Effect of Two Microshear Test Devices on Bond Strength and Fracture Pattern in Primary Teeth

Abstract

This in vitro study evaluated the influence of two devices for application of shear load in microshear tests on bond strength and fracture pattern of primary enamel and dentin. Eighty primary molars were selected and flat enamel (40 teeth sectioned mesio-distally) and dentin (40 teeth sectioned transversally) surfaces were obtained. Both surfaces were polished to standardize the smear layer. Two-step etch-and-rinse adhesive systems (Adper Single Bond and XP Bond) were used. Polyethylene tubes was placed over the bonded surfaces and filled with composite resin. The microshear testing was performed after storage in water (24 h/37 °C) using two devices for application of microshear loads: a notched rod (Bisco Shear Bond Tester) or a knife edge (Kratos Industrial Equipment). Failure modes were evaluated using a stereomicroscope. Bond strength data were subjected to ANOVA and chi-square test to compare the failure mode distributions (α=0.05). No significant differences were observed between the groups for dentin and enamel bond strength or fracture patterns (p>0.05). The predominant failure mode was adhesive/mixed. In conclusion, the devices for application of shear loads did not influence the bond strength values, regardless of adhesive system and substrate.

Effect of Silane Heat Treatment by Laser on the Bond Strength of a Repair Composite to Feldspathic Porcelain

“…Bond strength tests are simple tools used to evaluate the effectiveness of adhesive systems . Microadhesion tests use specimens with a small cross‐sectional area, which could prevent cohesive failures and a heterogeneous distribution of stresses.…”

Influence of a cylindrical crosshead on shear bond testing of composite-tooth interfaces

“…When the shear device applies forces on larger contact areas such as with the wire loop 9) , stainless steel tape 10) and the Ultradent device 11) , higher shear bond strength values are expected due to a more even distribution of the forces 12) . However, bond strength values can be affected by specimen size, loading length, adhesive layer thickness, and loading site 2) .…”

“…However, bond strength values can be affected by specimen size, loading length, adhesive layer thickness, and loading site 2) . In comparison to a knife edge, the use of a wire-loop may decrease stress concentration at the adhesive interface, but finite element analysis (FEA) has shown this method grossly underestimates bond strength values 7,12) .…”

“…Micro-tensile bond tests are an alternative which allow for testing of small areas, thus permitting a regional mapping or depth profiling of different substrates and preparing multiple specimens from the same tooth 13) . However, the method is not easily applied because of small sample size and brittleness 9,12) . Micro-tensile bond testing is subject further to the cross-sectional shape and surface area 14,15) , cutting speed 16) , and geometry of the samples, as well as the means of attachment and testing device 17) .…”

“…Micro-tensile bond testing is subject further to the cross-sectional shape and surface area 14,15) , cutting speed 16) , and geometry of the samples, as well as the means of attachment and testing device 17) . The shear load must also be applied precisely at the bonded interface to avoid subjecting the cylinder to rotation or bending rather than shear tension 7,12) . A relatively thicker adhesive layer in microshear tests, among other reasons, concentrates stresses which influence the maximum load, thereby rendering micro-tensile tests less accurate than shear tests 2) .…”