The mandibular third molar (3M) is the tooth that is most often impacted, with lack of space being one of the reasons. In some orthodontic treatments, premolars are extracted in order to create space. The aims of our study are: firstly, to assess the changes in the angulation and position of the 3M in cases treated either with or without extraction of the first or second premolars; secondly, to analyse the variation in the gonial angle and the degree of inclusion of the 3M; and lastly, to establish a predictive impaction model for 3M. This study included 88 patients: 28 patients treated with extractions of first premolars, 30 with second premolars and 30 without. The initial and final orthopantomography was analysed and the angulation of the 3M was measured, a new variable being created to determine the degree of 3M inclusion in the mandibular ramus. The results show that the angulation of 3M improves with time, regardless of treatment, and presents a greater disinclusion in cases treated with extractions. The gonial angle tends to diminish with age in all cases. The conclusions suggest that other factors may influence the angulation and position of 3M and that it is not possible to establish a predictive impaction model.