The viscoelastic behavior of dental adhesives: A nanoindentation study

Sadr, Alireza; Shimada, Yasushi; Lu, Hongbing; Tagami, Junji

doi:10.1016/j.dental.2008.05.001

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Volume 25, Issue 1 , Pages 13-19, January 2009

The viscoelastic behavior of dental adhesives: A nanoindentation study

Alireza Sadr
- Cariology and Operative Dentistry, Department of Restorative Sciences, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan
- Corresponding author. Tel.: +81 3 5803 5483; fax: +81 3 5803 0195.
Yasushi Shimada
- Cariology and Operative Dentistry, Department of Restorative Sciences, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan
Hongbing Lu
- School of Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, OK 74078, USA
Junji Tagami
- Cariology and Operative Dentistry, Department of Restorative Sciences, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan
- Center of Excellence Program for Frontier Research on Molecular Destruction and Reconstruction of Tooth and Bone, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan

Received 7 December 2007; received in revised form 15 April 2008; accepted 8 May 2008.

Abstract

Objectives

In order to predict the long-term performance of dental adhesives, it is necessary to understand their mechanical properties. The objective of this study was to use a new nanoindentation technique to characterize the in-plane linear viscoelastic properties of dental adhesive layers.

Methods

The dental adhesives used were Clearfil SE Bond (CSE) and Clearfil Tri-S Bond (CTS) by Kuraray Medical and Single Bond (SIB) and Single Bond Plus (SBP) by 3M ESPE. A thin film of each adhesive was made on a micro-glass slide, and was then tested on a nanoindenter system (ENT 1100, Elionix) with a Berkovich indenter at a constant loading rate of 0.1mN/s up to a maximum load of 1.8mN. The load–displacement data of the loading segment were fitted to a curve to find best fit parameters for a generalized Kelvin viscoelastic model, from which creep compliance and Young's modulus were calculated. The modulus results were compared to the values calculated by the nanoindentation device.

Results

The experimental data fitted well to the viscoelastic model for all materials (R>0.9999). SIB and CTS showed higher creep compliance compared to SBP and CSE. The modulus values obtained using the model were 4.0, 2.6, 2.4 and 4.2GPa for CSE, CTS, SIB and SBP, respectively. The nanoindentation default software designed for time-independent materials significantly overestimated the modulus values up to 2.5 times.

Conclusion

As generally expected for polymer materials, the adhesives tested showed time-dependent viscoelastic behavior. The mechanical evaluation techniques developed for time-independent materials ignore this behavior and may not be appropriate for dental adhesives.

Keywords: Dental adhesives, Bonding, Viscoelasticity, Nanoindentation, Young's modulus, Creep compliance, Resin polymer, Self-etch, Filled resin, Etch and rinse