The present study will be a single-center, split-mouth, randomized controlled clinical trial. Patients undergoing orthodontic treatment with Invisalign aligners will be enrolled after signing the informed consent. Two different flowable composite resins will be evaluated for the performing of attachments using a split-mouth design:

• group A: Filtek Supreme Flow (3M Unitek, Monrovia, Calif)
• group B: Grandioso Heavy Flow (VOCO GmbH, Cuxhaven Germany)

Digital impressions with iTero intraoral scanner will be performed. The resulting 3D images will be superimposed onto the reference STL model, representing the pre- planned ideal attachment configuration. Digital scans will be used to assess any changes in shape of the attachments. Each tooth will be separated from the others and superimpositions of the single tooth will be performed with ZEISS Inspect software.

The present study will be a single-center, split-mouth, randomized controlled clinical trial. Patients willing to start Invisalign treatment or refinement phases will be recruited from the Unit of Orthodontics and Pediatric Dentistry, Section of Dentistry, Department of Clinical, Surgical, Diagnostic and Pediatric Sciences, University of Pavia, Pavia, Italy. Each patient will sign the informed consent before participation. The bonding procedure will be the following: isolation of the working field with the placement of a cheek retractor, enamel etching with 37% orthophosphoric acid, rinsing and drying, application of a thin layer of ScotchBond adhesive (3M Unitek, Monrovia, Calif) and light curing. Then, patient will be divided into groups A and B: in group A, attachments will be realized using Filtek Supreme Flow (3M Unitek, Monrovia, Calif) for teeth belonging to mandibular left and maxillary right quadrants, whereas in the remaining quadrants, they will be realized using Grandioso Heavy Flow (VOCO GmbH, Cuxhaven Germany. In group B, quadrants will be inverted. After the bonding of the attachments, digital impressions with iTero intraoral scanner will be performed. The resulting 3D images will be superimposed onto the reference STL model, representing the pre-planned ideal attachment configuration. Digital scans will be used to assess any changes in shape of the attachments. Each tooth will be separated from the others and superimpositions of the single tooth will be performed with ZEISS Inspect software. For each of the five attachment surfaces the values obtained for the two composite resins will be compared using three key parameters: total mean discrepancy, mean of positive values only, and mean of negative values only. The analysis will be performed using R software, calculating descriptive statistics for each variable, including mean, standard deviation, median, minimum, and maximum values for each group. The normality of the distributions will be assessed using the Kolmogorov-Smirnov test. Subsequently, a t-test will be applied for inferential analysis of each variable.

For all tests, statistical significance will be set at P<0.05.

Inclusion Criteria:

• patients undergoing Invisalign orthodontic treatment

Exclusion Criteria:

• enamel demineralizations

Data will be available upon motivated request to the Principal Investigator.