A longitudinal evaluation of extraction versus nonextraction treatment with special reference to the posttreatment irregularity of the lower incisors

Development of a New Ramus Anterior Vertical Reference Line for the Evaluation of Skeletal and Dental Changes as a Decision Aid for the Treatment of Crowding in the Lower Jaw: Extraction vs. Nonextraction

Objectives: Anterior crowding in the lower jaw is a common orthodontic issue often managed through premolar extraction, which can affect facial profile development. This study aimed to evaluate skeletal and dental changes in moderate to severe crowding using a novel mandibular reference line-the Ramus Anterior Vertical (RaV)-to support treatment planning. Methods: A total of 140 patients (LII > 4 mm and < 9 mm; mean age ≈ 12.5 years) were divided into two groups (G1: extraction; G2: nonextraction; total n = 140; n = 70 per group). Skeletal and dental parameters were measured before (T0) and after (T1) orthodontic treatment using 280 lateral cephalograms. RaV was defined as a vertical line through the anterior ramus point, perpendicular to the occlusal plane. Results: Sagittal measurements relative to RaV were reproducible and unaffected by mandibular mobility. Significant vertical skeletal changes were observed in G2 females, with an increased anterior facial height (N-Sp' and Sp'-Gn) but a stable Hasund Index. In G1, the dental arch length and distances from RaV to i5 and i6 were reduced, while second molars (i7) remained stable. Sagittal incisor axis changes (L1-NB°, SAi1°) and skeletal-dental correlations (ML-NSL, Gn-tGo-Ar) were present only in G1. Conclusions: RaV proved to be a stable mandibular reference for assessing treatment effects. In this study, premolar extraction vs. nonextraction was comparably effective, though some vertical skeletal adaptations, especially in G2 females, took place.

Long-term relapse of anterior teeth in orthodontic patients treated with and without premolar extractions using a 3-dimensional surface mesh analysis

INTRODUCTION

The study evaluated the long-term postretention changes in patients with borderline crowding treated with and without premolar extractions using 3-dimensional surface registration analyses and 2-dimensional (2D) conventional measurements.

METHODS

The study sample comprised 29 nonextraction patients (nonextraction group [NG]) and 33 extractions (extraction group [EG]). Cephalometric radiographs and dental models of the included patients were used from pretreatment, posttreatment, and postretention. Retention durations were 3.76 ± 1.26 years and 4.52 ± 1.94 years in the NG and EG, respectively. The postretention follow-up period was 17.06 ± 5.83 years for the EG and 14.30 ± 5.70 years for the NG, with similar long-term observations. Maxillary and mandibular superimpositions were performed using 3-dimensional digital scans of the dental models and commercial software. In addition, conventional 2D model measurements and the irregularity index were also assessed.

RESULTS

The investigated parameters regarding the surface changes showed nonsignificant differences (P >0.05) between the 2 groups in the maxillary and mandibular anterior 6 teeth, except for the under tolerance value (the percentage of mesh points that is less than the lower tolerance limit) in mandibular surface registrations (P <0.044). In both groups, the maxillary and mandibular irregularity index and maxillary and mandibular intercanine distances showed significant relapses (P <0.05).

CONCLUSIONS

Comparable surface change outcomes were observed in the NGs and EGs. However, the percentage of meshes exceeding the negative threshold value (-1 mm) of the mandibular dentition in the NG exceeded the EG, indicating more significant lingual movement and relapse of the incisors. In addition, the 2D conventional linear relapse measurements were well below the 3.5 mm threshold value reported in the literature. This finding indicated that both treatment approaches provide acceptable long-term stability in borderline patients when similar retention regimens are employed.

