Stability of Anterior Open-bite Extraction

ORIGINAL ARTICLE

Stability of anterior open-bite extractionand nonextraction treatment in thepermanent dentitionGuilherme Janson,a Fabrício Pinelli Valarelli,b Rejane Targino Soares Beltrão,b Marcos Roberto de Freitas,c

and José Fernando Castanha Henriquesc

Bauru, São Paulo, Brazil

Introduction: Although stability of anterior open-bite extraction and nonextraction treatment has beeninvestigated, results suggesting that extraction treatment is more stable have not been confronted.Therefore, the purpose of this cephalometric study was to compare the long-term stability of anterioropen-bite extraction and nonextraction treatment in the permanent dentition. Methods: Group 1 consistedof 21 patients treated without extractions, and group 2 included 31 patients treated with extractions who hadorthodontic treatment with fixed appliances. Cephalometric headplates were obtained at pretreatment,posttreatment, and postretention. The groups were compared at these 3 times and during the treatment andposttreatment periods with independent t tests. The number of patients with a clinically significant relapse ofthe open bite was compared between the groups with chi-square tests. Results: During treatment, themaxillary incisors had greater retraction amounts, and the mandibular incisors had greater retraction andlingual tipping, and less extrusion in the extraction group. In the posttreatment period, the extraction groupdemonstrated statistically greater stability of the overbite. However, there was no statistically significantdifference in the percentages of patients with clinically significant relapse of the open bite between thegroups. Conclusion: Open-bite extraction treatment has greater stability of the overbite than open-bite
nonextraction treatment. (Am J Orthod Dentofacial Orthop 2006;129:768-74)
Stability of open-bite malocclusion correction inthe permanent dentition is the major concern inthe orthodontic treatment of this problem.1-8

Several authors investigated the stability of open-bitemalocclusion correction without differentiating betweenextraction and nonextraction treatment approaches.1,2,9

More recently, we conducted 2 studies that separatelyinvestigated the stability of nonextraction10 and extrac-tion11 treatment, and the results pointed toward greaterstability of extraction treatment. However, these resultshave not been directly confronted to elucidate whetherthe stability of extraction treatment is significantlygreater than that of the nonextraction approach. There-fore, our objective was to test the following nullhypothesis: stability of anterior open-bite treatment in

From the Department of Orthodontics, Bauru Dental School, University of SãoPaulo, Bauru, São Paulo, Brazil.aAssociate professor.bGraduate student.cProfessor.Supported by FAPESP (processes 00/00603-7 and 00/01199-5).Reprint requests to: Dr Guilherme Janson, Department of Orthodontics, BauruDental School, University of São Paulo, Alameda Octávio Pinheiro Brisolla9-75, Bauru, SP, 17012-901, Brazil; e-mail, [email protected], July 2004; revised and accepted, November 2004.0889-5406/$32.00Copyright © 2006 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2004.11.031
768

the permanent dentition with and without extractions issimilar in the long term.

MATERIAL AND METHODS

The sample comprised 2 patient groups of bothsexes from the orthodontic department at Bauru DentalSchool, University of São Paulo. Group 1 consisted of21 subjects (16 female, 5 male) with Class I malocclu-sions and a mean age of 12.4 years (range, 10.8-16.3years) at pretreatment (T1) treated without extractions.Thirteen patients underwent maxillary expansion witheither hyrax or Haas appliances to correct posteriorcrossbites or to provide space in the maxillary arch. Themean treatment time was 2.4 years (range, 1.1-4.1years) between T1 and posttreatment (T2). The meanposttreatment period for this group was 5.22 years(range, 3.08-9.33 years). Group 2 consisted of 31patients (23 female, 8 male) with a mean age of 13.22years at T1 treated with extractions. The mean treat-ment time was 2.46 years (range, 1.0-4.25 years)between T1 and T2. The mean posttreatment period forthis group was 8.35 years (range, 5.25-23.67 years).Sixteen patients had Angle Class I malocclusions, and15 had Class II malocclusions. Twenty-four weretreated with 4 first premolar extractions, 2 were treated
with 4 second premolar extractions, 1 was treated with

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Janson et al 769

2 second maxillary premolar and 2 first mandibularpremolar extractions, and 4 were treated with 2 maxil-lary premolar extractions. Seven underwent maxillaryexpansion with either hyrax or Haas appliances tocorrect posterior crossbites or to provide space in themaxillary arch. The primary selection criterion for bothgroups was an initial anterior open bite of at least 1mm. Additional criteria included all maxillary andmandibular teeth up to the second molars, and treat-ment with edgewise appliances, associated with ante-rior vertical elastics.

