OBJECTIVETo investigate the influence of different crown cutting mode on operation time and post-operation trauma in extracting the mandible third molar by dental drilling system.

METHODSAccording to different impaction types, the patients were divided into vertical impaction, horizontal impaction, and mesioangular impaction groups. The operation time, mouth opening, swelling, and pain degrees were recorded during traditional extraction, crown "T"-shaped cutting, crown three section cutting, and crown-root cutting in the extraction of mandibular wisdom teeth.

RESULTSIn the vertical impaction group, the operation time, the degree of swelling, limitation of mouth opening and the pain degree were (8.2 ± 2.5) min, (14.7 ± 2.0) mm, (3.9 ± 2.4) mm and 3.4 ± 1.8, respectively using crown cutting, and (14.0 ± 2.7) min, (18.2 ± 1.9) mm, (9. 7 ± 3.6) mm and 6.9 ± 2.3 using traditional extraction method (P < 0.05). In the horizontal impaction group, the operation time, degree of swelling, limitation of mouth opening and pain degree (14.0 ± 2.0) min, (19.2 ± 3.9) mm, (9.5 ± 2.5) mm, 5.6 ± 1.7 respectively using crown "T"-shaped cutting, and (18.0 ± 3.1) min, (23.6 ± 3.5) mm, (9.8 ± 2.7) mm and 8.5 ± 2.3 using crown three section cutting. There was significant difference in operation time, degree of swelling and pain (P < 0.05), but no significant difference in the limitation of mouth opening (P > 0.05). In mesioangular impaction group, operation time, degree of swelling, limitation of mouth opening and pain degree were (10.2 ± 2.6) min, (18.4 ± 2.9) mm, (6.4 ± 2.5) mm and 4.8 ± 1.8, respectively using "T"-shaped cutting, and (15.0 ± 3.5) min, (18.9 ± 3.0) mm, (7.0 ± 3.7) mm and 7.6 ± 2.3 using crown- root cutting. The operation time and pain degree were significantly different (P < 0.05), but not different in limitation of mouth opening and swelling degree (P > 0.05).

CONCLUSIONSDifferent impaction types of wisdom teeth should choose different cutting mode. Vertical impacted tooth uses distal crown cutting. "T"-shaped cutting is preferred with horizontal impaction. According to the angle and depth of the mesioangular impaction, "T"-shaped cutting or the crown-root cutting can be selectively used.