|Year : 2019 | Volume
| Issue : 3 | Page : 386-392
|Comparison of WALA ridge and dental arch dimensions changes after orthodontic treatment using a passive self-ligating system or conventional fixed appliance
Tarso Esteves1, Karina Maria Salvatore Freitas1, Darwin Vaz de Lima2, Paula Cotrin3, Rodrigo Hermont Cançado1, Fabrício Pinelli Valarelli1, Marcos Roberto De Freitas3, Renata Cristina Gobbi de Oliveira1
1 Department of Orthodontics, Inga University Center, Maringá, PR, Brazil
2 Department of Orthodontics, Darwin Dentistry Institute, Cuiabá, Brazil
3 Department of Orthodontics, Bauru Dental School, University of São Paulo, São Paulo, Brazil
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|Date of Web Publication||9-Aug-2019|
| Abstract|| |
Objective: To compare changes in WALA ridge and mandibular dental arch dimensions in orthodontic patients treated with a passive self-ligating system and conventional appliances. Design: Original paper. Setting: Orthodontic department at Inga University Center, Maringá, PR, Brazil. Materials and Methods: Pretreatment (T1) and posttreatment (T2) dental casts of 60 patients with Class I malocclusion treated with slight to moderate crowding that were divided into two groups. Group 1: 30 patients treated with a passive self-ligating system, at a mean initial age of 17.68 years and mean treatment time of 2.31 years. Group 2: 30 patients treated with conventional appliances, at a mean initial age of 19.23 years and mean treatment time of 2.56 years. Measurements were taken using a digital caliper directly on pre and posttreatment dental casts to evaluate the transversal dimension behavior of the mandibular dental arch and the WALA ridge width. Results: Self-ligating group presented an increase in WALA ridge width and mandibular transversal dimensions significantly greater than the conventional group, with the exception of intermolar cusp tip distance and intercanine WALA ridge. There was no statistically significant difference between the groups. There was also observed a significantly greater increase of the transversal buccal axis dimensions in the premolar area when compared to the WALA ridge increase in both groups. Conclusions: Treatment with a passive self-ligating system resulted in a significantly greater increase of the WALA ridge width and mandibular arch dimensions when compared to conventional appliance.
Keywords: Bracket, expansion, tooth movement, wire
|How to cite this article:|
Esteves T, Salvatore Freitas KM, Vaz de Lima D, Cotrin P, Cançado RH, Valarelli FP, De Freitas MR, Gobbi de Oliveira RC. Comparison of WALA ridge and dental arch dimensions changes after orthodontic treatment using a passive self-ligating system or conventional fixed appliance. Indian J Dent Res 2019;30:386-92
|How to cite this URL:|
Esteves T, Salvatore Freitas KM, Vaz de Lima D, Cotrin P, Cançado RH, Valarelli FP, De Freitas MR, Gobbi de Oliveira RC. Comparison of WALA ridge and dental arch dimensions changes after orthodontic treatment using a passive self-ligating system or conventional fixed appliance. Indian J Dent Res [serial online] 2019 [cited 2020 Nov 27];30:386-92. Available from: https://www.ijdr.in/text.asp?2019/30/3/386/264116
| Introduction|| |
The most common objectives of an orthodontic treatment are creation of facial harmony and dental aesthetics as well as improvement in masticatory function. To achieve these goals, some factors have to be taken into account when planning orthodontic treatment, like the size and shape of the dental arches. The dental arch forms and the teeth, bony ridges and adjacent soft tissues must be harmoniously related to each other. Therefore, proper planning and individualized determination of the dental arch forms becomes critical.
There are several studies , advocating the use of diagrams giving forms and predetermined dental arch and orthodontic sizes. However, another author  uses the WALA Ridge concept to determine the mandibular dental arch form and size (WALA is an acronym that incorporates the initials of Will Andrews and Lawrence Andrews. They suggested the use of an anatomical reference as a parameter, with the purpose of centering the roots of the teeth in the bone at baseline, which they called WALA ridge ). This ridge was defined by the band of keratinized soft tissue directly adjacent to the mucogingival line and represents the apex of the tooth. Their determination sought to address the need to find a stable anatomical structure that determines the ideal and individualized contour of the mandibular arch. Other authors , also consider the use of WALA ridge dental diagramming concept a reliable methodology to achieve posttreatment stability.
