Reactivity of zirconia with phosphate-bonded investments for hot-pressing.
OBJECTIVE
The aim of the present study was to investigate the reactivity of zirconia to phosphate-bonded investment on the process of hot-pressing technique.


METHODS
Disc-shaped specimens, 16 mm diameter and 0.4mm thick were prepared by cutting and grinding. These specimens were finally sintered. Half of them were sandblasted. The non-sandblasted specimens were used for controls. Both of zirconia discs with and without sandblasting were invested into the three kinds of phosphate-bonded investment. The investments were fired and broken to take out specimens. The biaxial strengths were measured in the way of the biaxial flexural tests according to ISO-6872.


RESULTS
The biaxial strengths were ranged 762-1200 MPa at the average. The biaxial strengths of sandblasted zirconia discs heated with phosphate-bonded investment were decreased significantly (p < 0.01). SEM and EPMA revealed that the various compounds were observed on the sandblasted specimens. XRD revealed that surfaces of specimens heated with the phosphate-bonded investment showed the formation of phosphate compounds.


CONCLUSIONS
The phosphate compounds inhibit stress-induction phase transformation of zirconia and decrease the biaxial strength.
Department of Removable Prosthodontics, School of Dentistry, Aichi Gakuin University, 2-11 Suemori-dori, Chikusa-ku, Nagoya, Japan. Electronic address: kentarou59117@gmail.com.
Kentaro
K
Yoshihara
Department of Removable Prosthodontics, School of Dentistry, Aichi Gakuin University, 2-11 Suemori-dori, Chikusa-ku, Nagoya, Japan.
Yoshinori
Y
Nakamura
Department of Dental Materials Science, School of Dentistry, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya, Japan.
Seiji
S
Ban
Department of Dental Materials Science, School of Dentistry, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya, Japan.
Tatsushi
T
Kawai
Department of Removable Prosthodontics, School of Dentistry, Aichi Gakuin University, 2-11 Suemori-dori, Chikusa-ku, Nagoya, Japan.
Yoshinobu
Y
Tanaka
D001840:Dental Bonding; D003734:Dental Casting Investment; D003764:Dental Materials; D003799:Dental Stress Analysis / Q000379:methods*; D004577:Electron Probe Microanalysis; D006358:Hot Temperature; D008422:Materials Testing / Q000379:methods*; D055595:Mechanical Phenomena; D008855:Microscopy, Electron, Scanning; D044367:Phase Transition; D010710:Phosphates; D033081:Shear Strength; D013718:Tensile Strength; D014961:X-Ray Diffraction; D015040:Zirconium / Q000737:chemistry*
D003734:Dental Casting Investment; D003764:Dental Materials; D010710:Phosphates; D015040:Zirconium; C028541:zirconium oxide
Biaxial flexural strength; Phosphate-bonded investment; Shear bond strength; Zirconia