Crown pattern waxes: a study of their behavior on heating and cooling

The values of the critical physical properties, flow and linear thermal expansion, of crown pattern waxes were determined and compared with those reported by previous investigators. The method is one proposed by the American Dental Association, and measurements were conducted in the temperature range of 27 to 52 degrees C. At temperatures higher than 37 degrees C most of the materials tested exhibited flow values that although rather low seem to be suitable for laboratory use. As expected, the linear thermal expansion was considerable, ranging from 1% to 1.5% or more as the temperature was increased from 27 degrees to 47 degrees C. The arrest points of the cooling curves, which are indicative of the composition of the materials, were recorded and studied. The possibility of correlating the arrest points with the transition points observed on the flow and expansion curves was investigated. Although attempts have been made to improve them, the commonly used dental waxes are not yet entirely free of their known drawback of large and perhaps uncontrollable thermal expansion.