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Amajor goal of orthodontic treatment is to achievelong-term stability of the occlusion. The mandibu-lar incisor segment has been described by severalauthors as the segment that is most likely to exhibit

relapse after active treatment and retention.1-3 Clinicalexperience has shown that orthodontic patients per-ceive the crowding of the anterior teeth as one of themost obvious problems for which they seek treatment.Therefore, relapse of the mandibular anterior teeth aftertreatment and retention phases is a challenge that clin-icians need to address.

Several studies have shown that arch lengths andintercanine widths decrease and intermolar distancesincrease during the development of adolescentsarches.4-7 Barrow and White8 evaluated 52 untreated

individuals and observed that intercanine widthdecreased after the midteen years. None of the subjectsobserved had maxillary incisor crowding at age 6, but24% did by age 14. Fourteen percent of the mandibular

anterior teeth experienced crowding by age 6, and 51%by age 14. In a study of 1000 children, Cryer9 reported62% incisor crowding by age 14; 60% showed anincrease in lower incisor alignment compared with age11. Foster et al10 reported a 70% incidence of mandibu-lar crowding by age 7; this increased to 90% by age 14,and then decreased slightly by age 25.

Sinclair and Little11 studied 65 untreated individ-uals with normal occlusion and found that archlength and intercanine width significantly decreasedinto early adulthood, whereas incisor irregularity, asdefined by Little,3 significantly increased. Whencomparing postretention irregularity indexes, thetreated cases were higher than the untreated normalgroup. In addition, the rate of increase in incisorcrowding for the treated group was approximatelytwice that in the untreated normal group.11 Little andRiedel12 evaluated 30 cases that were 10 yearspostretention and observed that arch width and archlength decreased with time; 53% demonstrated mini-mal irregularity indexes, 33% had moderate and 13%had severe postretention irregularity indexes.

aOrthodontic Department, School of Dentistry, Medical College of Georgia.bProfessor, Oral Diagnosis and Patient Services, School of Dentistry, and Pro-fessor, Oral Biology, School of Graduate Studies, Medical College of Georgia.cAssociate Professor, Medical College of Georgia.dAssociate Professor, Department of Orthodontics, University of Illinois; and inprivate practice, Cuyahoga Falls, Ohio.eProfessor and Interim Chair, Department of Orthodontics, School of Dentistry,Medical College of Georgia.Reprint requests to: Michael K. Shrout, DMD, School of Dentistry, School ofGraduate Studies, Medical College of Georgia, Augusta, Georgia 30912-1241.Submitted, 6/99; accepted, 11/99Copyright 2000 by the American Association of Orthodontists.0889-5406/2000/$12.00 + 0 8/1/104409doi.10.1067/mod.2000.104409

ORIGINAL ARTICLE

Relapse in Angle Class II Division 1 malocclusion treated by

tandem mechanics without extraction of permanent teeth: A

retrospective analysis

Javid Yavari, DMD, MS,a Michael K. Shrout, DMD,b Carl M. Russell, DMD, PhD,c Andrew J. Haas, DDS, MS,d

and Edward H. Hamilton, DDSe

Augusta, Ga, and Chicago, Ill

Ideal orthodontic treatment should achieve long-term stability of the occlusion. The mandibular incisor segment

has been described as the segment that is most likely to exhibit relapse after treatment and retention.Therefore,

relapse of this is a challenge that clinicians need to address.The purpose of this study is to evaluate the amount

of relapse that may occur in Angle Class II Division 1 patients, treated orthodontically with tandem mechanics.

All cases in this study were treated without extraction of permanent teeth, and the patients were followed for at

least 2 years after the end of the retention phase of treatment. Six predictors were investigated at pretreatment,

posttreatment, and postretention periods. A synopsis of this study shows the correction of lower incisor crowd-

ing as measured by the irregularity index was stable over 5.2 years of postretention follow-up; but longer follow-

up time revealed increased relapse of incisor irregularity. Intermolar width increased during treatment andremained stable in the follow-up period. Overjet and overbite corrections and changes in the lower incisor to

mandibular plane angle were also stable in the follow-up period. In addition, the amounts of overjet correction

and loss of expansion of intercanine distance after treatment were associated with increased irregularity index

in the follow-up period. It appears the discrepancies between this and previously published works are sufficiently

dramatic that the whole question of treatment philosophy and long-term stability may need to be reevaluated.

