presenting with a maxillary median diastema. AngleOrthod. 1996;66:131-8.22- Surbeck BT, Artun J, Hawkins NR, Leroux B. Associationsbetween initial, posttreatment, and postretention alignmentof maxillary anterior teeth. Am J Orthod Dentofacial Orthop.1998;113:186-95.23- Taylor JE. Clinical observations relating to the normaland abnormal frenum labii superioris. Am J Orthod Oral Surg1939;25:646-50.24- Witt M, Flores-Mir C. Laypeople's preferences regardingfrontal dentofacial esthetics: periodontal factors. J Am Dent Assoc.

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MORAIS JF, FREITAS MR, FREITAS KMS, JANSON G, CASTELLO BRANCO N

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