title: Effect of Two Polishing Systems on Surface Roughness, Topography, and Flexural Strength of a Monolithic Lithium Disilicate Ceramic.
abstract: OBJECTIVE
  To evaluate the effect of overglazing and two polishing procedures on flexural strength and quality and quantity of surface roughness of a monolithic lithium disilicate ceramic computer-aided design (CAD) after grinding.
  
  
  METHODS
  This in vitro study was conducted on 52 partially crystalized bar-shaped specimens (16 × 4 × 1.6 mm) of monolithic lithium disilicate ceramic. The specimens were wet polished with 600-, 800-, and 1200-grit silicon carbide papers for 15 seconds using a grinding/polishing machine at a speed of 300 rpm. Then, the specimens were crystalized and glaze-fired in one step simultaneously and randomly divided into four groups of 13: (I) Glazing group (control); (II) Grinding-glazing group, subjected to grinding with red band finishing diamond bur (46 μm) followed by glazing; (III) Grinding-D+Z group, subjected to grinding and then polishing by coarse, medium, and fine diamond rubber points (D+Z); and (IV) Grinding-OptraFine group, subjected to grinding and then polishing with a two-step diamond rubber polishing system followed by a final polishing step with an OptraFine HP brush and diamond polishing paste. The surface roughness (Ra and Rz) values (μm) were measured by a profilometer, and the mean values were compared using one-way ANOVA and Tamhane's test (post hoc comparison). One specimen of each group was evaluated under a scanning electron microscope (SEM) for surface topography. The three-point flexural strength values of the bars were measured using a universal testing machine at a 0.5 mm/min crosshead speed and recorded. The data were analyzed using one-way ANOVA and Tamhane's test (α = 0.05).
  
  
  RESULTS
  Statistically significant differences were noted among the experimental groups for Ra, Rz (p < 0.0001), and flexural strength values (p < 0.009). The lowest Ra and Rz values were found in the grinding-OptraFine group (0.465 ± 0.153), which were significantly lower than those in glazing (p < 0.03) and grinding-glazing (p < 0.001) groups. The Ra and Rz values were not significantly different between the two polishing systems (p = 0.23 and p = 0.25, respectively). The highest flexural strength was found in the glazing group (283.350 ± 49.854 MPa) without significant differences compared to grinding-glazing (p = 0.98) and grinding-OptraFine groups (p = 0.86). The lowest flexural strength was found in grinding-D+Z group (225.070 ± 17.299), which was significantly different from the value in glazing (p < 0.03) and grinding-glazing (p < 0.04) groups. SEM analysis of polished surfaces revealed regular morphology with some striations.
  
  
  CONCLUSIONS
  The OptraFine system created smoother and more uniform surfaces in terms of quantity (p < 0.03 for Ra, p < 0.01 for Rz) and quality of roughness compared to glazing. The flexural strength of lithium disilicate ceramic after polishing with the OptraFine system was similar to that after glazing (p = 0.86). Despite similar surface roughness after polishing with the two systems, the D+Z system reduced the flexural strength of ceramic (p < 0.03).
authors.affiliation: Department of Restorative Dentistry, School of Dentistry, Shahed University, Tehran, Iran.
authors.forename: Mahshid
authors.initials: M
authors.lastname: Mohammadibassir
authors.affiliation: Department of Restorative Dentistry, School of Dentistry, Shahed University, Tehran, Iran.
authors.forename: Mohammad Bagher
authors.initials: MB
authors.lastname: Rezvani
authors.affiliation: Department of Restorative Dentistry, School of Dentistry, Shahed University, Tehran, Iran.
authors.forename: Hossein
authors.initials: H
authors.lastname: Golzari
authors.affiliation: Department of Restorative Dentistry, School of Dentistry, Shahed University, Tehran, Iran.
authors.forename: Elham
authors.initials: E
authors.lastname: Moravej Salehi
authors.affiliation: Department of Restorative Dentistry, School of Dentistry, Shahed University, Tehran, Iran.
authors.forename: Mohammad Amin
authors.initials: MA
authors.lastname: Fahimi
authors.affiliation: Department of Epidemiology and Biostatistics, Faculty of Public Health, Tehran, Iran.|Dental Research Centre, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Mohammad Javad
authors.initials: MJ
authors.lastname: Kharazi Fard
mesh_terms: D017554:Carbon Compounds, Inorganic; D002516:Ceramics / Q000737:chemistry*; D017076:Computer-Aided Design; D003764:Dental Materials / Q000737:chemistry; D003775:Dental Polishing / Q000295:instrumentation / Q000379:methods*; D003776:Dental Porcelain / Q000737:chemistry*; D003793:Dental Restoration, Permanent; D018130:Diamond; D000077298:Flexural Strength; D006801:Humans; D066298:In Vitro Techniques; D008422:Materials Testing; D019558:Occlusal Adjustment; D017655:Silicon Compounds; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: D017554:Carbon Compounds, Inorganic; D003764:Dental Materials; C520133:IPS e.max CAD LT; D017655:Silicon Compounds; C493120:lithia disilicate; D003776:Dental Porcelain; D018130:Diamond; C023506:Glass ceramics; C022088:silicon carbide
keywords: Glass ceramic; IPS e.max CAD; glazing; surface roughness