(Am J Orthod Dentofacial Orthop 2000;118:34-42)

CE

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American Journal of Orthodontics and Dentofacial Orthopedics Yavari et al 35Volume 118, Number1

Little et al13 concluded that long-term alignment wasvariable and unpredictable; no descriptive characteristics(such as length of retention), Angle classification, age,gender, or measured variables (such as overbite, overjet,arch width, or arch length) were predictive. Satisfactory

mandibular anterior alignment is maintained in less than30% of the cases with nearly 20% likely to show markedcrowding many years after removal of retainers.13 Littleet al14 reported that lower anterior crowding continued toincrease during 10 to 20 years after retention with only10% of the cases having clinically acceptable mandibu-lar alignment. McReynolds and Little15 evaluated46 patients for changes over a minimum of 10 yearspostretention. Arch length and arch width decreasedwith time and incisor irregularity increased throughoutthe postretention period.

Shapiro16 studied a nonextraction sample of 22individuals at 10 years postretention; mandibular arch

length and intercanine width decreased during thepostretention period regardless of whether arch lengthhad increased or decreased during treatment. Thenonextraction group experienced significantly lessdecrease in intermolar width during postretention thanthe premolar extraction group. Glenn et al17 evaluatedlong-term stability in 28 nonextraction patients. Archlength decreased significantly for 96% of the patientsduring an average of 8 years postretention. Similarly,95% of the patients with an increase in intercaninewidth during treatment showed reduction in incisorirregularity during the postretention period. The inter-molar width was decreased, whereas overjet and over-bite showed no significant changes and incisor irregu-larity showed only a slight increase postretention.

Sadowsky et al18 assessed 22 patients with a mini-mum of 5 years postretention. Fifteen were treated ini-tially with tandem mechanics; all had light interproxi-mal stripping as the mandibular fixed lingual retainerwas removed. Average retention time with a mandibu-lar fixed lingual retainer was 8.4 years. In this study, allvariables showed relapse during the postretention stage

except for the maxillary canine and premolar archwidth region. The mandibular irregularity index lost33% of its improvement.

Cephalometric studies of postretention changeshave evaluated an additional aspect of relapse in ortho-

dontically treated cases. Brodie19 studied nonextrac-tion orthodontic cases and concluded the axial inclina-tion of teeth disturbed by orthodontic treatment tendsto return to pretreatment conditions. Cole20 reported asimilar observation in orthodontic cases treated withextractions. He noted that mandibular incisors tendedto return to their original inclination relative to themandibular plane.

Tweed1 believed placing the teeth upright over basalbone would ensure stability and suggested specificcephalometric angles to achieve stability. Schulaf et al21

reported that the lower incisors anteroposterior positionsrelative to various cephalometric values had no relation-

ship to postretention crowding of lower incisors.Shields22 assessed long-term postretention changes of54 orthodontically treated cases using premolar extrac-tions and concluded the long-term response to mandibu-lar anterior alignment was unpredictable and that noneof the cephalometric parameters were useful in predict-ing the relapse potential. However, there was a slighttendency for incisor inclination to return toward the pre-treatment value during the postretention period.

All cases in this current study were treated withtandem mechanics without extraction of permanentteeth. The patients were followed for at least 2 years ormore after the end of the retention phase of orthodon-tic treatment. Tandem mechanics, where the archlength is preserved by restricting mesial movement ofmaxillary and mandibular molars during orthodontictreatment, has been previously described.23-26 To sum-marize, as the dentofacial skeleton grows forward, themaxillary molars are restricted from moving mesially(anteriorly) with headgear. The mandibular molars arerestricted from moving mesially (anteriorly) by ClassIII elastics used in tandem with the headgear. The elas-

Table I. Sample groups divided by irregularity index (summary statistics)

Irregularity strata

Increased Decreased

Mean SD Mean SD P value*

Age at the beginning of treatment 14.5 3.8 11.5 2.4 .1233Periods of observation

Treatment 3.9 1.7 3.3 0.9 .1522Retention 5.7 1.9 7.1 1.5 .0517Postretention follow-up 7.0 5.0 3.8 1.3 .0159

*P value for a significant difference between the increased and the decreased irregularity groups.

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36 Yavari et al American Journal of Orthodontics and Dentofacial OrthopedicsJuly 2000

tics used with the headgear in tandem help preserve,and possibly create, arch length.

The specific predictors investigated in this studyincluded: intercanine width, intermolar width, overjet,overbite, irregularity index, and lower incisor to

mandibular plane angle. All these parameters wereexamined at pretreatment, posttreatment, and postre-tention periods. Azizi et al27 have previously describeda retrospective study of Angle Class I malocclusionstreated orthodontically without extractions using tan-dem mechanics and 2 palatal expansion methods. Thepurpose of this study is to evaluate the amount ofrelapse that may occur in Angle Class II Division 1patients, who were treated nonextraction orthodonti-cally with tandem mechanics. The intent is to searchfor clinically significant predictors or associations withvalues measured from the dental casts with particularemphasis on mandibular anterior alignment.