Treatment was conducted with the standard edge-wise technique, which is characterized by the use of0.022 x 0.028-in conventional brackets. For levelingand alignment, the usual wire sequence begins with0.015-in twist-flex or 0.016-in nitinol wire, followed by0.016-, 0.018-, and 0.020-in stainless steel round wires.In group 2, anterior retraction was accomplished by0.019 x 0.025-in or 0.021 x 0.025-in rectangular wires,and extraoral headgear and lip bumper to reinforceanchorage for the maxillary and mandibular teeth,respectively, when necessary. Extraoral headgear wasused either to help in correcting the Class II relationshipor to reinforce anchorage. Nineteen patients used high-pull, 10 used cervical-pull, and 2 did not use headgear.In both groups, detailing of tooth positioning andfinishing procedures were accomplished by 0.019 x0.025-in or 0.021 x 0.025-in rectangular wires and0.018-in round wires, respectively. Intermaxillary elas-tics (3/16 inch) were also used to help close the anterioropen bite. No additional auxiliaries were used tocontrol the vertical dimension. After the active treat-ment period, a Hawley retainer was used in the maxil-lary arch and a bonded 3 x 3 retainer in the mandibulararch. Myofunctional therapy was recommended to thepatients to correct tongue posture and function.

Lateral cephalograms of both groups were obtainedfrom each subject at 3 stages: T1, T2, and after meanfollow-up periods of 5.22 years for group 1 and 8.35years for group 2 (T3). Because of the long time spanbetween the evaluation stages, the lateral headfilmswere obtained with various x-ray machines, which pro-duced different magnification factors of the images—between 6% and 10.94%.

The cephalometric tracings and landmark identifi-cation were performed on acetate paper by a differentinvestigator (F.P.V. and R.T.S.B.) for each group andthen digitized with a DT-11 digitizer (Houston Instru-ments, Austin, Tex) and a Numonics AccuGrid XNT(model A30TLF digitizer, Numonics, Montgomer-yville, Pa) for groups 1 and 2, respectively (Figs 1 and2, Table I). These data were stored on a computer and
analyzed with Dentofacial Planner 7.02 (Dentofacial
Planner Software, Toronto, Ontario, Canada), whichcorrected the image magnification factors of the groups.

Because mandibular crowding is an important fac-tor in the extraction decision, it was calculated in bothgroups to help in understanding the 2 treatment plans.Mandibular crowding of the initial dental study modelswas calculated as the difference between arch length(circumference, from left to right first molars) and thesum of tooth widths from first molar to first molar inmillimeters. In a well-aligned arch, arch length is equalto the sum of the tooth widths. Negative values indi-

12

34

5

6

7

8 9

1011

Fig 1. Dental cephalometric variables. Maxillary: 1,Mx1.PP: maxillary incisor long axis to palatal planeangle; 2, Mx1.NA: maxillary incisor long axis to NAangle; 3, Mx1-NA: distance between most anterior pointof crown of maxillary incisor and NA line; 4, Mx1-PP:perpendicular distance between incisal edge of maxil-lary central incisor and palatal plane (maxillary incisordentoalveolar height); 5, Mx6-PP: perpendicular dis-tance between mesial cusp of maxillary first molar andpalatal plane. Mandibular: 6, Md1.NB: mandibular inci-sor long axis to NB line angle; 7, Md1-NB: distancebetween most anterior point of crown of mandibularincisor and NB line; 8, IMPA: incisor mandibular planeangle; 9, Md1-MP: perpendicular distance betweenincisal edge of mandibular incisor and mandibular plane(mandibular incisor dentoalveolar height); 10, Md6-MP:perpendicular distance between mesial cusp of man-dibular first molar and mandibular plane. Maxilloman-dibular: 11, Overbite: distance between incisal edges ofmaxillary and mandibular central incisors, perpendicularto functional occlusal plane (also magnified in Fig 2).

