The aim of the present study is to investigate and analyze the perception of pain and function impairment during the first week of activation with two different palatal expansion screw to identify an effective pain prevention protocol.

Maxillary expansion with fixed appliance is a well-known and consolidated practice in clinical orthodontics but current findings of "evidence based dentistry" have not yet identified a better clinical expansion protocol. This issue is due both to the several expansion screws available on the market and to the different screw activation protocols, which could be grouped into rapid and slow, with several customizations. A recent systematic review has shown that both rapid and slow expansion protocols are clinically effective on the primary outcome, i.e. the resolution of the crossbite with a significant increase of skeletal transversal dimension in the maxillary transverse deficiency subjects. If the type of appliance based on its ability to solve the maxillary constriction is not any more the main selection criteria, the choice of the orthodontist should, therefore, be based on the timing and on a "patient-oriented" device, that minimizes the side effects, such as e.g. appliance breakages, functional impairments and pain.

In the orthodontic daily practice, the pain of the little patient is the most frequent symptom during treatment and is the one that most frightens/worries the child and the family. Literature shows that rapid maxillary expansion is, among the early orthodontic therapies, the one with the highest frequency of pain (up to 98%) as an adverse symptom reported by patients. The pain is statistically linked to the rapid expansion protocol (2/turn/day), during which, for each activation of the screw (0.2 or 0.25 mm) the force expressed can reach up to 10 pounds which acts in an orthopaedic manner on the palatine suture and the circummascellar sutures. Following this orthopedic action, a disorganized and highly vascularized connective tissue (inflammatory) is formed in palatine suture area, which becomes the main receptor of the pain perceived by the patient during the active maxillary expansion. In the literature the prevention and management of pain during palate expansion is a poorly analyzed topic, despite being a daily problem in orthodontic clinical practice and so the aim of the present study is to investigate and analyze the perception of pain and function impairment during the first week of activation with two different palatal expansion screw to identify an effective pain prevention protocol.

Inclusion Criteria:

• Subjects with transversal maxillary deficiency (with or without crossbite).
• Class I or Class II dental malocclusion with uni- or bilateral crossbite and/or constricted maxilla
• Before the pubertal peak (CVM 1-3).

Exclusion Criteria:

• Patients with previous orthodontic treatment
• Hypodontia in any quadrant excluding third molars
• Inadequate oral hygiene
• Craniofacial syndromes, or cleft lip or palate