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2020, Number 4

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Rev Mex Ortodon 2020; 8 (4)

Comparative analysis of the intercanine width of the lower dental arch in patients with extraction and non-extraction treatment of first premolar extractions

Sáenz Nevárez, Paola1; Justus, Roberto2; Ondarza-Rovira, Ricardo3; García López, Salvador4

Language: English/Spanish [Versión en español]
References: 43
Page: 225-235
PDF size: 256.57 Kb.


ABSTRACT

Introduction: in orthodontic treatment it is essential to achieve harmony between the shapes of the dental arch and basal bone. The size and shape of the dental arches have considerable implications for diagnosis and treatment planning. Objective: compare the transverse dimension of the lower arch, measuring the intercanine width at the beginning and at the end of orthodontic treatment in patients of the Postgraduate Course in Orthodontics at the Universidad Intercontinental, who have been treated with and without lower first premolar extraction therapy. Material and methods: a quantitative study was carried out, in which 120 initial and final dental stone models of the mandible of 60 randomly selected patients were analysed, of which 30 corresponded to cases without premolar extractions and 30 to patients with first premolar extractions. Subsequently, the intercanine width was measured using a digital vernier caliper. Results: there was no statistically significant difference in the mean intercanine width in patients with non-extraction treatment (32.49 ± 1.57 mm) compared to post-treatment (32.72 ± 1.36 mm). However, there were statistically significant differences in cases treated with extractions at the beginning of treatment (32.19 ± 2.17 mm) compared to post-treatment (33.96 ± 1.47 mm), p < 0.05. Conclusion: a significant increase in the mandibular transverse dimension of the dental arch was observed in patients treated with first premolar extraction therapy. Whereas, in patients treated without extractions, the intercanine width maintained the pre-treatment values.



INTRODUCTION

During craniofacial growth and development, the dental arches grow, adapt and age. In the functional permanent dentition, modifications continue to be observed, although to a lesser extent.1 Changes in arch size occur mainly in two phases. The first occurs when the incisors and first permanent molars erupt, followed by a period of calm. The second phase is the replacement of premolars and canines. Previous studies2-4 suggest that the intercanine diameters increase in distance during two periods in both the upper and lower arches.

Moorrees et al5 showed that the second increase did not occur in the mandible, but in the maxilla. Barrow and White,6 showed that the intercanine width in the age period from three to five years showed little alteration, and in contrast, increases considerably from five to nine years of age. Furthermore, they showed that the maxillary and mandibular dental arches continuously decrease by 0.5 to 1.5 mm after the age of 14 years. In another study, they concluded that the lower intercanine width increases significantly at dentition change, but does not increase in the permanent dentition after the age of 12 years.7 Knott,8 observed that for most individuals the maximum intercanine width in both maxillae showed little alteration after reaching the permanent dentition stage and that, in the lower jaw, the greatest increase in this width occurred before the eruption of the permanent canine. Similarly, Bishara et al9 found that after complete eruption of the permanent dentition, there was a slight decrease in transverse dimensions, mainly at the intercanine level. In contrast, Eslambolchi et al10 showed that the mandibular intercanine width decreased significantly from childhood to old age. From other perspectives, masticatory function also plays an important role in arch development.11

Studies have shown that dietary hardness has a significant influence on arch development,12 in addition to some environmental factors.13 Another study showed that in the third decade of life (in both sexes) the intercanine width decreases.14,15

Apart from that, there is a trend that affirms that the shape of the mandibular arch represents a state of structural and functional balance for the individual, and should therefore not be altered during orthodontic treatment.16 This is why it has been proposed that the intercanine width in the lower arch should be considered as a stable position, which should basically be maintained before and after treatment.9,17-22 Also, it has been reported that in most cases arch dimensions change with growth. This leads to the need to distinguish changes induced by orthodontic therapy from those occurring from natural growth. Some authors mention that the transverse arch size continues to increase to a lesser extent in the third and fourth decade, which is associated with the decrease in arch length throughout life. The mandibular dental arch is one of the main references for orthodontic treatment planning, which has resulted in many studies that have aimed to define its ideal size and morphology.23

The purpose of this study was to compare the transverse dimension of the lower arch, measuring the intercanine width at the beginning and at the end of orthodontic treatment. In patients of the Postgraduate Orthodontic Programme of the Universidad Intercontinental in the last 10 years, treated with or without lower premolar extraction therapy.



