Expansion of the arches is generally considered highly unstable and prone to relapse regardless of the type of expansion. Retention appliances play a vital role in preserving these changes. Hawley retainer users often avoid wearing them due to speech difficulties and less aesthetic appeal. They are also more prone to breakage, costlier, and require more labour. Despite the relatively recent introduction of 3D-printed retainers, they offer potential advantages in orthodontics, including the accuracy of digitally scanned images, reduced labour and material costs, and improved patient comfort. While 3D-printed retainers are quite new, most studies focus on laboratory testing of their mechanical properties, there is limited evidence directly comparing their effectiveness in retaining arch width increases, patient acceptance, and cost estimation. This knowledge gap creates uncertainty about the optimal choice of retainer for long-term stability, necessitating a comparative assessment of their performance. This study addresses this knowledge gap by evaluating the retention of arch width increases achieved using Hawley retainers versus 3D-printed retainers

Maxillary dentoalveolar expansion is a procedure to correct transverse discrepancies between the maxillary and mandibular arches by applying forces to widen the maxillary arch. This procedure is inherently unstable and is susceptible to relapse. While Hawley retainers (HR) have served as the established standard for retention after maxillary expansion, recent studies have shown that modified thermoforming retainers can be as effective as HR. The emergence of computer-aided design and computer-aided manufacturing (CAD-CAM) and three-dimensional (3D) printing technology has significantly streamlined fabricating appliances and prostheses. 3D printing material is more rigid, with superior compression and tensile strength. Thus, a normal shape 3D-printed retainer may be a viable choice for the retention of maxillary expansion. A recent systematic review highlighted a critical gap in knowledge regarding the long-term clinical efficacy and durability of 3D-printed retainers. Thus, the present study aimed to address this research gap by investigating the long-term clinical effectiveness, patient acceptance, and cost estimation of 3D-printed retainers in expansion cases. This study will be carried out as a multicentre prospective randomized controlled clinical trial (RCT) conducted at Universiti Kebangsaan Malaysia (UKM), Universiti Malaya (UM), and Universiti Teknologi MARA (UiTM). Orthodontic patients who fulfil the inclusion criteria will be randomly allocated into the HR or 3D-printed retainer groups. Dental casts of patients will be measured at intercanine width (ICW), inter-premolar width (IPMW), inter-first molar mesiobuccal cusp width 1 (IFMW1), and inter-first molar distobuccal cusp width 2 (IFMW2) for both groups at debond(T0), 3(T1), 6(T2), and 12(T3). The outcome assessor and data analyst will be blinded to the retention method. The researcher will evaluate the patient's acceptance at T2 & T3 and conduct a cost analysis at T1 post-debond. The findings of this study will contribute valuable data to the field of orthodontics, aiding clinicians in determining the most effective long-term retention strategy for patients who have undergone maxillary dentoalveolar expansion.

Inclusion Criteria:

• Patients aged 16 years or older at the time of debonding
• Treatment plan of extraction or non-extraction followed by straight wire appliances in the upper arch only or both arches
• Undergone expansion treatment in the upper arch causing an arch width increase of 3-10mm, either using a Quadhelix, expansion with archwires, or URA with midline screw
• Had pretreatment dental cast
• Had no chronic medical condition.

Exclusion Criteria:

• Cleft lip and palate
• Chronic medical conditions
• Broken teeth or bubbles on study model at site of measurement.

Only data relevant to the study analyses will be provided. All personal identifiers and information that could reveal participant identity will be removed to protect confidentiality and comply with ethical requirements.

Investigators know who the participants are but will keep that information hidden from everyone else. Investigators will anonymize personally identifiable data so that it cannot be linked to other data by anyone else. Physical, social, psychological, and all other types of harm are kept to an absolute minimum.