Zhejun Wang

A New Noninvasive Model to Study the Effectiveness of Dentin Disinfection by Using Confocal Laser Scanning Microscopy

INTRODUCTION The present study was designed to develop a standardized model for quantification of the effectiveness of dentin disinfection by different antibacterial solutions including a new root canal irrigant, Qmix. METHODS Dentinal tubules from the root canal side in semicylindrical dentin specimens were infected with Enterococcus faecalis by centrifugation of the bacterial suspension into the tubules. Scanning electron microscopy (SEM) was used to verify the presence of bacteria in dentin. The outer side of dentin pieces was closed, and the specimens were subjected to 1-minute and 3-minute exposure to sterile water, 1%, 2%, 6% sodium hypochlorite (NaOCl), 2% chlorhexidine (CHX), and Qmix. Confocal laser scanning microscopy (CLSM) and viability staining were used to quantitatively analyze the proportions of dead and live bacteria inside dentin. RESULTS A heavy invasion by E. faecalis was detected by both SEM and CLSM throughout the dentinal tubules. The amount of dead cells in dentin increased with increasing NaOCl concentration and time of exposure (P < .05). Qmix was equally effective in killing bacteria in dentin as 6% NaOCl; more than 40% and 60% of the bacteria were killed by both at 1 minute and 3 minutes, respectively. One percent and 2% NaOCl and 2% CHX killed 20%-30% and 30%-40% bacteria after 1 and 3 minutes of exposure, respectively, with no statistically significant differences among the 3 agents (P > .05). In the control group, which was treated with sterile water, only 4%-6% of the bacteria were dead. CONCLUSIONS Centrifugation helped to create a heavy, evenly distributed infection deep into the dentinal tubules. The new model made it possible to compare the effectiveness of several disinfecting solutions in killing bacteria inside dentin by a noninvasive CLSM method.

In Vitro Cytotoxicity Evaluation of a Novel Root Repair Material

INTRODUCTION This study examined the effect of a new bioactive dentin substitute material (Biodentine) on the viability of human gingival fibroblasts. METHODS Biodentine, White ProRoot mineral trioxide aggregate (MTA), and glass ionomer cement were evaluated. Human gingival fibroblasts were incubated for 1, 3, and 7 days both in the extracts from immersion of set materials in culture medium and directly on the surface of the set materials immersed in culture medium. Fibroblasts cultured in Dulbecco modified Eagle medium were used as a control group. Cytotoxicity was evaluated by flow cytometry, and the adhesion of human gingival fibroblasts to the surface of the set materials was assessed by using scanning electron microscopy. The data of cell cytotoxicity were analyzed statistically by using a one-way analysis of variance test at a significance level of P< .05. RESULTS Cells exposed to extracts from Biodentine and MTA showed the highest viabilities at all extract concentrations, whereas cells exposed to glass ionomer cement extracts displayed the lowest viabilities (P< .05). There was no significant difference in cell viabilities between Biodentine and MTA during the entire experimental period (P> .05). Human gingival fibroblasts in contact with Biodentine and MTA attached to and spread over the material surface after an overnight culture and increased in numbers after 3 and 7 days of culture. CONCLUSIONS Biodentine caused gingival fibroblast reaction similar to that by MTA. Both materials were less cytotoxic than glass ionomer cement.

Surface Functionalization of Titanium with Chitosan/Gelatin via Electrophoretic Deposition: Characterization and Cell Behavior

The electrophoretic deposition (EPD) is a versatile and cost-effective technique for fabricating advanced coatings. In this study, chitosan/gelatin (CS/G) coatings were prepared on titanium substrates via EPD. The prepared coatings were characterized using fluorescence microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and shear bond strength testing. It was found that CS/G coatings had a similar macroporous structure. The gelatin content in the CS/G coatings gradually increased with the increase of the gelatin in the blend solutions. The shear bond strength of the CS/G coatings also increased with the increasing gelatin content. In vitro biological tests demonstrated that human MG63 osteoblast-like cells achieved better affinity on the coatings with higher gelatin content. Therefore, it was concluded that EPD was an effective and efficient technique to prepare CS/G coatings on the titanium surface and that CS/G coatings with higher gelatin content were promising candidates for further loading of functional agents.