MATERIAL AND METHODS

Patient records for 55 patients were obtained from DrAndrew J. Haas of Cuyahoga Falls, Ohio. An assistant inDr Haas office selected the cases on the basis of theiroriginal classification as Angle Class II malocclusion andthe existence of some postretention follow-up records.According to Dr Haas, neither treatment outcome norpatient satisfaction was an explicit criterion for selection.

Case records were sent to the Medical College ofGeorgia, Department of Orthodontics. These caserecords consisted of dental models and lateral cephalo-metric radiographs collected before treatment, after treat-ment, and at least 2 years after cessation of retainer wear.

Progress notes were included that contained date of birth,gender, and dates of treatment and follow-up event visits.

All subjects were treated by a single clinician. Theretention strategy used was first premolar to first pre-molar mandibular fixed lingual retention with maxil-lary Hawley retainer. In addition, 6 criteria were usedto select a study sample of 31 from the 55 cases:

1. Angle Class II Division 1 malocclusion2. No missing permanent teeth at pretreatment3. Treatment without the extraction of permanent teeth4. Good quality dental models and lateral cephalo-

metric radiographs at each time point

5. Minimal 2 years of follow-up after cessation ofretention6. Treatment involved the use of tandem mechanics

To ensure consistency with the requirement ofAngle Class II Division 1 malocclusion, an overjet ofat least 3.0 mm was required. The overbite wasrequired to be positive in order to eliminate openbitecases. Gender, age at the time treatment began, treat-ment time, retention time, and time of follow-up after

Table II. Summary statistics for variables (complete sample)

Values observed (mm) Mean SD Minimum Maximum

Intercanine distanceBefore treatment T0 26.2 2.1 20.3 30.7After treatment T1 27.3 1.5 24.7 30.4

After retention and follow-up T2 26.4 1.6 22.8 29.6Intermolar distance

Before treatment T0 43.1 2.5 38.6 47.8After treatment T1 46.4 3.1 37.7 52.4After retention and follow-up T2 46.5 3.1 41.0 52.0

OverjetBefore treatment T0 7.8 2.0 3.6 11.8After treatment T1 0.9 0.8 0.0 2.6After retention and follow-up T2 1.0 0.7 0.0 2.5

OverbiteBefore treatment T0 4.7 1.9 1.3 9.3After treatment T1 1.9 0.8 0.0 3.5After retention and follow-up T2 2.6 1.0 1.0 4.8

IMPABefore treatment T0 97.6 7.0 82.0 110.0

After treatment T1 95.7 7.0 81.0 109.0After retention and follow-up T2 96.1 6.2 84.0 111.0Irregularity index

Before treatment T0 4.5 1.7 1.2 7.6After treatment T1 1.0 0.9 0.0 4.6After retention and follow-up T2 1.0 1.0 0.0 4.1

*P value for a significant change.

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retention were recorded for each subject. The names ofpatients were not used for identification as the datawere collected. The Human Assurance Committee ofthe Medical College of Georgia approved this study.

The study variables were:

Intercanine distance: the distance (mm) betweenthe cusp tips of the mandibular canines or esti-mated cusp tips in cases of wear facets.13

Intermolar distance: the distance (mm) betweenthe mesiobuccal cusp tips of the mandibular firstpermanent molars or estimated cusp tips in casesof wear facets.13

Overjet: the horizontal distance (mm) parallel tothe occlusal plane from the lingual surface of themost labial maxillary incisor to the labial surfaceof the most lingual mandibular incisor.28

Overbite: the mean vertical overlap (mm) of upperand lower central incisors.29

IMPA (lower incisor to mandibular plane angle):angle formed by the intersection of the long axisof the lower central incisors with the mandibularplane as measured on the lateral cephalometricradiograph.1

Total irregularity index: the irregularity index (IR)is the summed displacement of the anatomic con-tact points of the lower anterior teeth.3

To ensure recording horizontal displacement, thecaliper was consistently parallel to the occlusal planewhile obtaining each measurement. The mesiodistal spac-ing was disregarded if teeth were in proper arch form.However, if displacement of the teeth in conjunction with

spacing occurred, then only the labiolingual displacementfrom proper arch form was recorded. For accurate mea-surements of mandibular incisors, the dial caliper used inthis study was precise to one-hundredth of a millimeter.29

Among the 31 subjects in the complete study sam-ple, 17 subjects showed a decrease or no change in irreg-ularity index during the retention and postretention fol-low-up periods. The remaining 14 subjects showed amild increase in irregularity index during this sameperiod of observation. In order to determine associationsbetween the relapse of mandibular anterior crowdingwith other study variables, the sample was divided intothese 2 groups. Statistical analysis of changes in studyvariables over time was performed using the paired ttest. Differences in groups with increased and decreasedirregularity were analyzed using the 2-sample ttest. Sig-nificant results of statistical tests were reported when theP value was less than or equal to .0500.

