Maxillary dental and skeletal effects after treatment with self-ligating appliance and miniscrew-assisted rapid maxillary expansion


The objective of the present study was to compare the maxillary dental and skeletal effects after treatment with self-ligating appliance and miniscrew-assisted rapid maxillary expansion (MARPE).


The sample comprised 37 patients with Class I malocclusion treated without tooth extraction, divided into 2 groups: group 1 comprises 21 patients with a mean age of 19.55 years (standard deviation = 1.31), submitted to orthodontic treatment with Damon self-ligating appliance, and evaluated until the end of the alignment and leveling stage. Group 2 comprises 16 patients with a mean age of 24.92 years (standard deviation = 7.60), with maxillary atresia, who underwent MARPE, and were evaluated after the removal of the expander. Buccal bone thickness; dental inclinations; and transverse distances of the maxillary arch, nasal base, and jugula widths were measured on cone-beam computed tomography scans before and after treatment. The intergroup comparison was performed with the independent t test.


With treatment, there was a significantly greater decrease in buccal bone thickness of canines and premolars in the self-ligating group, the premolars presented a greater buccal inclination in the self-ligating group, and the intercanine and intermolar distances and nasal base and jugula widths showed significantly greater increases in the MARPE group than in the self-ligating group.


MARPE treated more severe skeletal transverse maxillary discrepancies and obtained better results than self-ligating appliances in terms of buccal bone loss, tooth inclination, and transverse skeletal increase of the maxilla. MARPE presented more skeletal effects and self-ligating appliances, more dental effects.


  • Miniscrew assisted rapid palatal expansion (MARPE) and self-ligating appliances were compared.

  • MARPE produced more skeletal effects; self-ligating appliances more dental effects.

  • Both treatments resulted in some bone loss and buccal inclination of posterior teeth.

  • MARPE should be considered for patients with severe skeletal maxillary atresia and posterior crossbite.

  • Self-ligating appliances are indicated when transverse increase would be beneficial.

Currently, self-ligating systems, when compared with conventional appliances, present several advantages such as less plaque accumulation, low friction, longer intervals between appointments, and shorter chair time. When crowded teeth are aligned without interproximal stripping, expansion, and extractions, an inevitable increase in the transverse dimension of the dental arch occurs, causing buccal inclination of posterior teeth.

When present, maxillary atresia can result in severe malocclusions, such as crowding and crossbites, impairing the patient’s oral function and esthetics. Rapid maxillary expansion (RME) and surgically assisted rapid maxillary expansion are the most prescribed treatments for maxillary atresia and posterior crossbite in prepeak and postpeak growth patients, respectively. Commonly, surgery is indicated when the midpalatal suture is already mature, preventing maxillary disjunction with conventional RME, because it may cause undesirable effects on teeth and supporting tissues. With the increasing use of mini-implants in Orthodontics, the possibility to anchor expansion appliances directly to the palatal bone benefited patients with mature sutures, eliminating undesirable side effects and the need to perform a surgical procedure. In these patients, miniscrew-assisted rapid palatal expansion (MARPE) can be the treatment choice. ,

MARPE is an effective technique in correcting transverse maxillary discrepancies in nongrowing patients, providing expansion of sutures with reduced periodontal and dental side effects because orthodontic mini-implants support the appliance for palatal disjunction. It is essential to consider it as a treatment option to adults but with some restrictions.

Self-ligating appliances combined with heat-activated superelastic archwires produce low-force and low friction environment, allowing a great increase of the arch dimensions. , However, it is also accompanied by a significant buccal inclination of posterior teeth and alveolar bone loss in some teeth. , RME also causes reduction in the buccal alveolar bone of premolars and molars. , Recently, MARPE studies also showed some effects in periodontal tissue, including buccal bone loss and posterior teeth buccal inclination. , ,

Because self-ligating appliances, and MARPE, are often used to correct transverse discrepancies in adults, even in different severities, it would be interesting for the orthodontist to know the dental and skeletal effects of both therapies in order to help in orthodontic treatment planning, providing a better prognosis.

Thus, given that there is no comparison of the skeletal and dental effects between self-ligating appliances and MARPE, this study aimed to compare the buccal bone thickness, posterior teeth inclination, and transverse dimensions changes in patients treated with self-ligating appliances and MARPE.

Material and methods

The Ethics Research Committee of the Ingá University Center Uningá approved this retrospective study (no. 09677219.0.0000.5220).

The sample calculation was based on 5% alpha significance level and 20% beta to achieve 80% test power to detect a difference of 1.45 mm with a standard deviation of 1.4 mm for the jugula width change with treatment. Thus, the sample size calculation resulted in the need for at least 16 subjects in each group.