cated crowding.12

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770 Janson et al

Because the groups were traced and digitized bydifferent examiners, an interexaminer error study had tomade. Therefore, 15 randomly selected radiographs wereretraced, redigitized, and remeasured by the 2 examiners.The interexaminer casual error was calculated accord-ing to Dahlberg’s formula (Se2 � �d2/2n),13 where Se2

is the error variance and d is the difference between the2 determinations of the same variable. The systematicerror was evaluated with dependent t test, at P �05.

Statistical analyses

To apply the t test, normal distribution of thesamples was verified with the Kolmogorov-Smirnovtest. The results showed that all variables were nor-mally distributed in both groups. Therefore, indepen-dent t tests were used for comparison of the groups atT1, T2, and T3, and between the changes duringtreatment (T2-T1) and posttreatment (T3-T2) of thegroups. The results were regarded as significant at

Fig 2. Overbite measurement (magnified). Overbite:distance between incisal edges of maxillary and man-dibular central incisors, perpendicular to functional oc-clusal plane.

Table I. Skeletal cephalometric variables

Maxillary1. SNA: SN to NA angle

Mandibular2. SNB: SN to NB angle

Maxillomandibular3. ANB: NA to NB angle

Growth pattern4. FMA: Frankfurt mandibular plane angle5. SN.GoGn: SN to GoGn angle6. LAFH: Lower anterior face height7. SN.PP: SN to palatal plane angle8. SN.OP: SN to occlusal plane angle

P �.05. These analyses were performed with Statistica

software (Statistica for Windows 6.0, Statsoft, Tulsa,Okla).

A clinically significant relapse of anterior open bitewas defined as a negative overbite between the maxil-lary and mandibular incisors at T3. Therefore, toestablish a clinical parameter for the probability ofopen-bite correction stability, the percentages of pa-tients with and without clinically significant relapseswere calculated from the total patients in each group.The percentages of patients with clinically significantrelapses in each group were compared with the chi-square test.

RESULTS

The casual errors were between 0.27 (Mx6-PP) and1.65 (SN.OP), with only 2 variables above 1°. Of the 19variables, only the following 4 had interexaminer sys-tematic errors: SNB angle, FMA, SN-GoGn, and Mx1-PP. Therefore, the results for these variables should beinterpreted with caution. Group 1 had less crowding,posttreament time, and open bite than group 2 at T1. Atthis stage, group 2 had a slightly more accentuatedvertical pattern and more procumbent maxillary andmandibular incisors (Table II). During the treatmentperiod, the maxillary incisors had greater retraction,and the mandibular incisors had greater retraction andlingual tipping in group 2 than in group 1. In the sameperiod, the mandibular incisors had greater extrusion ingroup 1 than in group 2 (Table III). In the posttreatmentstage, the slightly more vertical pattern of group 2manifested again, and the mandibular incisors endedmore upright in this group (Table IV). During theposttreatment period, group 1 showed greater max-illary and mandibular anterior development, andgreater overbite decrease than group 2 (Table V). Inthe postretention stage, the mandible was shorter ingroup 2, which again continued to exhibit a slightlymore vertical pattern. The mandibular incisors re-mained more upright, and the amount of overbite wasalso greater in group 2. There was no statisticallysignificant difference in the percentages of patientswith clinically significant relapse between the groups(Table VI).

