Microtensile bond strength tests: scanning electron microscopy evaluation of sample integrity before testing

The failure of a certain number of microtensile specimens during their preparation and before loading is a common and undesirable occurrence. This study was aimed at observing, under a scanning electron microscope, enamel and dentin microtensile specimens, in order to find structural faults that might be responsible for their premature failure. In a sample of 80 sticks, none of the specimens was found to be free of defects. These may consist of microcracks in enamel, most often at the periphery of the stick, or in dentin at the level of hybrid layer. Gaps were often seen at the interfaces between the substrates. Voids were sometimes visible within the resin composite thickness. Enamel specimens tended to exhibit more defects than dentin specimens. It is fair to suspect that, because of the brittleness of the tissue, enamel microtensile specimens are intrinsically more prone to failure, thus yielding bond strengths which are not significantly higher than those measured on dentin specimens. This leads one to question the reliability of the microtensile method for testing adhesion on enamel. It seems sensible to develop a method for a quantitative assessment of specimens integrity before loading as a possible predictor for their performance under load.     

Evaluation of bond strength of various margin ceramics to a zirconia ceramic

OBJECTIVE: This study evaluated the bond strengths of four different margin ceramics based on fluoroapatite and feldspath to a zirconia ceramic. METHODS: Zirconia cores (Zirconzahn) (N=28, n=7/margin ceramic group) were fabricated according to the manufacturers' instructions (diameter: 4mm; thickness: 2mm) and ultrasonically cleaned. Four different margin ceramics (thickness: 5mm) (Cerabien Zr, Noritake; Ceramco PFZ, Ceramco; e.max, Ivoclar Vivadent and Triceram, Dentaurum) were vibrated and condensed in a stainless steel mould and fired onto their zirconia cores. After trying the specimens in the mould for minor adjustments, they were again ultrasonically cleaned and embedded in PMMA. The specimens were stored in distilled water at 37 degrees C for 1 week and shear bond strength (MPa+/-S.D.) tests were performed in a universal testing machine (crosshead speed: 0.5mm/min). Failure modes were recorded under SEM. RESULTS: Significant effect of margin ceramic types were found on the bond strength values (P<0.05). The mean bond strength values of Ceramco margin ceramic to zirconia was significantly lower (25.4+/-4.5MPa) (P<0.05) than those of Cerabien (31.6+/-6.4MPa), e.max (35.9+/-8.4MPa), and Triceram margin ceramic (38.8+/-7.1MPa) systems. CONCLUSIONS: Margin ceramics, compatible with zirconia framework material tested in the present study, exhibited high bond strength values. Variations in thermal expansion coefficients might influence their bond strength values.     

Dentin treatment with MMPs inhibitors does not alter bond strengths to caries-affected dentin

OBJECTIVES: This study aimed to investigate if the use of protease inhibitors (EDTA and chlorhexidine) may influence microtensile bond strength (MTBS) of an etch-and-rinse adhesive system to caries-affected human dentin. METHODS: Flat middle coronal dentin surfaces with a central region of caries-affected dentin surrounded by sound dentin were bonded with Adper Scotchbond 1 after: (1) etching with 35% H3PO4; (2) etching with 0.1M EDTA and (3) 35% H3PO4-etching followed by 5% chlorhexidine application. Resin composite build-ups were constructed incrementally and trimmed to yield hourglass specimens (0.8mm2 bonded area) that contained sound or caries-affected dentin (confirmed after debonding by microhardness measurements - KHN). Bonded specimens were tensioned at 0.5mm/min. Data were analyzed by ANOVA and multiple comparisons tests (p<0.05). Failure mode analysis was performed by scanning electron microscopy (SEM). RESULTS: H(3)PO(4), EDTA and chlorhexidine pre-treatments yielded similar MTBS values, in both dentin substrates. Bond strength to sound dentin was significantly higher than that to caries-affected dentin after H3PO4-etching. Caries-affected dentin exhibited lower KHN than sound dentin. CONCLUSIONS: Conditioning of caries-affected dentin with EDTA or a combined use with H3PO4 and chlorhexidine may be proposed as these protease inhibitors do not reduce MTBS to caries-affected dentin if compared to conventional H3PO4 treatment.     

