Results Postpreprative reaction was better in group B than in group A.Needl e breaking rate was lower in group A than in group B, but taking out the broken needle was more di...

• 结果B组的术后反应明显少于A组,A组的断针率低于B组,但因断于根管内,取出相当困难,B组扩大针折断处多位于超声挫的颈部,断针易于取出。