DISCUSSION

The sample sizes of 21 and 31 patients in groups 1and 2, respectively, can be considered satisfactorybecause of the rigid criteria of long-term posttreatmenttime for sample selection. They were selected from thefiles of the orthodontic department, which had morethan 2000 treated and documented patients, as pointedout previously.11 There might be some concern about
group compatibility because group 2 included 15 Angle


Janson et al 771

Class II malocclusions, whereas group 1 had only ClassI patients. However, behavior of the overbite is similarin both malocclusions with time.14-16 In addition, thereis no evidence that stability of open-bite correction inClass I malocclusions is different than in Class IImalocclusions; previous studies have not differentiatedthese 2 malocclusion types in their samples.1-3,17

The subjects in group 2 had significantly greatercrowding, more accentuated vertical pattern (SN.OP),more protruded maxillary and mandibular incisors, andgreater amounts of open bite than those in group 1(Table II). These factors contributed to performingextraction treatment in this group, as would beexpected.1,9,18-21 The posttreatment time of group 2was also longer than group 1. Therefore, it could becriticized that these groups could not be compared.However, a more accentuated vertical pattern22,23 and

Table II. Results of compatibility tests between groups1 and 2 at T1 for cephalometric variables

Variable

Group 1n � 21

Group 2n � 31

PMean SD Mean SD

Initial crowding (mm) 0.42 1.90 �3.54 2.11 .000*Initial age (y) 12.46 1.51 13.35 1.98 .085Treatment time (y) 2.29 0.66 2.32 0.69 .871Posttreatment age (y) 14.75 1.57 15.68 2.19 .102Posttreatment time (y) 5.22 1.55 8.35 5.14 .009*Maxillary component

SNA angle (°) 80.30 3.91 80.14 3.97 .884Mandibular component

SNB angle (°) 77.44 3.63 76.38 3.60 .305Maxillomandibular relationship

ANB angle (°) 2.87 2.32 3.74 2.18 .174Growth pattern

FMA (°) 29.78 5.83 30.55 5.05 .613SN.PP (°) 7.46 2.33 7.71 3.30 .758SN.OP (°) 16.84 6.37 20.63 4.49 .015*SN.GoGn (°) 36.94 5.66 39.10 4.16 .118LAFH (mm) 67.75 5.28 69.08 5.22 .373

Maxillary dentoalveolar componentMx1.NA (°) 28.40 4.28 29.55 5.67 .431Mx1-NA (mm) 5.98 1.89 7.57 2.45 .015*Mx1.PP (°) 116.15 6.13 117.41 6.98 .506Mx1-PP (mm) 26.51 2.62 30.13 15.29 .290Mx6-PP (mm) 23.26 2.51 23.93 2.47 .340

Mandibular dentoalveolar componentMd1.NB (°) 28.25 6.64 28.17 5.48 .959Md1-NB (mm) 5.45 2.21 6.52 1.59 .047*IMPA (°) 91.43 7.76 90.64 6.10 .683Md1-MP (mm) 38.26 2.93 38.47 2.70 .797Md6-MP (mm) 29.61 3.26 29.60 2.06 .988

Dental relationshipsOverbite (mm) �1.75 0.66 �2.73 1.80 .021*

*Statistically significant.

especially the greater amount of open bite and longer

posttreatment time of group 2 would tend to accentuatethe open-bite relapse of this group.2,22-25 Consequently,because the results showed otherwise, as will be furtherdiscussed, these dissimilarities provide additional sup-port for our results. It is exactly because group 2, whichhad the greatest tendency for greater relapse of the openbite, had a smaller relapse than group 1 that thiscomparison can be sustained. If the opposite hadoccurred—ie, group 1 had a smaller relapse than group2—the results could be questioned. It is obvious thatwhenever 2 groups are being compared, they must beideally similar for every characteristic. However, in thiscomparison, group 2 had all the expected factors thatcould contribute to a greater open-bite relapse ten-dency. Nevertheless, the results were contrary to theseexpectations, which mean that open-bite extractiontreatment provides greater stability of the open-bitecorrection. Still, one could argue that the longer post-treatment time of group 2 included a 3.13-year post-growth period that could favor its greater stability ofopen-bite correction. However, because the groups had

Table III. Comparison of treatment changes betweengroups (t tests)

Variable

Group 1n � 21

Group 2n � 31

PMean SD Mean SD

Maxillary componentSNA angle (°) 0.32 1.68 �0.41 2.19 .196

Mandibular componentSNB angle (°) 0.56 1.18 �0.05 1.39 .102

Maxillomandibular relationshipANB angle (°) �0.27 1.43 �0.32 2.10 .913

Growth patternFMA (°) �0.29 1.82 0.91 3.70 .172SN.PP (°) �0.22 1.56 0.25 2.42 .425SN.OP (°) �2.91 5.33 �3.57 3.15 .582SN.GoGn (°) �0.50 1.81 0.35 1.63 .080LAFH (mm) 2.45 2.59 2.30 3.26 .863