Comparative Assessment of Relapse Following Fixed Orthodontic Treatment in Patients Treated With and Without Extraction: A Systematic Review and Meta-Analysis

The present systematic review aimed to evaluate and compare the post-treatment relapse of overjet, overbite, and mandibular incisor crowding in patients treated with extraction and non-extraction orthodontic approaches and to assess the influence of treatment modality on long-term stability. The review was conducted following PRISMA guidelines. Data were extracted from 10 studies, including retrospective and longitudinal designs, with a total of 720 participants. The primary outcome measures included overjet, overbite, and Little's Irregularity Index. Standardized mean difference (SMD) was used as the summary statistic to compare extraction and non-extraction groups. The risk of bias was assessed using the ROBINS-I tool. The meta-analysis revealed no statistically significant differences in relapse between extraction and non-extraction groups for overjet (SMD: 0.52, 95% CI: -0.18 to 1.23, p>0.05), overbite (SMD: 0.41, 95% CI: -0.11 to 0.93, p>0.05), and incisor irregularity index (SMD: 0.71, 95% CI: -0 to 1.23, p>0.05). Funnel plots indicated no significant publication bias. Risk of bias assessment showed moderate concerns in confounding and participant selection across several studies, while bias due to missing data was notable in longer follow-up studies. The findings suggest that both extraction and non-extraction treatment approaches exhibit similar post-treatment relapse rates for overjet, overbite, and incisor irregularity. The choice of treatment should be based on clinical considerations along with concerns of long-term stability. Further high-quality randomized controlled trials are required to strengthen the evidence.

Extraction vs nonextraction orthodontic treatment: a systematic review and meta-analysis

OBJECTIVES

To compare four first premolar extraction and nonextraction treatment effects on intra-arch width, profile, treatment duration, occlusal outcomes, smile aesthetics and stability.

MATERIALS AND METHODS

An electronic search of the literature to June 2, 2023 was conducted using health science databases, with additional search of gray literature, unpublished material, and hand searching, for studies reporting nonsurgical patients with fixed appliances regarding sixteen sub-outcomes. Data extraction used customized forms, quality assessed with ROBINS-I (Risk Of Bias In Non-randomized Studies-of Interventions) and Cochrane RoB 2 (risk-of-bias) tool. GRADE (Grading of Recommendations Assessment, Development and Evaluation) assessed certainty of evidence.

RESULTS

Thirty (29 retrospective studies, 1 randomized controlled trial) studies were included. Random-effect meta-analysis (95% CI) demonstrated maxillary (MD: -2.03 mm; [-2.97, -1.09]; P < .0001) and mandibular inter-first molar width decrease (MD: -2.00 mm; [-2.71, -1.30]; P < .00001) with four first premolar extraction; mandibular intercanine width increase (MD: 0.68 mm; [0.36, 0.99]; P < .0001) and shorter treatment duration (MD: 0.36 years; [0.10, 0.62]; P = .007) in the nonextraction group. Narrative synthesis included three and five studies for upper and lower lip-E plane, respectively. For American Board of Orthodontics Objective Grading System and maxillary/mandibular anterior alignment (Little's irregularity index), each included two studies with inconclusive evidence. There were no eligible studies for UK Peer Assessment Rating (PAR) score. Class I subgroup/sensitivity analyses favored the same results. Prediction interval indicated no significant difference for all outcomes.

CONCLUSIONS

Four first premolar extraction results in maxillary and mandibular inter-first molar width decrease and retraction of upper/lower lips. Nonextraction treatment results in mandibular intercanine width increase and shorter treatment duration. There was no significant difference between the two groups regarding maxillary intercanine width, US PAR score, and posttreatment smile esthetics. Further high-quality focused research is recommended.

Analyzing the effects of tooth extraction on the lip in orthodontic treatment

INTRODUCTION

The aim of this study was to analyze changes occurring in the lip and facial soft-tissue profile after fixed orthodontic treatment, with or without tooth extraction, in patients with dental class II malocclusion.

MATERIALS AND METHODS

Measurements were made on cephalometric films of 75 individuals with dental class II malocclusion before and after fixed orthodontic treatment. The patients were divided into three groups: no extraction, extraction of upper two premolars, or extraction of four premolars. The parameters measured were: basic upper lip thickness (BULT), vermilion upper lip thickness (VULT), upper lip inclination (ULI), basic lower lip thickness (BLLT), vermilion lower lip thickness (VLLT), lower lip inclination (LLI), face axis angle (Ba-N/PtmGn), labiomental angle, facial convexity angle, and total face convexity angle. The results were analyzed statistically using the Wilcoxon, Kruskal-Wallis, and Mann-Whitney U tests.

