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UNIVERSIDADE DE SÃO PAULO FACULDADE DE ODONTOLOGIA DE BAURU JESSICA QUEREZA DE FREITAS Comparison of the tooth alignment stability using canine-to-canine retainers bonded in two different forms

ABSTRACT COMPARISON OF THE TOOTH ALIGNMENT STABILITY USING CANINE-TOCANINE RETAINERS BONDED IN TWO DIFFERENT FORMS Objective: The purpose is to evaluate the stability of the mandibular anterior teeth alignment by comparing two forms of bonding of the fixed canine-to-canine retainer, bonded only to the canines and bonded to each of the mandibular incisors and canines, with 5 years follow-up. Material and Methods: 43 patients (22 female, 21 male) with Class I and Class II malocclusion, were divided into 2 groups: Group 1: 25 patients (13 females, 12 males) with retainer bonded only to the canines. Mean initial age, treatment time, long-term posttreatment time were 13.42 (SD, 1.51), 3.06 (1.56) and 5.60 (SD, 1.36) years, respectively. Group 2: 18 patients (9 females, 9 males) with retainer bonded to the all mandibular anterior teeth. Mean initial age, treatment time, long-term posttreatment time were 13.01 (SD, 2.94), 3.62 (SD, 1.84), 5.31 (SD, 0.77) years, respectively. Dental casts were obtained and digitized at pretreatment (T1), posttreatment (T2) and at a mean of 5 years long-term posttreatment (T3). The following measurements were obtained: Little irregularity Index, intercanine, interpremolar and intermolar widths. The intergroup comparisons of the variables at pretreatment, posttreatment and long-term posttreatment stages and the treatment and long-term posttreatment changes were performed with independent t tests. Results: The mandibular irregularity index showed a statistically significant decrease with treatment and remained stable in the long-term posttreatment follow-up. In the group 1, there was a significantly increase in the mandibular inter first premolars width with treatment and it was stable in the long-term posttreatment. In the group 2, the mandibular inter second premolars width showed a significantly increase with treatment and it remained stable in the long-term. The intergroup comparison at all stages (T1, T2 and T3) showed no statistically significant differences between the groups. Group 2 showed a greater decrease in the mandibular intercanine width than the all teeth group in the long-term posttreatment phase. Conclusions: There was no difference in the amount of relapse of mandibular anterior crowding with fixed canine-to-canine retainers bonded only to the canines and bonded all the six anterior teeth. Thus, both retainers can be recommended. However, the canine group showed a decrease in the mandibular intercanine width in long term posttreatment.COMPARISON OF THE TOOTH ALIGNMENT STABILITY USING CANINE-TOCANINE RETAINERS BONDED IN TWO DIFFERENT FORMS Objective: The purpose is to evaluate the stability of the mandibular anterior teeth alignment by comparing two forms of bonding of the fixed canine-to-canine retainer, bonded only to the canines and bonded to each of the mandibular incisors and canines, with 5 years follow-up. Material and Methods: 43 patients (22 female, 21 male) with Class I and Class II malocclusion, were divided into 2 groups: Group 1: 25 patients (13 females, 12 males) with retainer bonded only to the canines. Mean initial age, treatment time, long-term posttreatment time were 13.42 (SD, 1.51), 3.06 (1.56) and 5.60 (SD, 1.36) years, respectively. Group 2: 18 patients (9 females, 9 males) with retainer bonded to the all mandibular anterior teeth. Mean initial age, treatment time, long-term posttreatment time were 13.01 (SD, 2.94), 3.62 (SD, 1.84), 5.31 (SD, 0.77) years, respectively. Dental casts were obtained and digitized at pretreatment (T1), posttreatment (T2) and at a mean of 5 years long-term posttreatment (T3). The following measurements were obtained: Little irregularity Index, intercanine, interpremolar and intermolar widths. The intergroup comparisons of the variables at pretreatment, posttreatment and long-term posttreatment stages and the treatment and long-term posttreatment changes were performed with independent t tests. Results: The mandibular irregularity index showed a statistically significant decrease with treatment and remained stable in the long-term posttreatment follow-up. In the group 1, there was a significantly increase in the mandibular inter first premolars width with treatment and it was stable in the long-term posttreatment. In the group 2, the mandibular inter second premolars width showed a significantly increase with treatment and it remained stable in the long-term. The intergroup comparison at all stages (T1, T2 and T3) showed no statistically significant differences between the groups. Group 2 showed a greater decrease in the mandibular intercanine width than the all teeth group in the long-term posttreatment phase. Conclusions: There was no difference in the amount of relapse of mandibular anterior crowding with fixed canine-to-canine retainers bonded only to the canines and bonded all the six anterior teeth. Thus, both retainers can be recommended. However, the canine group showed a decrease in the mandibular intercanine width in long term posttreatment.


