Repair of defective composite restorations instead of full replacement has been actualised over the last decades. The widely used composite restorations are repairable and modern philosophy of “Minimal Intervention Dentistry” has been more rooted among dentists all over the world. This fact raises the question: Is there anything we can do to make the repair interface durable and strong enough to match the physical and biological challenges in the oral environment. This topic has been addressed in a research project performed at NIOM by the Norwegian guest scientist, Frode Staxrud, DDS.
The aim of the project was to investigate whether silanising agents could play a part to improve the strength of repair interface in combination with commonly used bonding products. The project consisted of two parts. In part one, the repair of old composite was performed. Sixty 6 years old test substrates made from six different composite brands were repaired and tested according to a standard test procedure (ISO/TS 11405). The substrates were repaired with new composite using 3 different bonding procedures:
- bonding agent without silane,
- bonding agent with a separate silane step (freshly mixed 2-part silane), and
- a bonding agent containing silane. In part two, repair of newly made composite was performed and evaluated using 66 freshly made composite substrates and the same test protocol as described for old composite.
Repair interfaces where silane was not involved showed significantly lower shear bond strength than the repair interfaces with silanising agent. There was no statistical difference between the two bonding procedures involving silane. The increase in repair strength when using silane was almost 140 % for old composite and 50 % for new composite, indicating that older composite repair has a higher potential to benefit from using silanising agents. On the other hand new composite repair showed significantly higher shear bond strength values and hence the potential for increase of the bond strength at repair interface is lower.
Although in vitro studies cannot fully represent the real clinical situation, the present results indicate that the use of silane is recommended when repairing resin composite restorations either as a separate step in the bonding procedure or incorporated in the bonding agent.
Staxrud, F. and J. E. Dahl (2015). “Silanising agents promote resin-composite repair”. International Dental Journal, 65(6):311-5. doi: 10.1111/idj.12188. Epub 2015 Oct 9.