Use of extra-oral scanner for the study of arch form in a sample of Italian adolescents with ideal occlusion

The aim of this study was to evaluate the shape and the average size of the maxillary and mandibular arch in an Italian adolescents' sample with correct occlusion, using the digital technology. The study sample was composed, after the use of an extra-oral scanner and after the application of inclusion and exclusion criteria, by the digitized dental casts of 79 Italian adolescents (39 females and 40 males), aged 14±1 years, with correct occlusion. On each model, both upper and lower, the reference points of the dental arches (FA), of the alveolar bone (WALA ridges) and of the incisal edge of the central incisors were identified. With these points, using a software, fourteen parameters were evaluated for each cast: basal and dental intermolar and inter-canine width, basal and dental molar and canine depth, basal and dental molar and canine ratio, overjet, overbite. Finally, the shape of the arches was assessed, dividing it into ovoid, triangular or square. Chi-square test and Student's T-test for each parameter were adopted with a p<0,05 significance level. The results showed that the ovoid form was the most frequent, followed by the triangular one for the upper arch and by the rectangular one for the lower arch. On the canine level, both upper and lower, both for dental and for basal references, the triangular shape showed the lowest width and ratio values and the highest depth values in comparison with the other two groups. The square one showed the opposite situation, and the ovoid one presented in the intermediate value. On the molar level the trend is quite similar to the canine one. The results obtained maybe suggest that on a significant percentage of the patients of the sample is expected to use a preformed ovoid arch wire, and the data found could be useful to study the adequacy of the arch wires currently on the market or to design new ones. .