Journal of Aligner Orthodontics, 04/2022

Objectives: To investigate the differences in the mechanical properties of seven different commercial clear aligners, such as surface roughness, elastic modulus, tensile strength and chemical modifications of the materials. Materials and methods: Seven different clear aligner materials used around the world were assessed and their mechanical and optical performance were evaluated. Although Zendura FLX (Bay Materials, Fremont, CA, USA) and CA Pro (Scheu Dental, Iserlohn, Germany) are multilayered materials made from polyethylene terephthalate glycol, it is stated that Zendura FLX contains polyurethane. The tensile properties of thermoplastic materials were determined in accordance with the standard EN-ISO 527-1:2012. A Vickers hardness test was performed to evaluate the hardness of the materials, and Fourier transform infrared spectroscopy was used to analyse their molecular structure. The optical properties were determined using a UV-visible spectrophotometer, and surface roughness was ?measured using an optical profilometer. The data were examined using a one-way analysis of variance and a post hoc Tukey test. Results: The multilayered Zendura FLX and CA Pro materials were found to have the lowest modulus of elasticity and low tensile strength values. In line with the literature, the material with the highest ?hardness was determined to be ?Zendura. Duran+ (Scheu Dental), CA Pro, GT Flex (Good Fit Technologies, Boston, MA, USA) and GT Pro (Good Fit Technologies) materials were also found to have a smoother surface than the ?others. The Taglus Premium material (Vedia Solutions, Mumbai, India) with the lowest visible UV-visible absorbance value was the most transparent. Conclusion: Clinical studies should be conducted to confirm the mechanical properties of these seven clear aligner materials. Keywords: aligners, elastic modulus, hardness, physical properties, thermoplastic

Since the advent of aligner orthodontics, many aspects of the planning and production processes have evolved. One constant is the fabrication of aligners from thermoforming sheets. The present in vitro study investigates the possibilities of direct 3D printing of aligners with fused filament fabrication. Based on a virtual model, aligners of different thicknesses were created digitally. Activation was planned for 0.4 mm movement of the maxillary left first molar. Aligners were printed using a fused filament fabrication printer with different filaments: three elastic (thermoplastic polyurethane, thermoplastic elastomer and polypropylene) and two stiffer ones (thermoplastic copolymer and polypropylene). Using a special force measurement apparatus with three-axis force and moment sensors, the forces delivered were measured and the aligners were inspected visually. Aligners with a wall thickness greater than 0.9 mm were printed successfully. The surface showed the typical layer structure, and the surface quality was found to differ depending on the material. The forces measured ranged from 0.63 to 1.57 N and moments from 29 to 78 Nmm. Polyethylene terephthalate glycol aligners were too stiff for further investigation. The in vitro measurements indicate that it may be possible to generate biologically effective forces for tooth movement with fused filament fabrication 3D printed aligners. The results may be a starting point for further research on the application of printing elastomers in orthodontics. Keywords: 3D printing, aligners, forces, moments, thermoplastic copolymers, thermoplastic elastomers, thermoplastic polyurethane

Objective: To evaluate in vitro forces and moments generated by clear aligners in relation to attachment geometry and 3D printing technology. Materials and methods: Five different movements of a premolar were simulated in a virtual model. Combined with four attachment geometries, horseshoe models were printed using fused filament fabrication and digital light processing 3D printing. On these models, 120 aligners (100 active and 20 passive) were produced with 0.6- and 0.8-mm foils (Erkodur, Erkodent Erich Kopp, Pfalzgrafenweiler, Germany). Using a modular 3D printable orthodontic measurement apparatus, forces and moments were measured for all active aligners. Statistical analysis, including the intraclass correlation coefficient and a generalised linear model, was conducted to obtain information about the influence of model fabrication technology, attachments, movement and aligner foil thickness on force, which was calculated as a vector. Results: Error measurement showed an excellent intraclass correlation coefficient, greater than 0.93 for all directions. The printing technology had no significant influence on force development of the thermoformed aligners (P = 0.7123), and the aligner material showed borderline significance (P = 0.0531). The presence or absence of attachments was also not significant (P = 0.5153). In the generalised linear model, type of movement, aligner material and vertical rectangular attachments 1 mm in size were identified as predictors of the amount of force generated. Conclusion: Printing technology does not influence the amount of force generated by aligners. The presence or absence and variation in shape of attachments may be influential but do not show consistent behaviour. Keywords: 3D printing, aligner orthodontics, attachments, forces

Class II malocclusion in adult patients is challenging to treat and can require extraction, a long treatment time and a high level of compliance in wearing Class II elastics. Clear aligners can be a useful tool to treat Class II patients without extraction since they provide efficient control of tooth movement during distalisatio?n, but they also usually demand a long treatment time and a very high level of compliance. When treating Class II division 1 patients, it is necessary to manage incisor inclination during the retraction phase to prevent premature contacts that can lead to a posterior open bite. Generally, when treating Class II malocclusion using a distalisation protocol, Class II elastics need to be worn over the entire treatment period to create proper anchorage for posterior distalisation and prevent any side effects that may be caused by this method. The present case report illustrates the treatment of a Class II hypodivergent case with Invisalign aligners (Align Technology, San Jose, CA, USA) in an adult patient in which distalisation and compliance were facilitated by means of infrazygomatic crest screws positioned only in the molar areas after 4 months of treatment, thus eliminating the need for compliance in wearing Class II elastics for the majority of the treatment period. The digital setup was programmed to achieve sequential distalisation of the maxillary first and second molars, then ?infrazygomatic crest screws were inserted and 50% sequential distalisation followed in the maxillary second premolars, then en masse retraction from the maxillary left first premolar to the maxillary right first premolar began. Distalisation was combined with anterior intrusion following smile arc exposure and the treatment was completed in 18 ?months. The present approach for Class II treatment with severe protrusion, which involves combining sequential distalisation for the first part of the treatment until the molars achieve Class I occlusion and then insertion of infrazygomatic crest screws to create skeletal anchorage in the posterior molar area before starting the en masse retraction of the anterior teeth, seems to be effective for correcting Class II malocclusion, ensuring good posterior anchorage control and decreasing the overall treatment time and the need for compliance in using maxillomandibular elastics. Keywords: adult orthodontics, Class II treatment, distalisation, hypodivergent, Invisalign, skeletal anchorage

Treatment of severe or moderate Class II in adult patients using aligners requires sagittal movements for correction. Fortunately, extensive research has been conducted into this topic and the attachments commonly used for such treatment. The shape and position of the attachments influence the force applied to the teeth. This report presents a patient with a complete Class II division 2 bilateral molar and canine relationship where the treatment plan relied on the use of rectangular horizontal attachments on the molars to perform maxillary distalisation and mandibular mesialisation. After 22 months of aligner treatment, the desired results were achieved and the bilateral molar and canine relationship was corrected from Class II to Class I. Keywords: aligners, attachments, Class II, distalisation, mesialisation