Treatment and postretention changes in dental arch width dimensions—a long-term evaluation of influencing cofactors

Treatment and postretention changes in dental arch width dimensions-a long-term evaluation of influencing cofactors B~irbel KahI-Nieke, DDS, Dr.med.dent., Hendrik Fischbach, DDS, and Claus W. Schwarze, DDS, Prof.Dr.med.dent.

Cologne, Germany The aim of the present long-term follow-up study of orthodontically treated patients was to analyze postretention changes in arch width dimension and to isolate factors that may serve as predictors of long-term prognosis. Pretreatment, end-of-treatment, and postretention (at least 10 years) models of 226 cases with different malocclusions were used to measure intercanine and intermolar width, arch length, sum of the mesiodistal dimension of the incisors, Irregularity Index, crowding, molar and canine relationship, overjet, and overbite. To assess the influence of initial and end-of-treatment alignment, kind of treatment (extraction versus nonextraction) and the amount of expansion in postretention stability, the sample was divided into different subgroups. The findings indicate that postretention arch width relapse occurred more frequently in the upper intermolar (25.8%) and lower intercanine region (23.9%) than in the lower intermolar (19.0%) and upper intercanine (13.8%) region. Pretreatment and posttreatment alignment as well as the kind of treatment and the amount of expansion were found to be influencing factors. The study concludes by proposing a reassessment of the definition of stability. The influence of the pretreatment anomaly, kind of treatment, amount of expansion, and posttreatment alignment on long-term stability should be recognized. Patients should be apprised of treatment limitations before treatment. (AMJ ORTHODDENTOFACORTHOP1996; 109:368-78.)

O n e of the most controversial subjects in orthodontics has been the stability of an increase in dental arch width dimensions. Tooth movement influenced by the growth and development of the patient will affect the developing dentition, regardless of whether the person had orthodontic treatment. As documented by Moorrees and Reed, 1 Barrow and White, 2 Sillman,3 and DeKock, 4 a moderate increase in dental arch width can be expected, particularly in the anterior regions, until the permanent canines erupt. After this time, arch width usually decreases in the anterior and posterior regions. Steiner,5 McCauley,6 Strang, 7 Shapiro, 8 and others concluded that the mandibular intercanine and intermolar width dimensions show a strong tendency to relapse and should be considered inviolate. Walter, 9'~° however, reported that these dimensions could be successfully increased. Reports concerning changes of arch width dimension since 1948 up the present are varying from "arch width decrease to a pretreatment value" to "lower than the pretreatment dimension. ''~H3 From the Department of Orthodontics, University of Cologne, Germany. Copyright © 1996 by the American Association of Orthodontists. 0889-5406/96/$5.00 + 0 8/1/57601

368

Although all investigators recognize individual variation, there is general agreement on the typical tendency of lower intercanine width to decrease during postretention period, especially if expanded during treatment. 9'14"~5 Shapiro, 8 and Gardner and Chaconas 16 have even demonstrated lower arch width constriction to less than pretreatment values. Little et al., ~7 for example, have measured a postretention intercanine reduction in 60 of 65 patients, with most constricting more than 2 mm. Many cases even had an intercanine width at the long-term follow-up investigation much less than the initial dimension. This process of arch constriction appeared to continue well after the cessation of growth during the 20- to 30-year age span. From age 30 to 40 years and beyond, the process continued, but usually at a lessened degree or rate? 8 The intermolar distance, however, was found to be stable by Gardner and Chaconas. ~6 Sondhi et al., ~9 as well as Glenn et al., 2° reported a slight decrease of intermolar width. While many postretention studies have been conducted on various aspects of arch width stability and relapse, 21-25 the review of the literature points out the need for a quantitative and qualitative assessment of postretention changes in maxillary and mandibular arch dimensions, by using a sample that is large enough for

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Fig. 1. A, Intercanine width; B, intermolar width; C, arch length. statistical analysis consisting o f cases o u t of r e t e n t i o n for at least 10 years. I t was t h e p u r p o s e o f this s t u d y to find influe n c i n g c o f a c t o r s in t h e c a u s e o f p o s t r e t e n t i o n a r c h w i d t h changes. A s t h e r e s e e m s to b e little d o u b t t h a t e x p a n d e d as well as u n t r e a t e d a r c h e s have a t e n d e n c y to constrict, stability was n o t d e f i n e d as " l a c k o f c h a n g e " t o w a r d t h e p o s t t r e a t m e n t dim e n s i o n , b u t as a " m i l d o r m o d e r a t e a m o u n t o f arch width decrease." Consequently the group "relapse o f a r c h w i d t h " i n c l u d e d cases t h a t s h o w e d severe arch constriction during the postretention period. A s h y p o t h e t i c a l influencing cofactors, pretreatment anomaly, kind a n d amount of treatment, a n d posttreatment alignment w e r e a s s u m e d a n d t e s t e d .

