A laboratory evaluation of the construction of resin-bonded cast restorations

Objective To compare the effect of two construction techniques and two pattern materials on the fit of resin-bonded cast restorations. Design In-vitro study carried out by one operator. Setting Postgraduate university hospital. Subjects and methods 65 nickel-chrome castings were constructed using refractory die and lift-off techniques with wax and acrylic resin pattern material. They were cemented onto master silver dies, embedded in self-curing acrylic resin and sectioned along their long axes. Interfacial distance between the master silver die and casting was measured. Results A significant difference between the range of figures in each group (Mann-Whitney Test, P < 0.01) was found. Construction techniques can be ranked in order of fit of castings: 1. Refractory die, wax patterns: 42.6 mu m (SD 12.03). 2. Refractory die, acrylic resin patterns: 53.7 mu m (SD.16.06). 3. Conventional technique, acrylic resin patterns: 85.5 mu m (SD 31.62). 4. Lift-off technique, wax patterns: 139 mu m (SD 53.15). 5. Lift-off technique, acrylic patterns: 172.8 mu m (SD 74.04). Conclusions Castings constructed using refractory die technique and subsequently cemented resulted in a more accurate and less variable fit than those produced with the lift-off technique. Wax patterns lead to more accurate castings than acrylic resin and locating indentations may interfere with the cementation of castings when lift-off techniques are used.