In vitro microleakage of dentin adhesives.

This in vitro study measured the microleakage of current dentin bonding agents and glass-ionomer bases. Freshly extracted human molars were prepared to a flat surface, and dentin adhesives and composite resins were applied in a plastic matrix. Samples were stored in water at 37 degrees C, thermocycled, stained with AgNO3, embedded in epoxy resin, and sectioned for evaluation of stain penetration at the composite resin/tooth interface. The reliability index of the dentin adhesives varied significantly between materials. The enamel control had essentially no microleakage, and the aluminum oxalate dentin adhesive on dentin had significantly less microleakage than other dentin adhesives tested. Present dentin adhesives were unable to prevent, but may reduce, microleakage.     

In vitro performance of nano-heterogeneous dentin adhesive

Water is ubiquitous in the mouths of healthy individuals and routinely interferes with efforts to bond restorations to dental tissues. Our previous studies using tapping-mode atomic force microscopy (TMAFM) have shown that nanophase separation is a general feature of cross-linked polymethacrylates photocured in the presence of water. To explore the relationship between nanophase separation in dentin adhesives and their long-term mechanical properties, we evaluated model adhesives after 3 months of aqueous storage. The degree of contrast in the TMAFM phase image depended on the formulations used, ranging from 'not observable' to 'very strong'. Correspondingly, the mechanical properties of these model adhesives varied from 'minimal change' to 'significant depreciation'. The results support the hypothesis that a high degree of heterogeneity at the nano-scale is associated with poor mechanical durability in these model adhesives.     

In vitro interfacial relationship between human dentin and one-bottle dental adhesives.

OBJECTIVES: One-bottle dentin adhesives combine primer and adhesive resin into a single solution. This study was conducted to determine the bond strengths to dentin of four one-bottle bonding systems and to evaluate their SEM interfacial morphology. The hypothesis to be tested was that the water-based bonding system would produce lower bond strengths and less complete penetration into dentin than other bonding systems that are dissolved in organic solvents. METHODS: Forty extracted molars were ground to expose middle dentin and were randomly assigned to four groups (n = 10): Group 1--Experimental Single Bond (3M Dental Products Division); Group 2--Prime&Bond 2.1, pre-launch version (Dentsply DeTrey); Group 3--Syntac Single-Component (Vivadent); Group 4--Tenure Quik with Fluoride (Den-Mat Co.) The surfaces were treated according to manufacturers' instructions. After 24 h in water, the specimens were thermocycled, and the bond strengths were measured in shear. The data were analyzed with ANOVA and Duncan's test at a confidence level of 95%. Further, the adhesives were also applied to 600 microns thick dentin disks. After preparing polished cross sections, the bonded interfaces were demineralized, deproteinized, and observed under a FE-SEM. The morphological appearance of the resin-dentin interface surfaces was compared by screening the entire resin-dentin interface for each specimen. RESULTS: Two morphological characteristics were evaluated: 1) the depth of resin penetration into the tubules and 2) the thickness and density of the resin-dentin interdiffusion zone. Single Bond showed statistically higher mean shear bond strengths (p < 0.001) compared to the other three materials. Specimens prepared with Syntac Single-Component and Prime&Bond 2.1 were ranked in the intermediary Duncan's grouping. Specimens bonded with Tenure Quik with Fluoride exhibited the lowest mean shear bond strength. All materials penetrated and hybridized dentin. Single Bond formed a thick layer of adhesive resin on the top of the interdiffusion area without debonding, whereas some areas of debonding were observed on the top of the hybrid layers for Prime&Bond 2.1 and Syntac Single-Component. For the water-based adhesive Syntac Single-Component, the interdiffusion zone displayed a thick filigree pattern, containing scattered open spaces between the resin-enveloped collagen fibers. Tenure Quik with Fluoride did not thoroughly infiltrate the demineralized dentin zone, resulting in wide gaps in all specimens. Prime&Bond 2.1 formed the shortest resin tags, whereas Syntac Single-Component formed the longest resin tags. SIGNIFICANCE: Bonding to dentin remains unpredictable using one-bottle bonding systems. The chemistry of each individual material may be more important than the type of solvent.     