MATERIAL AND METHODS Sample An attempt was made to contact 1464 patients whose orthodontic treatment had begun between 1962 and 1977. Criteria for the follow-up examination were complete records at the time of beginning and end-oftreatment. From the total sample of 299 former patients who participated in the follow-up study at the Department of Orthodontics, University of Cologne, 226 cases, 95 male and 131 female patients, with complete records were collected. Excluded from this study were subjects with congenitally absent and traumatically lost incisors (n = 73). All original anomalies (Angle Classes I, II, III) were included. Patients had undergone treatment that used removable appliances, active plates, functional appliances (activators). In addition, 23 cases were treated by the edgewise technique to obtain bodily tooth movements for space closure after extraction. All cases achieved acceptable posttreatment results. The mean pretreatment age for the 226 patients was 11.3 _+ 2.0 years, the mean treatment time was 4.2 _+ 1.6 years. The mean postretention time for the 31.2 -+ 4.8-year-old patients was 15.7 ± 4.4 years.

Model analysis Dial calipers (Ztircher Model) with fine tips measuring within 0.10 mm were used by one person (orthodontist) to measure the following parameters on the maxillary and mandibular pretreatment (T1) , end-of-treatment (T2), and postretention (T3) dental casts: Intercanine width. (Fig. 1, A): The distance between cusp tips or estimated cusp tips in cases of wear facets. In some cases (17 upper and 7 lower arches), this value could not be measured at T 1 because permanent canines were frequently unerupted. Intermolar width. (Fig. 1, B): The distance between the upper molar centric fossa of both sides; the distance between the lower distobuccal cusp tips of first molars. Arch length. (Fig. 1, C): The length of the perpendicular from the midpoint of the incisal edges of the central incisors on the distance between mesial anatomic contact points of first molars.

Sum of the mesiodistal dimension of the incisors. (Fig. 2).

Irregularity index. As suggested by Little 2~ (Fig. 3): The sum of the five linear distances from anatomic contact point to adjacent anatomic contact point of anterior teeth. Crowding. (Fig. 4): The available space for incisors, canines, and premolars was measured with a flexible ruler and compared with the required s p a c e - t h e sum of the mesiodistal crown diameters of the incisors, canines, and premolars. Overbite. Amount of vertical incisal overlap of upper and lower central incisors in millimeters. Overjet. The distance from the incisal edge of the maxillary to the mandibular central incisor was recorded in millimeters. Occlusion. Molar and canine relationship for the left and right sides were recorded as either Class II or III if the anteroposterior deviation was a quarter of a cusp or greater. Statistical analysis To evaluate the influence of the previously defined variables, the total sample was divided into two groups:

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Fig. 2. Sum of mesiodistal

American Journal of Orthodontics and Dentofacial Orthopedics April 1996

(rod) dimension of incisors.

Fig. 4. Available space to calculate crowding.

Fig. 3. Irregularity Index. the stability group consisted of the cases with postretention arch width decrease within an acceptable range, for example, with less than 2.0 mm anterior arch constriction and the relapse group contained those cases outside this range with, for example, 2 or more mm of anterior arch relapse. The basis for this division was the scoring system proposed by Sadowsky and SakolsF Definitions and groups sizes, varying for the four main parameters that represent arch width dimension, are given in Table I. Subgroups were created to find associations between the degree of posttreatment arch width constriction and the hypothetical influencing independent variables. Pretreatment anomaly. The sample was categorized arbitrarily by the nature of the original anomaly, severe and mild. The definitions and the almost equal subgroup sizes for all independent and main variables are listed in Table II. The significant prevalence of stability and relapse in relation to the independent variables under investigation was assessed by means of one- and two-way tables and ×z test. The significance level was established at p -< 0.05 (Table II). Kind of therapy. The nonextraction group consisted of 135 patients. For statistical analysis, the different types of extraction therapy were combined and designed extraction cases (n = 91). Extraction of four premolars was performed in 83 patients; in three cases, premolars were extracted in the upper and in five cases in the lower arch. To analyze the influence of extraction, all patients with extraction of two teeth in one arch were put together in one subgroup. The comparison of means was achieved with the Student's t test for independent samples.