Reliability of study measurements was assessed. Asecond evaluator measured 30 models and radiographsselected at random. Interevaluator reliability was mea-sured with intraclass correlation coefficient (ICC),

Changes observed (mm) Mean SD Minimum Maximum P value*

During treatment T1-T0 1.1 2.1 3.6 4.7 .0039During retention and follow-up T2-T1 0.9 1.0 2.8 1.6 .0001

During treatment, retention, and follow-up T2-T0 0.2 2.0 3.9 4.2 .5972

During treatment T1-T0 3.3 2.6 1.9 10.2 .0001During retention and follow-up T2-T1 0.1 1.3 2.6 3.2 .8140During treatment, retention, and follow-up T2-T0 3.4 3.0 1.5 11.5 .0001



During treatment T1-T0 2.3 7.3 19.0 10.0 .0995

During retention and follow-up T2-T1 0.5 5.6 0.0 12.0 .6160During treatment, retention, and follow-up T2-T0 2.2 6.0 -13.0 10.0 .0599


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paired t test, and the variance component of theBradley-Blackwood test (BBT).30,31

RESULTS

To determine associations between the relapse of

mandibular anterior crowding with other study vari-ables, the sample was divided into 2 groups (Table I).They are designated in the text as group D (decreasedirregularity, N = 17) and group I (increased irregular-ity, N = 14). The mean postretention follow-up timein group D was 3.8 years and in group I was 7.0years. This difference of 3.2 years was significant (Pvalue = .0159).

Of the 31 subjects meeting the studys selection cri-teria, 22 were females and 9 were males. There is someevidence that sexual dimorphism could be a long-termconsideration because of greater incisor irregularity inmales as a result of final mandibular growth incre-

ments, unmatched by maxillary changes. The mean ageat the beginning of treatment was 11.0 years; the meantreatment time was 3.5 years; the mean retention timewas 6.4 years; and the mean postretention follow-uptime was 5.2 years. Summary statistics for each vari-able are provided in Table II.

Intercanine Distance (Table II)

Intercanine distance changed from a mean of 26.2mm to a mean of 27.3 mm during treatment. Thischange of 1.1 mm was significantly greater than zero(P = .0039). During the retention and postretention fol-low-up periods, the mean intercanine distance relapsed

from 27.3 mm to 26.4 mm. This relapse of 0.9 mm wassignificantly greater than zero (P = .0001). The residualchange measured across the treatment, retention, andpostretention periods was 0.2 mm. This was not a sta-tistically significant overall change (P = .5972).

Intermolar Distance (Table II)

Intermolar distance changed from a mean of 43.1 mmto a mean of 46.4 mm during treatment. This change of3.3 mm was significantly greater than zero (P = .0001).During the retention and postretention follow-up periods,the mean intermolar distance remained expanded: 46.4 to46.5 mm. This small difference of 0.1 mm was not sig-nificantly greater than zero (P = .8140). Thus, the changemeasured across the treatment, retention, and postreten-tion periods was 3.4 mm. This was a significant overallintermolar expansion of 3.4 mm (P = .0001).

Overjet (Table II)

Overjet was decreased from a mean of 7.8 mm to amean of 0.9 mm during treatment. This reduction of 6.9mm was significantly greater than zero (P = .0001).

During the retention and postretention follow-up peri-ods, the mean overjet was maintained: 0.9 mm to 1.0mm. This small difference of 0.2 mm (due to rounding)was not significantly greater than zero (P = .2057).Thus, the reduction in overjet measured across the

treatment, retention, and postretention periods was 6.8mm. This was a significant overall change (P = .0001).

Overbite (Table II)

Overbite was reduced from a mean of 4.7 mm to amean of 1.9 mm during treatment. This reduction of2.9 mm was significantly greater than zero (P = .0001).During the retention and postretention follow-up peri-ods, the mean overbite increased from 1.9 mm to 2.6mm. This small relapse of 0.8 mm was significantlygreater than zero (P = .0001). The reduction in overbitemeasured across the treatment, retention, and postre-tention periods was 2.0 mm. This was a significant

overall change (P = .0001).IMPA (lower incisor to mandibular plane angle)

(Table II)

IMPA was reduced from a mean of 97.6 to a meanof 95.7 during treatment. This reduction of 2.3 wasnot significantly different from zero (P = .0995). Dur-ing the retention and postretention follow-up periods,the mean IMPA changed by only 0.5. This change wasnot significant (P = .6160). Thus, the reduction inIMPA measured across the treatment, retention, andpostretention periods was 2.2. This reduction did notachieve the customary 0.05 alpha level and is therefore

considered a nonsignificant change (P = .0599).

