The aim of this study was to determine the effect of first premolar extraction with different anchorages as well as non-extraction on mandibular third molar angulation.

The pretreatment (T1) and posttreatment (T2) panoramic radiographs of one hundred patients from Hamadan (Iran), who underwent fixed orthodontic treatment were investigated and the angle between long axis of right mandibular third molars and a constructed horizontal plan (HRP) was measured. The sample was equally divided into four groups including first premolar extraction with maximum anchorage, that with moderate anchorage, that with minimum anchorage and non-extraction group.

In the first premolar extraction groups with moderate and minimum anchorages, third molar angulation increased (8.12 and 7.48°, respectively) significantly from T1 to T2 (P=0.001 and 0.003, respectively), but in the first premolar extraction group with maximum anchorage and non-extraction group, increase in third molar angulation (2.84 and 0.8°, respectively) was not statistically significant (P=0.082 and 0.943, respectively). Third molar uprighting was significantly different among four groups using one-way ANOVA (P=0.004). Tukey (HSD: honestly significant difference) post hoc test indicated that difference in third molar angulation was statistically significant between first premolar extraction group with moderate anchorage and non-extraction group (P=0.007) and also between the first premolar extraction group with minimum anchorage and non-extraction group (P=0.024).

The first premolar extraction groups with moderate and minimum anchorage may lead to more chance of third molar eruption and this can be helpful in borderline cases to consider third molar angulation as one of determining indicators to decide whether to extract or not to extract first premolars.