Degree of expansion. To evaluate the effect of the amount of expansion during treatment, the sample was divided into the subgroups mild and extensive treatment, definitions are given in Table III. The significant prevalence of stability and relapse in relation to the independent variables under investigation was assessed by means of one-way and two-way tables and X2 test. The significance level was established at p -< 0.05. End-of-treatment alignment. The sample was segregated arbitrarily into two subgroups "none to mild discrepancy" and "moderate discrepancy," definitions and the almost equal subgroup sizes are listed in Table IV. The influence of the posttreatment alignment on the postretention changes was tested by means of X~ test. Measurement error The measurement error was determined by remeasuring pretreatment, end-of-treatment, and postretention casts of 30 randomly selected cases several weeks after the initial measurement by the same examiner who did the first measurements. The median ranged from 0.0 mm (T1) to 0.5 mm (T2, T3) for intercanine and intermolar width and ranged from - 1.0 mm (lower crowding at T3) to 0.3 mm (upper crowding at T2) for the cofactots. The Pearson product-moment correlation coefficient between the two trials was between 0.8909 (lower intermolar width at T3) and 0.9866 (lower intermolar width at T~) for the main variables and between 0.7876 (upper crowding at T2) and 0.9890 (upper arch length at T1). There was no sign of a systematic error of method. RESULTS Postretention intercanine and intermolar width changes At postretention, 13.8% of the pooled sample s h o w e d an a n t e r i o r u p p e r arch w i d t h c o n s t r i c t i o n o f 2 m m o r m o r e . I n 86.2% o f t h e cases, an arch

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Table I. Definition and sizes of the groups "stability" and "relapse" of arch width Variables (ram)

]Mildchange[AbsolutelRelativefrequency]Severechange (Te--~T3) stability frequency (%) (T2--~Ts) relapse

Absolute frequency

Relativefrequency (%)

lntercanine width Maxillary Mandibular

< 2.0 < 2.0

194 172

86.2 76.1

->2.0 ->2.0

31 54

13.8 23.9

< 2.5 < 2.5

167 183

74.2 81.0

->2.5 ->2.5

58 43

25.8 19.0

Intermolar width Maxillary Mandibular

Table II. Definition and sizes of the subgroups "mild" and "severe" original anomaly for all variables

Variables (ram)

Mild deviation (TI)

Absolute frequency

Relativefrequency (%)

Severedeviation (T1)

Absolute frequency

Relativefrequency (%)

_>32.5 > 26.5

91 109

43.5 49.8

< 32.5 < 26.5

118 110

56.5 50.2

_>46.0 _>47.0

117 111

52.5 49.6

< 46.0 < 47.0

107 113

47,8 50.4

-> 29.0 _>23.5

122 108

54,5 48,2

< 29.0 < 23.5

102 116

45.5 51.8

< 32.0 < 24.0

101 135

45.1 60.3

_>32,0 -> 24,0

123 89

54.9 39.7

< 4.5 < 4.0

120 99

53.3 44.0

-> 4,5 _>4.0

105 126

46.7 56.0

-> - 1.5 -> - 1.0

124 97

55.6 43.3

< - 1.5 < - 1.0

99 127

44.4 56.7

< 6.2 < 3.5

37 81

50.0 58.7

_>6.2 _ 3.5

37 57

50.0 41.3

lntercanine width Maxillary Mandibular

Intermolar width Maxillary Mandibular

Arch length Maxillary Mandibular

Md size of incisors Maxillary Mandibular Overjet Overbite

Crowding Maxillary Mandibular

Irregularity index Maxillary Mandibular

Table Ul. Definition and sizes of the subgroups "mild" and "extensive" expansion during treatment

VariableS(mm)

IMildexpansi°nlAbs°lute]RelativefrequencY(T:--~T2) rfequency (%)

Extensiveexpansion(T:_,T2)frequencyAbs°lute]Relativefrequency(%)

Intercanine width Maxillary Mandibular

< 2.5 < 2.5

95 190

45.4 86.0

_>2.5 -> 2.5

114 31

54.5 14.0

< 4.0 < 4.0

170 187

75.6 82.7

--- 4.0 ___4.0

55 39

24.4 17.3

lntermolar width Maxillary Mandibular

width loss of less than 2 mm was found. The lower intercanine width decreased during the posttreatment period (T 2 ~ T3) more than 2 mm in 23.9% of the cases and showed constriction of less than 2 mm in 76.1%.

