In this study the investigators are going to assess and compare the predictability of distal movement of upper molars in patients with class II molar relationship when superimposing the initial malocclusion with the real end of distalization phase and the predicted end of distalization phase. Also, the investigators are going to study another dental movements, pain level, aligner properties, oral hygiene, posterior root resorption, patient satisfaction, quality of life and efficiency of these systems.~The aligner systems that are going to be used are Invisalign System (Align Technology, San José, CA), Spark Aligners (Ormco, Glendora, CA), Quicksmile (Madrid, España) and ClearCorrect (Straumann, Austin, TX). To help achieve the molar movement there is going to be place a TAD (temporary anchorage device) between two teeth. Before starting the study, the patients will need some pretreatment records (radiographs, photographs, dental casts and intraoral scan) to make a diagnosis and confirm if the patient is suitable for the study.~The required sample will be 98 subjects, assuming a sample loss of 15% the required sample will be 115 subjects per group. Patients will be randomly assigned to either group using a block randomization system and carried out by a researcher not involved in the study. Data normality will be examined with the Kolmogorov-Smirnov. Descriptive statistics of the different outcomes will be calculated for each group. Student's paired sample t-test will be used to analyze intragroup differences between T0 and T1. Intergroup comparison among different intervention groups will be performed using multiple analysis of variance (MANOVA), with Tukey's post-hoc test. The investigators will use the Pearson correlation coefficient to evaluate the linear relationship between the mm of distalization achieved and the mm of crowding and between the mm of distalization achieved and the patients age. The investigators will perform a binary logistic regression in order to assess the influence of confounding factor (clinical variables) on the primary outcome. All statistical analysis will be conducted using IBM SPSS 24.0 (SPSS Inc., Chicago, IL, USA) software with a 0.05 level of significance.
In this study the investigators are going to compare the predictability of the backward movement of upper first molars in patients with the upper dentition more advanced than the lower dentition. The investigators are going to study if the movements that they predict are achieved and in which proportion and compare it between four different aligner systems. The investigators hypothesis is that there are no differences in the predictability of this movement between the four aligner systems.