An In-Vitro Tubule Occlusion Model

Objectives: Brannstrom's Hydrodynamic Theory states that when the fluids within the dentinal tubules are subjected to temperature changes or physical osmotic changes, the movement stimulates a nerve receptor sensitive to pressure, which leads to the transmission of the stimuli or sensitivity.  The purpose of developing this model was to be able to evaluate dentifrices for their ability to occlude dentinal tubules in-vitro.  Methods: 3mm human dentin cores were mounted in acrylic disks.  The disks were serially ground and polished.  They were then treated with 1% citric acid for 30 seconds to remove the smear layer. The specimens were examined under 50X magnification for tubule occlusion using a numeric scale (1 [all open] to 5 75%< occluded]) as well as subjected to image analysis (Image J) identifying open tubules by the number of dark pixels.  A process was developed that would allow imaging the same area after treatment as before thus reducing variability.  Treatments were performed by brushing with undiluted paste (placebo, OTC control [Sensodyne Repair and Protect] and a 3 point dose response of the test active [nanoXIM CarePaste]) using a wet toothbrush for a total of two minutes.  This was repeated 7 times.  The specimens were then analyzed once again as outlined above.  Results: Post treatment analysis indicated that the desensitizing agents either occluded the tubules or produced a smear layer over the entire surface of the specimens.  There were significant differences in the degree of occlusion among different treatment groups.  Pla (10±2% occluded) < 2.3% active (40±6% occluded) < OTC control (56±5% occluded) =7.5% active (64±5% occluded) and OTC control <4.5% active (73±5% occluded).  Conclusions: These findings suggest that this model can be used to study dentinal tubule occlusion or formation of a smear layer by desensitizing dentifrices.