Effect of premolar extraction and anchorage type for orthodontic space closure on upper airway dimensions and position of hyoid bone in adults: a retrospective cephalometric assessment.

Background: This study aimed to assess the effect of premolar extraction and anchorage type for orthodontic space closure on upper airway dimensions and position of hyoid bone in adults by cephalometric assessment. Methods: This retrospective study was conducted on 142 cephalograms of patients who underwent orthodontic treatment with premolar extraction in four groups of (I) 40 class I patients with bimaxillary protrusion and maximum anchorage, (II) 40 class I patients with moderate crowding and anchorage, (III) 40 class II patients with maximum anchorage, and (IV) 22 skeletal class III patients with maximum anchorage. The dimensions of the nasopharynx, velopharynx, oropharynx, and hypopharynx, and hyoid bone position were assessed on pre- and postoperative lateral cephalograms using AudaxCeph v6.1.4.3951 software. Data were analyzed by the Chi-square test, paired t-test, and Pearson's correlation test (alpha = 0.05). Results: A significant reduction in oropharyngeal, velopharyngeal, and hypopharyngeal airway dimensions was noted in groups I, III, and IV (P < 0.001), which was correlated with the magnitude of retraction of upper and lower incisors (r = 0.6 - 0.8). In group II, a significant increase was observed in oropharyngeal and velopharyngeal dimensions (P < 0.001). A significant increase in nasopharyngeal dimensions occurred in all groups (P < 0.001). Also, in groups I and III, the position of hyoid bone changed downwards and backwards, which was correlated with reduction in airway dimensions (r = 0.4 - 0.6). Conclusion: According to the present results, extraction orthodontic treatment affects upper airway dimensions and hyoid bone position. Maximum anchorage decreases airway dimensions while moderate anchorage increases airway dimensions.

Radiographic Position of Impacted Mandibular Third Molars and Their Association with Pathological Conditions.

OBJECTIVES: This study aimed to assess the radiographic position of impacted mandibular third molars (IMTMs) and their association with pathological conditions. MATERIALS AND METHODS: The impaction depth, relationship with ramus, and angulation of 1600 IMTMs and their association with 2nd molar distal caries and root resorption, pathological conditions, and proximity to the mandibular canal were evaluated on panoramic radiographs. The IMTM position was determined based on the depth of impaction according to the Pell and Gregory classification, relationship with ramus according to the Pell and Gregory classification, and angulation according to the Winter's classification. The classical and Bayesian logistic regressions were applied to analyze the effect of IMTM position on the associated complications using the odds ratio (OR) and 95% confidence interval (credible interval for Bayesian models). Two-tailed P value < 0.05 was considered statistically significant. RESULTS: Of 1600 IMTMs evaluated in this study, 195 (12.2%), 252 (15.8%), and 119 (7.4%) had caused second molar distal caries, second molar root resorption, and pathological lesions, respectively, and 872 (54.5%) had contact with the mandibular canal. Impaction angulation was a risk factor for second molar distal caries (maximum OR = 5.01, 95% CI: 3.12-8.18). Changed angulation and greater impaction depth were the risk factors for second molar root resorption (minimum OR = 1.64, 95% CI: 0.58-4.02). Decreased distance between the ramus and distal side of the second molar was a risk factor for associated pathological lesions (minimum OR = 2.73, 95% CI: 1.79-4.25). Mesioangular and horizontal angulations and greater impaction depth were the risk factors for contact with the mandibular canal (maximum OR = 3.44, 95% CI: 2.6-4.57 and minimum OR = 1.3, 95% CI: 094-1.8). CONCLUSIONS: The frequency of complications associated with IMTMs was low, but considerable. The occurrence of these conditions might be affected by the impaction position. Thus, regular follow-ups are recommended in order to be able to surgically intervene when the first signs of pathologies arise.