True linear polymerization shrinkage of unfilled resins and composites determined with a linometer.

A device, which was given the name "linometer", has been developed for measuring linear polymerization shrinkage of both unfilled resins and composites. The results were in agreement with those obtained with the mercury dilatometer. The present method is simple, fast, insensitive to temperature fluctuations, is operational at any temperature and, if desired, samples can be maintained in a 100% relative humidity environment. The linometer offers an easy means for routine polymerization shrinkage determinations and therefore may be useful in evaluating new monomer systems for dental composites. The linear polymerization shrinkage for several unfilled resins and composites was measured with this device.