Posterior arch width relapse (decrease of 2.5 mm or more) was found in 25.8% of the upper jaws and 19.0% of the lower jaws. However, maxillary stability occurred in 74.2% and mandibular stability was assessed in 81.0% (Fig. 5).

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number of patients 2 1 0 -1§;i-(86]2q=-) ....................................................................................................................................................................... ] ~~~ " ~ ......................... 180

.........

150

........

1 2 0 ........... 9 0 ............ 6 0 ............. 3 0 ..........

0 maxillary mandibular intereanine width stability

maxillary mandibular intermolar w i d t h ~

relapse

Fig. 5. Distribution of postretention long-term staNlity/relapse of maxillary (nintercanine = 224, n~ntermo~a, = 225) and mandibular arch width in 226 cases. Cases with missing values were not included.

Table IV. Definition and sizes of the posttreatment subgroups "no to mild" and "moderate" discrepancy

Variables (ram)

Notomild discrepancy (Te)

AbsoluteRelativefrequency frequency (%)

M o d e r a t e l A b s o l u t e l R e l a t i v e f r e q u e n c 3, discrepancy (7"2) frequency (%)

Intercanine width Maxillary Mandibular

-> 35.0 -> 26.5

115 133

51.3 59.4

< 35.0 < 26.5

109 91

48.7 40.6

-> 48.0 ->48.5

116 109

51.8 48.7

< 48.0 < 48.5

108 115

48.2 51.3

-> 26.5 -> 21.5 < 2.5 < 3.0

115 115 121 94

51.3 51.3 54.0 42.0

< 26.5 < 21.5 ->2.5 -> 3.0

109 109 103 130

48.7 48.7 46.0 58.0

102 109

45.5 48.7

111 108

50.0 48.2

Intermolar width Maxillary Mandibular

Arch length Maxillary Mandibular Overjet Overbite

Crowding Maxillary Mandibular

-> 1.0 -> - 0.5

122

54.5

115

51.3

111

50.0 51.8

< 1.0 < - 0.5

Irregularity index Maxillary Mandibular

< 2.4 < 2.0

116

Cofactors

Pretreatment anomaly. When the sample was grouped into mild and severe parameter subgroups at pretreatment stage, significant differences were found for the mean postretention changes of upper and lower intercanine and intermolar arch width dimension. Upper intercanine width showed considerable relapse, significantly influenced by three pretreatment parameters: upper intermolar width, crowding, and overjet. As shown in Table Va, severe anterior arch constriction postretention occurred

->2.4 >2.0

significantly more often in cases with greater pretreatment posterior arch width deficiency, severe space lack, and an increased overjet. Of the 50.4% of the cases with severe lower posterior arch constriction before treatment, 64.8% showed a considerable decrease in anterior arch width during posttreatment period and 54.1% of those with a mild pretreatment deficiency (49.6%) remained stable (p = 0.0154). Table Va also shows that those cases with upper intermolar constriction and crowding before treatment tended to demon-

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Table Va. Percentages of relapse and stability of maxillary and mandibular intercanine width in relation

to the pretreatment cofactors under investigation. The numbers in parentheses are the total percentages of the independent variables (cofactors) Intercanine width Relapse + severe deviation (7"1)

Stability + mild deviation (7"1)

7"1 cofactor

%

(%)

p value

%

(%)

Maxillary intermolar width Maxillary crowding Overjet

19.4 19.0 19.2

(48.0) (44.6) (46.4)

0.0178 0.0445 0.0296

91.5 90.3 90.8

(52.0) (55.4) (53.6)

30.7 30.6 30.7

(50.4) (47.8) (44.9)

0.0154 0.0246 0.0338

83.0 82.2 81.5

(49.6) (52.2) (55.1)

Maxilla

Mandible

Mandibular intermolar width Maxillary intermolar width Maxillary crowding

Table Vb. Percentages of relapse and stability of maxillary and mandibular intermolar width in relation to

the pretreatment cofactors under investigation. The numbers in parentheses are the total percentages of the independent variables (cofactors) Intermolar width Relapse + severe deviation (T1) T 1 cofactor