Maxillary dentoalveolar componentMx1.NA (°) �4.17 4.83 �6.31 8.05 .280Mx1-NA (mm) �0.68 2.20 �3.52 3.34 .001*Mx1.PP (°) �4.07 4.74 �8.08 9.23 .073Mx1-PP (mm) 2.81 1.57 2.57 2.27 .670Mx6-PP (mm) 1.50 1.68 1.78 1.91 .584

Mandibular dentoalveolar componentMd1.NB (°) �1.12 4.88 �5.06 3.78 .001*Md1-NB (mm) 0.59 1.59 �0.86 1.33 .000*IMPA (°) �1.11 4.91 �5.44 4.15 .001*Md1-MP (mm) 2.70 1.38 1.68 1.56 .018*Md6-MP (mm) 1.30 1.32 1.82 1.39 .183

Dental relationshipsOverbite (mm) 3.19 0.72 3.83 1.94 .156


similar initial ages and were treated for similar time


772 Janson et al

periods, group 2 was observed during a similar 5.22-year growth period as group 1 and during an additional3.13-year nongrowing period. It is known that, gener-ally, the greater the posttreatment time, the greater thetendency for relapse of orthodontic corrections26-29 andespecially the greater the tendency for open-bite re-lapse.2,22-25 Through this rationale, the longer posttreat-ment time of group 2 would tend to cause greateropen-bite relapse; this is contrary to our findings andtherefore provides additional support for them. Crowd-ing was not evaluated and compared between thegroups at T2 and T3 because it is not correlated toopen-bite relapse.1,12,22

To minimize open-bite relapse, myofunctionaltherapy is usually recommended after orthodontictreatment.30-33 The treatment protocol of the groupsincluded myofunctional therapy after treatment. How-ever, because this was a retrospective study, it couldnot be ascertained from the clinical charts that allpatients in both groups followed the recommenda-tions and underwent such therapy. Because the prob-ability of patients who had myofunctional therapy

Table IV. Comparison of groups at T2 (t tests)

Variable

Group 1n � 21

Group 2n � 31

PMean SD Mean SD

Maxillary componentSNA angle (°) 80.62 3.49 79.72 3.30 .348

Mandibular componentSNB angle (°) 78.00 3.50 76.31 3.52 .093

Maxillomandibular relationshipANB angle (°) 2.60 2.05 3.41 2.04 .166

Growth patternFMA (°) 29.49 5.97 31.47 5.17 .208SN.PP (°) 7.23 2.24 7.97 3.09 .352SN.OP (°) 13.92 4.47 17.06 3.93 .010*SN.GoGn (°) 36.43 5.36 39.46 4.32 .028*LAFH (mm) 70.20 5.16 71.39 5.35 .431

Maxillary dentoalveolar componentMx1.NA (°) 24.22 4.99 23.24 6.33 .552Mx1-NA (mm) 5.30 1.87 4.04 2.91 .088Mx1.PP (°) 112.08 5.55 109.33 11.13 .300Mx1-PP (mm) 29.33 2.64 32.69 15.12 .320Mx6-PP (mm) 24.76 2.53 25.72 2.64 .197

Mandibular dentoalveolar componentMd1.NB (°) 27.13 5.54 23.10 5.10 .009*Md1-NB (mm) 6.04 2.08 5.66 1.35 .425IMPA (°) 90.32 6.56 85.20 6.21 .006*Md1-MP (mm) 40.97 2.74 40.15 2.54 .272Md6-MP (mm) 30.91 2.63 31.42 1.85 .416

Dental relationshipsOverbite (mm) 1.43 0.50 1.09 0.94 .137


was the same in both groups, they can be regarded as

compatible in this respect. It is difficult to assess thisfactor in retrospective studies as evidenced in theliterature.1,9,17

