Browsing by Subject "Clear aligners"
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Item The Effect of Size and Location of Composite Attachments on the Extrusive Force Delivered to a Maxillary Central Incisor by a Clear Aligner(2022-06) Slama, ZacharyIntroduction: One of the most challenging and least predictable tooth movements to achieve with clear aligner therapy is extrusion of maxillary central incisors. Composite attachments have been implemented to improve the biomechanical properties and make extrusion a more predictable tooth movement. Various attachment shapes have been investigated, but the effect of attachment size and location on the force delivered to a maxillary central incisor by a clear aligner has not been reported. Aim: To evaluate the effect of composite attachment size and location on the extrusive force delivered to a maxillary central incisor with a Zendura FLX clear aligner. Methods: Clear aligners designed to extrude a maxillary central incisor 0.25 mm using uLab software were fabricated using Zendura FLX .030 mil (0.75 mm) thickness clear aligner material. To evaluate the effect of attachment size, aligners were designed with three sizes of rectangular anterior extrusion attachments as well as no attachment. To evaluate the effect of attachment location, aligners were designed with a standard rectangular anterior extrusion attachment placed in the center of the facial surface of the crown, 2 mm apical, 2 mm incisal, in the center of the lingual surface of the crown and with no attachment. For each of the 9 groups, 5 aligners were fabricated with standardized margins trimmed 0.75 mm apical to the gingival margin. Extrusive force along the long axis of the crown was measured using a force gauge. Means and standard deviations were calculated and presented by group. The one-way analysis of variance (ANOVA) was conducted to compare the means between the groups and Tukey’s method was used as a post-hoc procedure for pairwise comparisons. P-values less than 0.05 were considered statistically significant. Results: Pairwise comparisons for all groups compared to No attachment were statistically significant (p <.0001). Pairwise comparisons for all attachment sizes were statistically significant (p < .0001). Although pairwise comparisons were statistically significant for the Incisal attachment group vs. Gingival attachment group (p = 0.033) and the Incisal attachment group vs. Mid-facial attachment group (p = 0.002), the observed differences may have been due to variation in aligner fabrication. No statistically significant differences were observed for pairwise comparisons of other attachment location groups. Conclusions: This is the first study in which the effect of attachment size and location on the extrusion of a maxillary central incisor with a clear aligner has been reported. In a benchtop model, all attachment configurations generated greater initial extrusive compared to the No attachment control. Attachment size has a positive relationship with initial extrusive force with larger attachments producing greater force. Attachment location did not appear to be as critical as attachment size in producing extrusive force. Biomechanically, larger attachments can be recommended to help generate the force required to predictably extrude maxillary incisors.Item Effect of the Periodontal Ligament on Clear Aligner Material Surface Strain when Measured In-Vivo(2023-06) Nelson, SamanthaIntroduction: Clear aligner therapy has become increasingly popular as an alternative to traditional braces. Despite advances in technology, the efficacy and efficiency of clear aligner treatment remains challenged. Numerous in-vitro studies into the force systems of clear aligners have been developed. Currently, there are no guidelines for evaluating orthodontic force systems intraorally with clear aligners. The effect of the periodontal ligament and intraoral environment on orthodontic tooth movement with clear aligners remains unknown. Aim: To determine if surface strain can be measured in-vivo with digital image correlation (DIC). And to evaluate the effect of the periodontal ligament and intraoral environment on the surface strain delivered by a clear aligner to a maxillary central incisor during lingual tipping. Methods: Clear aligners were designed with 2.0 degrees of lingual crown tipping about an estimated center of rotation on a maxillary central incisor for 33 subjects. Clear aligners were fabricated using two materials, Essix ACE and Zendura A, in 0.030 mil (0.75 mm) thickness. A dual-camera, three-dimensional DIC system was used to record the transverse strain on the facial surfaces on the subject’s model, in the subject’s mouth, and on the subject’s model after submersion in artificial saliva. The relationships between transverse strain and the predictors, aligner material and environment, were examined using linear mixed effects models, with a random intercept for subject. A statistical model was also fit to test associations between transverse strains and predictors aligner material, gender, and presence of artificial saliva. Estimates are reported as a means with 95% confidence intervals. The passive and active models and aligners were assembled and scanned by micro-CT to measure the gap size between the aligner and model. Displacement at the incisal half of the target tooth was measured with GeoMagic software. Results: Initial forces delivered by clear aligners produced a strain threshold high enough to be detected and captured intraorally by DIC. The strain distribution and contour differed between in-vivo and in-vitro, as well as between material types, but followed the same pattern and peaks. Mean transverse strain increased as the point of focus narrowed to the incisal half of the target tooth. The effects of the environment were statistically significant at the incisal half of the target tooth, with increased transverse strain in-vitro compared to in-vivo. Zendura A expressed significantly less transverse strain than Essix ACE within both environments. The effect of the material was more pronounced in-vitro for the entire dentition, but not at the incisal half of the target tooth. No differences in transverse strain were noted with the presence or absence of artificial saliva, as well as between genders. Strong reproducibility existed between trials, with more similar strain profiles in-vitro compared to in-vivo. Micro-CT images demonstrated a lack of gap between the aligner and passive model on the labial surface of the target tooth, while gap sizes increased at the interproximal contact points and on adjacent teeth. Based on inciso-gingival crown length of tooth, there was no difference in incisor displacement between subjects. Conclusions: This is the first study in which the strain distribution on a clear aligner has been studied in-vivo with DIC. Initial force delivered by clear aligners can be detected and evaluated intraorally. The difference in surface deformation between environments is only significant at the point of greatest tooth displacement, with increased transverse strain in-vitro. Material type influences clear aligner strain, with a more pronounced effect in-vitro. Clear aligners distribute strain to multiple teeth despite efforts to isolate movement to a single target tooth. And the presence of artificial saliva and influence of gender do not affect strain level or surface deformation.