RESULTS

It was found that the VULT value in the group with no extraction was lower than the four-extraction group (P = 0.001; P < 0.05). The VULT value in the upper-two extraction group was significantly lower than that in the four-extraction group, and the Ba-N/PtmGn in the no-extraction group was lower than that in the four-extraction group (P = 0.001; P < 0.05).

CONCLUSIONS

These findings suggest that tooth extraction in orthodontic treatment may affect the vermilion upper lip thickness and facial axis, but that this does not have any negative effects on the soft-tissue facial profile. Premolar tooth extraction can be performed by establishing an accurate diagnosis and treatment plan to avoid undesirable and negative effects on the facial soft-tissue profile.

Anterior tooth alignment and arch dimensions changes: 37-year follow-up in patients treated with and without premolar extraction

INTRODUCTION

The objective of this research was to evaluate the anterior tooth alignment and dental arch dimension changes after orthodontic treatments with and without premolar extractions in the long-term.

METHODS

Fifty-seven patients with Class I and Class II malocclusion were divided into 2 groups. Group 1 included 16 patients treated with nonextraction therapy, with mean initial (T1), final (T2), and long-term follow-up (T3) ages of 13.20 years, 15.07 years, and 50.32 years, respectively. The mean treatment (T2 - T1) and long-term follow-up (T3 - T2) times were 1.86 years and 35.25 years, respectively. Group 2 included 41 patients treated with extraction of 4 first premolars, with T1, T2, and T3 ages of 13.31 years, 15.63 years, and 53.60 years, respectively. The mean treatment and long-term follow-up times were 2.32 years and 37.96 years, respectively. The mean retention time was 2.26 years for both groups. The dental casts were obtained and digitized at T1, T2, and T3 stages. The following measurements were obtained: Little irregularity index, arch length, perimeter, and intercanine, interpremolar, and intermolar widths. Intragroup and intergroup comparisons were performed with repeated measures analysis of variance and t tests, respectively.

RESULTS

Anterior tooth irregularity index increased at T3 in both groups. In addition, all arch dimensions, except the intercanine width, were significantly smaller in the extraction group at T3. Both groups showed similar arch dimension changes at T3, except for the mandibular arch perimeter. The percentage of mandibular anterior tooth alignment change was significantly greater in the nonextraction than in the extraction group.

CONCLUSIONS

There was no difference in the changes of anterior alignment and transverse arch dimensions in patients treated with and without premolar extraction at T3, but the percentage of mandibular anterior tooth alignment changes was higher in the nonextraction than in the extraction patients at T3. The mandibular arch perimeter showed more of a decrease at T3 in extraction patients.

Mandibular alignment changes after full-fixed orthodontic treatment: a systematic review and meta-analysis

Background

Although post-treatment mandibular alignment has been extensively investigated, the findings remain controversial.

Objectives

The objective was to assess mandibular alignment changes, as measured by the irregularity index, of patients who underwent full-fixed orthodontic treatment and were followed up at least 1 year after retention.

Search methods

MEDLINE, EMBASE, and Cochrane library, in addition, the reference lists of included studies, were screened. The search was conducted up to April 2018.

Selection criteria

The study designs included both interventional and observational studies of orthodontic patients who received either extraction or non-extraction treatment.

Data collection and analysis

The interventional studies were assessed using the Cochrane Collaboration’s risk of bias assessment tool. The quality of the observational studies was evaluated using National Institution of Health quality assessment tools. The first two authors independently applied the eligibility criteria, extracted the data, and assessed the risk of bias. Any conflicts were resolved with consensus discussion with the third author.

Results

The search retrieved 11 326 articles, 170 of which were assessed for eligibility. There were 44 studies included in the qualitative assessments and 30 in the meta-analyses. The studies included 1 randomized control trial (RCT) and 43 observational studies. The RCT was judged to have a high risk of bias and all of the observational studies had either fair or poor quality. The meta-analysis was based on studies judged to be of fair quality, including a total of 1859 patients. All meta-analyses were performed using random-effect models. The standardized mean difference between post-treatment and post-retention irregularity was 1.22 (95% CI, 1.04–1.40) and 0.85 (95% CI, 0.63–1.07) after extraction and non-extraction treatments, respectively. There was a substantial heterogeneity for the extraction (I2 = 75.2%) and non-extraction (I2 = 70.1%) studies. The follow-up duration (1–10 versus 10–20 years) explained 33% of the heterogeneity, with longer follow-up studies showing more irregularity.

