Research On Cast Technology Of The Self-made Investment For Titanium And On Accuracy Of The Dental Titanium Castings

Titanium is regarded as biological metal for its advantages of good biocompatibility, corrosion resistance, great specific strength, etc. Vacuum cast is the most common method to produce dental titanium restorations. Investment with high quality and proper cast technology are essential to well-qualified titanium castings. This research was based on knowledge of the foregoing material study of a self-made investment for titanium. The primary purpose of this research was to find out proper cast technology of the new investment for its possible clinical application. Moreover, there were two other aims: to investigate if thermal expansion could be enhanced by way of granular size effect of spinel formation and to measure fit of removable partial denture (RPD) by three-dimensional measurement technique.In the first part, by metallographic microscopy, SEM (scanning electric microscopy), EDX (energy dispersive X-ray analysis), a mechanical testing machine and a stereomicroscope, the influence of mould temperature, cooling method and investing method on castability, reaction layer, mechanical properties and fit of titamum castings were investigated. The results indicated that titanium full crowns by 600℃ mould temperature , bench cooling and one-step investing exhibited better and clinically acceptable fit, that is, although its titanium castings exhibited 115μm thick reaction layer, the full crowns exhibited marginal and internal fit less than 120μm after sandblasting, and the mechanical properties were acceptable (0.2 proof strength 350.67MPa, tensile strength 477.50MPa, and percentage elongation after fracture 20.75%); titanium full crowns by 600℃ mould temperature and quenching in roomtemperature water exhibited fit beyond the clinically acceptable range (> 120pm ); titanium full crowns by 600X1! mould temperature and two-step investing also exhibited fit more than 120um and were not clinically acceptable.In the second part, by use of a thermal dilatometer and XRD (X-ray diffractometer), the influence of reduced AI2O3 particle sizes on thermal expansion ratio of the MgO/ AI2O3 investment was observed. The results showed that, although well powder processed investment had good manipulating properties, it was not seemed that the thermal expansion could be enhanced by reduction of AI2O3 particle sizes.In the third part, the casting accuracy of titanium RPD frameworks made from the investmerit was calculated by two ways: one to measure dimensional changes of the frameworks by a measuring microscope, and the other to measure the fit between the base of a framework and its model surface by a three coordinate measuring machine (3CMM). The results showed that the titanium RPD frameworks exhibited dimensional constriction, i.e. AD 1.235%, AE 0.9825%, BC 1.245%, and DE 1.188%, which were similar to the results of other researchers; and the average fit of RPD base was less than 200um and clinically acceptable.In conclusion, to made titanium full crowns and RPD frameworks with good comprehensive qualities (especially with clinically acceptable casting accuracy) , the self-made investment should be manipulated with 600 "C mould temperature , bench cooling and one-step investing; by dental titanium casting technology at present, it was not seemed that thermal expansion of the investment could be enlarged by way of granular size effect of spinel formation; the laser scanning 3D measuring method provided a new, nondestructive, accurate and full-scale way for fit measurement of RPDs.