Influence of drying time and temperature on bond strength of contemporary adhesives to dentine

Objectives

To evaluate the bond strength (μTBS) of self-etching adhesives in different solvent evaporation conditions.

Methods

Flat dentine surfaces from extracted human third molars were bonded with: (1) 2 two-steps self-etching adhesives (Clearfil SE Bond—CSEB); (Protect Bond—PB) and (2) 2 one-step self-etch systems (Adper Prompt L Pop—ADPLP); (Xeno III—XIII). Bonded dentine surfaces were air-dried for 5 s, 20 s, 30 s or 40 s at either 21 °C or 38 °C. Composite build-ups were constructed incrementally. After storage in water for 24 h at 37 °C, the specimens were prepared for microtensile bond strength testing. Data were analyzed by two-way ANOVA and Student–Newman–Keuls at α = 0.05.

Results

CSEB and PB performed better at warm temperature with only 20 s of air-blowing. The bond strength increased when XIII was performed at warm temperature at 40 s air-blowing. Extended air-blowing not affect the performance of ADPLP, except at 30 s air-blowing time at warm temperature.

Conclusions

The use of a warm air-dry stream seems to be a clinical tool to improve the bond strength to self-etching adhesives.     

Influence of different periodontal curette grips on the outcome of mechanical non-surgical therapy

AIM: To determine to whether successful scaling and root planing (SRP) depends upon the grip used on the periodontal curette. METHODS: The hand grips used by dentists for holding periodontal curettes were examined and the dentists were allocated to one of two matched groups, one in which they used a modified pen grip, the other in which they did not. Using a split-mouth technique, patients scheduled for SRP had one quadrant treated by a dentist from each group. Instrument application force was recorded as were periodontal measures at operation and 3-months later. RESULTS: During scaling, forces reached a mean of 0.77N in dentists using a curette with a non-pen grip and 0.54N in those using a pen grip and during root planing, 0.93N and 0.64N respectively. These forces were statistically significantly different between the two groups. Pocket depth reduction in teeth treated by the two groups was similar but attachment levels were statistically significantly different. CONCLUSIONS: Instrument grip had a significant effect on response to SRP, suggesting that dentists using a modified pen grip achieved better clinical results.     

不同SY-1硅橡胶被覆厚度对三明治式硅橡胶结构拉伸性能的影响

目的：比较不同SY-1硅橡胶被覆厚度的三明治硅橡胶结构的拉伸性能。方法：在相同条件下对表面被覆SY-1厚度分别为0mm,1mm,1.5mm,2mm的三明治式硅橡胶试件进行拉伸强度、扯断伸长率的测定,并对结果进行统计学分析。结果：被覆1mm SY-1硅橡胶的试件与单纯的GP-084泡沫硅橡胶试件拉伸强度及扯断伸长率的差异有显著性（p〈0.05）;被覆1.5mm SY-1试件与被覆1mm的SY-1试件的拉伸强度的差异无显著性（p〉0.05）,但是扯断伸长率的差异具有显著性（p〈0.05）;被覆2mmSY-1试件与被覆1mm SY-1试件的拉伸强度及扯断伸长率的差异有显著性（p〈0.05）。结论：由SY-1硅橡胶和GP-084泡沫硅橡胶组成的三明治式结构可以明显增加泡沫硅橡胶较低的拉伸强度和扯断伸长率。     

