dental materials 26 (2010) e11–e16 available at www.sciencedirect.com journal homepage: www.intl.elsevierhealth.com/journals/dema A review of adhesion science Sally J. Marshall a,c,* , Stephen C. Bayne d , Robert Baier b , Antoni P. Tomsia c,a , Grayson W. Marshall a,c a University of California, San Francisco, United States b University at Buffalo, United States c Lawrence Berkeley National Laboratory, United States d University of Michigan, United States article info Article history: Received 26 November 2009 Accepted 26 November 2009 Keywords: Adhesion Adhesive Adherend Bonding Interfaces abstract Objective. Adhesion or cohesion includes an adherend, adhesive, and intervening interface. Adhesive joints may include one or more interfaces. Adhesion science focuses on under- standing the materials properties associated with formation of the interfaces, changes in the interfaces with time, and events associated with failure of the interfaces. Methods. The key principles for good interface formation are creation of a clean surface, generation of a rough surface for interfacial interlocking, good wetting of the substratum by the adhesive/cohesive materials, adequate flow and adaptation for intimate interaction, and acceptable curing when phase changes are required for final joint formation. Results. Much more effort is needed in the future to carefully assess each of these using avail- able testing methods that attempt to characterize the energetics of the interfaces. Bonding involves potential contributions from physical, chemical, and mechanical sources but pri- marily relies on micro-mechanical interaction for success. Characterization of the interface before adhesion, during service, and after failure would be much more useful for future investigations and remains as a great challenge. Significance. Scientists should more rigorously apply techniques such as comprehensive con- tact angle analysis (rather than simple water wettability) for surface energy determination, and AFM in addition to SEM for surface texture analysis. © 2009 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. 1. Introduction to adhesion science in dentistry Everyone has an image of adhesion that includes glue, tape, barnacles sticking to boats, insects walking on ceilings, chil- dren’s stickers, and a host of dental materials examples. Adhesion involves the tendency of atoms or molecules to stick to each other. Strictly speaking, cohesion involves like materi- als sticking together, and adhesion involves dissimilar atoms ∗ Corresponding author at: University of California, San Francisco, S/D Preventive & Restorative Dental Science, 707 Parnassus Avenue, San Francisco, CA 94141-0758, United States. E-mail address: sally.marshall@ucsf.edu (S.J. Marshall). or molecules sticking together. Both events are relevant to den- tal materials. This paper deals with both but will focus mostly on adhesive events. Early records of cohesion techniques such as cold welding of gold and silver from the 1st and 2nd centuries BC [1] are applicable to the fabrication of direct gold foil restorations, which were used in restorative dentistry. Cold welding is an example of cohesion, not adhesion, but the dental example involves both cohesion of the gold and adhesion (mechanical interlocking) into the prepared cavity. Another early example 0109-5641/$ – see front matter © 2009 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.dental.2009.11.157