## 4 Discussion  
Most authors claim the importance of analyzing the etiology and the most appropriate cause of the crowding. For an appropriate diagnosis and treatment strategy in orthodontic practice, it is necessary to identify, among etiological factors, the tooth size-arch size relationship with crowding [24]. Searching the medical literature database, we found that the majority of studies regarding the etiology of dental crowding were performed on permanent dentition patients. Correlations between teeth dimensions, arch lengths, and crowding have been previously explored with sometimes conflicting results. Little research was conducted on primary or mixed dentition cases. Therefore, the authors of the present study considered the investigation of crowding on mixed dentition cases useful. Our study evaluated a sample of dental casts from orthodontic patients without skeletal discrepancies during the period of mixed dentition, when real or transitional crowding is often encountered. Dental crowding during mixed dentition in most of cases is considered an early sign of treatment need, and early orthodontic treatment has been suggested [25; 26]. Arch lengths and crown morphologies were assessed as possible determinant factors for crowding. Research data were collected from dental casts, using the procedure of space analysis for the assessment of crowding [5]. Measurements on dental casts were performed with a digital caliper. This method is still being used in similar studies [27]. A digital caliper with accuracy of 0.01 mm is considered by other specialists as a reliable method for the assessment of dental crowding; its accuracy was even compared to that of measurements on virtual computerized models with dedicated software [28]. Therefore, we appreciate that the analogical methods that are proposed in this study are extremely valid and repeated in all studies with similar objectives. Despite this, lately, the innovation and improvement of reworking software is allowing increasingly reliable and high-level evaluations based on multiplane 3D reconstructions, even in the treatment of severe malocclusions [29]. The 100 patients included in our study group met the inclusion criteria, with female orthodontic patients being more frequent (68% of the selected cases were females and 32% were males). The mean age of patients was 8.6 years. Conducting the space analysis for each dental arch, we found that 52% upper arches and 30% lower arches were crowded; 24% of maxillary arches and 40% of mandibular arches were normally aligned; 24% of upper arches and 30% of lower arches were spaced. There were no significant differences of crowding distribution between genders. Evaluating the degree of crowding in our study, the maxillary arches were more frequently affected by crowding than the mandibular ones. Regarding the extent of crowding, 30% of the upper arches were severely crowded, and 22% of the upper arches were moderately crowded. For the mandible, 14% and 16%, respectively, presented severe and moderate crowding. The number of crowded arches decreased at nine and ten years of age, with statistically significant differences related to patients' age. This clinical fact can be explained through the natural process of arch length development with age. Our results partially agree with other published data: in a research conducted on 489 children from the general population at the onset of the mixed dentition period, anterior crowding was detected in the maxillary arch in 11.6% of cases  
and in the mandibular arch in 38.9% of the cases, with girls being more frequently affected by mandibular crowding than boys [25]. In the present analysis, arch length measurements in mixed dentition in the crowded groups constantly showed smaller values than those found among the subjects with normal and spaced arches. The comparison of arch lengths was made for each year of age (subgroups of patients aged 7, 8, 9, and 10 years). Except for the lower arches at seven years, all other results were statistically significant.