Erosion Of Dentin Resulting From Cyclic Stress And pH Challenges

Non-carious lesions, like that occurring in exposed root surfaces, are not uncommon and believed to develop by a combination of erosion, abfraction and abrasion. Previous investigations have identified that erosion of dentin is a function of pH and cyclic stress. The influence of microstructure on the rate of erosion not been considered.  Objectives: The objective of this investigation was to evaluate the importance of dentin microstructure on the erosion process in environments of low pH and cyclic stress.  Methods: Rectangular beams were prepared from the outer-coronal and near-pulpal regions of the crown dentin of human third molars, representing low and high mineral to collagen ratios, respectively.  The beams were subjected to cyclic cantilever bending at room temperature under maximum stresses of between 30 to 50 MPa for periods of between 1x10^5 and 1x10^6 cycles.  Cyclic loading was performed in solutions of pH = 7 (control) or acidic environments (treated) with either pH=4.5 or pH = 6.  Material loss that resulted over a period of cyclic loading was measured using imaging processing techniques in the regions of maximum tension, compression and transverse shear stress. Results: The measured mean material loss was greatest in the treated group with pH=4.5, followed by the pH=6.0 and control groups, respectively.   Erosion of the outer-pulpal dentin occurred at a significantly greater rate (p<0.05) than in the near-pulpal region.   Though there was no apparent difference between regions of tension and compression, the locations of largest normal stress exhibited more erosion than regions of low stress.  The differences were most prominent in the treated group with intermediate pH.  Conclusion: Within coronal dentin, erosion occurs most rapidly under conditions of cyclic stress and low pH in regions nearest the DEJ.  (Supported by the National Institutes of Dental and Craniofacial Research R01 DE016904).