The Weakest Link

Figure 1 and Figure 2 | No matter how strong an individual component is, the weakest link of a system is most likely to break. In dentistry, this is often the bond between the tooth and restorative material. All-zirconia crowns exhibiting over 1,000 MPa of tensile strength can fail if the cement is not firmly attached to the restoration and tooth. Similarly, fiber-reinforced posts with excellent tensile strength will loosen if not firmly adhered to the internal root canal surfaces of the tooth.

Dentin bonding agents have achieved the highest bond strengths between the tooth and restorative material. However, there can be challenges to achieving the strongest and most reliable bonds to dentin, including hydrolyzation,¹ matrix metalloproteinase degradation,² bond incomparability,³ and incomplete polymerization.⁴ A bonding agent with a dual-cured capacity is often required to ensure optimal polymerization. Light-cured dentin bonding agents are available that can be mixed with a separate “dual-cured” activator. This can be a compromise if light never reaches the impregnated tooth surface because light energy is needed to achieve the highest bond strengths. Specifically designed 2-bottle, dual-cure systems allow for the highest bond strengths to occur in the dual-cure mode, even when light cannot reach the agent.