Influence of polyurethane resin dies on the fit and adaptation of full veneer crowns.

Context: Polyurethane resin is a possible alternative to type IV dental stone for fabrication of indirect restorations however its dimensional accuracy is questionable. Aim: The aim was to investigate the dimensional accuracy of silica filled polyurethane resin die material by evaluating the marginal fit and adaptation of indirect gold castings. Settings and Design: Experimental, in vitro study. Materials and Methods: Totally 40 copper plated replicas of a nickel chrome master die analogous to a veneer gold crown preparation were made and impressions recorded using polyvinylsiloxane material. Twenty impressions were poured in type IV dental stone (control group (Vel‑mix, Kerr, UK) and the remaining (n = 20) in silica filled polyurethane die material (test group) (Alpha Die MF, CA, USA). Gold castings were fabricated for each die using standardized techniques. The castings were seated on their respective copper plated dies, embedded in resin and sectioned. The specimens were analyzed by measuring marginal opening and the area beneath the casting at a ×63 magnification and using image analysis software. Statistical Analysis Used: Data were analyzed using a Student’s t‑test. Results: No significant difference was observed between the experimental groups (P > 0.05). The mean marginal opening for type IV, dental stone and polyurethane resin, was 57 ± 22.6 μm and 63.47 ± 27.1 μm, respectively. Stone displayed a smaller area beneath the casting (31581 ± 16297 μm2) as compared to polyurethane resin (35003 ± 23039 μm2). Conclusions: The fit and adaptation of indirect gold castings made on polyurethane and type IV dental stone dies were comparable.

The thermal expansion compatibility of a new infiltrated ceramic-low-temperat ure compensatory die stone / 实用口腔医学杂志

Objective: To study the thermal expansion compatibili ty of a newly developed low temperature compensatory die stone (CDS) with Al 2O 3 base coping and to determine its setting time and setting expansion rate. Methods: Using HDS (Hieraus Die Stone ) as control. The ther mal expansion compatibility of CDS with Al 2O 3 was determined with TMA method on Du point 2100 thermometer;the setting time and setting expansion rate of CDS were measured with routine technique. Results: CDS showed much smaller thermal expansion with Al 2O 3 base coping than HDS.When the wa ter/powder ratio increased from 0.20 to 0.30,the setting time (h) of CDS increas ed from 12.75?0.7546 to 19.85?0.7472,that of HDS from 12.25?0.7169 to 24.00? 0.8165. The setting expansion of CDS was similar to that of HDS at various water /powder ratio. Conclusion: CDS has suitable thermal expans ion compatibility with Al 2O 3, it also has proper setting time and setting ex pansion rate to meet the clinical needs.