Comparison of Changes in Incisors Position in Cases Treated with Damon Self-Ligating and Conventional Fixed Appliances

2.1.1. Criteria for Sample Selection

Only patients presenting the following prerequisites were selected:

1. Good oral and systemic health.
2. No dental absences.
3. Light degree of anterior crowding.
4. Class I Angle malocclusion treated nonextraction.
5. No skeletal discrepancy.
6. Normal growth pattern (equilibrated).
7. Absence of periodontal disease.
8. Absence of prosthetic rehabilitation.
9. Cases treated only orthodontically, without extractions.
10. Full orthodontic treatment documentation, including lateral cephalogram at the beginning and end of treatment and dental casts from the initial stage.

Only patients who presented the following were considered for the sample.

2.1.2. Sample Characteristics

The sample comprised 51 patients, divided into two distinct groups, according to the type of appliance used during treatment:

Group 1, formed by 20 patients (12 female and 8 male), treated orthodontically with Damon self-ligating appliance, with the mean initial age of 15.00 (s.d.=6.41) and mean final age of 17.01 years (s.d.=6.66). Mean treatment time was 2.01 years (s.d.=0.73). Mean Little index was 4.63 mm (s.d.=3.32) for the maxillary arch and 4.86 mm (s.d.=2.52) for the mandibular arch. The archwire sequence used was: 0.014” CuNiTi, 0.014”x0.025” CuNiTi, 0.018”x0.025” CuNiTi, 0.017”x 0.025” TMA and 0.019”x0.025” stainless steel. The diagram of the stainless steel archwire was made individually after alignment of the dental arches with the 0.014”x 0.025” CuNiTi wire, with reference to the bite registry in wax 7. This group was treated in a dental clinic at UNINGA Inga University Center, Cuiaba-MT-Brazil, by a single orthodontist.

Group 2, formed by 31 patients (17 female and 14 male), treated orthodontically with conventional Straight-Wire, Andrew’s prescription synthesis brackets, with the mean initial age of 14.98 (s.d.=3.54) and mean final age of 16.79 years (s.d.=3.45). Mean treatment time was 1.81 years (s.d.=0.60). Mean Little index was 5.47 mm (s.d.=2.45) for the maxillary arch and 4.40 mm (s.d.=1.91) for the mandibular arch. The archwire sequence used in orthodontic treatment was 0.014” NiTi, 0.016” NiTi, 0.016”, 0.018”, 0.020” and 0.019”x0.025” stainless steel. The diagram of stainless steel archwires was based on the initial arch form of each patient individually. This group was treated by students with a supervisor in an orthodontics course at UNINGA Inga University Center, Maringa-PR-Brazil.

Since patients present Class I malocclusion, in both groups, use of intermaxillary elastics was only for intercuspation for finishing the occlusion. No interproximal stripping was performed. After removal of the fixed appliances, patients used a Hawley plate as retention in the maxillary arch and a bonded 3x3 in the mandibular arch.

2.2.1. Lateral Cephalograms

Two lateral cephalograms were used for each patient, one from the beginning of the fixed orthodontics appliance treatment (T1) and other from the end (T2).

The cephalograms were scanned using the Microtek ScanMaker i800 (9600 x 4800 dpi, da Microtek International, Inc., Carson, CA, USA) table scanner and attached to a Pentium microcomputer. The images were transferred to Dolphin Imaging Premium 10.5 programme (Dolphin Imaging & Management Solutions, Chatsworth, CA, USA) through which the images were digitalized and the measurements were processed.

Magnification factors used, depending on the apparatus used to take the cephalogram, were: 6% e 9.8%.

Only measurements of maxillary and mandibular incisors and overjet and overbite were included. Cephalometric variables included Steiner, Tweed and McNamara’s analysis measurements.

2.2.2. Study Models

To analyse mandibular anterior crowding in the study models, Little's irregularity index was applied.

Little's irregularity index is a quantitative score used to evaluate mandibular anterior teeth irregularities. It involves measuring the real linear distance of anatomical contact points of each lower incisor to the anatomical contact point of the adjacent tooth, where the sum of these irregularities represents the distance to which the contact points should be moved to reach alignment.

The measurements were made using a Mitutoyo digital paquimeter, duly calibrated and using original active parts.

2.2.3. Method Error

To determine the methodological error, 15 initial and 15 final cephalograms were randomly selected. The cephalograms were retraced, and two measurements for the same variables were obtained, at different times. Dahlberg’s formula [8] was applied and it allows the estimation of the order of magnitude of casual errors. To analyse systematic errors, the dependent t test was applied [9].

2.2.4. Statistical Analysis

In order to evaluate the normality of the cephalometric variables, the test of Shapiro-Wilk was used.

Independent t test was used to check the compatibility of initial and final ages and treatment time. The non-parametric Mann-Whitney test was used to verify intergroup compatibility of the maxillary and mandibular crowding.

For intragroup comparison of the initial and final stages of treatment, dependent t or Wilcoxon tests were used. Intergroup comparison of initial and final stages and treatment changes were performed with independent t or Mann-Whitney tests.

All tests were made using Statistica software (Statistica for Windows 6.0, Statsoft, Tulsa, Okla, EUA). Significance level adopted was of 5% (p<0.05).

4.1.1. Maxillary Dentoalveolar Component

Maxillary anterior teeth showed no significant difference between the groups at initial and final stages and during treatment, indicating that both Damon self-ligating and conventional appliances caused similar maxillary incisor proclination and protrusion [12]. This does not corroborate the theory that the light forces caused by self-ligating brackets are not capable of promoting incisors proclination and protrusion. Said result implies that the use of superelastic wires is not able to overcome the strength of perioral muscles, especially the orbicular and mental muscle of the mouth, that should produce a “lip-bumper” effect on the incisors [2].

4.1.2. Mandibular Dentoalveolar Components

Regarding the mandibular arch, Pandis et al. [13] and Fleming et al. [12], described identical incisors proclination and increase in intercanine distance using both conventional and self-ligating brackets during alignment and levelling stage [14].

Both showed proclination and protrusion in mandibular incisors, therefore there was no significant difference between the groups.

Scott [6] observed, in his randomized study comparing treatment efficiency between conventional and Damon system brackets after dental alignment, the inclination and protrusion of mandibular incisors on both groups, which prove that the result of the present paper is corroborating the results of previous studies.

The treatment of mandibular crowding with no tooth extraction implies in an increase of arch perimeter, arch length and protrusion and buccal inclination of incisors. The effects of this treatment modality are similar when comparing self-ligating and conventional brackets [12, 13].

4.1.3. Dental Relationships

It has been shown that Damon self-ligating brackets are not clinically more effective than conventional brackets during orthodontic treatment [6].

Both groups showed correction in overbite and overjet after treatment, which is exactly an effect of dental crowding correction. However, both presented decrease in the two variables.

The decrease in overbite happens through molar extrusion, probably due to intermolar distance increase, characteristic present when dental crowding is treated nonextraction both in Damon and conventional groups [11].