Vertical Effects in Class II Patients Treated With Distalization

Class II malocclusion presents a major and common challenge to orthodontists. Treatment of Class II malocclusion is one of the most investigated and controversial issues in contemporary orthodontics because of the extensive variability of treatment strategies addressing the morphological characteristics of this malocclusion. The therapeutic approaches include tooth extractions, orthopedic appliances and extraoral or intraoral distalizing appliances. Maxillary molar distalization is one of the most common strategies to correct Class II molar relationship and it is commonly indicated for patients with maxillary dentoalveolar protrusion or minor skeletal discrepancies. One of the most used devices is Pendulum appliance, introducted by Hilgers in 1992.

In the last decades, the orthodontic treatment with removable clear aligners has become an increasing common choice because of the growing number of adult patients who ask for aesthetic and comfortable alternatives to conventional fixed appliances.

In 1997, Align Technology (Santa Clara, Calif) adapted and incorporated modern technologies to introduce the clear aligner treatment (CAT). Only few investigations have focused on the predictability of orthodontic tooth movement with CAT. A systematic review by Rossini et al. pointed out that among the dental movements analyzed in 11 studies, the bodily distalization was the most predictable.

Clinicians can consider the use of aligners in treatment planning for adult patients requiring 2 to 3 mm of maxillary molar distalization.

However, a detailed analysis of the skeletal and dental changes that compared pendulum appliance and clear aligners in class II treatment is still lacking.

On the basis of these considerations, the aim of the present prospective study was to analyze the effects on vertical dentoskeletal changes following maxillary molar distalization with pendulum and full fixed appliances and clear aligners.

Class II malocclusion presents a major and common challenge to orthodontists. Treatment of Class II malocclusion is one of the most investigated and controversial issues in contemporary orthodontics because of the extensive variability of treatment strategies addressing the morphological characteristics of this malocclusion. The therapeutic approaches include tooth extractions, orthopedic appliances and extraoral or intraoral distalizing appliances. Maxillary molar distalization is one of the most common strategies to correct Class II molar relationship and it is commonly indicated for patients with maxillary dentoalveolar protrusion or minor skeletal discrepancies. One of the most used devices is Pendulum appliance, introducted by Hilgers in 1992. It is a tooth-tissue-borne appliance that includes a Nance button on the palate for intraoral anchorage and titanium-molybdenum coils that deliver a mild and continuous force to the maxillary molars. Despite its efficacy for maxillary molar distalization, there are side-effects, including labial/mesial tipping and protrusion of the maxillary incisors and premolars, distal tipping of the maxillary molars, increase in lower anterior face height, clockwise mandibular rotation, and extrusion of the first premolars. Consequently, these side-effects have to be corrected during the following fixed appliance treatment phase.

In the last decades, the orthodontic treatment with removable clear aligners has become an increasing common choice because of the growing number of adult patients who ask for aesthetic and comfortable alternatives to conventional fixed appliances.

In 1997, Align Technology (Santa Clara, Calif) adapted and incorporated modern technologies to introduce the clear aligner treatment (CAT). Only few investigations have focused on the predictability of orthodontic tooth movement with CAT. A systematic review by Rossini et al. pointed out that among the dental movements analyzed in 11 studies, the bodily distalization was the most predictable.

Simon et al. reported a high accuracy (88%) of the bodily movement of upper molars with aligners when a mean distalization movement of 2.7 mm was prescribed. The authors reported the best accuracy when the movement was supported by the presence of an attachment on the tooth surface. Furthermore, they underlined the importance of staging in the treatment predictability.

Ravera et al. showed that clear aligners are effective in distalizing maxillary molars in non-growing subjects without significant vertical and mesiodistal tipping movements. The authors reported that the lower facial height did not change at the end of the treatment. Therefore, clinicians can consider the use of aligners in treatment planning for adult patients requiring 2 to 3 mm of maxillary molar distalization.

However, a detailed analysis of the skeletal and dental changes that compared pendulum appliance and clear aligners in class II treatment is still lacking.

On the basis of these considerations, the aim of the present prospective study was to analyze the effects on vertical dentoskeletal changes following maxillary molar distalization with pendulum and full fixed appliances and clear aligners.

All subjects were selected according to the following inclusion criteria: bilateral Class II or end to end Class II molar relationship, skeletal Class I or II malocclusion (ANB angle between 2° and 7°), normodivergence on the vertical plane (SN\^GoGn angle less than 37°), crowding in the lower arch (≤6 mm), good quality of pre and post treatment radiographs. All patients were in good general health with healthy periodontium, generalized probing depths not exceeding 3 mm, and no radiographic evidence of periodontal bone loss. The exclusion criteria were: patients who required functional appliance therapy, those who had previous orthodontic treatment or extraction, hypodontia, craniofacial syndromes or cleft, previous prosthodontic treatments of the upper molars.

A computer-generated random number list was used to allocate patients to treatments. Block randomization was used to assign the same number of patients to each treatment. The allocation sequence was concealed by the statistician, who used opaque and sealed envelopes, sequentially numbered for each patient. The observer (BA) who performed all the measurements was blinded to the group assignment. The study was blinded in regard to the statistical analysis: blinding was obtained by eliminating from the elaboration file every reference to patient group assignment.

Subjects enrolled in the study were randomly assigned to the two groups: Pendulum Group (PG) Clear Aligner Group (CAG)

The Pendulum Group (PG) consisted of 20 patients (15F, 5M) with a mean age of 17.2 ± 4.3 years. The Clear Aligners Group (CAG) comprised 20 patients (13F, 7M) with a mean age of 17.2 ± 3.2 years. Distalization's protocol in PG involved the activation of TMA wires till the achievement of Class I molar relationship. A protocol of sequential distalization was applied in the CAG. For each subject lateral cephalograms have been analyzed before treatment (T1) and at the end of the therapy (T2).

To determine the reliability of the method, 15 randomly selected radiographs were traced and digitized by the same investigator on two separate occasions at least 1 month apart. A paired t-test was used to compare the two measurements (systematic error). The magnitude of the random error was calculated by using the method of moment's estimator (MME) (32).

The primary outcome was considered the changes in total vertical dimension (SN\^GoGn) while secondary outcome was considered reduced Overjet. Exploratory statistics revealed that all cephalometric variables were normally distributed (Kolmogorov-Smirnov test) with equality of variances (Levene's test).

Descriptive statistics and statistical between-group comparisons (PG vs CAG) were calculated for the craniofacial starting forms at T1 and for the T2-T1 changes. Statistical between-group comparisons for the T2-T1 changes were performed with independent samples t-tests. The significance level was set at P \<0.05. All statistical computations were performed with SPSS software (Statistical Package for the Social Sciences, SPSS, version 12, Chicago, Illinois, USA).

Eligibility Criteria:
Inclusion Criteria:

* bilateral Class II or end to end Class II molar relationship
* skeletal Class I or II malocclusion (ANB angle between 2° and 7°)
* normodivergence on the vertical plane (SN\^GoGn angle less than 37°)
* crowding in the lower arch (≤6 mm)
* good quality of pre and post treatment radiographs
* good general health with healthy periodontium

Exclusion Criteria:

* patients who required functional appliance therapy
* those who had previous orthodontic treatment or extraction
* hypodontia
* craniofacial syndromes or cleft
* previous prosthodontic treatments of the upper molars