The concept of boundary layer physics plays a major role.
When a fluid fills a pipe, the layer of molecules adjacent to the pipe have an affinity for the material of the pipe.
They sort of stick to it.
Forming the "Boundary Layer"
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And this stickiness affects how a fluid flows through the pipe.
In actuality, the fluid does not flow through the pipe but through the pipe coated with the boundary layer of the fluid/pipe interface. Thus every pipe that conducts fluid is actually smaller than it appears depending on the thickness of this boundary layer. If the pipe is already very small, then the proportion of the pipe that is occupied by this boundary layer is relatively larger and thus the bore smaller, and has more of an effect on how well the fluid flows. |
As we know, the smaller the pipe, the greater pressure is needed to force a given volume to flow in a given amount of time.
I.e. the flow rate is diminished.
In syringes as used for endo we are dealing with two adverse factors.
and technically is not a fluid at all but a suspension of zinc oxide and other particles in eugenol.
To a great extent, what determines the pressure needed to attain a given flow rate is the ability of these particles to roll or tumble past one another as they move past the particles in the boundary layer. i.e. it helps if the particles themself are round and smooth vs. large and jagged.
Thus it takes a great deal of pressure to get a thick mix of ZOE to flow through a small needle. But contrary to what you might think at first, once the cement leaves the end of the needle, the pressure immediately returns to atmospheric pressure.
This is all but impossible to attain with normal hypodermic type syringes.
Some device to give us a mechanical advantage must be used.
Lever handle devices such as the PDL Intraligamentary Syringe and screw type devices such as the Fine-Cut Endo Cartridge Syringe, develop the pressure AND the control to solve this problem.
With the proper technique a canal can be filled in seconds with most cements. We recommend PCA Root Canal Sealer since it is ADA certified and because the particle size is extremely small. Other ZOE cements might work but some may clog up a syringe because no special effort is made to keep the particle sizes small.
Recently (April 2005 the Journal of Endodontics) reported studies show that cement is not only AS good as gutta percha plus sealer it is 24 times a better sealer. This is probably because in condensing gutta percha, there is always some rebound when the plastic material is condensed and this probably causes the leakage noted.