LIST OF TABLES
Retention strategies usually include removable and fixed retainers. Therefore, the purpose of this study is to evaluate the stability of the mandibular anterior teeth alignment by comparing two forms of bonding of the fixed canine-to-canine retainer, bonding only to the canines and all the six mandibular anterior teeth, with 5 years follow-up.

ARTICLE
The article presented in this Dissertation was formatted according to the American Journal of Orthodontics and Dentofacial Orthopedics instructions and guidelines for article submission. Keywords: Orthodontic retainer; Long-term stability; Relapse; Crowding.

INTRODUCTION
Orthodontic treatment has as its primary objective the correction of malocclusions. Retention is the phase of orthodontic treatment that aims to maintain the teeth in the correct position after active treatment and counteract relapse. 1 Without retention there is a tendency for the teeth to return to their initial position. 13 There is consensus in the orthodontic literature that some occlusal changes will inevitably occur after treatment. Therefore, orthodontic retainers are ideally suited to maintain dental alignment. 10 Throughout life, there are also changes in normal occlusion, such as arch length decreased and mandibular incisor crowding. 3,4 Many studies have demonstrated a high relapse rate of the alignment of the mandibular anterior teeth after orthodontic treatment and retention. 14,15 A long-term follow-up study found that postretention crowding and incisor irregularity increased more frequently in the mandible than in the maxilla. 16 The etiology of anteroinferior crowding after orthodontic treatment is multifactorial. Some of them are directly related to orthodontic treatment, such as: increased intercanine widht; 5,6 change in the shape of the dental arches; 7 excessive protrusion of incisors; 8,9 lack of harmony of occlusion; 1 professional skill; 1 failure to remove the causes of malocclusion; 15 retainer time. 1,10 Retention strategies usually include removable and fixed retainers. 11 In the lower arch fixed retainers in the anterior segment are a valid option for managing the significant relapse rate in this area. 12 Two different fixed canine-to-canine retainers can be used in the mandible, bonded only to the canines or a retainer bonded to each of the mandibular incisors and canines. 4,17 They are independent of patient cooperation, nearly invisible, and easy to fabricate, but they need regular check-ups, because occasional failures caused by wire fractures or bond failures can occur.
Studies have shown that bonded retainers represent an efficient and reliable retention appliance for long-term use, prevent posttreatment changes caused by relapse or the natural aging process in the alignment of the incisors. [18][19][20] Systematic reviews and original studies investigated the benefits and damage associated with fixed and removable retainers, focused on stability and clinical performance of both types of retainers, considering the different materials, design of the appliances. 13,[21][22][23][24] Another systematic review evaluated the difference between fixed orthodontic retainers bonded to all teeth and those bonded only to the canines, but only the periodontal condition and bonding failures were presented. 25 A few studies reported the effectiveness the two types of fixed canine-to-canine retainers in stability of mandibular anterior teeth alignment. 19,[26][27][28] Therefore, the purpose of this study is to evaluate the stability of the mandibular anterior teeth alignment by comparing two forms of bonding of the fixed canine-to-canine retainer, bonding only to the canines and all the six mandibular anterior teeth, with 5 years follow-up. The sample size calculation was based on an alpha significance level of 5% and 80% test power to detect a mean difference of 0.85 mm, with a standard deviation of 0.89 for the Little irregularity index. 29 Thus, the sample size calculation showed the need for 16 subjects in each group.