Limitations

The quality of evidence provided by the studies was low. There was a risk of publication bias, and the search was limited to English language.

Conclusions and implications

Post-treatment mandibular irregularity increases are limited. Irregularity increases are slightly greater in patients treated with mandibular premolars extractions, and in patients followed up over longer periods of time.

Registration

The study protocol was not registered.

Impact of third molars on mandibular relapse in post-orthodontic patients: A meta-analysis

BACKGROUND/PURPOSE

Whether third molars contribute to or aggravate relapse, particularly in the mandibular dental arch, after orthodontic treatment remains controversial. Orthodontic clinicians vary widely in their practice regarding prophylactic third molar removal after orthodontic treatment. The present study systematically reviewed and meta-analyzed the available literature, and assessed the impact of third molar removal on the relapse of mandibular dental arch alignment after orthodontic treatment.

MATERIALS AND METHODS

Relevant literature was searched on online databases, namely Pubmed, Embase, and Cochrane. Outcomes of post-orthodontic mandibular relapse were evaluated in terms of the Little's irregularity index, intermolar width, and arch length. Statistical analysis was conducted using the Review Manager software (Version 5.3, The Cochrane Collaboration, Oxford, England).

RESULTS

Our initial search strategy yielded 360 citations, of which three retrospective studies were selected. The Little's irregularity index (weighted mean difference = 0.80, 95% confidence interval = 0.13-1.47, P = 0.02) differed significantly between the erupted third molar extraction group and agenesis third molar group; whereas the arch length and intermolar width did not. No outcome differed significantly between the impacted third molar extraction group and agenesis third molar group.

CONCLUSION

Removal of the mandibular third molars is recommended for alleviating or preventing long-term incisor irregularity.

Rate of tooth movement and dentoskeletal effects of rapid canine retraction by dentoalveolar distraction osteogenesis: A prospective study

INTRODUCTION

The purpose of this study was to test the null hypothesis that duration of orthodontic treatment can be significantly reduced by accelerating canine retraction using dentoalveolar distraction (DAD).

METHODS

Thirty-six maxillary canines of 19 patients comprised the DAD group, and 28 canines of 14 patients were included in the distalization group (DG). The initial mean ages were 15.8 ± 1.96 years for the DAD group and 16.02 ± 2.8 years for the DG. A custom-made, rigid, tooth-borne intraoral distraction device was used for the DAD group, and intraoral elastics were applied for canine distalization in the DG. Six skeletal and 11 dental variables were measured for the cephalometric evaluation.

RESULTS

Canine retraction was 7.9 ± 1.49 mm in 11.8 ± 1.3 days and canine distal tipping was 11.48° ± 4.37° after DAD; the canines were distalized 5.29 ± 2.01 mm and tipped 13.64° ± 9.54° in 200 ± 57 days in the DG. The rates of posterior canine movement were 0.67 ± 0.14 mm per day after DAD and 0.03 ± 0.01 mm per day in the DG. No significant first molar anchorage loss was observed after DAD, although the DG showed some vertical and sagittal first molar movement.

CONCLUSIONS

We failed to reject the null hypothesis. DAD can reduce the duration of orthodontic treatment time by accelerating canine retraction in extraction patients without undesirable side effects.

Twelve-year follow-up of mandibular incisor stability: Comparison between two bonded lingual orthodontic retainers

OBJECTIVE

To compare the long-term outcome 9 years after removal of two different types of fixed retainers used for stabilization of the mandibular anterior segment.

MATERIALS AND METHODS

Sixty-four children who had undergone orthodontic treatment with fixed appliances in both arches were divided into two groups depending on which kind of retainer being used. Twenty-eight of the patients had a canine-to-canine retainer bonded to the canines and 36 had a bonded twistflex retainer 3-3, bonded to each tooth. Measurements were made on study models and lateral head radiographs, before and after treatment, 6 years after treatment, and 12 years after treatment, with a mean of 9.2 years after removal of the retainers.