In vitro cytotoxicity of one-step dentin bonding systems

The cytotoxicity of resinous monomers may vary on mixing, calling into question the cytotoxicity of the new dentin bonding agents that are mixed in a single vial. The cytotoxicity of fourth and fifth generation dentin bonding agents was compared in vitro. All-Bond 2, One-Step, Scotchbond Multi-Purpose, Scotchbond One, Syntac, Syntac Single Component, Tenure, and Tenure Quick were tested uncured. The cytotoxicity of several dilutions of fourth generation dentin primer, dentin bonding agent, dentin primer + dentin bonding agent, and fifth generation single component products diluted at 10(-1) to 10(-8) in culture medium was recorded with a MTT assay on L929 fibroblasts. Only one synergistic (increased cytotoxicity after mixing primer and bonding agent) cytotoxic effect was observed with Tenure at 10(-5) dilution. An antagonistic effect (decreased cytotoxicity after mixing primer and bonding agent) was observed with All-Bond 2 between 10(-4) and 10(-8) dilutions. Scotchbond and Syntac fifth generation dentin bonding agents were less cytotoxic than their fourth generation counterparts. All-Bond and Tenure fifth generation dentin bonding agents were more cytotoxic than their fourth generation counterparts only in low dilutions. Clinical studies should confirm these good results, because no dramatic synergistic cytotoxic effect could be detected.     

In vitro cytotoxicity of six dentin bonding agents

The cytotoxicity of six dentin bonding agents (Syntac, Solobond, Bond 1, Scotchbond 1, Heliobond and F-2000) was tested against an established cell line, L929. Under aseptic conditions 3, 5 and 10 microL dentin bonding agents were placed in the centre of Petri dishes. Each dish was covered with a 5-mL suspension of fibroblasts at a concentration of 40 000 cells mL(-1). The cultures were incubated at 37 degrees C and cytotoxicity was assessed by a quantitative technique at 24 and 72 h. All the dentin bonding agents were found to be cytotoxic. Scotchbond 1 and F-2000 showed the highest cytotoxicity followed by Solobond and Bond 1. Heliobond and Syntac were the least toxic materials.     

In vitro study of bacterial invasion in radicular dentin

The purpose of this study was to investigate whether plaque bacteria invade exposed radicular dentin after root planing or chemical root treatment in vitro. Pieces of dentin were cut out from impacted third molars. The surface of all dentin pieces was treated with sandpaper (#240) so as to make the surface roughness of dentin pieces equal to that of the root surface after root planing (RP surface). Half of the dentin pieces were treated with citric acid (pH 1.0) for 3 minutes (CA surface). After sterilization, each dentin piece was incubated at 37 degrees C in a culture medium inoculated with either S. mutans or S. sanguis. After 1, 3, 7 and 28 days of incubation, the invasion of microorganisms into the dentinal tubules was histologically examined using a light microscope. The following results were obtained. 1. The invasion of S. mutans and S. sanguis into the dentinal tubules was observed at 1, 3, 7 and 28 days. The depth and number of bacterial invasion into the dentinal tubules were positively correlated with incubation time on CA surfaces but not with RP surfaces. 2. The depth and the number of bacterial invasion into the dentinal tubules were higher on the CA surfaces than the RP surfaces. 3. Since the citric acid treatment of scaled and root planed root surfaces may accelerate bacterial invasion from treated root surfaces, the use of citric acid might be harmful in patients with inadequate plaque control.     

In vitro shear bond strength of dentin adhesives.

This in vitro study compared the shear bond strengths of current dentin adhesives. Freshly extracted human molars were prepared to a flat surface and treated with dentin adhesives and composite resin light polymerized in a plastic matrix. Completed samples were stored in 37 degrees C water and thermocycled 1,500 times. Samples were sheared at the tooth/composite resin interface using a wire loop. The reliability index varied significantly between materials. Large coefficients of variation were found for all dentin adhesives. One dentin adhesive was able to achieve a bond strength to dentin that was 47% of the control bond strength of enamel.     

In vitro evaluation of two new dentin adhesive systems

Two new experimental dentin adhesive systems were evaluated to determine in vitro dentin bond strengths and marginal microleakage. Scanning electron microscopy examinations were also conducted on one of the systems that was designed to modify the smear layer. Mean shear bond strength for the two experimental systems were 6.77 +/- 1.94 MPa and 18.73 +/- 2.4 MPa. Marginal microleakage from the enamel margin was not observed and the experimental primer system limited leakage from the dentin margins. The SEM examinations showed that the primer did not significantly alter the smear layer on the prepared dentin surface.     