MATERIAL AND METHODS

The present study was a quantitative, longitudinal and correlational study. The sample consisted of the initial and final lower models of 60 patients of both sexes distributed in 24 males and 36 females treated orthodontically at the Universidad Intercontinental. They were randomly selected and received consecutive treatment. Half were treated without tooth extractions and the other 30 cases were subjected to lower first premolar extractions, with an average age of 17.4 ± 5.02 years and 15.7 ± 4.13 years, respectively. The following criteria were used to select the individuals to form the sample: systemically healthy male and female patients with class I and class II division 1 and 2 dental malocclusion (according to Angle's classification) received orthodontic treatment. One group was treated without extraction therapy of any kind, and another group with extraction therapy of lower first premolars.

The selected patients did not receive expansion treatment or any previous orthopaedic functional appliances. In addition, they had to have complete erupted permanent dentition at the start of orthodontic treatment (excluding third molars), and initial dental crowding of at least 4-6 mm, according to Little's irregularity index,24 which corresponds to moderate irregularity. Patients with a healthy periodontal status who completed orthodontic treatment with fixed appliances using MBT Gemini system, 0.022" slot (3M™, UnitekTM, USA), who had initial and final study models in good condition, with acceptable anatomical definition and sufficient quality to be correctly analysed, were included. Patients who did not meet the aforementioned inclusion criteria were excluded, as well as those who presented the following characteristics: congenital anomalies, systemic diseases; maxillary or mandibular hypoplasia, with wear facets and/or dental restorations of lower canines; with morphological anomalies of the dental crown such as macrodontia, microdontia; hyperplasia, hypoplasia; bigeminal teeth, conoid lateral incisors; congenital absence of teeth as well as the presence of supernumerary teeth. Similarly, patients with posterior crossbite, class III dental or skeletal malocclusion and those who had undergone previous orthognathic surgery were also excluded.

A search was carried out in the archives of the Universidad Intercontinental over the last 10 years, identifying those patients who met the inclusion criteria and who had the initial and final record of the study models with the necessary quality to be analysed.

The treatment of each patient was carried out in the clinic of the institution, treatments were conducted by several instructors. The models were obtained by means of impressions in alginate (Dentsply Jeltrate Chromatic®, USA) by different operators, to be subsequently moulded in white dental stone gypsum type III (Whip Mix®, USA) according to the instructions of the commercial company.

Two groups were formed for the analysis:

  • Group 1: 30 orthodontically treated patients of both sexes without extractions of any kind.
  • Group 2: 30 patients of both sexes orthodontically treated with extractions of lower first premolars.

Evaluation of the Little's irregularity index

Once the 120 dental stone suitable for study (60 initial and 60 final casts of the selected patients) were identified, the degree of crowding was determined based on the Little's irregularity index24 in each of the previously selected lower models. When they did not meet a range of moderate irregularity (4-6 mm minimum), they were discarded. To obtain a more accurate measurement, the incisal edges of the anterior teeth were first highlighted with a graphite pencil.

The technique involved measuring the linear width from the anatomical contact point to the adjacent anatomical contact point of the mandibular anterior teeth, where the sum of the five measurements represented the irregularity index. Each measurement was made with a fine-tipped digital vernier (Truper®, Model CALDI-6MP, 0-150 mm, Mexico), which was held parallel to the occlusal plane, measuring only the horizontal linear displacement of the aforementioned contact points. It is worth mentioning that the measurements obtained from each dental stone models were performed by the same pre-calibrated operator (Figure 1A).

