Influence of root parallelism on the stability
of extraction-site closures
Kelly Chiqueto,a Guilherme Janson,b Carina Thaıs de Almeida,c Juliana Moura Storniolo,a Sergio Estelita Barros,a
and Jose Fernando Castanha Henriquesd
Bauru and Ribeir~ao Preto, S~ao Paulo, Brazil
Introduction:
In premolar extraction cases, root parallelism is recommended to preserve the stability of space closures. The influence of the degree of root parallelism on relapse of tooth extraction spaces has been a controversial topic in the literature. The aim of this study was to compare the angle between the long axes of the canine and the second premolarin patients with and without stability of extraction-space closures.
Methods:
A sample of 56 patients, treated with 4 premolar extractions, was divided into 2 groups: group 1, consisting of 25 patients with reopening of extraction spaces; and group 2, consisting of 31 patients without reopening of extraction spaces. Panoramic radiographs of each patient were analyzed at the posttreatment and 1-year posttreatment stages. The data were statistically analyzed by using chi-square tests, t tests, analysis of variance (ANOVA), and Pearson correlation coefficients. Results: The results showed that the groups did not differ regarding the angle between the canine and the second premolar, and there was no correlation between angular changes and reopening of extraction spaces, showing that dental angular changes are not determining factors for relapse, and other factors should be investigated.
Conclusions:
The final angle and the posttreatment changes observed in the angle between the long axes of the canine and the second premolar showed no influence on the relapse of extraction spaces. (Am J Orthod Dentofacial Orthop 2011;139:e505-e510)
aPostgraduate student, Department of Orthodontics, Bauru Dental School, University of S~ao Paulo, Bauru, S~ao Paulo, Brazil.
bProfessor and head, Department of Orthodontics, Bauru Dental School, University of S~ao Paulo, Bauru, S~ao Paulo, Brazil.
cPrivate practice, Ribeir~ao Preto, S~ao Paulo, Brazil.
dProfessor, Department of Orthodontics, Bauru Dental School, University of S~ao Paulo, Bauru, S~ao Paulo, Brazil.
The authors report no commercial, proprietary, or financial interest in the products or companies described in this article.
Reprint requests to: Kelly Chiqueto, Rua Padre Jo~ao, 14-68, apto 201, Bauru, S~ao Paulo 17012-020, Brazil; e-mail, kellychiqueto@yahoo.com.br.
Submitted, November 2009; revised and accepted, November 2010.
0889-5406/$36.00
Copyright 2011 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2010.11.019
Extractions are often required in orthodontic treatment because of crowded teeth, an unesthetic facial profile, and dentoskeletal malocclusions,
associated or not with an inadequate functional occlusion. Although stability is 1 goal of orthodontic treatment, reopening of extraction sites has been an unpredictable occurrence. When the first premolars are extracted, space reopening frequently produces esthetic and functional problems, because the absence of interproximal contact between adjacent teeth occurs in an esthetic area and allows food impaction in the cervical embrasure area and consequent damage to the gingival tissues. For this reason, absence of interproximal contacts between adjacent teeth can affect the occlusal
force on the area, propitiating additional trauma on the periodontium.1,2
There are many suggestions in the literature to avoid relapse of extraction spaces.1-5 Trying to prevent reopening of closed extraction sites, Edwards2 recommended surgical gingivoplasty associated with early and tight closure of the extraction site, adequate positions of the roots of the adjacent teeth, elimination of occlusal forces tending to separate the teeth, and appreciation for any tooth-size discrepancy in the extraction areas. This variety of procedures reflects the many factors related to relapse of extraction sites. Some factors were cited as responsible for reopening the extraction sites: angulation of the adjacent teeth to the extraction area, without root parallelism3,5,6; unsatisfactory tooth interdigitation5,7; abnormal muscle
function5,7; no bone maturation in the remodeling area due to immediate orthodontic appliance removal after obtaining the contact point1; and reaction of compressed gingival fibers.1,2,4,7-10
However, the literature is conflicting regarding the prevalence and the modus operandi of these factors on extraction-site relapse.8,9,11,12 Surgical gingivoplasty and root parallelism were for a long time frequently cited procedures to eliminate or, at least, to minimize the relapse of extraction-space reopening.2-4 Currently, few studies are dedicated to this topic. Because root parallelism is cited as a possible factor for relapse of extraction spaces, in this study, we aimed to evaluate the influence of tooth angulation on the stability of extraction-site closures in orthodontic patients treated with 4 first premolar extractions. Therefore, the following null hypothesis was investigated: there is no difference in root angulation at the end of orthodontic
treatment between patients with and without relapse of extraction spaces.
MATERIAL AND METHODS
The sample was retrospectively selected from the files of the Department of Orthodontics at Bauru Dental School, University of S~ao Paulo, in Brazil. The inclusion criteria were patients treated with 4 first premolar extractions, all extraction sites completely closed, Class I or Class II malocclusion, complete permanent dentition, standard edgewise appliances, no dental anomalies of number (agenesis or supernumerary teeth), no periodontal surgery in the extraction area, no occlusal adjustment at the end of the treatment, satisfactory occlusal results, and the same retention protocol. According to these inclusion criteria, 56 patients between 12 and 22 years of age were selected and divided into 2 groups with the following characteristics (Table I).