In vitro stimulation of human gingival epithelial cell attachment to dentin by surface conditioning.

BACKGROUND: Chemical root conditioning is widely used to improve the outcome of regenerative periodontal therapies by favoring the attachment of the regenerated periodontal structures. Although the effect of root conditioning on periodontal mesenchymal cells is well documented, very little is known about its potential effect on the re-formation of the junctional epithelium, a crucial event for the protection of the wound. The goal of the present study was to test in vitro the consequences of dentin conditioning with citric acid or minocycline on the attachment kinetics and morphology of human gingival keratinocytes (HGK). METHODS: The attachment kinetics of HGK to samples of powdered human dentin (particle size 44 to 76 microm) were examined by use of 3H-labeled cells. The morphology of attached epithelial cells was then determined by scanning electron microscopy (SEM). RESULTS: When the initial adhesion kinetics of cells on untreated dentin were tested, the percentage of attached HGK proved to be dependent on the number of plated cells and the time of incubation (from 0 to 12 hours). Conditioning the dentin by 3% citric acid or by minocycline-HCl (at 0.01, 0.1, or 2.5%) significantly increased (P <0.005) keratinocyte attachment beyond 6 hours, without notable differences between the 2 substances at any concentration. The attachment kinetics of HGK preincubated for 24 hours by 10 microg/ml minocyline-HCl on untreated dentin was found to be similar to that observed for non-preincubated cells. These results are in agreement with the SEM observations: indeed, the surface conditioning of dentin significantly modified the morphology of attached HGK, whereas the preincubation of these cells with minocyline-HCl did not. CONCLUSIONS: These results suggest that minocycline-HCl does not exert a direct effect on human gingival epithelial cells. In contrast, conditioning the dentin by citric acid or by minocycline stimulates the attachment of HGK, which could lead to a rapid periodontal healing by favoring the re-formation of a junctional epithelium.     

In vitro antimicrobial effect of bacteriophages on human dentin infected with Enterococcus faecalis ATCC 29212

This study assessed the effect of bacteriophages on the viability of Enterococcus faecalis. Human dental roots were inoculated with a suspension of E. faecalis at three different multiplicities of infection - 0.1, 1.0 and 10.0. The phage lysate was able to significantly inhibit bacteria growth when incubated at the multiplicities of infection of 1.0, 10.0 and 0.1. The dental roots were also inoculated with bacteria for 6 days to allow bacterial penetration into the teeth tubules. Addition of the phage lysate to the roots following the 6-day incubation period led to a substantial reduction in bacteria viability. Phage therapy may be an important alternative for the treatment of root canal infections refractory to conventional endodontic therapy.     

新型牙本质黏结剂体外细胞毒性研究

目的：评价一种新型牙本质黏结剂的细胞毒性，并与商品化的两种黏结剂细胞毒性进行比较。方法：采用琼脂覆盖法和四甲基偶氮唑盐(MTT)比色法，评价新型牙本质黏结剂优邦(UB)和商品化黏结剂Adper Prompt自酸蚀黏结剂(AP)与Prime＆Bond NT(PB)在人牙本质片上使用后，对L929小鼠成纤维细胞的毒性作用。结果：MTT实验中三种牙本质黏结剂细胞毒性均为1级；琼脂覆盖实验中，三种材料两种厚度牙本质片均出现脱色区和部分细胞溶解，细胞毒性评价均为1级。结论：新型牙本质黏结剂具有轻做的细胞毒性，UB对牙髓组织的影响还有待进一步研究。     

