Microtensile and Shear Bond Strength of Zirconia Ceramics

Objectives: The purpose of this study was to measure microtensile and shear bond strengths of zirconia with similar bonding areas.

Methods: Most of the documented studies of zirconia microtensile bond strength were conducted by cutting bonded zirconia samples into microtensile sticks. However, the long time required for cutting of zirconia (which is extremely strong) results in the generation of friction and heat, etc., which can introduce un-necessary errors to the final bond strength results. In this study, zirconia ceramics were cut into microtensile sticks before being sintered. After sintering, zirconia sticks (2.2×2.2×10mm) were lightly sandblasted (0.3MPa, 10sec, 10mm distance) with alumina sand. Two zirconia sticks were then treated with zirconia primers (or Control: without primer), cemented with Duolink (Bisco), light-cured (20sec/500mW/cm² each side), and stored in de-ionized water (37ºC, 24hours). Microtensile bond strength was measured (n=5, bonding area 2.2×2.2mm) with a microtensile tester (Bisco). In shear bond strength test groups, sintered zirconia ceramics were lightly sandblasted, treated with or without zirconia primers, cemented with Duolink using the ultradent jig method (bonding area 4.5mm²), light-cured (40sec/500mW/cm² from top), and stored in de-ionized water (37ºC, 24 hours).  Shear bond strength (n=8) was measured on an Instron tester (crosshead speed 1mm/min). The data were analyzed statistically by two-way ANOVA and Tukey Tests (p<0.05).

Results: The test results are shown in the table below. For each row or column, means with different letters (row) or numbers (column) are statistically different at p<0.05.

Average Bond Strength, MPa (Standard Deviation)	Control (No Primer)	Monobond Plus (Ivoclar Vivadent)	ZPrime Plus (Bisco)
Microtensile Bond	5.7(3.1)a,1	17.0(3.2)b,1	34.1(9.2)c,1
Shear Bond	3.6(2.8)a,1	17.5(6.6)b,1	28.7(5.7)c,1

 Conclusions: With the similar bonding areas, the microtensile bond strenths of zirconia were not significantly different from shear bond strengths (p>0.05). Both zirconia primers significantly improved both microtensile and sear bond strength of zirconia (p<0.05).