The three-dimensional stable mandibular landmarks in patients between the ages of 12.5 and 17.1 years.

BACKGROUND: With the aid of implants, Björk identified two-dimensional mandibular stable structures in cephalograms during facial growth. However, we do not know what the three-dimensional stable structures are with certainty. The purpose of this study was to identify the most stable mandibular landmarks in growing patients using three-dimensional images. METHODS: The sample was comprised of two cone-beam computed tomography (CBCT) scans taken about 4.6 years apart in 20 growing patients between the ages of 12.5 (T1) and 17.1 years (T2). After head orientation, landmarks were located on the chin (Pog), internal symphysis (Points C, D and E), and mandibular canals, which included the mental foramina (MF and MFA) and mandibular foramina (MdF). The linear distance change between Point C and these landmarks was measured on each CBCT to test stability through time. The reliability of the suggested stable landmarks was also evaluated. RESULTS: The total distance changes between Point C and points D, E, Pog, MF, and MFA were all less than 1.0 mm from T1 to T2. The reliability measures of these landmarks, which were measured by the Cronbach alpha, were above 0.94 in all three dimensions for each landmark. From T1 to T2, the distance changes from Point C to the right and left mandibular foramina were 3.39 ± 3.29 mm and 3.03 ± 2.83 mm, respectively. CONCLUSIONS: During a growth period that averaged 4.6 years, ranging from 11.2 to 19.8 years old, the structures that appeared relatively stable and could be used in mandibular regional superimpositions included Pog, landmarks on the inferior part of the internal symphysis, and the mental foramen. The centers of the mandibular foramina and the starting points of the mandibular canal underwent significant changes in the transverse and sagittal dimensions.

Airway and cephalometric changes in adult orthodontic patients after premolar extractions.

OBJECTIVE: To examine changes in the airway and cephalometric measurements associated with orthodontic treatment of adults with and without premolar extractions. The study investigated whether extractions had a direct or indirect effect on the airway and examined selected skeletal and dental features. MATERIALS AND METHODS: This retrospective study used pre- (T1) and posttreatment (T2) cone-beam computed tomography scans of 83 adult patients matched for age and sex. A total of 15 airway and 10 skeletal and dental measures were analyzed by means of repeated-measures analysis of variance. RESULTS: There were no results showing that extractions affected airway dimensions that could not be accounted for as reflections of measurement error. There was no evidence that extractions affected the airway indirectly through skeletal and dental changes. There were strong and consistent findings that patients with small airways showed larger ones after treatment and that patients with large airways showed smaller ones later. These effects were independent of whether or not extractions were part of treatment. The measurement phenomena of regression toward the mean and of differential unfolding of natural changes over time could have accounted for the results observed. CONCLUSIONS: There was no evidence that extractions in nongrowing patients have negative consequences on the size of various airway measures in the nasopharynx, retropalatal, or retroglossal regions.

Interpreting weightings of the peer assessment rating index and the discrepancy index across contexts on Chinese patients.

Objective: Determine optimal weightings of Peer Assessment Rating (PAR) index and Discrepancy Index (DI) for malocclusion severity assessment in Chinese orthodontic patients. Methods: Sixty-nine Chinese orthodontists assessed a full set of pre-treatment records from a stratified random sample of 120 subjects gathered from six university orthodontic centres. Using professional judgment as the outcome variable, multiple regression analyses were performed to derive customized weighting systems for the PAR index and DI, for all subjects and each Angle classification subgroup. Results: Professional judgment was consistent, with an Intraclass Correlation Coefficient (ICC) of 0.995. The PAR index or DI can be reliably measured, with ICC = 0.959 and 0.990, respectively. The predictive accuracy of PAR index was greatly improved by the Chinese weighting process (from r = 0.431 to r = 0.788) with almost equal distribution in each Angle classification subgroup. The Chinese-weighted DI showed a higher predictive accuracy, at P = 0.01, compared with the PAR index (r = 0.851 versus r = 0.788). A better performance was found in the Class II group (r = 0.890) when compared to Class I (r = 0.736) and III (r = 0.785) groups. Conclusions: The Chinese-weighted PAR index and DI were capable of predicting 62 per cent and 73 per cent of total variance in the professional judgment of malocclusion severity in Chinese patients. Differential prediction across Angle classifications merits attention since different weighting formulas were found.