Stability + mild deviation (T1)

%

(%)

p value

%

(%)

35.2 32.2

(48.0) (56.5)

0.0019 0.0166

82.9 82.4

(52.0) (43.5)

25.4 24.0 25.0 25.6 23.8

(50.4) (57.1) (54.9) (39.8) (56.0)

0.0132 0.0270 0.0116 0.0419 0.0431

87.5 87.6 88.2 85.3 86.9

(49.6) (42.9) (45.1) (60.2) (44.0)

Maxilla

Maxillary intermolar width Maxillary intercanine width Mandible

Mandibular intermolar width Mandibular crowding Sum of the mesiodistal diameter of maxillary incisors Sum of the mesiodistal diameter of mandibular incisors Overbite

strate considerable relapse of lower anterior arch width postretention. The X2 test revealed also statistically significant influences of upper intermolar and intercanine arch width dimension pretreatment on the postretention changes of maxillary intermolar width, which relapsed more often in cases with severe initial deficiency but remained stable in those cases with mild pretreatment upper anterior and posterior arch width deficiency (Table Vb). The relapse of the mandibular intermolar width was also found to be significantly associated with the degree of the initial anomaly (Table Vb). Posterior arch width constriction, severe crowding, great mesiodistal diameters of the incisors and an increased overbite were associated with the postretention relapse.

Kind of therapy. The means for the pretreatment and posttreatment maxillary and mandibular intercanine and intermolar widths of the extraction and nonextraction subsample are shown in Table VI. The mean pretreatment values were found to be significantly lower in the extraction group, with the exception of the lower intercanine width. During treatment, the mean arch width dimension increased in all subgroups, although there was a statistically significant difference between nonextraction and extraction groups, with the intercanine width increasing more in the extraction subgroup, while increasing less in the nonextraction cases. There was no apparent difference in the resultant intercanine width at T2, whereas a difference was found for the intermolar arch width. Mean decreases in intercanine and intermolar

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T a b l e VI. Comparison of means and standard deviations for the pretreatment and posttreatment arch width dimension and for the treatment and postretention changes

Pretreatment Nonextraction

Extraction Variables

Posttreatment Extraction

Nonextraction

Mean

SD

Mean

0.000 n.s.

32.4 26.4

2.2 2.0

34.9 26.8

2.1 1.6

n.s. n.s.

34.6 26.5

2.1 1.7

0.000 0.015

46.3 47.1

2.6 2.6

46.2 46.7

2.7 2.9

0.000 0.000

49.1 49.2

2.8 2.6

Mean

SD

p

31.0 26.1

2.8 1.7

44.8 46.2

3.0 3.0

[ SD

p

Mean

[

SD

lntercanine width Maxilla Mandible

Intermolar width Maxilla Mandible

Postretention change (T2---~7"3)

Treatment change (7"1--->7"2) Intercanine width Maxilla Mandible

3.9 0.7

2.9 1.7

0.000 0.040

2.3 0.2

2.0 1.6

- 1.2 - 1.5

1.3 1.3

0.001 n.s.

- 0.7 - 1.4

1.2 1.8

1.5 0.5

2.4 2.6

0.000 0.000

2.8 2.1

2.2 2.2

- 2.2 - 1.4

1.8 2.3

0.000 n.s.

- 1.2 - 1.0

1.8 1.8

Intermolar width Maxilla Mandible

nls.,p

> 0.05.

width were observed for the four parameters and both subgroups during the posttreatment period. Although the posttreatment upper intercanine values did not differ, the anterior upper arch constriction was significantly higher (p = 0.001) in the extraction group than in the nonextraction cases. In addition, marked intergroup variation of posttreatment intermolar width change was apparent: The upper intermolar width was maintained to a significantly higher amount in the nonextraction group (p = 0.000). Degree of expansion. One hundred fourteen patients (54.5%) showed an anterior upper arch width expansion during treatment of 2.5 mm or more. In 55 cases (24.4%), the gain in intermolar arch width was 4.0 mm or more. The lower intercanine width increase during treatment was found to be 2.5 mm or more in 31 cases (14.0%) and the intermolar width was increased 4.0 mm or more in 39 cases (17.3%). The arch width constriction from posttreatment to postretention showed statistically significant differences (Table VIIa and VIIb) on the basis of the degree of expansion during treatment, with "moderate gain in arch width cases" demonstrating a greater ability to maintain intercanine and intermolar expansion than the "severely expanded cases." End-of-treatment alignment. Subjects in the group with a postreatment overjet of 2.5 mm or less demonstrated significantlymore upper intercanine width maintenance than those with an increased overjet (p = 0.0241, Table VIIIa).