The advent of self ligating appliances brought with them increased expectations of certain advantages in orthodontic treatment when compared to conventional ones. According to Damon, using low friction brackets associated with light force wires produces a higher expansion in posterior arch sites when compared to the conventional brackets. Other researchers also observed some differences in treatment with self-ligating systems with greater dental arch expansion,, reduced treatment time and number of visits besides reduced chair time.
Scott et al. observed no statistically significant difference between intercanine and intermolar distances between self-ligating system and conventional appliances. Moreover, Chen et al. observed in a systematic review that the only advantages of self-ligating systems when compared to conventional brackets are the reduced chair time and a mandibular incisor inclination decrease of 1.5°.
Still more research is needed to study the previously mentioned differences in dental arch dimensional change brought about by the two bracket systems. There is no research comparing the WALA ridge dimensional change with the use of self-ligating and conventional appliances. So, the aim of this study was to compare the mandibular arch transverse dimensional changes of WALA ridge as well as the intercanine, interpremolar and intermolar distances in nonextraction orthodontic treatment performed with conventional appliances and passive self-ligating system.
| Materials and Methods|| |
This research was approved by the Ethics Committee in Human Research of Inga University Center.
The sample size calculation was obtained based on an alpha significance level of 5% (0.05) and beta of 20% (0.20) to detect a 0.7mm minimum difference in the distance obtained from the right mandibular canine to the left mandibular canine on the WALA ridge measure. The sample size calculation showed the need of 30 subjects in each group.
Pretreatment and posttreatment dental casts from 60 randomly treated patients were selected and then divided into 2 groups, treated with Damon system self-ligating or Straight Wire conventional appliance technique. The following inclusion criteria were used: all subjects must present all permanent teeth erupted until first molars, Class I malocclusion, mandibular irregularity index greater than 1mm and teeth and alveolar ridge visible in the dental cast models, compatible with the WALA ridge. The exclusion criteria had been as follows: no dental extraction, no incisor stripping and no extra-oral appliances.
Group 1: 30 subjects (21 female, 9 male), with mean pretreatment age of 17.68 years (s.d = 7.26), mean posttreatment age of 19.99 years (s.d = 7.36) and mean treatment time of 2.31 years (s.d = 0.54). These subjects were treated with Damon Self-ligating System (Damon Mx and Damon Q (Ormco, Glendora, Calif). Archwire sequence was: 0.014” Damon Cu-Ni-Ti (Ormco, Glendora, Calif), followed by 0.014 × 0.025 Damon Cu-Ni-Ti (Ormco, Glendora, Calif). More crowded cases underwent 0.014 × 0.025 Cu-Ni-Ti archwire for a longer period. In sequence, 0.018 × 0.025 Damon Cu-Ni-Ti (Ormco, Glendora, Calif), 0.017 × 0.025 TMA and 0.019 × 0.025 stainless steel archwire. The archwire diagram was made individually after the removal of the 0.014 × 0.025 Damon Cu-Ni-Tiarchwire, using as reference a wax number 7 bite [Figure 1]a. All archwires were diagrammed and then transferred to the patient's chart [Figure 1]b.
|Figure 1: (a) Bite register in a number 7 Wax. (b) Dental diagram transferred to subjects charts. (c) WALA ridge. (d) Little irregularity index|
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Group 2: 30 subjects (20 female, 10 male), with mean pretreatment age of 19.23 years (s.d = 8.47), mean post treatment age of 21.79 years (s.d = 8.57) and mean treatment time of 2.56 years (s.d = 0.89). Patients were treated with Straight Wire conventional appliances (A Company). Archwire sequence was: 0.014” and 0.016”NiTi, 0.018”, 0.020” and 0.019 × 0.025” stainless steel archwires. The dental arch diagram was performed using the WALA ridge at pretreatment dental cast how as reference [Figure 1]c.
For the axes, points and reference edges demarcation and also to obtain the measures in dental casts the following instrumentation were used: black pencil and a digital caliper (Mitutoyo, Japan). Measurements were made exclusively by a single operator.
The following anatomical points were used: Cusp tip, dental buccal axis, WALA ridge points and their demarcations.
