**3. Results**

Immediately after the application of PBD, SEM micrographs showed good coverage by PBD of the widely open dentinal tubule in EDTA-demineralized dentin as clearly observed in the comparison of the untreated and treated side (Figure **??**). The cross-sectional images showed that the nanoparticles form PBD have penetrated into the dentinal tubules and further sealed the nanospaces exposed through the collagen network and lateral branches in the tubule walls of demineralized dentin. Intratubular dentin seemed to be densely penetrated on the treated side. The depth of penetration was estimated to be 5–10 μm from the dentin surface. The thickness of the formed layer as a result of the PBD application was approximately 1 μm.

**Figure 2.** Cross-sectional SEM images immediately after application of PBD. The patency of dentinal tubules and open lateral branch orifice (arrow) have been well sealed on the treated side.

After four weeks of SBF immersion, SEM images of dentin treated with EDTA and PBD disclosed a highly dense and homogenous structure of dentin measuring at least 20 μm in thickness. In this structure, a surface layer was not easily distinguished from the bulk of subsurface dentin, indicating integrated mineralization of the surface zone through both mineral deposition on the surface and into the demineralized dentin, forming a highly mineralized unified structure whereas there was no such unification on untreated sides (Figure **??**).

The results of MSBS of each experimental group (mean and SD) were listed in Table **??** and Figure **??**. Two-way ANOVA indicated that both the use of desensitizers and application mode were significant factors in MSBS and their interaction was significant (*p* < 0.05). Generally, both PBD and TMD significantly reduced bond strength to dentin by 15–20% on average; however, the effect was adhesive dependent. For PUB, the groups using phosphoric acid etching (PUB-PA) consistently showed higher bond strength compared to the ones using self-etch (PUB). Bonding to PBD and TMD with either PUB-PA and CSE were comparable (*p* > 0.05).

**Figure 3.** SEM images four weeks after application of PBD and immersion in SBF. PBD-treated dentin demonstrates a solid layer of mineral formation while no coverage is distinguished in the untreated dentin away from the PBD-treated dentin.


**Table 2.** Mean microshear bond strength of the experimental groups (MPa).

**Figure 4.** Bond strength of the experiment group in MPa. Bars indicate no significant difference (*p* < 0.05). Two-way ANOVA indicated that both the use of desensitizers and application mode were significant factors in MSBS and their interaction was significant (*p* < 0.05). Predicta (PBD) and Teethmate (TMD) significantly reduced bond strength to dentin by 15%–20% on average; however, the effect depended on the adhesives. For Universal Adhesive (PUB), the groups using phosphoric acid etching (PUB-PA) consistently showed higher bond strength compared to the ones using self-etch (PUB). Bonding to PBD and TMD with either PUB-PA and Clearfil SE 2 (CSE) were comparable (*p* > 0.05).