In vitro push-out strength of seven luting agents to dentin

PURPOSE: New luting agents, described as resin-modified glass-ionomer cements and compomers, have been developed during the last decade to improve the retention of cemented restorations. The aims of this study were to (1) compare the push-out strength of these new luting materials against both conventional cements and bonding luting agents, and (2) evaluate the influence of dentin surface treatment on both glass-ionomer cement and 4-META adhesive resin push-out strength. MATERIALS AND METHODS: Conical standardized cavities were drilled in the center of coronal dentin disks. Ninety sandblasted Ni-Cr inlays, divided into nine batches, were luted into the cavities according to the surface treatment and the nature of the following luting agents: zinc phosphate cement, zinc polycarboxylate cement, type 1 glass-ionomer +/- polyacrylic acid, resin-modified glass-ionomer, polyacid-modified composite resin, filled bis-GMA phosphate ester resin, and 4-META adhesive resin +/- application of activated monomer. Each specimen was placed in a holding device, and a steel rod was used to apply a force on the inlay until rupture occurred. The push-out strength was calculated, and the failure mode was controlled. RESULTS: There were significant differences between some of the groups. The highest push-out strength was achieved by the 4-META adhesive resin after application of activated monomer. The lowest value was attained with zinc phosphate and polycarboxylate cements. CONCLUSION: Both resin-modified glass-ionomer and polyacid-modified composite resin luting materials exhibited a push-out strength similar to resin-based materials. Specific dentin surface treatments significantly enhanced the push-out strengths of glass-ionomer cement and 4-META adhesive resin.     

In vitro durability of one-bottle resin adhesives bonded to dentin

Recently, one-bottle resins adhesives have been developed to reduce the number of clinical steps of resin application. They are now widely used in clinical dental practice. However, little is known regarding the detailed mechanism of bond degradation. Therefore, this study evaluated the durability of one-bottle resin adhesives using long-term water storage testing. Resin-dentin bonded specimens were prepared using five commercially available one-bottle resin adhesives. The specimens were sectioned perpendicular to the adhesive interface to produce beams and stored in distilled water for 24 hours (control), 100, 200, and 300 days. After the water storage, each beam was subjected to a microtensile bond test and then SEM fractography was performed on the fractured surface. Compared to the bond strength at 24 hours after bonding (control), the bond strength of all tested adhesives were significantly decreased after 100 or more days in water. SEM fractography revealed a typical type of deterioration in the adhesive-composite interface that might cause a decline in bond strength after aging.     

The kinetics of mineralization of human dentin in vitro

The prospect of restoration of damaged dental tissues has recently attracted great interest. An understanding of the remineralization of human dentin in vitro was attempted by using super-saturated calcium phosphate solutions at sustained supersaturation by means of a constant solution composition method. The direct growth of HAP from solutions of low supersaturation on powdered whole human dentin was confirmed. Moreover, it was found that the kinetics were similar to those of the seeded growth at synthetic HAP. A high apparent activation energy pointed to a surface-controlled mechanism.     

五种牙本质粘接剂体外细胞毒性研究

目的 对5种牙本质粘接剂的体外细胞毒性进行对比研究,为临床应用提供参考依据.方法 采用体外细胞培养技术和四甲基偶氮唑盐(MTT)比色法,观察第7代牙本质粘接剂Clearfil tri-S Bond和4种第6代牙本质粘接剂Clearfil SE Bond、Adper Prompt、ONE UP BOND F、XenoⅢ粘接剂浸提液对L929小鼠成纤维细胞生长的影响,测定各组吸光度值(OD值),计算L929小鼠成纤维细胞的相对增殖率,用5级毒性分类法评级,并进行统计分析.结果 各组细胞生长均较好,Clearfil tri-S Bond组和Clearfil SE Bond组的OD值显著高于其它各组的OD值.结论 5种牙本质粘接剂的体外细胞毒性均较弱,其中第7代牙本质粘接剂Clearfil tri-S Bond和第6代牙本质粘接剂Clearfil SE Bond的细胞毒性最低.     

In vitro study of DP-bioglass paste for treatment of dentin hypersensitivity

Sealing of exposed dentinal tubules is generally considered the most effective strategy to treat dentin hypersensitivity. On this account, we fabricated a DP-bioglass paste that created a homogeneous blockage on open dentinal tubules and formed a deep precipitate within dentinal tubules. DP-bioglass paste was prepared by mixing 20% to 60% phosphoric acid and DP-bioglass to treat dentin surfaces. CO2 laser irradiation was used to melt the DP-bioglass paste. The results demonstrated that 30% phosphoric acid was the optimum concentration to produce homogeneous occlusion on exposed dentinal tubules and 60 microm of sealing depth. CO2 laser irradiation could melt the DP-bioglass paste and create about 10 microm of sealing depth. Moreover, temperature rise during CO2 laser irradiation was only 4.86 +/- 0.47 degrees C. The results presented in this work suggested that DP-bioglass paste could produce considerable sealing depth in dentinal tubules with the potential of prolonging the therapeutic effect efficaciously.