Anders Sundh

Cytotoxicity and bonding property of dental ceramics

OBJECTIVES Yttria partially stabilized zirconia (YPSZ) ceramic is suitable for dental and medical use because of its high fracture toughness and chemical durability. The purpose of this study was to estimate the cytotoxicity and bonding property of zirconia ceramic compared to other dental ceramics. METHODS Eight commercial dental ceramics including Denzir (YPSZ) are used in this cytotoxicity test. The human gingival fibroblast (GF) cells were cultured using extraction solutions of ceramics. The cytotoxicity was estimated by two different methods. The bonding strength of Denzir was compared to Empress2 using zinc phosphate, glass ionomer, and adhesive resin cements. A brass plate was prepared with drilled tapered holes and ceramic specimens were prepared to fit the holes and bonded. The bonding strength was estimated by the punching test. RESULTS No significant (p>0.05) cytotoxicity was observed in all ceramic extractions. The two evaluation methods showed no significant differences. Denzir and Empress2 showed similar bonding strength with zinc phosphate or glass ionomer cement bonding. For both Empress2 and Denzir the glass ionomer cement showed significantly (p<0.001) higher bonding strength compared to the zinc phosphate cement. Empress2 showed significantly higher bonding strength with adhesive resin cement. However, the Denzir showed lower bonding strength with adhesive resin cement. SIGNIFICANCE No ceramic extractions showed any evidence of cytotoxicity. Therefore, the low in vitro cytotoxicity of ceramic extractions including Denzir was confirmed. Denzir showed a similar bonding strength to Empress2 with zinc phosphate or glass ionomer cement bonding with this testing method and lower bonding strength with adhesive resin cement than with Empress2.

Fracture resistance of all-ceramic crowns placed on a preparation with a slice-formed finishing line

The purpose of this study was to determine the fracture resistance of all-ceramic crowns with a core of a zirconia ceramic, using various stabilizing oxides and luted on a preparation with a slice-formed finishing line. Ten cores made of HIPed yttrium-oxide partially stabilized zirconia (HIPed Y-TZP) and five cores of densely-sintered magnesia partially stabilized zirconia (Mg-PSZ) were made. The Mg-PSZ cores and five of the HIPed Y-TZP cores were made with a thickness of 0.2 mm. A further five cores 0.1-mm thick were made of HIPed Y-TZP. All 15 cores were then veneered with a feldspar ceramic and luted onto a stylized steel master die model with a slice-formed finishing line. The specimens were then loaded until fracture occurred. The HIPed Y-TZP specimens with the 0.2 mm core exhibited significantly higher fracture resistance than the Mg-PSZ specimens (P = 0.004) and the HIPed Y-TZP specimens with the 0.1 mm core (P = 0.001). The fracture resistance of the Mg-PSZ specimens was significantly (P = 0.015) higher than that of the HIPed Y-TZP specimens with the 0.1 mm core. The fracture resistance determined was equal or superior to reported values for bite forces and all-ceramic crowns. Thus, it seems likely that the type of restorations evaluated have the potential for successful use on a slice-formed preparation. However, long-term studies are essential in order to assess the performance of this ceramic system in a clinical context.

Effects of pretreatments and hydrothermal aging on biaxial flexural strength of lithium di-silicate and Mg-PSZ ceramics

OBJECTIVES To evaluate the effect of specimen thickness, pretreatment and hydrothermal aging on the biaxial flexural strength (BFS) of lithium di-silicate glass (e.max Cad) and magnesia-stabilized zirconia (ZirMagnum) ceramic discs. METHODS The e.max Cad discs was studied: i) crystallized, ii) crystallized and glazed and iii) crystallized, glazed and unglazed side etched with hydrofluoric acid. The ZirMagnum discs were studied: i) as delivered, ii) after sandblasting and iii) after heat treatment similar to veneering. Hydrothermal aging was simulated by autoclave treatment. RESULTS The BFS of all the ZirMagnum specimens was superior (p<0.001) to all the e.max Cad specimens. Glazing the 0.4mm e.max Cad discs reduced (p<0.05) their BFS compared with the unglazed 0.8mm specimens, whereas glazing of 0.8mm discs had no influence (p>0.05) on the strength. Etching and autoclaving of e.max Cad did not affect (p>0.05) the BFS. For ZirMagnum sandblasting with 0.2MPa or 0.6MPa did not influence the biaxial flexural strength (p>0.05), whereas heat treatment reduced (p<0.01) the BFS of 0.6MPa sandblasted ZirMagnum. Autoclaving reduced the strength (p<0.05) compared with ZirMagnum as delivered, whereas autoclaving of the 0.6MPa sandblasted and heat-treated specimens did not influence (p>0.05) the BFS. Glazing, etching and sandblasting increased (p<0.05) surface roughness. CONCLUSIONS The effects of glazing, heat treatment, aging and mechanical treatment of the materials evaluated should be considered since their strength could be affected. CLINICAL SIGNIFICANCE Mechanical properties of restorations made from prefabricated ceramic blocks could be affected of various treatments and could change over time.