title: The development and testing of glaze materials for application to the fit surface of dental ceramic restorations.
abstract: OBJECTIVE
  The aims of the study were to develop and test overglaze materials for application to the fit surface of dental ceramic restorations, which could be etched and adhesively bonded and increase the flexural strength of the ceramic substrate.
  
  
  METHODS
  Three glaze materials were developed using commercial glass powders (P25 and P54, Pemco, Canada). P25 (90 wt%) was mixed with P54 (10 wt%) to produce (P25/P54). P54 (90 wt%) was mixed with P25 (10 wt%) to produce (P54/P25). P25 (90 wt%) was mixed with 10 wt% of an experimental glass powder (P25/frit). Eighty-two disc specimens (14 mm x 2 mm) were produced by heat pressing a leucite glass-ceramic and were sandblasted with 50 microm glass beads. Group 1 control specimens (10) were sandblasted. Groups 2-4 (10 per group) were coated using P25/frit (Group 2), P25/P54 (Group 3) and P54/P25 (Group 4) overglazes before sintering. Groups 1-4 were etched for 2 min using 9.5% HF (Gresco, USA). Composite cylinders (Marathon v, Den-Mat) were light cured and bonded to the glazed and prepared disc surfaces and groups water stored for 8 days. Groups were tested using shear bond strength (SBS) testing at 0.5mm/min. Disc specimens (42) were tested using the biaxial flexural strength (BFS) test at a crosshead speed of 0.15 mm/min. Group 1 was tested as sandblasted (21) and Group 2 (21) after coating the tensile surface with P25/frit. Xrd, Eds and Sem analyzes were carried out.
  
  
  RESULTS
  Mean SBS (MPa+/-S.D.) were: Group 1: 10.7+/-2.1; Group 2: 9.8+/-1.9; Group 3: 1.8+/-1.0 and Group 4: 2.6+/-1.7. Groups 1 and 2 were statistically different to Groups 3 and 4 (p<0.001), but there was no difference between Groups 1 and 2 and 3 and 4 (p>0.05). The mean BFS (MPa+/-S.D.) of the overglazed Group 2 (200.2+/-22.9) was statistically different (p<0.001) to Group 1 (150.4+/-14.3).
  
  
  CONCLUSIONS
  The P25/frit overglaze significantly (p<0.001) increased the biaxial flexural strength of the leucite glass-ceramic substrate and produced comparable shear bond strengths to an etched and bonded control. The application of etched overglaze materials to dental glass-ceramic and ceramic substrates may be useful in adhesive dentistry.
authors.affiliation: Centre for Adult Oral Health, Barts and The London, School of Medicine and Dentistry, University of London, Turner Street, Whitechapel E1 2AD, UK. m.cattell@qmul.ac.uk
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Cattell
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Chadwick
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Knowles
authors.forename: Richard L
authors.initials: RL
authors.lastname: Clarke
mesh_terms: D000134:Acid Etching, Dental; D000538:Aluminum Silicates; D002516:Ceramics; D020099:Coated Materials, Biocompatible; D018360:Crystallography, X-Ray; D001840:Dental Bonding; D003776:Dental Porcelain; D003793:Dental Restoration, Permanent / Q000379:methods*; D003799:Dental Stress Analysis; D005898:Glass / Q000737:chemistry*; D008422:Materials Testing; D018583:Pliability; D033081:Shear Strength; D013499:Surface Properties; D016019:Survival Analysis
chemical_list: D000538:Aluminum Silicates; D020099:Coated Materials, Biocompatible; D003776:Dental Porcelain; C078519:leucite; C023506:Glass ceramics