## 1 _Eiditorial_ Special Issue on Recent Developments in Orthodontics on Cranioiden Orthopedics  
**[PERSON] 1,2,*(r)**, [PERSON] 1,2(r) and [PERSON] 1,2,*(r)  
This Special Issue was proposed with the aim of highlighting the recent developments in orthodontics on craniofacial orthopedics. In this regard, all the works respected the proposed theme and made significant contributions to the development of knowledge in the sector [1, 2, 3, 4, 5, 6]. Most of the papers dealt with the issue of maxillary expansion, confirming the clinical importance of the posterior crossbite from maxillary transverse deficiency in children [1, 3, 4]. As reported in the literature, rapid maxillary expansion (RME) of the maxilla is the best-known technique that allows you to correct these problems and prevent the development of skeletal complications such as mandibular deviation [7]. The rapid palatal expansion also allows increasing the volumes of the nasal and upper airways, reducing nasal resistance and improve breathing [8]. Many authors have proposed different expansion methods, differing in technical and biomechanical characteristics and in the type of modifications produced, using different clinical protocols [9, 10]. Many studies have shown that rapid and slow expansion protocols are clinically effective on the primary outcome, i.e., the resolution of the crossbite with a significant increase in the transverse skeletal dimension in subjects with maxillary transverse deficit [10]. The type of appliance based on its ability to resolve jaw constriction is no longer the main selection criterion, and the choice of the orthodontist should, therefore, be based on a \"patient-oriented\" device, which minimizes side effects. Recently, the clinical efficacy of the expander characterized by Ni-ti leaf springs has been confirmed by studies that have shown significant changes in the maxillary transverse diameters, when acting in younger subjects, with sutures still active [11]. [PERSON] et al. [12] comparing fast and slow maxillary expansion, based on low dose CT observations, stated that RME is no more effective than slow maxillary expansion (SME) in correcting posterior crossbite. In the meta-analysis proposed by [PERSON] et al. [13] on non-surgical expansions, SME proved effective in achieving maxillary expansion and can bring superior results to RME in the molar region. During SME, the maxillary intercanine diameter shows a change equal to or slightly greater than the excursion of the screw, reflecting the \"fan-like\" expansion of the maxilla, like what occurs in the RME. The intercanine diameter in the mandibular arch tends to increase due to spontaneous self-expansion, in accordance with the findings of [PERSON] et al. [14]  
In recent years, the use of skeletal anchorage adopting mini screws has greatly revolutionized our clinical practice. The easier management of anchorage using such devices has meant that scientific researchers in the last decade have concentrated a lot on this issue, with the aim of providing safe application protocols and indicating the limits and risks of their use. In the present Special Issue, [PERSON] et al. [6] evaluated the distribution of compressive and tension stress around the roots of the teeth and the influence determined by the position of a temporary anchoring device and the length of the retraction hook during dental distalization. This new photo elastic model demonstrated that the distribution of compressive and tension stress during retraction of the maxillary dentition is significantly influenced by the position of the TAD and the length of the retraction hook. Relatively uniform compressive stress was found in the cervical position of the TAD with medium hook and in the apical position of the TAD with a long hook. This means that the maxillary arch could be distalized parallel to the occlusal plane. The digital photoelastic analysis method has great potential for the evaluation of orthodontic biomechanics and can also provide very useful indications for the clinician.