This retrospective study consisted of patients treated at different institutions (Advanced Dentistry Institute, Asunción, Paraguay; Bauru Dental School, University of São Paulo, Bauru, Brazil; and Freitas Dentistry Institute, Bauru, Brazil). All participants signed informed consent form.

Inclusion criteria were patients with no previous orthodontic treatment, all erupted teeth up to first molars, healthy periodontium and supporting tissues, Class I malocclusion, aged at least 16 years.

The sample consisted of the documentation and the initial and final tomographies of 37 patients, divided into 2 groups: group 1 (self-ligating): 21 patients (11 male; 10 female), with a mean age of 19.55 years (standard deviation = 1.31), with Class I malocclusion and moderate dental crowding, presence of slight maxillary atresia requiring transverse maxillary enlargement, treated with self-ligating appliances. Cone-beam computed tomographies (CBCTs) were taken before fixed appliance installation and at the end of the alignment and leveling phase. Orthodontic treatment was performed without extractions using Damon 3MX self-ligating appliances (Ormco, Orange, Calif). This sample was obtained from the archives of Bauru Dental School, University of São Paulo and Freitas Dentistry Institute, Bauru, Brazil. The following archwire sequence was used, as recommended by the Damon system: 0.014-in copper nickel-titanium, 0.014-in × 0.025-in copper nickel-titanium, and 0.016-in × 0.025-in copper nickel-titanium (Ormco). Finally, 0.019-in × 0.025-in stainless steel archwires (Morelli, Sorocaba, São Paulo, Brazil) were installed, contoured based on the arch form of each patient after leveling with the 0.014-in × 0.025-in copper nickel-titanium archwire. The alignment and leveling phase time lasted 6 months on average. Figure 1 shows the intraoral photographs of a patient from the self-ligating group at pretreatment (T1) and after alignment and leveling phase (T2).

Fig 1
Intraoral photographs of a patient from the self-ligating group at pretreatment (T1) and after the alignment and leveling phase (T2).

Group 2 (MARPE): 16 patients (11 female; 5 male), with a mean age of 24.92 years (standard deviation = 7.60), with Class I malocclusion, maxillary atresia, and posterior crossbite, treated with MARPE. This sample was obtained from the archives of Advanced Dentistry Institute, Asunción, Paraguay, treated by 2 orthodontists. The patients underwent maxillary disjunction using the MARPE technique, with the PecLab appliance (Belo Horizonte, Minas Gerais, Brazil), supported by 4 titanium mini-implants of 1.8 mm diameter and 8 mm length, with bands on the first molars. The activation protocol was 2/4-turn a day until the palatal cusps of the maxillary first molars touch the buccal cusps of the mandibular first molars. No additional treatment was performed in this group. The opening of the midpalatal suture was clinically confirmed by assessing the patients’ interincisive diastema and an occlusal radiograph right after the end of the activations. The expander appliance was maintained for 4 months. Patients in whom the opening of the midpalatal suture was not observed were excluded from the sample. Figure 2 shows the intraoral photographs of a patient from the MARPE group before (T1) and after expansion with MARPE (T2).

Fig 2
Intraoral photographs of a patient from the MARPE group before (T1) and after expansion with MARPE (T2).

CBCT scans were performed before the beginning of treatment (T1) in both groups, and after alignment and leveling in the self-ligating group and after expansion in the MARPE group (T2).

In group 1, all CBCT exams were performed in i-Cat Cone Beam 3D Dental Imaging System (Kavo, Brea, Calif), 5 mA, 120 kV, exposure time of 40 seconds, voxel size of 0.25 mm, scanning area of 13 × 16 cm.

In group 2, CBCT scans were performed in Orthophos SL 2D/3D appliance (Dentsply Sirona, Bensheim, Germany), 7 mA, 85 kV, exposure time of 14.4 seconds, voxel size of 0.08 mm, scanning area of 8 × 5.5 cm.

The images were saved in digital imaging and communications in medicine format and measured in Dolphin 3D software (version 11.95 Premium; Dolphin Imaging and Management Solutions, Chatsworth, Calif).

The head position was standardized to allow reliable measurements. In the frontal view, the reference plane passed through the lowest points of the infraorbital foramen; in the lateral view, the plane passes through the anterior and posterior nasal spines; and in the axial view, the line passing through the galli crest and the center of the foramen magnum.