Group 1 included 25 patients (8 male, 17 female) who had relapse of extraction spaces in 62 quadrants (29 in the maxillary arch, 33 in the mandibular arch), as shown in Figure 1, with the maxillary spaces reopening. Eight patients had Class I and 17 had Class II malocclusions at the pretreatment stage. The mean age at the end of treatment was 16.56 6 2.16 years (range, 12.58-22.77 years). The posttreatment observation time was 1.61 6 0.87 years.
Group 2 consisted of 31 patients (19 male, 12 female) with no relapse of extraction spaces. Eleven patients had Class I and 20 had Class II malocclusions at the pretreatment stage. The mean age at the end of treatment was 15.28 6 1.38 years (range, 12.32-17.89 years). The posttreatment observation time was 1.49 6 1.11 years.
Orthodontic mechanics included 0.022 3 0.028-in fixed standard edgewise appliances and extraction of 4 first premolars. Patients with severe initial anterior tooth crowding required canine retractions, followed by leveling and alignment with the usual wire sequence characterized by an initial 0.015-in twist-flex or a 0.016-in Nitinol, followed by 0.016-, 0.018-, 0.020-, and 0.019 3 0.025-in stainless steel archwires (3M Unitek, Monrovia, Calif). Deepbite was corrected with accentuated and reversed curve of Spee. The extraction spaces were closed with en-masse retraction of the anterior teeth, with
elastic chains on a rectangular archwire. At the end of treatment, the canines and the second premolars were in contact. Also, a Class I molar relationship and satisfactory overbite and overjet relationships were obtained. A modified Hawley retainer was used in the maxillary arch, and a canine-to-canine retainer was bonded in the mandibular arch. The Hawley retainer had its labial arch welded to the horizontal bar of the Adams clasp, without auxiliary clasps or occlusal interference between the canine and the premolar (Fig 2). The Hawley retainer was recommended to be used full-time for 6 months, followed by nights-only use for 6 months. The mandibular canine-to-canine bonded fixed retainer was used for
Fig 1. Orthodontic treatment with 4 first premolar extractions.
Spaces were closed at the end of treatment (A), and,
1 year later the maxillary extraction sites relapsed (B).
Fig 2. Modified Hawley retainer used by the patients in
both groups.
Fig 3. Long axes of maxillary and mandibular canines
and second premolars were traced to measure the angulation
between them.
a mean period of 3 years. Twenty patients of group 1 (80%) and 24 (77.4%) of group 2 were still using their Hawley retainers at the time of evaluation.
Panoramic radiographs from each patient were evaluated at the final and the 1-year posttreatment stages. The maxillary and mandibular teeth up to the first molars were delimited by 1 operator (C.T.A.) in a dark room. Then, the long axes of the maxillary and mandibular canines and second premolars were traced following the root canal path, without considering apical dilacerations (Fig 3).13 Angulations between those teeth were measured, by using positive values for long axes that converged occlusally and negative values for long axes that converged toward the apex.
Tooth angulation was classified according to the angulation between the long axes of the canines and the second premolars at the end of treatment (Table II): satisfactory parallelism from 6 to 16, apical convergence of less than 7, or apical divergence of more than 17.
The relapse amount was measured as the distance between the distal surface of the canines to the mesial surface of the second premolars on dental casts at the 1-year posttreatment stage. Twenty randomly selected panoramic radiographs were retraced and remeasured to verify the error of the
method. Casual errors were calculated according to Dahlberg’s formula (S 5 S d2/2n),14 and systematic errors were evaluated with dependent t tests at P\0.05.
Statistical analysis
Intergroup malocclusion type distributions were compared with chi-square tests, and posttreatment ages and observation times were compared with t tests. To compare the final tooth angulations between groups 1 and 2, t tests were used. The chi-square test was used to compare the root-angulation categories between the groups. To compare the amount of relapse between the 3 angulation categories in group 1, 1-way analysis of variance (ANOVA) was used. To investigate any significant correlation between angular changes and the amount of relapse of the extraction spaces in group 1, the Pearson correlation coefficient was used.
RESULTS
There were no statistically significant systematic errors (P 5 0.485), and the casual error was within acceptable limits, as shown in Table I. The groups were similar regarding the distribution of malocclusion types and follow-up periods, but group 1 had a greater final mean age than group 2 (Table II).
There was no statistically significant difference between the groups regarding the angle between the canine and the second premolar and regarding the percentages of the root-angulation categories at the end of treatment (Tables III and IV). There was no statistically significant difference in the amount of relapsed space between the parallel, convergent, and divergent roots in group 1 (Table V). There was no significant correlation between the posttreatment angulation changes and the amount of space relapse (Table VI).