As shown in Table VIIIb, the amount of lower anterior arch constriction postretention was weakly associated with the posttreatment level of alignment. The intercanine width was stable in cases with more crowding (p = 0.0498) and with smaller lower intercanine width dimension (p = 0.0486). A relapse of the upper intermolar width occurred more often in cases with shortened lower arch length, greater lower intercanine width, mild or no lower crowding, and incisor irregularity (Table Villa). The lower intermolar relapse, also was found more often in cases with greater posttreatment lower intercanine width and mild to no upper crowding (Table VIIIa). DISCUSSION

Overall, considerable maxillary intercanine longterm stability was found for the majority of the cases. The upper intermolar and lower intercanine width, however, were decreased beyond the accepted range in nearly 25% of the cases. As documented in 1952 by Barrow and White 2 and also reported 31 years later by Sinclair and Little,28 arch width after the puberal growth normally decreases. During treatment, however, maturation processes of arch width have to be considered in our study sample. The hypothesis of several cofactors having association with the degree of postreatment changes was supported by our data. During postreatment period, maxillary and mandibular arch width stabil-

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Table Vlla. Percentages of relapse and stability of maxillary intercanine and intermolar width in relation to

degree of treatment. The numbers in parentheses are the total percentages of the independent variables (cofactors) Maxillary width Relapse + severe expansion T I-~ T 2 cofactor

Stability + mild expansion

%

(%)

p value

%

[

(%)

19.3 23.6

(54.5) (24.4)

0.0129 0.0146

92.6 89.4

(45.5) (75.6)

32.5 45.5

(54.5) (24.4)

0.0166 0.0001

82.1 80.6

(45.5) (75.6)

Intercanine

Maxillary intercanine width Maxillary intermolar width lntermolar

Maxillary intercanine width Maxillary intermolar width

Table VIIb. Percentages of relapse and stability of mandibular intercanine and intermolar width in relation

to degree of treatment. The numbers in parentheses are the total percentages of the independent variables (cofactors) Mandibular width Relapse + severe expansion T1---~Te cofactor

Stability + mild expansion

%

(%)

p value

%

(%)

41.9 40.0 43.6

(14.0) (24.4) (17.3)

0.0115 0.0013 0.0015

78.9 81.2 80.2

(86.0) (75.6) (82.7)

25.4 32.7 46.2

(54.5) (24.4) (17.3)

0.0112 0.0031 0.0000

88.4 85.3 86.6

(45.5) (75.6) (82.7)

lntercanine

Mandibular intercanine width Maxillary intermolar width Mandibular intermolar width Intermolar

Maxillary intercanine width Maxillary intermolar width Mandibular intermolar width

ity have been influenced by pretreatment and posttreatment factors. The findings have also shown distinct differences between extraction and nonextraction groups, as well as the influence of the degree of expansion during treatment. An intermolar expansion of 4 mm or more and an intercanine arch width increase of 2.5 mm or more were found to be significantly correlated with the arch width relapse. Besides the direct influence of the "destiny" of certain variables, intraarch and interarch relationship were found to be predictors of relapse respectively stability. The maintenance of mandibular arch width, for example, was associated with the degree of posterior expansion in the upper arch. Relapse of the intercanine width in cases with severe initial anomaly (arch constriction, crowding or space loss, and increased overjet) and stability in cases with mild pretreatment discrepancy are distinct predictors of the rigidity of anatomic structures (morphogenic pattern).

