J Adv Prosthodont.  2019 Feb;11(1):1-6. 10.4047/jap.2019.11.1.1.

The effects of surface grinding and polishing on the phase transformation and flexural strength of zirconia

Affiliations
  • 1Department of Prosthodontics, School of Dentistry, Chosun University, Gwangju, Republic of Korea. son0513@chosun.ac.kr
  • 2Good Face Dental Clinic, Seoul, Republic of Korea.
  • 3Department of Prosthodontics, Faculty of Dentistry, University Airlangga, Kota SBY, Jawa Timur, Indonesia.

Abstract

PURPOSE
The purpose of this in vitro study was to evaluate the effect of surface grinding and polishing procedures using high speed zirconia diamond burs with different grit sizes on the phase transformation and flexural strength of zirconia.
MATERIALS AND METHODS
Forty disc shape specimens (15 × 1.25 mm) with a cylindrical projection in the center of each disc (1 × 3 mm) were fabricated with 3Y-TZP (Prettau, Zirkonzahn, Italy). The specimens were divided into 4 groups (n=10) according to the grinding and polishing procedures: Control group - grinding (coarse-grit diamond bur), Group 1 - grinding (coarse-grit diamond bur) + polishing, Group 2 - grinding (fine-grit diamond bur) + polishing, and Group 3 - grinding (fine grit diamond bur). Each specimen was analyzed by 3D-OM, XRD analysis, and biaxial flexural strength test.
RESULTS
Based on the surface morphology by 3D-OM images, polished specimens showed smoother surface and lower roughness value (Ra). In the result of XRD analysis, partial phase transformation from tetragonal to monoclinic zirconia occurred in all groups. Control group, ground with a coarse grit diamond bur, showed more t→m phase transformation and lower flexural strength than Groups 1 and 2 significantly.
CONCLUSION
The flexural strength in all specimens after grinding and polishing showed over 500 MPa, and those were clinically acceptable. However, grinding with a coarse grit diamond bur without polishing induced the phase transformation and low strength. Therefore, surface polishing is required for the occlusal adjustment using a high speed zirconia diamond bur to reduce the phase transformation and to prevent the decrease of flexural strength of zirconia.

Keyword

3Y-TZP; Phase transformation; XRD; Roughness; Biaxial flexural strength

MeSH Terms

Dental Instruments
Diamond
In Vitro Techniques
Occlusal Adjustment
Diamond

Figure

  • Fig. 1 Configuration of the specimen. (A) Upper view, (B) Schematic lateral view.

  • Fig. 2 FE-SEM images of the high speed zirconia grinding bur. (A) Coarse bur (× 100), (B) Fine bur (× 100), (C) Coarse bur (× 300), (D) Fine bur (× 300).

  • Fig. 3 Preparation for the biaxial flexural strength: ISO Standard 6872 for Dental Ceramic.12 (A) Schematic diagram for biaxial flexural strengh test, (B) Jig with 3 balls, (C) Specimen placed on the jig.

  • Fig. 4 FE-SEM images of the specimen surface after grinding and polishing. (A) Control group, (B) Group 1, (C) Group 2, (D) Group 3 (× 10,000).

  • Fig. 5 FE-SEM images of the fracture surface (× 500). (A) Control group, (B) Group 1, (C) Group 2, (D) Group 3. Arrows indicate microcrack lines and circles show that fractures start from uneven surfaces by grinding.


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