Dentin Bonding Testing Using a Mini-interfacial Fracture Toughness Approach

Abstract

Measurement of interfacial fracture toughness (iFT) is considered a more valid method to assess bonding effectiveness as compared with conventional bond strength testing. Common fracture toughness tests are, however, laborious and require a relatively bulky specimen size. This study aimed to evaluate a new simplified and miniaturized iFT (mini-iFT) test. Four dentin adhesives, representing the main adhesive classes, and 1 glass ionomer cement were applied onto flat dentin. Mini-iFT (1.5 × 2.0 × 16 to 18 mm) and microtensile bond strength (µTBS; 1.5 × 1.5 × 16 to 18 mm) specimens were prepared from the same tooth. For the mini-iFT specimens, a single notch was cut at the adhesive-dentin interface with a 150-µm diamond blade under water cooling; the specimens were loaded until failure in a 4-point bending test setup. Finite element analysis was used to analyze stress distribution during mini-iFT testing. The correlation between the mean mini-iFT and µTBS was examined and found to be significant; a strong positive correlation was found (r(2) = 0.94, P = 0.004). Weibull data analysis suggested the mini-iFT to vary less than the µTBS. Both the mini-iFT and the µTBS revealed the same performance order, with the 3-step etch-and-rinse adhesive outperforming the 2-step self-etch and 2-step etch-and-rinse adhesive, followed by the 1-step SE adhesive and, finally, the glass ionomer cement. Scanning electron microscopy failure analysis revealed the adhesive-dentin interface to fail more at the actual interface with the mini-iFT test, while µTBS specimens failed more within dentin and composite. This finding was corroborated by finite element analysis showing stress to concentrate at the interface during mini-iFT loading and crack propagation. In conclusion, the new mini-iFT test appeared more discriminative and valid than the µTBS to assess bonding effectiveness; the latter test nevertheless remains more versatile. Specimen size and workload were alike, making the mini-iFT test a valid alternative for the popular µTBS test.

Mini-interfacial fracture toughness as a new validated enamel-bonding effectiveness test

“…The new mini-iFT test was before validated to assess bonding effectiveness to dentin (Pongprueksa et al, 2016);…”

“…After testing, all fractured surfaces were processed for SEM (JSM-6610LV; JEOL, Tokyo, Japan) using common specimen processing, including fixation, dehydration and gold-sputter coating, this to determine the fracture location, the crack propagation and possible specimen imperfections. Finally, the exact dimensions of the mini-iFT notch were measured using a measuring optical microscope (400-NRC; Leitz, Wetzlar, Germany) at 250 Â magnification, after which K Ic was calculated in MPa m 1/2 , as described in detail in the previous study (Pongprueksa et al, 2016).…”

“…However, a major disadvantage of this conventional iFT test method is that it requires a relatively large interfacial area. Therefore, a new mini-iFT test was recently developed and validated on its potential to assess bonding effectiveness to dentin (Pongprueksa et al, 2016); specimen preparation was found to be easier, entailing a much smaller interfacial area. Moreover, a significant (po0.001) correlation of 80% was found between the mini-iFT data obtained at dentin and the corresponding mTBS data; the method revealed a higher discriminative power and appeared to generate more reliable data associated with failure at the actual interface.…”

“…In light of the recently developed mini-iFT test (Pongprueksa et al, 2016), we aimed with this study to determine the mini-iFT of adhesive-enamel interfaces prepared using dental adhesives representing the different adhesive classes, in a similar way as in our previous study. The hypothesis advanced was that no difference in mini-iFT at enamel exists for the different adhesives tested.…”

Bonding measurement —Strength and fracture mechanics approaches

“…They also recommended that toughness approach should possibly be used to compare studies instead of strength since toughness values are intrinsic to the materials 34,35) . Recently, many studies have applied fracture mechanics concept to the tests and recommended that they were more appropriate approaches to determine the bonding quality between two materials compared with traditional tests such as microtensile or shear bond tests [37][38][39][40][41] . There should be further studies on the interfacial toughness to compare the reliability of this technique with other different test methods and on many types of materials and products.…”