Arch width relapse after marked expansion in cases of a high amount of discrepancy with an acceptable end-of-treatment result is a distinct sign of the limitations of treatment. Maxillary and mandibular intercanine width

In addition, postretention relapse of the anterior upper arch width was influenced by the degree of pretreatment and posttreatment overjet. Assuming lack of interincisor relationship and intercanine contact, in cases with an increased overjet, a collapse of the upper intercanine arch width is predictable. Relapse of the lower anterior arch width was found more often in cases with severe pretreatment upper crowding, possibly caused by the extensive treatment efforts. Relapse tendencies in the upper arch affected the lower arch maintenance. An important finding that should be taken into consideration before the end-of-treatment is the

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Table Villa. Percentages of relapse and stability of maxillary intercanine and intermolar width in relation

to posttreatment cofactors under investigation. The numbers in parentheses are the total percentages of the independent variables (cofactors) Maxillary width Relapse + moderate deviation (T1)

Stability + mild deviation (T1)

%

(%)

p value

%

Intercanine Overjet

19.4

(45.8)

0.0241

91.0

(54.2)

Intermolar Mandibular intercanine width Mandibular arch length Mandibular crowding Mandibular Irregularity Index

17.4 33.0 18.3 19.3

(40.9) (48.4) (48.4) (48.4)

0.0167 0.0159 0.0135 0.0304

68.4 81.0 67.2 68.1

(59.1) (51.6) (51.6) (51.6)

T2 cofactor

I I

(%)

Table VIIIb. Percentages of relapse and stability of mandibular intercanine and intermolar width in

relation to posttreatment cofactors under investigation. The numbers in parentheses are the total percentages of the independent variables (cofactors) Mandibular width Relapse + moderate deviation (T2)

Stability + mild deviation (T2)

T2 cofactor

%

(%)

p value

%

(%)

lntercanine Mandibular intercanine width Mandibular crowding

17.2 18.2

(41.2) (48.7)

0.0486 0.0498

71.4 70.7

(58.8) (51.3)

Intermolar Mandibular intercanine width Maxillary crowding

10.8 11.7

(41.2) (45.8)

0.0080 0.0089

75.2 74.6

(58.8) (54.2)

lesser percentage of cases that relapsed, having moderate posttreatment crowding and a minor lower arch width. The conclusion is that the acceptance of a moderate lower crowding will not increase the danger of relapse. Maxillary and mandibular intermolar width

Relapse of the upper posterior arch width was associated with the amount of pretreatment anterior and posterior deficiency, whereas lower relapse was related only to the posterior arch width lack. In addition, the mandibular relapse was affected by the disharmony between arch width and tooth size, severe crowding, and an increased overbite. The posttreatment lower intercanine width was a predictor for both arches; relapse occurred less often in cases with less arch width, another argument to treat within the anatomic limitations. As already establishe~t by Little and coworkers, 13'~7'18 the process of late arch constriction in treated and untreated persons has to be considered as a normal

developmental change. However, in treated patients, two components are playing a role: the physiologic maturation process and the reactive part of change. The comparison of patients with moderate and severe expansion in this study reveals that the treatment induced part of change is not solely influenced by the amount of expansion. The knowledge of influencing factors and the probability of their influence consequently should be taken into account when planning and realizing an orthodontic treatment. In the past, other authors, for example, Nance, 29 have suggested that an overexpansion should be avoided. In particular, the discrepancy between arch and tooth size in cases of great mesiodistal tooth dimension and small apical base is a predictor for the decision to reduce the numbers of teeth. The current study revealed a statistically significant relationship between the mesiodistal incisor size and the postretention mandibular arch width

American Journal of Orthodontics and Dentofacial Orthopedics Volume 109, No. 4

constriction. In those cases with a great mesiodistal incisor dimension, the lower arch relapsed more often than in those cases with small incisors. Probably more expansion has been achieved in cases with large tooth size. "Do these data support the hypothesis of longterm stability in cases where permanent teeth have been extracted?" After treatment no intercanine but an intermolar arch width difference was found that was stable up to the time of the follow-up examination. However, the intermolar and intercanine constriction changes in the upper arch were double in extraction cases. A simple explanation may be the fact that in extraction cases, first molars are moving mesially, despite a maximum of anchorage, which leads to the decrease of posterior arch width caused by sagittal tooth movement. Assuming that in cases of severe anterior crowding, the canines are moved distally, the upper intercanine width should not decrease. This also throws a light on the findings that extraction cases had less posterior postretention arch width than pretreatment ones and that the upper anterior arch width was apparently stable. Sondhi et al. 19 mentioned "unknown unexamined factors" to explain differences in postretention changes of molars and canines, the maxilla and the mandible. They had also found stability of upper canines and relapse of lower canines. Although lower canines, which were moved distally after extraction, showed more relapse, the difference was not significant. Gardner and Chaconas 16 also did not find any difference of arch width constriction in extraction and nonextraction cases, Shapiro 8 stated no significant difference for the lower intercanine width, but the intermolar distance was reduced significantly more in extraction cases. Since late arch width changes have been observed in treated and untreated persons by many authors, grouping of the present sample was done, including a certain amount of change as "normal." This way the variables that have been proposed as influencing cofactors were found to affect the multicaused postretention change of arch dimension and tooth position, whereas other investigators did not find any predictors of relapse in cases ignoring the wide range of "normal" posttreatment adolescent and adult developments. CONCLUSION