Because the primary objective of this study was todirectly compare these 2 groups, no control group wasused. Behavior of the posttreatment overbite of thesegroups was compared with a normal occlusion controlgroup in our previous studies.10,11 Since at the end oftreatment an artificial normal occlusion is obtained, it isexpected to behave as such. Therefore, the groups werecompared with a normal occlusion control group andnot to an open-bite control group, in those previousstudies,10,11 because for ethical reasons it would bedifficult to follow open-bite subjects for such a longtime without providing treatment, and because behaviorof the overbite is similar in open-bite malocclusionsand normal occlusions with time.14-16

Treatment and posttreatment

The overbite changes were analyzed primarily dur-ing the posttreatment period, comparatively between

Table V. Comparison of posttreatment changes (T3-T2,t tests)

Variable

Group 1n � 21

Group 2n � 31

PMean SD Mean SD

Maxillary componentSNA angle (°) 0.78 1.76 �0.33 1.74 .028*

Mandibular componentSNB angle (°) 0.48 1.16 �0.24 1.32 .048*

Maxillomandibular relationshipANB angle (°) 0.33 1.28 �0.11 1.65 .303

Growth patternFMA (°) �0.21 1.87 �1.29 2.87 .135SN.PP (°) �0.47 1.47 0.12 1.41 .150SN.OP (°) 0.00 5.54 �0.61 2.77 .597SN.GoGn (°) �1.02 1.90 �0.56 2.08 .420LAFH (mm) 1.48 1.69 0.73 2.35 .218

Maxillary dentoalveolar componentMx1.NA (°) 0.48 3.05 1.17 5.51 .603Mx1-NA (mm) �0.07 1.81 1.17 3.03 .099Mx1.PP (°) 0.79 2.21 2.05 9.55 .557Mx1-PP (mm) �0.14 1.16 0.36 1.34 .163Mx6-PP (mm) 0.63 1.27 0.75 1.92 .800

Mandibular dentoalveolar componentMd1.NB (°) 1.44 3.50 1.95 3.93 .634Md1-NB (mm) 0.49 0.65 0.55 0.91 .783IMPA (°) 1.61 3.57 2.79 4.34 .308Md1-MP (mm) 0.33 1.04 0.59 1.38 .471Md6-MP (mm) 1.00 0.99 0.97 1.10 .940

Dental relationshipsOverbite (mm) �1.36 0.54 �0.06 1.50 .000*


the groups, which is the main focus of this investigation


Janson et al 773

(Table V). Subsequently, changes in overbite and othervariables during treatment and posttreatment betweenthe groups were analyzed to elucidate whether theycould explain overbite behavior during the posttreat-ment period. Group 1 had a statistically greater overbitedecrease than did group 2, confirming previous specu-lation that nonextraction open-bite treatment is lessstable than extraction treatment17 (Table V). Duringtreatment, changes in maxillary, mandibular, maxillo-mandibular relationships, growth pattern, and overbitedo not seem to explain this different behavior becausethey were similar between the groups (Table III). Thedifferences in the maxillary and mandibular componentforward-displacement changes in the posttreatment pe-riod might have occurred because group 2 had slightlymore vertical growth than group 1. Vertical growersusually have less apical base anteroposterior displace-ment than normal or horizontal growers.14,34-36 How-

Table VI. Comparison of groups at T3 (t tests) andpercentages of patients with clinically significantrelapse between groups (chi-square test)

Variable

Group 1n � 21

Group 2n � 31

PMean SD Mean SD

Maxillary componentSNA angle (°) 81.41 3.57 79.38 3.63 .052

Mandibular componentSNB angle (°) 78.49 4.30 76.07 3.79 .037*

Maxillomandibular relationshipANB angle (°) 2.93 2.12 3.30 2.29 .560

Growth patternFMA (°) 29.27 6.33 30.17 4.59 .554SN.PP (°) 6.76 2.60 8.10 3.45 .139SN.OP (°) 13.93 6.77 16.44 4.29 .106SN.GoGn (°) 35.41 6.55 38.90 4.51 .027*LAFH (mm) 71.69 5.67 72.12 5.44 .780