RESULTS

No significant differences were found between the two groups at the long-term follow-up according to Little's Irregularity Index or available space for the mandibular incisors. The overjet and overbite were reduced after treatment in both groups and stayed stable throughout the observation period. Also, no differences in bonding failures between the two retainers were found.

CONCLUSIONS

Both a canine-to-canine retainer bonded only to the canines and a twistflex retainer 3-3 bonded to each tooth can be recommended. However, neither of the retention types prevented long-term changes of mandibular incisor irregularity or available space for the mandibular incisors after removal of the retainers.

Change in proportion of extraction and non-extraction in orthodontic patients

The purpose of this study was to determine whether there has been an increase in the number of non-extraction cases over recent years and investigate the selection of treatment devices. Patients attending the Department of Orthodontics at Tokyo Dental College Chiba Hospital in whom orthodontic treatment was commenced between July 1989 and July 1990 (Group A) or between June 1998 and May 2003 (Group B) were included in the study. The orthodontic diagnostic records of the patients were examined. Patients requiring orthognathic surgery, those with congenital diseases or cleft palate, and those with an uncertain diagnostic record were excluded. The characteristics, initial age, and classification of malocclusion in the two groups were almost the same. The patients in both groups were further divided into two subgroups: one in which treatment was commenced in mixed dentition and another in which it was begun in permanent dentition. The final therapeutic strategy, that is to say, non-extraction or extraction, was investigated in all groups. The final observation date in the mixed dentition group in Group B was September 2011. No major differences were observed in pattern or type of malocclusion between the two groups. Group B, however, showed an increased rate of non-extraction treatment. A policy of non-extraction was pursued in a higher proportion of patients in whom treatment was commenced in mixed dentition than in those in which it was begun in permanent dentition.

Transversal changes in dental arches from non-extraction treatment with self ligating brackets

OBJECTIVE

The present study aimed at analyzing, with the use of dental casts, the transverse changes of the upper and lower dental arches, after non-extraction orthodontic treatment, with self-ligating brackets.

METHODS

The sample comprised 29 patients, all presenting Class I malocclusion with upper and lower crowding of at least 4 mm and treated only with a fixed appliance, without stripping, extraction or distalization. The dental casts were obtained before and after leveling with 0.019 x 0.025-in stainless steel archwires.

CONCLUSIONS

The results indicated that the majority of transverse changes occurred at the premolar areas, both the first and the second, as well as on the upper and lower dental arches. The intercanine distance increased 0.75 mm, on average, in the upper arch and 1.96 mm in the lower arch. The molars also demonstrated a tendency towards an increase in their transverse dimension, however, at a lower intensity comparing to premolars. All measurements presented statistically significant differences with the exception of the maxillary second molars.

Posttreatment and physiologic occlusal changes comparison

Objective:

To compare posttreatment and postretention occlusal changes with the physiologic occlusal changes caused by natural development of untreated subjects.

Materials and Methods:

The sample was divided into three groups. Group 1 comprised 97 subjects treated with four premolar extractions at a mean pretreatment (T0) age of 13.03 years, a mean posttreatment (T1, first observation) age of 15.12 years, and a mean postretention (T2, second observation) age of 20.52 years. The mean observation period (T2-T1) was 5.39 years. Group 2 comprised 58 subjects treated nonextraction at a mean pretreatment age of 12.83 years, a mean posttreatment age of 14.99 years, a mean postretention age of 20.22 years, and a mean observation period of 5.22 years. Group 3 comprised 114 untreated subjects at a mean age at T1 of 14.91 years and at T2 of 20.48 years. The mean observation period was 5.56 years. Dental casts were evaluated using the Peer Assessment Rating (PAR) index and the Little irregularity index in maxillary and mandibular arches. Changes in PAR and Little indexes were compared among the three groups by analysis of variance and Tukey tests.

Results:

Intergroup comparison showed that at T1 and T2 the treated groups presented smaller PAR and Little indexes than the untreated group. In the observation period, the treated groups showed greater increase in PAR and Little maxillary indexes than the untreated group. The extraction group showed a greater increase of the Little mandibular index than the untreated group.

