The primary aim of the study is to compare the perception of pain and discomfort with two different protocols of attachments' placement during clear aligner therapy: the conventional protocol (CP), when attachments' placement is performed are placed at the delivery of the first aligner; the delayed protocol (DP), when the attachments' placement is performed at the delivery of the third aligner. The rationale of this study is to evaluate whether dividing the two phases most associated with the onset of pain and discomfort, namely the initiation of aligner therapy and the placement of attachments, can improve patients' quality of life during clear aligner treatment. Patients' discomfort will be evaluated with a questionnaire adapted by OHIP-14 (Oral Health Impact Profile 14)

: The study was approved by the Institutional Review board of the Catholic University of the Sacred Hearth, Rome, Italy (prot. n. 17048/23). All adult patients with class I and II malocclusion referred to the Fondazione Policlinico Universitario Agostino Gemelli will be consecutively enrolled for this study. All patients will be treated with Biomax Nuvola aligners built based on the individual patient's characteristics. The number of aligners and the number/ type of attachments will be chosen on the basis of the individual malocclusions.

Patients will be randomly allocated in two different groups: the study group includes patients following the delayed protocol (DP), while the control group is composed of patients' following the conventional protocol (CP). The aligner will be changed every 15 days, so the attachment placement in the DP will be performed around 30 days from the beginning of the clear aligner treatment. The modified OHIP Italian version has 20 questions categorized into 7 sections, concerning the limitation generated by deterioration of oral health in relation to clear aligners: functional, pain, psychological discomfort, physical or psychological or social disability, and handicap. The answers range from 0 (never) to 4 (very often). Possible categories are: never (0), rarely (1), sometimes (2), habitually (3), and very often (4). Low scores indicate better self-perception of quality of life. The customised questionnaire has 9 questions, concerning the limitation generated by discomfort caused by attachments. For 8 questions, the answers range from 0 (never) to 4 (very often). Possible categories are: never (0), rarely (1), sometimes (2), habitually (3), and very often (4). Low scores indicate better self-perception of quality of life. For the last question the answer is based on NRS scale, in fact it ranges from 0 to 10. Lower score indicates less pain perceived by the patient. The questionnaires will be filled out at different phases of orthodontic treatment, specifically: at the delivery of the first aligner, after 3 and 7 days; at the delivery of the third aligner, after 3 and 7 days. The survey scheduling is arranged according to White, who stated that the patients' perception of pain and discomfort occurred within 7 days after the beginning of the orthodontic treatment; then, patients' quality of life tends to return to a baseline condition.

The study will be single-blind, because the person collecting the results and making the assessments will not know which treatment was used. In fact, the patient will anonymously submit the answers to the questionnaires uploaded on Microsoft Form, using an acronym that will be provided to him/her by the clinical operator. In this way, the person collecting and analysing the data will not know to which group the patient who sent the answers belongs.

Inclusion Criteria:

• Age between 18 and 40 years;
• Class I malocclusion
• Non-extractive treatment;
• No missing teeth (third molars excluded);
• Good oral and general health.
• Signature of written informed consent to participate in the study

Exclusion Criteria:

• Patients with tooth-related pain (presence of dental and/or periodontal abscesses and presence of gingivitis)
• Presence of semi-included elements;
• Patients taking bisphosphonates or other anti-resorptive drugs;
• Patients with conditions involving chronic pain and/or on chronic therapy with antifiammatories/opiods or other drugs that may act on pain perception;
• Patients with temporomandibular disorders;
• Patients with conditions that may impair the ability to objectively report any sensations of discomfort or pain (e.g., mental retardation, dementia);
• Refusal to sign the written informed consent to participate in the study

The investigator does not know to which group the patient who sent in the questionnaire belongs