Composite Shrinkage Vectors in Silanized Ceramic-Cavities with Layer of Bonding-Agent

To visualize the polymerization shrinkage of a light-initiated resin-composite in form of displacement vector fields (DVF) and to detect the shrinkage direction in relation to the light source inside a silanized ceramic-cavity with a layer of bonding agent. 

Method:

A cylindrical cavity (diameter 6mm, depth 3mm, n=9) was prepared into a ceramic block, (IPS Empress CAD, Ivoclar Vivadent), etched (hydrofluoric-acid 5%), silanized (ESPE Sil, 3M ESPE), one layer of bonding agent (OptiBond FL, Kerr) applied and filled with a flowable composite (Tetric EvoFlow, Ivoclar Vivadent) to which 2wt% traceable glassbeads were added. Two micro-CT scans were performed of each specimen (uncured, cured), subjected to image segmentation for extraction of glass beads and followed by registration based on a block-matching algorithm.

The DVF exhibited the distribution of shrinkage vectors three-dimensionally. Additionally, shrinkage vectors were analyzed in the vertical dimension (in relation to the light source).

Result:

Mean vector length (41.6μm; SD=18.9) was computed irrespective of their direction. Analyzing the shrinkage direction in relation to the light-source, the filler movement (FM) was investigated in the z-direction only, where negative values denoted an upward movement towards the light-source and positive ones meant downward shrinkage. The mean-FM (19.2μm; SD=16.0) moved away from light. Large shrinkage vectors in the upper part of the restoration directed downward, then deviated to one side of the restoration in the lower part and were smaller.

Conclusion:

DVF showed the marked shrinkage movement away from the light-source. Disruption of the adhesion to some areas of the cavity wall might cause deviation to one side in the lower cavity part. Boundary conditions seem to play an important role in the behavior of polymerization shrinkage.