Conclusions:

The treated groups showed more changes according to PAR and Little maxillary indexes than the untreated group. The posttreatment change of the mandibular anterior crowding of the treated extraction group was greater than the mandibular crowding caused by physiologic changes in the untreated group.

Profile changes of patients treated with and without premolar extractions

INTRODUCTION

In this study, we evaluated and compared treatment effects and long-term soft-tissue profile changes in patients treated with extraction of 4 first premolars and with a nonextraction protocol.

METHODS

Cephalometric records of 98 patients were evaluated. For half (n = 49) of the patients, treatment included the extraction of 4 first premolars; the other 49 patients had no premolar extractions. The groups were evaluated before treatment (T1), at the end of treatment (T2), and at least 4 years postretention (T3).

RESULTS

At T1, the extraction group had more protrusive lower lips than the nonextraction group, as measured by the Z-angle. At T2, the Z-angles had improved in both groups and were not significantly different. During treatment, upper lip vermilion and superior thicknesses increased, whereas lower lip vermilion thickness decreased in both groups. Except for lower lip inferior thickness, which increased significantly in the nonextraction group, no other soft-tissue differences were significant. Significant growth of the nose occurred during from T1 to T2 in both groups, and there was a tendency for the incisors in both groups to return to pretreatment values. The nose also continued to grow during that period.

CONCLUSIONS

Overall, the soft-tissue facial profile measurements for both extraction and nonextraction samples were similar at T3, and there were no clinically significant correlations between hard- and soft-tissue variables at T1, T2, and T3.

Long-term stability of orthodontic treatment and patient satisfaction. A systematic review

OBJECTIVE

To evaluate morphologic stability and patient satisfaction at least 5 years after orthodontic treatment.

MATERIALS AND METHODS

Published literature was searched through the PubMed and Cochrane Library electronic databases from 1966 to January 2005. The search was performed by an information specialist at the Swedish Council on Technology Assessment in Health Care. The inclusion criteria consisted of a follow-up period of at least 5 years postretention; randomized clinical trials, prospective or retrospective clinical controlled studies, and cohort studies; and orthodontic treatment including fixed or removable appliances, selective grinding, or extractions. Two reviewers extracted the data independently and also assessed the quality of the studies.

RESULTS

The search strategy resulted in 1004 abstracts or full-text articles, of which 38 met the inclusion criteria. Treatment of crowding resulted in successful dental alignment. However, the mandibular arch length and width gradually decreased, and crowding of the lower anterior teeth reoccurred postretention. This condition was unpredictable at the individual level (limited evidence). Treatment of Angle Class II division 1 malocclusion with Herbst appliance normalized the occlusion. Relapse occurred but could not be predicted at the individual level (limited evidence). The scientific evidence was insufficient for conclusions on treatment of cross-bite, Angle Class III, open bite, and various other malocclusions as well as on patient satisfaction in a long-term perspective.

CONCLUSIONS

This review has exposed the difficulties in drawing meaningful evidence-based conclusions often because of the inherent problems of retrospective and uncontrolled study design.

Alignment stability in Class II malocclusion treated with 2- and 4-premolar extraction protocols

INTRODUCTION

The purpose of this study was to compare the postretention stability of the correction of mandibular anterior-tooth irregularity in patients with Class II malocclusions whose orthodontic treatments included extraction of 2 or 4 premolars.

METHODS

A total of 66 patients were selected who initially had at least one-half-cusp Class II malocclusions. Nineteen patients (9 male, 10 female) with an initial mean age of 14.04 years were treated with extraction of 2 premolars (group 1); 47 patients (20 male, 27 female) with an initial mean age of 13.03 years were treated with extraction of 4 premolars (group 2). A subgroup of group 2, with a similar amount of initial anterior-tooth irregularity as group 1, was also compared with group 1. Little's irregularity index was used to evaluate anterior tooth irregularity in dental casts obtained from each patient before treatment, after treatment, and 5 years after active treatment. Initial cephalometric variables, initial treatment priority index, pretreatment age, treatment time, and posttreatment time of the groups were compared with t tests. Similarly, Little's irregularity index values at prettreament, posttreatment, and postretention were also compared with the t test. Cephalometric treatment changes within groups were evaluated with dependent t tests.

