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UBC Theses and Dissertations

Long term palatal & molar angulation changes associated with slow maxillary expansion : a retrospective study Alalola, Bassam


Objectives: To compare, the short & long-term, palatal dimensions, palatal symmetry and upper molar angulation after early, mixed-dentition, slow-maxillary expansion with similar parameters in control subjects. Methods: Thirty patients were treated with a Haas-type slow maxillary palatal expander for unilateral posterior crossbite with a functional shift. Records were taken before (T1) and after expansion (T2), and 4 years after expansion (T3). Palatal width, surface area, volume, and molar angulations were measured on digitized models. Palatal symmetry was assessed by division through the midline, then calculation of surface areas and volumes for the anterior, middle, and posterior segments of each half. Orientation of the first molars was expressed by vectors perpendicular to their occlusal planes, and mean orientations by stereographic projection. The data was compared to 30 control subjects matched for dental age, gender, and molar relationships. Results: T1-T2: The mean intercanine width increased 4.7 mm, and intermolar width 4.8 mm. The treated mean surface area increased by 130.6 mm² compared with 14.0 mm² in controls. The treated palatal volume increased 946.4 mm³ compared with 200 mm³ for controls. T2-T3: Mean intercanine width reduced by 3mm, and intermolar width reduced by 1.1mm. At T3, there was no significant difference between the treated and control samples for intercanine width, total surface area and total volume. After expansion, the first permanent molars showed an increased buccal and distal inclination. At T3, the molars on both sides became more upright than originally, but maintained the previous distal inclination. Conclusions: Slow maxillary expansion with a Haas-type appliance results in similar expansion across the canines and first molars. A palate that is symmetrical before expansion may become asymmetric immediately after expansion, but only in its middle and posterior segments. Long-term results show no significant difference between treated and controls subjects in intercanine width, total palatal volume and surface area. Tipped molars uprighted in the long term. Changes in molar orientation following palatal expansion can be evaluated without the need for imaging involving radiation.

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