Objective: This study was conducted to compare two techniques for fabricating dental models with attachments (additive 3D printing versus subtractive milling). Materials and Methods: a random model was selected and scanned with an intraoral scanner Medit I600 and the STL file of the model was used to create another STL file of a new model with rectangular attachments on the labial and buccal surfaces of the anterior and posterior teeth respectively was created by Maestero software. The new STL file was 3D printed three times by the same 3D printer (Anycubic mono X) to produce 3D printed models that consitituted group 1. Three 3D printed discs were created by the same 3D printer with dimensions matching the discs of the milling machine. Group 2 consisted of three milled models that were fabricated by a milling machine ROLAND 51 ( Kemet corporation, Cairo, Egypt). The models of both groups were scanned with the same intraoral scanner Medit I600, and the STL files generated were superimposed over the original STL file by the same software (cloudcompare). The linear deviations of attachment position, measured in millimeters, were as follows; A) Mesio-distal: The X-axis movement B) Occluso-gingival: The Z-axis C) Bucco-lingual: The Y-axis movement. One way ANOVA and t tests were used to compare the deviation within each group and between the two groups, the significant level was set at p-value < 0.05. Results: statistically significant differences between the molars, incisors, canines, and premolars were observed in both groups in all ways of space. Comparing the two groups revealed a non statistically significant difference between both groups. Conclusion: 3d printing provided a more economic and less time and material wasting way for fabrication of clear aligners models with attachments than milling.

Objectives: The present study was conducted to evaluate the dentoskeletal changes after distalization of maxillary molars using skeletally-anchored modified Hyrax appliance in the treatment of dental Class II orthodontic patients. Subjects and methods: Ten participants having Class II molar relation with deep overbite with age ranged from 11 to 14 years old were enrolled in the current study. All patients involved in the present study were selected from those seeking orthodontic treatment at different clinical orthodontic centers. Maxillary molar distalization was performed using modified skeletally anchored Hyrax palatal expander. The appliance was activated twice weekly. For each participant, skeletal and dental measurements were recorded from standardized cephalometric analyses before and after molar distalization. Statistical analyses including t-test were performed at a significance level of p<0.05. Results: The maxillary first molars were distalized successfully (6.16 mm) without tipping and Class Ι molar relation was obtained within a period of 6.2 months. Slight extrusion of the maxillary molars was observed which was reflected on the non-significant increase in lower anterior facial height, as the mandibular plane angle was increased by 0.58 0 . A marked improvement of the deep bite was observed. Conclusion: The modified Hyrax can be used as palatally skeletally anchored distalizer to effectively move the maxillary first molars distally. They are effective, minimally invasive and compliance free alternative for molar distalization and hence, molar Class II correction without anchorage loss.