PGO Scientific journal

Introduction: After orthodontic treatment it is important to know the position of the teeth and whether they respect the osseo-miofunctional balance. Wala Ridge is one of the parameters used to objectively quantify ideal crown positions.

Objectives: To test the efficacy of the Universal Smile System (USS) passive self-ligation technique in terms of lower arch development, taking as a reference the ideal values of L. Andrews.

Methods: The distance between the CCC (centre of the clinical crown) of the canines, first premolars, second premolars and lower molars and the WALA line is calculated in dental models treated with the U.S.S. orthodontic technique at the Alcalá de los Gazules Dental Clinic (Cádiz), and its approximation to Andrews’ ideal values is evaluated. The result is quantified by means of a statistical analysis.

Results: average deviation from ideal values proposed by Andrews: canines 0.13 mm, first premolars 0.91 mm, second premolars 1.08 mm, first molars 1.96 mm, second molars 1.45 mm.

Conclusion: With the U.S.S. self-ligation technique, the final position of the teeth is close to Andrews’ ideal values, being its maximum approach at the level of the canines.

Keywords: orthodontics; self-ligation; U.S.S.; Wala Ridge.

In the past, the general tendency was to treat patients with standard arches without taking into account their individual shapes and sizes, which clinically resulted in unstable treatment with numerous recurrences. The therapies used prioritised sagittal and vertical malocclusions, as the most popular cephalometric study was the profile teleradiography, which did not provide any transverse information. Ricketts1 , with his frontal skull X-ray, provides more information and completes the study of pathologies in a transversal sense, including norms and standard deviations for each age in his bone and dental analysis. It is now known that these positional dental changes must preserve the original shape of each patient’s arch, which is unique and individual.

In general, the most frequent orthodontic anomalies are usually related to a lack of space on the alveolar ridge to accommodate the dental material (negative osseodentary discrepancy), representing between 40% and 85% of malpositions (McNamara)2, with the classic manoeuvres to reverse these deficiencies being tooth extractions, reductions in tooth size due to wear and expansion. If the latter is carried out without criteria, it would lead to dental alveolar over-expansion, gingival recession and instability in the changes made.

In 2000, Andrews3 described a formula for calculating individual and unique arch forms for each patient, which brought the teeth closer to their most ideal and stable positions in the alveolus 4,5,6,7, by determining the distance between the centre of each of the clinical dental crowns and the mucogingival junction (described below). He carried out a study on 120 models of Class I patients, relating these to an anatomical reference that was easy to distinguish for the orthodontist and which was stable and unalterable by race, sex and age in the permanent dentition. This anatomical reference is the mucogingival junction in the mandible, which is very close to the junction between the basal and alveolar bone, as well as to the centre of resistance of the tooth, de-named WALA Ridge, an acronym of Will Andrews and Larry Andrews, promoters of the study (fig. 1). The ideal distances of each tooth from the WALA Ridge were established, and are considered useful both in determining the final shape of the arches in orthodontic treatment and the position in which the teeth should be left at the end of treatment.7,8,9,10 (fig. 2). These distances were kept constant for each tooth, so that the ideal distance between the CC of the canine and the WR at that level was 0.6 mm on each side. At the level of the first premolars 0.8 mm/side, 1.3 mm/side for second premolars and 2 mm/side for lower first molars.

At the end of 2014, the Universal Smile System (U.S.S.) passive self-ligation technique was developed by Dr. Luis Fernando Morales Jiménez¹¹. It uses Mini-Twin convertible passive self-ligating brackets, with rounded and smooth edges to avoid hurting the patient’s mucous membranes and a rhomboid-shaped base for quick identification of the spatial position of the bracket on the tooth surface. The base carries information on the torque and angulation of each tooth. The centre of the slot and the centre of the base are in the same horizontal plane, which favours the sliding mechanics¹². The bracket incorporates an 80 Gauge¹¹ mesh for greater retention during cementation. To facilitate handling, it has a colour code on the gingivo-distal flange of the tooth to which it belongs and another colour code determining the torque prescription located on the opening and closing gate.

The system is designed to perform an indirect luting technique, therefore, without being an obligation, it is highly recommended ^{13,14,15,16,17}. It requires high precision to be effective and to avoid bracket repositioning during treatment, minimise the need for archwire offsets and reduce treatment time.

The study begins with the measurement of 20 lower plaster models of patients who were treated in the dental clinic Alcalá de los Gazules (Cádiz), with U.S.S. passive self-ligating fixed orthodontics, where the mucogingival line can be seen, with complete dentition from the lower right second molar to the left, regardless of the sex, race or age of the patient.

The sequence of archwires used was: Cu-NiTi (Copper-Nickel Titanium) .014″, .016″, .014″ x .025″ and .016″ x .025″ for 10 weeks each. In the major mechanical stage, .017″ x .025″ steel archwires were used for as long as it took to achieve proper arch coordination. In the final detailing and finishing phase, .017″ x .025″ TMA (Titanium Molybdenum Arch) archwires were used until proper intercuspidation was achieved.