The measurements obtained from each dental stone model were recorded in a spreadsheet (Excel version 16.10) on a MacBook Pro, 4 GB, 1,600 MHz, Intel HD.

Evaluation of the transverse measurements

Next, the analysis of the intercanine width was conducted. The measurements were obtained only from the mandibular dental arch models because, as Angle pointed out in 1899: "The lower arch exerts a controlling influence on the shape of the upper part and the position of the teeth in it".

Transverse measurements at the canine level were performed directly on each model using a digital Point Caliper (fine type) (Truper®, model CALDI-6MP, 0-150 mm, Mexico). According to Gianelly's proposal,25 measurements were taken at the most labial part of the vestibular surfaces of these teeth (Figure 1B).

In addition, the torque has a great influence on the inclination of the canines, so it was measured by taking the most gingival portion of the canines. To achieve a more accurate measurement, the vernier was opened starting from 0 mm until the width corresponding to the transverse dimension of the arch was obtained. The measurements obtained from each dental stone model were recorded in the spreadsheet under the same specifications mentioned above, invariably performed by the same operator. Each dental stone model was measured three times to reduce the possible error and the average of the three values was used as the final measurement (Figure 1C and D).

Statistical analysis. In order to determine the possible existence or not of statistically significant differences, an analysis of variance (ANOVA)26,27 and Tukey's post hoc test were used.



RESULTS

For the study, the sample consisted of 120 mandible dental stone models of 60 patients, of which 24 patients were males and 36 females. The mean age of the study groups at the start of orthodontic treatment was 17.4 ± 5.02 years for the non-extraction group and 15.7 ± 4.13 years for the extraction group, resulting in an overall mean age of 16.5 ± 1.2 years. According to the exclusion criteria, patients with class III malocclusion were excluded, so the total sample consisted of 39 class I cases and 21 class II cases. Table 1 summarises the characteristics for all subjects in the sample in terms of sex, age and malocclusion, as well as the specific distribution for each group analysed in this study.

At the start of treatment, the mean intercanine width in the lower jaw of patients treated without extraction therapy (group 1) was 32.49 ± 1.57 mm, while at the end of treatment the mean was 32.72 ± 1.36 mm (Figure 2). The difference in the mean transverse dimension in group 1 was 0.23 ± 0.16 mm, being greater in the final stage of treatment. On the other hand, in the cases treated with extraction therapy (group 2), the values obtained show that the average intercanine width in the lower jaw at the beginning was 32.19 ± 2.17 mm and 33.96 ± 1.47 mm at the end of the treatment (Figure 3). The difference in the averages of the transverse dimension was 1.77 ± 1.25 mm, being greater in the final stage of the treatment.

The average size of the mandibular intercanine width was 0.30 ± 0.21 mm larger in the sample without tooth extractions at the start of treatment compared to the sample treated with extraction therapy. While the average transverse arch at completion was 124 ± 0.88 mm larger in the sample with tooth extractions compared to the sample without extractions.



DISCUSSION

For almost a century, extraction therapy for the resolution of malocclusions has been discussed with both pro- and anti-extraction groups arguing the case for their possible treatment plans. However, the plan to be followed may vary according to the treating orthodontist and even the patient's conditions. Orthodontics has different paradigms, mechanisms and therapeutic plans but which can often achieve comparatively acceptable results.28 According to the literature, it is accepted that when orthodontic treatment involves the extraction of teeth, dimensional changes occur in the arch and that these continue to change after active treatment.29

