Effect of two desensitizing agents on dentin permeability in vitro

Abstract

Objective: The aim of this in vitro study was to investigate the effect of two desensitizing agents and water on hydraulic conductance in human dentin.

Material and methods: GLUMA Desensitizer PowerGel (GLU) contains glutaraldehyde (GA) and 2-hydroxyethyl methacrylate (HEMA), and Teethmate Desensitizer (TD) is a powder comprising tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA) that is mixed with water. Deionized water was used as a negative control (CTR). Thirty discs with a thickness of 1.2 mm were cut from the coronal dentin of the third molars and cleaned with 0.5 M EDTA (pH 7.4). After being mounted in a split-chamber device, the discs were pressurized with water at 1 kPa and 3 kPa in order to measure flow rates with a highly sensitive micro-flow sensor and to calculate hydraulic conductance as a baseline value (BL). Following the application of GLU, TD, and CTR (n=10), hydraulic conductance was remeasured with intermittent storage in water after 15 min, 1 d, 1 w, and 1 m. Reduction in permeability (PR%) was calculated from hydraulic conductance. Data were statistically analyzed using nonparametric methods (α<0.05). Representative discs were inspected by SEM.

Results: PR% for GLU and TD were 30-50% 15 min and 1 m after their application. Post hoc tests indicated that PR% of CTR was significantly greater than those of GLU and TD at all time points tested. The PR% of GLU and TD were not significantly different. SEM examinations showed noncollapsed collagen meshes at the tubular entrances after GLU, and crystalline precipitates occluding the tubular orifices after TD, whereas CTR specimens showed typical patterns of etched dentin.

Conclusions: The present study on hydraulic conductance in dentin discs treated with two chemically different desensitizing agents and water as a control demonstrated that both products may be characterized as effective.

Figure 1. Mid-coronal section of a dentin disc cut perpendicularly to the long axis of a human third molar

Figure 2. Materials used

Figure 3. Schematic illustration of the device used to measure the permeability of dentin discs. Water is perfused under adjusted pressure through the dentin sample, clamped between two O-ring sealed chambers, and passes through an electronic micro-flow sensor, in which flow data are registered each 0.1-second intervals and transferred to a data recorder. A target area on the surface of the dentin specimen for the permeation of liquid has been sectioned with a contact sealing circle of O-rings

Figure 4. Mean percentage reductions in hydraulic conductance (PR%) and related 95% confidence intervals after one month of storage following two different perfusion pressures of 1 and 3 kPa (n=10). PR% was calculated at each stage after the application of the desensitizing agents and water, respectively, relative to the baseline value measured after EDTA-cleaning (maximum permeability). Bars with the same upper-case letter were not significantly different using Steel-Dwass test. Bars with the same lower-case letter were not significantly different using Wilcoxon Sign Rank test with Bonferroni correction

Figure 5. Representative scanning electron microscopy (SEM) micrographs of dentin surfaces and perpendicularly fractured aspects of the same specimens. Regarding GLU (Figures 5A and B), the exposed collagen mesh after EDTA cleaning was not collapsed, but presumably cross-linked by glutaraldehyde with the fibers kept apart. The collagen mesh is observed to a depth of several micrometers. In the case of TD (Figures 5C and D), all tubules are occluded with crystalline precipitates, with similar precipitation being noted on the intertubular surface. Fine precipitates are observed inside the tubules close to the surface (white arrows). The specimen from the CTR group (Figures 5E and F) shows a clean surface and empty tubules, free of precipitates and debris