The buccal bone thickness was evaluated at the first molars (16 and 26; mesiobuccal and distobuccal roots), first premolars (14 and 24 Buccal), second premolars (15 and 25 Buccal), and canines (13 and 23 Buccal), in axial slices obtained 4 mm above the cementoenamel junction in the mesial of the maxillary right first molar ( Fig 3 ). The inclinations of the canines, premolars and first molars were measured by the line passing through the long axis of the tooth and vertical line parallel to the midsagittal plane ( Fig 4 ). Interdental distances measures included intercanine width (3-3), interpremolar width (first premolars 4-4 and second premolars 5-5), and intermolar width (6-6) ( Fig 5 ). Skeletal transverse measurements included the nasal base width and jugula width ( Fig 6 ). The maxillary Little irregularity index was used to measure the maxillary anterior teeth crowding.

Fig 3
Measurement of buccal bone thickness.

Fig 4
Measurement of tooth inclination.

Fig 5
Measurement of interdental widths.

Fig 6
Measurement of the nasal base and jugula widths.

The intraexaminer reliability was assessed by intraclass correlation coefficients. After a month interval, 20 CBCT scans were remeasured, and the 2 measurements were compared.

Statistical analysis

The normality of data was verified by the Shapiro-Wilk test. The compatibility of the groups of the age and maxillary Little irregularity index was performed by independent t test and the sex distribution, with the chi-square test. Intergroup comparison of the measurements in the initial (T1) and final stages (T2) and the changes with treatment (T2-T1) was performed with independent t tests.

The tests were performed with the software Statistica (version 10.0; StatSoft, Tulsa, Oklahoma), and data were considered significant at P <0.05.


Intraclass correlation coefficients varied from 0.86 to 0.97, indicating excellent intrarater agreement.

The self-ligating group was significantly younger than the MARPE group ( Table I ). There was compatibility between the groups of the gender distribution and maxillary Little irregularity index ( Table I ).

Table I
Intergroup compatibility of the age, sex distribution, and maxillary Little irregularity index
Variables Self-ligating (n = 21) MARPE (n = 16) P value
Mean (SD) Mean (SD)
Age, y 19.55 (1.31) 24.92 (7.60) 0.003
Sex X 2 = 1.65 degree of freedom = 1
P = 0.198
Male 11 5
Female 10 11
Maxillary Little irregularity index, mm 7.57 (2.66) 6.58 (2.91) 0.144

SD, Standard deviation.

Independent t test.

Chi-square test.

The groups were initially compatible in terms of bone thickness, dental inclinations, dental transverse measurements, and nasal base width ( Table II ). Only the jugula width was significantly smaller at the initial stage in the MARPE group than the self-ligating group ( Table II ).

Table II
Intergroup comparison at the initial stage (T1) (independent t test)
Variables Self-ligating (n = 21) MARPE (n = 16) P value
Mean SD Mean SD
Buccal bone thickness
16MB (mm) 1.24 0.56 0.78 0.89 0.063
16DB (mm) 1.80 0.53 1.48 0.78 0.152
15B (mm) 1.98 0.52 1.50 1.05 0.077
14B (mm) 0.99 0.64 0.75 0.67 0.289
13B (mm) 0.76 0.37 0.83 0.65 0.705
23B (mm) 0.43 0.48 0.59 0.71 0.428
24B (mm) 0.82 0.63 0.66 0.68 0.460
25B (mm) 1.73 0.69 1.20 0.97 0.065
26MB (mm) 0.93 0.52 0.69 0.70 0.247
26DB (mm) 1.62 0.72 1.26 0.88 0.176
Tooth inclination
16 (°) 1.63 6.95 1.67 4.96 0.986
15 (°) 7.37 6.41 6.29 7.34 0.650
14 (°) 5.14 4.98 8.33 5.73 0.084
13 (°) 21.50 8.13 17.16 5.21 0.096
23 (°) 23.34 9.71 19.86 6.44 0.249
24 (°) 6.20 5.52 10.48 7.15 0.051
25 (°) 8.28 7.52 7.04 4.92 0.593
26 (°) 3.45 6.69 2.56 5.42 0.667
Transverse dimensions
3-3 (mm) 35.26 2.59 35.06 2.92 0.829
4-4 (mm) 41.61 2.29 41.37 4.31 0.832
5-5 (mm) 46.20 3.90 44.08 3.84 0.122
6-6 (mm) 50.34 2.92 50.31 3.98 0.982
NB-NB (mm) 29.05 3.90 28.14 3.65 0.477
J-J (mm) 59.89 4.35 56.89 2.88 0.023
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Feb 28, 2021 | Posted by in Orthodontics | Comments Off on Maxillary dental and skeletal effects after treatment with self-ligating appliance and miniscrew-assisted rapid maxillary expansion
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