Journal of Aligner Orthodontics, 04/2023

The assignment of the mandible to the maxilla and thus the occlusal relationship in the virtual treatment simulation was previously performed exclusively in centric occlusion by means of a buccal scan. When the tooth position is changed in the virtual treatment simulation, the assignment of the mandible to the new occlusion is made by means of “best fit”, a pure vertical elevation of the mandible that differs from the closing and opening movement of the mandible in real motion according to the global centre of rotation, formerly known as the hinge axis. Thus, the occlusal relationship set at the end of the virtual treatment simulation always differs from the patient’s occlusion at the end of treatment. Recording the real motion and subsequent matching in the virtual treatment simulation, on the other hand, makes it possible to correct virtual tooth positions under the patient’s individual opening and closing movement using their real motion within the global centre of rotation. In addition, the assignment of the mandible to the maxilla in the virtual treatment simulation can take place in a corrected, physiological condylar position. Arch motion analysis, followed by use of the virtual articulator in the virtual treatment simulation, represents the missing link in a fully digital orthodontic workflow. Keywords: aligner orthodontics, articulator, digital joint recording, Digital Motion Decoder, occlusion, temporomandibular disorder, temporomandibular joint, virtual articulator, virtual treatment simulation

Objective: The present study focused on the biomechanical dynamics of clear aligners in managing translational movement with a view to exploring the effects of trimline design and buccopalatal translation on the force and moments acting on the maxillary right central incisor in vitro. Materials and methods: The Orthodontic Force Simulator (Institut Straumann, Basel, Switzerland), a device proficient at evaluating the biomechanical performance of aligners, was used to examine buccopalatal translations of the maxillary right central incisor. The present authors used a human head model to prepare a model of the maxilla with independent teeth, which was then segmented and interfaced with the Orthodontic Force Simulator. Thirty aligners were crafted from ClearQuartz material (ClearCorrect, Round Rock, TX, USA) in a process that encompassed intraoral scanning, digital superimposition, 3D printing, thermoforming and laser trimming. The central incisor’s forces and moments were assessed across four scenarios combining flat/scalloped trimlines and buccal/palatal translation. Results: The highest translational force (7.51 N) and tipping moment (15.94 Ncm) were recorded for palatal translation coupled with a flat trimline. This was followed in descending order by buccal translation with a flat trimline (5.49 N and 12.46 Ncm), palatal translation with a scalloped trimline (4.93 N and 10.64 Ncm), and buccal translation with a scalloped trimline (2.96 N and 6.58 Ncm). Each tested scenario generated a clinically relevant translational force; however, the presence of undesirable buccopalatal tipping moments indicated potential off-target movements in an in vivo context. Conclusion: The present findings highlight the substantial influence of the aligner trimline design and direction of translation on force and moment generation. Flat trimlines and palatal translation were associated with higher forces and moments compared to scalloped designs and buccal translation, respectively. These findings underscore the importance of careful aligner design in achieving the desired orthodontic outcomes; however, further research is required to gain a comprehensive understanding of aligner–tooth interactions and their implications for clear aligner therapy. Keywords: aligner biomechanics, bodily movement, flat trimline, orthodontic force simulator, scalloped trimline

Aim: To compare the satisfaction and psychosocial and physical discomfort levels of patients who receive orthodontic treatment with clear aligners or labial fixed appliances.Materials and methods: The study included 44 participants who were aged over 16 years, had no severe transverse or vertical problems, had easy to moderate severity of malocclusion, and needed treatment in both arches without extraction. Patients were divided into clear aligner and labial fixed appliance groups according to their treatment preferences. A visual analogue scale was used to evaluate the results of the questionnaires obtained after 1 (T1), 3 (T2) and 6 months (T3) of treatment.Results: In both groups, negative social reactions, discomfort due to appearance, and impact on social life and daily activities were found to be highest at T1 and decreased gradually over time. Impact on social life, difficulty adapting to the treatment system, discomfort due to appearance and difficulty maintaining hygiene were found to be lower in the clear aligner group than in the labial fixed appliance group (P 0.05). The pain level was similar between the groups at all periods. Tongue discomfort was more frequent in the clear aligner group, whereas lip and cheek discomfort were more frequent in the labial fixed appliance group. Satisfaction with the treatment process was found to be similar between the groups; however, satisfaction with the cost was higher in the clear aligner group.Conclusion: Patients experienced similar pain levels and a similar degree of satisfaction in both groups, but reduced psychosocial and physical discomfort with clear aligners compared with labial fixed appliances over the 6-month observation period. Keywords: clear aligners, Invisalign, labial fixed appliances, oral health–related quality of life, pain perception, patient perspective

Objective: The aim of this study was to investigate the incidence and severity of root resorption in patients treated with Invisalign aligners (Align Technology, San Jose, CA, USA) and to examine a larger number of factors with a higher number of patient treatments, in comparison to the current literature, to show correlations between these factors and root resorption.Materials and methods: The study group comprised 108 patients treated with Invisalign appliances. From these 108 patients, a total of 1,567 teeth were measured twice in panoramic radiographs before (T1) and after (T2) orthodontic treatment. The following teeth (according to FDI notation) were assessed: 16, 14, 13, 12, 11, 21, 22, 23, 24, 26, 36, 33, 32, 31, 41, 42, 43 and 46. The parameters determined from the patient records and examined were as follows: sex, age, arch (mandible or maxilla), side (right or left), tooth position (anterior or posterior), tooth type (central incisor, lateral incisor, canine, first premolar, first molar), position in the arch (anterior mandible, anterior maxilla, posterior maxilla, posterior mandible), Angle Class (I, II, III), reverse articulation, deep bite, open bite, gap position, crowding, use of elastics, use of motion appliances, extrusion, intrusion, translation, rotation, angulation, inclination, number of ClinCheck plans, total number of aligners (treatment time), and number of aligners per ClinCheck. Root resorption was determined by root–crown ratio and calculated according to the Linge-Linge formula.Results: All patients displayed root resorption, but only 20 of the 1,567 teeth showed clinically relevant root resorption of more than 20%. Three-quarters (75.2%) of the total sample had only mild root resorption (under 9.7% resorption). The following parameters were statistically significant and showed a correlation with the occurrence of root resorption: central incisors, intrusion, posterior maxilla and anterior mandible. Increased angulation also tended to be associated with increased root resorption, but this did not reach the 5% threshold. Finally, the treatment duration (total number of aligners) and the average number of aligners per ClinCheck were significantly associated with increased root resorption.Conclusions: Orthodontic treatment with Invisalign aligners can lead to root resorption. All patients showed root resorption, but this was mainly mild, without recorded clinical relevance. In order to reduce root resorption during orthodontic treatment, the orthodontist should pay special attention to the movement of the central incisors, movements through the cortical bone, intrusions and angulations, and slower staging. Keywords: aligners, Invisalign, orthodontics, root resorption