Maxillary dentoalveolar componentMx1.NA (°) 24.71 4.36 24.41 6.60 .858Mx1-NA (mm) 5.22 1.91 5.21 2.62 .989Mx1.PP (°) 112.88 5.57 111.38 7.46 .438Mx1-PP (mm) 29.19 2.93 30.36 2.79 .246Mx6-PP (mm) 25.39 2.58 26.47 2.15 .107

Mandibular dentoalveolar componentMd1.NB (°) 28.57 6.74 25.05 4.29 .025*Md1-NB (mm) 6.53 2.36 6.21 1.53 .559IMPA (°) 91.93 8.15 88.00 5.42 .041*Md1-MP (mm) 41.31 2.79 40.74 2.59 .458Md6-MP (mm) 31.91 3.06 32.40 1.86 .479

Dental relationshipsOverbite (mm) 0.07 0.62 1.02 1.62 .020*

Clinically significant relapse (chi-square test)Percentage of

patients (%)Stability

61.9Relapse38.1

Stability74.2

Relapse25.8 .346


ever, it is unlikely that these changes contributed to the

differences in overbite behavior between the groups.During treatment, there were only significant differ-ences in the maxillary and mandibular dentoalveolarcomponents between the groups (Table III). The max-illary incisors had greater retraction, and the mandibu-lar incisors had greater retraction and lingual tipping,and less extrusion in the extraction group (Tables IIIand IV). It can be speculated that these factors, espe-cially the smaller mandibular incisor extrusion of theextraction group, could explain the different behaviorof the posttreatment overbite between the groups.Greater retraction and lingual tipping of the incisors,through the “drawbridge principle,” would providegreater bite closure with less extrusion of the incisors.If the incisors are less extruded, they would tend tohave better posttreatment stability.1,9,18 This was ob-served with the mandibular incisors that had compara-tively greater extrusion during treatment in the nonex-traction group (Md1-MP). The posttreatment changesof the vertical development of the maxillary and man-dibular incisors showed only a tendency of greaterdevelopment in group 2, without statistical signifi-cance. Perhaps the cumulative effects of these nonsig-nificant changes in the maxillary and mandibular inci-sors’ vertical development also contributed to thegreater stability of the overbite (Table V). The overbitedecrease in group 1 was greater than in group 2, despitethe nonsignificant greater amount of overbite at T2 ingroup 1 in relation to group 2 (Table IV). As a result ofthe smaller relapse of group 2 in relation to group 1,overbite at T3 was also greater in group 2 (Table VI).

As mentioned before, the longer posttreatment timeof group 2 in relation to group 1 would tend to causegreater relapse for that group2,22-25 (Table II). Never-theless, group 2 had greater stability of the open-bitecorrection. Therefore, the longer posttreatment time ofthis group supported even more consistently the resultsobtained. Direct comparison of these results with othersin the literature was not possible because of the lack ofsimilar studies.

Despite the statistically significant difference inoverbite relapse between the groups, there were nosignificant differences in the percentages of patientswith clinically significant relapses.10,11 This mighthave occurred because of the relatively small numberof patients in the groups for the nonparametricstatistical test used, which is usually less precise thana parametric test and requires more patients to showsubtle differences. Future studies with more patientsin the groups are necessary to confirm these specu-
lations.


774 Janson et al

Clinical implications

One should not take these results as a reason forextracting to correct open bites in the permanentdentition. The extraction group had several other fac-tors that required extractions to be performed, aspreviously mentioned. These results should, rather, beused to help in decision making in open-bite borderlinepatients, but all other characteristics should be considered.

CONCLUSIONS

The null hypothesis was rejected because open-biteextraction treatment provides greater stability of theoverbite correction than nonextraction treatment. How-ever, there was no statistically significant differencebetween the percentages of patients with clinicallysignificant relapse between the groups.

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2. Huang GJ, Justus R, Kennedy DB, Kokich VG. Stability ofanterior openbite treated with crib therapy. Angle Orthod 1990;60:17-24.

3. Denison TF, Kokich VG, Shapiro PA. Stability of maxillarysurgery in openbite versus nonopenbite malocclusions. AngleOrthod 1989;59:5-10.

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Stability of Anterior Open-bite Extraction

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