# A Novel Digitized Method for the Design and Additive Manufacturing of Orthodontic Space Maintainers
## 1 Introduction and Background  
Primary teeth, particularly the first and second primary molars, play an important role in maintaining vertical space because they not only allow proper positioning and occlusion of permanent molars but also guide the correct eruption of the corresponding permanent teeth. Thus, maintaining these teeth in position improves esthetics, mastication, and speech [1]. Premature loss of posterior primary teeth, both upper and lower, can lead to undesirable tooth movements resulting in space loss in the permanent dentition. This can have side effects on the developing occlusion, including crowding, impaction or ectopic eruption, over-eruption of unopposed teeth, and center-line discrepancies [2]. Ectopic eruption of permanent teeth or premature primary tooth loss due to caries and/or trauma may result in undesirable primary and permanent tooth movements, loss of space between permanent teeth, extrusion of teeth without an antagonist, and mesialization or distalization of teeth adjacent to the gap, resulting in a loss of arch length, crowding, and impaction of permanent teeth [3, 4]. The space maintainer can also be used in the case of permanent tooth genesis when it is not possible to close the space through orthodontic therapy, allowing future management of space. To ensure the proper development of occlusion, which is a key responsibility of pediatric dentits and orthodontists, it is important to understand both thefactors that contribute to improper occlusion development and the complications arising from arch space loss. When early loss of primary teeth occurs, the clinician should conduct a thorough clinical and/or radiographic examination to determine the need for intervention. If intervention is necessary, the clinician must decide whether to use fixed or removable space maintainers based on the specific case. Space Maintenance can be defined as the provisional cementation of an appliance whose main goal is to control and prevent the loss of space [5]. These devices prevent space loss by occupying it in different ways depending on the design, so that when the permanent teeth erupt, there will be no crowding, impaction, or ectopic eruption, and no mesial drifting [6]. When designing a specific space maintainer, it is important to consider several key factors, including the type of maintainer, recommended usage guidelines, aesthetic requirements, and the effectiveness of maintaining cleanliness [7,8]. Different types of space maintainers have been designed in the last three decades and can be found in the literature. Although these space maintainers are classified as fixed or removable space maintainers, they are all used to prevent loss of space [9,10]. The type of appliance is determined by several factors, including the stage of dental development, the number of lost teeth, the occlusion, the dental arch involved, the child's age, and his/her ability to cooperate [8]. Pediatric dentists have used and recommended conventional metal space maintainers in the form of a band cemented to the tooth distal to the space and a horizontal loop that maintains the space by resting on the tooth mesial to the space (Figure 1). However, conventional metal space maintainers incur some drawbacks, particularly in terms of their design and manufacture [11]. Researchers observed a correlation between space maintainers and a higher periodontal index score, which is associated with an increased risk of oral cavity bacteria growth [12, 13, 14]. Additionally, nickel is a common and severe allergen, and nickel sensitivity was found to be higher in children who had intraoral devices that contained nickel [15]. The use of a stainless-steel alloy or a biocompatible material is then recommended in the production of the appliance to prevent any health concerns, especially for young patients. Additionally, the great variability of the anatomy of primary teeth can lead to longer chair time for the selection of the appropriate bands, and their adaptation to the teeth is not always perfect.