The final conclusion of this study is the proposal to renew the definition of stability and to take into

Kahl-Nieke, Fischbach, a n d Schwarze

377

account in case of theoretical consideration before as well as during and after treatment that pretreatment anomaly, kind and amount of treatment, and posttreatment alignment are long-term affecting factors. Also the existence of definite limitations in every patient associated with the individual key anatomic features should be realized by the orthodontist, and patients should be apprised before treatment. We express our gratitude to Dr. Elizabeth K. Gesenhues for her review of the manuscript. REFERENCES 1. Moorrees CFA, Reed RB. Biometrics of crowding and spacing of the teeth in the mandible. Am J Phys Anthrop 1952;12:77-88. 2. Barrow GV, White JR. Developmental changes of the maxillary and mandibular dental arches. Angle Orthod 1952;22: 41-6. 3. Sillman JH. Dimensional changes of the dental arches: longitudinal study from birth to 25 years. AM J ORTHOD 1964;50:824-42. 4. DeKock WH. Dental arch depth and width studied longitudinally from 12 years of age to adulthood. AM J ORTHOD 1972;62:56-66. 5. Steiner CC. Orientation of the teeth in dental arches, Angle Orthod 1934;4:35-6. 6. McCauley DR. The cuspid and its function in retention. AM J ORTHOD ORAL SURG 1944;90:196-205. 7. Strang RHW. The fallacy of denture expansion as a treatment procedure. Angle Orthod 1949;19:12-7. 8. Shapiro PA. Mandibular dental arch form and dimension. Treatment and postretention changes. AM J ORTHOD 1974; 66:58-70. 9. Walter DC. Changes in the form and dimensions of dental arches resulting from orthodontic treatment. Angle Orthod 1953;23:3-18. 10. Walter DC. Comparative changes in mandibular canine and first molar widths. Angle Orthod 1962;32:232-41. 11. Litowitz R, A study of the movement of certain teeth during and following orthodontic treatment. Angle Orthod 1948; 18:113-32. 12. Ades AG, Joondeph DR, Little RM, Chapko MK. A longterm study of the relationship of third molars to changes in the mandibular dental arch. AM J ORTHOD DENTOFAC ORTHOP 1990;97:323-35. 13. Little RM, Riedel RA, Engst D. Serial extraction of first premolars -- postretention evaluation of stability and relapse. Angle Orthod 1990;60:255-62. 14. Peak JD. Cuspid stability. AM J ORTHOD 1956;42:608-14. 15. Johnson KC. Cases six years postretention. Angle Orthod 1977;47:210-21. 16. Gardner SD, Chaconas SJ. Posttreatment and postretention changes following orthodontic therapy. Angle Orthod 1976; 46:151-61. 17. Little RM, Wallen TR, Riedel RA. Stability and relapse of mandibular anterior alignment-first premolar extraction cases treated by traditional edgewise orthodontics. AM J ORTHOD 1981;80:349-65. 18. Little RM, Riedel RA, Artun J. An evaluation of changes in

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American Journal of Orthodontics and Dentofacial Orthopedics

April 1996

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Reprint requests to: Dr. B/irbel Kahl-Nieke Department of Orthodontics University of Cologne Kerpener Stal3e 32 50931 Cologne Germany

AAO MEETING CALENDAR

1996 - Denver, Colo., May 11 to 15, Colorado Convention Center 1997 - Philadelphia, Pa., May 3 to 7, Philadelphia Convention Center 1998 - Dallas, Texas, May 16 to 20, Dallas Convention Center 1999 - San Diego, Calif., May 15 to 19, San Diego Convention Center 2000 - Chicago, II1., April 29 to May 3, McCormick Place Convention Center 2001 - Toronto, Ontario, Canada, May 5 to 9, Toronto Convention Center 2002 - Baltimore, Md., April 20 to 24, Baltimore Convention Center