In the mandibular dental casts, the following anatomical points were marked using a visual scale and a black pencil, in two distinct treatment times (T1: pretreatment and T2: posttreatment):
- Cusp tip point (CP): mandibular canines incisal edge, mandibular first and second premolars occlusal buccal cusp tips and mandibular first molar mesiobuccal cusp point [Figure 2]a
- Buccal axis point (BA): Point on the buccal axis of the clinical crown which splits the clinical crown in two halves: gingival half and occlusal half. This demarcation was made with the pencil in the crowns of mandibular canines until the first molars, and in the molars the long axis of the mesiobuccal cusp [Figure 2]b
- WALA ridge (WR): Mandibular buccal outer edge surface marked by sliding a tangential line with the pencil over perpendicular dental cast, so delimiting a row [Figure 2]c
- WALA ridge Point (WR): BA point projection over the WALA ridge line from mandibular canines to mandibular molars [Figure 2]d.
|Figure 2: (a) Cusp tip point. (b) Buccal axis point. (c) WALA ridge. (d) WALA ridge point|
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The following linear measurements (mm) were performed directly on the mandibular dental casts:
- Mandibular intercanine distance between their incisal edges (CP 3x3); buccal axis points (BA 3x3) and WALA ridge points (WR 3x3): distance between mandibular right and left canines in their respective points: CP, BA and WRs
- Mandibular inter first premolars distance between cusp points (CP 4x4), buccal axis points (BA 4x4) and WALA ridge points (WR 4x4): distance between mandibular right and left first premolars in their respective points: CP, BA and WR
- Mandibular inter second premolars distance between cusp points (CP 5x5), buccal axis points (BA 5x5) and WALA ridge points (WR 5x5): distance between mandibular right and left second premolars in their respective points: CP, BA and WR
- Mandibular intermolar distance between cusp points (CP 6x6). Buccal axis points (BA 6x6) and WALA ridge points (WR 6x6): distance between mandibular right and left first molars in their respective points: CP, BA and WR
- Little Irregularity index  [Figure 1]d: This technique involves measuring the linear distance from anatomic contact point of mandibular anterior teeth, the sum of five measurements representing the Irregularity Index.
Error study and statistical analysis
The error of the method was calculated using all variable measurements of 15 randomly selected dental casts from each study phase (T1 and T2), within a 30-day interval. The random error was calculated according to Dahlberg's formula  and the systematic error with dependent t-test with significance level of 5% (P > 0.05).
Normality was verified by Kolmogorov-Smirnov tests.
To check the intergroup comparability of pretreatment and posttreatment ages, number of visits, treatment time and Little index, independent t-tests were used.
Dependent t-tests were used to compare pretreatment and posttreatment stages of each group separately.
The intergroup comparison of pretreatment and posttreatment stages and treatment changes, independent t-tests were used.
Comparison treatment changes of buccal axis and WALA ridge distances were performed with independent tests.
Results were considered statistically significant for P < 0.05. All statistical analyses were performed on Statistica software (Statistica for Windows 6.0; Statsoft, Tulsa, Okla).
| Results|| |
Error study showed statistically significant systematic error for the second premolar inter caste tip distance. Random errors varied from 0.07 mm for intersecond premolar buccal axis distance to 0.38 mm for the intercanine cusp tip distance.
Groups were comparable regarding pre and posttreatment ages, treatment time and Little irregularity index [Table 1]. The number of visits was significantly greater for conventional group than in the self-ligating group [Table 1].
|Table 1: Intergroup comparability results of mean pre- and post-treatment age, treatment time, number of visits and mandibular anterior crowding measured by little irregularity index (independent t-tests)|
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Treatment with self-ligating system caused significant increase in all transversal measurements of the WALA ridge, cusp tips and buccal axis [Table 2]. Cases treated with conventional appliances presented increases in interpremolar and intermolar distances (BA and CP) [Table 2].
|Table 2: Results of pre and posttreatment stages of Damon and conventional groups (dependent t-tests) (n=30)|
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Intergroup comparison of pretreatment and posttreatment stages showed no statistically significant difference between the groups [Table 3].
