Objectives: Evaluate the effect of a new resin-modified glass ionomer (RMGI) liner on the polymerization shrinkage stress of two commercially available resin cements. The RMGI liners were Vitrebond™ Plus Liner/Base (VBP), and Vitrebond™ Liner/Base (VB); the resin cements were Unicem™ Self-Adhesive Resin Cement (UNI), and RelyX™ ARC Adhesive Resin Cement (RXA) (All materials from 3M ESPE). VBP is a new light-curing RMGI material in a paste/liquid delivery, which exhibits the aluminum-carboxylate crosslinking reaction and fluoride release of a true glass ionomer.

Methods: Volumetric polymerization shrinkage by the deflecting disc method [Watts & Cash. Dent Mater 1991;7:281] was used to measure polymerization shrinkage of a 2mm thickness of each cement alone, and in combination with 0.5mm thickness of liner. The material combinations are shown below (n=3) along with percent shrinkage reduction for each cement – liner combination. Data were analyzed via one-way ANOVA Tukey's T-test (p=0.05).

Results: Resin Cement Liner Mean volumetric shrinkage % (sd) of cement with liner. % reduction in shrinkage over cement alone UNI no liner 4.0 (0.1) - - UNI VB 2.1 (0.1) 47% UNI VBP 2.1 (0.2) 47% RXA no liner 5.5 (0.1) - - RXA VB 3.1 (0.2) 43% RXA VBP 2.5 (0.4) 55%

Use of RMGI liners VBP and VB resulted in a statistically significant reduction in the volumetric shrinkage of RXA and UNI (p<0.05). The shrinkage of UNI/VB is statistically equivalent to UNI/VBP; all other groups are statistically different.

Conclusions: VB and VBP reduced the volumetric polymerization shrinkage of two resin cements as measured in the study by 43% to 55%. Since this method of measuring shrinkage reflects the stress due to polymerization, it can be concluded that the liners buffer this effect.

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