Ya-Ming Chen

Effect of fluoride iontophoresis on the microtensile bond strength between dentin and two adhesive systems

AIM To evaluate the effect of fluoride iontophoresis on the microtensile bond strength (MTBS) between coronal dentin and two resin-based adhesive systems, and to measure quantitatively dentinal tubule occlusion. METHODS Twelve freshly extracted intact human mandibular third molars were divided randomly into four groups. The superficial occlusal dentin of each tooth was exposed and treated. Group A1: One-Step Plus total-etch adhesive system; group A2: One-Step Plus total-etch adhesive system after fluoride iontophoresis; group B1: ACE BOND SE self-etching adhesive system; group B2: ACE BOND SE self-etching adhesive system after fluoride iontophoresis. A resin composite buildup was made for each tooth, which was then sectioned along its long axis to produce 10 beams (1.0 mm x 1.0 mm) for the microtensile bond strength (MTBS) test. Five dentin disks were cut in half and their occlusal surfaces etched with 6% citric acid. The test halves were treated with fluoride iontophoresis. Four SEM photomicrographs were taken from corresponding sites on each test and each non-treated control half-disk. Image-Pro Plus 4 software quantified the percentage of tubule occlusion. Data were analyzed using one-way ANOVA, chi(2)- and t-tests, with the probability level set at alpha=0.05. RESULTS The mean MTBS (MPa) for each group was, A1: 30.86 (S.D. 6.84); A2: 25.04 (8.49); B1: 19.22 (6.88); B2: 19.40 (6.92). There were significant differences among all groups (P < or = 0.02), except between groups B1 and B2 (P=0.92). Fluoride iontophoresis resulted in significantly increased dentinal tubule occlusion (P<0.001). CONCLUSIONS Fluoride iontophoresis treatment reduced significantly the dentin bond strength of One-Step Plus total-etch adhesive, but not that of ACE BOND SE self-etching adhesive. However, the bond strength of the former remained significantly higher than that of the latter adhesive system.

Antimicrobial effects of a bioactive glass combined with fluoride or triclosan on Streptococcus mutans biofilm

OBJECTIVE The objective of this study was to investigate the antibacterial effects on a cariogenic biofilm of a bioactive glass (BAG) combined with either sodium fluoride (NaF) or triclosan (TCS). DESIGN According to minimal bactericidal concentrations, 37.5mg/ml of BAG, 4.69 mg/ml of NaF, and 15.53 μg/ml of TCS solutions were prepared. When used alone, the three antimicrobial solutions were increased to double-dosage strength (2 MBC). The study contained the following experimental groups: group 1, BAG (2 MBC); group 2, NaF (2 MBC); group 3, TCS (2 MBC); group 4, BAG+NaF; group 5, BAG+TCS; group 6, control (saline). Streptococcus mutans biofilm was cultured with 0.1% sucrose anaerobically on 66 sterilized coverslips (1 × 1 cm(2)) for 24h uninterrupted. After 10 min of exposure to the experimental groups, the microbial kinetics, morphology, and viability of the S. mutans biofilms were assessed by evaluation of colony-forming units (CFUs), scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM). RESULTS BAG (2 MBC) used alone showed significantly stronger antibacterial effects than the other two antimicrobials used alone. The combination groups also displayed the same or greater biofilm inactivation effects as BAG (2 MBC) in the plate count test. SEM showed smaller stacks (towers) and fewer surrounding bacteria in groups BAG (2 MBC), BAG+NaF, and BAG+TCS. Confocal microscopy also determined higher live/dead ratios in groups NaF (2 MBC), TCS (2 MBC), and control than in groups BAG (2 MBC), BAG+NaF, and BAG+TCS. CONCLUSIONS The combinations of BAG with either NaF or TCS enhanced the inactivation effects of BAG (2 MBC) on S. mutans biofilm, and these findings should be further investigated clinically for the control of dental biofilms.

The Effects of Water on Degradation of the Zirconia-Resin Bond

OBJECTIVES 10-methacryloyloxydecyldihydrogenphosphate (MDP) containing primers improve bonding of yttria-stabilised tetragonal zirconia (Y-TZP) to methacrylate resins. The present study investigated the role played by water in the deterioration of MDP-mediated zirconia-resin bonds. METHODS Grit-blasted Y-TZP plates were conditioned with two MDP primers and bonded with resin for shear bond strength (SBS) testing. Additional bonded plates were aged hydrothermally and compared with unaged Y-TZP after 24h of water-storage or 6 months of water/acid/alkali-storage. The monoclinic phase (m-ZrO2) in different groups was determined by X-ray diffraction. Hydrolytic stability of the coordinate bond between MDP and zirconia in neutral/acid/alkaline environment was analysed using thermodynamic calculations. Microleakage and release of the element phosphorus from MDP-mediated Y-TZP/resin-bonded interfaces were evaluated via methylene blue dye infiltration and inductively coupled plasma-mass spectrometry (ICP-MS). RESULTS Hydrothermal ageing did not significantly alter SBS. Ageing in acidic or neutral medium led to significant decline in SBS. The m-ZrO2 phase increased after hydrothermal ageing but no m-ZrO2 was detected in the water/acid/alkali-aged specimens. A higher equilibrium constant was identified in the MDP-t-ZrO2 complex when compared with the MDP-m-ZrO2 complex. MDP-conditioning failed to prevent infiltration of the methylene blue dye. Phosphorus was detected by ICP-MS from the solutions used for soaking the resin-bonded specimens. CONCLUSIONS Hydrolysis of the coordinate bond between MDP and ZrO2, rather than t→m phase transformation, weakens the bond integrity between MDP-conditioned Y-TZP and methacrylate resin. CLINICAL SIGNIFICANCE Hydrolysis of the coordinate bond between MDP and zirconia is responsible for deterioration of the integrity of the bond between MDP-conditioned Y-TZP and methacrylate resin.