|Table 3: Intergroup comparison results of WALA ridge and dental arches dimensions changes at pre and posttreatment (T1) (independent t-tests)|
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Self-ligating group presented greater increases in WALA ridge and dental arch dimensions than conventional groups, except the intermolar cusp tip distance and intercanine WALA ridge dimension [Table 4].
|Table 4: Intergroup comparison results of WALA ridge and dental arches dimensions changes between T1 and T2 (T2-T1) (independent t-tests)|
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Comparison of WALA ridge and buccal axis dimensions showed differences in inter first and second premolars distances for all sample and for the two groups separately, and in intermolar for the conventional group [Table 5]. The buccal axis distances showed greater increase in the premolar region than the WALA ridge [Table 5].
|Table 5: Results of comparing buccal axis point and WALA ridge point point variables changes (T2-T1) (independent t-tests)|
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| Discussion|| |
In this present study was evaluated the WALA ridge changes as well the mandibular dental arch dimensions changes in dental casts pre and post orthodontic treatment. The accuracy of using these measurements in dental casts was corroborated with Moura's  study, which compared the WALA ridge measurements from dental casts, radiographs and volumetric CT scans and found no statistically significant difference between them. Although we evaluated WALA ridge and dental dimensional changes in outlined dental casts, they were produced in a single Dental Radiological Clinic and the photographs were also used to promote a visual comparison if the alveolar ridge in the plaster casts was compatible with that displayed in the photograph thus eliminating the bias. Furthermore, the WALA ridge used to assess the skeletal base dimensions has been shown before to not necessarily remain stable during dental tooth movement/expansion, but we tried to measure the skeletal and dental expansion using WALA ridge even knowing that it is not accurate, but it is clinically valid as several studies demonstrate ,, rather than the use of CBCT scans, which are often not approved by ethics committees.
The groups were comparable regarding pre and posttreatment ages, treatment time and Little irregularity index  [Table 1]. The number of visits was significantly smaller for the self-ligating than in conventional group [Table 1]. The ages presented a high standard deviation because ages ranged from 9 to 45 years at pretreatment, and 10 subjects had their age range between 9 and 12 years old for each group, however all of them presented complete permanent dentition. According to Bishara  in a longitudinal study comparing the dental arch widths in subjects with age from 6 months to 45 years old, a dental arch width increase should not be expected after eruption of complete dentition therefore, the age range did not influence the results of the present research.
Treatment changes in the passive self-ligating system group showed a statistically significant increase in all transversal dimensions [Table 2]. Conventional appliance treatment changes demonstrated statistically significant increase in interpremolar and intermolar cusp tip and buccal axis distances [Table 2]. According to this, Pandis  observed the same results to intercanine width changes in the conventional group, meanwhile Fengler  found a WALA ridge expansion that was statistically significant in patients treated with conventional appliances, but this was not clinically significant. In addition, Conti et al. longitudinally evaluated the dental and WALA ridge dimensions changes in subjects treated with conventional appliance, where subjects had their dental archwires individually coordinated with WALA ridge as reference. There was no statistically significant difference in the intercanine distance and WALA ridge transversal dimensions between orthodontic pretreatment and 3 years of follow-up posttreatment, thereby concluding that using the WALA ridge as a reference to coordinate the dental archwires is a favorable tool to reach posttreatment stability.
When comparing the intergroup distances measured in pretreatment and posttreatment stages, it was not observed a statistically significant difference between the groups [Table 3]. Treatment changes comparison between self-ligating and conventional groups showed greater transversal increases in all measurements with the exception of intermolar cusp tip distance and intercanine WALA ridge for the self-ligating group, when compared to conventional group [Table 4]. The absence of significance in pre and posttreatment intergroup comparisons and differences found in treatment changes comparison is explained because, although not statistically significant, the variables from passive self-ligating system group presented slightly lower values at T1 and similar or slightly higher values in T2, causing treatment (T2-T1) changes to be statistically significant.
Other authors , did not find statistically significant differences in the mandibular dentoalveolar expansion in cases treated with self-ligating and conventional appliances; however Fleming et al. evaluated only the alignment and leveling phase. It is important to highlight that this current study compared not only different orthodontic appliance types, but different appliance systems including a different dental arch coordination diagraming method for each group, where the conventional group had their dental arch diagramming with pretreatment WALA ridge as reference, and the passive self-ligating system group had their dental arch diagramming according with their recommended technique, after levelling with 0.014 x 0.025 Damon Cu-Ni-Ti archwire.
