Biomedical engineering for the conservation of teeth--the use of a Nd-YAG laser for a treatment of apical focus.

When the apical focus (root cyst) is treated, if the tooth concerned can be preserved, the root canal should first be enlarged and cleaned sufficiently, and then sealed with filling materials. However, if an expensive prothesis is placed on the crown of the tooth concerned, or if the root canal is blocked with a post core of calcification, root canal treatment becomes difficult from a practical point of view. We therefore tried irradiation using the Nd-YAG laser, which is known for its high transmissibility into teeth, to the root canal, and the apical area. In its histological images it is considered to the action on bacteria and bacteria-infected substances inside the root canal through calcification of the dentinal surface layer facing the dental pulp, closure of the dentinal canal opening, and there was substantial change in the dentine in the outer layer. We have achieved good clinical results using this method; we eventually extracted only two teeth in 200 cases; it is thus very significant that most of the teeth of the patients still maintain their function, although they were diagnosed as non-preservable using conventional methods.