Dental materials with antibiofilm properties

OBJECTIVES Oral bacteria have evolved to form biofilms on hard tooth surfaces and dental materials. The antibiofilm effect of materials used for the restoration of oral function affects oral health. In this review we describe the features involved in the formation of oral biofilms on different surfaces in the oral cavity and the antibiofilm properties of dental materials. METHODS An electronic search of scientific papers from 1987 to 2013 was performed with PubMed, ScienceDirect and Google search engines using the following search terms: antibiofilm, dental material, dental hard tissue, endodontic material, implant material, oral biofilm, and restorative material. RESULTS Selected inclusion criteria resulted in 179 citations from the scientific, peer-reviewed literature. Oral biofilms form not only on dental hard tissue, but also on a wide range of dental materials used in cariology, endodontics, restorative dentistry and periodontology, resulting in destruction of dental hard tissue and even infection. Therefore, there has been a continuous effort to develop the antibiofilm properties of dental materials used for different purposes. Specific antimicrobial design in the composition and application of new materials (e.g. bioceramic sealer, resin composite, implant coating) demonstrates an improvement of the antibiofilm properties of these materials compared to earlier generations. SIGNIFICANCE A significant number of dental materials have been shown to affect biofilm growth by inhibiting the adhesion of bacteria, limiting their growth or killing microbes in the biofilms formed in vitro. Incorporation of an appropriate amount of antibacterial agent could provide dental materials with antibiofilm activity without significantly influencing their mechanical properties. However, more randomized and double-blind clinical studies of sufficient length with these materials are needed to confirm long term success following their use in the dental clinic.

Effect of desensitising toothpastes on dentinal tubule occlusion: A dentine permeability measurement and SEM in vitro study

OBJECTIVES The purpose of this study was to evaluate the in vitro effectiveness of a new bioglass-containing and two commercial desensitising toothpastes on dentinal tubule occlusion after citric acid challenge or artificial saliva (AS) immersion. METHODS One hundred dentin discs from human third molars were used. Specimens were randomly divided into five groups (n=20), Group 1: EDTA-treated dentin; Group 2: brushing with distilled water; Group 3: brushing with Novamin; Group 4: brushing with Sensodyne Freshmint; Group 5: brushing with Colgate Sensitive. In each group, samples were then equally split into two subgroups (n=10) to test two post-treatments: 6% citric acid challenge or 24h immersion in artificial saliva. Dentine permeability of each specimen was measured before and after each treatment using a hydrostatic device working at 20cm H(2)O pressure. Data were analysed by two-way repeated measures ANOVA to determine if there were any significant differences within or between groups. Dentine morphology and surface deposits were observed by SEM. RESULTS All three desensitising toothpastes significantly reduced dentine permeability and created precipitates on the treated dentine surfaces. Moreover, the reductions in dentine permeability showed partial recovery after a citric acid and artificial saliva immersion. Sensodyne showed significant resistant to acid attack and Novamin exhibited the lowest permeability after artificial saliva immersion for 24h. CONCLUSIONS The application of the three toothpastes resulted in effective dentinal tubule occlusion. However, the new bioglass-containing toothpaste (Novamin) represented excellent occlusion effects after brushing treatment and AS immersion, while Sensodyne demonstrated more reduction in permeability when citric acid challenged.

The Effect of Detergents on the Antibacterial Activity of Disinfecting Solutions in Dentin

