## 1 Introduction  
Maxillary molar distalization is a commonly employed effective treatment strategy, which is useful not only for patients with Class II malocclusion but also for resolving crowding caused by maxillary arch length discrepancy. In the early 2000s, before the advent of temporary anchorage devices (TADs), removable or dental anchorage devices were mainly used, whose inherent disadvantages included the need for patient cooperation and the possibility of undesired tooth movement [1; 2; 3; 4; 5; 6; 7]. Since the 2000s, many of the designs of various existing orthodontic treatment devices have been modified to incorporate the use of TADs, and new designs of maxillary molar distalization using TADs have also been posited by numerous clinicians [8; 9; 10; 11].  
In most of the reported maxillary molar distalization cases, the force vector is designed to pass in the molar occlusal direction of the center of resistance of the maxillary dentition because of anatomical limitations. Molar distalization with conventional appliances, or TADs-assisted appliances, results in a substantial amount of simultaneous undesirable distal tipping tooth movement [12; 13; 6; 11].  
Distal tipping movement of the maxillary molar can cause unplanned clockwise rotation of the entire maxillary dentition, resulting in a steepening of the maxillary occlusal plane. Numerous studies have reported an increase in the slope of the maxillary occlusal plane after maxillary molar distalization [12; 14; 15; 16; 17; 18; 19]. However, different results have been reported depending on the device design and location of the TADs; some studies have reported no change in the angle of the maxillary occlusal plane [20; 21].  
Although the importance of the occlusal plane is not yet fully understood, changes in this plane are known to affect the position of the mandible during oral functions such as mastication and pronunciation. Oral function and esthetics and maxillofacial growth have been reported to be influenced by the inclination of the occlusal plane [22; 23; 24; 25]. In Class II malocclusion, an increase in the occlusal plane angle can be a useful treatment strategy for achieving a dental Class I relationship, but excessive steepening can have a detrimental effect on oral function and esthetics, necessitating a cautious approach [26]. Furthermore, several studies have reported an increase in the facial vertical dimension after maxillary molar distalization [15; 16; 19; 27; 28; 29]. This change in the facial vertical dimension is due to maxillary molar extrusion, which results in clockwise rotation of the mandible, and can cause unfavorable facial changes in patients with Class II malocclusion.  
Changes in the angle between the occlusal plane and mandibular plane that can be caused by maxillary molar distalization affects oral function and facial esthetics; however, the few studies that have been conducted on maxillary molar distalization have reported conflicting results. Since the introduction of orthodontic skeletal anchorage, maxillary molar distalization has been actively used as a clinical treatment method. More research is needed on the dental and skeletal changes resulting from maxillary molar distalization. Therefore, in this study, we aimed to conduct a narrative review of studies with a special focus on the occlusal plane angle. In addition, a preliminary study was performed using lateral cephalogram measurements to compare the alterations in the occlusal plane and mandibular plane angle based on the maxillary molar distalization appliance design.