Hydrophobicity and Bond Strength Durability of Single-Step Self-Etch Adhesives

Objectives: Most single-step self-etch adhesives are hydrophilic and permeable even after cured. Water sorption and hydrolysis cause bond degradation. The purpose of this study was to test the hydrophobicity and bond strength durability of self-etch adhesives , and to analyze the relationship between them.

 Methods: Human dentin was polished by 320-grit SiC paper and rinsed with water. According to manufacturer’s instructions, the dentin was treated with AceAll-BondSE (Bisco), Multilink PrimerA/B (Ivoclar Vivadent), OptibondAll-in-One (Kerr), G-ænialBond (GC), EasyBond (3M ESPE), or Experimental Universal Adhesive (EUA, Bisco). Shear bond strength (n=8) on dentin was tested using the ultradent jig method, bonded with Duolink (Bisco), light-cured (40sec/500mW/cm²), stored in de-ionized water for 24hours/37ºC (Control) or 96hours/80ºC (accelerated aging), and tested by Instron tester (1mm/min). Contact angle (hydrophobicity) was measured on fully cured adhesives with a water droplet using a contact angle meter (NRL CA Goniometer)  (n=10). The data were analyzed statistically by one-way ANOVA and Tukey Tests (p<0.05). The quantitative relationship between bond strength decrease (after aging) and contact angle was analyzed by Regression Analysis (Excel) at confidence level 95%.

 Results: For each column, means with different letters are statistically different (p<0.05).

	Control: 37ºC-water/1day	Accelerated Aging: 80ºC-water/4days	Bond Strength Decrease(%)	Contact Angle
Ace All-BondSE	28.4(7.0)ab	18.3(8.9)ab	35.5	56.7(6.5)b
Multilink PrimerA/B	22.7(5.1)b	14.0(5.4)b	38.3	---
Optibond All-in-One	29.1(9.5)ab	6.3(2.0)c	78.3	46.4(2.9)c
G-ænialBond	12.0(2.9)c	6.3(2.5)c	52.5	55.4(4.5)b
EasyBond	33.7(5.3)a	18.0(3.8)ab	46.6	58.8(4.6)ab
EUA(Bisco)	31.0(3.0)a	22.4(4.5)a	27.7	62.2(2.8)a

 The Regression Analysis (df= 4) between bond strength decrease and contact angle showed the p-value is 0.016 (<0.05), and R-square is 0.89.

 Conclusions: The experimental adhesive EUA was the most hydrophobic (highest contact angle value) and had the lowest percentage of bond strength decrease. For the adhesives tested, the percentage decrease in bond strength is observed to exhibit a liner relationship to adhesive hydrophobicity (contact angle values, R-square=0.89).