Taking into account that the ideal position of each tooth in the arch, according to Andrews, is determined by subtracting the following values from the distance between WR of each hemiarch: 1.2 mm (0.6 mm per side) at the level of the canines, 1.6 mm (0.8 mm/side) at the level of the first premolars, 2.6 mm (1.3 mm/side) at the level of the second premolars, 4 mm (2 mm/side) at the level of the first molars and 4.4 mm (2.2 mm/side) at the level of the second molars.  For the analysis of our study, the distance between the Wala Ridge line of each hemiarch was recorded, and the same was done for the centre of the clinical crown of each tooth (figs. 3 and 4). The models were marked with a mechanical pencil at the described points and measurements were taken with an electronic digital caliper (Stainless Hardened) by a single operator, and the values obtained were recorded in a table for each plaster model (Table 1).

The following formula was applied to obtain the unilateral distance of each orthodontically treated tooth and its Wala:

Wala patient – CCC patient – ideal Andrews x 2

= difference between patient/Andrews / 2

= one-sided position of the tooth at the Andrews value.

The Andrews ideal is subtracted from this position value to find the proximity to the Andrews ideal.

• Example at canine level:

31.46 mm (Wala patient) – 29.20 mm (CCC patient) = 2.26 mm – 1.2 mm (Andrews’ ideal 0.6 x 2) = 1.06 mm

1.06 mm (difference between patient/Andrews) / 2 = 0.53 mm

0.53 mm (one-sided tooth position at Andrews value).

0.53mm – 0.6mm (Andrews ideal) = 0.07mm (proximity to Andrews value)

A descriptive statistical analysis of the quantitative variables of the 20 models was performed using SPSS 25.0 for Windows. The minimum, maximum, mean and standard deviation values were calculated to measure the degree of dispersion or variability with respect to the values described by Andrews (Tables 3, 4, 5 and Graph 2).

After reading and interpreting the measurements taken on the plaster models of patients treated with the U.S.S. passive self-ligation technique at the Alcalá de los Gazules Dental Clinic (Cádiz), we obtained an average deviation at the level of:

• Canines: 0.13 mm in relation to the ideal value proposed by Andrews.
• First Premolar: 0.91 mm with respect to the ideal value proposed by Andrews.
• Second Premolar: 1.08 mm with respect to the ideal value proposed by Andrews.
• First Molar: 1.96 mm with respect to the ideal value proposed by Andrews.
• Second Molar: 1.45 mm with respect to the ideal value proposed by Andrews.

The results are summarised in Table 2 and Figure 1.

After having carried out the research work on twenty plaster models of patients treated with the U.S.S. passive self-ligation technique in the Alcalá de los Gazules dental clinic (Cádiz), it is interesting to know if the ideal values described by Andrews ^18,19,20 can be reached in order to obtain information and, in the future, to be able to compare it with other self-ligation techniques in order to find their similarities and differences or, on the contrary, these values are far away as described by other authors ^21,22.

It has been observed that there is a high percentage of coincidence with Andrews at the canine level (0.13mm) but more distally, the measurements are moving away at the expense of a rapprochement of the CCC to the Wala Ridge: 1st premolar (0.91mm), 2nd premolar (1.8mm), 1st molar (1.96mm) and 2nd molar (1.45mm). It is well known that with this technique, space problems can be solved with less need for extractions, as the forces applied by most of the arches used in this technique do not exceed the limits of the forces of the perioral musculature, even favouring bone formation ^23,24,25.

Also from the analysis of the results it has been proven that the anterior sector in the canines coincides with the ideal Andrews values, this being one of the pillars of post-treatment stability, mainly in the anterior sector due to the optimal implantation of the canine roots and also indirectly in the posterior sector according to the lateral disocclusion functions avoiding posterior interferences.

Taking into account that the study intentionally included models of patients with transverse, vertical and sagittal problems indistinctly, in order to evaluate the effectiveness of the U.S.S. technique on a clinical and practical level, it can be stated that with this technique satisfactory and stable results can be obtained, since the difference found in the post-treatment values and Andrews’ ideal values is very small and without perceptible aesthetic and clinical repercussions.

1. The U.S.S. passive self-ligating orthodontic technique is suitable and recommended for treatment in the permanent dentition, in those situations of great osseodental compromise, due to the characteristics of the system that combines passive self-ligating brackets with state-of-the-art wires and minimally invasive treatment mechanics.
2. With the values found, which are very close to those described by Andrews, the orthodontist can estimate that the treatments carried out with this technique will have a high success rate and that the results will remain stable over time.
3. This study confirms that the final position of the teeth is close to Andrews’ ideal values, even in some of them, such as the canines, both values coincide, which means that the tooth is in an excellent position in the centre of the alveolar bone, respecting the intercanine distance and providing a correct group function, which increases confidence in the use of this technique in patients and also the peace of mind that the feared recurrences will be minimised.
4. The values obtained in this study are very close to those expected, although it would be advisable to carry out other studies with a larger sample and with different variables in order to corroborate the results obtained.

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