The purpose of this study was to evaluate the secular trend of dental development in the period of 30 years by dental age estimation. The study also investigated the correlation between dental and chronological age. Patients and Methods The sample consisted of 1200 panoramic radiographs of school children: 600 panoramic radiographs from Istarska and Primorsko-goranska županija, taken between the years of 1977 and 1979 (group A), and 600 panoramic radiographs from Primorsko-goranska županija, obtained between the years of 2007 and 2009 (group B). The dental age was determined according to the Demirjian′s method. The determination of chronological age was based on development of the lower third molars, and it was analyzed using the Nolla method on 979 panoramic radiographs in children from Istria. Results The difference in dental age between group A and group B was statistically significant (P=0,002). Group B had significantly advanced dental age. Both groups demonstrated significantly higher chronological age compared to dental age in the range from 0.4 (B) to 1,2 (A) years. In group B, the development of all left lower teeth, except the first molar, was statistically more advanced, as well as the development of the left lower incisors, canines, premolars and second molar in girls (all P‹0.001), and the development of the first left lower molar in boys (P‹0.001). In group A, the dental age of male patients was significantly higher than dental age of female patients (P‹0.001). In group B, the dental age of male patients was lower than dental age of female patients (no statistical significance) (P=0.072). The correlation between dental and chronological age was high (r=0.746 for group A, and r=0.885 for group B). The presence of all four third molars was statistically higher in group B (p‹0.001), and they were in statistically significantly more advanced stage of development (stage B) in group B (P‹0.001). Mineralization of the lower third molars began after the age of six, and mineralization of the root lasted from the eleventh till fifteenth year. Conclusion Our study showed a significant difference in dental age between group A and group B. Children in group B had more advanced dental age, which confirms the hypothesis of a positive secular trend in dental development. The comparison of developmental stages for each tooth between the two groups demonstrated more advanced stages of development of all teeth in group B. Tooth development was advanced for all teeth except the first molar and third molars. The correlation between dental and chronological age was high, and the dental age was underestimated for 0.4 (B) to 1,2 (A) years. The secular trend had a positive influence on the development and presence of all four third molars, which was more pronounced in group B. Statistically significant correlation between mineralization of the mandibular third molars and chronological age was found (from 0.725 to 0.793) in Istria by the Nolla method of dental age estimation.