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IntroductIonThe search for the elusive "ideal" arch form to suit every individual has been the focus of several reports. However, dental arch form and shape varies in individuals based on anatomic dimensions of the craniofacial skeleton. 1,2 Qualitative description of the dental arch use terms like elliptic, parabolic or U-shaped; whereas mathematical methods include several curve-fitting algorithms like parabola, semi ellipse, catenary's curve, conic section, cubic plane curve and second to eighth order polynomials.3,4 Despite the huge efforts and research works done to determine the ideal arch form, there is little agreement among investigators about the natural shape of the dental arches.
5-7Hawley; 8 based on the earlier work of Bonwill 9 described the ideal arch as being constructed upon an equilateral triangle with slight modifications. The six anterior teeth were thought to be arranged on the arc of a circle whose radius was determined by the combined width of incisors and canines, with the premolars and first permanent molars arranged in a straight line and the second and third molars turning towards the midline. Catenary arch design depends on inter-molar distance measured at central fossae, it could be described as a central core around which the teeth arrange themselves.
10Brader 3 proposed that the dental arch is best considered as a closed curve with the properties of a trifocal ellipse with the teeth occupying only the narrower end of the total curve.Raberin et al 11 examined 278 dental casts of untreated French adults with normal occlusion. Six measurements of mandibular dental arch were performed, and five independent ratios were determined. They developed an arch form guide and defined five mandibular dental arch forms (narrow, wide, mid, pointed and flat).Thus it is worthwhile to mention that determination of the dental arch form relies in the majority of the research works upon dental arch width and length dimensions.
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MaterIals and MethodThe sample consisted of 199 adults aged between 18 to 26 years, among whom 97 were males and 102 females, selected from the clinical examination of 1703 Yemeni adults.Following criteria were used for sample selection: full complement of permanent dentition (excluding third molars); Class I molar and canine relation; Class I skeletal relationship (decided visually by using two-finger technique); free of local factors that disturb the integrity of dental arches (e.g. congenital missing teeth, retained deciduous teeth, supernumerary teeth); normal overjet and overbite relation; no heavy restorations that may affect the dental arch size and form; no previous orthodontic or facial surgical treatment; well-aligned arches with less than 2 mm of spacing or crowding in either arch.Measurements were taken from 398 maxillary and mandibular dental casts, which were made of dental stone with plaster of Paris base. The base was trimmed and numbered corresponding to the number given to the subjects. Dental arch dimensions were measured using the modified sliding calipe...