Irregularity Index (Table II)

The irregularity index was reduced from a mean of4.5 mm to a mean of 1.0 mm during treatment. Thisreduction of 3.5 mm was significantly greater than zero(P = .0001). During the retention and postretention fol-low-up periods, the mean irregularity index remainedconstant at 1.0 mm. Thus, the reduction in irregularityindex measured across the treatment, retention, andpostretention periods was 3.5 mm. This was a signifi-cant overall change (P = .0001).

Associations With Irregularity Index (divided sample)

The following results involve the divided sample(Table I), designated as group D (decreased irregular-ity, N = 17) and group I (increased irregularity, N =14). The summary statistics for these groups are listedin Table III. The mean age at the beginning of treat-ment for group I was 14.5 years, and the mean forgroup D was 11.5 years. The difference in age was notsignificant (P = .1233). The mean treatment time was

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3.9 years in group I and 3.3 years in group D. This dif-ference in treatment time was not significant (P =.1522). The mean retention time was 5.7 years in groupI and 7.1 years in group D. The difference of 1.4 yearswas not significant (P = .0517). The mean postretentionfollow-up time was 7.0 years in group I and 3.8 years

in group D. This difference in postretention follow-uptime was significant (P = .0159).

Intercanine Distance (divided sample) (Table III)

The mean intercanine distance before treatmentwas the same in groups I and D, 26.2 mm. Group I

Table III. Summary statistics of divided sample variables

Irregularity strata

Increased Decreased

Mean SD Mean SD P value*

Intercanine distance (divided sample)

Values observed (mm)Before treatment T0 26.2 1.7 26.2 2.4 .9930After treatment T1 26.8 1.4 27.8 1.4 .1033After retention and follow-up T2 25.5 1.1 27.1 1.5 .0037

Changes observed (mm)During treatment T1-T0 0.6 1.9 1.5 1.6 .2290During retention and follow-up T2-T1 1.3 1.0 0.6 0.9 .0575During treatment, retention, and follow-up T2-T0 0.6 2.0 0.9 1.7 .0288

Intermolar Distance (divided sample)

Values observedBefore treatment T0 42.6 2.1 43.5 2.8 .3435After treatment T1 46.0 2.3 46.8 3.7 .4827After retention and follow-up T2 45.6 2.9 47.1 3.2 .1898


Overjet (divided sample)

Values observedBefore treatment T0 8.9 1.8 7.0 1.8 .0067After treatment T1 0.6 0.7 1.1 0.8 .0409After retention and follow-up T2 0.9 0.6 1.1 0.8 .4001


Overbite (divided sample)

Values observed (mm)Before treatment T0 5.0 2.1 4.5 1.7 .5389

After treatment T1 2.0 0.8 1.9 0.8 .5222After retention and follow-up T2 2.8 1.3 2.6 0.7 .5161


IMPA (divided sample)

Values observed (mm)Before treatment T0 96.1 8.0 98.9 6.2 .2885After treatment T1 94.3 5.4 96.7 8.0 .3622After retention and follow-up T2 95.9 6.6 96.3 6.2 .8920


*P value for a significant difference between the increased irregularity group (N = 14) and the decreased irregularity group (N = 17).

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experienced slightly less expansion during treatment(0.6 mm) than group D (1.5 mm), but this differencewas not significant (P = .2290). During retention andpostretention follow-up, group I experienced 1.3 mmof loss of expansion; group D experienced 0.6 mm ofloss of expansion. This difference was not quite sig-

nificant (P = .0575). However, considering the over-all change throughout the treatment, retention, andpostretention follow-up periods, group I experienceda net decrease in intercanine distance (0.6 mm) incontrast to a net increase in intercanine distance (0.9mm) in group D. This difference of 1.5 mm was sig-nificant (P = .0288).

Intermolar Distance (divided sample) (Table III)

The mean intermolar distance before treatment was42.6 for group I, and the mean intermolar distance was43.5 for group D. Intermolar distance was expandedduring treatment and maintained after treatment in each

group. Treatment expansion was 3.4 mm in group I and3.3 mm in group D. Overall net expansion was 3.1 mmin group I and 3.7 mm in group D. There were no sig-nificant differences between groups I and D in inter-molar distance across any of the periods of observation.

