Crowding and spacing in the dental arches: Long-term development in treated and untreated subjects


The purposes of this study were to analyze long-term changes in anterior spacing and crowding and to compare the development in orthodontically treated and untreated subjects.


The sample comprised 308 adolescents in the late mixed or early permanent dentition who were examined clinically at the ages of 7 to 17 years and again 25 years later. The treated subgroup of 58 subjects had received orthodontic treatment with fixed or removable appliances or both. All subjects had a full complement of teeth, except for 19 who had premolar extractions as part of their orthodontic treatment plan.


The prevalence of maxillary anterior spacing was substantially and significantly reduced in both the untreated and treated groups from the first examination to the second. The prevalence of mandibular crowding increased significantly in the untreated and the nonextraction treated groups. The prevalence of mandibular crowding in patients treated without extractions increased by 25.6%, significantly more than in the untreated controls. The prevalence of maxillary crowding decreased by 15.8% in patients treated with maxillary premolar extractions, significantly more than in the untreated controls.


Long-lasting developmental factors seem to result in universally reduced maxillary anterior spacing, orthodontic treatment notwithstanding. Compared with untreated subjects, the long-term development of mandibular anterior crowding was unfavorable in subjects treated without extractions. Compared with untreated subjects, the long-term development of maxillary anterior crowding was favorable when treatment included extraction of the maxillary premolars.

Several longitudinal studies have been conducted to describe the development of arch dimensions or space conditions in adolescents and adults, but large samples of untreated subjects with full dentitions are not easily obtained for repeated examinations in countries with adequate orthodontic services.

Comparisons between or with previous studies of untreated subjects are complicated and unreliable, since standardization of research approaches is minimal. The criteria vary, and the objectives can include intermolar arch widths, intercanine widths, arch lengths or perimeters, arch length discrepancy or space analysis, or incisor irregularity. Subjects might be randomly selected or limited to 1 class of occlusion. Subjects with missing teeth are usually excluded, but not always.

Most studies, but not all, describe the sexes separately or include tables comparing the sexes.

Some studies include development in the mixed dentition or late adolescence, whereas others are confined to adults after active growth. Studies on development in untreated subjects are for good reasons mostly longitudinal, but important information can also be derived from extensive cross-sectional population surveys.

In studies on treated subjects conducted to determine changes with orthodontic treatment and beyond, the many research approaches and variables in untreated subjects are repeated and then complicated further by diversity in the treatment procedures, retention protocols, and timing of treatment and examinations, as discussed previously.

Some aspects of posttreatment changes have been made clear in previous articles and summarized in discussions and reviews. Fundamental knowledge is still lacking, however, because of impeding factors such as individual variations in subject groups, the confounding effects of normal aging processes, and a general lack of experimental research with proper controls and randomization.

The purposes of this study were to analyze long-term changes in anterior spacing and crowding, and to compare the development in orthodontically treated and untreated subjects.

Material and methods

The original sample of randomly selected subjects comprised 1641 primary schoolchildren in Reykjavík, Iceland, examined clinically at the ages of 7 to 17 years. This study was based on 832 subjects (50.7%) from this sample who were available for a second examination 25 years later.

Sex, age, initial dental stage (DS), and treatment categories are described in Table I . DS 4 refers to subjects with all permanent teeth mesial to the first molars fully erupted, DS 3 subjects are in the late mixed dentition, and DS 2 subjects are in the intermediate mixed dentition with all permanent incisors fully erupted.

Table I
Subject characteristics at T1 and T2
Untreated Nonextraction treatment Extraction treatment Total
Total (n) 250 39 19 308
Male (n) 90 17 5 112
Female (n) 160 22 14 196
T1, DS 2 (n) 26 6 3 35
T1, DS 3 (n) 99 26 10 135
T1, DS 4 (n) 125 7 6 138
T1, mean age (y) 11.8 10.7 10.7 11.6
T1, age range (y) 7-17 8-17 8-15 7-17
Fixed appliance (n) 0 15 17 32
Removeable appliance (n) 0 24 2 26
T2, mean age (y) 37.9 37.4 37.2 37.8
T2, age range (y) 33-43 34-42 34-41 33-43

All subjects with congenitally missing teeth were excluded, as were those who had lost any permanent teeth. Those who were in the early mixed dentition at the initial examination (T1) were also left out to eliminate the least mature of the initial group. The selection process therefore resulted in a longitudinal sample of 58 orthodontically treated and 250 fully dentate untreated subjects examined in adolescence and again 25 years later at the ages of 33 to 44 years.

The treated sample of 58 was then split into subgroups of 39 subjects treated without extractions and 19 subjects treated orthodontically with extractions of premolars.

In the subgroup of 19, there were 9 patients with maxillary extractions only, and 8 of these patients had the maxillary first premolar extracted. The other 10 subjects had 4 premolars extracted; there were maxillary first premolar extractions in 9 of the 10 patients and mandibular first premolar extractions in 6 of the 10 patients.

The T1 registrations were done by the second author (T.E.M.). He was also in charge of the second examination (T2), when the registrations were done by a qualified hygienist, after training and calibration. The registrations were carried out with a measuring instrument designed specifically to record occlusal traits and space condition according to the comprehensive method of Björk et al. The marking lines on the instrument are easily readable and limited to those that categorize the variables in question. Since the T2 examiner was uninformed about the treatment history of the subjects, any systematic or interexaminer bias would have affected to the same degree both treated and untreated subjects, the groups that were compared in this study. The registration method has been tested thoroughly for intraexaminer and interexaminer reliability, and has been used in several studies dealing with epidemiology and development of occlusion.

A detailed description of the material and methods was published previously.

