Syringe Pressure in Root Canal Irrigation: Physics, Clinical Implications, and Risk of Apical Extrusion

After cleaning and shaping during endodontic therapy the root canal space can be disinfected with any number of disinfectants. Sodium hypochlorite is very effective for this. Intracanal lavage via syringe and needle may be done but there is a risk for extrusion of the solution through the tooth apical foramen into the medullary bone. This work studies the canal as a closed system such as when the needle is wedged against the canal walls that prevents solution escape to the coronal. The clinician should appropriately control the pressure placed on the syringe barrel to prevent this extrusion. This article reviews physics, fluid dynamics and factors that may influence an aqueous irrigant to be thrust into the bone. Understanding these factors can prevent perioperative mishaps and tissue damage such as to neural structures. Factors such as syringe diameter, needle lumen, depth of insertion, and flow rate contribute to this occurrence. Experimental and mathematical models were created to investigate this issue. These models were used to quantify a range of forces that would cause breaching of a tooth foramen when using a syringe and needle to deliver the solution. Hand pressure on a syringe is enough to extrude an aqueous solution through an endodontically instrumented tooth apical foramen. There are available side exit needles and other products and techniques that may minimize any apical extrusion.