Overjet (divided sample) (Table III)

The mean value for overjet before treatment was 8.9mm in group I and 7.0 mm in group D. This differencewas significant (P = .0067). The mean value for overjetafter treatment was 0.6 mm in group I and 1.1 mm ingroup D. This difference was significant (P = .0409).Group I started with more overjet before treatment andended with less overjet after treatment than group D.The treatment reduction in overjet for group I was amean of 8.3 mm and for group D, a mean of 5.9 mm.This treatment reduction difference was significant (P= .0031). The change in overjet during the retentionand postretention follow-up periods was not significantin either group. Therefore, the overall reduction inoverjet in group I was 7.9 mm and in group D was 5.8mm. This difference was significant (P = .0059).

Overbite (divided sample) (Table III)

The mean value for overbite before treatment was5.0 in group I and 4.5 in group D. Overbite wasreduced during treatment and approximately main-tained after treatment in each group. Treatment reduc-tion was 2.9 mm in group I and 2.7 mm in group D.

Overall net reduction was 2.1 mm in group I and 1.9mm in group D. There were no significant differencesbetween groups I and D in overbite across any of theperiods of observation.

IMPA (divided sample) (Table III)

The mean value for IMPA before treatment was96.1 in group I and 98.9 in group D. IMPA wasreduced during treatment and approximately main-tained after treatment in each group. Treatment reduc-tion mean value was 2.4 in group I and 2.2 in groupD. Overall net mean reduction was 1.4 in group I and2.8 in group D. There were no significant differences

between groups I and D in IMPA across any of theperiods of observation.

The reliability indicators (Table IV) were appliedand interpreted as recommended by physical anthro-pology studies.32 The intraclass correlation coefficients(ICCs) for the variables in this study were between0.92 and 0.99. Excellent reliability is considered at thelevel of ICC greater than or equal to 0.85. For interca-nine distance there were minor differences betweenevaluators. This difference was 0.4 mm in the meanand 0.2 mm in the SD. Though statistically significantin the paired ttest and BBT components, the ICC was0.94. This indicated that the differences were smallcompared with the scale and range of measurements,and no corrective action was indicated.

DISCUSSION

The 3.2 year difference in the mean postretentionfollow-up time between group D and group I was sig-nificant (P value = .0159). These results support previ-ous work by Katz32 who reported that potential forrelapse increased with more years out of retention. How-

Table IV. Summary of interevaluator reliability indicators

Evaluator 1 Evaluator 2 P values

Variables Mean SD Mean SD ICC Paired t test Variance test (BBT) 2-df BBT

Intercanine distance 26.6 2.0 27.0 1.8 0.94 .003 .049 .002

Intermolar distance 45.5 3.6 45.6 3.6 0.99 .078 .669 .198Overjet 3.3 3.4 3.3 3.4 0.99 .916 .709 .926Overbite 3.1 1.5 3.2 1.5 0.98 .524 .841 .803Irregularity index 1.7 1.8 1.9 1.7 0.92 .220 .359 .311IMPA 94.5 7.8 94.1 7.3 0.95 .357 .253 .339

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ever, there was no relationship between the number ofyears in retention and the other variables that he studied.

Intercanine distance increased as a result of treatment;however, it relapsed to near pretreatment level in the mainsample. Intercanine distance relapsed approximately

80%, maintaining 0.2 mm of expansion in the lower ante-rior segment. This observation was also reported by oth-ers.14,33,34 The data from the present study for the 2groups suggested that there was postretention relapse ofintercanine distance that was associated with an increasein the irregularity index. In fact, the mean value of inter-canine distance for group I at postretention was 0.7 mmless than the pretreatment value. This finding is in con-trast with the findings of Little et al,14 who reported thatthe maintenance of initial canine distance during treat-ment had little apparent influence on the postretentioncrowding. Our results were in agreement with rtun etal35 who found an association between postretention

reduction of intercanine distance and relapse of incisoralignment in Angle Class II Division 1 patients.Intermolar distance was also increased as a result of

treatment. In contrast to intercanine distance, expan-sion of intermolar distance remained stable throughoutthe postretention period. These findings support previ-ous studies, which reported long-term stability of inter-molar distance.17,19

This study focused on Angle Class II Division 1malocclusion characterized by a large overjet. The over-all overjet changes from pretreatment to the end of theobservation period were significantly stable, maintain-ing 89% of correction throughout the entire observation

period. These findings are in agreement with the resultsof previous studies17,19,36 that suggested that overjetdisplayed long-term stability. Analyzing the results forthe 2 groups in the present study revealed that a largeoverjet at pretreatment was associated with an increasedirregularity index. In addition, samples with large over-jet corrections were also associated with increasedirregularity indexes during postretention. Therefore, weconcluded that the magnitude of overjet correction maybe associated with the relapse of lower incisor align-ment in Angle Class II Division 1 malocclusions.