Space anomalies were recorded according to the definitions of Björk et al, with a 2-mm criterion for spacing and crowding in the maxillary or mandibular anterior regions.

Statistical analysis

The data were analyzed with SPSS software (version 15.0, SPSS Sweden AB, Kista, Sweden). Space anomalies were expressed as dichotomous variables, and the Wilcoxon signed rank test used to analyze changes over time in each group, and the Mann Whitney U test was used to analyze differences between the groups.


The Figure shows a strong decrease in maxillary anterior spacing in all subject groups, and Table II confirms that the change in maxillary spacing was significant in the untreated group, the combined treatment group of 58 subjects, and the nonextraction treatment group of 39 subjects. The Figure and Table II also show that the prevalence of mandibular anterior crowding increased significantly from T1 to T2 in the untreated group, the combined treatment group, and the nonextraction treatment group.

Prevalence of anterior spacing and crowding at T1 and T2 in percentages.

Table II
Anterior spacing and crowding at T1 and T2 in untreated and treated subjects
T1 T2 T1 % T2 % Difference % P value T1 T2 T1 % T2 % Difference % P value
No orthodontic treatment n = 250 Any orthodontic treatment n = 58
Maxillary spacing ≥2 mm 29 7 11.6 2.8 −8.8 0.000 9 2 15.5 3.4 −12.1 0.008
Maxillary crowding ≥2 mm 11 14 4.4 5.6 1.2 0.491 6 6 10.3 10.3 0.0 1
Mandibular spacing ≥2 mm 7 5 2.8 2.0 −0.8 0.480 2 0 3.4 0.0 −3.4 0.157
Mandibular crowding ≥2 mm 22 39 8.8 15.6 6.8 0.002 4 13 6.9 22.4 15.5 0.020∗
Nonextraction orthodontic treatment n = 39 Extraction orthodontic treatment n = 19
Maxillary spacing ≥2 mm 7 2 17.9 5.1 −12.8 0.025∗ 2 0 10.5 0.0 −10.5 0.157
Maxillary crowding ≥2 mm 3 6 7.7 15.4 7.7 0.257 3 0 15.8 0.0 −15.8 0.083
Mandibular spacing ≥2 mm 2 0 5.1 0.0 −5.1 0.157 0 0 0.0 0.0 0.0 1
Mandibular crowding ≥2 mm 1 11 2.6 28.2 25.6 0.002 3 2 15.8 10.5 −5.3 0.655
Significance levels: ∗ P <0.05; P <0.01; P <0.001.
T1-T2 differences within groups were analyzed with the Wilcoxon signed ranks test.
Negative signs for T1-T2 difference indicate reduced prevalence.

Table III compares the untreated group of 250 subjects with each of the treated groups. A higher prevalence of anomalies would be expected in the treated groups at T1, and this can be seen for most of the variables. A significantly higher prevalence in the treated groups at T1, however, was seen only in the comparison of maxillary crowding in the extraction treatment group of 19 patients vs 250 untreated subjects.

Table III
Differences in spacing and crowding between untreated and all treated groups at T1 and at T2 with data from Table II
T1 T2
39 vs 250 19 vs 250 58 vs 250 39 vs 250 19 vs 250 58 vs 250
Difference P Difference P Difference P Difference P Difference P Difference P
% value % value % value % value % value % value
Maxillary spacing ≥2 mm 6.3 0.265 −1.1 0.888 3.9 0.415 2.3 0.437 −2.8 0.461 0.6 0.792
Maxillary crowding ≥2 mm 3.3 0.374 11.4 0.031∗ 5.9 0.075 9.8 0.025∗ −5.6 0.290 4.7 0.187
Mandibular spacing ≥2 mm 2.3 0.437 −2.8 0.461 0.6 0.792 −2.0 0.374 −2.0 0.535 −2.0 0.278
Mandibular crowding ≥2 mm −6.2 0.182 7.0 0.313 −1.9 0.639 12.6 0.053 −5.1 0.554 6.8 0.213
Significance level: ∗ P <0.05.
Differences between treated and untreated groups were analyzed with Mann-Whitney U tests.
Table III compares untreated and treated groups with data from Table II and the Figure .
Negative signs indicate a lower prevalence in the treated group than in the untreated group.

At T2, the nonextraction treated group of 39 subjects had a higher prevalence of maxillary crowding than did the untreated group.

Table IV describes the development in the treated groups, by using changes in the untreated group as the control. The development in the treated subjects was more favorable regarding most variables and significantly for maxillary crowding in the extraction treatment group of 19 subjects. Favorable in this context means decreased prevalence of the anomaly from T1 to T2. Development of mandibular crowding was, conversely, unfavorable in the nonextraction treatment group of 39 subjects.

Table IV
Changes of prevalence in treated groups vs untreated subjects with data from Table II
Baseline T1-T2 change n = 250 Untreated % T1-T2 change in treated subjects and comparison with untreated control group
n = 39 Nonextraction treated n = 19 Extraction treated n = 58 All treated
% P % P % P
Maxillary spacing ≥2 mm −8.8 −12.8 0.463 −10.5 0.822 −12.1 0.482
Maxillary crowding ≥2 mm 1.2 7.7 0.202 −15.8 0.013∗ 0.0 0.797
Mandibular spacing ≥2 mm −0.8 −5.1 0.176 0.0 0.843 −3.4 0.314
Mandibular crowding ≥2 mm 6.8 25.6 0.002 -5.3 0.171 15.5 0.089
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Apr 13, 2017 | Posted by in Orthodontics | Comments Off on Crowding and spacing in the dental arches: Long-term development in treated and untreated subjects
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