The comparison of WALA ridge transversal expansion and buccal axis transversal dimension changes [Table 5] showed a higher dentoalveolar expansion that was statistically significant in mandibular premolar region in both groups and for the whole sample and in the mandibular molar region in conventional group. According to Andrews  the adjacent muscular forces can tip the dental crowns after eruption across their center of resistance but not modifying it. In this manner, since the WALA ridge is close to them, it will also remain unchanged when these environmental forces occur. Therefore, it is expected that the dentoalveolar expansion overcomes the possible expansion of the WALA ridge.
As shown by the results, the expansion of the dental arch by the self-ligating system to relieve dental crowding was significantly and distinctly greater than the achieved expansion of the alveolar skeletal base, as assessed by the WALA ridge. This would mean that the teeth have been moved to the buccal edge (cortical bone) of the respective jaw or perhaps even further if they had been positioned in the center of the alveolar bone at the beginning. Some might say that this position, however, is not physiological, since it is associated with numerous problems such as gingival recession and periodontal problems, root resorption, relapse after treatment and dysfunction of the stomatognathic system by disrupting the equilibrium of muscular forces on the dental arch. All these problems mentioned above have been studied by several authors and, according to the studies, these assumptions can be refuted as follows: Orthodontic treatment along with patient compliance and absence of periodontal inflammation can provide satisfactory results without causing irreversible damage to periodontal tissues. In addition, this system allows the teeth to move towards the path of least resistance with little or no friction between the bracket and the wire, besides providing another alternative to an already periodontally compromised patient. Recent studies have shown that insignificant differences were detected in the periodontal status of adolescents undergoing orthodontic treatment with either conventional or self ligating brackets. There was no sigificant difference in the periodontal response to orthodontic treatment with either self ligating or conventional bracket. The risk of root resorption using self-ligating brackets is not greater than the conventional ones.
In relation to stability after treatment, it is possible to affirm that the expansion of the dental arches had not influenced in the relapse of dental crowding. and in the long term, the increases in transverse dimensions of arches obtained with self-ligating brackets remain stable. Finally regarding the dysfunction of the stomatognathic system brought about by the change in the muscular equilibrium of forces on the dental arch, it has long been known that the claim that orthodontic treatment (even with self ligating brackets) causes temporomandibular dysfunction is anecdotal, so the affirmation that self-ligating systems change the muscular equibilibrium of forces causing dysfunction of the stomatognathic system should not be taken too seriously.
Dental arch expansion occured mostly due to buccal tipping mainly in the premolar region for both groups.
The use of different diagrammed dental archwires for the two groups was crucial to reach this result. In other words, there was less dental and WALA ridge expansion in conventional group, where the archwire diagram was based on the WALA ridge of the pretreatment dental cast while the archwire design used in passive self-ligating system group was determined after dental arch expansion in initial leveling phase performed with Damon Cu-Ni-Ti archwires.
Thus, it should be highlighted the importance of the entire system related to the chosen technique, and not collate the results with appliance choice. If greater dental arch expansion is desired, passive self-ligating appliances can be used, with its unique archwire design and proper expanded Cu-Ni-Ti archwires, providing these effects. On the other hand, if the aim is to restrict dental arch expansion, conventional appliance and the method of arch diagram based on pretreatment dental cast must be chosen, both using the WALA ridge or using the predetermined shapes and sizes dental arches diagrams.
Limitations: Both groups had not used the same model or archwire sequence.
| Conclusions|| |
There was a significantly greater increase in the WALA ridge and mandibular dentoalveolar transversal dimensions in the passive self-ligating system group when compared to conventional group. It was also observed that there was a greater increase in buccal axis transverse dimensions in premolar region when compared to the WALA ridge transversal increase, independent of the appliance used.
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Conflicts of interest
There are no conflicts of interest.
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Dr. Paula Cotrin
Department of Orthodontics, University of São Paulo, Alameda Dr. Octávio Pinheiro Brisolla, 9-75, Bauru, São Paulo 17012-901
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]
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