Apical Patency-Dependent Extrusion Rate Using a Micro-Flow Testbed

Objectives: Root canal therapy entails disinfection of the channel by using sodium hypochlorite, in combination with one of several methods: side-vented 30G needle irrigation or energy-based devices. However, risk of extrusion of tissue-toxic disinfectant through the apical end remains. Using a programmable open-loop microflow system, the current project aims to study apical fluid extrusion from model teeth with endo-prepared root canals.
Methods: Five model teeth each (#8, real-t endo), were prepped under endodontist supervision, by deploying appropriate rotary and hand-files: 25 mm length, 0.04 taper, and 0.25 mm, 0.45 mm patencies. Patency was ensured with a 20 and 40 handfile. The crown was connected with silicone tubing in an over-the-tooth configuration, to a computer-controlled, constant-microflow setup using hi-purity water, and inlet pressure logged. Extruded fluid was collected in a receptacle on a 0.1 mg resolution microbalance; flowrate was continuously calculated by dividing the weight by elapsed time. Time-pressure-flow data were saved as a text file during each run. Extrusion test for each tooth was performed for 60 seconds and was repeated three times, providing 15 datasets individually, for 25- and 45-teeth. Flow dynamics and predicted extrusion pressures at apex were estimated using Hagen-Poiseuille model for tapered tube, as well as Bernoulli’s equation.
Results: Using a constant flow open-loop microflow system, the 25-teeth recorded 229.92 mbar(+/-42.49) inlet pressure and 2.59 ml/min(+/-0.46) extrusion rate, while 153.08 mbar(+/-14.70) and 3.42 ml/min(+/-0.15) were recorded for 45-teeth. Pressure and extrusion rates were statistically differentiable, p<0.001 between groups. Numerically predicted apical pressures were reasonable for the experimental fluid-dynamic conditions.
Conclusions: The developed test bed enables systematic assessment of apical fluid extrusion for various root canal geometries and flow conditions. Extrusion rate was greater for 45-teeth (lower pressure), compared to 25-size teeth. Numerical considerations for flow through tapered channel can help predict apical pressures to promote procedure safety.