Effect of phosphate-bonded investments on titanium reaction layer and crown fit

Abstract

This study analyzed the reaction layer and measured the marginal crown fit of cast titanium applied to different phosphate-bonded investments, prepared under the following conditions (liquid concentration/casting temperature): Rema Exakt (RE) - 100%/237 degrees C, 75%/287 degrees C, Castorit Super C (CS)-100%/70 degrees C, 75%/141 degrees C and Rematitan Plus (RP)- 100%/430 degrees C (special to titanium cast, as the control group). The reaction layer was studied using the Vickers hardness test, and analyzed by two way ANOVA and Tukey's HSD tests (alpha = 0.05). Digital photographs were taken of the crowns seated on the die, the misfit was measured using an image analysis system and One-way ANOVA, and Tukey's test was applied (alpha = 0.05). The hardness decreased from the surface (601.17 VHN) to 150 microm (204.03 VHN). The group CS 75%/141 degrees C presented higher hardness than the other groups, revealing higher surface contamination, but there were no differences among the groups at measurements deeper than 150 mum. The castings made with CS - 100%/70 degrees C presented the lowest levels of marginal misfit, followed by RE -100%/237 degrees C. The conventional investments CS (100%) and RE (100%) showed better marginal fit than RP, but the CS (75%) had higher surface contamination.

A quality assessment of titanium castings produced in an experimental short-heating-cycle investment

“…The highest values that were found in the first levels of RP was expected because of the Si and Al present in phosphate-bonded investments 12,[17][18][19][20][21][22] . At depths greater than 100 µm, there is no statistically significant difference among the levels of the various investments, revealing that 100 µm represents a typical reaction layer thickness.…”

“…The most common investments used for titanium are phosphate-bonded investments based on silica phases (crystalline quartz or cristobalite) that are inexpensive and exhibit a thermal expansion compatible with Ti casting shrinkage 4 . However, SiO 2 can be reduced by Ti, and this affects the physical and mechanical properties of the titanium castings [5][6][7][8][9][10][11][12] . On the other hand, spinel-based investments produce enough thermal expansion to compensate for the Ti casting shrinkage and produce a minor reaction layer thickness but are more expensive 10,[13][14][15][16][17][18][19][20][21] .…”