The amount of overbite was decreased by the ortho-dontic treatment, and it showed a slight relapse by theend of the postretention period. However, this differ-ence was not statistically significant. These findings arein agreement with previous studies.17,19,36

The irregularity index decreased significantly dur-ing treatment. This may be one of the most distin-guishing features of the study. The mean value forirregularity index was reduced from 4.5 mm at pre-treatment to a mean value of 1.0 mm at the end oftreatment. This reduction in irregularity remained sta-

ble to the end of the observation period, which sup-ports the findings of another recent study use27; bothare in contrast to results of Little et al12-15 thatreported 89% of orthodontically treated cases withoutextractions exhibited unacceptable lower anterior

alignment. As a minimum, this suggests it may be pos-sible to achieve long-term stability, which is betterthan has been reported. These particular differencesmay be related to the practitioner or the protocol. Withtandem treatment mechanics, forces are directedtoward distalizing or preventing maxillary andmandibular first molars from moving mesially whilethe maxillary and mandibular complex is growinganteriorly. Hopefully, arch length is preserved orgained especially in crowded malocclusions withoutmoving incisors anteriorly into unstable positions. Forbest results, our practitioner believes cases should bestarted in the late mixed dentition stage before the loss

of primary second molars and leeway spaces. To usethis technique, the clinician must be a believer inheadgear therapy, growth and development concepts,and possess the ability to convince patients that tan-dem treatment will be beneficial before long-term sta-bility can be achieved. This practitioner selected hisprotocol based on his diagnosis and treatment experi-ence; one must be cautious in applying these results topatients with more crowding or more protrusion.

IMPA was reduced by orthodontic treatment in thisstudy. The results indicated that there was no signifi-cant correlation between the changes in IMPA and theirregularity index. Our results are in agreement with

the results of previous studies14,22,23 that indicated nosignificant correlation between the long-term stabilityof the mandibular anterior teeth and any of the cephalo-metric measurements.

This study examined patients with one type ofmalocclusion, Angle Class II Division 1, thus, main-taining this variable constant. The majority of pub-lished studies include a variety of different types ofmalocclusions. Furthermore, the present studyincluded only subjects treated with tandem mechanicswithout previous extractions of permanent teeth.Treatment mechanics may have an impact on the sta-bility of the orthodontic results and is not addressedin many studies. For example, a unique feature of tan-dem mechanics is thought to be the class III elasticsin tandem with the headgear that preserves the archlength needed to decrease the amount of crowding inthe mandibular anterior region. This factor may be areason for stability of lower incisor alignment in thisstudy. Another possible consideration is removal ofthird molars, which increases arch length in the alve-olar trough. This was not recorded in this study.

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Finally, all subjects in this study were treated by asingle clinician. This eliminates the variability of mul-tiple clinicians but may reduce generalization ofresults. Furthermore, this study was retrospective.Elimination of case selection bias in this kind of study

is impossible because of the self-selection of patientsas they are recalled. All cases were selected based onthe availability of complete records and not on treat-ment outcome. However, future study models shouldinclude prospective randomized trials.

CONCLUSIONS

A synopsis of this study shows that the correctionof lower incisor crowding as measured by the irregu-larity index was stable over 5.2 years of postretentionfollow-up; but longer follow-up time revealedincreased relapse of incisor irregularity. Intermolarwidth increased during treatment and remained stable

in the follow-up period. Overjet and overbite correc-tions and IMPA changes were also stable in the follow-up period. In addition, the amounts of overjet correc-tion and loss of expansion of intercanine distance aftertreatment were associated with an increased irregular-ity index in the follow-up period.

This and a previous study27 have demonstrated thatit is possible to combine case diagnoses with treatmentprotocols to achieve outcomes superior to what hasbeen reported. It appears the discrepancies betweenthese reports are sufficiently dramatic that the questionof current treatment philosophies and long-term stabil-ity of mandibular incisors may need to be reevaluated.