RESULTS

There were no statistically significant differences in posttretention anterior-tooth irregularity between groups 1 and 2 or the subgroup.

CONCLUSIONS

Treatment of Class II malocclusion with extraction of either 2 maxillary premolars or 4 premolars provides the same mandibular anterior-tooth alignment stability.

Relapse of anterior crowding in patients treated with extraction and nonextraction of premolars

INTRODUCTION

The purpose of this study was to evaluate long-term stability of incisor crowding in orthodontic patients treated with and without premolar extractions.

METHODS

Dental casts and cephalometric records of 98 patients were evaluated before treatment (T1), at posttreatment (T2), and at postretention (T3). Half of the patients had been treated with extractions, and half were treated nonextraction.

RESULTS

Irregularity, as measured by the irregularity index, decreased 5.51 mm in the extraction group and 2.38 mm in the nonextraction group. Mandibular incisor irregularity increased 0.97 mm in the extraction group and 0.99 mm in the nonextraction group, respectively, in the postretention period. Maxillary incisor irregularity relapse was smaller than mandibular incisor relapse for both groups. Intercanine width expanded during treatment. At T3, mandibular intercanine width decreased in both groups, but the differences were not statistically significant. At T3, intermolar width was stable, arch depth decreased, overbite and overjet slightly increased, SN mandibular plane angle decreased, and incisor positions in both groups tended to return to T1 values. Clinically acceptable stability was obtained.

CONCLUSIONS

With the exception of the interincisal angle, no statistically significant differences were recorded between the extraction and nonextraction groups from T2 to T3. No statistically significant correlations were found between any variables studied and mandibular incisor irregularity at T1, T2, and T3.

Postretention relapse of mandibular anterior crowding in patients treated without mandibular premolar extraction

Treatment stability is one of the most important objectives in orthodontics, but, despite decades of research, it is still agreed that the stability of aligned teeth is variable and largely unpredictable. This study aimed to evaluate the relapse of mandibular anterior crowding in patients treated without mandibular premolar extraction. The sample comprised 40 patients of both sexes with Class I or II malocclusions who received nonextraction treatment in the mandibular arch with edgewise mechanics. Lateral cephalograms and dental casts of each patient were obtained at pretreament, posttreatment, and 5 years postretention. Relapse of mandibular anterior crowding was assessed, and associations between this relapse and other clinical factors were also investigated. Mandibular anterior crowding was measured by the Little irregularity index, and the data were evaluated by the Mann-Whitney test. The mean relapse of mandibular anterior crowding was 1.95 mm (26.54%) over the long term. No clinical factor studied was predictive of crowding relapse in the long term.

An evaluation of growth and stability in untreated and treated subjects

This retrospective longitudinal study compared skeletal and dental changes in orthodontically treated patients with changes in a comparable untreated group to evaluate the relationship between skeletal changes and mandibular incisor crowding. Cephalograms and models of 44 untreated subjects from the Broadbent-Bolton Growth Study and 43 treated patients were evaluated at "posttreatment" (14.3 +/- 1.5 and 15.2 +/- 1.1 years, respectively) and at "postretention" (23.2 +/- 3.4 and 28.9 +/- 3.6 years, respectively). Cranial base and mandibular superimpositions were used to measure cephalometric changes. Tooth-size-arch-length discrepancy, contact irregularity, and space irregularity were measured. In both groups, growth in the vertical dimension was twice that in the horizontal dimension. The untreated subjects, who were younger, exhibited greater yearly vertical growth increments than did the treated subjects. The treated subjects exhibited greater overjet and overbite increases than did the untreated subjects. Yearly changes in tooth-size-arch-length discrepancy were greater in the untreated than in the treated subjects, but there were no differences in the changes in irregularity between the 2 groups. A multivariate regression model, relating posterior facial height (Ar-Go) increase and lower incisor eruption to change in space irregularity, explained 42% of the variation in the untreated group (r = 0.64; P <.001). A weaker relationship was found in the treated group. Overjet change was negatively correlated with tooth-size-arch-length discrepancy. Changes in lower incisor crowding were related to growth in the vertical dimension and lower incisor eruption in both untreated (r = 0.64) and treated (r = 0.51) subjects.