Experimental Binder-free Investments Reused to Cast Dental Precious Alloys

Abstract

This study aimed to develop reusable dental investments. SiO 2 and MgO were selected as refractory materials to prepare three types of investment（coded as 60S -40M, 80S -20M, 100S）with 40, 20, and 0 wt％ of MgO. Each type of investment was reused twice. Thermal expansion and compressive strength were examined and statistically evaluated by ANOVA. To evaluate fit of castings, full crowns were cast by using a commercial Au-Ag-Pd alloy with all investment types. Marginal fit was statistically analyzed by cement thickness. It was found that although MgO strengthened the mold, it had little influence on expansion. The strength of 60S-40M was the highest, and 100S had the greatest advantage with regard to thermal expansion. In the evaluation for clinical applicability, all investments were able to cast successfully, but their castings might be undersized. Among the experimental binder-free investments reused for dental casting in this study, 100S in particular showed to be a good candidate for repeated fabrication of precision fit castings.

Production of a calcium silicate cement material from alginate impression material

“…We have already reported the development of a series of reusable investment materials from cristobalite investment materials mixed with a crushed glass binder, which are not necessarily inferior to the original gypsum investment material [1][2][3][4] . However, such studies were aimed at the development of reusable laboratory materials instead of clinically acceptable materials.…”

Experimental Paste-paste Type Phosphate-bonded Investment with Colloidal Silica Solution

“…Although the strength at setting does not have a major infl uence on the mechanical properties of the mold, the strength value after firing becomes important to complete the casting procedure without mechanical damage. In light of our results, some casting defects may occur becausethe fi red strengths of B and C were less than 1 MPa 14).…”

Soda-lime glass as a binder in reusable experimental investment for dental castings

“…Because the experimental investments were not strong enough to be removed from a ready-made rubber crucible former, a handmade crucible was prepared using paraffin wax (GC Co.,Ltd., Tokyo, Japan) 5) . A single cast liner (Fitting liner, Shofu Co. Ltd., Kyoto, Japan) was placed inside the ring (ø 30 mm, height 35 mm).…”

“…We also developed a new type of dental casting investment consisting of only refractory materials without binder, which could also be reused 5) . We crushed broken laboratory glassware with a milling machine to prepare glass powder 6) .…”

“…For example, unnecessary parts of precious alloy castings, such as the sprue, vent or bottom of the casting, have been melted and reused. However, most of the ceramic materials, such as gypsum and the investment, are discarded 5) . Although dentistry is not a major contributor to industrial waste, it would be beneficial to reduce this waste.…”