Analysis of Tackiness of Dental Resin Composites

Objectives: Stickiness or tack, which is one of handling properties of dental resin composites before setting, has not been well characterized although it is very important to develop non-sticky composite to dental instruments. It is well known that filler level, filler size, filler shape, and variation in matrix monomer formulations affect the degree of stickiness. Resin composite materials are viscoelastic and material properties including stickiness are dependent on speed of applied load. Objective of this study was to develop a rheology-based, quantitative methodology to identify a clinically-relevant indicator of tackiness of dental resin composites. Methods: Four different types of light-cured composites typically used in anterior and posterior restoration were tested using a rheometer with normal force sensor (AR-2000ex, TA instruments). Unset composite samples were compressed lightly (< 40N) using 8mm stainless steel parallel plate for 2 seconds. Immediately, pull-off force was applied with constant speed (500 microns/second) until samples were separated from the parallel plate. From force vs. displacement data logged into PC, maximum detachment force and detachment energy (area under the curve) were calculated. Results: It was observed that each composite group has distinctive pattern when it is compressed lightly and detached from the stainless steel parallel plate. Both maximum detachment force and detachment energy of sample A were significantly higher than any other samples (p < 0.05). Detachment energy of sample B was significantly greater than sample C (p < 0.05) although difference between samples B and C was not noticed when only maximum detachment force was considered. Conclusion: Detachment energy was more consistent with degree of stickiness measured by clinicians qualitatively and therefore seems to be clinically-relevant indicator of stickiness. This methodology might provide valuable information when clinicians make decisions for selection of composites used in different clinical applications or manufacturers develop new dental composites.