Systems and methods for using a liquid jet apparatus for dental treatments are disclosed. In one implementation, the liquid jet apparatus may include a handpiece configured to deliver a high velocity liquid jet to a desired location in the mouth of a patient. The handpiece may include a positioning member having a channel through or along which the jet can propagate. The positioning member may have a distal end portion configured to be at least partially disposed in a pulp cavity, canal space, or opening in the tooth under treatment. During operation, the jet may impact an impingement surface of the distal end portion of the positioning member and be deflected as a spray through one or more openings in the distal end portion. The liquid jet apparatus may be used for root canal treatments.