DISCUSSION
The etiology of extraction-space relapse is still undetermined. Graber15 pointed out that extraction sites can reopen if the roots of the adjacent teeth did not remain parallel. Edwards1 and Parker4 recommend that the teeth adjacent to the extraction sites should remain in close proximity and the roots should be parallel before the retention period. Hatasaka3 analyzed the behavior of tooth roots adjacent to extraction sites during the retention and postretention stages, and found that overcorrected roots, with the apices barely touching, do not allow contact of the tooth crowns, leaving spaces between them and, in addition, do not solve the relapse problem. The author also found that divergent roots at the end of treatment tend to keep the same position or become more divergent, and concluded that the best procedure is to maintain the teeth upright and parallel, with an even amount of alveolar bone between the roots. Although parallelism between adjacent teeth has been recommended, in this study, patients with and without relapse had similar final mean angulations between the canines and the second premolars (Table III).3,5,6 This result suggests that root parallelism between adjacent extraction sites does not ensure long-lasting crown contact. Because of the large range of tooth angulations observed in the groups (23 to 119), we classified root positions into satisfactory parallelism, apical convergence, and apical divergence. Many overtreated teeth (apical convergence) were primarily observed in group 1, which had reopening of extraction spaces (Table IV). Group 2 also had overtreated patients (33%). In both groups, mesial angulation was used to upright the canine roots in extraction patients.16,17 This procedure counterbalanced the canines’ distal angulation that
can occur during retraction,18-21 because the elastic force is applied on the crown and not on the center of resistance.22 Many patients were finished with mesially angulated canines, with the long axes apically converging with the long axes of the second premolars. The overtreatment observed in both groups could have been an attempt to prevent reopening of the extraction spaces, but this does not solve the problem, as pointed out by Hatasaka.3 Moreover, there was no difference in the amount of relapse between the parallel, convergent, and divergent roots (Table V). In root
convergence, when there is 0.8 mm or less of bone or interdental tissue, root proximity must be considered as a risk for periodontitis.23-25 Orthodontic treatment can suppress the interdental soft tissues, deform the interdental papillae, and reshape the interdental contact areas. An infectious process can appear and destroy the septum, and cause pockets and bone defects. Root proximity might affect the risk for periodontitis by limiting access for personal oral hygiene or professional cleaning.25-27 On the other hand, extremely divergent roots can change the location of interproximal contacts, creating black triangular spaces that are unesthetic and can affect the periodontium by causing chronic food retention.28,29 There was no significant correlation between the amounts of posttreatment angulation change and extraction-space relapse (Table VI). This means that spaces do not reopen as an attempt by the roots to become more parallel in patients with diverging roots. Therefore, other factors should be investigated. Compression of transseptal fibers has also been claimed to cause relapse after space closure.1,4,8,10 Teeth that are orthodontically moved together after extraction of an adjacent tooth do not move through the gingival tissue but appear to push the gingiva ahead to create a fold of epithelial and connective tissues.1,5 After final closure of an extraction site, the excessive gingival tissue appears in papillary form buccally and lingually between the approximated teeth. A gingival groove is associated with these papillae. Although these altered tissues were suggested as strong factors for orthodontic relapse in extraction
areas,1,2,4,8 other studies did not find a relationship between gingival invaginations and extraction-space reopening. 5,11,12 Thus, surgical removal of this excessive gingival tissue should not be considered as the only way to ensure the stability of space closure. Some criticisms could be made to this study regarding the use of panoramic radiographs to evaluate tooth angulations. Since the panoramic image is created in a layer or a focal trough supposing a standard jaw form and size, deviations from this standard form will result in an object that is not centered in the focal trough, causing image distortions.30 However, considering this image-generation principle of the panoramic radiograph, if the same patient has a serial radiographic evaluation, similar degrees of image distortion should be expected.31 Therefore, evaluation of the correlation between interradicular angulation changes during the 1-year posttreatment period with relapse of the extraction sites (Table VI) should not be significantly affected by panoramic distortions because the same subject with identical dentoskeletal characteristics was longitudinally evaluated.31 Regarding the intergroup cross-sectional
comparison, the relevant number of patients in both groups minimizes the risk of systematic image distortion of the panoramic radiographs that could affect the comparisons. 32,33 Both groups were treated with 4 premolar extractions and had comparable initial malocclusions; therefore, there is no reason to suspect that any specific characteristic of the groups would cause a systematic image distortion that could affect the comparison.
In spite of these methodologic limitations, panoramic radiographs were used because not all patients had full-mouth periapical radiographs available, and computerized tomography scans are not usually taken as posttreatment records. Also, because of the retrospective nature of the study, computerized tomography was not developed when many of the patients were treated. Although there was no relationship between tooth angulation and extraction-space reopening, ideal tooth angulation after treatment contributes to a better morphologic, esthetic, and functional occlusion. In this study, we addressed the issue of the stability of extraction-site closure in the maxillary and mandibular arches combined. Future studies should investigate whether there is a difference in the stability between the maxillary and mandibular arches and its causes.
CONCLUSIONS
The null hypothesis was accepted because there were no differences in root angulation at the end of treatment in patients with and without relapse of the extraction spaces. Consequently, the angulation between the canines and the second premolars after treatment had no influence on the relapse of the extraction spaces.
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