Effect of artificial saliva contamination on pH value change and dentin bond strength
Introduction
In order to obtain successful adhesion between resin composite and tooth structure, it is necessary that the adhesive substrate should not be contaminated with fluids, such as saliva [1], [2], [3], [4], [5], blood [2], plasma [1], [4], saline [1] or debris from temporary cements [4], [6]. Sites at or near the gingival margins can be easily contaminated with saliva or gingival crevicular fluid. Dentin bonding systems have been shown to be sensitive to contamination with saliva and plasma [7]. However, in the case of enamel, re-etching with phosphoric acid is able to remove the precipitated proteins from saliva [8]. For dentin etching, phosphoric acid is able to open dentin tubules and clean the peritubular region that has been contaminated with temporary cement debris [4]. The influence of contamination before and after dentin conditioning has been studied by measuring bond strengths and scanning electron microscopic observations [1], [2], [3], [4], [5], [6], [7].
Recently, the SCHEM-100 has been developed to facilitate pH analyses on flat surfaces of solid specimens [9], [10], [11]. The pH distribution formed in a thin agar film on the pH-imaging sensor can be measured quantitatively, and a pH dependent electric signal at each measurement point is converted and displayed as a pH image. The pH-imaging sensor is based on photocurrent characteristics of semiconductor silicon [12]. The pH values obtained by the sensor at each pH-measurement point are converted to a grayscale pixel, and the color scale of each pH value is displayed as the image of pH value. By taking advantage of the flat pH-sensing surface and capability of multiple-point pH measurement, a new concept of performing the chemical analysis of a solid sample has been established. The preparation for the SCHEM-100 does not require samples to be destroyed by dissolution. The SCHEM-100 has been applied in industrial research, food science, biological and medical science. For example, characteristic features of metal surfaces [9], damage to human hair, freshness of rice, and metabolic activity of E. coli [10] have been assessed by measurement of pH changes with the SCHEM-100. However, few attempts to apply the SCHEM-100 to dental tissues have been performed [13], [14].
The purpose of this study was to examine the effect of artificial saliva contamination and treatment of the contaminated dentin surface with respect to pH change and the micro-shear bond strength (MSBS) of a self-etching primer and a one-bottle adhesive system. The hypothesis of this study was that artificial saliva contamination and re-treatment with the dentin conditioning agents would influence the pH of the dentin surface and the MSBS. The result from pH value measurement is important to evaluate the condition of dentin because the chemical characteristic of dentin surface had been less studied using dentin adhesive systems.
Section snippets
Materials
Two bonding systems were used: a self-etching primer system, Clearfil SE Bond (SE Bond, Kuraray Medical Inc., Tokyo, Japan), and a one-bottle adhesive system, Single Bond (3M-ESPE, St. Paul, MN). Two resin restorative materials were used for the MSBS, namely AP-X (Kuraray) for SE Bond and Z100 (3M) for Single Bond. Their ingredients and methods of application are listed in Table 1.
An artificial saliva (Salivert, TEIJIN, Osaka, Japan) was substituted for human saliva. Salivert is devoid of a
pH of the dentin surface
Representative TIFF images are shown in Fig. 4, with the pH image patterns varying for each treatment group. The pH changes of dentin surfaces are summarized in Table 2. The intact dentin surfaces showed a neutral pH of 6.9. The dentin surfaces conditioned with SE primer produced a significantly lower pH of 5.4, and those treated with phosphoric acid etchant had a pH of 5.9. After saliva contamination of the conditioned dentin, the pH increased to 6.2 in both the primer and etchant groups.
Discussion
A conventional pH measurement of solid materials requires samples to be destroyed by dissolution. However, the SCHEM-100 allows the pH of the surface of a flat solid material to be measured when the sample is placed on the agar film. The pH distribution formed in a thin agar film can be measured quantitatively. Since a 1 mm-thick agar film is positioned between the sensor and the tested sample, and the pH distribution is obtained as what was formed at the bottom of the agar film, the measured pH
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