INTRODUCTION Detergents have been added into different disinfecting solutions to lower their surface tension and to enhance their antibacterial effects. The purpose of this study was to evaluate the effectiveness of dentin disinfection by different antibacterial solutions in the presence and absence of detergents using a novel dentin infection model and confocal laser scanning microscopy (CLSM). METHODS Semicylindrical dentin specimens were infected with Enterococcus faecalis by centrifugation according to a previously described protocol. After 1 day of incubation, the infected dentin specimens were subjected to 1 and 3 minutes of exposure to sterile water, 0.1% cetrimide (CTR), 2% sodium hypochlorite (NaOCl), 2% NaOCl + 0.1% CTR, 6% NaOCl, 6% NaOCl + 0.1% CTR, Chlor-Xtra (Vista Dental, Racine, WI), 2% chlorhexidine (CHX), CHX-Plus (Vista Dental, Racine, WI), 2/4% iodine potassium iodide (IPI), and IPI + 0.1% CTR. The specimens were then stained for bacterial viability and examined by CLSM to analyze the proportions of dead and live bacteria inside dentinal tubules. RESULTS More bacteria in dentin were killed after 3 minutes of exposure than after 1 minute of exposure to the disinfecting solutions in all experimental groups (P < .05). The antibacterial solutions with detergents (0.1% CTR, 2% NaOCl + 0.1% CTR, CHX-Plus, and IPI + 0.1% CTR) showed a statistically higher proportion of dead bacteria than the corresponding solutions without detergents (sterile water, 2% NaOCl, 2% CHX, and IPI) (P < .05) except for the 6% NaOCl group (6% NaOCl, 6% NaOCl + 0.1% CTR, and Chlor-Xtra) (P > .05). Six percent NaOCl, 6% NaOCl + 0.1% CTR, and Chlor-Xtra were the most effective solutions, killing over 45% and 65% of the bacteria after 1 and 3 minutes of exposure, respectively. Only 3% to 4% of the bacteria were dead in the sterile water group, whereas 0.1% CTR alone was able to kill 24% to 36% of the E. faecalis cells. CONCLUSIONS The addition of detergents in the disinfecting solutions used in the present study increased their antibacterial effects against E. faecalis in the dentinal tubules. When used alone as a single agent, CTR showed antibacterial effectiveness comparable to 2% NaOCl, 2% CHX, and 2/4% IPI.

Phase Transformation Behavior and Resistance to Bending and Cyclic Fatigue of ProTaper Gold and ProTaper Universal Instruments

INTRODUCTION The purpose of this study was to compare the flexibility and cyclic fatigue resistance of ProTaper Universal (PTU; Dentsply Tulsa Dental Specialities, Tulsa, OK) and ProTaper Gold (PTG; Dentsply Tulsa Dental Specialities, Tulsa, OK) instruments in relation to their phase transformation behavior. METHODS Sizes S1, S2, F1, F2, and F3 of PTU and PTG instruments were subjected to rotational bending at a curvature of 40° and a radius of 6 mm. The number of cycles to fracture (NCF) was recorded. The fracture surface of all fragments was examined with a scanning electron microscope. Flexibility was determined by 45° bending tests according to the ISO 3630-1 specification. Unused and fractured instruments were examined by differential scanning calorimetry. RESULTS PTG had a cyclic fatigue resistance superior to PTU in all sizes (P < .001). The NCF of the nickel-titanium files of sizes S1 and S2 was significantly higher than those of sizes F1 to F3 (P < .001). No significant difference in the NCF of PTU instruments was detected between F1 and F2. The fractured files of both PTU and PTG showed the typical fracture pattern of fatigue failure. The bending load values were significantly lower for PTG than for PTU (P < .05). The differential scanning calorimetry analyses showed that each segment of the PTG instruments had a higher austenite finish temperature (50.1°C ± 1.7°C) than the PTU instruments (21.2°C ± 1.9°C) (P < .001). PTG instruments had a 2-stage transformation behavior. There was no significant difference in the austenite finish between unused files and instruments subjected to the fatigue process. CONCLUSIONS PTG files were significantly more flexible and resistant to fatigue than PTU files. PTG exhibited different phase transformation behavior than PTU, which may be attributed to the special heat treatment history of PTG instruments. PTG may be more suited for preparing canals with a more abrupt curvature.

Surface alteration of human tooth enamel subjected to acidic and neutral 30% hydrogen peroxide