SHEAR BOND STRENGTH OF METALLIC BRACKETS PHOTO-ACTIVATED WITH LIGHT-EMITTING DIODE (LED) AT DIFFERENT EXPOSURE TIMES

The purpose of this study was to compare the shear bond strength of orthodontic metallic brackets photo-activated with two different light-curing sources at different exposure times: halogen light (XL 1500, 3M ESPE) and LED light (Ortholux, 3M Unitek). Sixty bovine permanent lower incisors were inserted into PVC tubes containing plaster. The buccal surfaces were cleaned with pumice and water, and then etched with 37% phosphoric acid gel. The XT Primer bonding agent (3M Unitek) was applied to the enamel surfaces and the metallic pre-coated brackets (Transbond APC II system, 3M Unitek) were attached to upper central incisors. The teeth were randomly divided into four groups (n=15). In Group I (Control), halogen light was used for 40 seconds, while in Groups II, III, and IV were light-cured with LED light unit for 40, 10, and 5 seconds, respectively. The teeth were stored in distilled water at 37°C for 24 hours. The brackets were submitted to shear bond strength test in universal testing machine (Instron) at a crosshead speed of 0.5 mm/minute. Shear bond strength means (MPa) were 4.87 for Group I; 5.89 for Group II; 4.83 for Group III, and 4.39 for Group IV. Tukey''s test detected no statistically significant differences among the groups regarding the shear bond strength (p>0.05). Neither of the types of light-curing sources or exposure times influenced the shear bond strength of metallic brackets.     

The effect of denture base surface pretreatments on bond strengths of two long term resilient liners

PURPOSE

Purpose of this study was to evaluate effect of two surface treatments, sandblasting and monomer treatment, on tensile bond strength between two long term resilient liners and poly (methyl methacrylate) denture base resin.

MATERIALS AND METHODS

Two resilient liners Super-Soft and Molloplast-B were selected.Sixty acrylic resin (Trevalon) specimens with cross sectional area of 10×10 mm were prepared and divided into two groups of 30 specimens each. Each group was surface treated (n = 10) by sandblasting (250 µ alumina particles), monomer treatment (for 180 sec) and control (no surface treatment). Resilient liners were processed between 2 poly(methyl methacrylate) surfaces, in the dimensions of 10×10×3 mm. Tensile strength was determined with Instron Universal testing machine, at a crosshead speed of 5 mm/min; and the modes of failure (adhesive, cohesive or mixed) were recorded. The data were analyzed using one-way ANOVA, followed by Tukey HSD test (α = 0.05).

RESULTS

Monomer pretreatment of acrylic resin produced significantly higher bond strengths when compared to sandblasting and control for both resilient liners (P < .001). Sandblasting significantly decreased the bond strength for both the liners when compared to monomer pretreatment and control (P < .001). Mean bond strength of Super-Soft lined specimens was significantly higher than Molloplast-B in various surface treatment groups (P < .05).

CONCLUSION

Surface pretreatment of the acrylic resin with monomer prior to resilient liner application is an effective method to increase bond strength between the base and soft liner. Sandblasting, on the contrary, is not recommended as it weakens the bond between the two.     

An effect of immediate dentin sealing on the shear bond strength of resin cement to porcelain restoration

PURPOSE

The aim of this study was to determine differences in shear bond strength to human dentin using immediate dentin sealing (IDS) technique compared to delayed dentin sealing (DDS).

MATERIALS AND METHODS

Forty extracted human molars were divided into 4 groups with 10 teeth each. The control group was light-cured after application of dentin bonding agent (Excite® DSC) and cemented with Variolink® II resin cement. IDS/SE (immediate dentin sealing, Clearfil™ SE Bond) and IDS/SB (immediate dentin sealing, AdapterTM Single Bond 2) were light-cured after application of dentin bonding agent (Clearfil™ SE Bond and Adapter™ Sing Bond 2, respectively), whereas DDS specimens were not treated with any dentin bonding agent. Specimens were cemented with Variolink® II resin cement. Dentin bonding agent (Excite® DSC) was left unpolymerized until the application of porcelain restoration. Shear strength was measured using a universal testing machine at a speed of 5 mm/min and evaluated of fracture using an optical microscope.

RESULTS

The mean shear bond strengths of control group and IDS/SE group were not statistically different from another at 14.86 and 11.18 MPa. Bond strength of IDS/SE group had a significantly higher mean than DDS group (3.14 MPa) (P < .05). There were no significance in the mean shear bond strength between IDS/SB (4.11 MPa) and DDS group. Evaluation of failure patterns indicates that most failures in the control group and IDS/SE groups were mixed, whereas failures in the DDS were interfacial.

CONCLUSION

When preparing teeth for indirect ceramic restoration, IDS with Clearfil™ SE Bond results in improved shear bond strength compared with DDS.