Abstract
Bonding of dental restorative materials to tooth tissues is one of the most important aspects in dentistry. Adhesion at the interface has been the topic of never-ending and growing discussion in the research field of adhesive dentistry for quite some time. Prosthetic materials have to be cemented in the moist oral cavity either to the remaining tooth structure or to another prosthetic dental material. The affinity of most of the dental materials to each other is inherently inadequate. Thus, to meet this harsh oral environment many so-called coupling agents are used after the surface modification to further enhance the adhesion between different materials. There has been considerable research on coupling agents, with most of it focusing on silane coupling agents as compared to studies on some other coupling agents. One of the main problems with silanes is their susceptibility to humidity, and thus other coupling agents have been investigated to provide a more hydrolytically stable bonding agent. Some phosphate, zirconium and titanium based inorganic-organic hybrid compounds are also actively being investigated for the purpose. This review is focused on the coupling agents used in the contemporary adhesive dentistry including silanes which have and are being extensively studied. This review starts briefly from the history of the coupling agents and finally moving on to the current trends in research on coupling agents. This review is aimed to give better view and understanding of the different coupling agents and how these can be used in adhesive dentistry in the future.