Background: The development of personalized and high-precision dental treatment is inseparable from the accurate measurement and analysis of the model. Compared with traditional plaster models, digital models allow dentists to obtain richer and more detailed inspection results. However, the measurement of digital models in clinical practice usually ignores the influence of the overall three-dimensional (3D) structure of teeth and tooth arrangement on the measurement results. The purpose of this study was to evaluate the effect of calibrated tooth axis and tooth arrangement on tooth width and arch length.Methods: A total of 110 digital models from 80 participants were used to measure teeth width and dental arch length using the following methods: Method A, simple positioning of the proximal and distal of teeth; Method B: calibration of the clinical crown axis; and Method C: calibration of the overall 3D axis of the teeth. The Measurand model included pre-and post-orthodontic models of the same patients to assess the impact of tooth alignment on outcomes.Results: In the aligned dentition, whether the tooth axis was calibrated had no effect on the measurement results. On unaligned dentitions, calibrating the pinion allowed for more accurate measurements, with Method C the closest to the true size. Furthermore, the arrangement of teeth affected the measurement, but there was no continuous linear correlation with arch length discrepancy (ALD).Conclusions: Clinicians should choose appropriate measurement methods according to actual needs when performing model measurement, and should pay attention to the influence of tooth axis, tooth shape, and arrangement on the measurement results.
Objectives Skeletal class II malocclusion is one of the most common malocclusions. Among functional appliances for skeletal class II malocclusion, the Twin-Block appliance with maxillary expander is effective in reposition the mandible forward. In this study, we focused our efforts on investigating the effects of Twin-Block appliances with maxillary expander on the upper airway in growing children with skeletal class II malocclusion by tracing and measuring lateral cephalograms after evaluating the consistency of three-dimensional CBCT data and two-dimensional lateral cephalogram data. Materials and Methods One hundred and two patients with skeletal class II malocclusion from 9 to 15 years old (11.37 ± 2.80, Male/Female ratio = 1:1) were selected to evaluate the consistency of CBCT data and lateral cephalogram data. The strongly and moderately correlated segments were then selected to study the effects of Twin-Block with maxillary expander on the upper airway in 66 growing children with skeletal class II malocclusion (11.31 ± 1.23 years old, Male/Female ratio = 1:1) on lateral cephalograms. Results The results showed strong significant correlation in the nasopharynx (r = 0.708), moderate significant correlations in the overall upper airway (r = 0.641), velopharynx (r = 0.553) and glossopharynx (r = 0.575), but weak correlation in the hypopharynx (r = 0.323). The corresponding determination coefficient (R2) was also showed by the Scatter Plot analysis. Moreover, compared with the pre-treatment data (T1), the total area of the upper airway, the area of nasopharynx, velopharynx and glossopharynx after functional treatment (T2) increased statistically and significantly. Conclusions Lateral cephalogram can reflect the volume of nasopharynx and oropharynx in skeletal class II children to a certain extent, while the Twin-Block appliances with maxillary expander can widen the volume of nasopharynx and oropharynx significantly. Clinical relevance The lateral cephalogram is reliable to analyze the nasopharynx,velopharynx and glossopharynx in orthodontic clinical practice. The Twin-Block appliances with maxillary expander has a positive effect on skeletal Class II patients with airway stenosis.
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