REFERENCES

1. Tweed CJ. The indication, for extraction of teeth in orthodonticprocedure. Am J Orthod 1944;30:405-28.

2. Riedel RA. A review of the retention problem. Angle Orthod1960;30:179-94.

3. Little R. The irregularity index: a quantitative score of mandibu-lar anterior alignment. Am J Orthod 1975;68:554-63.

4. Nance HN. The limitation of orthodontic treatment. Am J Orthod1947;33:253-301.

5. Moorrees CF. The dentition of the growing child. Cambridge,MA: Harvard University Press; 1959.

6. Moorrees CF, Chadha MJ. Available space to the incisors duringdental development. Angle Orthod 1965;35:12-22.

7. DeKock WH. Dental arch depth and width studied longitudinallyfrom 12 years of age to adulthood. Am J Orthod 1972;62:56-66.8. Barrow GV, White JR. Development changes of the maxillary

and mandibular dental arches. Angle Orthod 1952;22:41-6.9. Cryer S. Lower arch changes during the early teens. Transactions

of The European Orthodontic Society, 1966;87:99.10. Foster TD, Hamilton MC, Lavelle CL. A study of dental arch

crowding in four age groups. Dent Pract Dent Rec 1970;21:9-12.11. Sinclair P, Little R. Maturation of untreated normal occlusions.

Am J Orthod 1983;83:114-23.12. Little RM, Riedel RA. Postretention evaluation of stability and

relapse-mandibular arches with generalized spacing. Am JOrthod 1989;95:37-41.

13. Little R, Wallen T, Riedel R. Stability and relapse of mandibularanterior alignment-first premolar extraction cases treated by tra-ditional edgewise orthodontics. Am J Orthod 1981;80:349-65.

14. Little R, Riede R, rtun J. An evaluation of changes in mandibu-

lar anterior alignment from 10 to 20 years postretention. Am JOrthod 1988;93:423-8.15. McReynolds DC, Little RM. Mandibular second molar extrac-

tion-postretention evaluation of stability and relapse. AngleOrthod 1991;61:133-44.

16. Shapiro P. Mandibular dental arch form and dimension. Am JOrthod 1974;66:58-70.

17. Glenn G, Sinclair P, Alexander R. Nonextraction orthodontictherapy: posttreatment dental and skeletal stability. Am J Orthod1987;92:321-8.

18. Sadowsky C, Schneider B, BeGole E, Tahir E. Long-term stabil-ity after orthodontic treatment: nonextraction with prolongedretention Am J 0rthod 1994;106:243-9.

19. Brodie AG. Cephalometric appraisal of orthodontic results.Angle Orthod 1938;8:261-351.

20. Cole HJ. Certain results of extraction in treatment of malocclu-

sion. Angle Orthod 1948;18:103-13.21. Schulaf RJ, Allen RW, Dreskin M. The mandibular dental arch:

part I, lower incisor position. Angle Orthod 1977;47:280-7.22. Shields T, Little R, Chapko M. Stability and relapse of mandibu-

lar anterior alignment: a cephalometric appraisal of first-premo-lar extraction cases treated by traditional edgewise orthodontics.Am J Orthod 1985;87:27-38.

23. Haas AJ. Rapid expansion of the maxillary dental arch and nasalcavity by opening the midpalatal suture. Angle Orthod 1961;31:73-89.

24. Haas AJ. The treatment of maxillary deficiency by opening themidpalatal suture. Angle Orthod 1965;35:200-17.

25. Haas AJ. Palatal expansion: just the beginning of dentofacialorthopedics. Am J Orthod 1970;57:219-54.

26. Haas AJ. Long-term posttreatment evaluation of rapid palatal

expansion. Angle Orthod 1980;50:189-217.27. Azizi M, Shrout MK, Haas AJ, Russell CM,Hamilton EH. A ret-

rospective study of Angle class I malocclusions treated ortho-dontically without extractions using two palatal expansion meth-ods. Am J Orthod Dentofacial Orthop 1999;116:101-7.

28. Lundstrom A. Tooth size and occlusion in twins. New York: SKarger; 1948.

29. Peck H, Peck S. An index for assessing tooth shape deviations asapplied to the mandibular incisors. Am J Orthod 1972;61:384-401.

30. Bradley EL, Blackwood LG. Comparing paired data: a simultane-ous test for means and variances. Am Statistician 1990;43:234-5.

31. Katz R. The long-term stability of mandibular arch length andwidth changes following rapid maxillary expansion [MSD The-sis]. The Ohio State University; 1990.

32. Russell CM, Williamson DF, Bartko JJ, Bradley EL. Simulation

study of a panel of reliability indicators applied to paired mea-surements. Am J Hum Bio 1994;6:311-20.33. Arnold ML. A study of the changes of the mandibular interca-

nine and intermolar widths during orthodontic treatment and fol-lowing postretention period of five or more years [MSD Thesis].University of Washington; 1963.

34. Riedel RA. A review of the retention problem. Angle Orthod1960;30:179-94.

35. rtun J, Garol JD, Little RM. Long-term stability of mandibularincisors following successful treatment of Class II Division Imalocclusions. Angle Orthod 1996;66:229-38.

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