Early loss of permanent first molars which are known as “the key of the occlusion” may cause occlusal disorders. The purpose of this study was to evaluate the changes of mandibular permanent second molars and mandibular second premolars after obligatory extraction of mandibular permanent first molars. The study sample consisted of 12 children (2 boy, 10 girl) with a mean age of 9.5±1.38 years. 13 mandibular segments were study group; 11 mandibular segments were control group. Lateral cephalograms, panoramic and periapical radiographs, intraoral photographs and study models were taken before the extraction (Tl), 1 year after the extraction (T2) and 6.5±0.45 years after the extraction (T3). The angular and linear measurements measured on the “Corpus Axis of Ric-ketts” were calculated and evaluated by Wilcoxon and Mann Whitney-u statistical analysis. Results: (1) Mandibular permanent second molars tipped mesially at the end of first year (T1-T2), then uprighted in the long-term (T2-T3) (2) Mandibular second premolars in both extraction and non-extraction groups uprighted during eruption.

Keywords: Mandibular permanent first molar. Early extraction, Dental arch changes