Sample characteristics
The sample comprised the dental casts of 43 patients (

Methods
All dental casts were digitized using a R700 3-dimensional scanner (3Shape, Copenhagen, Denmark). Dental casts measurements were performed using the

Error study
The pretreatment, posttreatment and long-term posttreatment dental casts of 17 patients were randomly selected, retraced and remeasured by the same examiner (J.Q.F.) after a month interval. The intraclass correlation coefficient (ICC) was used for test reliability of the measurements. 32

Statistical analysis
The normality of data was verified by the Shapiro-Wilk test.
The intergroup comparability of the ages, treatment and long-term posttreatment times was performed with independent t tests and the sex distribution and type of malocclusion was compared with chi-square tests.
The intragroup comparison of the pretreatment, posttreatment and long-term posttreatment stages was performed with repeated measures ANOVA and Tukey tests when necessary.
The intergroup comparisons of the variables at pretreatment, posttreatment and long-term posttreatment stages and the treatment and long-term posttreatment changes were performed with independent t tests.
The statistical analysis was performed with Statistica software (version 12.0, Statsoft, Tulsa, Okla, USA), and the results were considered significant at p<0.05.

RESULTS
Intraclass correlation coefficients (ICCs) of the variables varied from 0.89 to 0.98, indicating excellent intra-rater agreement. 33 The groups were comparable regarding ages at all stages (T1, T2 and T3), treatment time, long-term posttreatment time, sex distribution and type of malocclusion (Table I).
In the canine group, there was a significantly increase in the mandibular inter first premolars width with treatment and it was stable in the long-term posttreatment (Table II). In the all teeth group, the mandibular inter second premolars width showed a significantly increase with treatment and it remained stable in the long-term (Table   II). The mandibular irregularity index showed a statistically significant decrease with treatment and remained stable in the long-term posttreatment follow-up (Table II).
The intergroup comparison at all stages (T1, T2 and T3) showed no statistically significant differences between the groups (Table III).
Intergroup comparison of the treatment changes (T2-T1) was similar between the groups (Table IV). The canine group showed a greater decrease in the mandibular intercanine width than the all teeth group in the long-term posttreatment phase (Table IV).

DISCUSSION
The groups were comparable regarding several parameters that could influence comparisons: type of malocclusion, ages at all stages, treatment time, longterm posttreatment time, sex distribution and type of malocclusion (Table I). This manner, achieved orthodontic treatment results could be evaluated with increased reliability. Furthermore, digital dental casts were used in this study and the measurements were performed with digital software. Three-dimensional dental casts' measurement has been an optimal alternative to plaster dental casts with excellent agreement. 34 Little Irregularity Index 30 was used to quantify mandibular incisor crowding.
Thereupon, mandibular crowding at T1 was considered minimal 3.42 mm and 3.31 mm in the canine group and all teeth group, respectively (Table II). At T2, anterior crowding was corrected with treatment and had minimal irregularity for both groups: 1.18 mm and 1.12 mm, for canine groups and all teeth groups, respectively (Table II).
Mandibular incisors presented stability from T2 to T3, maintain a minimal irregularity: 1.89 mm for canine group and 1.50 mm for all teeth group (Table II).
Interpremolar widths showed significantly increased with treatment in both groups and continued stable in the long-term (Table II). In the canine group, mandibular inter first premolars width increased, while in the all the six teeth group, increased inter second premolars width. These widths were expanded during treatment and stable posttreatment long-term, however, it is recommended to obtain the best treatment stability has been maintain patients' pretreatment arch form. 31,35 Intergroup comparison at T1, T2 and T3 (Table III) showed that both bonded retainers may still be considered as an effective and safe method to stabilize outcomes of orthodontic treatment, maintaining long-term mandibular anterior alignment. Artun et al. 26 , Steinnes et al. 19 and Schütz-Fransson et al. 28 , also observed that there was no difference in stability between the two types of retainers, those bonded to all teeth or those bonded only to canines. Therefore, mandibular fixed retainer may prevent posttreatment changes caused by relapse or the natural aging process in the alignment of the incisors also in the very long term. 19 Canine group showed a change in the long term posttreatment: a decreased in the mandibular intercanine width (Table IV). Schütz-Fransson 28 reported similar result, however, presented in yours two groups. Wolf 36 noted that changes in tooth position occur even with the patient is using a permanent fixed mandibular retainer after orthodontic treatment. In addition, analyzed in your study with superpositions of the virtual 3D models, that canines underwent the most pronounced rotation and translation.
Perfect stability cannot be expected in the long term, changes have can also be found even in untreated people. 37 There are several studies reporting this maturational changes, indicating a decrease in arch length and perimeter and an increase in anterior alignment. 38,39 Abdulraheem et Al. 40 stated that as about 25% of the displaced incisors can be considered as an effect of natural growth, not a relapse of the orthodontic treatment. Watted 41 observed that the irregularity of the anterior incisors in the mandible increased considerably more in participants without a retainer compared with those who had a fixed retainer in place. This suggests that, although the fixed retainer did not prevent a certain amount of unwanted occlusal changes, it had a significant role in maintaining the alignment of the mandibular anterior teeth. Thus, a permanent fixed lingual retainer in the lower anterior segment is one of the most effective and used technics to stabilize orthodontic treatment outcomes. 12

