###### Abstract  
**Aims:** The purpose of this study was to evaluate the accuracy of the slot height of in-house 3D-printed resin brackets, comparing them with other types of brackets on the market today, both ceramic and metallic. **Methods:** Seven different types of bracket systems were selected. For each system, ten brackets for tooth 2.1 with 0.022 \(\times\) 0.028-inch slots were selected (total n\({}^{c}\) 70). Considering the whole sample, five types were commercially available and two were in-house 3D-printed. The entire sample was divided into four different groups according to the bracket material and the method of holding the archive. Precision pin gauges with 0.002-mm increments were inserted inside the slot of each bracket, and the slot heights were measured, microscopically ensuring that the gauge completely filled the slot, with full contact between both the bottom and the top of the slot. **Results:** With respect to the other five types of brackets on the market, the two types of in-house 3D-printed resin brackets showed great accuracy of slot height (0.558 \(\pm\) 0.001 mm). There was a statistically significant difference between the real height measured and the nominal height declared by the manufacturers (\(p<0.05\)) of all the samples investigated, with the exception of in-house 3D-printed resin brackets. Furthermore, the difference in slot height accuracy between commercially manufactured and in-house 3D-printed resin brackets was statistically significant. **Conclusions:** In-house 3D-printed resin brackets have a remarkably precise slot height, unlike commercially available brackets, whose slot heights tend to be significantly oversized with respect to the nominal values declared by the manufacturers. custom-made appliance; digital orthodontics; CAD-CAM +
Footnote †: journal: Applied Sciences  
Vestibular fixed orthodontics with ceramic brackets are therefore often a preferred option. However, despite the superior optical properties of ceramic brackets, they have several mechanical disadvantages compared to traditional metal ones [10]. In particular, ceramics being a fragile material means that ceramic brackets are more prone to fracture (for example at the level of the bracket fins) upon mastication or the application of torque bends on the archive. In addition, having a low resistance to tension, they do not have the ability to deform plastically, and debonding is therefore associated with an increased risk of enamel damage [10; 11; 12; 13]. The brackets currently on the market, both metal and ceramic, are produced through procedures such as casting, injection moulding, milling and sintering [14; 15; 16; 11]. The choice of material and the manufacturing technique influence both the final quality of brackets and their degree of precision in transmitting orthodontic forces, especially second- and third-order information [17; 18]. [PERSON] et al., in a study carried out in 2019, demonstrated that the manufacturing techniques of brackets currently on the market do not offer an adequate degree of precision, with as many as 90-97% of brackets presenting slot height inaccuracies with respect to the nominal values declared by the manufacturers [17]. Although slot height is one of the fundamental aspects influencing third-order archive-slot play and torque expression [18], according to the literature, the slot heights of brackets on the market, both ceramic and metal, tend to be oversized with respect to the nominal values declared by the manufacturers [19; 20; 21]. In fact, [PERSON] et al. showed that in reality, bracket slots, both vestibular and labial, tend to be oversized by a percentage of between +0.56% and +11.6% [18]. Dimensional imprecision in orthodontic brackets, especially slot height, can affect the archive-slot play [22; 23; 24; 25; 26]. In fact, [PERSON] et al. have shown that even a slight increase in slot height leads to a considerable increase in the archive-slot play, reducing the torque exerted on the teeth [22].