In the present study, the results obtained quantified an increase in the transverse dimension of the arch in both groups analysed. Furthermore, they showed a statistically significant difference between the initial and final dimensions of the mandibular intercanine width in patients treated with first premolar extraction therapy. While patients treated without extraction therapy did not show a significant change, which confirms previously published results and at the same time contradicts many others.7,30 Based on the data analysed in the study, a net increase in the lower intercanine width was observed in 57% of the cases without extraction and in 90% of the cases with extractions. Changes in the upper transverse dimension were not recorded as the maxillary dentition does not usually set the widths of the dental arches while the therapeutic possibilities are more limited in the mandible than in the maxilla.31 In a study by Little et al,32 according to an analysis of 65 cases treated with first molar extraction, they showed that in the long term the mandibular intercanine width had widened by more than 1 mm during treatment in 60% of the cases. In our investigation, we found similar results, with an increase in 63% of cases. Furthermore, we demonstrated that in the group treated with first premolar extractions the intercanine width increased by 0.77 mm post-treatment, which was statistically significant and consistent with the literature.25,29,33-37 In contrast, another study showed that there is generally a transverse increase in the arch, irrespective of whether treatment was with extraction or non-extraction therapy.16

Concerning the evaluation of the intercanine width in the non-extraction group, where there was no statistically significant difference, this was due to the fact that the shape of the dental arch was respected during treatment. Maintaining the arch form and trying to preserve the intercanine width before and after treatment serves the purpose of achieving long-term stability. However, the limitation of our study was that the degree of lower incisors proclination was not assessed as the space required was compensated by suchproclination. Further studies are needed to determine this aspect.

Bishara et al28 studied a group of patients with class II division 1, treated with and without extractions, and found that during treatment there was a tendency for the intercanine width to increase in both groups, with a significant increase in the group treated with tooth extractions, a result that does not coincide with the present study. On the other hand, our study partially agrees with Glenn et al38 where they concluded that in the case of patients treated without extractions, 68% of them presented an increase in the intercanine width, but this was not statistically significant. Similarly, Kim and Gianelly39 showed that the transverse dimension of both dental arches increased by less than 1 mm, the difference was also not statistically significant between the extraction and non-extraction groups. However, it does not coincide with the results of our investigation.

Lee and Ward et al7,30 demonstrated that extractions reduce the transverse dimension of the arch, which partially coincides with the present study, where 10% of the cases presented a reduction or maintenance of the intercanine dimension, although the changes were not statistically significant.

According to our results, the recommendation is to maintain the original transverse dimensions of the dental arch as much as possible during orthodontic treatment. There are already studies17,18,40-42 where it has been proven that, by respecting the initial shape and dimension of the arch, better results are obtained from long-term stability and a more harmonious relationship between the arches, as well as adequate occlusal relations. Some authors, such as McNamara,43 argue in favour of increasing arch size at an early age so that skeletal, alveolar and muscular adaptations can occur before eruption of the permanent dentition, however, this is still a matter of debate.

While a large body of literature has contributed to the extraction debate, fewer studies have examined the effects of appliance type on outcomes in relation to transverse dimension of the arch.



CONCLUSIONS

There were statistically significant differences in the increase in mandibular intercanine width in patients treated with lower first premolar extractions due to distalisation of the canine to the premolar extraction site.

There was no statistically significant difference in lower intercanine distance in patients treated without extractions. However, the lower incisors tend to procline.

Clinical recommendations
  • 1. Maintain the original intercanine width in the lower arch as much as possible during treatment.
  • 2. Try to avoid over-expansion of the dental arch, because it compromises the therapeutic plan and requires permanent retention.
  • 3. Consider the success of treatment based on the individual characteristics of each patient.
  • 4. Do not assume that 100% long-term stability will always be achieved, so a retention perspective must be established to avoid further undesirable changes.


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AFFILIATIONS

1 Exresidente del programa de la Maestría en Ortodoncia. Universidad Autónoma Metropolitana-Xochimilco.

2 Asesor de proyectos. Universidad Autónoma Metropolitana-Xochimilco.

3 Asesor de investigación y estadística, Instituto Nacional de Investigaciones Nucleares. Universidad Autónoma Metropolitana-Xochimilco.

4 Director de tesis. Profesor de Ortodoncia. Universidad Autónoma Metropolitana-Xochimilco.



CORRESPONDENCE

Salvador García López. E-mail: drsalvadorgarcialopez@gmail.com




Received: Agosto 2019. Accepted: Enero 2020.

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