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To determine the number of cases that are at risk of poor stability in terms of arch width changes following fixed appliances treatment at the Orthodontic Unit, Klinik Pergigian Cahaya Suria, Kuala Lumpur. In a retrospective audit, 101 pre- and post-treatment lower study casts were selected from cases completed
in the year 2015 at the Orthodontic Unit, Klinik Pergigian Cahaya Suria, Kuala Lumpur. Samples were measured using a universal caliper by a single calibrated operator. Samples was categorised as extraction or non-extraction types. Arch width changes was determined using paired T-test. The recommended limit
was 0mm for inter-canine width, 2 mm for inter-first premolar width and 3mm for inter-second premolar and inter-molar width. Differences were considered “within limits”, if the changes were within the recommended limit ±0.25mm (for possible marginal measurement error) and “expanded”, if above the range for within limits. 42.6% were non-extraction while 57.4% were extraction cases. In the non-extraction group, 52.2% cases had expanded inter-canine widths, followed by inter-first and second premolars (27.9%) and interfirst molar (20.9%) widths. Arch width changes for the inter-first and second premolars and inter-molars
widths were statistically significantly different (p<0.05) but bot clinically significant. In the extraction group, 67.2% had expanded inter-canine widths, followed by inter-first premolar (64.3%), inter-second premolar (9.1%) and inter-first molar (5.2%) widths. The inter-canine (M=1.43; SD=2.71, p<0.05) and inter-first
premolar (M=2.87; SD=2.61, p<0.05) widths statistically and clinically significant expansion but the intersecond premolar and molar were significantly contracted (p<0.05). The number of cases with expanded arch widths was high regardless of the extraction type.