A comparison of the dimensional stability of three inlay pattern materials

This study investigates the dimensional stability of 3 inlay pattern materials stored for different periods of time. Three indices were formulated to assess changes. These were: deviation and area change which both indicate a proportional contraction or expansion, and ratio which shows distortion. A brass master model was constructed to represent a cavity with 4 intersecting reference lines on the base, which were transferred to the bottom of the inlay pattern. The materials tested were Kerr's Type II blue inlay casting wax, Duralay (an autopolymerizing acrylic resin) and Modilux (a light-curing resin). Ten inlay patterns were prepared from each material in the brass master model cavity. Measurements of pre-determined points on the reference lines were recorded with a reflex microscope immediately after removal of the inlay patterns and then repeated at intervals of 1 hour and 24 hours. These measurements were compared to corresponding measurements on the brass master model and then converted into the three indices previously mentioned. Analysis of data showed that none of the materials distorted and that all the patterns underwent a proportional contraction, with wax contracting more than Duralay and Modilux. Significantly more contraction occurred at 24 hours than between onset (0 hour) and 1 hour. As contraction only occurred after 1 hour and wax contracted the most, it is recommended that Duralay or Modilux be used as the pattern material, especially if a delay in investing is anticipated.