Hard cements can be difficult to remove and usually need to be drilled out. This is a hazardous procedure, especially in the apical region of the root canal, where the use of hand instruments is safer. Some cements, however, such as zinc phosphate may be impossible to remove from the root canal as there is no known solvent. An ultrasonically powered file may be used in an effort to chip the cement away, although often with limited success. An apicectomy with retrograde root filling may be necessary in these cases.
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