Development and testing of multi-phase glazes for adhesive bonding to zirconia substrates.
OBJECTIVE
The aims of the study were to develop and test multi-phase glaze coatings for zirconia restorations, so that the surface could be etched and adhesively bonded.


METHODS
Zirconia disc specimens (n=125, 16 mm x 1 mm) were cut from cylinders of Y-TZP (yttria-stabilized tetragonal zirconia polycrystals) ZS-Blanks (Kavo, Everest) and sintered overnight. Specimens were subjected to the recommended firing cycles, and next sandblasted. The specimens were divided into 5 groups of 25, with Group 1 as the sandblasted control. Groups 2-5 were coated with overglaze materials (P25 and IPS e.max Ceram glazes) containing secondary phases. Group 2 was (wt%): 10% hydroxyapatite (HA)/P25 glaze, Group 3: 20% IPS Empress 2 glass-ceramic/glaze, Group 4: 20% IPS Empress 2 glass/glaze and Group 5: 30% IPS Empress 2 glass/glaze. After sintering and etching, Monobond-S and composite resin cylinders (Variolink II, Ivoclar-Vivadent) were applied and light cured on the test surfaces. Specimens were water stored for 7 days. Groups were tested using the shear bond strength (SBS) test at a crosshead speed of 0.5 mm/min. Overglazed and the fractured specimen surfaces were viewed using secondary electron microscopy. Room and high temperature XRD and DSC were carried out to characterize the materials.


RESULTS
The mean (SD) SBS (MPa) of the test groups were: Group 1: 7.7 (3.2); Group 2: 5.6 (1.7); Group 3: 11.0 (3.0); Group 4: 8.8 (2.6) and Group 5: 9.1 (2.6). Group 3 was significantly different to the control Group 1 (p<0.05). There was no significant difference in the mean SBS values between Group 1 and Groups 2, 4 and 5 (p>0.05). Group 2 showed statistically lower SBS than Groups 3-5 (p<0.05). Lithium disilicate fibres were present in Groups 3-5 and fine scale fibres were grown in the glaze following a porcelain firing cycle (Groups 4 and 5). XRD indicated a lithium disilicate/minor lithium orthophosphate phase (Group 3), and a tetragonal zirconia phase for the sintered Y-TZP ZS-Blanks. DSC and high temperature XRD confirmed the crystallization temperatures and phases for the IPS Empress 2 glass.


CONCLUSIONS
The application of a novel glass-ceramic/glaze material containing a major lithium disilicate phase might be a step in improving the bond strength of a zirconia substrate to a resin cement.
Ntala
Polyxeni
P
Centre of Adult Oral Health, Queen Mary University of London, Barts and The London School of Medicine and Dentistry, Institute of Dentistry, Turner Street, London, E1 2AD, UK.
Chen
Xiaohui
X
Niggli
Jason
J
Cattell
Michael
M
D000134:Acid Etching, Dental / Q000379:methods; D002152:Calorimetry, Differential Scanning; D002516:Ceramics / Q000737:chemistry*; D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D003460:Crystallization; D003738:Dental Cements / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry; D017886:Durapatite / Q000737:chemistry; D006358:Hot Temperature; D006801:Humans; D055115:Light-Curing of Dental Adhesives / Q000379:methods*; D018020:Lithium Compounds / Q000737:chemistry; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D019279:Resin Cements / Q000737:chemistry; D033081:Shear Strength; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
D020099:Coated Materials, Biocompatible; D003738:Dental Cements; D003764:Dental Materials; C118557:Empress 2; C508050:IPS e.max Press; D018020:Lithium Compounds; C076808:Monobond S; D019279:Resin Cements; C493120:lithia disilicate; C499362:yttria stabilized tetragonal zirconia; D014867:Water; D003776:Dental Porcelain; C103502:Variolink; D015019:Yttrium; C023506:Glass ceramics; D017886:Durapatite; D015040:Zirconium; C028541:zirconium oxide