Clinical implications
Orthodontists expect that the treatment results remain stable for many years.
However, long-term stability of the mandibular incisors after orthodontic treatment is variable and unpredictable. 8 With the findings of this study, orthodontists will be able to plan an efficient retention protocol, as well as explain to the patient the changes that may occur in their occlusion along many years posttreatment. The professional can choose the best form of retainer bonding for each patient, warning about their proper care and regular check-ups. In addition, to being aware that, fixed canine-tocanine retainers are efficient in long-term mandibular anterior alignment. 41

CONCLUSIONS
Based on the results of this study, it could be concluded that:  Increased in interpremolar width may occur with orthodontic treatment;


The canine group showed as change in long term posttreatment, a decrease in the mandibular intercanine width;  Fixed canine-to-canine retainer bonded only to the canines or bonded to each tooth, can be recommended since both are equally effective during the retention period;  The fixed canine-to-canine retainers are still the most effective to contain mandibular anterior segment relapses in long-term.         (Table II). At T2, anterior crowding was corrected with treatment and had minimal irregularity for both groups: 1.18 mm and 1.12 mm, for canine groups and all teeth groups, respectively (Table II). Mandibular incisors presented stability from T2 to T3, maintain a minimal irregularity: 1.89 mm for canine group and 1.50 mm for all teeth group (Table II).
Interpremolar widths showed significantly increased with treatment in both groups and continued stable in the long-term (Table II). In the canine group, mandibular inter first premolars width increased, while in the all the six teeth group, increased inter second premolars width. These widths were expanded during treatment and stable posttreatment long-term, however, it is recommended to obtain the best treatment stability has been maintain patients' pretreatment arch form. (R; SAMPSON; LITTLE; ÅRTUN et al., 1995; Intergroup comparison at T1, T2 and T3 (Table III)  Canine group showed a change in the long term posttreatment, as decreased in the mandibular intercanine width (Table IV)

Clinical implications
Orthodontists expect that the treatment results remain stable for many years.
However, long-term stability of the mandibular incisors after orthodontic treatment is

CONCLUSION
Conclusion 47

CONCLUSION
Based on the results of this study, it could be concluded that:  Increased in interpremolar width may occur with orthodontic treatment: canine group increase in the mandibular inter first premolars width, while the all teeth group, the mandibular inter second premolars width showed a significantly increase;


The canine group showed a greater decrease in the mandibular intercanine width than the all teeth group in the long-term posttreatment phase;  Fixed canine-to-canine retainer bonded only to the canines or bonded to each tooth, can be recommended since both are equally effective during the retention period;  The fixed canine-to-canine retainers are still the most effective to contain mandibular anterior segment relapses in long-term.