OBJECTIVES To investigate the effects of acidic and neutral 30% hydrogen peroxide (HP) on human tooth enamel in terms of chemical structure, mechanical property, surface morphology and tooth colour. METHODS Twenty-seven human dental blocks were obtained from premolars and randomly divided into three groups (n=9): Group acidic HP (30% HP, pH≈3.6), Group neutral HP (30% HP, pH≈7.0) and Group DW (distilled water, pH≈6.8). Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy, atomic force microscopy (AFM) investigation, microhardness test and colour measurements were carried out before and after treatments. ATR-FTIR and Raman spectroscopy were analysed and then the carbonate:mineral ratio (C:M), Raman absolute intensity (RAI), Raman relative intensity (RRI), and laser-induced fluorescence intensity (FI) were obtained for evaluation. RESULTS The C:M, percentage microhardness and percentage RRI of group acidic HP decreased more significantly than those of group neutral HP (P=0.02, P=0.001, P<0.001, respectively) and group DW (P=0.01, P=0.008, P<0.001, respectively). Whilst group neutral HP and group DW had no statistical difference in above terms (P=0.818, P=0.528, P=0.158, respectively). Significant morphological alterations were observed in group acidic HP. Group acidic HP and neutral HP had no significant difference in percentage FI (P=0.652) and ΔE (P=0.906). CONCLUSIONS This study suggested that neutral 30% HP had the same efficiency in tooth bleaching and it caused less deleterious effects on enamel than acidic 30% HP.

Dentine remineralization induced by two bioactive glasses developed for air abrasion purposes

OBJECTIVES The present study aimed to evaluate dentine remineralization through a 7-day period of artificial saliva (AS) storage induced by bioactive glass 45S5 (BAG) and by bioactive glass modified with soda-lime spherical glass. METHODS Partially demineralized dentine disks were treated by BAG or the spherical-glass modified bioactive glass (M-BAG) and subsequently immersed in AS for 7 days. Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) was used to quantitatively analyse the mineral variation of the dentine surface by calculating the spectra parameters. X-ray diffraction (XRD) and energy-dispersive X-ray analysis (EDX) were performed on completely demineralized dentine to confirm the apatite formation. The roughness of the dentine surface was evaluated by atomic force microscopy (AFM) and the morphology was also examined by scanning electron microscopy (SEM). RESULTS ATR-FTIR showed a significant increase of the mineral matrix area ratio in dentine specimens treated with the two bioactive glasses subsequent to 7 days of AS storage. The XRD spectrum exhibited apatite growth and mineral elements could be found on completely demineralized samples analysed by EDX after remineralization treatments. The dentine specimens treated with bioactive glass showed lower roughness, and most of the dentinal tubules appeared completely occluded during the AFM and SEM examination. CONCLUSIONS Although the concentration of bioactive glass in the M-BAG is 60% of that contained in the original version, both formulations have similar potential in dentine remineralization. These bioactive powders developed for air-abrasive use may be considered as innovative bioactive materials for therapeutic remineralization of dental hard tissues.

In Vitro Cytotoxicity of Calcium Silicate–containing Endodontic Sealers

INTRODUCTION The cytotoxicity of 2 novel calcium silicate-containing endodontic sealers to human gingival fibroblasts was studied. METHODS EndoSequence BC (Brasseler, Savannah, GA), MTA Fillapex (Angelus Indústria de Produtos Odontológicos S/A, Londrina, PR, Brazil) and a control sealer (AH Plus; Dentsply DeTrey GmbH, Konstanz, Germany) were evaluated. Human gingival fibroblasts were incubated for 3 days both with the extracts from fresh and set materials in culture medium and cultured on the surface of the set materials in Dulbecco-modified Eagle medium. Fibroblasts cultured in Dulbecco-modified Eagle medium were used as a control group. Cytotoxicity was evaluated by flow cytometry, and the adhesion of the fibroblasts to the surface of the set materials was assessed using scanning electron microscopy. The data of cell cytotoxicity were analyzed statistically using a 1-way analysis of variance test at a significance level of P < .05. RESULTS Cells incubated with extracts from BC Sealer showed higher viabilities at all extract concentrations than cells incubated with extracts from freshly mixed AH Plus and fresh and set MTA Fillapex, esspecially for the high extract concentrations (1:2 and 1:8 dilutions). Extracts from set MTA Fillapex of 2 weeks and older were more cytotoxic than extracts from freshly mixed and 1-week-old cement. With extract concentrations of 1:32 and lower, MTA Fillapex was no longer cytotoxic. After setting, AH Plus was no longer cytotoxic, and the fibroblast cells grew on set AH Plus equally as well as on BC Sealer. CONCLUSIONS BC Sealer and MTA Fillapex, the 2 calcium silicate-containing endodontic sealers, exhibited different cytotoxicity to human gingival fibroblasts.