[Effect of premolar extractions on third molar angulation changes: a meta-analysis].

Objective: To assess the effect of premolar extractions on third molar angulation changes in orthodontic patients.

Methods: The Cochrane library, PubMed, Embase, China Science and Technology Periodical Database, China National Knowledge Infrastructure (CNKI), Chinese Biomedical Literature Database (CBM) and Wanfang database were searched from January 1, 1990 to May 20, 2014 to identify all the studies about third molar angulation changes in orthodontic patients with or without premolars extraction, which was assigned as a extraction group and a control group. Th e extraction group was further divided into a fi rst premolar extraction subgroup and a second premolar extraction subgroup. Literature filtering, data extraction and methodological quality evaluation were finished independently by two researchers. After cross checking, the disagreements were solved by discussion. Meta-analysis was carried out by RevMan 5.3.3 software.

Results: Ten studies involving 712 patients were included. Meta-analysis revealed that: compared with the control group, the changes of third molar angulation in maxillary and mandible in the extraction group were statistically significantly different (all P<0.05); the difference in angulation between the two groups was about 5.19° in maxillary and 3.55° in mandibul. As for the premolar extraction subgroups, there was no significant difference in mandibular third molar angulation between them (P>0.05).

Conclusion: The orthodontic treatment involving first or second premolar extractions can improve the maxillary third molar angulation, and the second premolar extraction is the best option.